Environmental analysis

Mark R. Cave; Owen Butler; Jennifer M. Cook; Malcolm S. Cresser; Louise M. Garden; Douglas L. Miles

doi:10.1039/B000063I

DOI: 10.1039/B000063I (Atomic Spectrometry Update) J. Anal. At. Spectrom., 2000, 15, 181-235

Environmental analysis

Mark R. Cave*^a, Owen Butler^b, Jennifer M. Cook^a, Malcolm S. Cresser^c, Louise M. Garden^d and Douglas L. Miles^a
^aBritish Geological Survey, Keyworth, Nottingham, UK NG12 5GG. E-mail: m.cave@bgs.ac.uk
^bCentre for Analytical Sciences, University of Sheffield, Dainton Building, Sheffield, UK S3 7HF
^cThe University of York, Heslington, York, UK YO10 5DD
^dICI Research and Technology Centre, P.O. Box 90, Wilton, Middlesbrough, Cleveland, UK TS90 8JE

Received 23rd December 1999, Accepted 0th Invalid month: [00] 2000

First published on UnassignedUnassigned11th February 2000

Abstract

This is the fifteenth annual review published in JAAS of the application of atomic spectroscopy to the chemical analysis of environmental samples. Over the period there have been no major breakthroughs in atomic spectrometry, but environmental scientists are discovering the wide variety of applications that can be addressed with current analytical instrumentation. In particular, the low detection limits and isotopic measurement capabilities of ICP-MS are being widely exploited.

There is continued emphasis on the need for improvements in analytical data quality in all areas. The need for and production of reference materials, ranging from air filters to the most challenging production of RMs for metal speciation, are widely discussed. There is also increased reporting of the results of interlaboratory collaboration trials, especially in the area of air analysis where this type of study has, in the past, lagged behind other environmental analyses.

Despite the ever decreasing trend in instrument detection limits much effort continues to be expended in the development of preconcentration methodologies, many of which involve traditional complexation chemistries on solid phase extraction supports. Pre-instrument chemistries are also the subject of many studies in the area of speciation, which often combine a complexation and/or species separation step prior to atomic spectrometric quantitation.

For solids analysis through the dissolution route, there continues to be much re-working of a variety of permutations and combinations of digestion methodologies using different acids mixtures under varying heating and pressure regimes. The advantage of by-passing the vagaries of the dissolution step by direct analysis of solids continues to fuel some very fertile research using laser ablation sample introduction, while XRF methods continue to be used widely.

1 Air analysis

This section of the update covers the analysis of aerosols, particulates and gases by analytical atomic spectrometry. Papers published in the last 12 months are summarized in Table 1. Noteworthy areas of research and development are highlighted below. There were a number of useful reviews: development of mass spectrometry for the real time interrogation of individual particles;^1,2 microprobe XRF for the characterization of atmospheric particles;³ bulk analysis using TXRF⁴ and AA/ICP techniques;⁵ and a compendium of techniques for both surface and bulk analysis.⁶

Table 1 Summary of analyses of air and particulates

Element	Matrix	Technique; atomization;presentation*	Sample treatment/comments	Ref.
*Hy indicates hydride and S, L, G and Sl signify solid, liquid, gaseous or slurry sample introduction, respectively. Other abbreviations are listed elsewhere.
As	Airborne particulate matter	MS;ICP;S	Mixed acid digestion (HNO₃–H₂O₂–HF) in high-pressure bombs utilized. CRMs used for method validation. Isobaric overlap noted if chlorinated acids used	18
As	Workplace air	AE;ICP;G	Bubbler sampler system used with concentrated HNO₃ in front two flasks and with an alkali end-trap. Alkali and alkaline-earth metals found to interfere at concentrations >0.1%	41
As	Airborne dust	AE;ICP;S	Closed vessel microwave assisted dissolution utilized	19
Br	Aerosol samples	PIXE;—;S	Br impurity contained in Nucleopore^™ filters used as an in-sample internal standard	42
C	Gaseous	AMS;—;S	Method for the preparation of carbonyl compounds for ¹⁴C analysis described. The method involved sampling air onto DNPH coated silica gel cartridges and extracting with CH₃CN with purification over activated silica gel to remove excess DNPH and non-target compounds	43
C	Gaseous	AMS;—;—	Approaches for the measurement of ¹⁴C in µg carbon samples by optimizing sample preparation, instrument operation and data evaluation described	44
Cl	Gaseous	AE;GD;G	Use of gas-jet glow discharge AES investigated as a means of destroying gaseous pollutants. CCl₄ used as a model contaminant. Extent of decomposition under optimized conditions was found to be >96%. Potential of using Cl (I) 452.6 nm to monitor decomposition on a real time basis discussed	45
Cd	Airborne dust	AA;ETA, F;S	Speciation carried out using an operationally defined sequential extraction procedure. Method validation carried out using synthetic mixtures of Cd salts. Extraction protocol applied to dust samples collected using an electrostatic precipitator at a coal powered electricity generation station	46
Cr	Airborne particulate matter	MS;ICP;S	Mixed acid digestion in high pressure bombs developed and optimized (HNO₃–HClO₄ plus addition of HF in a second step). LOD <10 ng g⁻¹ when analysed using HR-ICP-MS. Results obtained using LA-ICP-MS compared well with data obtained using dissolution procedure (LOD 0.05 µg per filter)	47
Hg	Gaseous	AE;—;G	Photo fragmentation emission spectroscopic technique described for the gas phase detection of HgCl₂, Hg(CH₃)Cl and HgI₂	48
Hg	Gaseous	AF;F;G	Vapour in humid air trapped onto Au impregnated silica and desorbed from this trap, concentrated on a fixed Au impregnated sand trap prior to analysis. Method applied to the measurement of exhaled air. RSD 8.7–10.7% at 10–250 pg (LOD 0.6 pg)	49
Hg	Gaseous	MS;ICP;G	Cryogenic sampling compared to Au amalgamation sampling. Levels found in the Amazon basin ranged from 2 to 20 ng m⁻³. Mainly found in metallic form	36
Hg	Urban particulate	AF;—;S	Particulate trapped on a quartz fibre filter within a quartz trap followed by heating to release Hg and concentrated on an analytical Au trap. Measured total particulate Hg concentrations in the range 3–91 pg m⁻³	50
I	Ambient air	MS;ICP;G	¹²⁹I measured using precipitation techniques with on-line analysis (decomposition of PdI₂, I₂ swept into plasma). ¹²⁹Xe can interfere with the analysis. Application used non-proliferation monitoring programs (LOD <50 fg)	22
In	Urban dust	AF;ETA;S	Laser excited AF system with platform atomization within graphite furnace gave best performance. Absolute LOD 1 fg (10 µl sample injection). RSD 4.1% at 10 ng ml⁻¹ (n = 10)	51
Mn	Air	AA;ETA;S	Filter samples digested in concentrated HNO₃ for 1–2 h with measurement precision typically better than 3% (LOD 0.06 µg per filter)	52
Ni	Airborne factory dust	AA;—;S	Soluble Ni determined after extraction using ammonium citrate (buffered at pH 4). Insoluble Ni determined following dissolution using HNO₃–HClO₄–H₂SO₄. Dust studied using XRD and SEM. Implications of findings regarding occupational exposure discussed	33
Pb	Ultrafine aerosols	AE;F;S AF;LIPS;S	Differential mobility particle sizer used to segregate particle sizes. Air–acetylene flame and LIP used as atomization sources. AES system used with a CCD detector or a laser excited AFS system (LOD 55–130 ng m⁻³ for particles in the range 44–300 nm)	53
Pb	Airborne particulate matter	XRF;—;S	Analysis using a thin film approach carried out. Italian city of Lecce monitored	54
Pb	Airborne particulate matter	MS;ICP;S	Isotopic measurements performed for source apportionment studies. Unequivocal evidence that ore derived Pb from local mining sources had become the dominant source in dust fallout samples	26
Pb	Dust particles	XRF;—;S	Portable system evaluated for use in paint stripping and removal abatement programs. (LOD ranged from 0.01 to 0.1% (in the solid) for elements with Z>50 using 15 s measurement interval)	55
Pb	Airborne particulate matter	XRF;—;S AA;F;S	Filter samples analysed following dissolution with a mixture of HNO₃–H₂O₂. Good agreement obtained between methods	56
Pb	Airborne particulate matter	XRF;—;S	In-field evaluation of portable instrument data from TSP and PM₁₀ samples compared with that from ICP-AES following dissolution. Results showed feasibility of portable systems to provide accurate air data	20
Pd	Airborne particulate matter	AA;ETA;S	Electrodeposition on graphite tube prior to insertion of tube into furnace described	57
Pt	Airborne particulate matter	AA;ETA;S	See Pd, ref. 57	57
S	Airborne particulate matter	XPS;—;S XAS;—;S	Comparison made between the two techniques for interrogating particle surfaces. Concluded that XAS was more suitable for the chemical state analysis of S within aerosol samples	40
S	Airborne particulate matter	AE;—;G	Air sampled onto glass fibre filters and subsequently extracted with CH₂Cl₂. Following clean-up on deactivated silica gel columns, S containing PAHs analysed using a GC-AES system	58
Sb	Airborne particulate	AF;Ar–H₂;S	Improved hydride generation procedure developed (stibine generated at 70°C; cooled phase separator and drying tube used; auxiliary stream of H₂ introduced to support flame). Calibration linear to 2.7 mg l⁻¹, RSD 1.4% at 8 µg l⁻¹ and 0.6% at 100 µg l⁻¹. NIST SRM 1648 used as QC material. Bilbao air found to contain 13.2 ± 0.3 ng m⁻³ (LOD 0.3 µg l⁻¹)	59
Se	Gaseous	MS;ICP;G	Cryogenic sampling compared to Au amalgamation sampling. Levels found in the Amazon basin ranged from 10–100 pg m⁻³. Cryogenic sampling demonstrated that Se present in biogenic forms such as Me₂Se, Me₂Se₂ and Me₂SeO	36
Si	Airborne particulate matter	MS;ICP;S XRF;—;S	LA performed on samples collected onto PTFE filters. NIST 1648 urban particulate matter used to prepare calibration filters. Good agreement with data from XRF	25
V	Airborne particulate matter	MS; ICP;S	Mixed acid digestion (HNO₃–H₂O₂–HF) in high-pressure bombs utilized. CRMs used for method validation. Isobaric overlap noted if chlorinated acids used	18
Various	Atmospheric particles	XRF;—;S	Aerosols collected on PTFE filters within virtual impactors in a study of air mass movements in Western Scandinavia	60
Various	Process gases	AA;ETA;G	Modified system used to determine metal traces in gaseous HCl, Cl₂ and trichloroborane. Calibration carried out using standard addition of both gaseous samples and standard solutions	61
Various	Stack gas	AE;ICP;S	Correction of spectral interference arising from CN emissions in an on-line air-Ar ICP-AES system. Correction protocol involved the measurement of CN emission at 359.255 nm (introduction of known amounts of CO₂ into the plasma prior to analysis in order to derive a correction factor)	8
Various	Landfill and fermentation gases	MS;ICP;G	Ion trap EI-MS-MS and ICP-MS coupled to the same GC to provide qualitative molecular (qualitative) and elemental data (quantitative) on volatile Bi, Sb and Sn compounds	35
Various	Airborne particulate matter	AA;ETA;S	Particulate matter collected on phenylpolypropylene filter dissolved in IBMK to form a colloidal solution. 10 µl aliquots injected into furnace. RSD in the range 2–8% (LODs 0.05, 1, 1, 2 and 5 ng m⁻³ for Cd, Cr, Cu, Pb and Ni)	62
Various	Aerosol samples	AA;—;S	Size fractionated particulate matter collected onto filters in a cascade impactor. Three stage operationally defined sequential extraction procedure carried out to study the fractionation of elements as a function of particle size	63
Various	Particulate and vapour phase samples	—;—;—	Patent application for a sampling system to collect mixed phased samples from gases that cannot be hydrolysed. Twin filter system with first filter at ambient temperature to collect particulate phase and second filter at temperature below ambient to remove vapour phase	38
Various	Atmospheric dust samples	XRF;—;S	Thin film calibration standards and samples prepared by dispersing powdered standards onto hydrophilized PTFE filters and drying under an IR lamp. Standards prepared by impregnating activated C powders with standard elemental solutions	64
Various	Cigarette smoke	AE; ICP;S AA;ETA;S	Smoke condensate collected by electrostatic precipitation. Condensate extracted from collection tubes with methanol. Evaporation and subsequent dissolution carried out in a microwave oven	65
Various	Airborne particulate matter	MS;ICP;S XRF;—;S	NIST CRM 1648 Urban Particulate Matter used to prepare calibration filters for laser ablation studies. Prepared filters characterized by LA-ICP-MS, XRF and ICP-MS following dissolution	66
Various	Airborne particulate matter	AE;ICP;S	Dust discharges from coal burning electricity generating plant analysed for Be, Cd, Co, Cr, Cu, Ni and Pb	67
Various	Airborne particulate matter	EPMA;—;S	Electron probe X-ray microanalysis used for the assessment of homogeneity IAEA candidate reference materials (coarse and fine fraction urban dusts)	68
Various	Atmospheric aerosols	XRF;—;S	Synchrotron excitation used for elemental analysis. Variability in measurement results attributed to the change in the intensity of excited synchronous radiation. Impurity levels in the filter media determined the LODs	69
Various	Atmospheric aerosols	PIXE;—;S	Particulates from atmosphere around a steel smelter collected on a time resolved streaker sampler. Counting period of 5 min used (LODs ranging from 2 ng m⁻³ for Cu to 0.1 µg m⁻³ for K)	70
Various	Air particles	XRF;—;S	Time resolved samples collected on a streaker sampler. Performance of capillary optics EDXRF system compared to PIXE for the analysis of urban aerosols	71
Various	Air particles	XRF;—;S	Receptor model source apportionment study undertaken as part of a pollution control strategy using fine, coarse and TSP samples	72
Various	Atmospheric aerosols	XRF;—;S	Synchrotron radiation source used in the analysis of Siberian aerosols	73
Various	Air particles	XRF;—;S	Interlaboratory trial compared synchrotron radiation source data obtained using XRF with that obtained using INAA, AA and AES techniques	74
Various	Air particles	XRF;—;S	Synchrotron source technique used to study the impact of anthropogenic aerosols	75
Various	Car exhaust emissions	XRF;—;S	Emission rates determined over different driving cycles. Elemental determinations suggest that 10–30% of samples are composed of metals, S and Si compounds	76
Various	Urban aerosols	PIXE;—;S INAA;—;S XRF;—;S	Analytical quality assessment of data carried out through exchanging filter samples and by the analysis of a set of multiple filters collected in parallel at one site	27
Various	Air	AE;—;G	F (685.604 nm), Cl (837.594 nm), S (921.29 nm) and C (833.515 nm) determined by time resolved LIPS using SF₆ and a number of fluorocarbons as surrogate analytes (LODs 20, 90, 1500 and 36 mg l⁻¹ respectively)	12
Various	Volatile metal and metalloids	MS;ICP;G	Air samples collected on a cryotrap (silanized wool, −175°C). Analytes flash desorbed onto an analytical column (10% of Supelco SP2100 on Chromosorb W HP (60–80 mesh) immersed in liquid N₂. Analytical column gently heated and the analytes flushed into the plasma using a stream of He. O₂ makeup used to minimize C-containing species and Xe used as an internal standard (LODs <1 pg for alkylated species)	34
Various	Urban aerosols	PIXE;—;S	Determination of elements collected on Whatman 41 filters. Effects of filter thickness and penetration of particles into the filter on beam attenuation and X-ray emission intensity studied	77
Various	Urban aerosols	MS;—;S	Review of methods currently used to make MS techniques into a tool for particle size determination presented	1
Various	Urban aerosols	MS;—;S	Review of TOF methods for real time analysis of individual particles	2
Various	Stack gas	AE;ICP;G	Effect of water vapour and alkali metal salts upon online air plasma system studied. Best LODS obtained for 50% Ar–50% air mixed plasma	9
Various	Urban aerosols	—;—;—	Review of techniques for the topochemical analysis of airborne particles	6
Various	Power plant emissions	MS;ICP;S	Microwave assisted dissolution procedure developed (HNO₃–HCl–HF) for the digestion of filter samples. NIST CRM 1633a and 1648 used in method development. Results for real samples compared with data obtained using INAA, GFAAS and HGAAS	78
Various	Atmospheric dust	AE;ICP;S	Water and acid soluble (0.1 M HCl) components measured	16
Various	Air particles	AE;ICP;S MS;ICP;S	Particulate matter collected on glass fibre filter from a beta gauge monitoring system subjected to a microwave assisted dissolution procedure (HNO₃–HClO₄–HF)	17
Various	Air particles	XRF;—;S PIXE;—;S	Fast, sensitive, non-destructive analysis carried out as part of research programme into air quality in Northern Italy	79
Various	Airborne particles	—;—;—	Review on compositional heterogeneity of airborne particles. Number of differing surface techniques highlighted	80
Various	Air particles	MS;—;S	Aerosol TOF system used to provide aerodynamic sizing and compositional data on individual particles. Chemical composition obtained by performing laser desorption ionization of individual particles using a Nd∶YAG laser (266 nm)	81
Various	Aerosols	XRF;—;S NAA;—;S AE;—;S	Interlaboratory comparison carried out on aerosol samples collected on Whatman 41 filters	28
Various	Air particles	XRF;—;S PIXE;—;S	Interlaboratory comparison carried out. Good agreement for most elements obtained. Differences noted for S in lightly loaded samples and with data generated using IC. Variability significantly decreased when identical samplers employed	29
Various	Air particles	XRF;—;S AA;F;S	Non-destructive analysis carried out as part of research programme into air quality near Greek lignite power plants. Pb analysed using AAS. Levels significantly lower than current regulatory limits	82
Various	Air particles	XRF;—;S	Non-destructive analysis carried out as part of research programme into air quality in Natal, Brazil	83
Various	Air particles	XRF;—;S PIXE;—;S INAA;—;S	Intercomparison trials between the three techniques carried out. The need for reference filter samples highlighted in order to assess bias between the techniques	30
Various	Air articles	TXRF;—;S	Evaluation of a microwave assisted vapour phase acid digestion procedure carried out	84
Various	Urban air	XRF;—;S	Impact of pollution sources assessed using a receptor model	85
Various	Air	;—;—;—	Atomic Spectrometry Update—Environmental analysis	7
Various	Atmospheric particulates	XPS;—;S	Surface analysis of particulates collected on Cu foils (passive samplers) carried out. C and O identified as the major species with traces of Na, NO₃⁻, Cl and SO₄²⁻ detected. Work demonstrated the variability in chemical composition across particle surfaces	39
Various	Sedimenting dusts	AA;—;S	Samples dried at 105°C and mineralized by boiling with 10 M HNO₃ under reflux for 4 h	86
Various	Atmospheric aerosols	AA;—;S	Elemental analysis carried out after precipitation in a gas discharge tube atomizer. Both impact and electrostatic precipitation investigated. Electrostatic precipitation exhibited a higher sampling efficiency than the impaction strategy	87
Various	Atmospheric particles	XRF;—;S	Review of microprobe techniques with tube and synchrotron excitation sources presented	3
Various	Airborne particulate matter	MS;ICP;S	LA (Nd∶YAG at 1064 nm) performed on samples collected onto PTFE filters. NIST 1648 Urban Particulate Matter used to prepare calibration filters. >20 elements determined	24
Various	Flue gas	AE;—;G	Real-time multi-metal continuous-emission monitor prototype developed. Tests conducted in conjunction with US EPA at an incinerator plant showed promise for the measurement of metals such as Be, Cd, Cr and Pb	10
Various	Wood and cooking fumes	XRF;—;S	Data used to help construct specific profiles for use in model for apportionment of fine particle sources in the Denver region of Colorado USA	88
Various	Airborne dust	TXRF;—;S	Review of methods for sample preparation, microwave-assisted vapour phase acid dissolution or slurry formation recommended	4
Various	Airborne particulate matter	AE;MIP;S, L	He plasma sustained within graphite furnace containing coaxially placed graphite rod antenna. Sequential thermal desorption used for metal fractionation studies. Size fractionated air samples from Hong Kong analysed	89
Various	Workplace air	AE;ICP;L	Five sample dissolution procedures tested within an inter-laboratory trial. Closed vessel microwave assisted procedures gave the best performance	31
Various	Workplace air	AE;ICP;G MS;ICP;G	Volatile metal and metalloid species trapped on AgNO₃ impregnated quartz filters. Samples analysed after dissolution in 10% HNO₃Alternatively, samples cryogenically trapped at –175°C onto glass wool packed column followed by analysis by GC-ICP-MS	37
Various	Airborne particulate matter	AE;ICP;S MS;ICP;G	Filter samples digested and analysed. Magnetic sector-multicollector instrument used to determine Pb isotopic ratios. Direct filter sampling using LA proved to be a rapid means of obtaining data	90
Various	Airborne particulate matter	—;—;—	Sampling techniques to produce realistic filter samples for method evaluation studies discussed	32
Various	Flue gases	AE;ICP;G	Flue gas analysed on-line. Desolvated USN used to produce calibration aerosols. To minimize errors, calibration should ideally be carried out with a gas of similar composition to the flue gas being analysed	91
Various	Arctic haze	MS;ICP;S	Particulate matter collected onto graphite discs mounted behind nozzles of a cascade impactor. Discs analysed using an ETA sampling system	15
Various	Airborne particles	AA;—;— —;ICP;—	Review of AA and ICP techniques for the analysis of airborne particles	5
Various	Air	—;—;—	Environmental analysis review. Section entitled Air analysis applications	92
Various	Air	AE;ICP;S MS;ICP;S	Book chapter review. Filtration sampling, sample dissolution and analysis discussed	93
Various	Airborne particulate matter	AE;ICP;S MS;ICP;S	Pt group elements leached from filter media. Separation and preconcentration carried out using modified C₁₈ silica gel column (as ion associates of their chlorocomplexes). Analytes eluted using ethanol, evaporated and analysed. Recoveries 100 ± 3% at the 1–20 µg level	94
Various	Air particulates	EMPA;—;S	C, O and N measured in individual particles using optimized windowless EMPA	95
Various	Air	—;—;—	Industrial hygiene chemistry review	96

1.1 Sample collection and pretreatment

Continuing on from last year's review,⁷ publication of papers detailing the development of continuous emission monitoring (CEM) instruments for on-line gas monitoring continue to grow. Research groups investigating CEM systems based upon on-line ICP-AES continue to address problems associated with introducing waste air into plasmas. Selzer describes his approach to correct for CN emission bands⁸ whilst Gomes et al. studied the effects of water vapour loading on the plasma temperature and resultant detection limits obtainable.⁹

Alternative laser based techniques such as LIBS and LIPS have been proposed for applications such as trace metals in stack gases,¹⁰ in ventilation hoods above electroplating baths¹¹ and the determination of C, S and halogens in air for potential use in chemical weapons verification programmes.¹² The development of these systems aided by advances in laser, fibre optic and solid state detector technologies will bring the goal of portable instrumentation for field use a step closer.

Advocates of impaction and electrostatic precipitator type samplers continue to research this sampling option. Luedke¹³ has studied the elemental composition of size fractionated aerosol collected at an Arctic research station. Graphite plates were used as targets behind the nozzles of a cascade impactor sampler. These plates were subsequently placed within an ETV-ICP-MS system for analysis. In a similar vein, and carrying on the work of the Sneddon group, Lee and co-workers^14,15 studied the sampling characteristics of an graphite impactor system coupled to ETAAS.

1.2 Instrumental analysis

1.2.1 Atomic absorption and atomic emission spectrometry. Such is the established nature of these techniques, operating in a conventional fashion, that few or no novel papers have appeared over the last year. The majority of papers reviewed were concerned with the use of these techniques for routine monitoring/survey work.^16–19

1.2.2 X-ray fluorescence. As highlighted in previous reviews, XRF techniques remain popular for the analysis of airborne particulate matter. The portability of small energy dispersive XRF instruments continues to be exploited for field use. Kienbusch and co-workers²⁰ used an EDXRF instrument for the analysis of Pb on air filter samples taken at paint removal operations. Comparisons with results obtained on filters dissolved and analysed by ICP-AES were encouraging and demonstrated the feasibility of this approach. However, it was disappointing to note the lack of papers detailing the use of online EDXRF systems for air analysis.

1.2.3 Mass spectrometry. Like ICP-AES/AA techniques, the maturity of ICP-MS systems has been exploited for the routine analysis of airborne particulate matter.^17,21 An interesting application published was the determination of ¹²⁹I in ambient air.²² Condensate samples (from chilled surfaces) were initially stabilized in a 0.25 M NaOH solution. Samples were then precipitated onto a filter membrane as PdI₂ by the addition of PdCl₂. The filter samples were placed within a miniature quartz furnace and heated to liberate I₂, which was subsequently flushed into the plasma torch. Correction from ¹²⁹Xe was required but the detection limit calculated from standards was found to be 30 fg. Improvements are required for quantitative sample collection and to reduce the Xe interference. Nomizu and co-workers in Japan²³ are developing an ICP-MS system for the elemental analysis of individual airborne particulates. Direct sampling of air into the plasma is used. Currently, they are using a newly developed high-speed pulse counting digital circuit board to measure flash signals from individual particles.

Use of alternative solid sample introductory systems such as the above mentioned ETV^13,15 and laser ablation^24,25,859 remain hindered by calibration difficulties and the knowledge that XRF techniques can at times do the job more efficiently. The ability of ICP-MS techniques to perform rapid isotopic measurements continues to be exploited for source apportionment studies as highlighted in an investigative study of dustfall in the vicinity of a Pb mining operation.²⁶

1.3 Trends

Three areas of development have been highlighted: namely, the use of round-robin trials to improve analytical quality, speciation of metals and metalloids and the examination of single atmospheric particles.

1.3.1 Interlaboratory trials. Air analysis, in this author's opinion, remains the poor relation, with respect to other fields of environmental analysis. The lack of suitable reference materials and the slow development of proficiency testing schemes employing realistic samples has lead to a number of workers questioning the quality of data obtained.^27–32 However, these researchers are making attempts to improve the situation. Cortes and Chilean co-workers exchanged filters between laboratories and compared data obtained using INAA, PIXE, XRF, IC and AAS.²⁷ In an attempt to minimize variability between samplers, a second batch of filter samples was taken at one location with identical samplers and was subsequently distributed. Canadian workers compared PIXE with XRF and similarly found better correlation when identical air samplers were employed.²⁹ Staff at IAEA noted good agreement between INAA, PIXE and EDXRF when used for the analysis of bulk samples and particulates captured on filters.³⁰ They concluded that reference materials would help increase data quality. Following on from this, the work of scientists at the Health and Safety Laboratory demonstrated that it is possible to produce large numbers of near identical filter samples using multi-port sampler technology.^31,32

1.3.2 Speciation. The interest in the speciation of airborne particulate matter continues to grow. Operationally defined speciation experiments using sequential leaching protocols are now being applied to airborne particulate matter. Andersen and co-workers studied the degree of exposure to soluble (leached with ammonium citrate) and insoluble nickel (HNO₃–HClO₄–H₂SO₄ digestion) in Ni refinery dust.³³ Researchers in Italy used a similar approach (4-step procedure) for the speciation of Cd in samples obtained from a coal fired power station. Careful consideration is required as to the validity of carrying out such experiments and how the data fits in with the understanding of exposure and health effects.

As reported last year a number of workers continue to exploit GC-ICP-MS^34–36 for the analysis of volatile metal(loid) species, e.g., methylated Pb, Se and Sn species. In an interesting presentation, French workers investigated the work environment in the microelectronic industries where highly toxic metal(loid) species are used in vapour phase deposition operations.³⁷ They recognised that it was important to have simple, robust methods if routine regulatory sampling for such species will be required in the future. In conjunction with the use of hyphenated systems they examined the use of chemically impregnated filters (AgNO₃) to trap volatile species. Samples are simply analysed by ICP techniques following digestion in dilute nitric acid. Along similar lines, a patent application for a sampling system to collect mixed phase samples was presented.³⁸ This sampler utilizes a twin filter system with the first filter, at ambient temperature, to collect the particulate phase and the second filter, at a temperature below ambient, to remove the vapour phase.

1.3.3 Single particle analysis. The analysis of single particles, looking at both bulk and surface properties, is attracting a great deal of attention. Current status of many of the techniques employed can be found in the review articles noted above. Hutton and Williams demonstrated the potential of imaging XPS to show localized variations across surfaces of individual particulates.³⁹ In a similar vein Japanese workers compared XPS and XAS techniques and concluded that XAS was more suitable for the chemical state analysis of S in aerosol samples.⁴⁰ This demanding area of analysis is providing aerosol scientists with a better understanding of particle source and formation and the consequences to human health arising from exposure.

2 Water analysis

In the period covered by this review the volume of papers describing analytical research and applications was considerable. A large amount of work was devoted to the preconcentration and separation of trace elements. Research into speciation has broadened and a greater number of elements were studied. There was, as in previous years, a considerable volume of research into how methodology could be improved to reduce detection limits.

The purpose of this part of the review is to highlight significant areas of development in the subject of water analysis. For an overview of the papers published during the review period the reader should consult Table 2.

Table 2 Summary of the analyses of water

Element	Matrix	Technique; atomization;presentation*	Sample treatment/comments	Ref.
*Hy indicates hydride and S, L, G and Sl signify solid, liquid, gaseous and slurry sample introduction, respectively. Other abbreviations are listed elsewhere.
Al	Groundwater	AE;ICP;L	Cation exchange fast protein LC used to determine different species. Al fluoro complexes determined by ion exchange chromatography and ETAA and Al organic complexes determined by colorimetric methods	173
Al	Waters	AA;ETA;L	Instrument suitable for on-site and online analysis. (LOD 0.9 ng ml⁻¹). Slurry produced LOD 0.02–0.6 µg g⁻¹	228
As	Drinking water	AA;ETA;L	Transversely heated graphite atomizer used with Zeeman background correction and Pd(NO₃)₂ and/or Mg(NO₃)₂ matrix modifiers (LOD 2.6 µg l⁻¹)	229
As	Drinking water	AF;Hy;L	Species separated using 1 or 2 RP 5 µm ODS guard columns with tetrabutylammonium hydroxide–1 mM malonic acid–5% methanol	182
As	Cloud water	MS;ICP;L	Meinhard concentric and ultrasonic nebulizers compared. Internal standards of Y and Rh. Calibration linear to 1.05 ng ml⁻¹. RSD of 1.8%. Correction required for ArCl interference (LOD 20 pg ml⁻¹ with pneumatic nebulizer and 5 pg ml⁻¹ with ultrasonic nebulizer).	230
As	Sea-water	AA;ETA;L	Sample mixed with Pd(NO₃)₂. Furnace conditions given. Comparison of D₂ and Zeeman background correction. LOD 0.6 µg l⁻¹ (D₂) and 0.8 µg l⁻¹ (Zeeman). RSD of 2–9% for both systems. Under-compensation by D₂ occurred in the presence of Na, K, Ca, Cl⁻ and SiO₂	231
As	Natural waters	MS;ICP, Hy;L	Compared chemical (NaBH₄) and electrochemical (electrochemical HG/Nafion membrane) processes. Interferences evaluated. RSD for 10 µg l⁻¹, <3%. Higher sensitivity for NaBH₄ (LOD 0.05 µg l⁻¹) than electrochemical HG (LOD 0.2 µg l⁻¹)	167
As	Sea-water	AF;Hy;L	Speciation of arsenate, arsenite, monomethylarsonate and dimethylarsinate at 193.7 nm. (LOD 2.3, 0.9, 2.4 and 3.7 ng l⁻¹ for As^III, As^V, MMA and DMA, respectively, in a 5 ml sample	232
As	Waters	MS;ICP;L AA;Hy;—	HPLC sample introduction into both systems compared. LOD (0.04–0.28 ng) for ICP-MS, 20 times lower than HPLC-HG-AAS	233
As	Waters	MS;ICP;L	Mathematical correction procedures for either ⁴⁰Ar³⁷Cl∶⁴⁰Ar³⁵Cl, ³⁵Cl¹⁶O∶⁴⁰Ar³⁵Cl or ³⁷Cl¹⁶O∶⁴⁰Ar³⁵Cl ratios combined with standard addition method. Results agreed well with CZE	178
As	Well and sea-water	AA;ETA;Sl	Sample (1 l) containing <0.5 µg As reacted to form molybdoarsenate complex and adsorbed onto activated charcoal. Calibration linear to 0.1 mg l⁻¹. Recoveries of 95–110% and 92–97% obtained with RSD <3.6% (n = 6) for 0.1 µg from well and sea-waters, respectively. (LOD 0.02 µg l⁻¹)	139
As	Natural waters	MS;ICP;G	Hg used for speciation. Interferences removed using Chelex 100 resin (LOD 39.7 ng l⁻¹ As^V and 11.8 ng l⁻¹ As^III)	234
As	Groundwater	MS;ICP;G	ET sample introduction used. Particular and colloidally bound species detected in the presence of high concentrations of Fe, Mn and S. Ultrafiltration (30 and 1 nm) used	235
As	Waters	MS;ICP;L	HPLC used to separate 6 compounds with anion exchange and isocratic elution. RSD of <7% (LOD 0.04–0.6 µg l⁻¹)	181
As	Various waters	AA;ETA;L	Determinand separated on-line by collection on a Pd coated pyrolytic platform after hydride generation. Speciation undertaken. Recoveries of 100% with RSD of 5%. Digestion of low organic containing samples eliminated (LOD 0.3 ng l⁻¹ for 25 ml sample)	207
As	Untreated water, tap water and bottled water	AA;Hy;L AF;Hy;L	Anion exchange and reverse phase cartridges separated As^III and As^V. Conditions investigated. HPLC and ICP-MS used to compare results (LOD 0.2 and 0.4 ng ml⁻¹ for As^III and As^V, respectively)	236
As	Natural waters	MS;ICP;L	Stability studies of As^III and As^V investigated. Protocol designed and tested	114
As	Mineral water	MS;ICP;L	Capillary electrophoresis used to separate As^III, As^V, monomethylarsonic acid and dimethylarsinic acid (LOD 1–2 µg l⁻¹)	180
As	River water	AA;ETA;L	<0.4 µg in 100 ml retained on a mixed cellulose ester membrane filter (MF). Resultant ion associate and MF dissolved in TMAH. Zirconyl nitrate used as matrix modifier (LOD 0.04 µg l⁻¹)	237
As	Natural and waste waters	AA;Hy;L	Samples spiked with tetraphenylarsonium chloride. Microwave digestion at low and high pressure gave low recoveries. High concentrations of organic matter interfered with analysis	238
As	Sea-water and hot spring water	AA;ETA;L	Analyte trapped on Zr coated graphite tube after HG (LOD 56 ng l⁻¹ for total As, 50 ng l⁻¹ for As^III and As^V and 80 ng l⁻¹ for As^III by alternative reduction methods)	179
As	Waters	MS;Hy, ICP;L	Speciation studies using ion exclusion IC. RSD 0.8–2.8% for 1 ng ml⁻¹ (n = 5). (LOD 1.1 pg ml⁻¹ As^V, 0.5 pg ml⁻¹ As^III and MMA)	183
As	Pore-water	MS;ICP;L	As^III extracted and detected by selective formation of As^III–pyrrolidine dithiocarbamate complex at pH 0.01–0.7. Complex adsorbed onto inner walls of knotted reactor and eluted with 1 M HNO₃. Schematics provided. RSD 2.8–3.9% (LOD 0.021 µg l⁻¹ for As^III and 0.029 µg l⁻¹ for total inorganic As)	177
As	Waters	MS;ICP;L	Solid phase micro extraction used with fibre coated in poly-(3-methylthiophene)	132
As	Mineral water	MS;ICP;L	Speciation carried out using capillary electrophoresis (LOD 1–2 µg l⁻¹)	239
As	Waters	MS;ICP;L	Comparison of species preservation techniques made	115
As	Sea-water	AA;ETA;G	In-situ collection of hydride in graphite furnace using high voltage electrostatic field. Generation/collection efficiencies 80 ± 5%. RSD 4% at 40 times LOD. (LOD 30 pg)	208
As	Natural waters	AE;ICP;G	Coprecipitation with poly(aluminium chloride) used for preconcentration. RSD 3.5% with recoveries of 94–112%	240
As	Pure water	MS;ICP;L	0.1–100 ng l⁻¹ detected	241
As	Drinking water	MS;ICP;L	High resolution instrument with HG introduction used. Membrane desolvation, mixed gas plasmas and addition of organic solvents evaluated (LOD 0.3 µg l⁻¹)	242
Au	River and sea-water	AA;ETA;L	Mg–W cell used for atomization. Calibration graphs linear up to 75 ng ml⁻¹ with recoveries of 91–94% and RSD of 0.6–8%. Interference from Cu observed (LOD 0.02 ng ml⁻¹)	243
B	Water	MS;ICP;L	µg l⁻¹ LOD obtained	244
B	Sea-water	MS;ICP;L	ETV sample introduction used with mannitol as matrix modifier. LOD 0.68 ng ml⁻¹	245
B	Waters	AE;DCP;L	Comparison made of colorimetric, fluorimetric and DCP techniques. produced best precision (LOD 0.002 mg l⁻¹ for colorimetric method and 0.1 mg l⁻¹ for DCP)	246
B	Natural waters	MS;ICP;L	Importance of blanks and removal of memory effects discussed	247
B	Rain water	MS;ICP;L	ID used with quadrupole system: ng ml⁻¹ concentrations detected	248
B	Natural water	MS;ICP;L	No preconcentration or separation required with high resolution system	249
B	Rain water	MS;ICP;L	ID (¹¹B∶¹⁰B) and negative thermal ionization isotope dilution (BO₂⁻) MS used (LOD 0.2 and 0.3 ng ml⁻¹, respectively)	250
Be	Waters	MS;—;—	3 MV tandem accelerator used for ¹⁰Be detection	251
Be	Natural waters	AA;ETA;L	Samples, filtered (0.1 µm) and acidified with HNO₃. (LOD 0.02 µg l⁻¹)	252
Bi	Sea-water and river water	AA;ETA;L	Preconcentration using electrodeposition in a Mg–W cell. Atomization conditions given. RSD 5.1% for 500 pg ml⁻¹ (LOD 7.8 ng l⁻¹)	253
Br	Swimming pool water	MS;ICP;L	Polyether ketone column (10 cm × 2 mm id) packed with polystyrene crosslinked with divinylbenzene (5 µm) and functionalized as an ion exchanger. 2-(Dimethylamino)ethanol used with a mobile phase (0.5 ml min⁻¹) of 60 mM NH₄NO₃. Eluent run into ICP-MS system. Sr used as internal standard. RSD 5% (n = 10) with a calibration range from 50–1000 ng l⁻¹(LOD 50–65 ng ml⁻¹)	254
Br	Waters	AE;MIP;L	Organobromine separated from inorganic chlorine using activated C followed by pyrolysis at 950°C under O₂. Bound halogens collected in 0.1 M NaOH solution. Recoveries of 92–105% (LOD 8 ng ml⁻¹)	255
C	Groundwater	MS;—;L, S	Samples placed in quartz sleeve, combusted at 1000°C in a stream of He and O₂. CO₂ removed by cryogenic trapping and transferred to GC column. After GC separation, CO₂ transferred to an ion source of a gas isotope ratio MS. Reproducibility <1% for >25 nmol C. Blanks problematic	256
C	Waters	MS;—;—	3 MV tandem accelerator used for ¹⁴C detection	251
C	Ice and snow	MS;—;—	AMS used to determine ¹⁴C in particlulates	257
C	Sea-water	MS;—;—	AMS used to investigate variability in ¹⁴C measurement on stored samples	258
C	Waters	MS;ICP;L	Dissolved C determined (LOD 0.1 mM)	224
C	Waters	MS;—;—	Curie point pyrolysis connected to GC carbon isotope ratio instrument. Used for aquatic humic substances	259
C	Sea-water	AMS;—;—	3-D data visualization techniques used for determination of ¹⁴C	260
C	Sea-water	AMS;—;—	New method of forming graphite from CO₂ stripped from matrix described	261
Cd	Waste-water	AA;CV;L	Cu, Ni, Pb and Zn interferences removed by adding KCN to borohydride solution. FI used. Results compared to ETAAS	164
Cd	Stream water	AA;ETA;L	Portable system powered by 12 V car battery described. W coil used for atomization. Purge gas of H₂ in Ar. Detection using a miniature CCD system. Near line method for background detection obtained an RSD of 10% (LOD 3 µg l⁻¹)	262
Cd	Sea-water	AA;ETA;L	Preconcentration using quaternary ammonium salt bonded onto a C₁₈ silica gel (Aliquat 336). Recoveries 99–100%. RSDs 1.8% (n = 5) for river water and 5.3% (n = 6) for sea-water (LOD 0.2 ng l⁻¹)	263
Cd	Various	AA;ETA;L	Preconcentrated with NaDDC and passed through a mini-column containing silicon tubing packed with fullerene C₆₀. W coil atomizer. Matrix effects of cations investigated (LOD 22 ng l⁻¹)	150
Cd	River water	MS;ICP;L	Assessment of sampling time, mass bias, detector dead-time and spectroscopic interferences when using isotope ratio measurements made	227
Cd	Sea-water	AA;ETA;L	On-line preconcentration using 4-(2-pyridylazo)resorcinol (PAR) or 2-(2-pyridylazo)-5-dimethylaminophenol (PADMAP). Other conditions given. Linear calibration up to 1 µg l⁻¹ with RSD of 2.7–15% (PAR) and 1.2–8% (PADMAP). (LOD 4 mg l⁻¹ and 1.7 mg l⁻¹, respectively)	264
Cd	Sea-water	AA;ETA;L	On-line preconcentration using APDC complex formation and separation with a C₁₈ column. RSD 3.2% for 200 pM (LOD 42 pM)	265
Cd	River and sea-water	AA;F;L	Preconcentration using Saccharomyces cerevisiae immobilized on sepiolite (regeneration of column took 1 h). 1 M HCl used for elution	148
Cd	Sea-water	—;—;—	A comparison made of the use of silica immobilized poly(L-cysteine) and 8-hydroxyquinoline immobilized on controlled-pore glass for preconcentration. FI system used; numerous parameters and properties compared	153
Cd	River water	MS;ICP;L	Double focusing sector field system used for ID and compared with quadrupole based instrument. Experimental parameters investigated. Precision 0.2–0.3%	266
Cl	Ice	MS;—;—	Static SIMS used to study interactions between molecular Cl, dichloromonoxide and hypochlorous acid in solid ice films	267
Cl	Waters	AE;MIP;L	Organochlorine separated from inorganic Cl using activated C followed by incineration at 950°C under O₂. Bound halogens collected in 0.1 M NaOH solution. Recoveries 92–105%. (LOD 3 ng ml⁻¹)	255
Cl	Waters	AE;MIP;G	Polyacrylate fibre used for solid phase micro-extraction. Nafion used to dry moisture from fibre (LOD 9 µg l⁻¹)	134
Cl	Melt inclusions	MS;—;L	Ion microprobe SIMS used	268
Cl	Groundwater	AMS;—;—	³⁶Cl used to date groundwaters	269
Cr	River water and sea-water	AA;ETA;L	Spirulina platensis (a cyanobacterium) and Phaseolus (a plant-derived material) used to accumulate Cr^III and Cr^VI. Experimental conditions investigated for different species. Uptake modelled (LOD for river water with concentration factor of 10, 0.1 µg l⁻¹ and for sea-water with a concentration factor of 20, 0.05 µg l⁻¹)	149
Cr	Waste water	AE;ICP;L	On-line separation of Cr^III and Cr^VI using a 5 cm RP C₁₈ column. Hydraulic high pressure nebulization used. Analysis time 5 min. Recoveries >98% (LOD 4 µg l⁻¹ for both species)	188
Cr	Sea-water	AA;ETA;L	Sample in 10 mM HCl and a flow (1.3 ml min⁻¹) of aqueous 0.05% APDC passed into a mixer for 1 min. Cr^VI complex adsorbed onto walls of knotted reactor which was washed with 0.02% HNO₃ at 2 ml min⁻¹ for 15 s. Complex desorbed with 55 µl of ethanol and transported to furnace for detection. Interference from Co^II tolerated when ratio of Co^II∶Cr^VI < 250∶1. (LOD 4.2 ng l⁻¹)	270
Cr	Ground, river, sea-water and CRM (WP-15)	XRF;—;S	Cr^VI retained on activated alumina and Dowex 1-X8; Cr^III on Dowex 50W-X8, Zeolite and activated alumina. Dowex resins best for Cr speciation. RSD 4%. Preconcentration factors (PF) of 50 and 500 used. Limitations found for saline solutions (LOD 0.03 and 0.04 mg l⁻¹ with PF of 500)	189
Cr	Water	AA;ETA;L	Instrument suitable for on-site and on-line analysis (LOD 0.03 ng ml⁻¹)	228
Cr	Tap water	AA;—;—	HPLC separation of species followed by LA sample introduction. (LOD 30 pg ml^–1 for Cr^VI)	271
Cu	Sea-water	MS;ICP;L	Amberlite IRC-718 removed interfering ions of Na, S, P and polyatomic ions. ²⁰⁹Bi detected. Average recovery for 100 mg, 97.9%	272
Cu	Waters	Various	Review of analytical practice for waters and eluates presented	273
Cu	Groundwater	MS;ICP;L	No sample pretreatment. ⁶⁵Cu tracer added for ID calibration. Biased isotope ratios avoided using a double focusing sector field instrument operated at a high resolution setting (R = 3000)	203
Cu	Sea-water	MS;ICP;L	Amberlite IRC-718 removed interfering ions of Na, S, P and polyatomic ions. ¹¹⁸Sn and ¹²⁰Sn detected. Recovery 99.6% for 100 mg	272
Cu	River water	AE;ICP;L	Induction coil used for vaporizing analyte. HCl used as carrier gas (0.04–0.7 ng ml⁻¹)	218
Cu	Sea-water	AA;ETA;L	Simultaneous detection with Mn using either Pd or Pd–Mg matrix modifier. Longitudinal Zeeman background correction used. RSD <10% (LOD 0.06–0.15 µg l⁻¹)	274
Cu	Waters	AA;ETA;L	Sample pretreatment using acid digestion automated using robotics. Preconcentration on a PTFE knotted reactor as the pyrrolidine dithiocarbamate chelate. Linear calibration from 0.2–2.0 g l⁻¹	275
Cu	Pore-water	AA;ETA;L	Comparison made of acidification methods used for the storage of sulfidic samples	116
Cu	Sea-water	MS;ICP;L	Amberlite IRC-718 removed interfering ions of Na, S, P and polyatomic ions. ⁶³Cu and ⁶⁵Cu detected. Average recovery 99.8% for 100 mg	272
Cu	River and sea-water	AA;F;L	See Cd ref. 148	148
Cu	Sea-water	—;—;—	See Cd ^ref. 153	153
Cu	Waters	AA;ETA;L	W metal furnace used after preconcentration onto chitosan. Calibration graphs linear to 0.3 µg. RSD 3.8% (n = 5) for 0.1 µg Cu in 100 ml (LOD 0.002 µg l⁻¹)	276
Cu	Waters	AA;F;L	Cu complexed with 1-(2-pyridylazo)-2-naphthol and separated on column providing a 200 fold enrichment factor. Calibration linear to 250 µg. 95–99% recovery with an RSD of 3.8%	277
Cu	Sea-water	MS;—;—	Metal speciation and characterization of complexing ligands described	278
Cu	River water	AA;—;—	Determinand separated from Al, Ca, Cd, Fe, K, Mg, Na, Pb and Zn with sequential metal vapour elution analysis using a Mo column with three alumina ring supports set in a glass dome. Vaporization temperature of 1950°C and a column temperature of 1900°C used. Calibration graphs linear to 20 ng. RSD 4.8% with recoveries of 94–107%	279
Cu	Waters	AA;ETA;L	Preconcentrated with activated C impregnated with 1,2-cyclohexanedione-dioxime.W metal furnace used. Linear calibration range to 12 µg l⁻¹ and RSD of 2.9% at 1 µg l⁻¹. Interferences investigated (LOD 0.13 µg l⁻¹)	280
D	Natural waters	MS;—;L	Deuterium : hydrogen isotope ratio measured using Mn as reducing agent. Reaction time of 40 min at 520°C used. Reproducibility ±1%	281
F	Drinking and sea-waters	AF;—:L MS;ICP;L	Excess Al³⁺ added, F determined by measurement of AlF²⁺ after separation on an ion exchange column. Fe, Mg and Zn interfered with fluorescence detection	282
F	Melt inclusions	MS;—;L	Ion microprobe SIMS used	268
Fe	Sea-water	MS;ICP;L	Samples spiked with ⁵⁷Fe. Mg(OH)₂ precipitated with Fe in co-precipitation. ⁵⁶Fe∶⁵⁷Fe ratio determined. LOD 0.05 nM	283
H	Waters	MS;—;L	H/D/O equilibration technique used smaller sample volumes, 0.25–4.0 ml. High precision obtained with 0.25 ml of sample	284
H	Waters	MS;—;L	Calibration of an isotope ratio MS working standard for ²H∶¹H using ²H₂O described. Sample handling caused most variability	285
Hf	Sea-water	MS;ICP;L	200 ml sample acidified to pH 2 and spiked with 100 ng Zr and pumped through a Teflon column (10 cm × 8 mm id) packed with Chelex-100 resin (100–200 mesh). Column washed with 0.01 M HCl, analytes displaced with 3 × 10 ml aliquots of 2 M HNO₃. In used as internal standard. Concentration calculated from¹⁷⁸Hf∶¹⁷⁷Hf. RSD 22–9% for 0.28–1.4 pmol kg⁻¹ (LOD 0.03 pmol kg⁻¹)	286
Hg	Sea-water	AE;ICP;L	Determinand preconcentrated on-line with a 3 cm × 3 cm silica packed column, functionalized with methylthiosilicylate (TS-gel) and placed in an injection valve of a FI manifold. Resin synthesis rapid and simple. Metal separated from column using thiourea and mixed on-line with NaBH₄. Linear range 5–1000 ng ml⁻¹ Hg^II with an RSD of 2.1% for 10 ng ml⁻¹	287
Hg	Waters	AE;ICP;L	Preconcentration by sorption on anion-exchange resin loaded with 1,5-bis-[(2-pyridyl)-3-sulfophenylmethylene]thiocarbonohydrazide. CV used. Linear from 5–1000 ng ml⁻¹ with an RSD of 3.6% at 10 ng ml⁻¹ and 1.3% at 100 ng ml⁻¹ (LOD 4 ng ml⁻¹)	126
Hg	Waters	—;—;—	Review with 162 references discussing strategies for speciation extraction and determination	194
Hg	Drinking water	MS;ICP;L	Au added to concentrate Hg into an amalgam. Recovery 99% (LOD 0.032 µg l⁻¹)	117
Hg	Drinking water	AA;ETA;L	Complexation with 2,3-dimercaptopropane-1-sulfonate used. Complex concentrated on Sep-Pak C₁₈ SPE cartridge. Zeeman background correction used giving a linear calibration from 5 to 100 ng with an RSD of 1.22% (n = 5) for 50 ng Hg (LOD 0.053 µg l⁻¹)	196
Hg	Brine	MS;ICP; L	CV sample introduction used for complex matrices, e.g., salinity 3–200 parts per thousand and samples of >95% CaCO₃	288
Hg	Natural and waste waters	AA;CV;L	Samples spiked with 10–100 µg l⁻¹ 2-[(ethylmercury)thio]benzoic acid. Compared microwave digestion at low and high pressure; good recoveries found at high pressure (200°C, 400 kPa)	238
Hg	Natural waters	AA;CV;G	Inorganic and alkylmercury extracted using a chelating sorbent of thionalide loaded Bio-beads SM-7. Stability of Hg forms such as Hg^II, CH₃Hg and C₂H₅Hg⁺ during sample processing investigated	289
Hg	Waste water	—;—;L	Preconcentration performed using a dithizone impregnated ultra-high molecular weight polyethylene membrane. Conditions optimized for speciation studies	162
Hg	Waste water	AA;ETA;L	Sample mixed with NaBH₄ and gaseous species transported to graphite tube coated with Rh modifier. Linear calibration to 34.2 pg with RSD of 2.3% for 4 ng. Recoveries between 95–104% (LOD 37 pg)	290
Hg	Waters	MS;ICP;G	Comparison made of cryotrapping and Au amalgamation techniques	36
Hg	Waters	—;—;—	Use of enriched isotopes as tracer isotopes described	291
Hg	River water	MS;ICP;G	Study of extraction and preconcentration in mini-columns for field sampling described. HPLC and vapour generation used	292
Hg	Waters	AA;CV;G AF;—,—	SnCl₂ reduction used after digestion of organic species by bromination. Linear calibration to 12000 ng l⁻¹ (LOD 2.5 ng l^–1)	293
Hg	Geothermal water	AA;CV;—	Hg trapped onto Au wire wool	294
Hg	Waters	AA;—;—	Review of organomercurial determination with 87 refs.	295
I	Waters	MS;—;L	¹²⁹I in 100 l sample absorbed onto an anion exchange resin. ¹²⁹I eluted with 8% NaClO₄, extracted with CCl₄ and back extracted with water. AgI source prepared by precipitation. ¹²⁹I detected by accelerator MS. Recovery >60% (LOD 2 × 10⁻¹⁰ Bq l⁻¹)	296
I	Sea-water	MS;—;—	Determination of ¹²⁹I∶¹²⁷I using carrier free method based on reacting I₂ with metallic Ag. Solution centrifuged and Ag powder separated. After washing, drying and pressing of the powder, the resulting support used as a cathode in a Cs sputter ion source	297
I	Sea-water	NAA;—;L	¹²⁹I and ¹²⁹I∶¹²⁷I ratio measured. Recoveries of 60–95% during preconcentration and 98% in post-irradiation purification. (LOD 2–3 × 10⁻¹³ g for ¹²⁹I)	298
In	Natural waters	MS;ICP;L	Use of ID with ¹¹³In∶¹¹⁵In and ⁸⁹Y as internal standard. (LOD 0.01–0.02 pmol kg⁻¹)	299
Mn	River water	AE;ICP;L	See Cu, ref. 218	218
Mn	Sea-water	AA;ETA;L	See Cu, ref. 274 (LOD 0.04–0.14 µg l⁻¹)	274
Mn	Sea-water	AA;ETA;L	Comparison made of different operating parameters	300
Mn	Lake water	AE;plasma;L	Solid phase micro extraction of methylcyclopentadienylmanganese tricarbonyl followed by GC separation. RSD 7.1% and recovery of 96 ± 3% for 10 pg l⁻¹ (LOD 0.3 pg l⁻¹ as Mn)	301
Mo	River water	AA;—;—	See Cu, ref. 279	279
Mo	Sea-water	MS;ICP, ETV;L	NH₄F modifier used. (LOD 0.30 ng ml⁻¹)	245
N	Waters	MS;—;—	Isotope ratio MS used to measure N turnover. Acidified filters used to collect samples. Recovery rates 98–102%	302
N	Natural water	MS;—;L	ID method based on the analysis of the volatile derivative of 1-phenylazo-2-naphthol (Sudan-1)	303
N	Waters	MS;—;—	Modified noble gas instrument used to measure ⁴⁰Ar∶³⁶Ar, N₂∶⁴⁰Ar, ⁴He∶⁴⁰Ar and C∶N ratios as well as the δ¹³C and δ¹⁵N	304
Ni	Waters	AA;ETA;L	Electrochemical reduction carried out in a flow-through electrolytic cell followed by generation and transfer of Ni(CO)₄ to atomizer; 70% efficient (LOD 87 ng l⁻¹ for a 1.0 ml sample)	210
Ni	Sea-water	AA;ETA;L	Microcolumn packed with 1-(di-2-pyridyl) methylene thiocarbonohydrazide in the autosampler tip used for preconcentration with direct elution into graphite furnace. Simplex optimization used. Sample throughput of 36 samples h⁻¹ for 60 s preconcentration time (LOD 0.06 ng ml⁻¹)	305
Ni	Natural waters	MS;ICP;L	Sample introduced by on-line carbonyl vapour generation. ID used. Uncertainty of 4.56% found	168
O	Waters	—;—;—	On-line method used with the traditional CO₂–H₂O equilibration technique	306
O	Waters	AA;—;—	Chemical oxygen demand determined by measuring Cr^VI after appropriate pre-treatment. Recoveries of 98–108% with RSD of 3.3%	307
Os	Waste water	AA;ETA;L	Sample (50 ml) oxidized by the addition of 30% H₂O₂, treated with 4 ml of 12 M HCl and 1 ml of 0.1 g ml⁻¹ thiourea. Solution diluted to 100 ml. Atomization at 318°C using 290.9 nm line. RSD 3% (LOD 3.6 ng)	308
P	Production water	MS, AE;ICP;L	P in phosphino-polycarboxylates. SEP-PAK^™ used to separate inorganic and organic P. Various nebulizers tested (LOD 0.8 µg ml⁻¹ and 46 µg ml⁻¹ with ultrasonic cross-flow nebulizers, respectively)	309
P	Waters	AE;ICP;L MS;ICP;L	Low flow high efficiency nebulizers assessed. Effects of dissolved solids investigated	310
Pb	Various	AA;ETA;L	Preconcentration with NaDDC and passed through a mini-column containing silicon tubing packed with fullerene C₆₀. W coil atomizer used. Matrix effects of cations investigated (LOD 75 ng l⁻¹)	150
Pb	Tap and sea-water	—;—;—	Novel ion exchange resin based on an ion templated polymer used for removal and preconcentration	125
Pb	Snow, rain, river water and tap water	AA;ETA;L	Coating the pyrolytically coated graphite tube with Hf, Nb, Pd, W and Zr investigated to improve sensitivity	311
Pb	Waters	AA;ETA;L	See Cu, ref. 312. Linear calibration range to 12 µg l⁻¹ and RSD of 3.8% at 1 µg l⁻¹ (LOD 0.75 µg l⁻¹)	280
Pb	Waters	AE;MIP;G	Gaseous analytes purged from aqueous solutions with inert gas and dried using Nafion membrane; compounds trapped in a thick film-coated capillary tube and separated isothermally on a 1 m GC column before detection. Speciation analysis, including sample preparation, carried out in <5 min (LOD 5 pg l⁻¹)	214
Pb	Various	AA;ETA;L	See Cd, ref. 150 (LOD 23 ng l⁻¹)	150
Pb	River and tap water	AA;ETA;L	50 mM Zephiramine added to 10 ml of sample and filtered through a 5 mm diameter membrane to collect pyrrolidinedithiocarbamate complex. 3 mm diameter disc punched from membrane and dissolved in methyl cellulose. 40 µl analysed. Recovery 100% with RSD of 4.51% at 40 ng l⁻¹ (LOD 10 ng l⁻¹)	160
Pb	Sea-water	AA;ETA;L	Determinand separated from NaCl (up to 3 g l⁻¹) by adsorption on a polymer modified with Cryptand (222B) followed by elution with 0.1 M HNO₃. Recoveries 85–95%	313
Pb	Lake and drinking water	AA;ETA;L	Platform atomization used with pyrocoated electrographite tubes and a combined modifier of Ni, ammonium dihydrogenphosphate and NaOH. Recoveries 85–97%	314
Pb	Tap water	AE;MIP;G	Water (20 ml) adjusted to pH 4 with 1 ml of acetate buffer and mixed with 0.5 ml of 0.1 M Na₂EDTA and 400 µl methanolic 0.3% tetrabutylammonium tetrabutylborate followed by extraction with 500 µl hexane. Extract stored at –20°C in the dark. Calibration graphs linear to 3 pg (as Pb) of butylated organolead. Recoveries were 83–95% (LOD 43–83 pg l⁻¹)	191
Pb	Natural waters	AA;ETA:L	Speciation and preconcentration carried out using Chelex resin (LOD 0.1 µg l⁻¹)	315
Pb	Waters	AE;ICP;L MS;ICP;L	Low flow high efficiency nebulizers assessed. Effects of dissolved solids investigated	310
Pb	River water	MS;ICP;L	²⁰⁶Pb∶²⁰⁸Pb and ²⁰⁶Pb∶²⁰⁷Pb ratio compared	316
Pb	Waters	MS;ICP;L	²⁰⁶Pb∶²⁰⁷Pb, ²⁰⁷Pb∶²⁰⁸Pb and ²⁰⁶Pb∶²⁰⁸Pb determined	317
Pb	Sea-water	—;—;—	See Cd, ref. 153	153
Pb	Tap water	AE;ICP;L	FI on-line preconcentration used with a knotted reactor and ultrasonic nebulization. 140 enhancement factor achieved. (LOD 0.2 ng ml⁻¹)	157
Pb	Natural waters	AA;ETA;L	On-line separation and electrochemical preconcentration used with a W coil atomizer. Enrichment factor 25 after 120 s electro-deposition. RSD <5%. Interferences investigated (LOD 0.2 µg l⁻¹)	318
Pb	Sea-water	—;—;—	Diethyldithiophosphate ammonium complex separated on a C₁₈ microcolumn. Calibrations linear from 25–100 and 250–1000 µg l⁻¹ in 5 and 10 ml samples, respectively. (LOD 1.48 and 0.51 µg l⁻¹ for 16- and 48-fold enrichment factors, respectively)	319
Pd	Snow and ice	MS;ICP;L	Double focusing system used	320
Pd	Snow and ice	MS;ICP;L	Micro-concentric nebulizer used with a double-focusing system. RSD 28% (LOD 0.09 pg g⁻¹ for ¹⁰⁶Pd)	321
Pt	Sea-water	MS;ICP;L	FI sample introduction with ultrasonic nebulization and membrane desolvation used. U removed by co-precipitation with NdF₃ followed by ion exchange. Enrichment factor 1000 (LOD 5 fg l⁻¹)	322
Pt	Tap water	AA;ETA;L	100 ml sample containing 0.1–1 µg l^–1 of determinand mixed with 0.7 M HNO₃ containing 1 ml of 1% APDC for 120 min at room temperature. Mixture passed through PTFE knotted reactor. Complex desorbed with CH₃OH. Analysis conditions given. Recoveries >90% with an RSD of 2.5% (LOD 10 ng l⁻¹)	155
Pt	Snow and ice	MS;ICP;L	See Pd, ref. 320	320
Pt	Snow and ice	MS;ICP;L	See Pd, ref. 321. RSD 28% (LOD 0.009 pg g⁻¹ for ¹⁹⁵Pt)	321
Ra	Ground water	MS;—;—	Thermal ionization MS method developed for the analysis of ²²⁶Ra to sub-picogram levels in <200 ml sample	323
Ra	Mineral water	MS;ICP;L	Cation resin (AG 50W-X8, 100–200 mesh) used. Recovery of 97% for ²²⁶Ra. (LOD 0.01 pg l⁻¹)	324
REE	Sea-water	MS;ICP;L	Monisotopic REE (Ho, Pr, Tb, Tm) determined	325
REE	Sea-water	MS;ICP;L	Determinands extracted using poly(acrylaminophosphonic dithiocarbamate) fibres cut to <0.25 mm and slurry packed in a column (5 cm × 4 mm id). Sample at pH 5 pumped through at 7 ml min⁻¹, washed with water and eluted with 5 ml 0.01 M ammonium citrate (1 ml min⁻¹). 200 fold enrichment factor achieved with an RSD of <5% (n = 3) (LOD 0.2–2 ng l⁻¹)	135
REE	River water	MS;ICP;L NAA;—;—	10 elements measured	326
Various	Sea-water	MS;ICP;L	Optimized method for 15 REE described. 8-Hydroxyquinoline immobilized on a polyacrylonitrile hollow fibre membrane produced a 300 concentration factor. Recovery between 91–107% and RSD <5%	137
Rh	Snow and ice	MS;ICP;L	See Pd,^ref. 320	320
Rh	Snow and ice	MS;ICP;L	See Pd, ref. 321. RSD 28% (LOD 0.03 pg g⁻¹ for ¹⁰³Rh)	321
Ru	Waters	AA;ETA;L	Metals preconcentrated using chitosan. Calibration linear to 5 µg l⁻¹, 3–4% RSD at 1 µg l⁻¹ (LOD = 0.06 µg l⁻¹)	327
S	Sea-water	MS;ICP;L	Hexapole device used to reduce interfering polyatomic species in the determination of isotope ratios	226
S	Melt inclusions	MS;—;L	Ion microprobe SIMS used	268
Sb	River water and sea-water	AA;ETA;L	See Cr, ref. 149 (LOD for river water with concentration factor of 4, 0.9 µg l⁻¹, and for sea-water with a concentration factor of 40, 0.09 µg l⁻¹)	149
Sb	Natural waters	Various	Review of speciation analysis at trace and ultra-trace levels	110
Sb	Sea-water and tap water	AF;—;L	Reduction of acid and borohydride concentration achieved by generating stibine at 70°C using an additional hydrogen flow to sustain the flame. New phase separator used with Triton X-100 wetting agent. (LOD 0.3 µg l⁻¹)	59
Sb	Tap water	AA;ETA;G	Pd electrodeposited on graphite tube produced a more viable coating than thermally formed Pd coatings for preconcentration of SbH₃ after HG. Calibration linear up to 9.5 ng. (LOD 71 pg)	328
Sb	Landfill seepage waters	MS;ICP;L	Organic Sb, Sb^III and Sb^Vseparated by HPLC prior to detection. Conditions given. Chloride interfered with analysis	175
Sb	Cloud water	MS;ICP;L	Meinhard concentric and ultrasonic nebulizers compared. Internal standards of Te and Rh. Calibration linear to 0.5 ng ml⁻¹; RSD 1.9%.(LOD 100 pg ml⁻¹ with pneumatic nebulizer and 20 pg ml⁻¹ with ultrasonic nebulizer)	230
Sb	Waters	MS;ICP;L	Review of preconcentration, separation and analysis methods for speciation with 98 references	174
Sb	Sea-water	AA;ETA;G	In-situ collection of hydride in graphite furnace with high voltage electrostatic field described. Generation/collection efficiencies of 62 ± 6% achieved. RSD 4% at 40 times LOD. (LOD 33 pg)	208
Sb	Waters	AA;ETA;— AA;Hy;G	Separation techniques discussed 113 references cited	329
Se	Sea-water	AA;ETA;L	Se^IV determined using FI with HG and trapping in a graphite furnace. 1000-fold concentration factor found. Various sample pretreatment methods allow speciation studies and detection of Se^IV, Se^VI and Se^II (LOD 1.5 ng l⁻¹ for Se^IV in 25 ml sample)	199
Se	Sea-water	AF;Hy;L	Selenite determined by acidification with HCl and merging online with 5% m/v KH₂PO₄ to remove interferences. Total inorganic Se determined by merging with 30% m/v NaBr and pre-reduction online using microwave irradiation at 210 W for 60 s. RSDs 94–104% and 92–98%, respectively (LOD 5 ng l⁻¹ (Se^IV) and 4 ng l⁻¹ for total inorganic Se)	198
Se	Cloud water	MS;ICP;L	Meinhard concentric and ultrasonic nebulizers compared. Internal standards of Y and Rh used. Calibration linear to 1.38 ng ml⁻¹; RSD 2.2% (LOD 20 pg ml⁻¹ with pneumatic nebulizer and 5 pg ml^–1 with ultrasonic nebulizer)	230
Se	Groundwater	MS;ICP;G	ETV sample introduction used. Particular and colloidally bound species, separated by ultrafiltration (30 and 1 nm), detected in high concentrations of Fe, Mn and S	235
Se	Waters	MS;ICP;L AA;ETA;L	Se^IV, Se^VI, selenomethionine (SeMet) and trimethylselenonium iodide (TMSe) analysed with Pd modifier. Se^VI, 37% less sensitive than others using ETAAS. Less variation in sensitivity found between species by ICP-MS	330
Se	Waters	AA;Hy;L	Investigated sorption properties of oxides of SeO₄²⁻∶SeO₃²⁻ between soil and water systems	200
Se	Waters	AA;ETA;L	Extraction from perchlorate–bromide medium into hexane used for preconcentration. Enrichment factors of 2–40 achieved. Ni(NO₃)₂ modifier used	331
Se	Natural and waste waters	AA;Hy;L	Samples spiked with D,L-selenomethionine chloride. Microwave digestion of samples at low and high pressure carried out, good recoveries reported	238
Se	Mineral water	AA;Hy;L	Hydride absorbed into alkaline solution (2% m/v NaOH–0.05 mol l⁻¹ H₂O₂). RSD 2.8% for 1 ng ml⁻¹ (LOD 5.7 pg ml⁻¹)	165
Se	Mineral water	AF;Hy;L	SeH₂ collected on Au wire at 200°C and released for detection at 600°C. RSD 3% for 1 ng ml⁻¹ (LOD 5 pg ml⁻¹)	166
Se	Waters	MS;ICP;G	Comparison of cryotrapping and Au amalgamation techniques made	36
Se	Sea-water	AA;ETA;G	In-situ collection of hydride in graphite using high voltage electrostatic field described. Generation/collection efficiencies of 71 ± 3% achieved. RSD 4% at 40 times LOD (LOD 16 pg)	208
Se	Waters	MS;ICP;L	Ion exchange, chromatographic separation and addition of H₂SO₄ used	332
Se	Groundwater	AF;—;—	Se^IV and Se^VI separated by HPLC on a C₁₈ Rutin column modified with 10 mM didodecyldimethylammonium bromide in methanol–H₂O (1∶1) at 1 ml min⁻¹. Ultrasonic nebulization used. Se determined at 196 nm. Recoveries of 200 ng ml⁻¹ of Se^IV and 280 ng ml⁻¹ of Se^VI 104–110% (LOD 8.6 ng ml⁻¹ Se^IV and 30 ng ml⁻¹ Se^VI)	333
Si	Waters	AE;ICP;G	Volatile species generated using interaction of Si and F^– in H₂SO₄. Linear response from 0.1–200 mg l⁻¹ and 0.1–1000 mg l⁻¹ with RSD of 2 and 8% (LOD 0.004 and 0.02 mg l⁻¹)	334
Sn	River water	MS;Hy, ICP;L	0.015 M H₂SO₄–0.2% (m/v) sodium tetraborate–0.015 M NaOH and Ar at 1.1 l min⁻¹ used with strongly basic anion exchanger to remove transition elements. Recoveries between 95–115% found (LOD 12 ng l⁻¹)	335
Sn	Sea-water	AA;ETA;G	HCl and NaCl added to sample and analyte extracted in hexane. Extract concentrated and residue dissolved in ethanol and separated on a cation exchange column. Adsorbed compounds eluted with HCl–methanol and reduced with NaBH₄. Hydrides extracted into hexane and separated by GC	336
Sn	Sea-water	AA;ETA;L	Amberlite XAD-2 impregnated with tropolone used for preconcentration. Retained organotin compounds eluted with MIBK. RSD <4.1% for 0.1–0.4 µg l⁻¹ (LOD 13 ng l⁻¹)	337
Sn	Waters	MS;ICP;L	See As, ref. 132	132
Sn	Waters	MS;ICP;G	Solid phase micro-extraction used with headspace analysis and GC separation. Experimental conditions investigated	133
Tc	Surface waters	MS;ICP;L	Preconcentration and separation achieved, using Teva Spec column. Removal efficiency of 99.93% (LOD 0.06 ng l⁻¹)	338
Th	Fresh water	AA;ETA;L	Colloid precipitate flotation used for preconcentration. Recoveries of 95% for 0.5–1 µg l⁻¹ (LOD 0.08 µg l⁻¹)	339
Th	Sea-water	MS;ICP;L	On-line solid phase extraction removed ²³²Th prior to detection with ETV sample introduction. CRMs used for comparison	129
Th	Natural waters	MS;ICP;L	Solid phase extraction used with TRU spec (EiChrom) and Hyphan (Riedel-de Haen) resins; ng to pg ml⁻¹ detected	131
Th	Sea-water	MS;ICP;L	Vapour generation sample introduction and ID used. Precision <10%. (LOD 0.01 ng ml⁻¹)	169
Tl	Freshwater and waste water	AA;ETA;L	Extraction method using tributyl phosphate resin described. Recoveries between 95–105%; RSD 7.5% for 0.032 mg l⁻¹ (LOD = 3 µg l⁻¹)	121
U	Groundwater	MS;—;—	Thermal ionization method developed for the analysis of ²³⁴U and ²³⁵U at sub-picogram levels in 1–2 ml sample	323
U	Sea-water	MS;ICP;L	ETV sample introduction used with NH₄F modifier. Matrix problems due to strong memory effects observed (LOD 0.03 ng ml⁻¹)	245
U	Sea-water	MS;ICP;L	ASV with Pr gallate used for preconcentration. 1% HNO₃ released U for detection.	340
U	Waste water and sea-water	XRF;—;—	Powdered polyurethane foam used for preconcentration. Potential interfering ions investigated and conditions optimized. RSD 5% for 50 µg l⁻¹ (LOD 5.5 µg l⁻¹)	147
U	Sea-water	MS;ICP;L	See Th, ref. 129	129
U	Natural waters	MS;ICP;L	See Th, ref. 131	131
U	Sea-water	MS;ICP;L	FI sample introduction used	341
U	Natural waters	MS;ICP;L	²³⁴U∶²³⁸U ratio determined. Recovery of 80–85% found when coprecipitated with Fe^III	342
Zn	River water	AE;ICP;L	Induction coil used for vaporizing analyte. HCl used as carrier gas (LOD 0.04–0.7 ng ml⁻¹)	218
Zn	River and sea-water	AA;F;L	Saccharomyces cerevisiae immobilized on sepiolite used for preconcentration. Regeneration of column took 1 h. Determinand eluted with 1 M HCl	148
Zn	Sea-water	MS;—;—	HPLC used and Zn–pyrithione detected using Cu chelate formation. Linear from 2.5–12.5 ng ; recovery 70% with RSD of 17% (LOD 20 ng l⁻¹)	343
Zr	Sea-water	MS;ICP;L	200 ml sample acidified to pH 2, spiked with 100 ng Zr and pumped through Teflon column (10 cm × 8 mm id) packed with Chelex-100 resin (100–200 mesh). Column washed with 0.01 M HCl, analytes displaced with 3 × 10 ml aliquots of 2 M HNO₃. In used as internal standard. Concentration calculated from ⁹¹Zr∶⁹⁰Zr. RSD 7–2.5% for 42–480 pmol kg⁻¹ (LOD 0.21 pmol kg⁻¹)	286
Various	Waters	AA;ETA;L	Review of environmental applications at ultra-trace level with 51 references	106
Various	CRM river water	MS, AE;ICP;L	37 elements determined with and without preconcentration on Chelex 100 resin. Poor recovery for Cr found	344
Various	Waters	MS;—;—	Current literature from Nov–Dec 1997 reported	98
Various	Waters	MS;—;—	Current literature from Jan–Feb 1998 reported	99
Various	River water	XRF;—;—	PIXE determination of Ca, Cr, Cu, Fe, Hg, K, Mn, Ni, Pb, S, Ti, and Zn. 100 µl of 1000 µg ml⁻¹ Pd (internal standard) added to 50 ml sample and mixture adjusted to pH 9 using NH₄ solution. 1 ml of NaDDC added and resulting precipitate collected by filtration (pore size 0.4 µm, thickness 10 µm). Filter bombarded with collimated beam of 2 MeV protons and X-rays examined with Si(Li) detector positioned at 135°. Precision of 5–10% reported with an accuracy of ±10%	158
Various	Waters	MS;—;—	Review of accelerator methods presented	97
Various	Sea-water	MS;ICP;L	Mo, Mn and U determined with FI sample introduction after 1 + 9 dilution with a stream of 0.028 mol l⁻¹ HNO₃ (LOD 1.4, 0.7 and 0.1 µg l⁻¹, respectively). ETV sample introduction used to determine Cd and Pb (LOD 4.1 and 0.8 ng l⁻¹, respectively)	345
Various	Waters	MS;—;—	Current literature review presented	100
Various	Waters	—;—;—	Studies comparing 180 laboratories in 29 countries for 14 trace elements in 2 water samples. Part of the international evaluation programme IMEP-6	204
Various	Groundwater	MS;ICP;L	Cu, Mo, Ni, Pb and Zn analysed in fulvic acid fractions	346
Various	Waters	—;—;—	Requirements for preparation of CRM for speciation analysis of As, Cr, Pb, Se and Sn discussed	201
Various	Sea-water	MS;ICP;L	On-line preconcentration of Eu, Ho, Lu, Tm and Tb using quinolin-8-ol and Amberlite XAD-7 at pH 10 described. RSD 2%. (LOD 0.016, 0.0017, 0.0015, 0.0023 and 0.0035 pg ml⁻¹, respectively)	347
Various	Waters, RM	—;—;—	Survey of available RMs presented	348
Various	Drinking water	AA;F;— XRF;—;—	As, Ca, Cd, Co, Cr, Cu, Fe, Hg, K, Mg, Mn, Na, Ni, Pb, Se and Zn determined in three states of south eastern Nigeria	349
Various	Waters	—;—;—	Variety of techniques used to assess natural contamination	350
Various	Groundwater	AA;F;L	Sorption of pyridylazoresorcinol complexes of Cd, Co, Cu, Cr, Ni, Pb and V on activated charcoal at pH 5.5 ± 0.5 described. Desorption achieved with 1.6 M HNO₃. RSD 15% with an enrichment factor of 200	138
Various	Tap water	AA;air–C₂H₂;L	25–500 ml sample pretreated with HNO₃ and preconcentrated on a column impregnated with NaDDC. Metal ions eluted with 20 ml of propan-1-ol. Eluate diluted with water prior to determination	351
Various	Waters	MS;—;—	Review of inorganic trace analysis presented	352
Various	Waters	MS;ICP;L	On-line separation of As, Bi, Cd, Cu, Hg, In, Pb, Se, Tl with ammonium salt of O,O-diethyldithiophosphoric acid in HNO₃ on C₁₈ immobilized on silica. Metals eluted with methanol and introduced with a pneumatic nebulizer. Enrichment factors between 5 and 61. (LOD from 0.43 ng l⁻¹ for Bi to 33 ng l⁻¹ for Cu)	353
Various	Various	MS;ICP;L	Review of isotopic analysis in applications related to cosmochemistry, geochemistry and paleoceanography presented	354
Various	Waters	AA;F, ETA;L AE;ICP;L	Comparison of criteria for the selection of techniques used to determine trace elements discussed	355
Various	Waters	MS;ICP;L	Review of methods for environmental analyses presented	109
Various	Sea-water	MS;ICP;L	Multi-element determination of As, Pb, Sb, Sn and Tl using isotope monitoring of ⁷⁵As, ²⁰⁸Pb, ¹²¹Sb, ¹¹⁸Sn and ²⁰⁵Tl and ETV sample introduction. Pd used as matrix modifier. Recoveries 99–113% (LOD 0.015–0.042 µg l⁻¹)	356
Various	River water	MS;ICP;L	FI sample introduction used with silica immobilized 8-hydroxyquinoline preconcentration. Conditions given. Sub mg l⁻¹ concentrations measured for Cd, Co, Pb, Sb and V. Zn proved problematic	357
Various	Waters	AE, MS;—;L	7–50 ml sample pumped at 5 ml min⁻¹ onto a 10 µm PLRP-S precolumn (1 cm × 2 mm id). After drying with N₂, retained analytes eluted and separated with ethyl acetate and analysed on a fused silica column (2 m × 0.25 mm) coated with HP5MS (0.25 µm) operated from 75°C to 300°C (held for 3 min) at 10°C min⁻¹ (LOD 0.02–1.0 µg l⁻¹)	358
Various	Sea-water	MS;ICP;L	Effect of high salt content on B, Ba, Cd, Co, In, Mg, Pb and U measurement reported	359
Various	Waters	XRF;—;— MS;ICP;L AA;ETA;L	Comparison of techniques for multielement analysis of 8 international standard RMs reported	360
Various	Sea-water	MS;ICP;L	Effects of Na and Cl on ⁷⁵As, ⁵³Cr, ⁶³Cu, ⁵⁴Fe, ⁷⁰Ge, ⁵⁵Mn, ⁶²Ni, ⁷⁷Se, ⁴⁶Ti, ⁴⁷Ti and ⁶⁷Zn with pneumatic nebulization and ETV sample introduction reported. Se below limit of quantitation	361
Various	Sea-water	MS;ICP;L	FI sample introduction used to determine Y and lanthanides	362
Various	Waters	MS;ICP;L	Sc, Th, U and Y determined. Combined membrane desolvation unit with a microconcentric nebulizer used for sample introduction. Non-spectral interferences investigated	363
Various	Mineral and tap water	AA;ETA;L	Co, Cu, Fe and Ni preconcentrated using water insoluble 8-quinolinolate chelates using poly-(N-isopropylacrylamide)(PNIPAAm) at room temperature. 100-fold concentration achieved	364
Various	Highly mineralized water	AA;ETA;L	Sulfoxine cellulose microcolumn used with FI sample introduction to preconcentrate Cd, Co, Ni, Pb and V. Complexing agents such as citrate used. Recovery quantitative at pH 5	145
Various	Natural waters	XRF;—;L	Heavy metals determined using extraction of their carbamate complexes with subsequent re-extraction of elements into an aqueous phase or by directed crystallization of aqueous eutectic salt solutions. Gelatin used to increase viscosity	365
Various	Waters	TXRF;—;—	Ag, Cd, Cu, Fe, Ni, Pb, Sr and Zn determined in waters of relevance to food control	366
Various	River water	XRF;—;—	Mobile spectrometer for heavy metal pollution described	367
Various	Drinking water	XRF;—;L	Comparison made of total reflection and grazing emission techniques for Ca, Cu, K, Na, Mg, Ni, Sr and Zn. The latter under-performed for Na and Mg	222
Various	Waters	—;—;—	Discussion of high-performance, flow based sample pretreatment and introduction procedures given	368
Various	Natural waters and RMs	MS;ICP;L	Cu, Mn, Ni, Pb and Zn concentrated on-line using Toyopearl TSK-immobilized 8-hydroxyquinoline resin and ultrasonic nebulization (LOD 1.5, 0.26, 0.86, 0.44 and 10 ng l⁻¹ for Cu, Mn, Ni, Pb and Zn, respectively)	369
Various	Waters	—;—;—	Review of environmental applications presented	7
Various	Drinking water	AA;ETA;L	Simultaneous determination of Cd, Co, Cr and Pb described with HCLs placed on the perimeter of Rowland circle with a CCD detector. Background correction by continuum source method. LOD similar to published single element analysis	370
Various	River and waste water	AE;ICP;L	Co-precipitation of Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Se and Zn with NaDDC producing an enrichment factor of 40. Recovery dependent upon pH, 100% at pH ≥4.7. [LOD 0.001 mg l⁻¹ (Co, Cu, Cr, Mn), 0.0007 mg l⁻¹ (Zn, Cd), 0.003 mg l⁻¹ (Se), 0.004 mg l⁻¹ (Fe), 0.007 mg l⁻¹ (Ni) and 0.01 mg l⁻¹ (Pb)]	371
Various	Sea-water	MS;ICP;L	Cd, Co, Cu, Fe, Ni and Zn complexed with bis(2-hydroxyethyl)- dithiocarbamate. Extraction of neutrally charged but polar complex by C₁₈ columns with elution with acidic methanol described (LOD ≤5 pM)	372
Various	Waters	MS;ICP;L	Purification technologies and system features for purified water assessed by determination of Al, Cr, Mg, Na, Ni, Pb, Th and U	111
Various	Rain and snow water	MS;ICP;L	Al, Ce, La, Mn, Nd, Sm and V determined	373
Various	Ice core	MS;ICP;L	Desolvated micro-concentric nebulizer (MCN-6000) employed for use with small sample volume. ng l⁻¹ concentrations of Al, Ag, As, Cd, Cr, Cu, Fe, Pb, U, V and Zn detected	374
Various	Waters	AA;ETA, F;L	Cd, Co, Cr, Ni, Mn and Pb determined in fish by ETA, Cu and Zn determined by flame, As and Se determined by HG	375
Various	Various	MS;—;—	Review of current literature from September to October 1998	376
Various	Waters	XRF;—;L	The abilities and limitations of XRF to determine trace elements discussed	377
Various	Radioactive water	XRF;—;L	Comparison made of XRF and TXRF techniques. Results compared to ICP-MS	378
Various	Mineral water	XRF;—;—	17 trace elements determined in 4 samples. Use of single calibration curves with multi-element standards and a single internal standard (10 mg l⁻¹ Ga) described	379
Various	Natural waters	AF;ETA;L	Excitation by laser. High detection limits reported with time-gated techniques	380
Various	Sea-water	MS;ICP;L	Direct sample insertion used for the determination of Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn. Effect of salts and solvents investigated	219
Various	Waters	MS;ICP;L	Comparison made of multiple linear regression (MLR), principal components regression (PCR) and partial least squares (PLS) multivariate calibration models for analysis of Cd, Cu, Pb and Zn by anodic stripping voltammetry	381
Various	Sea-water	MS;ICP;L	Quantitative adsorption of Cu (pH 2–9), Pb (pH 3–9), Co, Ni and Cd (pH 4–9) onto dithizone impregnated admicelles on alumina described	143
Various	Waters	MS;—;—	Review of current literature from Aug–Sept 1998	103
Various	Waters	MS;—;—	Review of current literature for Jan 1999	104
Various	Natural waters	AA;ETA;L	Preconcentration onto immobilized NaDDC or ammonium hexamethylenedithiocarbamate on silica gel to extract Cd, Co, Cr, Cu, Fe, Mn, Ni and Pb described. Back elution carried out using IBMK (LOD 0.04 µg l⁻¹ Cd, 0.1 µg l⁻¹ Cr, Cu and Mn and 0.3 µg l⁻¹ Co, Fe, Ni and Pb)	382
Various	Surface water	MS;ICP;G	Organometallic separation carried out using solid phase micro-extraction and capillary GC. Analysis time 10 min (LOD 0.13–3.7 ng l⁻¹)	383
Various	Waters	AA;—;—	Review discussing FIA with 103 references	384
Various	Sea-water	MS;ICP:L	Ion exchange chelating fibre with aminophosphoric and dithiocarbamate groups bound to polyacrylonitrile fibre used to separate Ag, Bi, Cd, Cu, Pb, Mn and In. Experimental parameters optimized	136
Various	River water	MS;ICP;G	Portable in-situ HG systems coupled with FI and cryogenic trapping (-196°C) for metalloid speciation described (LOD 0.5–10 pg)	385
Various	Spring water	MS;ICP;G	Speciation of metalloid compounds using cryotrapping and GC described	386
Various	Lake water	MS;ICP;L	³²S, ³⁴S, ³⁹K, ⁸⁴Sr, ⁸⁶Sr, ⁷⁴Se, ⁵¹V and ¹³⁸Ba determined in water from Lake Baikal	387
Various	Waste water	AE;—;—	Adsorbable organic halogen compounds measured. On line system used	213
Various	Surface water	—;—;—	Protocol for collection, filtration and preservation of samples for determination of dissolved, Al, Ag, As, Cd, Co, Cr, Cu, Hg, Fe, Mn, Mo, Ni, Pb, Sb, Se, Tl and Zn presented	113
Various	Waste water	AE;ICP;L	Ag, Al, As, B, Ba, Bi, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Sb, Sr, V and Zn determined using microwave digestion (LOD 0.5–2 mg l⁻¹)	388
Various	Rain water	AE;ICP;L	Use of ultrasonic nebulization described	389
Various	Sea-water	MS;ICP;L	High resolution system used for the determination of Al, Cd, P, Pb, REEs, U, and transition metals	390
Various	Waters	MS;ICP;L	Cd, Cu, Mn, Ni, Pb, Zn and Zr and REE measured at ng l⁻¹ and sub-ng l⁻¹. Protocols developed	122
Various	Natural waters	MS;ICP;L	Comparison of results from 200 laboratories for round 9 of the International Measurement Evaluation Programme described	205
Various	Drinking water	MS;ICP;L	Al, As, Ag, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Sb, Se and Zn determined in a single analysis	391
Various	Sea-water	MS;ICP;L	Strategies for measuring trace elements discussed	392
Various	Waters	MS;ICP;L	Cryofocusing used for determination of Hg, Pb, Se and Sn (LODs of 0.2, 0.08, 0.8 and 0.05 pg l⁻¹, respectively)	120
Various	Waters	MS;ICP;L	Actinides determined at sub-ng l⁻¹ concentrations	393
Various	Sea-water	MS;ICP;L	Complexes of DDC formed with Cd, Co, Cu, Fe and Zn. Sample volume of 1 ml used	394
Various	Sea-water	MS;ICP;L	Direct determination of Cd, Co, Cr, Fe, Mn, Ni, Pb, U, V and Zn in 10-fold diluted sample using a microconcentric nebulizer combined with a shielded torch described. Sensitivity variations corrected using Sr; RSD 7%	395
Various	Water	—;—;—	Review with 672 refs.	396
Various	Various	—;—;—	Review of environmental analysis with 955 refs.	92
Various	Freshwater	MS;ICP;L	UV irradiation of samples carried out prior to preconcentration of Ag, Cd, Cu and Pb by adsorption onto Chelex-100. Recoveries of Ag reduced after UV irradiation	397
Various	Various	MS;—;—	Environmental and biological applications	398
Various	River water	MS;ICP;L NAA;—;—	Results for 50 elements compared by the two methods	399
Various	Various	MS;ICP;— AE;ICP;—	Review with 101 refs.	93
Various	Waters	—;—;—	Review of methods for on-line preconcentration of trace metals and organometallic compounds with 31 refs.	400
Various	Tap and river waters	AA;F;L	Preconcentration carried out by precipitation of metal hydroxides on Zr spheres in a PTFE micro-column or by separation on a Spherisorb SCX column and complexation with 4-(2-pyridylazo)resorcinol. Calibration graphs linear to 100 µg l⁻¹	401
Various	Waste waters	AE;ICP;L	Acid requirements, human intervention and analysis time reduced by on-line microwave digestion	402
Various	Various	—;—;—	Regulatory compliance monitoring using atomic spectrometry discussed	403
Various	Waste water	AE;MIP;G	Simultaneous determination of As, Hg, Se and Sb by HG after preconcentration in a cryogenic trap described. Optimum conditions determined. Recoveries 95% (LOD 2.0, 13, 2.2 and 3.3 µg l⁻¹, respectively)	404
Various	Water CRM	AE;MIP;L	31 elements determined with wet aerosol introduction after ultrasonic nebulization (LOD 0.3–1000 µg l⁻¹)	405
Various	Sea-water	MS;ICP;L	Cd, Co, Cr, Fe, Mn, Ni, Pb, V and Zn determined. Desolvation after micro-nebulization of 50 µl sample used with Sr as internal standard; RSD 10%	406
Various	Snow and ice	MS;ICP;L	Ag, Au, Ba, Bi, Cd, Co, Cr, Cu, Fe, Mn, Mo, Pb, Sb, Ti, U, V and Zn determined at ng g⁻¹ and pg g⁻¹ with a microconcentric nebulizer (1 ml sample). RSD 9–34%	407
Various	Waters	MS;ICP;—	Development of interface for CE and SFC extraction	408
Various	Waters	MS;—;—	Current literature from April–May 1998. 270 references cited	101
Various	Waters	XRF;—;—	Review with 81 refs.	409
Various	Waters	MS;ICP;L	Development of a dynamic reaction cell used for removing polyatomic and isobaric interferences. Interferences reduced by a factor of 10⁷, improving LODs for As, Ca, Cr, Fe, K and Se	410
Various	Waters	AE;MIP;L	Analytical performance of low power systems evaluated	411
Various	Waters	—;—;—	Bias between sampling methods investigated	412

Several important reviews of literature were produced during the period of this review. These included the review of X-ray fluorescence spectrometry⁹⁷ and of Environmental analysis⁷ produced within this journal. A new monthly review of mass spectrometry is now produced and includes a section on environmental analysis.^98–105 The application of graphite furnace AAS to complex environmental analyses was comprehensively reviewed by Sturgeon.¹⁰⁶ Sturgeon was also an author in a review of the development of furnace atomization plasma emission spectrometry and its use as a detector in gas chromatography for the purposes of speciation.¹⁰⁷ In a review of the determination of the Pt group metals and Au in environmental water samples by ICP-MS the sensitivity, accuracy and susceptibility of the technique to interferences were discussed.¹⁰⁸ The performance of ICP-MS in the determination of primary contaminants (As, Ba, Be, Cd, Cr, Cu, Hg, Ni, Pb, Sb, Se and Tl) in water samples was reviewed by Wolf et al.¹⁰⁹ In a review of different analytical methods for Sb speciation at trace and ultratrace levels, chemical methods (extraction, co-precipitation, hydride generation), chromatographic methods (with hybrid techniques), as well as electrochemical and kinetic methods, were described in detail.¹¹⁰ The need for a reliable certified reference material for such analyses was highlighted.

2.1 Sample preparation

2.1.1 Reagents. Ultrapure water is essential if ICP-MS is to be applied successfully to the determination of ultratrace metals. The Milli-Q system has been successfully used to produce a continuous supply of ultrapure water which contained sub ng l⁻¹ concentrations of most elements.^111,112

2.1.2 Sample collection and preservation. A cost effective protocol for collection, filtration and preservation of surface waters for detection of 17 trace elements at µg l⁻¹ and ng l⁻¹ was described by Hall.¹¹³ The bottle type, cleaning methods for the bottles, filtration methods and preservation reagents were studied. Hall et al.^114,115 also studied the preservation of As species, including inorganic As, monomethylarsonic acid and dimethylarsinic acid, using HPLC-ICP-MS and hydride generation-AAS. It was ascertained that reduction of As^V to As^III occurred within hours but that this change could be prevented by ensuring that samples were maintained in a cold state by refrigeration. Acidification of samples with HCl altered the species distribution significantly, increasing the concentration of As^III substantially and, to a lesser extent, that of As^V. Use of HNO₃ caused a higher degree of oxidation of As^III to As^V than HCl. In the determination of Cu in sulfidic pore-waters Simpson et al.¹¹⁶ studied the effect of preservation using different reagents on the concentrations of dissolved Cu. If samples were preserved with only acid there was significant underestimation of the dissolved Cu. If samples were oxidized with H₂O₂ prior to acidification the losses of Cu were minimized.

A method for the determination of Hg in potable water samples by ICP-MS, which used Au for stabilization of samples, was described by Allibone et al.¹¹⁷ The method met the analytical performance criteria of the UK Drinking Water Inspectorate over the range 0–1.2 g l⁻¹. The preservation of water samples for subsequent determination of tributyltin and triphenyltin was studied over a period of 18 months.¹¹⁸ Butyltins were stable on C₁₈ cartridges or in unacidifed sea-water in polycarbonate bottles, in the dark at 4 [thin space (1/6-em)] °C, for periods of up to 7 months. Triphenyltins were not stable beyond 60 days on C₁₈ cartridges. Half the concentration of phenyltins was lost after 540 d if the samples were stored as unacidified waters in polycarbonate bottles in the dark at 4°C.

An in situ purge and cryogenic trapping method for the pre-concentration of volatile metal and metalloid compounds has been developed.^119,120 The analytes were collected in a cryogenic trap and stored at –196 [thin space (1/6-em)] °C until analysis was carried out in the laboratory. The traps were flash desorbed and recondensed on a cryofocusing gas chromatography system linked to an ICP-MS. Volatile compounds of selected elements in aqueous solution could be simultaneously detected by scanning the stable isotopes. Blank levels and recoveries were obtained for several compounds (Me₂Se, Me₂Se₂, Me₂Hg, Et₂Hg, Me₄Sn, Et₄Sn, Me₄Pb, Et₄Pb). The method was applied to the determination of volatile species of Hg, Pb, Se and Sn in water samples from three major European estuaries.

2.1.3 Preconcentration and separation procedures. Preconcentration and separation using chelation and ion exchange methodologies were subject to continued development. There were also several novel developments, including adsorption of trace and ultratrace metals on biological substrates such as yeast.

Preconcentration and matrix removal may be required where the concentrations of elements in the water samples are particularly low and the interferences caused by the matrix dominate any direct analysis. Tributyl phosphate resin was used for extraction and preconcentration of Tl from freshwater and waste water by Jin-Xin.¹²¹ The detection limit for the method was 3 µg l⁻¹ and the RSD was 7.5% for a water sample containing 0.032 mg l⁻¹ Tl. A macroporous iminodiacetate chelating resin was used for matrix separation and preconcentration of transition metal ions and REE in interstitial waters and high alkalinity waters.¹²² A nitrilotriacetate chelating resin was used for the elimination of matrix effects in the determination of a range of metals in sea-water.¹²³ The results for 10 metals in NASS-4 sea-water reference material agreed reasonably with the certified values. A new spherical macroporous epoxy–melamine chelating resin was synthesised by Bo-Lin¹²⁴ and was applied sucessfully to the preconcentration of Bi^III, Ga^III, In^III, Sn^IV and Ti^IV from aqueous solution.

A templated ion-exchange resin was synthesised by Bae et al.,¹²⁵ which was then applied to the separation and preconcentration of Pb²⁺ from tap water and sea-water. Selectivity for Pb²⁺ was produced by creating polymers with complexing ligands arranged so as to match the charge, co-ordination number, co-ordination geometry and size of the Pb²⁺ ion. Samples preconcentrated using the templated ion-exchange resin contained almost no other cations and therefore offered a virtually interference-free method of preconcentration. Rudner et al.¹²⁶ developed a procedure for on-line preconcentration of Hg on an anion exchange resin loaded with 1,2-bis-[(2-pyridyl)-3-sulfophenylmethylene]thiocarbonohydrazide. Calibration graphs were linear from 5–1000 ng ml⁻¹ and the detection limit was 4 ng ml⁻¹. Hg was also preconcentrated on a cation exchange resin which had been impregnated with quinine.¹²⁷ The resin was found to have good recovery and a capacity of 19.7 mg g⁻¹ of Hg and the enrichment factor was 20. Appelblad et al.¹²⁸ compared two systems for the quantitation of metal–humic complexes and free metal ions consisting of separation by coupled ion-exchange columns followed by detection by ICP-MS or cold vapour AFS. The systems evaluated were coupled anion and cation exchangers Sephadex A-25/Chelex 100 and Dowex 1X8/Chelamine Metalfix. It was found that the Sephadex/Chelex 100 system could be used reliably to determine the metal–humic complexes. However, when trying to determine total element concentrations there was non-quantitative recovery of Al, Cu, Hg, Mn, U and Zn. Therefore, a combination of speciation and total concentration measurement was required to study the distribution of trace elements in water.

On-line solid phase extraction with an actinide specific resin was applied successfully as part of the determination of ²³⁸U and ²³²Th in a number of standard reference water samples, including NASS-4 Open sea-water and SLRS-3 River water.¹²⁹ Solid phase extraction was automated by Gerwinski and Schmidt¹³⁰ using the Zymark Autotrace sample preparation system for the extraction of trace metals in sea-water. Contamination effects were minimized by replacement of some of the stainless steel parts in the system. The choice of complexing agent and type of silica gel could be used to extract and hence determine different elements in different oxidation states. The efficiency of two different extraction resins for preconcentration of U and Th in natural waters was studied by Unsworth et al.¹³¹ The resins were evaluated in terms of their capability to concentrate and elute low concentrations of U and Th and their applicability for at-line analysis. The potential of the resins to separate the analytes from matrices containing humic and fulvic acids or a high salt content was also studied.

Solid phase microextraction was used to extract organotin and organoarsenic compounds from aqueous solutions.¹³² A non-polar poly(dimethyl)siloxane coated fibre was used to extract monobutyl-, dibutyl-, tributyl-, tetrabutyl-, tetraethyl- and trimethylphenyltin from solutions. The extraction equilibrium profile, desorption time profile, fibre durability and fibre to fibre reproducibility were studied. Detection limits were improved when an ion-pair reagent was used in the sample solutions. Organoarsenic compounds were extracted using a fibre coated with poly(3-methylthiophene), a conducting polymer. When coupled with headspace-GC-ICP-MS, solid phase microextraction using a poly(dimethyl)siloxane fibre for the extraction of organotin pesticides resulted in improved analysis speed and sensitivity.¹³³ A polyacrylate fibre was used for the extraction of organohalogen compounds from water and was found to remove interferences from inorganic halides.¹³⁴ The first calibration of the system resulted in a detection limit of 9 µg l⁻¹ of organically bound chlorine. Polyacrylonitrile fibres were modified to produce poly(acrylaminophosphonic dithiocarbamate) chelating fibre and were used to preconcentrate REEs from sea-water.¹³⁵ Recoveries were quantitative and an enrichment factor of 200 was obtained. In a second paper by the same group, the experimental parameters affecting the preconcentration efficiency of the modified fibre (including fibre capacity, pH, sample flow rate and volume, eluent and effect of matrix ions) were investigated and optimized.¹³⁶ The same group also studied how REE in sea-water could be preconcentrated using 8-hydroxyquinoline immobilized on a polyacrylonitrile hollow fibre membrane.¹³⁷ The exchange capacity of the modified polyacrylonitrile hollow fibre membrane was sufficient for the preconcentration and separation of REE from sea-water.

A variety of solid supports were used to immobilize a number of complexation agents. Chakrapani et al.¹³⁸ preconcentrated metals as a metal–pyridylazoresorcinol (M-PAR) complex on activated carbon. A complexation factor of 200 or more was easily achievable. Trace elements could be determined down to 1 µg l⁻¹ with an RSD of 15%. The advantage of the technique was that it was possible to preconcentrate samples at the sampling site and a small sample volume could be transported for analysis. Arsenic in natural water and sea-water was preconcentrated by conversion of the As to molybdoarsenate and collection on activated carbon.¹³⁹ When a concentration factor of 200 was used 0.02 µg l⁻¹ of As could be determined. Activated carbon impregnated with 1,2-cyclohexanedionedioxime was used for the preconcentration of Cu and Pb from water.¹⁴⁰ Detection limits were 0.13 and 0.75 µg l⁻¹ for Cu and Pb, respectively, when sample volumes of 100 ml were used. Silica functionalized with methylthiosalicylate was employed by Rudner et al.¹⁴¹ to preconcentrate Hg in sea-water. The recoveries of 25 ng ml⁻¹ of Hg^II added to tap water, sea-water and synthetic sea-water were quantitative. Dithizone immobilized on surfactant coated alumina¹⁴² was used to preconcentrate Hg from river water, tap water and synthetic drinking water. Recovery of 70–500 ng of Hg^II and methylmercury(I) from distilled water was 97–101%. Hiraide and Shibata¹⁴³ produced alumina containing dithizone impregnated admicelles and used it to adsorb heavy metals from sea-water. There was quantitative adsorption of Cu, Pb, Cd, Co and Ni. Chelating 2-mercaptobenzimidazole(I)-immobilized cellulose was used as a solid phase extraction absorbent for preconcentration of Cd, Cu, Pb and Ni from lake water and waste water.¹⁴⁴ Recoveries of 95–102% were found and co-existing ions did not interfere. Zih-Perenyi et al.¹⁴⁵ synthesised a new chelating cellulose with immobilized 8-hydroxyquinoline-5-sulfonic acid groups and used it for preconcentration of trace Cd, Co, Ni, Pb and V from highly mineralized water. Elements were determined in eluates by graphite furnace-AAS. The detection limits for the method were 0.004 µg l⁻¹ Cd, 0.134 µg l⁻¹ Co, 0.35 µg l⁻¹ Ni, 0.063 µg l⁻¹ Pb and 0.244 µg l⁻¹ V.

There were other novel developments in the preconcentration area. A rapid, simple, on-line method for preconcentration of Cd, Co, Cu, Mn, Ni, Pb and Zn from sea-water using 8-hydroxyquinoline immobilized on a 2 m long silicone tube was described by Willie et al.¹⁴⁶ Good agreement was achieved with CRMs NASS-4 and CASS3 when the preconcentration method was used with FI-ICP-MS. Polyurethane foam was used for preconcentration of U.¹⁴⁷ The U was adsorbed as the salicylate complex onto powdered polyurethane foam. The foam was filtered through a filter paper and used for XRF measurements. For 50 µg l⁻¹ of U, the detection limit was 5.5 µg l⁻¹. Matrices studied included reference materials, waste water, mine drainage water and sea-water. Bakers' yeast (Saccharomyces cerevisiae) was one of the more exotic agents used for preconcentration.¹⁴⁸ The yeast was immobilized on sepiolite and was loaded into a column. Samples were passed through the column and metal ions were retained. Cd, Cu and Zn were quantitatively recovered from river water and sea-water. Two biologically active materials, Spirulina platensis (a cyanobacterium) and Phaseolus (plant derived material) were applied to the bioextraction of Sb and Cr from natural and industrial waters by Madrid et al.¹⁴⁹ The detection limits for Sb in river water (preconcentration factor 4) and sea-water (preconcentration factor 40) were 0.9 µg l⁻¹ and 0.09 µg l⁻¹, respectively. Those for Cr in river water (preconcentration factor 10) and sea-water (preconcentration factor 20) were 0.1 µg l⁻¹ and 0.05 µg l⁻¹ respectively.

A fullerene (C₆₀) minicolumn was used for on-line separation and preconcentration of Cd, Pb and Ni in tap water, bottled mineral water and sea-water by Silva et al.¹⁵⁰ The column retained cations, which were then eluted from the column with methanol. Detection limits were 2.2 ng l⁻¹, 75 ng l⁻¹ and 23 ng l⁻¹ for Cd, Ni and Pb, respectively. He and Zu¹⁵¹ developed a method for preconcentration of Cu in natural waters using dithizone supported on naphthalene. Chitosan was packed into a column and used to preconcentrate Cd^II from natural waters prior to determination by flame AAS.¹⁵² The calibration graph was linear to 15.5 ng ml⁻¹ Cd with a detection limit of 21 pg ml⁻¹. The interference effects of 13 inorganic foreign ions were listed. Howard et al.¹⁵³ compared the effectiveness of poly(L-cysteine) and 8-hydroxyquinoline immobilized on controlled pore glass and used in an FI system for the separation of Cd, Cu and Pb from synthetic sea-water. Both resins allowed the quantitative recovery of 50 µg l⁻¹ of Cd and Pb from synthetic sea-water. However, neither of the resins showed reproducible or complete recoveries of Cu²⁺ when HNO₃ (1 M) was used for stripping.

Several groups were using knotted reactors to effect preconcentration and separation of complexed analytes. Nielsen et al.¹⁵⁴ used a knotted PTFE reactor for preconcentration and separation of Cr^VI complexed with ammonium pyrrolidine dithiocarbamate (APDC). The complex was adsorbed onto the tube walls, then washed with nitric acid prior to elution with ethanol (55 µl). The solution was transported into a graphite furnace for determination of Cr by ETA-AAS. Calibration graphs were linear from 5–800 ng l⁻¹ Cr with a detection limit of 4.2 ng l⁻¹ Cr. The method was used successfully for determination of Cr in a drinking water CRM and for a synthetic sea-water sample. A similar procedure was used to preconcentrate and separate Pt from spiked tap water.¹⁵⁵ The Pt was complexed by APDC, then the complex was adsorbed onto the walls of the reactor. The complex was eluted with methanol and determined by ETA-AAS. The working concentration range was 0.1–1 µg l⁻¹ and the detection limit was 10 ng l⁻¹. Cu, Mn and Ni were preconcentrated in a knotted reactor coupled with ETA-AAS.¹⁵⁶ The complexing agents used were ammonium pyrrolidine-1-carbodithioate and quinolin-8-ol in HNO₃–potassium hydrogen phthalate solution. Desorption was carried out using methanol and ethanol or methanol alone. The method was used to analyse sea-water. Salonia et al.¹⁵⁷ used FI on-line preconcentration with a knotted reactor coupled to ICP-AES for the determination of Pb in tap water. The lead–diethyldithiocarbamate complex was adsorbed at pH = 9.5. HCl was used to elute the complex from the reactor walls. The detection limit with preconcentration of 10 ml of sample was 0.2 ng ml⁻¹.

Membranes could be used as a means of separating solid complexes of the analytes of interest. Kennedy et al.¹⁵⁸ precipitated 12 elements from river water using NaDDC and ammonia. The precipitate was collected on a nucleopore polycarbonate membrane filter. PIXE was used to determine the Ca, Cu, Cr, Fe, Hg, K, Mn, Ni, Pb, S, Ti and Zn. Typical errors for cited elements in NIST river water were ±5–10%. Heavy metals in water samples were concentrated onto sorbent filters with active aminocarboxylic ligands.¹⁵⁹ Measurements of 15 analytes of interest on the filter were carried out using XRF. A miniature membrane concentration/dissolution method was used to collect and determine Pb in river water and tap water.¹⁶⁰ The sample solution was mixed with pyrrolidine dithiocarbamate and zephiramine to give the Pb–pyrrolidinedithiocarmbamate complex. The sample was filtered through a filter paper 5 mm in diameter. A circle of 3 mm diameter was punched out of the filter and dissolved in methyl cellusolve. The resulting solution was analysed by ETAAS. The detection limit was 10 ng l⁻¹ when the filter was dissolved in 200 µl of methyl cellusolve. In a similar study by the same authors, the methodology was extended to other heavy metals and the effect of zephiramine as a stabilizer for the complexes formed was investigated.¹⁶¹ Hg compounds were preconcentrated and separated using a dithizone impregnated ultra-high molecular weight polyethylene membrane coupled with reverse phase chromatography.¹⁶² The separation process was studied and it was ascertained that the chelates could be separated by reverse phase chromatography using a mobile phase of THF–methanol (2 + 1) and a 0.05 M acetate buffer (pH = 4).

A flow though preconcentration cell was designed by Wang et al.¹⁶³ for preconcentration of 7 elements from freshwater and sea-water. The cell consisted of two iminodiacetic acid–ethylcellulose membranes (0.2 mm thick), separated by a PTFE gasket (0.5 mm), with a centre slot (4.2 mm² in area) that acted as a flow channel. During sample enrichment the sample and ammonium acetate buffer solutions flowed through the sample inlet into the membrane cell. The trace elements in the solution were adsorbed onto the membrane for 90 s as the sample solution flowed over the membrane. The sample then flowed out of the cell. Preconcentrated elements were eluted from the membrane with HNO₃ and the elution stream was introduced into a flame-AAS instrument or an ICP-AES system for determination of 7 elements (Cd, Co, Cu, Mn, Ni, Pb and V).

2.1.4 Hydride and cold vapour generation. A rapid and simple method for determination of Cd in wastewaters was developed by Garrido et al.¹⁶⁴Cd was generated as cold vapour then determined by AAS. Wastewater samples did not need pre-treatment prior to analysis. A protocol involving the use of hydride generation twice, for preconcentration then for analysis, was developed for determination of ultra-trace amounts of Se in mineral water.¹⁶⁵ The detection limit was 5.7 pg ml⁻¹ Se. In a second paper by the same group, hydride generation was again used for preconcentration of Se but on this occasion the hydride was decomposed and collected on a Au wire trap prior to determination.¹⁶⁶ The detection limit was 5 pg ml⁻¹ for a 5 min collection period.

The efficiency and selectivity of stibine generation was improved in a new development by Moreno et al.⁵⁹ The improved method involved generation of the stibine at 70 [thin space (1/6-em)] °C using an additional H₂ flow to sustain the atomization flame. This made it possible to reduce the acid and borohydride concentration. Under the optimized conditions a limit of detection of 0.3 µg l⁻¹ Sb was obtained. The improved method was applied successfully to the determination of Sb in sea-water and tap water.

Chemical hydride generation and electrochemical hydride generation of arsine were compared in a study by Machado et al.¹⁶⁷ Interferences from Co^II, Cu^II, Ni^II, Pb^II and Zn^II were evaluated for both systems and they caused a decrease in the As signal when the hydride was generated using NaBH₄. Chemical methods of hydride generation gave better sensitivity than electrochemical.

Ni was determined in natural water samples by ICP-MS with sample introduction by on-line carbonyl vapor generation.¹⁶⁸ ID was used for quantification with ⁶⁰Ni and ⁶²Ni as the major isotopes. The purpose of using carbonyl generation was to remove the possibility of spectral interferences from molecular ions such as CaO, ArMg and Na₂O. The analyte transport efficiency of the hydride was estimated to be 50%. Good agreement was achieved with the certified values in the analysis of two water reference materials (SLRS-3 Riverine Water and CASS-3 Sea-water). Vapour generation was also used for determination of Tl in sea-water by flow injection ICP-MS.¹⁶⁹ The method had a detection limit of 0.01 ng ml⁻¹ and was successfully applied to the determination of Tl in CASS-3 Near Shore Sea-water reference material and NASS-4 Open Ocean Sea-water.

2.2 Speciation

Speciation continued to be an area of considerable research, with much emphasis placed on separation of species by chromatography followed by determination of elements by one of the atomic spectrometry techniques.

Olesik et al.¹⁷⁰ reviewed the potential of capillary electrophoresis inductively coupled mass spectrometry and ion spray mass spectrometry for elemental speciation. Whilst it was considered that although the ICP-MS sensitivity was high the sample volumes produced by CE could result in detection limits which were too high. One of the other challenges of CE was to resolve species in samples with high conductivity. Ion spray mass spectrometry resulted in more complex spectra than CE-ICP-MS and in poorer detection limits. However, the spectra could give more information to identify species. Progress towards understanding the capabilities and limitation of these techniques was discussed.

The quantitative determination of aluminium species (Al^III and AlF²⁺) in natural and potable waters by separation with HPLC then ICP-MS was studied by Fairman et al.¹⁷¹ The ICP-MS technique gave better selectivity and was less prone to interferences than fluorimetric detection of the Al–8-hydroxyquinoline-5-sulfonic acid complex. Chelating resin titration using Chelex 100 as a sorbing resin was successfully applied to real freshwater samples.¹⁷² The method was also used to study speciation by evaluating the side reaction coefficient (α_M(I))of the metal ion in the presence of a resin. A more extensive study of Al speciation was carried out by Milacic et al.¹⁷³ Three speciation techniques were used, including fast protein liquid chromatography-ICP-AES, microchelating ion-exchange chromatography-ETAAS and the 8-hydroxyquinoline spectrophotometric method. When all three methods were used together the Al species could be comprehensively quantified.

A brief review of methods for the separation and determination of Sb^III and Sb^V and organoantimony compounds in water was presented by Russeva et al.¹⁷⁴ Limits of detection varied widely depending on the methodology and methods of preconcentration were discussed. The separations of organic Sb from landfill seepage water as trimethylantimony dichloride and inorganic Sb^III and Sb^V were studied using anion-exchange HPLC-ICP-MS.¹⁷⁵ Ultrasonic nebulization for sample introduction improved detection limits for Sb^V but was unsuitable for determination of trimethylantimony chloride. Extraction of samples with KOH in a stainless steel system enabled measurement of the organic and inorganic Sb^V without interference from Sb^III but Cl⁻ interfered with the analyses. The process of demethylation of trimethylantimony species in aqueous solution was found to occur during analysis by hydride generation-GC.¹⁷⁶ Demethylation of trimethylstibine during the determination of trimethylantimony dichloride was studied using two different analysis procedures, namely semi-continuous flow HG-GC-AAS and batch type HG-GC-ICP-MS. Differences in analytical results were obtained at high and low pHs and for samples which were fungal extracts. It was recommended that for determination of Sb in samples using hydride generation only the standard additions method should be used.

There was continued application of the `difference method' for calculation of As^V concentrations in situations where direct determination of both species was not possible. Yan et al.¹⁷⁷ determined trace amounts of As^III and As^V in water by ICP-MS following on-line preconcentration and separation in a knotted reactor. The As^III–pyrrolidine dithiocarbamate complex was selectively adsorbed onto the inner walls of a PTFE knotted reactor. The complex was eluted with HNO₃ and the As was detected by ICP-MS. The total As concentration was determined by reduction of the As^V to As^IIIwith cysteine and measurement as above. The As^V concentration was then calculated by difference. Detection limits were 0.021 µg l⁻¹ for As^III and 0.029 µg l⁻¹ for total As. Mathematical correction procedures were used to correct for the interference effects of high Cl⁻ concentrations in the ICP-MS determination of As in treated and untreated percolated waters from a landfill site.¹⁷⁸ HG-ICP-MS was used to determine As^III in both waters, which had been buffered to pH 5 thereby preventing the formation of As^V hydrides. The As^V concentrations were determined by difference. Using selective media reactions Bermejo-Barrera et al.¹⁷⁹ determined As^V, As^III, dimethylarsinic acid and monomethylarsonic acid. Total As was obtained by reaction with NaBH₄ in thioglycollic acid. Arsenic^III and As^V were determined by reduction with NaBH₄ in HCl. As^III was determined by reduction of the samples with NaBH₄ in citric acid–NaOH buffer solution at pH 5. As^III and dimethylarsinic acid were reduced with NaBH₄ in acetic acid. As^V and monomethylarsonic acid were determined by difference.

Capillary eletrophoresis was used to separate four anionic, arsenite (As^III), arsenate (As^V), monomethylarsonic acid and dimethylarsinic acid, and two cationic (arsenobetaine and arsenocholine) forms of As.¹⁸⁰ The determination of As was accomplished using ICP-MS. The limit of determination was found to be 1–2 µg l⁻¹ As for each species. The recovery of the compounds of interest was determined using a spiked mineral water sample. The method was applied to mineral water and soil leachate. As species were also separated and determined by HPLC-ICP-MS, using an anion exchanger and with tartaric acid (15 mM, pH = 2.91) as a mobile phase.¹⁸¹ The detection limits for arsenocholine, arsenobetaine, dimethylarsinic acid, methylarsonic acid, arsenous acid and arsenic acid were in the range 0.04–0.6 µg l⁻¹. The method was applied to the determination of As compounds in groundwater. In a similar study, separation of four As species was carried out on one or two reversed-phase 5 µm Phenomenex guard columns at 30 [thin space (1/6-em)] °C with tetrabutylammonium hydroxide (10 mM)–malonic acid (1 mM)–methanol (5%) at pH 6 as mobile phase.¹⁸² Detection of the As species was by hydride generation AFS. Taniguchi et al.¹⁸³ developed a sensitive and robust method for separation and determination of arsenate (As^V), arsenite (As^III) and monomethylarsonic acid in water samples. The method used an ion exclusion column packed with sulfonated polystyrene resin and dilute trifluoroacetic acid at pH 2.1 as mobile phase. Hydride generation ICP-MS was used to improve sensitivity and remove interferences from Cl⁻ ions. The detection limits for the species were 1.1 ng l⁻¹ for As^V, 0.5 ng l⁻¹ for As^III and 0.5 ng l⁻¹ for monomethylarsonic acid with an injection volume of 50 µl. Anionic, neutral and cationic species of As in ferric contaminated leachates of lignite spoil and seepage water from Sn ore tailings were separated, speciated and determined using IC-ICP-MS.¹⁸⁴ A strong anion exchange column was used, with gradient elution with HNO₃ (0.5–50 mM, pH 3.3–1.3). The detection limits for arsenite, phenylarsonate, dimethylarsinate, arsenate, arsenobetaine and arsenocholine were 0.58–0.91 µg l⁻¹. Solid phase extraction cartridges were used by Yalcin and Le¹⁸⁵ as low pressure chromatographic columns for separation of As species. Both anion exchange and reverse phase SPE columns were used successfully to separate arsenite (As^III) and arsenate (As^V) from untreated water, tap water and bottled water samples. Results from the speciation of As in standard reference material water samples were in good agreement with the certified value and with interlaboratory comparison results.

Cr^III and Cr^VIspecies were determined in tap water using online simultaneous sorption preconcentration with AAS detection.¹⁸⁶ The method was based on the formation of a Cr^III complex with Chromazurol A in weakly acid solution and formation of a Cr^VI complex with sodium diethyldithiocarbamate in strongly acid solution. The complexes were selectively adsorbed onto a C₁₈ column by altering the adsorption conditions. Methanol was used to elute the complexes. The detection limits were 2.5 µg l⁻¹ for Cr^VI and 0.2 µg l⁻¹ for Cr^III. A similar study was carried out using the diethylammonium salt of diethyldithiocarbamate to preconcentrate both Cr^VI and Cr^III species¹⁸⁷ on a C₁₈ microcolumn. Methanol was the eluent, transferring concentrated species into the flame-AAS. The detection limit for both species was 0.02 µg l⁻¹. In a study by Luo and Berndt¹⁸⁸ Cr^III and Cr^VI species were determined in waste water by on-line sorption with ICP-AES detection. On-line separation of the two species was effected with a 5 cm reversed-phase C₁₈ column. The eluent was introduced into the ICP-AES using hydraulic high-pressure nebulization. The detection limit for both oxidation states was 4 µg l⁻¹.

In a different approach, Cr^III and Cr^VI in waters were retained on ion-exchange media then determined by energy dispersive XRF.¹⁸⁹ The species in aqueous media were retained sequentially on activated alumina and Dowex 1-X8 for Cr^VI, and three different cation exchangers, Dowex 50W-X8, Zerolite and activated alumina, for Cr^III. The results showed that the Dowex resins were best for speciation of Cr in waters. The method was tested using a 100-fold diluted groundwater and waste water pollution check standard (WP15), which contains Cr^III and was spiked with Cr^VI. The detection limits for a preconcentration factor of 50 were 0.3 mg l⁻¹ for Cr^VI on Dowex 1-X8 and 0.4 mg l⁻¹ for Cr^III on Dowex 50W-X8. Sea-waters and river waters were also spiked with Cr^III and Cr^VI in order to further investigate the scope of the method.

A speciation method using ion IC-ICP-MS was developed for simultaneous determination of eight halogenides and oxyhalogens in drinking water samples from water treatment plants.¹⁹⁰ The species determined were Cl, ClO₂⁻, ClO₃⁻, ClO₄⁻, Br⁻, BrO₃⁻, I⁻ and IO₂⁻. Water samples were collected before and after disinfection to obtain information about species conversion during the purification processes. The detection limits for all Cl species were 500 µg l⁻¹, for Br species 10 µg l⁻¹, for I⁻ 0.1 µg l⁻¹ and for IO₂⁻ 0.2 µg l⁻¹.

A simplified derivatization method was developed for speciation analysis of organolead compounds in water.¹⁹¹ The water sample was adjusted to pH 4 with acetate buffer, mixed with Na₂EDTA and methanolic tetrabutylammonium tetrabutylborate. The mixture was extracted with hexane. The extract was stored in the dark at –20 [thin space (1/6-em)] °C until analysis by GC-MIP-AES. Calibration graphs were linear up to 3 pg as Pb in butylated organolead compounds. Detection limits were 43–83 pg l⁻¹ organolead compounds in tap water. In-situ propylation using Na tetrapropylborate was used as a simplified and fast sample preparation method for speciation analysis of organolead compounds in snow.¹⁹² Detection of the organolead compounds was by GC-MIP-AES. A new method for speciation of Pb in rain water by ID using direct coupled HPLC-ICP-MS was developed by Ebdon et al.¹⁹³ Samples containing trimethyllead chloride and triethyllead chloride in the presence of large amounts of inorganic Pb were analysed by HPLC-ICP-MS using reversed phase ion pairing chromatography. The detection limit was 3 ng g^–1 for trimethyllead as Pb and 14 ng g⁻¹ for triethyllead as Pb.

A review of different strategies for Hg speciation analysis in environmentally-related samples was published.¹⁹⁴ The different approaches for preservation of Hg species during the storage of samples were considered. Different extraction and preconcentration methodologies were discussed. Chromatographic and non-chromatographic separations of mercuric ions and methylmercury and the different techniques for sensitive and selective detection of Hg were also critically reviewed. An overview of the methodology and the instrumentation available for determination of Hg species in environmental samples was given by Frech.¹⁹⁵ The preconcentration and extraction approach using SPE was explored by Wang et al.¹⁹⁶ The Hg was complexed as Hg–dimercaptopropane-1-sulfonate, separated on a C₁₈ solid-phase extraction cartridge, then eluted with methanol. Hg concentrations were determined by ETA-AAS with Zeeman background correction. The RSD (n = 5) was 1.2% for 50 ng Hg. Crosslinked chitosan, which was insoluble in aqueous solution, acid and alkali, was used for preconcentration of Hg species from water.¹⁹⁷ Eluted Hg species were determined by cold vapour-AAS after oxidation with K₂Cr₂O₇–CdCl₂ and reduction with K₂BH₄. The detection limits for Hg species were 7.8 ng l⁻¹ for inorganic Hg, 9.8 ng l⁻¹ for phenylmercury and 12 ng l⁻¹ for alkylmercury.

A flow injection-hydride generation-atomic fluorescence method was developed by He et al.¹⁹⁸ for the determination of dissolved Se^IV and total inorganic Se in sea-water. For determination of the Se^IV the acidified sample was mixed with HCl and K₂HPO₄, then with NaBH₄ in NaOH to generate H₂Se. The hydride was dried, then determined by non-dispersive AFS in a mini-hydrogen diffusion flame. For determination of the total Se the acidified sample solution was mixed with HCl, then with NaBr. The solution was reduced by microwave irradiation, then treated with NaBH₄ and HCl to generate the hydride. Limits of detection for Se^IV were 5 ng l⁻¹ and for inorganic Se were 4 ng l⁻¹. Results for Se^IV and total Se in sea-water samples and sea-water CRM were presented and discussed. A similar approach for generation of the hydride was used for determination of different Se species in sea-water, but with in-situ trapping for preconcentration and ETA-AAS for detection.¹⁹⁹ An extensive study of the analysis and speciation of Se ions in environmental waters was conducted by Sharmasarkar et al.²⁰⁰ IC and hydride generation were applied to the determination of Se species and it was found that the hydride generation-AAS method was capable of determining Se down to 0.002 mg l^–1 (far below that of IC). IC was capable of determining SeO₃²⁻ and SeO₄²⁻ directly without sample pre-treatment, whereas the HG-AAS method measured SeO₃²⁻ + SeO₄²⁻ and SeO₃²⁻ in separate runs and SeO₄²⁻ was calculated by difference. A study of the adsorption properties of different oxides (CaO, CuO, La₂O₃, MgO, MnO₂ and WO₃) towards SeO₄²⁻ and SeO₃²⁻ was carried out using the methodology developed. The results were used to define the influence of oxides on the Se speciation in a soil–water system.

2.3 Reference materials and standard methods

In a fundamental paper by Quevauviller,²⁰¹ the requirements for preparation of a Certified Reference Material for speciation analysis have been specified. A range of chemical compounds in various environmental matrices were discussed, including trimethyllead in artificial rainwater. An outline of the difficulties that have to be tackled when trying to certify chemical species in environmental matrices was given. The paper emphasised the necessity of increasing the awareness by legislators, regulators and industries of the importance of determining the chemical species and not just total element contents.

The application of ID-ICP-MS for the production of CRMs and particularly for the determination of P and Si in sea-water (MOOS-1) and butyltins in PACS-2 sediment was described by Lam et al.²⁰² The accurate determination of Cu in two groundwater candidate RMs (BCR CRM 609, BCR CRM 610) was carried out using a high resolution double focusing sector field ICP-MS. ID was used for calibration.²⁰³ The results obtained were in good agreement with those obtained by other techniques in other laboratories.

The results of the sixth round of the International Measurement Evaluation Programme (IMAP) were published by Van Nevel et al.²⁰⁴ In this study, 180 laboratories in 29 countries analysed two water samples for 14 trace elements using their own techniques, methods and instrumentation. Reference values were established by isotope dilution-ICP-MS. In the 9th round of the International Measurement Evaluation Programme (IMAP-9) a study of the quality of analysis of fifteen trace elements in water, which involved 200 laboratories from more than 30 countries, was carried out. The results and uncertainties were plotted. The results were also grouped according to experience, accreditation status, method used and geographical location.²⁰⁵ The certification of B, Cd, Mg, Pb, Rb, Sr and U in the natural water sample submitted to the 200 laboratories was carried out using isotope dilution-ICP-MS.²⁰⁶

2.4 Instrumental analysis

The most significant developments in methodology and equipment are discussed in this part of the review.

2.4.1 Atomic absorption spectrometry. In a new method for determining total As in environmental waters As was preconcentrated by collection of arsine on a Pd coated pyrolytic platform cuvette, then atomized and detected by AAS.²⁰⁷ Water samples with a low organic content were analysed without digestion but samples with high organic content were subjected to a HNO₃–H₂SO₄–HClO₄ digestion procedure. The detection limit was 0.3 ng l⁻¹ for a 25 ml sample. Samples analysed included tap, ground, lake, rain, river, sewage effluent and saline waters originating from the USA, China and Canada. A system was developed and evaluated which involved the in-situ collection of generated hydrides of As, Sb and Se in a graphite furnace using a high voltage electrostatic field.²⁰⁸ The accuracy of the approach was demonstrated through the analysis of coastal sea-water reference materials. Absolute detection limits for As, Sb and Se were 30, 33 and 16 pg. In a similar study, the determination of Pb in estuarine waters using in-situ preconcentration of Pb hydride on Ir, Zn and W coated graphite tubes was investigated.²⁰⁹ The Pb hydride was generated and trapped in the furnace tube at 20 [thin space (1/6-em)]

°C (for Ir and Zr coated tubes) or 400 [thin space (1/6-em)]

°C for W coated tubes. The Pb was atomized at 1800 [thin space (1/6-em)]

°C for 5 s. The detection limit for Pb was 60 ng l^–1 when the Ir-coated tube was used and 70 ng l⁻¹ for the other tubes. Sample throughput was 40 per hour. Johansson et al.²¹⁰ designed and developed a method for continuous flow electrochemical reduction of Ni. The online method then generated and transferred nickel carbonyl to a graphite furnace where it was decomposed, trapped, atomized and detected. The method had a detection limit of 87 ng l⁻¹ based on a 1.0 ml sample volume.

2.4.2 Emission and fluorescence spectrometry. Chlorides in water samples were determined by GD AES following on-line continuous generation of Cl₂.²¹¹ Cl₂, generated from Cl⁻ by oxidation, was passed into a He stream and then transferred directly into a plasma for analysis by GD-AES. Two types of GD were used (r.f. and d.c.) and results from these were compared. The detection limits were 0.14 and 0.5 ng ml⁻¹ Cl with the r.f. and d.c. devices, respectively. Adsorbable organically bound elements such as Cl, Br, I, F, S and P were determined in water samples following thermal desorption and detection by MIP-AES.^212,213 The elements were preconcentrated on activated charcoal, desorbed at 850 [thin space (1/6-em)]

°C, cryofocused at –170 [thin space (1/6-em)]

°C, heated to 300 [thin space (1/6-em)]

°C and transferred into the MIP-AES for detection. A detection limit of 0.2 µg of Cl was obtained. A new semi-automated compact interface, which allows time resolved introduction of gaseous analytes from an aqueous solution into an atomic spectrometer without the need for a full-sized GC-oven, was developed by Wasik et al.²¹⁴ The gaseous analytes were purged with an inert gas, dried in a 30 cm tubular Nafion membrane and then the compounds were trapped in a thick-film coated capillary tube followed by their isothermal separation on a 1 m multicapillary GC column. The gaseous products from the separation were introduced into a MIP-AES system for elemental detection. The interface allowed a full speciation analysis to be carried out in less than 5 min with detection limits down to 5 pg l⁻¹.

A computer controlled electrothermal hollow cathode emission spectrometric source was developed for the simultaneous multi-element determination of trace elements in river, ground and tap waters.²¹⁵ The sample (10 µl) was dispensed into the cavity, then dried at room temperature in Ar. The sample was excited with a 200–600 V d.c. discharge during vaporization. The elements determined included Cr, Cu, Mn, Ni and Pb and the detection limits were 2.1, 0.6, 4.8, 2.6 and 1.2 µg l⁻¹, respectively. Park et al.^216,217 studied a new GD emission source for the determination of trace metals in flowing water. An atmospheric GD in Ar gas applied between an electrolyte solution cathode and Pt rod anode led to the formation of a stable discharge. The intensity of the emission lines observed were found to strongly depend on the acidity of the water, the current and the discharge gap. Sub mg l⁻¹ detection limits were obtained for Al, Cd, Cr, Cu, Hg, Mn, and Pb.

Goltz et al.²¹⁸ developed a new system for sample introduction into the ICP-AES using a larger volume graphite cup (200–400 µl) heated inductively in an induction coil. The device used HCl_(g) in the carrier gas to prevent arcing in the induction furnace. Compared with solution nebulization, detection limits for a number of elements were improved by 2–3 orders of magnitude. The applicability of the system was demonstrated by the successful determination of Cu, Mn and Zn in river water.

In an investigation of the effect of matrix on the direct determination of trace metals in sea-water by direct sample insertion ICP-AES it was found that the matrices tended to decrease the ICP emission intensity.²¹⁹ The extent of the matrix effects was dependent on the element being measured.

2.4.3 X-ray fluorescence spectrometry. There were relatively few papers in which novel and new approaches to XRF were elucidated. A desktop energy dispersive micro-X-ray spectrometer was used for determination of trace elements in river water.²²⁰ A newly developed X-ray tube with a thin window was used to generate an optimized energy distribution of the primary beam. Sensitivity was dramatically improved by reduction in scattered X-rays, thereby improving the peak to background ratio of the primary X-ray beam. The spectrometer was successfully applied to the determination of metals at sub-nanogram concentrations. In a new development for portable X-ray fluorescence, a filter for liquids was designed for selective extraction of heavy metals.²²¹ Used in combination with the multi-element thin sample analyser the system was ideal for on-site screening of liquid pollutants. Using the filtration process for Pb in tap water a detection limit of 8 µg l⁻¹ Pb for a 500 ml sample was obtained. An extraction efficiency of 85–95% for a 4 ml min⁻¹ flow rate was observed. An interlaboratory comparison of two related X-ray fluorescence techniques (total reflection XRF, i.e., TXRF and Grazing Emission XRF, i.e., GEXRF) was carried out to evaluate the performance of the techniques for analysis of water samples.²²² The elements determined were Ca, Cu, K, Mg, Na, Ni, Sr and Zn. The analyses were performed in 11 laboratories. The results obtained suggested that TXRF was suitable for direct determination of heavy elements in water (above K, Z = 19). The initial results obtained with GEXRF indicated that the technique was suitable for determination of the lighter elements. However, results for Na and Mg were systematically too low, indicating that further work was required to improve the procedures for determination of the lighter elements.

2.4.4 Mass spectrometry. An extensive overview of mass spectrometry for inorganic trace analysis was published by Becker et al.²²³ Techniques such as SSMS, laser ionization mass spectrometry (LIMS), LA-ICP-MS, GDMS, SIMS and ICP-MS were discussed in the context of multi-element analysis and were considered to be applicable to a wide range of matrices. Other MS techniques, such TIMS, accelerator mass spectrometry (AMS) and RIMS, were used for mono- or oligo-elemental analyses and for precise determination of isotope ratios in solid samples. Techniques such as ICP-MS, although used very frequently, were susceptible to interferences, particularly if sample dissolution was carried out prior to analysis. The application of double-focusing sector field MS was believed to help to overcome some of the interference problems.

A method for determination of dissolved organic carbon in environmental waters by ICP-MS was developed by Paucot et al.²²⁴ Several parameters were investigated to reduce the levels of background carbon signals by removing CO₂ from the ICP-MS system. The background observed at m/z 12 and 13 was reduced by more than 15%. By further optimization of the analytical procedures it was possible to reduce the detection limit to 0.1 mM l⁻¹. The use of molecular ions for quantitative analysis of water was investigated by Takahashi et al.²²⁵ It was ascertained that it was possible to determine P as its oxide under cool plasma conditions. The detection limit was 8.4 ng l⁻¹ P (as the oxide).

Mason et al.²²⁶ described a method for determination of S isotope ratios and concentrations in water using ICP-MS with hexapole ion optics. S isotope ratios are often difficult to determine by quadrupole ICP-MS because of interferences caused by O₂⁺ and NO⁺ molecular ions on ³²S and ³⁴S isotopes. The recent introduction of RF-only hexapole devices into ICP-MS has facilitated ion transfer from interface to analyser. A mixture of gases may be introduced into the hexapole and thence a series of ion-molecule reactions may be induced to help remove or reduce interfering polyatomic species. The effects of various gas mixtures on the transfer of S ions through the interface and the breakdown of O₂⁺ and NO⁺ species were investigated. The isotope ratio of S in crater-lake waters and in water samples obtained from springs and rivers near volcanoes in Java, Indonesia, were determined.

The potential of FI sample introduction for determination of Cd in water samples by ID-ICP-MS was studied by Mota et al.²²⁷ Two different flow approaches for the determination were explored and compared with the more conventional ID methodology. In the first approach, the sample was mixed with the spike solution immediately prior to nebulization. In the second, volatile Cd species were generated with Na tetraethylborate by merging zones flow injection ICP-MS. All three approaches were successfully applied to the determination of Cd in SLRS-3 Riverine Water.

3 Analysis of soils, plants and related materials

Since the publication of the 14th JAAS environmental update a year ago,⁷ continued concerns over environmental pollution have resulted in yet another torrent of publications and conference papers exploiting the capabilities of atomic spectrometry. However, real progress in soil and plant analysis has been more of a trickle than a flood. Thus, while Table 3 flags many interesting and worthwhile applications of spectrometry to the analysis of soils and plants, the work reported is perhaps more exciting to environmentalists than it is to analytical spectroscopists. Analytical `developments' have often involved minor tinkering with existing methods, and improvements are often claimed. Unfortunately, many modifications are not based on time consuming, systematic, scientific evaluation, making worthwhile critical evaluation of progress difficult, and leaving the door open for many more papers of the same type. This is especially true in the field of sample preparation, where it sometimes seems that almost every laboratory in the country is using its own `optimized' procedure.

Table 3 Summary of the analyses of soils, plants and related materials

Element	Matrix	Technique;atomization;presentation*	Sample treatment/comments	Ref.
*Hy indicates hydride and S, L, G. and Sl signify solid, liquid, gaseous or slurry sample introduction, respectively. Other abbreviations are listed elsewhere.
Al	Soil drainage water	AE;ICP;L AA;ETA;L	Three procedures compared for Al speciation	173
Al	Leaf mitochondria	MS;—;—	Novel application of accelerator MS	487
Al	Soil leachates	AA;ETA;L	Cation exchange fast protein LC used for speciation; NH₄NO₃ mobile phase pre-cleaned with Chelex-100	508
Al	Plants	AA;F, air–C₂H₂;L	It is claimed that if samples are digested with HCl, and (C₄H₉)₄NBr added, the air–C₂H₂ flame can be used for Al	509
As	Mushrooms	MS;ICP;L	As speciation performed on species known to accumulate As; arsenobetaine and trimethylarsine oxide found in low amounts	510
As	Environmental and biological samples	MS;ICP;L	HPLC used in As speciation study	181
As	Soil leachate	MS;ICP;L	Capillary electrophoresis used for As speciation	180
As	Soils	AE;MIP;G	Lewisite and degradation products extracted with dilute HCl, then derivatized with 1,3-dimercaptopropane for GC separation	458
As	Fucus distichus	MS;ICP;L	Water-soluble As species in the marine brown algae separated by HPLC	511
As	Fly-ash-amended soils	MS;ICP;L	Dionex IC used for separation of As and Se species; eluent output coupled to MS	512
As	Soils, sediments	AA;ETA;Sl	See Co, ^ref. 464	464
As	Soils, sediments	MS;ICP;L	Focused microwaves used in digestions with H₃PO₄, EDTA, NH₃OHCl and HCl–HNO₃ at various concentrations for speciation studies	513
As	Soil leachates	MS;ICP;L	Capillary electrophoresis used for separation of As species	239
As	Plants	AE;ICP;L	Effects of 4 As species on growth and As accumulation by tomato plants studied	514
Au	Soils	MS;ETA;—	Application of resonance ionization time-of-flight MS described	483
B	Plant cells	MS;ICP;L	Coupling LC sample introduction for B speciation described	437
B	Soil extracts, plant digests	AE;DCP;L	Method compared with colorimetric and fluorimetric methods; all reasonable, but AE was less sensitive	246
B	Soils	AE;ICP;L	Microwave-assisted digestion with HNO₃–HF; contents of PTFE vessel then treated with H₂O₂ and SiO₂	427
B	Plant parts	MS;ICP;L	¹⁰B-enriched boric acid used to study fate of B taken up by peach trees	474
Bi	Soils	AA;ETA;Sl	Slurry atomized with (NH₄)₃PO₄ as modifier; RSD of 2.8–4.2% claimed	515
C	Humic substances	MS;ICP;L	IDMS using ¹³C-enriched benzoic acid used for DOC determinations	346
Cd	Soils	MS;ICP;Sl	Ultrasonics used to disperse slurry for ETV	481
Cd	Vegetables	AA;F, air-C₂H₂;L	Ashed samples extracted with 1% HNO₃; or samples digested with HNO₃–HClO₄; stainless steel atom trap used to enhance sensitivity	467
Cd	Aquatic plants	AA;ETA;Sl	Dried material sonicated with 3% HNO₃; 5 µl aliquot of supernatant used with Pd modifier	461
Cd	Soils, water	AA;ETA;L	A novel mobile AA spectrometer with battery-powered tungsten coil atomizer described for field use	262
Cd	Tea	AA;ETA;L	Pd–Mg used as modifier with graphite platform	516
Cd	Plants	MS;ICP;L	HPLC used for investigation of phytochelatin complexes of Cd and Cu	517
Cd	Lichens	MS;ICP;L	On-line ID shown to be more convenient than off-line ID method for generation of volatile Cd species	227
Cd	Soil extracts	AA;ETA;L	Cd complex with KI extracted into IBMK	518
Cd	Soil leachates	MS;ICP;L	¹¹¹Cd tracer used to study movement of Cd added to soil	473
Cd	Tea leaves	AA;F;L	Extraction with APDC used for preconcentration in MIBK	519
Cd	Soils	AA;ETA;L	Samples digested, in turn, with aqua regia, HClO₄, HF, HClO₄ and HNO₃	520
Cd	Soil leachates	MS;ICP;L	¹¹¹Cd used to study migration of Cd through soil columns; modified ID equation used	521
Co	Soils, sediments	AA;ETA;Sl	Ground samples suspended (with care!) in 50% HF; for samples with Cu and Ni, 1 min mild heating in microwave oven also used	464
Cr	Roadside soils	AA;F;L AA;ETA;L	Microwave-assisted digestion with HNO₃; claimed that no modifier or BG correction needed with the L'vov platform	522
Cr	Plant samples	MS;ICP;L	Interferences from ArC⁺ and ClO⁺ investigated; matrix matching and a correction equation required	480
Cr	Plants	AA;ETA;L	Open-focused microwave-assisted digestion using HClO₄ favoured over classical wet ashing for Cr	426
Cr	Soil extracts	AA;—;L	Cr^III complex with Chromazurol S and Cr^VI complex with NaDDC adsorbed on Separon SGC C₁₈ column, then eluted with CH₃OH	186
Cr	Soils	XRF;—;S	Field portable instrument used for rapid screening	495
Cr	Tomato leaves	AA;ETA;Sl	Samples mixed with HNO₃, PTFE suspension and plant gum	523
Cs	Pine needles	MS;ICP;L	CRMs analysed without separation or pre-concentration, using Re internal standard; samples digested with HNO₃–HClO₄–H₂O₂, evaporated to near dryness and dissolved in dilute HNO₃	524
Cu	Soils	AA;F;L AA;ETA;L	5-step sequential extraction procedure described	446
Cu	Plants	MS;ICP;L	See Cd,^ref. 517	517
Cu	Plants	MS;ICP;L	Validation of protocol for ID-ICP-MS determination described	525
Cu	Environmental materials	AA;ETA;L	Robotic sample preparation method for preconcentrating Cu as PDC complex on PTFE knotted reactor	275
Cu	Soil, sediment	AA;ETA;Sl	See Co, ref. 464	464
Fe	Soil extracts	AA;F;L	Determination by FIA	526
Hg	Soils	AA;CV;L	FIA system used to evaluate effects of high NaCl concentrations; conditions carefully optimized	466
Hg	Soil organic matter fractions	AA;CV;L	26 extractants tested; unsuccessful due to contamination	447
Hg	Soils	MS;ICP;Sl	See Cd, ref. 481	481
Hg	Soils	AF;—;G	GC used to separate methylmercury after aqueous phase ethylation using sodium tetraethylborate in KOH	440
Hg	Trees, vegetation	XRF;—;S	Samples dried, ground in ethanol and deposited on foil or digested with H₂O₂–HNO₃, and digest spiked with Y and Sc, before transfer of small aliquot to foil for drying	527
Hg	Environmental materials	Various	A review, with 162 refs., of methods for speciation	194
Hg	Soils	MS;—;G	Methylbis(dimethylglyoximato)pyridinecobaltate(III) used to convert inorganic Hg in soil to methylmercury iodide with 95% efficiency prior to GC separation	528
Hg	Foliage	AF;CV;L	Optimization of a microwave-assisted digestion process described	469
Hg	Soils	AA;CV;L	Thermal generation of Hg⁰	529
Hg	Soils	AF;—;G	AFS used as GC detector for methyl- and ethylmercury; 3 extraction methods compared	439
¹²⁹I	Soils	MS;—;—	The role of accelerator MS in evaluating background (pre-nuclear level of ¹²⁹I is critically reviewed)	488
I	Soils, plants	MS;ICP;L INAA;—;S	Review in German with 79 refs.	530
In	Soils	AF;ETA;L	Optimization of conditions by LEAFS described (LOD 1 fg)	51
Mg	Plant chlorophyll	AA;F;L	Chlorophyll determined by extraction into petroleum ether and back extraction of Mg into 1 mol l⁻¹ HCl	531
Mn	Tea	AA;F;L	Leaves digested with HNO₃–HClO₄ for total Mn; Soxhlet or batch extraction methods also used for Mn speciation	532
N	Soils, soil extracts	AE;MIP;L	Used for ¹⁵N determination in N speciation studies	533
Ni	Soils	AA;F;L AA;ETA;L	See Cu, ref. 446	446
Ni	Vegetables	AA;—;L	Ashed samples extracted with HNO₃–H₂O₂, or dried sample extracted with more of the same mixture; diluted digest treated with buffer plus oxine or cupferron and activated C suspension; filtered residue dried and extracted with HNO₃	534
Ni	Soils, sediments	AA;ETA;Sl	See Co, ^ref. 464	464
Ni	Tea leaves	AA;F;L	See Cd, ^ref. 519	519
Pb	Soils	MS;ICP;Sl	See Cd, ref. 481	481
Pb	Plant ash, peat	XRF;—;S	Ashing improved precision, especially at low concentrations	535
Pb	Mushrooms	AA;ETA;L	A routine environmental contamination study, showing traffic pollution effects	536
Pb	Vegetation	AF;Hy;L	KBH₄–potassium ferricyanide used to generate the hydride, some of which adsorbed on the quartz atomizer	468
Pb	Algae	XRF;—;S	Use of miniature X-ray tube described	54
Pb	Peat	AE;MIP;G	In-situ butylation used for speciation of organolead compounds by GC	191
Pb	Tea leaves	AA;F;L	See Cd, ref. 519	519
Pb	Soil solution	AA;ETA;L	AA and differential-pulse ASV used for Pb speciation	445
Pb	Plant tissue	AA;ETA;Sl	Ultrasonic treatment used to improve analysis	462
Pb	Soils	AA;quartz tube;G	An improved hydride generation procedure described in detail	465
Pb	Plant materials	MS;ICP;L	Samples decomposed with HNO₃–H₂O₂ with ²⁰⁴Pb spike; ID improved precision	537
Pt	Roadside grass	MS;ICP;L	Roadside air and verges studied in Belgium	538
Pt	Grass clippings	MS;ICP;L	HPLC-ICP-MS used for Pt speciation	539
Pt	Soils, tunnel dust	MS;ICP;L	On-line capillary electrophoresis used for speciation	540
Pu	Environmental materials	MS;—;—	RIMS used to attain high sensitivity	541
Pu	Soils	MS;—;S	RIMS applied to give LOD of 10⁶–10⁷ atoms	484
Pu	Soils	MS;ICP;L	Element separated and pre-concentrated by ion-exchange and extraction chromatography	542
Pu	Algae, lichen, soil	MS;ICP;L	Concentrations and isotope ratios determined after separation/preconcentration	543
²²⁶Ra	Soils	MS;—;—	TIMS used for determination of Ra and U isotopes after separation from matrix	323
REE	Wheat flour, twigs, tea	MS;ICP;L	Dry ashing and 2 wet digestions shown to give similar results	425
REE	Rice plant parts	MS;ICP;L	Microwave-assisted digestion with HNO₃–H₂O₂; re used as internal standard; RSD 2.3–4.2%	544
REE	Algae	MS;ICP;L INAA;—;S	Techniques compared; INAA not useful for REE because of ²⁴Na and ³²P interference	545
REE	Plants	MS;ICP;L	Microwave-assisted digestion with HF–HClO₄–HNO₃	546
S	Plant tissues	AA;F;L	After HNO₃–HClO₄ digestion, diluted digest treated with BaCrO₄; after 1 h, Cr liberated, filtered and determined	460
S	Plant materials	AE;ICP;L	Samples digested with 4 mol l⁻¹ HCl	295
Sb	Plant materials	AA;Hy;L	Samples digested with HNO₃–H₂SO₄–HF–HClO₄	547
Se	Edible mushrooms	INAA;—;S	2 species shown to accumulate Se	548
Se	Leaves	AA;ETA;L	Slurry formed with Triton X-100; Pd used as matrix modifier	549
Se	Plant tissues	MS;ICP;L	External standards and stable isotope dilution used simultaneously for determination using hydride generation. Samples digested with HNO₃–HClO₄, digests evaporated, and Se^VIreduced by heating with 4 mol l⁻¹ HCl	476
Se	Vegetables	MS;ICP;G AE;—;G	Selenoaminoacids esterified with H₂SO₄ in methanol or ethanol, or derivatized with H₂O–ethanol–pyridine, prior to chromatographic separation	443
Se	Mine soils	AA;Hy;L	Se^IV and Se^VIseparated by IC	200
Se	Clover	AA;ETA;L	HPLC used for speciation in enzymic extracts	550
Se	Cultured Se-rich mushrooms	AE;ICP;L	Study of cultivation effects	551
Se	Grain	AA;Hy;L	Continuous flow system used in Se deficiency study	552
Se	Fly-ash-amended soils	MS;ICP;L	See As,^ref. 512	512
Sn	Fruit, vegetables	MS;ICP;L	Sn from cyhexatin residues determined after acid digestion	553
⁹⁹Tc	Soils	MS;ICP;L	Element in HNO₃ enriched on a `Teva resin' column, prior to separation by HPLC	554
⁹⁹Tc	Seaweed	MS;ICP;L	Chromatography used to separate Tc from Ru; results agreed well with those by radiation counting methods	555
Th	Pine needles	MS;ICP;L	ETV used to enhance sensitivity	129
U	Soils	MS;—;—	TIMS used to measure ²³⁸U and ²³⁵U	485
U	Soils	MS;—;—	See Ra, ref. 323	323
U	Pine needles	MS;ICP;L	See Th, ref. 129	129
U	Contaminated soil particles	XRF;—;S	Particles imbedded in non-reactive Si polymer; micro XRF and micro X-ray absorption near edge structure used	493
U	Tree bark	MS;ICP;L	Study to show tree bark is comparable to air filters for monitoring	556
Various	Scots pine	XRF;—;S	Needles from Kola peninsula and north Finland analysed	557
Various	Soils	MS;ICP;Sl	Trace metals in soil slurries in HCl–Triton X-100 volatilized by ETV	481
Various	Soils	AA;—;L	Three digestion procedures compared and gave similar results; aqua regia gave similar results to microwave assisted digestion for Cu and Ni	558
Various	Grapes	AA;—;L	Samples dry ashed; Cd, Cu, Pb and Zn attributable to industrial pollution determined	559
Various	Parts of bean plant	AA;—;L	Plant tissues digested with HNO₃–HClO₄–HF; mixture dried and residue dissolved in HCl; soil extracted with HCl–HNO₃	560
Various	Soils	LIBS;—;S	Design of a LIBS cone penetrometer probe described, and system tested in field; sensitivity depended on grain size and moisture	490
Various	Plant materials	MS;ICP;L AA;F;L AA;ETA;L	Microwave-assisted digestion, classical dry ashing and dry ashing in mixed oxidizing gases compared; all approaches gave similar results for Cd, Cu, Pb and Zn	424
Various	Tree ring wood	MS;ICP;S	LA used with ²³C as internal standard; discoloured rings gave abnormal results, and should be avoided	561
Various	Martian soils	XRS;—;S	Preliminary results from the alpha proton X-ray spectrometric analysis of Martian soils presented from the Pathfinder Mission	507
Various	Pine needles	XRF;—;S	Needles from along transects through smelters analysed	562
Various	Medicinal plants	INAA;—;S AA;—;L	Samples of 17 plants digested with HNO₃–HCl	563
Various	Plants	AE;ICP;L	Optimization described for 26 trace elements	564
Various	Mushrooms	AA;F;L	Dried ground samples digested overnight with HNO₃; digest boiled to small bulk and diluted with H₂O	565
Various	Tea	XRF;—;L	TXRF applied to acid digests or infusions	566
Various	Contaminated soils	MS;ICP;L	Application of the technique critically reviewed	470
Various	Peas	MS;ICP;L	55 elements determined in peas from 10 major areas in Denmark	567
Various	Lichens	AE;ICP;L	Samples digested with acid and matrix-matched standards used in a study of biomonitoring	568
Various	Soils	MS;—;—	Plasma-based secondary neutral MS used to examine trace metals in soil overburden at historic mining sites	569
Various	Onions	MS;ICP;L	10 samples from each of 11 sites in Denmark analysed for 63 elements	570
Various	Soils	AA;—;L	APDC complexes of Cd, Cu, Pb and Zn extracted from acid digests with CCl₄ and back extracted into HNO₃–H₂O₂	571
Various	Trees, vegetation	XRF;—;S MS;ICP;L AA;ETA;L	Techniques compared favourably for 7 CRMs; 28 elements determined in environmental samples near mining areas in Vietnam	360
Various	Plants	MS;ICP;Sl	Ultrasonic slurry sampling used with ETV for As, Cd, Ge, Pb and Se; procedure tested well on CRM	482
Various	Plants	MS;ICP;L	HPLC used to investigate phytochelation complexes of Cd, Cu, Pb and Zn in detoxification mechanism study	517
Various	Tree rings	MS;ICP;S	LA used to examine variation in 20-year old trees near Al smelter, 4 years after it closed down; Al, Ba, Ca, Fe and Sr increased after closure	572
Various	Soils, aquatic plants	MS;ICP;L	Soils microwave digested with HNO₃–HCl–HF; plants digested with HNO₃–HF; H₃BO₃ added prior to analysis for REE, Th and U	363
Various	Soils, sediments	MS;ICP;S	Ag added as internal standard, and dried samples pelletized at 35 MPa; results for SRMs within 20% except for Ba, Rb, Sr and Y	478
Various	Leaves	AE;ICP;L AA;ETA;L	High pressure, high temperature microwave digestion system evaluated	431
Various	Roadside soils	AA;F;L AA;ETA;L	Of 12 elements tested, Cd, Cu, Pb and Zn related to traffic density	573
Various	Soils	XRF;—;S	Protocol for field instrument described; results often differed from those by AAS	494
Various	Peat cores	XRF;—;S	Depth profiles studied for 18 elements and related to peat age	574
Various	Diuretic herbs	XRF;—;S	A radioisotope excited XRF–XR transmission technique used to look for toxic elements	575
Various	Tea leaves	AA;ETA;Sl AE;ICP;L	Slurry ETA-AAS worked well, but for multi-element analysis was slower than HNO₃–HF–HCl microwave-assisted digestion-ICP-AES	576
Various	Plants, soils	AA;—;L	Range of sample preparation procedures employed	577
Various	Medicinal plants	AA;F;L AE;F;L	Nutrient elements and Al determined	578
Various	Medicinal plants synthesising saponin	AA;—;L	The species selectively accumulated Al, Ba, Co, Cr, Cu, Fe, Mn and V	579
Various	Taiwanese paddy soils	AA;—;—	Heavy metals extracted with 0.1 mol l⁻¹ HCl	580
Various	Soils of north Jordan	AA;—;—	Trace metal pollutants related to particle size distribution	581
Various	Pteris semipinnata L.	—;ICP;L	20 elements determined in the anti-tumour herb	582
Various	Soils	AA;F;L	Nitrilotri(methylenephosphonic) acid compared with NTA for extracting Cu, Mn, Fe and Zn from soils; results similar except for Fe	449
Various	Plants	INAA;—;S AE;ICP;L	Substantial inter-laboratory comparison to evaluate the techniques	506
Various	Peach leaves	AE;ICP;L	W coil filament evaluated for ETV; generally good agreement for CRM	456
Various	Soils	AA;F;L	4 digestion procedures compared; HF–HClO₄, then H₃BO₄ followed by HCl, or microwave-assisted digestion with HF–HCl–HNO₃, then H₃BO₃ best	423
Various	Plants	MS;ICP;Sl	Samples slurried in 2% HNO₃–0.2% Triton X-100 using ultrasonics; ETV used with 10 ms dwell time on mass peaks of As, Cd, Ge, Pb and Se	583
Various	Sea plants	AE;ICP;L	Cd, Cu, Pb and Sb from sample in 0.5 mol l⁻¹ HCl solution treated with KI and concentrated on polyaniline column (preparation described); determinands leached with HNO₃. Sb recovery only 75%	584
Various	Cherry leaves, petals	AE;ICP;L MS;ICP;L	Samples digested with HNO₃ or HNO₃–HF; 41 elements determined, using internal standard	585
Various	Plants	MS;ICP;L	Microwave-assisted digestion with HNO₃–H₂O₂; technique shown to be suitable for 20 elements	586
Various	Algae	XRF;—;Sl	TXRF applied to slurries or microwave-assisted vapour-phase acid digests of 3 algae species	502
Various	Fruit, vegetables	MS;ICP;L	Metal–carbohydrate complexation studied by coupling HPLC to MS	444
Various	Soils	AE;ICP;G	C, P, S and Si determined after Ar supercritical-fluid extraction of contaminated soils	421
Various	Teas	XRF;—;S	Tea and associated infusions from main tea growing regions in China examined; 5 µl dried acid digest or acidified infusion used	505
Various	Seaweeds	XRF;—;S	Seaweeds screened for use as bioindicators of pollution from the KwaZulu-Natal coast	587
Various	Algae	XRF;—;L AE;ICP;L	Slurry samples prepared by sonication; aliquot oxidized by vapour-phase microwave digestion; TXRF then applied and results compared with those by AE	503
Various	Plant materials	XRF;—;S	Rotating moveable sample holder employed to compensate for heterogeneity	492
Various	Plants	AE;ICP;L	Wet ashing, with and without microwave assistance and dry ashing compared: S, K and Na lost by dry ashing; HNO₃–HClO₄ inadequate for Al and B	588
Various	Environmental materials	XRF;—;S	Applications of TXRF reviewed	589
Various	Tea leaves	AE;ICP;G	F-containing modifiers compared for use with ETV; PTFE best	455
Various	Teas	XRF;—;S	Aliquot of acid digest or acidified infusion dried for TXRF determination	504
Various	Soils	XRF;—;S	Portable field XRF spectrometer data compared with laboratory data, and gave unexpectedly poor correlation	590
Various	Plants	AE;ICP;L	Interferences encountered with axially viewed plasma due to matrix elements affecting plasma; higher power and lower aspiration rate overcame the problem	454
Various	Plant materials	MS;ICP;L	Microwave-assisted HF–HNO₃ digestion evaluated to show H₃BO₃ unnecessary	428
Various	Plants	INAA;—;S AE;ICP;L AA;—;L XRF;—;S	Comparison of techniques suggested INAA plus ETAAS best for pollution monitoring for plants	415
Various	Soils	XRF;—;S	Samples compressed to pellets with H₃BO₃	591
Various	Plant materials, water	AE;ICP;L	Al or La hydrous oxides used as carriers to separate/concentrate Cd, Co, Cu, Ni and Pb	419
Various	Soils, sediments	AE;—;L	Results of inter-laboratory study for Ag, B, Ge, Mo, Sn, Tl and W reported	592
Various	Soils, sediments	MS;ICP;—	Speciation of As, Bi, Hg, Ni, Mo, Pb, Se, Te and W discussed, and virtues of GC-ICP-MS extolled	386
Various	Soil clay fractions	MS;ICP;Sl	Suspensions nebulized with Babington-type nebulizer	593
Various	Oak leaves, pine needles	MS;ICP;S	Application of LA described for 10 elements	594
Various	Plants	AE;ICP;L	Matrix interferences in axially viewed plasma studied in detail; effects attributed to modification to plasma at high concentrations	312
Various	Pongamia pinnata seeds	AA;—;L	8 elements measured in defatted seeds	595
Various	Mushrooms	AE;ICP;L	Mn application to compost increased yield, but not uptakes of Cd, Ni and Pb	596
Various	Soils	AE;ICP;L	Need for H₂O₂ in microwave-assisted HNO₃ digestion assessed; effect negligible	429
Various	Roadside soils	AA;—;L	Heavy metal accumulation in surface soils demonstrated	597
Various	Wood	AE;plasma;S	Laser induced plasma used for detecting inorganic wood preservatives	598
Various	Feather moss	AA;—;L	Use of bryophytes for heavy metal deposition monitoring described	599
Various	Soils	AA;—;L	Pollution effects of smelter assessed	600
Various	Spinach leaves and stems	AE;ICP;L	16 elements determined in 22 local samples	601
Various	Pine needles	AA;ETA;L XRF;—;S	Samples analysed with and without washing to quantify surface deposition	416
Various	Tree rings	MS;—;S	SIMS used to generate data for element diffusion models for wood; synchrotron XRF also used	602
Various	Plant samples	AE;ICP;L	Samples digested with H₂SO₄–H₂O₂	603
Various	Plant materials	MS;ICP;L AE;ICP;L	Open vessel digestion with HNO₃ and microwave assisted digestion with HNO₃–H₂O₂ compared	604
Various	Soils	MS;ICP;S	Thesis on laser ablation sample introduction applications to soils, glass and ceramics	605
Various	Organically grown potatoes	MS;ICP;L	44 elements determined for background study	606
Various	Soils, road dust, leaf dust, leaves	MS;ICP;L	Samples from area around Pb smelter digested with HNO₃–H₂O₂	607
Various	Soils	AE;ICP;L AA;ETA;L	Operationally defined fractionation procedure applied to Cd, Cu, Ni and Zn in 4 soils; Cd determined by ETAAS, other elements by AE	608

One advantage of approaching a steady state in terms of real progress is that reviews and comparisons of techniques become more valuable and durable. Benton Jones⁴¹³ has reviewed 40 years of progress in soil testing in the USA, highlighting the benefits of multi-element analytical capabilities. Another review, covering the same time interval but with more international coverage, stresses the importance of quality assurance.⁴¹⁴ The results of a critical comparison of a range of analytical techniques for plant analysis, including INAA, ED-XRF, ICP-AES and AAS, have been published.⁴¹⁵ The authors concluded that INAA and ETAAS were best suited for monitoring environmental pollution in plants. A useful text has been published on the applications of atomic spectrometry to regulatory compliance monitoring;⁴⁰³ this includes sludges, sediments and soils. Readers of this update may also wish to peruse a recent review of environmental analysis published in Analytical Chemistry,⁹² or a chapter on environmental applications of plasma spectrometry in a text on ICP spectrometry.⁹³

3.1 Sample preparation

Sample contamination with heavy metals clearly has to be avoided if meaningful data are to be obtained. This is not a trivial task: even before a sample is dried and ground prior to sub-sampling it is necessary to decide what is, and what is not, part of the sample. For plant materials, superficial deposits may be removed by washing, but selecting washing conditions that ensure no leaching loss of species which should have been retained is not always straightforward. The extent of the problem of superficial deposits is clear from a paper describing the results of measuring elements in and on Scots pine needles.⁴¹⁶ In this study, CHCl₃ was used for washing. Grinding machines too can be a source of contamination, although if a mild acid digestion of ground plant material is used, it is not easy to decide whether higher results obtained by one grinding method rather than another are due to contamination or to improved extraction efficiency from more finely ground particles.⁴¹⁷ Contamination may also occur during digestion, so those interested in ultra-trace analysis may be interested in an evaluation of a block digestor which uses a graphite heating area enclosed within a high temperature thermoplastic box, with no metallic parts.⁴¹⁸

A real `blast from the past' to make it into the literature this year was the suggestion of using Fe(OH)₃ or La(OH)₃ to co-precipitate trace elements from water or soil leachate solutions.⁴¹⁹ The possibility of using such approaches should not be dismissed too lightly, bearing in mind the multi-element capabilities of modern spectroscopic techniques, and the occasional need to transport large numbers of samples from isolated areas. Transport of small amounts of precipitate might sometimes be a very attractive possibility.

3.1.1 Sample dissolution procedures. Sample preparation and dissolution remain the most time-consuming and labour intensive stages of soil and plant analyses, and probably always will. Flow-based techniques for sample pre-treatment are therefore always worthy of careful consideration. Tyson³⁶⁸ has reviewed critically the application of such methodology. A group in Spain has evaluated the coupling of robotic sample acid digestion with FI preconcentration of Cu after complexation with APDC using a PTFE knotted reactor;²⁷⁵ final analysis was by ETAAS. Gräber and Berndt⁴²⁰ have described the development of a new high temperature (up to 260 [thin space (1/6-em)]

°C), high pressure (up to 300 bar) flow system for continuous digestion of biological samples; a tomato leaves CRM was included in the materials successfully used to validate their approach.

A particularly interesting and unusual application of flow methodology has been the use of argon supercritical fluid extraction of organic contaminants from soil.⁴²¹ The extractor was connected on-line to the ICP of an AE spectrometer, and C, P, S and Si were determined.

From time to time, reports appear on the apparently successful use of dilute acid extractants for plant analysis. In one such study, K was extracted simply by 5 min shaking with 0.5 mol l⁻¹ HCl.⁴²² Two hours shaking with 1 mol l⁻¹ NH₄Cl was also successful.⁴²²

Papers on microwave-assisted digestion continue to proliferate, in part no doubt reflecting the need of analysts to justify their purchase to scrutinizing employers! A number of useful and comprehensive comparisons of conventional and microwave-assisted (MA) digestions have appeared, however. For example, MA digestion of soil with HF–HCl–HNO₃ gave comparable results for Cr, Cu, Fe, K, Mg, Mn, Na, Pb and Zn to digestion with HF–HClO₄, H₃BO₃ treatment, followed by dissolution in HCl.⁴²³ In another study, MA digestion of plant materials with HNO₃ was shown to give comparable results to HNO₃ extractions of dry-ashed samples.⁴²⁴ Conventional wet ashing, dry ashing, and MA digestion with H₂O₂–HNO₃, followed by HClO₄, were shown to give similar results for REE determination in wheat flour by ICP-MS.⁴²⁵

Advantages of microwave-assisted digestion for particular elements have been claimed in a number of studies. Sahuquillo and colleagues⁴²⁶ claimed that the shorter time of plant digestions involving HClO₄ when open-focused MA attack was used reduced losses of volatile Cr compounds to acceptable levels. A method for MA digestion with HF–HNO₃ for the determination of total B in soils has been described in detail.⁴²⁷

Some workers have investigated the possibility of omitting one or more reagents when using microwave-assisted digestion. In one study, it was found that the use of boric acid was unnecessary when analysing plant and grain SRMs by ICP-MS after MA digestion with HNO₃–HF.⁴²⁸ From another investigation it was concluded that HNO₃ MA digestion alone was adequate for determination of Al, Cd, Cu, Cr, Fe, Mg, Mn, Ni, Pb and Zn in soils; the addition of H₂O₂ did not increase significantly the concentrations found.⁴²⁹

Schlemmer et al.⁴³⁰ pointed out that, in spite of the attractive features of MA digestions, many approved procedures encompassed in European legislation for soils and sludges depend on elution of samples with strong oxidizing acids such as HNO₃ or aqua regia, and not upon total mineralization. Such approaches could give different results from MA digestion.

It is refreshing once in a while to see published reminders of potential problems with microwave-assisted digestions. With a high pressure, high temperature system in which the programme temperature could not be monitored, it was pointed out that vessel rupture was common during method development, resulting in complete vessel destruction and release of potentially dangerous fumes.⁴³¹ The more timorous amongst us might feel this more than outweighs the advantage of speed of analysis! Before leaving the subject of MA digestions for sample mineralization, it is worth pointing out that attempts have also been made to use microwave energy to facilitate extraction of elements from soils for speciation studies. However, As^IIIwas oxidized to As^V at high microwave powers, indicating that care is needed in optimization of extraction conditions.⁴³²

Two reports have appeared on the use of high pressure ashers for the decomposition of selected plant materials, as an alternative to MA digestion systems.^433,434 It remains to be seen whether these reports herald a serious comeback for such systems.

3.1.2 Speciation. Interest in speciation of toxic elements in soils and sediments has shown no sign of abating over the past year. The speciation of As, as in previous years, has continued to figure prominently.⁴³⁵ At a fairly simple level, this may merely involve selective chemical reduction to differentiate between As^III and As^V in soil extracts or surface waters.⁴³⁶ For separating more species, such as arsenocholine, arsenobetaine, dimethylarsinic acid, methylarsonic acid, arsenous acid and arsenic acid, in surface waters or soil leachates, coupling HPLC^181,437 or capillary electrophoresis^180,239 to ICP-MS may be necessary, the latter providing the essential sensitivity. Donais⁴³⁷ has discussed the interfacing of LC to ICP-MS for, for example, As speciation.

There appears to be growing interest in Hg speciation in environmental samples at the present time, and this topic has been comprehensively reviewed in the literature by Sánchez Uría and Sanz-Medel¹⁹⁴ and by Zavadska and Zemberyova.²⁹⁵ Frech¹⁹⁵ has also reviewed, but in a conference presentation, the methodology and instrumentation available to tackle this problem. A helpful note of caution about working in this area comes from Pongratz and Heumann⁴³⁸ who, by studying rates of release of organomercury, -lead and -cadmium compounds by polar microalgae, found that the volatilization was such that this could pose significant contamination problems in clean rooms. A useful comparison has been reported of 3 methods for the extraction of methyl- and ethylmercury from soils and sediments;⁴³⁹ acidic KBr–CuSO₄ isolation–CH₂Cl₂ extraction, if necessary after an alkaline digestion pre-treatment, was best. Huang⁴⁴⁰ has described an optimized procedure for conversion of methylmercury in aqueous solutions and soils to methylethylmercury, prior to determination by GC-AFS.

Al inorganic speciation remains a topic of considerable interest in the context of ecotoxicity studies of acid soils and drainage waters. A cation exchange fast protein LC-ICP-AES system has been fully described and evaluated in the literature.¹⁷³ The system allowed quantification of Al³⁺, Al(OH)²⁺ and Al(OH)₂⁺, but AlF²⁺ co-eluted with Al(OH)²⁺, and Al(SO₄)⁺, AlF²⁺ and negatively charged organic Al complexes co-eluted with Al(OH)₂⁺ species.

Interest in Pt in the environment has grown substantially over recent years, primarily in response to contamination from catalytic converters, so the appearance of two papers on speciation of Pt is perhaps not surprising.^441,442 The first of these was concerned with the use of HPLC-ICP-MS for speciation of Pt in plant materials.⁴⁴¹ The second employed capillary electrophoresis and ICP-MS in the analysis of leachates of soils and tunnel dust.⁴⁴²

Other noteworthy speciation-related studies include the quantification of selenoaminoacids in vegetables by LC-ICP-MS,⁴⁴³ a simplified derivatization method for the determination of organolead compounds in water and peat samples by GC-MIP-AES,¹⁹¹ and the speciation of metal–carbohydrate complexes in fruit and vegetable samples by size exclusion HPLC-ICP-MS.⁴⁴⁴ Readers interested in Sb who also speak Czech may find a review (with 113 refs.) of Sb speciation helpful.

Finally here, mention should be made of anodic stripping voltammetry, which is still often used to quantify the fraction of total element (as determined by atomic spectroscopy) that is in a particular free ionic form. This approach has been used to study the effects of soil pH and organic matter content on Pb speciation.⁴⁴⁵

3.1.3 Selective extraction methods. Operationally defined element fractionation procedures are still attracting attention. A 5-step sequential extraction has been described for Cu and Ni fractionation in soils.⁴⁴⁶ A sequential multi-step dissolution/precipitation scheme for the characterization of soil organic matter has been applied to the study of soil Hg speciation.⁴⁴⁷ The scheme produced 26 fractions, and the Hg in each was measured by a CV technique.

A problem associated with selective extraction procedures is re-adsorption of displaced element. This has been discussed at length for the extraction of Au, because of problems encountered particularly with organic-rich and with Fe-rich lateritic soils.⁴⁴⁸ Addition of activated carbon to the extraction mixtures circumvented the problem.

Novel selective extractants are suggested in the literature from time to time. Nitrilotris(methylenephosphonic acid) has been suggested for the simultaneous extraction of trace elements from soils, and shown to be similar to the better known nitrilotriacetic acid.⁴⁴⁹

A paper which the writer of this section feels is worthy of particular attention is one warning of the limitations to the use of correlation coefficients for choosing extractants for assessment of plant availability of elements.⁴⁵⁰ The point was well made that correlations between concentrations of elements in extracts and plant uptake may be highly significant when concentrations of a test element range from deficient to excess, but may not be significant at all if only deficient or near deficient samples are analysed.

3.2 Reference materials

New CRMs are nearly always welcome in environmental analysis. Roelandts³⁴⁸ has reviewed newly available CRMs in this field, and provides contact addresses for suppliers. Because of the lack of suitable forest soil CRMs, Hislop and colleagues⁴⁵¹ prepared their own reference standards for USDA use. Their published details of the sample preparation and analysis procedures will be useful to others planning on going down this route. CRMs for speciation are particularly difficult to obtain. Quevauviller²⁰¹ has discussed this problem, with particular reference to organotins and methylmercury in sediments and other environmental materials. One interesting addition to the recent literature on CRMs was an appraisal of the contribution which uncertainty in analytical certification data makes to overall analytical uncertainty in sample analysis.⁴⁵²

3.3 Instrumental methods of analysis

This section discusses particularly noteworthy applications of, or developments in, atomic spectrometric analysis of soils, plants and related materials. Additional examples of applications of particular analytical techniques are listed in Table 3.

3.3.1 Atomic emission spectrometry. Applications of ICP-AES to soil and plant analysis are now commonplace, and have been comprehensively reviewed with particular reference to plant tissue digests or ash extracts.⁴⁵³ Axially viewed ICPs are also now in regular use, and it is therefore helpful to find systematic studies of matrix element interferences when they are employed for plant analysis.^454,312 Major matrix components such as Ca, K and Mg may modify the plasma temperature, influencing both atomic and ionic emission line intensities.

Interferences in ICP-AES may also be observed when electrothermal vaporization is employed for sample introduction. The chemical modifiers recommended differ significantly from those commonly encountered in ETAAS. For example, 6% PTFE added to the sample was shown to be more effective than NH₄F, NaF or CuF₂·2H₂O for elements such as Ni, Pb and Ti.⁴⁵⁵ Incorporation of ETV in ICP-AES may significantly increase cost. Therefore a 15 V, 150 W tungsten filament projector bulb has been suggested as an inexpensive system, and was shown to function well for a peach leaves SRM.⁴⁵⁶

The acceptability of ICP-AES as a method for leaf analysis is confirmed to some extent in its choice as a comparative method in the evaluation of solution spectrophotometric methods for determination of Ga, Sc and V in cabbage leaves.⁴⁵⁷ The spectrophotometry was sensitive, precise and, of course, much cheaper (at least in terms of instrumental costs!).

Plasmas other than the ICP are not widely used in AES. However, a MIP has been used as a GC detector for the determination of lewisite in soil.⁴⁵⁸ The lewisite and its degradation products were derivatized with 1,3-dimercaptopropane to yield volatile cyclic compounds. Recovery was in the range 71–88%. Few other examples of MIP use may be seen in Table 3. For the determination of B in soils, plants and water samples, DCP-AES was found to be adequate, but less sensitive than colorimetric or spectrofluorimetric procedures.⁴⁵⁹

3.3.2 Atomic absorption spectrometry. Atomic absorption spectrometers are not usually regarded as mobile instruments suited to field use. However, a miniaturized system using a tungsten coil atomizer, which could be run from a 12 V cigarette lighter outlet in a car, has been described.²⁶² The system performed adequately for the determination of Cd in soil and natural waters, with a detection limit of 3 ng ml⁻¹.

Few analysts would automatically think of AAS for the determination of S in plant tissues. Nevertheless, a procedure has been described based upon HNO₃–HClO₄ digestion, followed by dissolution of CrO₄^2– from a BaCrO₄ suspension under specified conditions, by reaction with SO₄²⁻ in the digest.⁴⁶⁰ The dissolved Cr was then filtered, and determined by AAS in an air–acetylene flame, using Ca as a releasing agent.

Slurried samples may be analysed with care by ETAAS. Use of ultrasound appears to have been very useful for maintaining Cd from aquatic plant samples in suspension when using ETA, although less success was achieved with sewage sludge and river sediment samples.⁴⁶¹ A similar approach was satisfactory, according to data for plant tissue CRMs, for Pb determination.⁴⁶² In a refreshingly systematic study, ultrasound was shown to significantly effect particle size distributions of plant tissue slurries.⁴⁶³ Even more care, but for safety reasons, would be needed if a method for analysing soil and sediment slurries in concentrated HF was routinely adopted, as recommended by one group of workers.⁴⁶⁴

Cold vapour and hydride generation methods can be very useful for pushing down detection limits for some elements. In one study, solid NaBH₄ and tartaric acid were used to generate Pb hydride for the determination of Pb in soils.⁴⁶⁵ Atomization was in a flame-heated quartz tube. The CV determination of Hg in saline waters has been shown to be strongly influenced by Cl^– concentration, reflecting the strong affinity for the element towards formation of anionic Cl^– complexes.⁴⁶⁶ Gold amalgamation pre-concentration could be used to overcome the problem.

Atom trapping is not widely used at the present time, but a reminder has been published that it may be used to determine volatile elements like Cd in ashed vegetable extracts.⁴⁶⁷

3.3.3 Atomic fluorescence spectrometry. Atomic fluorescence spectrometry tends to be perceived as a bit of an academic curiosity, with great potential for a handful of elements, but not enough to ever make it commercially viable. Nevertheless, applications appear from time to time in the literature. Over the past 12 months, for example, papers have appeared on the determination of In in soil and urban dust samples, using laser excitation and ETA to obtain the necessary sensitivity,⁵¹ Pb in vegetation using hydride generation,⁴⁶⁸ and Hg in foliage using CVAFS.⁴⁶⁹ It is tempting to think of these papers as solutions in search of a question, rather than the other way around, but all three approaches gave very good sensitivity, so perhaps the publications were justifiable.

3.3.4 Mass spectrometry. As might be expected, ICP-MS has dominated the literature, which includes atomic MS data for soils and plant tissues, as was generally the case in recent years. This is reflected in its abundant appearance as the technique of choice in Table 3, especially for multi-element analysis under the `various' elements category. This reflects the maturity of the technique for plant and soil analysis, and this maturity is also reflected in the publication of a number of reviews^{97,223,470,471} and a bibliography³⁷⁶ for the applications of the technique in inorganic analysis of soils, plants and other environmental materials. However, one other area especially seems worth flagging, namely the coupling of an elemental analyser to a mass spectrometer;⁴⁷² this allowed simultaneous determination of total C, ¹³C, total N and¹⁵N in up to 80 samples of plant or soil material over a 20 h run.
3.3.4.1 Inductively coupled plasma mass spectrometry. The ability of ICP-MS to discriminate between isotopes of elements has been a key feature of a number of the more interesting applications of the technique. For example ¹¹¹Cd has been used as a tracer to study the fate of Cd added to soil columns,⁴⁷³ and ¹⁰B-enriched boric acid has been employed in a study of the movement and distribution of B applied to peach trees.⁴⁷⁴ Natural isotopic discrimination of B has also been under investigation this year,⁴⁷⁵ although ICP-MS is not always regarded as being sufficiently precise for this sort of work. One novel application of the technique was to use ¹³C-enriched benzoic acid spikes in a method for the determination of DOC in fractionated humic substances by ICP-IDMS.³⁴⁶ Stable ID has also been used in the development of a double calibration technique for the determination of Se in plant tissue.⁴⁷⁶ Three Se isotopes were measured, and it was claimed that the double calibration (ID and external standards) approach allowed the quality of the result for any individual sample to be assessed. Isotope dilution procedures have been automated successfully for the determination of very low concentrations of Cd in lichens and marine sediments.²²⁷

Although this particular writer is yet to be convinced about all the positive attributes of slurry sample preparation methods, they continue to find advocates. A paper has been published describing the determination of Cd, Hg and Pb in soils using slurry sampling ETV-ICP-MS.⁴⁷⁷ The proposed method was claimed to give a precision of better than 5% and an accuracy of better than 2% for a SRM soil.

The precision reported above was a lot better than that found using laser ablation inductively coupled plasma mass spectrometry to analyse soil and sediment reference materials.⁴⁷⁸ Using¹⁰⁷Ag as an internal standard, plus or minus 20% was typical, and results for Ba, Rb, Sr and Y were low by factors of 2–3.

A noteworthy application of ICP-MS was its use as a capillary GC detector in the ion trap MS determination of volatile Bi, Sb and Sn compounds in landfill and fermentation gases.⁴⁷⁹ Such research is of interest in the contexts of biogeochemical cycling and human health considerations, quite apart from its intrinsic interest to analytical spectroscopists, in showing how low detection limits can be pushed.

Most polyatomic ion interferences in ICP-MS are now well documented. However, it is worth flagging a report that has appeared of potential problems from ArC⁺ and ClO⁺ species in the determination of Cr in aquatic plants, rye grass and sewage sludge.⁴⁸⁰

There are a number of possible reasons for employing electrothermal vaporization in ICP-MS. One of these is to convert slurry samples to a more appropriate form for introduction to the plasma. Soil slurries in HCl and Triton X-100 have been analysed this way for Cd, Hg and Pb;⁴⁸¹¹¹¹Cd, ²⁰¹Hg and ²⁰⁴Pb were added as spikes to allow application of ID methodology for calibration, which is an interesting development worthy of further attention. A more routine application of ETV was to the determination of As, Cd, Ge, Pb and Se in plant tissue slurries, using a standard additions technique for calibration.⁴⁸² Another reason for applying the technique is to enhance sensitivity. This was the case in a paper on the determination of natural U and Th in pine needles after a dry and wet ashing sample preparation method.¹²⁹

3.3.4.2 Resonance ionization mass spectrometry. A novel application of resonance ionization mass spectrometry was the determination of Au in soil using ETV.⁴⁸³ A 5-l sample of gas obtained from the test soil was first absorbed by a special sampler, which was then ashed, and the residue extracted with acid. The determination of Pu in soil by RIMS has also been described.⁴⁸⁴ A detection limit of 10⁶–10⁷ atoms was achieved, an impressive demonstration of the potential of RIMS for determination of ultra-trace amounts of long-lived radioisotopes.
3.3.4.3 Thermal ionization mass spectrometry. Many regard thermal ionization mass spectrometry as the technique of choice for the precise determination of isotope ratios. It was therefore used for monitoring ²³⁸U∶²³⁵U ratios of 500 soil samples in a contamination survey of the Greenham Common Air Base in England.⁴⁸⁵ Reproducibility was better than 0.2% at concentrations around twice the standard deviation. The use of TIMS for measurement of U isotope ratios was also discussed in another study, together with its application to the determination of ²²⁶Ra.³²³ The excellent precision and sensitivity allowed elucidation of isotopic enrichment during interactions between pore waters and associated solid phases.
3.3.4.4 Secondary ionization mass spectrometry. Secondary ionization mass spectrometry allows quantification of light elements with good spatial resolution and excellent sensitivity, and therefore some plant physiologists may be interested in a concise review of potential applications of SIMS in plant physiological research.⁴⁸⁶
3.3.4.5 Accelerator mass spectrometry. Although never destined to become a routine tool in the environmental analytical laboratory, accelerator mass spectrometry does occasionally find specialized environmental applications. Over the review year, these have included the very timely topic of the transport of Al from plant roots to leaves and the study of Al in leaf mitochondria of Brachiaria ruziziensis,⁴⁸⁷ and the monitoring of ¹²⁹I and ¹²⁷I in soils from the vicinity of Chernobyl.⁴⁸⁸ AMS surpasses the sensitivity of INAA for the determination of ¹²⁹I.

3.3.5 Laser ionization breakdown spectrometry. Another atomic spectrometric method of analysis still in the `rather exotic' league is laser ionization breakdown spectrometry. This does not detract, however, from its potential to analyse soils directly in the field. A system based on an 80 mJ Nd∶YAG laser and a cone penetrometer has been evaluated for the direct determination of Cd, Cr, Fe, Hg, Mn, Pb, Ti and Zn in sub-surface soils.⁴⁸⁹ A rather similar system has been described by other workers.⁴⁹⁰ It remains to be seen if this approach will become widely used in the not-too-distant future. Another applications paper on LIBS used soil or airborne dust samples in a small sample vial.⁴⁹¹

3.3.6 X-Ray fluorescence spectrometry. An interesting development over the past 12 months for plant analysis was that of a rotating and moveable sample holder, for use with powdered plant samples.⁴⁹² The purpose of the design was to provide simulated homogeneous excitation conditions, thereby improving precision and lowering detection limits.

A method for embedding particles of soil and sediment in non-reactive Si polymer has been developed for use in XRF and XANES.⁴⁹³ The approach allowed in-situ examination of U-contaminated soil particles at spatial scales of 1–25 µm.

3.3.6.1 Field portable XRF spectrometers. Following on from preliminary evaluation studies over the past few years, interest in field portable XRF spectrometers appears to be growing. For example, papers have appeared on a protocol for monitoring Pb pollution in contaminated soils,⁴⁹⁴ Cr in soil during remediation operations,⁴⁹⁵ and a range of heavy metals in soils.⁴⁹⁶ The last contribution discussed the importance of sample preparation procedures and sub-sampling. A particularly interesting paper was on the analysis of sub-surface soils, using a cone penetrometer system.⁴⁹⁷ Numerous other applications papers have appeared, the conclusions drawn usually being favourable about the potential of the technique.^{367,498–501} One of these papers also included a description of a ‘Joule–Thompson’ type cooled detector.⁵⁰⁰ Another discussed use of a range of other techniques in addition to XRF for characterization of organic pollutants alongside the heavy metal pollutants.⁵⁰¹
3.3.6.2 Total reflection XRF spectrometry. Two groups appear to be advocating the use of total reflection XRF spectrometry, one in Hungary, analysing freshwater algae,^502,503 the other analysing teas in Germany.^504,505 Their studies continue to demonstrate the potential of this approach to multi-element analysis, but not to the extent that ardent followers of other techniques are likely to switch methodologies.

3.3.7 Instrumental nuclear activation analysis. Based on the results of a world-wide inter-laboratory comparison of results of the analysis of plant CRMs, it has been concluded that INAA is suitable for the determination of Ce, Co, Mn, Na, Rb, Th and V, whereas ICP-AES is appropriate for Ba, Ca, Cr, Fe, K, Mn, Mo, P, S, Sr and Ti.⁵⁰⁶

3.3.8 Alpha proton X-ray spectrometry. Alpha proton X-ray spectrometry is a technique with which most readers of this review will be totally unfamiliar. This perhaps makes it all the more impressive that the APXS on board the Mars Pathfinder mission measured the composition of six soil samples and five rock samples at the Ares Vallis landing site.⁵⁰⁷

4 Analysis of geological materials

4.1 Introduction

In considering current developments in atomic spectrometry in relation to geochemical applications, recent reviews often provide useful background commentary.^7,92,609 A particularly succinct and thought-provoking perspective by Potts⁶¹⁰ not only reviewed the major developments in geoanalytical techniques over the last 50 years but speculated on future trends. He concluded that, for bulk analysis of silicate rocks, XRF and ICP-MS will have important roles but, in terms of progress in geochemical research, microbeam analytical techniques will be the most influential. There is little evidence in this update to contradict these sentiments.

Up-to-date information on sources of reference materials are always invaluable to the geoanalyst. The reader's attention is drawn to two recent compilations, one dealing specifically with geochemical and cosmochemical materials⁶¹¹ and the other with biological and environmental reference materials.³⁴⁸ New reference materials are always welcome: the Geological Survey of Japan has prepared a basalt and a coal fly-ash;⁶¹² the Chinese Academy of Geological Sciences has conducted a preliminary study on four candidate materials, two Pacific Ocean polymetallic nodules and two marine sediments;⁴⁹⁶ and two marine sediments have been characterized by the Chinese Institute of Marine Geology, using several techniques.⁶¹³

Although emphasis is so often placed on analytical error, sampling bias should not be overlooked. Thompson and Patel⁴¹² have devised a method for investigating the possibility of bias between sampling methods. Proficiency testing is becoming increasingly accepted as one of the standard quality control procedures used to help laboratories detect unsuspected errors and deficiencies in their analytical methodology. Results from two rounds of the GeoPT proficiency testing scheme for analytical geochemistry laboratories run by the International Association of Geoanalysts have been published.^614,615

4.2 Sample treatment

4.2.1 Solid sample introduction..
4.2.1.1 Laser ablation. For newcomers to laser ablation coupled to ICP-MS, a practical guide with 118 references has been written by Günther and co-workers especially for their benefit, with a view to raising awareness of the technique's potential, particularly in relation to geological materials.⁶¹⁶

The use of laser ablation for sample introduction has significant advantages for the geoanalyst. It enables the determination of elemental concentrations and isotopic ratios with very high spatial resolution. Moreover, it removes the necessity for sample dissolution, thus enhancing productivity. This latter advantage has attracted a number of workers concerned with bulk analysis of geological materials.^617–620 The concept of ablating fused glass beads is not new. A homogeneous sample is obtained by fusion with lithium borate, although every laboratory appears to have its own recipe for the proportion of sample to Li borate and/or metaborate. Internal standards can be added during preparation, e.g., Mn,⁶¹⁷ Sc and Y.⁶¹⁸ XRF fused glass beads were analysed for REE by LA coupled to double focusing magnetic sector ICP-MS, using Ba as an internal standard.⁶²¹ The magnetic sector instrument not only conferred superior sensitivity, but also enabled LREE oxides to be more easily distinguished from the HREE, leading to better accuracy than is obtainable by quadrupole ICP-MS.

While fusion provides a uniform matrix, volatile species may be lost. However, the difficulties of quantitative analysis of soil or sediment polymineralic powders, by ablating pressed powder pellets, should not be underestimated. One such study⁴⁷⁸ obtained reasonably accurate results (±20%) for most trace elements using a spiked internal standard and solution calibration. Unsurprisingly, particle size was found to influence the precision and sensitivity of the measurements and the applicability of the internal standard. Thus, a systematic study of the influence of the physical and chemical properties of analogues of geological samples by Motelica-Heino et al. is welcomed.⁶²² Both single phase and complex matrices were analysed by LA-ICP-AES at 1064 and 266 nm. The LA-ICP-AES response factors of the analytes were found to be strongly influenced by their chemical form and the bulk composition of the matrix. These effects were also found to be wavelength dependent and the use of a UV laser did not reduce them.

In previous years there has been much debate on the relative merits of different laser wavelengths. While UV wavelengths are now accepted to be the preferred mode of operation for most applications, the argument for very low UV wavelengths has not been so keenly contested; neither have the issues surrounding fractionation effects. The role of active focusing of the laser during ablation seems to have overcome many of these effects, even at 266 nm.⁶²³

The analysis of fluid inclusions (FI), typically 5–50 µm in diameter, is still one of the most demanding applications for laser ablation sample introduction. Commercially available systems are being improved with this in mind,⁶²⁴ although it remains to be verified whether these systems are capable of viewing the FI with the clarity of a petrological microscope. High temperature brine inclusions have been shown to contain 0.3 ppm of Au using a sophisticated custom-built laser system.⁶²⁵ The elements of interest in FI studies include Na, K, Ca and Li, which are arguably more easily determined by optical emission spectrometry (OES) than by ICP-MS. A recent study⁶²⁶ has demonstrated that synthetic glasses, synthetic inclusions and minerals can all be used to construct calibration curves for OES, enabling the detection limits required for the analysis of FIs to be achieved.

An inter-laboratory comparison to assess the merits of LA-ICP-MS and cryogenic-SEM-energy dispersive (cryo-SEM-EDS) analysis has been carried out⁶²⁷ using samples of halite containing homogeneous 1–100 µm diameter brine inclusions. Cryogenic-SEM-EDS was chosen because it is one of the few well-established FI techniques which can provide absolute concentrations for the major solutes. Overall, the analytical precision for cryo-SEM-EDS is 2–3 times better than LA-ICP-MS, but the two techniques are complementary in the elements they can determine.

Various attempts have been made over the years to determine Au and the Pt group elements (PGE) by ICP-MS after ablating NiS buttons. Workers in Brazil have extended their earlier studies using buttons, prepared by doping quartz with liquid standard solutions, as calibration standards.⁶²⁸ Analytical precision was generally better than 10% RSD and detection limits for Au and all the PGE are given in Table 4. The distribution of PGE in Fe meteorites has been determined directly using laser ablation combined with the extra sensitivity of an ICP double focusing sector mass spectrometer.⁶²⁹

Table 4 Summary of the analyses of geological materials

Element	Matrix	Technique;atomization;presentation*	Sample treatment/comments	Ref.
*Hy indicates hydride and S, L, G, and Sl signify solid, liquid, gaseous or slurry sample introduction, respectively. Other abbreviations are listed elsewhere.
Ag	Geological material	AA;F;L	Digested with HCl and HNO₃, passed through a column of diphenylurea cellulose and Ag eluted with 5% thiourea	648
Ag	Geological material	AA;F;L	Treated with HF followed by aqua regia. Analytes complexed with ammonium O,O-diethyldithiophosphate. Triton X-114 is added and the phases separated at the cloud point	651
Ag	Geological RMs	AA;F;L	On-line coprecipitation preconcentration with copper diethyldithiocarbamate in a FI system	667
Ag	Geological material	AA;F;L	Dissolved in HCl followed by aqua regia, diluted and injected into FI system containing a triphenylphosphine-loaded glass bead column. Eluted with 4% thiourea	668
Al	Sediment	AE;arc;S	Treated with HNO₃ and La₂O₃ to form slurry and introduced via monosegmented flow system	755
As	Sediment	AA;Hy;L	As species extracted from iron oxide rich samples with 0.4 M hydroxyammonium chloride for 8 h at 95°C and separated by LC	756
As	Coal	—;ICP;G	Introduced as AsBr₃	757
As	Sediment	MS;ICP;L	Effects of handling, preservation and storage conditions on speciation investigated	758
As	Marine sediment	AA;ETV;Hy	Hydride collected in situ in a graphite tube using a high voltage electrostatic field	208
As	Geological material	AF;—;Hy	Digested with aqua regia	751
As	Rock and sediment	AA;ETA;L	Digested with HNO₃, HClO₄ and HF (5∶5∶3), evaporated to dryness and dissolved in HCl (1 + 10). Extracted with benzene, stirred with IBMK and cobalt(III) oxide powder and filtered. Filtrate slurried with H₂O₂ and injected into W atomizer	669
As	Geological material	MS;ICP;L	Ground to 50 µm powder. Microwave-assisted digestion with mixture of HNO₃, HF and saturated H₃BO₃	759
Au	Geogas	AF;ETA;L	Trapped on polyurethane foam, ashed and dissolved in aqua regia. Determined using time-gated laser excited AF	752
Au	Geological material	AA;F;L	See Ag, ref. 651	651
Au	Soil and regolith	MS;ICP;L	Study of re-adsorption of iodide-extractable Au	448
Au	Copper concentrates	AE;ICP;L	10–20 g calcined at 700°C, pulverized and boiled with 100 ml H₂O and 25 ml H₂SO₄ (sp. gr. 1.84). Insoluble residue dissolved in 20 ml aqua regia	760
Au	Ore	AF;—;L	Calcined at 570°C and digested with aqua regia and HCl. Dissolved residue passed through XAD-8 column, washed with 1 M HCl and Au eluted in the opposite direction with 95% ethanol	761
Au	Pyrite	MS;—;S	Determined by SIMS using the infinite velocity method	762
Au	Rocks	AA;ETV;L	Au preconcentrated electrolytically using Mg–W cell	243
Au	Geological material	AA;F;L	Heated to 600°C, dissolved in either aqua regia or mixed mineral acids and Au either extracted with MIBK or precipitated with Te, depending on sulfide content	763
Au	Geological material	MS;—;—	Determined by TOF-RIMS	764
Au	Rocks	AE;ICP;L	Solid–liquid extraction using microcrystalline naphthalene	649
Au	Minerals	AE;—;L	Calcined at 650°C, decomposed with aqua regia and the residue boiled with NaF. Analytes extracted with activated carbon powder in acetone	650
B	Geological material	AE;ICP;L	0.1 g fused with 0.5 g Na₂CO₃ and dissolved in 6 M HCl	765
B	Lake sediment	MS;—;—	¹⁰B determined by accelerator mass spectrometry	766
B	Geological RMs	AE;ICP;L	Sequential extraction	767
Be	Geological material	AA;ETA;S	Ground to <75 µm for slurry sampling	768
Bi	Geological material	AA;ETV;L	Effect of tartaric acid and five Ni-containing modifers investigated	788
Bi	Sediment	AA;ETA;S	Ultrasonic slurry sampling	770
Bi	Geological material	AF;—;Hy	Digested with aqua regia	771
Bi	Rock and sediment	AA;ETA;S	Digested with HNO₃ + HF + HClO₄ (5 + 3 + 5), diluted with HCl (1∶1) and filtered. pH adjusted to pH 3 with ammonia–H₂O and cobalt(III) oxide powder added. Sonicated for 15 min and the solid collected on a nitrocellulose membrane filter. Filter washed with H₂O and 10 µl of the suspension injected into W atomizer	670
Bi	Geological material	AA;ETV;L	Effect of five Ni-containing modifers investigated	772
Bi	Geological material	AF;—;Hy	See As,^ref. 751	751
Br	Geological RMs	MS;ICP;L	Pyrohydrolysis in heated quartz tube under wet oxygen flow	688
C	Geological material	MS;—;—	¹⁴C age determined by accelerator mass spectrometry	773
Cd	River sediment	AA;ETV;L	Tungsten coil atomizer used in inexpensive multielement AA spectrometer	774
Cd	Sediment	MS;ICP;L	Microwave assisted digestion of 0.15 g with 3 ml HNO₃ and 1 ml HF in sealed PTFE vessel. Quantification by isotope dilution using ¹¹¹Cd spike	227
Cd	Geological RMs	MS;ICP;L	Digestion with HF and HNO₃followed by ion exchange separation	775
Cd	Sediment	MS;ICP;L	Selective leaching using BCR protocol and quantitation using isotope dilution	776
Cd	Marine sediment	AA;ETA;S	0.1 g powder slurried with glycerin and water. 10% NH₄H₂PO₄ used as matrix modifier	777
Cd	Marine sediment	MS;ICP;L	Microwave-assisted digestion of 0.15 g with 1 ml HF plus 3 ml HNO₃. Comparison of ID using double focusing and quadrupole MS	266
Cl	Geological material	MS;—;G	Stable Cl isotope content determined after digestion with HF followed by ion exchange chromatography	778
Cl	Geological RMs	MS;ICP;L	See Br, ref. 688	688
Co	High silica sediment	AA;ETA;S	5–100 mg of 74–97 µm particles mixed with 0.5 ml of 60% PTFE slurry, 0.4 ml HNO₃ (1 + 1) and diluted to 5 ml with 0.1% aqueous solution of plant glue	642
Cr	Marine sediment	MS;ICP;L	Closed vessel microwave-assisted digestion with a mixture of HNO₃ and HF, followed by open beaker reflux with HClO₄ and H₂SO₄	647
Cr	Soil	AA;F;L AA;ETV;L	Microwave-assisted digestion with HNO₃	522
Cr	Iron ore	AA;F;L	0.2–1 g dissolved in 10 ml 6 M HCl	779
Cu	Sulfide minerals	AA;ETA;L	Dissolved in HNO₃ and HCl with H₂O₂, complexed with sodium diethyldithiocarbamate and extracted with MIBK, CHCl₃ or CCl₄	780
Cu	Rock and sediment	AA;ETA;L	Analyte preconcentrated with activated carbon impregnated with 1,2-cyclohexanediondioxime. W furnace	140
Cu	River sediment	AA;ETV;L	See Cd,^ref. 774	774
Cu	Marine sediment	XRF;—;S	Evaluation of field portable instrument having ⁵⁵Fe, ¹⁰⁹Cd and ²⁴¹Am sources	9
Cu	Geological material	MS;ICP;L	Digested and purified by macroporous anion exchange. Isotopic composition determined precisely	781
Cu	Sediment	MS;ICP;L	See Cd, ^ref. 776	776
Cu	Environmental material	AA;ETA;L	Robotic weighing and digestion system followed by preconcentration as pyrrolidine dithiocarbamate chelate on PTFE knotted reactor	275
Cu	Soil	AA;F;L	Paired samples used to estimate sampling bias	412
Cu	Geological material	MS;ICP;L	Precise determination of isotopic composition using multiple collector magnetic sector MS	782
Dy	Rare earth concentrate	AE;F;L	Heated to 850°C and dissolved in 50% HCl. Determined by dual wavelength monoxide emission	675
F	Geological material	MS;—;S	Determined using a sensitive high resolution ion microprobe (SHRIMP)	722
Fe	Geothermal fluid	AA;ETA;L	Automated on-line microwave precipitation–dissolution system	783
Fe	Calcite	XRF;—;S	Theoretical detection limits of TXRF calculated	784
Fe	Ore	AA;F;L	0.2 g heated for 2 min with 2–3 drops HF and 5 ml 1 + 1 HCl, then mixed with 5 ml 1 + 1 HNO₃ and evaporated. Residue dissolved sequentially with 6 M HCl and 1 + 1 H₂SO₄ and heated. Residue dissolved in 20 ml H₂O and filtered. Filtrate mixed with 1 ml 1% hydroxyammonium chloride, 5 ml acetic acid–acetate buffer of pH 5 and 1.5 ml 0.15% 1,10-phenanthroline	785
Ge	Rock and sediment	AE;ICP, Hy;—	Dissolved in HF–HNO₃–H₃PO₄ mixture and reacted with 1% NaBH₄	664
Ge	Geological RMs	AF;Hy;—	Gas-phase interference from As eliminated by passing the GeH₄ stream through a HgCl₂ column	665
Ge	Rock and sediment	AE;ICP;G	Microwave-assisted digestion with HNO₃–HF–HCl. GeCl₄ generated by treatment with 5 M HCl	666
Ge	Coal	—;ICP;G	Introduced as GeCl₄	757
Hf	Basalt	MS;—;L	High precision isotope ratio measurements using TIMS	715
Hf	Geological material	MS;ICP;L	Dissolution with HF followed by nebulization of HF solution via FI	786
Hf	Rocks	MS;ICP;L	Zr∶Hf and Hf isotope ratios determined after two-stage ion exchange combined with ID and detection by multiple collector magnetic sector MS	704
Hg	Sediment	AA;ETA;G	Methylmercury determined after solid phase extraction and GC	658
Hg	Sediment	MS;ICP;G	Hg species determined after microwave digestion and multicapillary GC	657
Hg	Coal	AA;CV;G	0.1 g digested with 3 ml HNO₃ at 140°C for 24 h under pressure. Two-stage amalgamation	661
Hg	Coal	AA;CV;G	Combustion in O₂, Hg trapped on Au	662
Hg	Coal and sediment	XRF;—;S	Ground in ethanol and deposited on foil. Comparison of EDXRF with CV-AAS measurements	527
Hg	Coal	MS;ICP;GAA;CV;G	Microwave-assisted digestion with aqua regia	663
Hg	Sludge	MS;ICP;S	Dried, sieved and homogenized. Introduced by ETV at 700°C	711
Hg	Sediment	AA;CV;G	Freeze-dried, ground and microwave-assisted digestion with HNO₃	787
Hg	Sediment	AA;—;—	Review with 87 references	295
Hg	Geological material	AF;—;Hy	See As, ref. 751	⁷⁵¹
Hg	Environmental materials	—;—;—	Review of Hg speciation with 162 references	194
In	Geological material	AA;ETV;L	See Bi, ref. 788	788
In	Geological RMs	MS;ICP;L	See Cd, ref. 775	775
In	Geological material	AF;ETA;L	0.25 g dissolved in 15 ml mixture of H₂SO₄–HNO₃–HF (1∶2∶2). Determined by LEAFS	754
In	Geological material	AA;ETV;L	See Bi, ref. 772	772
Li	Geological material	MS;ICP;L	Li isotopic composition determined by multi-collector MS	703
Mg	Titanium ore	AA;F;L	0.1 g heated with 5 ml HF and 2 ml H₂SO₄ in a Pt crucible	789
Mo	Meteorite	MS;—;—	Isotopic analysis of presolar grains by secondary neutral mass spectrometry	725
N	Geological material	MS;—;G	Isotopic measurements at the sub-nanomole level	304
Nb	Ore	XRF;—;S	2 g mixed with 0.5 g microcrystalline cellulose and pressed into disc	790
Nb	Geological material	MS;ICP;L	See Hf, ref. 786	786
Ni	High silica sediment	AA;ETA;S	See Co, ref. 642	642
Np	Marine sediment	MS;ICP;L	LC plus liquid–liquid extraction followed by detection using high resolution MS	709
O	Olivine	MS;—;S	Isotope ratios determined by SIMS	791
Os	Geological material	MS;—;—	Investigation of ionization processes in negative ion TIMS	718
Os	Rocks	MS;ICP;L	Direct injection nebulization used to reduce memory problems	792
Os	Molybdenite	MS;—;—	Alkali fusion followed by negative ion TIMS	720
Os	Ore concentrate	MS;ICP;L	Fused with NaOH and Na₂O₂ at 650°C, extracted with H₂O and treated with H₂SO₄ and KMnO₄. The mixture was distilled at 110°C and Au internal standard added to the OsO₄ condensate	793
Pa	Manganese crust	MS;—;L	High precision determination using TIMS. LOD 10 fg	794
Pa	Manganese crust	MS;—;L	Determined by TIMS using a double filament without carbon coating	716
Pa	Silicate rocks	MS;—;L	Measured as double oxide by TIMS using a tungsten filament	717
Pb	Geological material	AA;ETV;L	See Bi, ref. 788	788
Pb	Sand	AE;LA;S	Temporally gated and spatially resolved LIBS spectra observed	795
Pb	Sediment	AA;F;S	Slurry dried on filter paper, cut and placed in pyrolytically coated graphite in air–C₂H₂ flame	672
Pb	Rock and sediment	AA;ETA;L	See Cu, ref. 140	140
Pb	Coral	AE;DCP;Hy	Dissolved in dilute HCl and reacted in a hydride generator with 1.5% potassium ferricyanide solution and 1.5% NaBH₄ in 0.2% NaOH solution	796
Pb	River sediment	AA;ETV;L	See Cd, ref. 774	774
Pb	Sulfides	MS;—;L	Assessment of precision and accuracy of isotope ratio measurements by TIMS	797
Pb	Marine sediment	XRF;—;S	See Cu, ref. 9	9
Pb	Rock and sediment	AA;ETA;S	See Bi, ref. 670	670
Pb	Geochemical RMs	AF;—;Hy	0.1 g heated with 5 ml HCl, 2 ml HNO₃ and 1 ml HClO₄, diluted and centrifuged. Supernatant reacted with mixture of 0.02% phenanthroline, 0.2% KSCN and 0.4% oxalic acid in 1.5% HCl. 2 ml portions reacted in a hydride generator with 0.8% KBH₄ and 2% potassium ferricyanide	798
Pb	Zircon	MS;ICP;S	²⁰⁷Pb∶²⁰⁶Pb ratios determined by LA-ICP-MS using Nd:YAG laser at 1064 nm	632
Pb	Geological material	MS;ICP;L	Accuracy and long-term reproducibility of Pb isotope ratios obtained by multiple collector MS compared with those obtained by TIMS	705
Pb	Coal	AA;ETA;S	5–15 mg powder weighed into autosampler cups and slurried with HNO₃, Triton X-100 and 10% ethanol	799
Pb	Sediment	MS;ICP;L	See Cd, ref. 776	776
Pb	Soil	AA;F;L	See Cu, ref. 412	412
Pb	Geological material	AA;ETV;L	See Bi, ref. 772	772
Pb	Zircon	MS;ICP;S	Pb∶Pb and Pb∶U ages determined by LA-ICP-MS	635
Pb	Zircon	MS;ICP;S	LA-ICP-MS used to determine age	633
Pd	Marine sediment	AF;ETA;L	Adsorbed onto xanthate cotton, dissolved and determined using laser-excited AF	753
Pd	Copper ore	AA;ETA;L	Extraction with dimethylglyoxime into chloroform. Interferences from Fe and Pb investigated	800
Pd	Geological material	MS;—;—	See Au, ref. 764	764
Pd	Minerals	AE;—;L	See Au, ref. 650	650
Pt	Geological material	MS;—;—	See Au, ref. 764	764
Pt	Minerals	AE;—;L	See Au, ref. 650	650
Pu	Soil and sediment	MS;—;—	Determined by TOF-RIMS	484
Pu	Marine sediment	MS;ICP;L	See Np, ref. 709	709
Pu	Soil and marine sediment	MS;ICP;L	Large amounts of Fe removed before analysis by extraction with isopropyl ether	801
Pu	Sediment	MS;ICP;L	Mixed with ²⁴²Pu tracer, dry ashed, multi-stage digestion with aqua regia, HCl and HNO₃, followed by separation on AG 1-X4 anion exchange resin	543
Ra	Geological material	MS;ICP;S	Slurried with 5% v/v HNO₃ and introduced by ETV (LOD 186 fg ml⁻¹ on a 20 µl aliquot of slurry containing 21 mg ml⁻¹ sample)	712
Re	Molybdenite	MS;—;—	See Os, ref. 720	720
Rh	Geological material	MS;—;—	See Au, ref. 764	764
Rh	Minerals	AE;—;L	See Au, ref. 650	650
S	Coal	XRF;—;S	Standard addition proved unsuccessful for XRF in a comparison with 10 national standard wet chemical methods	802
S	Geological material	MS;—;G	Off-line methods of SO₂ production described	803
S	Coal	AA;F;L	Indirect determination at 357.9 nm following treatment with BaCrO₄	804
S	Sulfides	MS;—;G	New faster technique for isotopic measurement proposed	805
Sb	Sediment	AA;ETA;S	Automated ultrasonic slurry sampler used with 2–150 mg powder suspended in 1 ml 0.5% v/v HNO₃	641
Sb	Marine sediment	AA;ETV;Hy	See As, ref. 208	208
Sb	Environmental materials	AA;ETA;— AA;Hy;—	Review with 113 references	329
Sb	Geological material	AF;—;Hy	See As, ref. 751	751
Sc	Geological material	AE;ICP;L	Treated with HF–HCl–H₂SO₄ and extracted with di(2-ethylhexyl)phosphoric acid in hexane or benzene	806
Sc	Red mud	AE;ICP;L	0.25 g fused with 1 g LiBO₂ at 1100°C, dissolved in 1 + 1 HCl and diluted to 50 ml with 1.5 M HCl. 25 ml applied to Dowex 50W-X8 resin column, eluted with HCl and extracted with di(2-ethylhexyl)phosphoric acid	807
Se	Sediment	MS;ICP;L	Pressurized digestion with HF–HNO₃ at 150°C. Introduction by ETV after addition of citric acid (LOD 10 pg)	713
Se	Marine sediment	AA;ETV;Hy	See As, ref. 208	208
Sn	Marine sediment	MS;ICP;L	Organotin compounds separated by reversed phase LC	808
Sn	Marine sediment	MS;ICP;Hy	Combination of anion exchange, hydride generation and high resolution ICP-MS	335
Sn	Candidate sediment RM	—;—;—	Evaluation of methods for the determination of butyl- and phenyltin compounds	660
Sn	Rocks	AA;ETA;S	Digested with HNO₃, HClO₄ and HF (3 + 1 + 3). Tin iodide extracted into benzene and collected on cobalt(III) oxide powder, slurried and injected into W atomizer	671
Sn	Marine sediment	MS;APCI;L	Butyl- and phenyltin compounds separated by reversed phase LC	809
Sn	Sediment	MS;ICP;G	Species-specific spike used with GC separation of organometallic compounds	810
Sn	Sediment	MS;ICP;L	Fusion with LiBO₂ rather than acid digestion necessary to obtain total Sn values	811
Ta	Geological material	MS;ICP;L	See Hf, ref. 786	786
Tc	Bentonite	MS;ICP;L	Leached with 10 ml of mixture of 2 M H₂SO₄ and 0.01 M Na₂BrO₃, centrifuged and extracted with 0.05 M Alamine-336 in CHCl₃	687
Te	Geological RMs	MS;ICP;L	See Cd, ref. 775	775
Th	Ore	XRF;—;S	See Nb, ref. 790	790
Th	Opal	MS;ICP;S	²³⁸U∶²³⁴U∶²³⁰Th ratios determined using laser ablation and multiple collector ICP-MS	637
Th	Geological material	MS;ICP;L	Comparative review of TIMS, SIMS, ion microprobe and ICP-MS for the determination of Th isotope ratios	708
Th	Soil and marine sediment	MS;ICP;L	See Pu, ref. 801	801
Tl	Rocks and sediment	AA;ETA;L	Digested with HF, HNO₃, HClO₄ and H₂SO₄	812
Tl	Sediment	MS;ICP;L	Digested with HF–HNO₃–HClO₄	813
Tl	Geological material	MS;ICP;L	Tl isotopic ratios determined precisely using added Pb to correct for mass discrimination	706
Tl	Sulfides	XRF;—;S	0.5 g fused with 0.5 g KNO₃ and 10 g Li₂B₄O₇ at 1100°C	732
U	Sediment	MS;ICP;L	Sequential extraction and digestion with aqua regia	656
U	Carbonates	MS;ICP;L	²³⁴U∶²³⁸U ratios determined after dissolution with HNO₃ followed by chromatographic extraction	342
U	Zircon	MS;ICP;S	See Pb, ref. 633	633
U	Zircon	MS;ICP;S	See Pb, ref. 635	635
U	Opal	MS;ICP;S	See Th, ref. 637	637
U	Soil and marine sediment	MS;ICP;L	See Pu, ref. 801	801
W	Scheelite	XRF;—;L	<200 mesh powdered ore leached with 4% oxalic acid at 100°C	814
W	Tungsten ore	XRF;—;S	80–100 mg powder fused with 3.4 g Na₂B₄O₇, 2.8 g Li₂B₄O₇ and 250 mg NaNO₃ at 1050–1100°C	815
Zn	Geological material	AA;—;S	Matrix effects in solid sampling investigated	816
Zn	Marine sediment	XRF;—;S	See Cu, ref. 9	9
Zn	Geological material	MS;ICP;L	See Cu, ref. 781	781
Zn	Sediment	MS;ICP;L	See Cd, ref. 776	776
Zn	Soil	AA;F;L	See Cu, ref. 412	412
Zn	Geological material	MS;ICP;L	Precise determination of isotopic composition using multiple collector magnetic sector MS	782
Zr	Zircon	MS;ICP;S	Isotopic ratios determined using frequency quadrupled Nd∶YAG laser and multiple collector ICP-MS	616
Zr	Meteorite	MS;—;—	See Mo, ref. 725	725
Zr	Terrestrial and meteoritic zircon	MS;ICP;S	Laser ablation	817
Zr	Geological material	MS;ICP;L	See Hf, ref. 786	786
Zr	Rocks	MS;ICP;L	See Hf, ref. 704	704
Various	Rocks	MS;ICP;L	PGE determined using nickel sulfide fire assay followed by Te coprecipitation	690
Various	Martian soil and rock	XRF;—;—	In situ analysis using a mobile alpha proton X-ray spectrometer	507
Various	Geological material	XRF;—;S	Review of sample preparation techniques with 92 refs.	730
Various	Geological material	MS;ICP;L	Discussion of application of selective extraction procedures in exploration	653
Various	Geological material	AE;ICP;L MS;ICP;L	Application of extractable trace metals to geochemical exploration	654
Various	Geological material	MS;ICP;L	Comparison of enzyme leaching and selective extraction in mineral exploration	655
Various	Reference materials	MS;ICP;S	Au, Ir, Os, Pd, Pt, Rh, Ru and determined on NiS buttons using ablation with a frequency quadrupled Nd∶YAG laser (LOD 1.7, 0.7, 1.3, 3.3, 8.3, 1 and 5 ng g⁻¹, respectively)	628
Various	Silicate rocks	—;—;—	Review of evolution of geoanalytical techniques, with 41 refs.	610
Various	Diamond	MS;—;G	Light elements determined after heating in steps from 200 to 1500°C under O₂	818
Various	Geological material	MS;ICP;L	Au and the PGE determined following fusion of 1–20 g samples with KOH, NaKCO₃ and Na₂O₂, dissolution with HCl, reduction with SnCl₂ and precipitation with Se and Te carriers	695
Various	Volcanic tuff	—;—;—	Report of proficiency testing scheme for geoanalytical laboratories	614
Various	Rocks	XRF;—;S	Finely ground and pressed into 2.5 cm diameter pellets with 100–200 mg starch binder	819
Various	Rocks and minerals	—;—;—	Review of techniques, in Chinese with 481 refs.	609
Various	Geological material	MS;—;—	Review of trace analysis by MS	352
Various	Gold	MS;ICP;S	Laser ablation used to fingerprint gold origins through trace element content	630
Various	Garnet	MS;—;S	REE determined on 60 µm spot by SIMS	710
Various	Geological material	MS;ICP;L	Review of multiple collector MS applications	354
Various	Gold	MS;ICP;S	Trace element signatures of placer gold obtained by IR laser ablation linked to parent lodes	631
Various	Geological material	—;—;S	Review with 144 refs. of ion and photon beam techniques	748
Various	Geological material	—;—;—	Proficiency testing scheme for geological laboratories reviewed	820
Various	Geological material	AA;ETA;L	Au, Pd, Pt, Rh and Ru determined after fluorination with liquid BrF₃ or molten KBrF₄ followed by solvent extraction	821
Various	Coal	AE;ICP;S	Pulsed emission signals observed to characterize particles	822
Various	Coal	AE;GD;S	Pelletized without binder	823
Various	NIST 612 glass	MS;ICP;S	Fractionation of 55 elements studied during ablation with frequency quadrupled Nd∶YAG laser	824
Various	Soil and sediment	—;ICP;S	Halogenated with Freon-12 in high power gas phase solid sample digester	825
Various	Granite	AE;—;S	Combined LIBS and Raman imaging	826
Various	Carbonate rocks	AE;ICP;L	Al, Ba, Fe, K, Mg, Na, P and Sr determined after selective leaching	827
Various	Ziron	MS;ICP;S	Minor and 30 trace elements determined by LA-ICP-MS using 193 nm ArF laser and SIMS	634
Various	Uranium ore	AE;ICP;L	REE determined after dissolution with HCl∶HNO₃ (2∶1) and separation from U by co-precipitation with iron	828
Various	Coal and sediment	XRF;—;S MS;ICP;L AA;ETA;L	Comparison of techniques	360
Various	Sediment	AE;ICP;L XRF;—;S	Residue remaining after acid leaching pressed into pellet	829
Various	Rocks	MS;ICP;L	Fusion with LiBO₂ compared with various acid decomposition mixtures in the determination of the REE	698
Various	Cometary material	MS;—;—	Stable isotope ratios of light elements to be determined in space	723
Various	Geological material	MS;ICP;L	Pt-group elements determined in K–T boundary samples after eight-stage selective extraction scheme and preconcentration by NiS fire assay	830
Various	Rocks	MS;ICP;S	0.8 g fused with 4 g Li₂B₄O₇ spiked with Mn as internal standard and ablated with Nd∶YAG laser	617
Various	Sediment	MS;ICP;L	Microwave assisted digestion with HNO₃–HCl–HF. PGE, Th and U determined by double focusing sector field MS	363
Various	Soil and sediment	MS;ICP;S	Treated with 2.5 ml g⁻¹ Ag solution (100 ppm)^,dried at 110°C, homogenized and pressed at 35 MPa into pellets. Ablated with frequency quadrupled Nd∶YAG laser. ¹⁰⁷Ag used as internal standard	478
Various	Coal and sediment	AE;ICP;L AA;ETA;L	Evaluation of a high-pressure, high-temperature microwave digestion system	431
Various	Rocks	XRF;—;S	Study of effects of surface geometry on in situ analysis	831
Various	Environmental material	—;—;—	Overview of flow-based sample pretreatment and introduction procedures	368
Various	Geological material	MS;ICP;L	0.1 g sintered with Na₂O₂, diluted to 500 ml with 0.03 M HNO₃ and the REE preconcentrated by precipitation in a PTFE knotted reactor coupled to an on-line FI system	652
Various	Geological materials	—;—;—	Review of environmental analysis, with 1035 refs.	775
Various	Rock RMs	MS;ICP;L	PGE determined after preconcentration from 50 g samples by NiS fire assay	691
Various	Rocks	MS;ICP;L	Au and the PGE determined after preconcentration by NiS fire assay	693
Various	Black shale	MS;ICP;L	PGE determined after preconcentration by nickel sulfide fire assay	692
Various	Marine hydrothermal vent particulates	MS;ICP;L	REE determined using a desolvating microconcentric nebulizer and magnetic sector MS (LOD 1–21 fg)	700
Various	Volcanic fluids	MS;ICP;L	Gases passed through 5 M NaOH. Precipitates digested with HNO₃	832
Various	Rocks	MS;ICP;S	0.8 g finely ground sample fused with 5.6 g Li₂B₄O₇ at 1000°C. Ablated with Nd∶YAG laser and REEs determined using double-focusing MS	621
Various	Geological material	MS;—;S	Performance characteristics of the sensitive high resolution ion microprobe (SHRIMP) described	833
Various	Geological material	XRF;—;S	Fifty year review of quantitative analysis by electron microprobe	744
Various	Petrified wood	XRF;—;S	Microbeam techniques compared	834
Various	Geological material	XRF;—;S	Automated peak-overlap and modelled background corrections used in the determination of the REE by EPMA	747
Various	Coal	MS;ICP;L	Comparison of microwave-assisted digestion with HNO₃ and open vessel digestion with a mixture of H₂SO₄, HF, HClO₄ and HNO₃	646
Various	Rocks	XRF;—;S	5 g ground to 76 µm and pressed into a 35 mm diameter pellet	835
Various	Tungsten ore	AE;ICP;L	0.5–1 g decomposed with 10 ml ammonia–water and 5 ml 20% ammonium citrate on gentle heating	836
Various	Geological material	MS;ICP;L	REE determined following LC separation on ion exchange resin	837
Various	Mollusc shells	MS;ICP;S	Ba, Cd, Mn, Pb and Sr determined in aragonite by LA to deduce climate signals	838
Various	Geological material	MS;—;—	Cosmogenic radionuclides determined by accelerator mass spectrometry	726
Various	Sediment	AA;F;S	Cu, Cr, Pb, Mn, Ni and Zn determined using slurry sampling	839
Various	Sediment	AE;ICP;L	Al, Ca, Cd, Cu, Fe, Mn, Ni, P, Pb, S and Zn determined after leaching with 0.1 M HCl	840
Various	Rocks	MS;ICP;L	Mixed REE spike added. Dissolution with HF–HNO₃ followed by separation of REE on Truspec resin	841
Various	Rocks	MS;ICP;L	Sequential pressurized microwave assisted digestion of powdered sample with mineral acids followed by separation of Au, PGE and Re on noble metal specific chelating resin. Yields monitored by isotope dilution	842
Various	Rocks	MS;ICP;L	Dissolution in Pyrex Carius tubes. Quantification of the PGE by isotope dilution	696
Various	Geological material	MS;—;S	Review with 154 references of advances in age determination via measurements of isotopic ratios	843
Various	Geological RMs	AE;CCP;S	Dried at 105°C, sintered at 1050°C and pressed into cylindrical pellets. Cd, Cr, Cu, Na, Pb and Si determined	844
Various	SiC powder	AE; d.c. arc;S	Evaluation of operating parameters of LECO-750 spectrometer	679
Various	Synthetic geological powders	AE;ICP;S	Ablation behavior of pressed powders studied at 1064 and 266 nm using Nd∶YAG laser	622
Various	Soil and sediment	AE;ICP;— MS;ICP;—	Comparison of microwave-assisted acid leaching techniques	644
Various	Coal	XRF;—;S	Standard addition calibration	845
Various	Geological material	XRF;—;S	Discussion of lithium borate flux compositions	731
Various	Marine sediment	XRF;—;S	Evaluation of shipboard instrument for core logging	741
Various	Coal	XRF;—;S	On line analysis of pulverized coal in a feed line	742
Various	Geological material	AF;ETA;L	Time-gated laser-induced fluorescence	380
Various	Geological material	MS;ICP;L	Analytical characteristics of high efficiency ion transmission interface investigated	684
Various	Geological material	MS;ICP;S	Fractionation effects during ablation with a frequency quadrupled Nd∶YAG laser studied	623
Various	Geological material	XRF;—;S	Comparison of neural network and theoretical correction models	846
Various	Geological material	MS;ICP;S	Review (118 refs.) of laser ablation, arc and spark sample introduction into ICP-MS	616
Various	Fluid inclusions	AE;ICP;L	Ca, K, Li and Na determined using frequency quadrupled Nd∶YAG laser	626
Various	Sulfide ore	XRF;—;S	As, Bi, Cu, Fe, Mo, Pb, S and Zn determined after fusion with Li₂B₄O₇, LiBO₂ and SiO₂	847
Various	Sediment	AE; d.c. arc;S	Diluted 1∶1 with graphite powder or silica	848
Various	Sediment	MS;ICP;G	Treated with concentrated acetic acid, solid phase micro-extraction and capillary CG	383
Various	Ore	AA;F;L	Review in Russian of FI-AAS with 148 refs.	105
Various	Hydroxyapatite	AA;F;L	2 g dissolved in 20 ml HCl (1∶1 v/v). Cd, Cu, Pb and Zn determined by AAS, As by Hy-AAS and Hg by CV	849
Various	Environmental material	AA;F;L	Review in Czech of FI-AAS with 103 refs.	384
Various	Silicates and limestone	AE;ICP;S	Samples fused with lithium tetraborate (10∶6) and ablated with frequency tripled Nd∶YAG laser. Sc₂O₃ and Y₂O₃ added as internal standards to achieve single calibration graph for major elements	618
Various	Coal	AA;ETA;L AA;F;L	Trace metals determined after digestion with HNO₃ or HNO₃ and HF under pressure	645
Various	Ilmenite ore	XRF;—;S	Matrix matched standards prepared	850
Various	Bauxite	AE;DCP;S	15 elements determined in slurry introduced via cross-flow nebulizer	851
Various	Rocks	AE;ICP;L	Digested with HNO₃ and HClO₄. Residue fused with Na₂CO₃ and boric acid. REE and Y determined after solvent extraction with a mixture of 2-ethylhexyl dihydrogenphosphate and bis(2-ethylhexyl) hydrogenphosphate in kerosene	852
Various	Coal	AE;ICP;L	Study of temperature effects on digestion with HNO₃ in high pressure asher	434
Various	Geological material	MS;ICP;L AE;ICP;L	Discussion of selective leaching	853
Various	Chromites	MS;ICP;L	Dissolution at 320°C and 125 bars in quartz tubes in Paar high pressure asher. Os extracted with CCl₄. PGE separated on anion exchange resin	697
Various	Zeolites	MS;ICP;S	Fused at 1050°C with mixture of 9 + 1 Li₂B₄O₇ + LiBO₂ and ablated with frequency quadrupled Nd∶YAG laser	619
Various	Granite, basalt and zeolite	MS;ICP;S	Fused at 1050°C with mixture of 9 + 1 Li₂B₄O₇ + LiBO₂ and ablated with frequency quadrupled Nd∶YAG laser	620
Various	Malchite ore	XRF;—;S	Ba, Cu, Fe, I, In, Sb, Sn, Sr and Zr determined on <300 mesh powder by EDXRF using an ²⁴¹Am source	738
Various	Geological material	MS;ICP;L	Analytical characteristics of high efficiency ion transmission interface investigated	685
Various	Silicate rocks	AE;ICP;L	0.5 g fused with 2.5 g LiBO₂ in Pt–Au crucible, cooled and dissolved in 150 ml 5% HNO₃	674
Various	Single mineral grains	XRF;—;S	Effect of grain size and orientation on synchrotron XRF measurements investigated	854
Various	Granite	—;—;—	Report of proficiency testing scheme for geoanalytical laboratories	615
Various	Geological RMs	XRF;—;S	Fused with mixture of 90% LiB₄O₇ and 10% LiF. Compared with measurement by INAA	749
Various	Geological RMs	MS;ICP;L	Fused with lithium metaborate. Comparison with INAA for determination of REE	750
Various	Rocks	MS;ICP;L	100 mg powdered sample decomposed with either 2 ml HF plus 0.5 ml HNO₃ or 3 ml HF plus 3 ml HClO₄ in sealed vessels	702
Various	Lake sediments	AE;ICP;L MS;ICP;L	Fused with LiBO₂ and dissolved in 1 M HNO₃	855
Various	Iron meteorites	MS;ICP;S	Major and Pt group elements determined by UV LA-ICP-MS	629
Various	Environmental materials	—;—;—	Review of environmental analysis	92
Various	Rocks	MS;ICP;L	Au, Ir, Pd, Pt, Rh and Ru determined after NiS fire assay and Te coprecipitation	694
Various	Geological material	MS;ICP;L	Au and the PGE determined after cation exchange and ultrasonic nebulization	856
Various	Geological material	MS;—;L	Applications of negative ion TIMS	719
Various	Black smokers	MS;ICP;S	Distributions of Ag, Au, Ba, In, Pb, Te, U and V in chimney walls determined using UV laser ablation	857
Various	Fluid inclusions	MS;ICP;L	Single fluid inclusions analysed for B, Br, Ca, Cl, K, Li, Mg and Sr by LA-ICP-MS. Results normalized to Cl determined by cryo-SEM-EDS	627
Various	Environmental material	MS;ICP;— AE;ICP;—	Review with 101 refs. of environmental applications of plasma spectrometry	93
Various	Fluid inclusions	MS;ICP;L	As, B, Cu, Li and Sb determined by laser ablation	625
Various	Geological material	MS;—;S	Review of high-resolution SIMS	858
Various	Geological material	MS;ICP;L	Analytical characteristics of high efficiency ion transmission interface investigated	686
Various	Geological material	MS;ICP;Hy	Ethanol added to the tetrahydroborate reductant	269
Various	Geological material	XRF;—;S	Crystal placed on millepore filter	734

Laser ablation ICP-MS is a powerful tool for trace element fingerprinting. One of its leading exponents has recently published a review of the use of this technique to source modern and ancient Au.⁶³⁰ It can also be used as a potential aid for Au exploration by examining distinct trace element signatures in placer deposits and tracking them back to their original tributaries within a river watershed.⁶³¹

Although not an entirely new development, there has been great interest in the analysis of zircons by LA-ICP-MS during the year under review.^632,633 A single zircon crystal may contain multiple internal structures that record a succession of individual geological events. The use of SIMS and LA-ICP-MS have been compared for U–Pb geochronology and found to be competitive for routine analysis but complementary for non-routine samples.⁶³⁴ Another study reported differences of ≪1% and <3%, respectively, in the Pb∶Pb and Pb∶U ages obtained by LA-ICP-MS compared with TIMS.⁶³⁵

Although there are still relatively few multiple collector magnetic sector ICP-MS instruments around, it is clear that they have the potential to become a very versatile technique for many isotopic measurements.⁶³⁶ Preliminary in situ U–Th isotope determinations at very high spatial resolution have been reported.⁶³⁷ The absolute amount of analyte required for this technique is typically of the order 1 µg. Hirata and Yamaguchi⁶³⁸ enhanced the sensitivity of their instrument by the addition of a large capacity rotary pump to the first vacuum stage and an optimized size of shielding plate for the ICP ion source, in order to determine in situ Zr isotope ratios from 10–15 µm diameter craters. The precisions for the isotopic measurements were only a factor of 2–3 worse than those achieved by solution analysis, but the results displayed a systemic bias from those obtained by TIMS which has yet to be resolved. Laser ablation has also been used in the determination of O isotope ratios in quartz and meteorite inclusions.^639,640

4.2.1.2 Slurry nebulization. The commercial availability of an ultrasonic probe for the homogenization of slurry prior to its introduction into a graphite furnace has advanced the practical possibilities of this technique. An almost fully automated ultrasonic slurry sampling-ETAAS analytical scheme for the determination of Sb in soils and sediments has been devised.⁶⁴¹ Chemometric techniques were used to optimise the large number of variables during method development.

A novel method for the direct measurement of Co and Ni in high silica matrices (silicon dioxide) by slurry sampling ETAAS may have more general geochemical application.⁶⁴² The sample is introduced into the furnace as a PTFE slurry in nitric acid. PTFE acts as a fluorinating reagent converting the matrix and analytes into their corresponding fluorides; the highly volatile silicon fluoride can then be vaporized prior to the determination of the analytes. This seems preferable to an alternative approach of injecting slurries consisting of ground samples suspended in 50% HF to determine Co, Cu and Ni in soils and sediments.⁴⁶⁴

4.2.2 Sample dissolution. Microwave-assisted dissolution is an attractive alternative to conventional open vessel wet digestion procedures, not least because of the retention of volatile species and speed of digestion. However, for any practical digestion of silicate materials the presence of HF is essential, with the consequent implications for safety. An evaluation of a high-pressure, high-temperature microwave system⁴³¹ concluded that, although it provided a more complete destruction of organic matrices, such as coal, it would be impossible to use HF in such a system because of the unexpected vessel ruptures!

Various strategies have been employed to render coal and fly-ash into solutions suitable for analysis by ICP-MS or ETAAS,^643–645 often with the aid of microwave digestion. However, an open vessel digestion using a mixture of HF, HClO₄ and HNO₃ still proved to be very effective for all elements in ash and most in coal, with an additional microwave-assisted leach in nitric acid for volatile elements such as As and Se.⁶⁴⁶ A commercial block digestor for preparing environmental samples for trace metal analysis has also been evaluated.⁴¹⁸

Total dissolution of Cr in geological matrices is often difficult to achieve, particularly when it is present as the mineral chromite. Experimental work using various combinations of HF, HNO₃, HClO₄ and H₂SO₄, with and without microwave-assisted digestion, concluded that complete dissolution of Cr in marine sediments could only be achieved through high temperature refluxing of the materials with a mixture of H₂SO₄ and HClO₄.⁶⁴⁷ Although the dissolution procedure is cumbersome to implement, open vessel focused microwave digesters with the capability for high temperature refluxing are available to allow unattended operation and multiple sample processing.

4.2.3 Separation and preconcentration. There is continued interest in methods for the separation and preconcentration of the precious metals, including Ag using diphenylthiourea cellulose,⁶⁴⁸ Au using naphthalene⁶⁴⁹ and the platinum group elements by a method of which any alchemist would be proud.⁶⁵⁰ A novel method for preconcentrating Ag and Au, using cloud point extraction, has been proposed.⁶⁵¹ After a mixed acid digestion, O,O-diethyldithiophosphoric acid (DDTP), HCl and Triton X-114 surfactant are added to an aliquot and the mixture held at 40 [thin space (1/6-em)]

°C for 15 min. The analytes are concentrated in the surfactant-rich phase, which is then separated and analysed by AAS after the addition of a small amount of methanol to reduce the viscosity. The best enrichment factors obtained were 91 for Ag and 130 for Au.

A flow-injection, on-line, filterless precipitation–dissolution system has been developed for the determination of rare earth elements by ICP-MS.⁶⁵² A home-made knotted reactor, made from PTFE tubing, acted as the filterless collector. Rock digests, prepared using a Na₂O₂ sinter technique, were diluted with nitric acid prior to mixing with an ammonia buffer solution and on-line precipitation and collection of the REE on the walls of the knotted reactor. HNO₃ was then introduced to dissolve the precipitates and transport them to the ICP-MS instrument. A single preconcentration of the REE and their separation from alkali and alkaline earth elements with an enhancement factor of 55–75 was achieved within 5 min.

4.2.4 Sequential extractions. The use of selective extraction methods to distinguish analytes held in different phases in soils and sediments is of particular interest in exploration geochemistry to locate deeply buried mineral deposits. Phases likely to scavenge mobile elements include the humic and fulvic components of humus, amorphous Mn and Fe oxides. Such phases are targetted by selective digestions such as the enzyme leach and mobile metal ion (MMI) extraction, which are both commercially available and rely on the sensitivity of ICP-MS to quantify the trace elements. Several authoritative accounts of the advantages and limitations of this approach to exploration using these methods are worth consulting.^653–655 Problems of re-adsorption, which could occur more widely, were reported in the use of a soil extraction method for Au exploration, based on a mixture of NaHCO₃ and KI saturated with CO₂ and adjusted to pH 7.4.⁴⁴⁸

The BCR sequential extraction protocol has been successfully applied to inter-tidal sediments to discriminate between potential sources of U contamination.⁶⁵⁶ Any matrix effects observed during measurement by ICP-MS were minimized by diluting the solutions five-fold with 5% nitric acid and adding ²³⁶U as an internal standard; the solution detection limit was 0.04 µg l⁻¹.

4.2.5 Speciation studies. Continued interest in Hg speciation in environmental samples is reflected in reviews by Sánchez Uria and Sanz-Medel¹⁹⁴ and Zavadska and Zemberyova,²⁹⁵ with 162 and 87 references, respectively. An accessory has been developed to assist the separation of Hg species. It involves multicapillary GC coupled to ICP-MS without the need for a heated interface.⁶⁵⁷ This fully automated device integrates a derivatization-gas phase extraction step of MeHg⁺ and Hg²⁺ from a sample, cryofocusing of the derivatized species and their separation on a multicapillary column. Details of a laboratory-built solid phase microextraction (SPME) device for extracting methylmercury from sediments prior to determination by GC-AAS have been reported.⁶⁵⁸

In any speciation study of solid matrices such as sediments, it is vital that the distribution of the species is preserved at each stage. One of the most critical steps is in their extraction. With this in mind, a procedure for the extraction of As species from Fe oxide rich estuarine sediments has been devised using hydroxylammonium chloride as the extractant.⁶⁵⁹ If further evidence were needed, the reader need look no further than the conclusions from an interlaboratory study of the measurement of organotin species in a freshwater sediment.⁶⁶⁰ A systematic comparison of extraction methodologies showed that the six organotin species considered did not behave in the same way for different extraction methods. It was concluded that there was no universal method which could be optimized for all compounds and that participants should use their own method providing it was properly validated.

4.2.6 Vapour generation. Various methods, based on cold vapour AAS, for the determination of Hg in coal have been reported.^661–663 Usually dissolution was undertaken in closed vessels but a simpler approach employed a LECO analyser to heat the sample in oxygen, in a four-stage cycle during which the Hg was trapped on gold amalgam prior to measurement by AAS.⁶⁶² Cold vapour introduction into ICP-MS is attractive for coal and other samples because of its potential for excellent detection limits as long as memory problems can be solved.^288,663

It is recognized that acid media and reaction conditions are important parameters to optimise when minimizing interferences while generating GeH₄ (germane) for vapour introduction of germanium compounds to AFS and ICP systems.^664–666 An alternative strategy, in which GeCl₄ was produced in a gas–liquid separator connected to the inlet of an ICP-AES instrument, has been shown to provide superior performance with respect to tolerance to transition metals and other hydride-forming elements.⁶⁶⁶

4.3 Instrumental analysis

4.3.1 Atomic absorption spectrometry. Flame atomic absorption spectrometry (FAAS) offers a simple, inexpensive and robust means of analysis and, as such, still has a role in many geochemical laboratories. However, it is limited by insufficiently low detection limits, restricted working range and matrix interferences. The coupling of flow injection techniques to FAAS enables the analyst to separate analyte from matrix, usually with analyte preconcentration. Relevant geochemical applications can be found in extensive reviews of FI-AAS,^105,384 with examples of the use of solid phase extraction and chemical vapour generation for elements such as As, Cd, Pb and Se.³⁶⁸ Two Chinese groups have used on-line FI to preconcentrate Ag from geological materials prior to measurement by FAAS.^667,668

Complex chemical processing can also be conveniently accomplished on-line to graphite furnace AAS.¹⁰⁶ A novel example is a system for collecting hydrides of As, Se and Sb in a graphite furnace using a high voltage electrostatic field.²⁰⁸ More often than not, however, the extraction is performed off-line. Narukawa and co-workers have devised a series of methods, based on solvent extraction, collection on Co₂O₃ and use of a W furnace, for the determination of total As,⁶⁶⁹ Bi and Pb⁶⁷⁰ and total Sn.⁶⁷¹ After collection, the Co₂O₃ is dispersed as a slurry before manual injection into the furnace. However, the use of benzene for the solvent extraction of the Sn compounds does prohibit its use in the majority of laboratories.

Although rarely seen nowadays, tube-in-flame atomization has been advocated for the determination of Pb in sediments.⁶⁷² A slurry of the finely ground material was prepared, filtered and dried, before pieces of the filter paper were inserted into a graphite tube which was then introduced into an air–acetylene flame for atomization. Calibration was performed using aqueous standards. The overall convenience of its operation should be tempered against the precision of the method, which was highly dependent on the uniformity of the layer of solid sample deposited on the filter papers.

4.3.2 Atomic emission spectrometry. Although ICP-AES has been used routinely for geochemical analysis for many years, the advent of axially viewed plasmas offers much sought after improvements in limits of detection. Studies undertaken by Brenner and co-workers to assess the performance of an axially viewed ICP for the analysis of silicate rocks are therefore very timely.^673,674 The geological materials were prepared by fusion with LiBO₂to ensure refractory minerals were fully decomposed and the system found to be robust for major and minor element determination using aqueous standards matched in acid and LiBO₂ concentrations.⁶⁷³ Further work using a different instrument examined interference effects from Ca and Na at high and low aerosol loadings.⁶⁷⁴ The Mg II 280.270∶Mg I 285.213 nm intensity ratio continues to be an important analytical criterion in assessing plasma robustness in response to changes in power, aerosol loading and sample composition.

Spectral interferences are the major obstacle in the analysis of REE by ICP-AES, not least from the REE themselves, which have line-rich spectra. Thus, the determination of trace levels of the other REE in a virtually pure matrix of one REE oxide presents a formidable problem, but one which is of great commercial interest. Several groups have set themselves the task of cataloguing the spectral data for each REE acting as interferent on the others.^675,676 Chinese workers employing a high resolution sequential spectrometer with a grating of 3600 grooves mm⁻¹ for this type of study would appear have an advantage in line selection.^677,678

For a long period in spectroscopic analysis, excitation with a direct current arc was the leading technique for the direct sampling of powdered samples, especially for geochemical work. A critical evaluation of this technique⁶⁷⁹ confirmed that a new modernized dc arc connected by quartz-fibre optics to a multi-channel spectrometer is a viable alternative to existing solid sampling techniques for OES and AAS. Whether there is a resurgence in this technique, now that modern instruments are commercially available, may depend on the degree of automation inherent in these systems. An atmospheric pressure capacitively coupled device for rf sputtering and direct analysis by AES of non-conductive samples, such as oxides and silicates, has also been reported.⁶⁷⁹

4.3.3 Inductively coupled plasma mass spectrometry. Over this review period there has been a flood of papers illustrating new applications of ICP-MS and it is now clearly one of the techniques of choice for the analysis of geological materials (see Table 4). Several improvements in instrument design have helped to increase the versatility of the technique and will be the source of new applications in years to come. The availability of a detector that permits the detection of analyte concentrations over a dynamic range of up to 9 orders of magnitude within a single mass scan⁶⁸⁰ will be beneficial for many routine applications, including laser ablation ICP-MS, and offers much further scope for real-time correction for interfering matrix species. Other examples are the introduction of collision cells to reduce selected polyatomic interferences⁴¹⁰ and the possibilities that may be afforded by time-of-flight (TOF) ICP-MS,⁶⁸¹ still in its infancy. The strengths and limitations of quadrupole ICP-MS, along with these developments, are discussed in relation to the analytical requirements of a geochemical laboratory.⁶⁸²

In a continuing quest to improve detection limits, particularly for laser ablation ICP-MS, instruments with high efficiency ion transmission interfaces, the so-called S-option, were designed. The characteristics of such a system for trace element determinations in geological and environmental samples using conventional nebulization and flow injection have been published;^683–686 several times in the same journal it would appear!

A method has been developed for the extraction of ⁹⁹Tc from samples of bentonite clay.⁶⁸⁷ A detection limit of 0.45 pg ml⁻¹, comparable to that obtained by more conventional radiometric detection, was obtained with scope for a five-fold improvement using a desolvating nebulizer.

ICP-MS offers the potential for determining halogens in rocks after pyrohydrolysis and it is particularly attractive for iodine, which is difficult to determine by other methods. Schnetger and co-workers⁶⁸⁸ added sodium sulfite as a reducing agent to all the solutions to maintain the chemical form of iodine as I⁻, rather than IO₃⁻. This minimized the absorption of I, reduced its volatility and increased the sensitivity of the measurement compared with IO₃⁻. Theoretical detection limits of 5 µg kg⁻¹ I and 30 µg kg⁻¹ Br were elusive because of memory effects and contamination, a situation with which the present author has much sympathy.

The precious metals are one of the most difficult groups of elements to determine accurately at low concentrations. Two recent reviews of the use of ICP-MS for their measurement in geological and other materials^108,689 contain a host of valuable references and useful summary tables. Inevitably, the key to success in this field is sample treatment prior to analysis. NiS fire assay preconcentration is still popular,^{628,690–694} although the procedural blanks tend to be high. Fusion with Na₂O₂ followed by separation with Se and Te as carriers produced >95% recovery for the Pt group elements (PGE) but Au was less well extracted.⁶⁹⁵ Os is often neglected in the routine analysis of PGE but two conference presentations reported dissolutions in sealed containers followed by solvent extraction of the Os prior to separation of the remaining PGE by anion exchange.^696,697

Although ICP-MS is routinely used for the determination of REE, it is still worth emphasising that the method of sample decomposition must be appropriate.^363,698 Using high purity acids, very low levels of REE have been determined in chondritic meterorites,⁶⁹⁹ with quantitation limits between 0.2 and 4 ng g⁻¹ in the solid. The more interesting developments centre on the use of magnetic sector ICP-MS.^{363,700–702} In addition to its superior detection capability, oxide formation for the majority of the REE was reported to be 0.15–0.25%, much lower than that for quadrupole ICP-MS instruments.⁷⁰² Potential interferences likely to occur during determination of the REE can be more readily evaluated at high resolution.⁷⁰¹ In practice, most interferences cannot be resolved from the isotope of interest, so analysis was undertaken at a resolution of 300 for maximum sensitivity with a small number of oxide corrections.⁷⁰² Alternatively, the use of a membrane desolvation system in conjunction with a microconcentric nebulizer reduced the oxide interferences to a negligible amount, of the order of 0.01% for CeO/Ce.³⁶³ At medium resolution,⁴⁵Sc could be resolved from the relevant silica polyatomics, making it possible to determine this element accurately along with the other REE.

The development of methods for the determination of isotope ratios by magnetic sector ICP-MS instruments, often equipped with multiple collectors, has proceeded apace during the period under review. The technical demands on these machines have been driven by the requirements of geochemists interested in the precise measurement of isotopes of Li,⁷⁰³ Hf and Zr,⁷⁰⁴ Pb,⁷⁰⁵ Tl⁷⁰⁶ and Th.^707,708 The determination of Pu using a high resolution magnetic sector instrument^543,709 is an attractive alternative to techniques such as alpha spectrometry and TIMS, not only because of its higher throughput but its ability to measure concentration and isotopic ratio on the same sample.

Much use is made of these instruments for the very accurate measurement of trace elements using isotope dilution methodologies. New sample preparation and ion-exchange separation methods have been developed for Cd, In and Te;⁷¹⁰ mass biases for In and Te were corrected using Pd and Sb, respectively, whereas that for Cd was calculated from the measurement of a standard solution. Detection limits were <1 ng g⁻¹ for Cd, and <0.02 ng g⁻¹ for In and Te. A group of Spanish workers have used both quadrupole and single collector magnetic sector ICP-MS to determine Cd by on-line isotope dilution^227,266 in a variety of materials including sediments.

Introduction of samples by electrothermal vaporization (ETV) for ICP-MS is usually reserved for specialized single element applications, such as the direct determination of Hg in sludge samples,⁷¹¹ Ra in slurries⁷¹² and Se in sediments.⁷¹³ An extensive review of ETV sample introduction for ICP-MS⁷¹⁴ highlights many of its potential advantages, such as minimizing the transport of matrix components, altering the release of volatile elements, and in situ preparation, preconcentration and speciation.

4.3.4 Other mass spectrometric techniques. A comprehensive review by Becker and Dietze,³⁵² containing 269 references, tabulates the strengths and weaknesses of various mass spectrometric techniques for the analysis of inorganic solids and aqueous solutions for trace impurities. This usefully complements the 1999 update covering atomic mass spectrometry;⁹⁷ both these reviews include extensive sections on ICP-MS.

Thermal ionization mass spectrometry (TIMS) is still the benchmark for the precise and accurate measurement of isotope ratios, although time-consuming sample preparation is often required. Nowell and co-workers⁷¹⁵ developed a procedure to obtain high precision Hf isotope ratios on mid-ocean ridge basalts using TIMS. Internal precisions of 0.002–0.006% for the ¹⁷⁶Hf∶¹⁷⁷Hf ratio were achieved only by paying great attention to clean conditions throughout a complex separation scheme and analysis. Such precision was comparable to that obtained using a multicollector magnetic sector ICP-MS instrument. Thus, for various reasons, not least higher productivity, it is likely that multicollector magnetic sector ICP-MS will be used routinely in future, wherever possible, to determine Hf ratios.

Improvements in the determination of protactinium (²³¹Pa) by TIMS in samples of manganese crust⁷¹⁶ and silicate rocks⁷¹⁷ have been reported. The former method achieved a detection limit of 10 fg of ²³¹Pa and allowed concentrations in older sections of crust to be estimated.

Following the trend of recent years, applications of negative TIMS seem to be increasing, particularly in the study of the Re–Os isotope system.^718–720 These are not easy measurements to make and Hattori et al.⁷¹⁸ explain some of the difficulties experienced in the determination of Os isotopes; their views are not always in accord with the prevailing wisdom on the ionization processes. B is often measured by negative TIMS, but positive TIMS was used by Nakano and Nakamura⁷²¹ with a newly developed double collector package that reduces the data acquisition time by an order of magnitude without compromising the analytical precision obtained for ¹¹B∶¹⁰B.

Secondary ion mass spectrometry (SIMS) is becoming increasingly important for depth profiling and characterizing surfaces or thin layers.³⁵² Analysis of mantle rocks for F is particularly difficult because of its low abundance; EMPA has a detection limit of about 50 µg g⁻¹. Using the SIMS technique, calibrated with synthetic glasses prepared with varying weights of CaF₂, Hoskin⁷²² was able to determine fluorine at µg g^–1 levels and below. This work should allow the NIST glass SRM 610 to be used as a quality control standard for the quantitative measurement of fluorine by this and other techniques.

Some potentially far reaching developments, in more senses than one, involve stable isotope ratio mass spectrometry. One of the current challenges is the design of remote control instruments for use in space missions for examining cosmic materials. Pillenger and colleagues have proposed a measurement philosophy called Modulus^723,724 for determining a number of light element stable isotope ratios to a high level of accuracy within a self-contained and space-compatible experiment. Fundamental aspects of the system are that the elements of interest are converted into specific gases with low molecular weights, thus enabling a mass spectrometer which covers only low masses and has limited mass resolution to be employed. Apparently, such a device could be made with a mass of less than 3 kg using materials currently available, but the ultimate aim is to produce one which weighs less than 2 kg. Back on earth, the isotopic composition of Mo and Zr in micro-sized presolar grains (SiC and graphite) from a meteorite have been measured by secondary neutral mass spectrometry using resonance laser ionization (RIMS).⁷²⁵ While the high sensitivity of RIMS has been reported before, here the researchers focused on its very low noise properties and ways in which the noise could be minimized. A review of accelerator mass spectrometry⁷²⁶ also placed particular emphasis on cosmogenic radionuclides ¹⁰B, ²⁶Al, ³⁶Cl and ¹²⁹I measured on large tandem accelerators.

4.3.5 X-ray techniques. XRF is still one of the standard techniques for geological analysis and several recent reviews contain extensive information about the fundamentals of the technique^727,728 as well as environmental and geological applications.^728,729

In spite of the maturity of the technique, there is still interest in methods of preparing samples for analysis by wavelength and energy-dispersive XRF; a review by Creasy et al.⁷³⁰ is dedicated to this subject. Several alternative approaches to fusing samples with high sulfur contents involving various fluxes have been reported, usually based on lithium borates in varying proportions⁷³¹ and often including an oxidant.^731,732 A system for the automatic preparation of pressed powder pellets will be of interest to any high production laboratory.⁷³³ Jurczyk and co-workers⁷³⁴ have developed a so-called in situ method of preparing micro-samples, including crystals, for presentation to an XRF instrument. This involves the deposition of multi-element solutions or powdered samples onto a filter, which is then digested with concentrated HF. The solvent is then evaporated using an IR lamp and the residue retained for analysis by XRF. The effect of sample thickness on the XRF response is discussed.

The predominance of applications involving energy-dispersive XRF (EDXRF) rather than wavelength dispersive XRF during the current review period reflects the growing importance of the former for the analysis of geological materials, and the routine use of the latter where there are fewer innovations. Several authors have seen fit to demonstrate the comparability of results obtained by EDXRF for Hg in coal, soils and sediments⁵²⁷ and trace elements in coal and other environmental samples³⁶⁰ with solution techniques, such as CVAAS and ICP-MS, respectively. The use of EDXRF for the analysis of sediments and ores is gathering momentum;^735–738 it may well become the technique of choice for geochemical surveys of stream sediments.⁷³⁹

Portable XRF is being deployed in an increasing number of geological applications. Kirtay and co-workers⁷⁴⁰ have validated its use for the analysis of metals in marine sediments. The samples were homogenized and analysed wet. Although the values obtained were low compared with those from standard laboratory techniques, these discrepancies may be related to the moisture content. Jansen et al.⁷⁴¹ used an XRF-scanner to log split sediment cores at sea. They found that a 1 m core section could be scanned at 2 cm intervals in 1 h with a maximum resolution of 1 mm. An on-line XRF monitoring system has been employed to analyse pulverized coal on a coal feed line.⁷⁴² One of the most recent successes is the analysis of Martian soil and rocks by a mobile alpha proton XRF instrument during the Mars Pathfinder mission.⁵⁰⁷ In parallel, Sarrazin and co-workers⁷⁴³ are developing a miniature XRD/XRF instrument for the in-situ characterization of the surface of Mars, where the concept is to make XRD and XRF measurements simultaneously.

Developments in electron-probe microanalysis (EPMA) have not featured greatly in this series of updates over the past few years, in spite of its routine application to the examination of geological materials. However, the March 1999 issue of JAAS carried papers from the 15th International Congress on X-ray Optics and Microanalysis, in which EPMA featured strongly. Duncombe,⁷⁴⁴ in a review of quantitative analysis using the electron microprobe, highlighted the drive towards instruments equipped with an intelligent interface to guide the user in setting up the instrument, running the experiment and processing the results. Advances have been made in the measurement of the ultra-light elements, i.e., atomic number less than 11, for which this technique is not normally considered particularly sensitive. Scott and Love⁷⁴⁵ describe EPMA studies using low-energy X-rays with particular reference to light elements. They claim that minimum detection levels for these elements are now similar to those for heavier elements; these are, under ideal circumstances, about 100 ppm using wavelength-dispersive spectrometry and about 1000 ppm with energy-dispersive spectrometry. By employing a low-voltage electron probe to restrict X-ray excitation to surface layers and recording low-energy X-ray emission, surface films down to about 1 nm thickness may be investigated. Kleykamp⁷⁴⁶ used a commercial synthetic Mo–B₄C multilayer X-ray diffracting device to extend X-ray microanalysis to determine Be and B with an existing instrument. A new EPMA technique for the determination of REE involving automated peak-overlap and modelled background corrections has also been reported.⁷⁴⁷

An extensive review of the characterization of geological materials using ion and photon beams has been compiled by Torok and co-workers.⁷⁴⁸ It concentrates on techniques based on particle accelerators, showing some applications that are hardly possible with conventional methods, including synchrotron radiation induced X-ray emission and particle-induced X-ray emission (PIXE).

4.3.6 Other techniques. Only limited use is now being made of instrumental neutron activation (INAA) for geochemical analysis because of factors such as limited access to nuclear reactors and turnround time. Several comparative studies have assessed data obtained by INAA against those obtained by other techniques. El Maghraoui et al.⁷⁴⁹ used XRF and INAA to determine 44 major and trace elements in magmatic rock, while Kin et al.⁷⁵⁰ compared ICP-MS and INAA for the determination of REE in geological reference materials. In the latter study, the authors concluded that, despite the limited number of REE that can be determined by INAA, its precision and accuracy were at least as good, if not better, than by ICP-MS. They attributed this in part to the sample preparation required for ICP-MS, whereas in INAA the solid is analysed directly. They were particularly concerned that the interference correction performed on the ICP-MS Eu data did not seem to be entirely effective.

Developments in atomic fluorescence spectrometry (AFS) in the current review period have been limited. A useful analytical scheme for the determination of As, Bi, Hg and Sb has been devised by Li,⁷⁵¹ in which separate aliquots of an aqua regia digest were treated in different ways before measurement by AFS. Ma and co-workers⁷⁵² determined ultra-trace concentrations of gold in geogas samples using laser excited AFS combined with graphite electrothermal atomization. A time-gated technique was used to reduce the background radiation caused by the furnace. The highly sensitive technique of laser excited AFS has also been used to determine Pb in ice and snow, Au and Pd in marine sediments and Ga and In in geochemical samples.^380,753,754

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P. Thomas, K. Pereira, (Inst. Pasteur de Lille, Service Eaux Environ., 59019 Lille, France). Presented at European Winter Conference on Plasma Spectrochemistry, Pau, France, January 10–15, 1999..
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V. N. Mitkin, A. A. Galitsky, (Inst. Inorg. Chem., Siberian Branch, Russian Acad. Sci., Novosibirsk 630090, Russia). Presented at Analitika `98, Midrand, Gauteng, South Africa, October 12–14, 1998..
G. Horlick, B. Bitterli, (Dept. Chem., Univ. Alberta, Edmonton, AB, Canada). Presented at 25th FACSS, Austin, TX, USA, October 11–15, 1998..
R. K. Marcus, W. Luesaiwong, (Dept. Chem., Clemson Univ., Clemson, SC, USA). Presented at 25th FACSS, Austin, TX, USA, October 11–15, 1998..
G. MacPherson, D. Gravatt, T. Plank, (Univ. Kansas, USA). Presented at 25th FACSS, Austin, TX, USA, October 11–15, 1998..
E. Salin, J. Hamier, (Dept. Chem., McGill Univ., Montreal, PQ, Canada). Presented at 25th FACSS, Austin, TX, USA, October 11–15, 1998..
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L. V. Gatti, A. A. Mozeto, E. de Oliveira, (Inst. Pesq. Energetica e Nuclear CNEN-SP/Div. Quim. Ambiental, Univ. Federal Sao Carlos, Sao Carlos, Brazil). Presented at 5th Rio Symposium on Atomic Spectrometry, Cancun, Mexico, October 4–10, 1998..
D. G. Pearson, M. Greselin, C. J. Ottley, C. Parker, P. Krause, H. A. Armstrong, (Dept. Geol. Sci., Durham Univ., Durham, UK DH1 3LE). Presented at 6th International Conference on Plasma Source Mass Spectrometry, Durham, England, September 13–18, 1998..
P. J. Sylvester, (Dept. Earth Sci., Memorial Univ. Newfoundland, St. John's, NF, Canada A1B 3X5). Presented at 6th International Conference on Plasma Source Mass Spectrometry, Durham, England, September 13–18, 1998..
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M. O. Figueiredo, M. T. Ramos, T. Pereira da Silva, M. J. Basto, P. Chevallier, X-Ray Spectrom. 1999, 28, 251 Search PubMed.
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R. A. Brown, J. M. Piper, K. E. Jarvis, S. J. Parry, R. Hutton, (NERC ICP-MS Facility, Imperial College, Environmental Technology, Ascot, Berkshire, UK). Presented at 6th International Conference on Plasma Source Mass Spectrometry, Durham, UK, September 13–18, 1998..

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