Atomic Spectrometry Update. Environmental analysis

Contents

• 1 Air analysis
  • 1.1 Sample collection and pretreatment
  • 1.2 Instrumental analysis
  • 1.3 Method validation, standardisation and data quality
  • 1.4 Future requirements

• 2 Water analysis
  • 2.1 Sample preparation
  • 2.2 Speciation
  • 2.3 Instrumental analysis

• 3 Analysis of soils, plants and related materials
  • 3.1 Sample preparation
  • 3.2 Reference materials
  • 3.3 Instrumental methods of analysis

• 4 Analysis of geological materials
  • 4.1 Sample treatment
  • 4.2 Instrumental analysis

• References

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Abstract

This is the sixteenth annual review published in JAAS of the application of atomic spectroscopy to the chemical analysis of environmental samples. In line with last year's review there have been no major breakthroughs in atomic spectrometry. Developments in environmental analysis have mainly been confined to improvements of existing techniques to produce more reliable and robust analytical methods. Developments in ICP-MS applications for environmental analysishave been the most active area of research where its low detection limits and isotopic measurement capabilities have again been widely exploited. In the analysis of air, the most promising advances are in the area of continuous emission monitoring and portable XRF instrumentation. Water analysis continues to be dominated by pre-instrument chemistries studies for preconcentration and speciation. The variety of metal and non-metal species being studied has significantly increased this year. The need for risk assessments of brown field sites has raised the profile of methods to determine the chemical form and bioavailability of metals in contaminated soils. In geological analysis, aided by the improved stability of modern instruments and the wider availability of high resolution spectrometers, isotope ratio determinations by ICP-MS are becoming increasingly important. Over all areas of environmental analysis there has been a small but significant increase in the use of chemometric methods to aid data interpretation and reduce interference effects.

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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 summarised in Table 1. Noteworthy areas of research and development are highlighted below. Five useful reviews have been published: a review of mass spectrometry techniques for the characterisation of aerosols,¹ containing 204 references; development of on-line Hg analysers for stack gas analysis² (five commercially available instruments plus a further six prototypes assessed); application of XRF techniques for the analysis of ambient air,³ containing 58 references; measurement methods for the determination of Ni in workplace air,⁴ containing 14 references; and the use of AAS in the fossil fuel power industry,⁵ containing 64 references.

Table 1 Summary of analyses of air and particulates

Element	Matrix	Technique; atomization; presentation^a	Sample treatment/comments	Ref.
a Hy indicates hydride and S, L, G and Sl signify solid, liquid, gaseous or slurry atomization, respectively. Other abbreviations are listed elsewhere.
As	Airborne particulate matter	MS;ICP;L	Bomb digestion method using HNO3 + H2O2 + HF validated using four reference materials including NIST 1648 (urban particulate matter) and BCR 176 (waste incineration ash)	38
C	Ambient air and point source samples	MS;-;S	Accelerator MS (^14C) used to provide direct fossil versus biomass C source discrimination data in a metropolitan area	57
C	Air samples	MS;-;G	GC-IR technique developed for the high precision isotopic analysis of ^13C in atmospheric CO2.	42
Cd	Stack gases	AE;MIP;G	Development of a continuous emission monitor. Self absorption at Cd 228.8 nm and Hg 253.65 nm lines examined	11
C	Breath samples	MS;-;G	^13CO2∶^12CO2 ratio determined by IRMS and by a cheaper non-dispersive IR technique. Patients administered with 1-^13C-phenylalanine and duplicate samples taken. Data showed a good correlation between the two techniques. IRMS superior when concerned with ^13CO2 kinetics over longer time periods	43
Cr	Industrial exhaust streams	AE;LIPS;S	Developmentof an on-line monitoring system attempted using a Nd:YAG laser. Measurements made at 520.4, 520.6 and 520.8 nm lines in a total measurement time of 20 s. Good correlation found with analysis by filtration/ICP-AES (r^2 = 0.84). LOD 14 µg m^−3	58
Cr	Airborne particulate matter	MS;ICP;S	Laser ablation of PTFE filters attempted. Good correlation with results obtained using a bomb digestion procedure (HNO3 + HClO4 mixture). LOD 0.05 µg per filter	28
Cr	Welding fume	AE;ICP;L	Analytical techniques for the measurement of Cr^VI in welding fume compared (colorimetric, IC and ICP-AES)	59
Cu	Sedimented dust	AE;ICP;L	Samples collected at varying distances from selected point and line sources within a mining community	19
Hg	Ambient air	AFS;CV;S, G	Quartz filter filtration system for particulate phase compared to a filtration system with a front ended denuder (Au coated) to remove gaseous phase Hg. Denuder based system gave higher results in parallel sampling trials. Result attributed to Hg-coated Au particles flaking off the denuder	56
Hg	Stack emissions	AA;-;G	Continuous emission monitoring instrumentation for Hg reviewed. Five commercially available instruments reviewed as well as six further instruments under development. Cold vapour AAS found to be the dominant mode of operation	2
Hg	Stack gases	AES;MIP;G	Development of a continuous emission monitor using an atmospheric microwave sustained plasma. Self absorption of Cd 228.8 nm and Hg 253.65 nm lines examined	11
Hg	Air samples	AF;CV;G	Au amalgamation trapping system discussed	60
Hg	Flue gases	XRF;-;G	Silvered quartz fibre filters used for collection with efficiencies of 88% in laboratory tests. Average capacity of the filters determined to be 15 µg cm^−2 and that ageing of the filters for up to 96 hours had no effect on collection efficiency	6
Hg	Environmental	-;-;-	Overview of the environmental analysis in China including the determination in air	61
Hg	Urban air	AA;-;G	Prototype cavity ringdown laser absorption spectrometer developed and evaluated in laboratory trials. LOD 0.5 ppt	62
Hg	Flue gas	AF;CV;G	Automated measurement system with Au amalgamation sampler utilised. System set up to measure elemental and total concentrations thus giving ionic concentrations by difference	63
Kr	Atmospheric samples	MS;-;G	Accelerator sytem used to establish that ^81Kr is a long-lived cosmogenic radionuclide essentially unaffected by anthropogenic contributions and therefore suited for dating applications	64
Mn	Sedimented dust	AE;ICP;L	Samples collected at varying distances from selected point and line sources within a mining community	19
Mn	Airborne particulate matter	AA;ET;L	Graphite furnace method developed. Mg(NO3)2 used a modifier. Measurement precision < 3.0%. LOD (3σ) 0.3 µg per filter	16
N	Air samples	MS;-;G	Measurement of ^15N in NO enhanced by preconcentration using cyrogenic trapping	65
Ni	Airborne particulate matter	AA;ET;L MS;ICP;L	Operationally defined speciation carried out in both laboratory and field trials	52
Ni	Workplace air	-;-;-	Review of methods used at BIA (Germany) for monitoring Ni in airborne dusts. Role played by the methods in the meeting of legal requirements in workplace air monitoring discussed	4
O	Air samples	MS;-;G	Development of a continuous flow IRMS system for the measurement of stable isotopic composition in air samples, soil gas samples and in water samples. Field sampling techniques for gaseous and dissolved O2 described	66
Pb	Airborne particulate matter	TIMS;-;S	Aerosols sampled onto acid washed 0.45 µm PTFE filters. Low blanks of 15 pg Pb enabled reliable isotopic data to be obtained on filter samples containing 400 pg Pb (for sectioned filters). Blanks were lower for uncut filters (11 ± 8 pg), enabling samples containing as little as 120 pg Pb to be examined	29
Pb	Airborne particulate matter	MS;ICP;L	Pb isotopic measurements made using magnetic sector multi-collector system. Solution nebulisation and laser ablation approaches studied	30
Pb	Workplace air	XRF;-;S	Evaluation of portable system described. Study led to the development of a standardised method (NIOSH 7702)	23
Pb	Airborne particulate matter	AA;F;L XRF;-;S	Comparison of two analytical techniques reported. NIST SRM 1648 (urban particulate matter) used in the evaluation process. Sequential extraction based on the method of Tessier et al. also attempted	67
Pb	Paint particle	XRF;-;S	On-site measurements made during operations to remove paint from bridges. Comparable performance obtained with traditional laboratory analysis using ICP-AES	25
Pb	Airborne particulate matter	-;-;-	Airborne concentrations correlated to blood levels found in school children	68
Pb	Atmospheric particulates	MS;ICP;L	Nature of ^206Pb∶^207Pb isotopic ratio in rainwater, particulates, pine needles and leaded petrol in Scotland examined over the period 1982–1998. Data collected suggested that the contribution of leaded petrol to atmospheric Pb in urban environments has declined from 84–86% (1989–1991) to 48–58% (1997–1998)	33
Pb	Aerosol samples	MS;ICP;S	Isotopic measurements made on samples collected on an impactor sampler. Enhanced measurement precision with a multi-collector instrument allowed slight variations to be detected between samples collected with different prevailing wind directions	32
Pb	Atmospheric particulate matter	MS;ICP;S	Isotopic measurements made on samples collected on membrane filters with a high volume sampler. Microwave assisted dissolution utilised (HNO3 + HClO4 + HF)	31
Pb	House dust	AA;F;L	High throughput microwave assisted dissolution (using disposable digestion vessels) compared to traditional hotplate procedure (ASTM method). NIST SRM 2582 (low lead paint) and NIST SRM 1648 (urban particulate matter) used during the evaluation process	69
Pd	Airborne particulate matter	AA;ET;L	Samples collected on glass fibre filters subjected to a microwave assisted dissolution. Samples preconcentrated on the inner wall of a graphite tube through electrodeposition. Precision at the 1.01 µg l^−1 was 5.1%. LOD 0.06 µg l^−1	70
Pt	Airborne particulate matter	AA;ET;L	See Pd, ref.70	70
S	Breath samples	AE;GD;G	Speciation of volatile compounds from anaerobic bacteria in the mouth carried out using a GC coupled system	71
Si	Airborne particulate matter	MS;ICP;L XRF;-;S	LA technique compared to direct analysis by XRF. Calibration standards prepared by loading aliquots of NIST 1648 CRM onto PTFE filters	39
Sb	Airborne particulate matter	MS;ICP;L	Speciation (III and V) carried out on aqueous extracts using a silica based anion exchange column connected on-line. Precision at 5.0 µg l^−1 <5%. LOD 100 pg ml^−1 Sb^V and 300 pg ml^−1 Sb^III	72
V	Airborne particulate matter	MS;ICP;L	Bomb digestion method using HNO3 + H2O2 + HF validated using 4 reference materials including NIST 1648 (urban particulate matter) and BCR 176 (waste incineration ash). Sector field instrument used. See As, ref. 38	38
Various	Car exhaust fumes	MS;ICP;L	Exhaust fumes analysed for PGE content following EUDC drive cycles on cars (gasoline and diesel) equipped with catalytic converters. Microwave assisted dissolution using aqua regia–HF mixture. NIST SRM 2557 (used auto catalyst monolith) used for quality control	34
Various	Airborne particles	MS;-;S	Particle spectra classified and interrogated using commercial and in-house software packages	73
Various	Aerosol particles	MS;-;S	Near-surface examination of particles carried out on samples collected with size selective sampler. Fine particles (<1 µm) had Na and S dominated shell of 13 nm around a C core (traffic soot). Coarse particles (>1 µm) consisted of soil dust, fly ash and Na salt containing particles	55
Various	Diesel exhaust particulates	TXRF;-;L	Trace element distribution examined. Quartz fibre filter most suitable for sample collection. Wear metal content of particulates emitted during engine start up higher than particulates emitted during normal engine working temperature	74
Various	Laboratory air sample	AE;LIPS;G	Development of a calibration-free procedure for quantitative analysis described	10
Various	Aerosols	AE;LIPS;S	Laser beam focused onto filter surface. System used with an on-line filter sampling interface monitoring emissions from a waste incineration facility. LOD typically <0.4 µg cm^−2 for a sample size of 1 m^3 sampled onto a 3 cm^2 filter	75
Various	Atmospheric aerosol samples	AA;F;L	Filter samples subjected to a microwave assisted dissolution (HNO3 + H2O2 + HF). High sensitivity Pt–Ir nebuliser used to enhance performance	17
Various	Arctic air	MS;ICP;S	Particulates collected on graphite impaction plates within a cascade impactor sampler. ETV used to vaporise from impaction plates	8
Various	Airborne particulate matter	AA;-;L	Eight heavy metals determined in samples collected on membrane filter	18
Various	Aerosol deposits	PIXE;-;S	Development of a new analysis chamber with a rotating target to handle film targets from Berner-type impactors described	27
Various	Airborne particulates	PIXE;-;S	Lower impaction stages (fine particle collection) of cascade impactors not ideal thin targets for PIXE analysis. SEM used to measure density and target thickness in order to calculate thick target correction factors	46
Various	Aerosol deposits	PIXE;-;S	Spray technique for preparing uniform large area calibration standards from standard solutions evaluated	48
Various	Aerosol deposits	PIXE;-;S	Time resolved air sampling system described. Sequential samples (1 h) taken using a 14 channel system (each with its own sampling nozzle, impaction plate and pumping system)	76
Various	Antarctic aerosol deposits	PIXE;-;S	Snow samples melted and evaporated on polycarbonate foil. Complementary analysis carried out using SEM-EDAX following filtration of thawed samples through a nucleopore filter	77
Various	Aerosol samples	SIMS;-;S	Preparation of standards from pure metal salts. Results compared to analysis by ICP-AES, <20% error found	47
Various	Aerosol samples	PIXE;-;S	Interactive software packaged developed to aid quantitative analysis of samples of intermediate thickness	78
Various	Aerosols	MS;-;-	Review of mass spectrometric techniques for the analysis of aerosols and their constituents (204 references)	1
Various	Combustion particles	AA;ET;L	Particulates from combustion of waste mineral oil sieved, wet ashed and analysed in order to determine environmental safety of particles escaping from filters in combustion plants	20
Various	Classroom air	XRF;-;S	Elemental composition of PM10 samples measured. High indoor PM10 concentrations attributed to resuspension of soil derived particles	79
Various	Atmospheric aerosols	XRF;-;S	Metals and common cations/anions determined. Three factors isolated: particulates from anthropogenic emissions, resuspended soil particulates and sea-salt particles	80
Various	Aerosol particles	TXRF;-;S	Development of an electrostatic precipitator sampler described	7
Various	Vehicle exhaust particulate matter	XRF;-;S	Elements determined averaged between 3–9% of PM10 mass from gasoline and diesel engined cars tested using Federal Test Urban Dynamometer Driving Cycles	81
Various	Urban aerosols	PIXE;-;S	Principle component analysis carried out to apportion measured air pollution to sources	82
Various	Indoor particulate matter	MS;ICP;L	Low flow rate cascade impactor sampler with either quartz filters or coated (apiezon grease) PTFE filters used for sampling. HNO3 + HClO4 + HF acid mixture used for digestion	83
Various	Ambient air samples	AE;ICP;L	Research into the effect of metal catalysed oxidative stress. Catalytically active metals measured in water soluble and insoluble particulate fractions with their oxidant generation ability measured by in-vitro testing	54
Various	Air samples	-;-;-	ASU environmental update	84
Various	Marine aerosols	MS;ICP;S	Concentration, distribution and occurrence of metals in airborne particulate matter interrogated using LA sample introduction. Crustal elements lower in winter months due to frozen land masses. Concentrations of crustal and anthropogenic elements lower in summer than in spring due to dilution of offshore winds with oceanic winds	85
Various	Airborne particulate matter	AES, MS;GD;S	Direct introduction of particulates into AE/MS systems via particle beam/momentum separator device described. Feasibility of this approach demonstrated by collection of emission spectra for NIST 1648 CRM and mass spectra from a caffeine powder doped with PAHs	14
Various	Airborne particulate matter	AA;F,ET;L	Deposits collected using a water layer surface sampler. Water filtered and analysed. Filter wet ashed and analysed	21
Various	Airborne dust samples	TXRF;-;L	Oxygen ashing procedure (directly onto TXRF carrier) compared to two high pressure acid digestion procedures. Elemental recoveries for the ashing procedure in the range 90–97% for NIST 1648 SRM (urban particulate matter)	9
Various	Atmospheric dust	AA;F;L	Samples collected on PVC membrane filters, subsequently dry ashed with carbonised residues, treated with HNO3 and re-ashed, and finally taken up in 1 M HCl	22
Various	Ambient air	XRF;-;S	Review of the application use of XRF techniques for air quality studies with 58 refs.	3
Various	Marine aerosols	XRF;-;S	Light elements determined in aerosol samples collected using a 5-stage Battelle impactor	86
Various	Atmospheric particulates	XRF;-;S	Research into the weathering mechanisms of marble and granite monuments carried out	87
Various	Stack gas emissions	XRF;-;S	Filter calibration standards prepared by nebulisation of standard solutions	49
Various	Airborne particulate matter	XRF;-;S	Samples analysed following collection using a Gent-type PM10 stacked filter unit. Maximum concentrations determined below WHO guideline values	88
Various	Airborne particulate matter	NAA;-;S	PM10 and TSP samples collected and analysed from three Indonesian sites	89
Various	Stack gas	XRF;-;S	On-line instrument used with particulates collected on quartz fibre filters. System also used to monitor toxic elements in ambient air	15
Various	Ambient aerosols	XRD;-;S	Elemental distribution on filter samples obtained with high volume samplers examined. 150 mm diameter filters sub-sampled (32 mm diameter) and examined. Loading differences between centre and edge of filter found (8–10% decrease for course particulates; 2–4% for fine particulates).	45
Various	Dust samples	XRF;-;S	Virtues of using portable XRF extolled	26
Various	Airborne particulate matter and road dust	MS;ICP;L	Environmental samples analysed following dissolution. USN equipped quadrupole and sector instruments used. Authors conclude that, following examination of this data and data from samples collected in 1991, emission of PGEs from catalytic converters into the environment can no longer be neglected	36
Various	Cleanroom air	MS;-;S	TOF-SIMS instrument used to monitor contamination from ionic and organic species	90
Various	Occupational dust particles	MS;-;S	SIMS spectra recorded for individual particles of dust emitted from nuclear plants giving chemical and isotopic information	91
Various	Airborne particulate matter	MS;ICP;L	Interferences in the determination of Pd, Pt and Rh using a quadrupole instrument examined. Microwave dissolution utilising aqua regia + HF. Conclusion that Pt could be measured without major errors and that Rh could be measured after mathematical correction. Pd analysis hampered by high contribution from coexisting interferent elements	37
Various	Coastal aerosols	MS;ICP;L	High volume air sampling at selected sites in NW England. Hotplate dissolutions employed (HNO3 + HF). Al and Fe determined alternately by FAAS	92
Various	Fly ash	AA;-;L	Use of methods in the fossil fuel power industry discussed	5
Various	Indoor/workplace air	AE;-;G	Development of continuous emission monitoring instrumentation described. Field tests carried out over chrome plating baths and at an indoor shooting range. LOD for Cr and Pb 10 µg m^−3	12
Various	Clean room air	MS;ICP;S	Droplet scanning ICP-MS methodology used to investigate surface contamination	93
Various	Atmospheric particulate matter	MS;ICP;S	Interrogation of tree bark pockets using LA sample introduction for the retrospective monitoring of the atmosphere	94
Various	Electric arc furnace dust	AE;ICP;L	Sequential operationally defined speciation carried out to assess environmental impact of fugitive emissions	53
Various	Workplace air	XRF;-;S	Generation of filter calibration standards through aerosol generation from standard solutions using a desolvated USN system described	50
Various	Atmospheric samples	MS;-;G	Stable isotope concentrations in CO2 and O3 measured by a laboratory built quadrupole instrument	44
Various	Air particles	AE;MIP;S	Development of a novel portable on-site instrument with CCD detector and efficient in situ sampling system. Characterisation, optimisation and calibration carried out in the laboratory with aerosols generated from an in-house high efficiency nebulisation/desolvation system	13
Various	Sediment core	MS;ICP,L	Historic atmospheric deposition measured by the analysis of sectioned core samples. Samples digested in a HNO3 + H2O2 mixture in a microwave oven digestion bomb	95
Various	Car exhaust fumes	MS;ICP;S	Exhaust fumes analysed for PGE content on cars (gasoline and diesel) equipped with catalytic converters. Catalytic surface examined using SEM-EDX and LIBS techniques. PGE content of exhaust fume found to decrease with ageing of catalyst	35

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1.1 Sample collection and pretreatment

For the measurement of gas phase Hg by EDXRF, Kurunczi and co-workers⁶ assessed the efficiency of collection using silver-coated quartz fibre filters. Collection efficiencies were found to average 88% in laboratory tests with an average filter capacity of 15 µg cm⁻². Ageing of the filters for up to 96 hours had no effect on collection efficiency.

Dixkens and his group⁷ evaluated an electrostatic precipitator for the collection of representative samples on analytically suitable sample plates for subsequent off-line analysis by SEM and TXRF. The use of graphite targets within cascade impactors and subsequent analysis by ETV-ICP-MS, previously reported at conferences, has now been published.⁸ A number of workers continue to compare dissolution procedures and an example of this type of work is the efforts of Theisen and co-workers in Germany.⁹ They assessed the performance of a low pressure oxygen ashing procedure against more conventional high pressure acid dissolution procedures. Good recoveries were obtained (90–97%) in studies using NIST SRM 1648 (urban particulate matter).

1.2 Instrumental analysis

1.2.1 On-line measurements. The development of continuous emission monitoring (CEM) instruments goes from strength to strength. A number of workers are actively developing portable atomic emission spectrometers using a variety of excitation sources, e.g., LIP, MIP, SIB.^10,11–13 These technologies are still at an early stage with much work focusing on instrument optimisation within a laboratory setting. Furthermore, the limited number of field trials carried out so far have often taken place under simulated conditions.

A group at Clemson University¹⁴ is currently investigating glow discharge based systems. They are developing a system with both AES and MS systems that enables both elemental and molecular information to be obtained. A particle beam/momentum separator device is being developed to sample airborne particulates. Initial experiments have concentrated on introducing NIST SRM materials into the prototypes. However, they believe that strengths such as (potential) small size, low power consumption, ease of use and multimode analysis could be applied to the development of field instruments.

Dannecker and his group¹⁵ continue to develop their on-line EDXRF system. This half way house approach (particulates are collected on filter media and analysed shortly afterwards) nevertheless remains a promising compromise for commercial development.

1.2.2 Atomic absorption and atomic emission spectrometry. Such is the established nature of these techniques that 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.^16–22

1.2.3 X-ray techniques. X-ray techniques remain popular for the analysis of airborne particulate matter. The portability of small energy dispersive XRF instruments has enabled a number of workers to make onsite field measurements, most notably in the United States under the Lead Abatement Scheme.^23–26 Measurement of lead on air filter samples has been aided by the production of a standardised method—NIOSH 7702. For the analysis of bulk (sedimented) dust, good correlation is obtainable with laboratory based techniques provided that the samples are sieved i.e., control of particle size.

Impactor samplers are often used for particle size classification studies. In an interesting paper, Halder et al.²⁷ developed a rotating target holder for the analysis of sample spots on targets from such samplers.

1.2.4 Mass spectrometry. Determination of lead isotope ratios, using ICP-MS and thermal ionisation mass spectrometers, for source apportionment studies continues to attract interest.^28–33 Increasing use of automobiles fitted with catalytic converters has led groups to undertake determinations of PGE in car exhaust fumes,^34,35 in airborne particulate matter and road dust³⁶ and to assess the extent of interferences in the determination of PGE using quadrupole based instruments.³⁷

Laser ablation as a means of presenting sample to the plasma from a filter surface continues to be reported.^28,38–40 Whilst the ability to present sample directly without a dissolution step is attractive, this approach does not compete well with X-ray techniques for routine monitoring purposes. However the ability to interrogate filter samples quickly and to generate qualitative data is useful for certain fingerprinting or apportionment type studies.

Specialised mass spectrometry techniques continue to be used and developed for the determination of stable isotope composition in molecules such as CH₄,⁴¹ CO₂,^42–44 N₂O⁴² and O₃.⁴⁴

1.3 Method validation, standardisation and data quality

Often overlooked with filter based samplers is the inhomogeneity of particulate deposition. Dannecker and co-workers⁴⁵ analysed the radial distribution of elements collected on a 150 mm diameter filter from a high volume air sampler by subsampling and analysing by EDXRF. They found that elemental concentrations decrease 8–10% from the centre to the edge of the filter for coarse particulates and 2–4% for fine particulates. In a similar vein, for smaller diameter filters that fit directly into XRF instruments, consideration of the XRF beam profile is required.

An assumption often used in the analysis of filter samples by XRF and PIXE is that these samples can be considered as thin films. Orlic and co-workers⁴⁶ attributed discrepancies found between concentrations, as measured by PIXE, of lighter elements in particulate matter collected in a PM2.5 sampler and the lower stages of a single-orifice cascade impactor sampler to this assumption not holding true. They used optical and scanning transmission ion microscopic techniques to measure the density and thickness of these lower target stages in the impactor sampler and to calculate a thick-target correction factor for each of the elements in question.

Generation of filter samples for the calibration of X-ray techniques continues to interest a number of groups.^47–50 The approach is essentially the same in each laboratory. Aerosols are generated from standard solutions using various nebulisers, or jet spraying techniques are carried out. Filter loadings are determined (after generation of an instrument calibration) by an alternative technique such as ICP-AES.

It was disappointing to note the lack of sampling/instrumental intercomparisons reported as compared to previous years. However, workers at the GKSS institute in Geesthacht, Germany,⁵¹ carried out an international field intercomparision measurement of atmospheric mercury. Eleven laboratories took part and measured gaseous and particulate phase mercury as well as mercury in precipitation samples. Good agreement was found for measurements carried out on gaseous and precipitation samples but significant differences in the levels of particulate phase mercury were observed.

1.4 Future requirements

A study of the accompanying table demonstrates that many analysts rely heavily on a small range of certified reference materials such as NIST SRM 1648 (urban particulate matter). As highlighted in previous reviews there is a pressing need for new bulk reference materials and, more importantly, filter-based reference materials with more realistic loading and particle sizes. Some progress has been made such as the development of a road tunnel dust certified for PGE content and the production of new NIST materials. There is a need for more round robin trials to be carried out, although a number of laboratories, where possible, produce complementary data using alternative techniques.

As in other measurement fields, there is a need for speciation studies, particularly in the area of workplace air monitoring, where exposure to pollutants is generally higher than in ambient environments. Some work in this field has been carried out over the period of this review: investigation into operationally defined speciation protocols for Ni in ambient air⁵² and metals in electric furnace dust;⁵³ investigation into the potential role of metals associated with particulate matter to catalyse an oxidative stress;⁵⁴ and the use of SNMS to probe the surfaces of particulates.⁵⁵

There is a need to consider sampling technologies where mixed phase aerosols can exist, especially within a workplace setting. The challenge to sample concurrently gaseous and particulate phases can be illustrated by the work of a Canadian group.⁵⁶ They compared the performance of a quartz filter filtration system for the collection of particulate phase Hg against a similar filtration system fitted with a front ended denuder (gold coated) to remove gaseous phase Hg. The denuder based system gave higher results in parallel sampling trials. This they attributed to Hg-coated gold particles flaking off the denuder and ending up on the filter.

2 Water analysis

The application of atomic spectrometry to the analysis of water samples continues to produce a wide range of applications in the published literature. Papers published in this area in the last 12 months are summarised in Table 2. As with last year's environmental update,⁸⁴ a large proportion of the publications involve the development of techniques for preconcentrating the analyte prior to instrumental determination. Given the ever-decreasing detection limits of methods such as ICP-MS, the author cannot decide whether this trend is driven by a true analytical need or by the fact that the variety of methods available for preconcentration makes it a fruitful area to gain publications.

Table 2 Summary of the analyses of water

Element	Matrix	Technique; atomization; presentation^a	Sample treatment/comments	Ref.
a Hy indicates hydride and S, L, G and Sl signify solid, liquid, gaseous or slurry atomization, respectively. Other abbreviations are listed elsewhere.
Ag	Waste water	AA;MIP;L	ETA of small samples from W filament	204
Ag	Drinking water	AA;ETA;slurry	Separation and pre-concentration on N,N-diethylaminoepoxypropyl–crosslinked chitin chelate resin from solution buffered to pH 11 with NaOH. Resin re-suspended as slurry for analysis	112
Ag	Waste water	MS;ICP;L	Standard additions and sequential injection analysis	280
Al	Environmental water	MS;ICP;L	Speciation and size fractionation on-line with HPLC after chemical modification	177
As	Saline water	AA;ETA;L	Gaseous hydride generation used and dried using Nafion tube. Passed over negatively charged W or Pt electrode. Electrostatic deposition on atomizer. LOD 30 pg	148
As	Water	XRF;-;S	Different As species collected on specific metal loaded activated charcoals. LOD 0.02 mg l^−1	164
As	Mine water	MS;ICP;L	Ion chromatography used for speciation	157
As	Saline water	AA;-;L	Samples filtered and microwave digested. Mixed in FI system with buffered quinolin-8-ol–sulfonic acid before sorption onto alumina column. HCl used for separation and desorption	281
As	Saline water	AA;-;L	Speciation method using chelation with quinolin-8-ol–5-sulfonic acid, separation using alumina micro-column. HCl used as eluent and coupled into HG system	282
As	Saline water	AA;ETA;L	Gaseous hydride generation mixed with He flow used with in-furnace trapping. LOD 14 pg ml^−1	149
As	Environmental and drinking water	AE;ICP;L	As speciation carried out using chemical pre-treatment and hydride generation. LOD 1 µg l^−1	155
As	Environmental water	MS;ICP;L	Capillary electrophoresis used for speciation	161
As	Saline water	MS;ICP;L	Collision/reaction cell to used to remove chloride interference	246
As	Saline water	MS;ICP;L	Ion chromatography used for speciation. Ultrasonic nebulisation and membrane desolvation aided sensitivity	158
As	Water	AA;-;L	Speciation using FI-hydride generation	152
As	Saline water	MS;ICP;L	Na and Ca removal by cation exchange column and collision cell used to remove chloride interference	283
As	Environmental water	FID;GC;L	Speciation study performed using complexation with buffered thioglycollic acid methylester and extraction with cyclohaxane prior to analysis	284
As	Drinking water	AA;ETA;L	As^III and As^V speciation carried out. As^III complexed with 2,3 dimercaptopropane-1-sulfonate, separated on Sep-Pak C18 cartridges and eluted with methanol. As^V reduced to As^III with L-cysteine before separation. LOD As^III0.11 µg l^−1 and As^V 0.15 µg l^−1	162
As	Water	AA;-;L	Methodology for quantification of 6 species using HG described	153
As	Water	AA;F;L	HG sample introduction used with electrolytic flow through cell	145
As	Environmental water	AA;-;L	Speciation carried out using HG coupled with GC before determination	285
As	Saline and environmental water	MS;ICP;L AF;Hy;L	Comparison of speciation using HPLC-HG with both detectors carried out	156
As	Environmental water	AA;-;L	Speciation performed using microwave assisted distillation and hydride generation	143
As	Environmental water	AA;-;L	Speciation methodology using HCLO4 reaction matrix described	154
As	Environmental water	AA;ETA;L	W-coated furnace used with large 100 µl sample and Pd chemical modifier	286
As	Environmental water	MS;ICP;L	HG sample introduction used thiourea for improved sensitivity. LOD 0.02 µg l^−1	150
As	Water	MS;ICP;L	Speciation carried out using ion chromatography	187
As	Water	MS;ICP;L	Use of collision/reaction cell to remove chloride interference	250
Au	Saline water	AA;F;L	Separation and preconcentration carried out in xylene using diethyldithiophosphate as complexing agent. LOD 2.9 ng l^−1	287
B	Water	MS;ETA;L	Conversion to sodium metaborate carried out prior to loading on filament for isotopic analysis	288
Be	Environmental water	AA;ETA;L	Calcium used as matrix modifier	289
Be	Drinking water	AA;ETA;L	Determinand chelated with acetylacetone and separated onto Sep-Pak C18 cartridge. Chelate eluted with methanol. LOD 0.23 ng	133
Bi	Saline water	AA;ETA;L	Mo chemical modifier used	290
Bi	Environmental water	AE;ICP;L	Effects of various acids on HG tested with respect to efficiency and minimisation of interferences. LOD 0.3 µg l^−1	291
Br	Environmental water	TXRF;-;L	Bromate ions separated by ion chromatography and dried onto quartz substrate	189
Br	Drinking water	MS;ICP;L	Coupled ion chromatography used to separate bromate	186
Br	Water	MS;ICP;L	see As, ref. 187	187
Br	Environmental water	MS;ICP;L	Comparison of techniques made when coupled to ion chromatography for determination of bromate	292
Br	Water	MS;ICP;L	Comparison of ion chromatography coupled to different detection systems	188
C	Saline water	AMS;-;-	Tandem type AMS developed for determination of ^14C	276
Ca	Water	AE;F;L	LOD 0.5 µg ml^−1	293
Cd	Saline water	AA;ETA;L	Two-step graphite furnace developed. First stage used a transverse heated vaporiser linked to a second end-heated atomizer. Background absorption interferences reduced	212
Cd	Saline water	MS;ICP;L	Sample mixed with HCl and thioacetamide and isotope dilution spikes. ETA sample introduction used	247
Cd	Water	AA;ETA;L	Sample mixed with 5-sulfo-8-hydroxyquinoline followed by separation and pre-concentrated on C18 silica gel column. LOD 0.7 ng l^−1	129
Cd	Waste water	AA;MIP;L	see Ag, ref. 204	204
Cd	Saline water	AA;ETA;L	Muromac A-1 chelating resin used for matrix separation and preconcentration. Elution using HNO3. LOD 1.2 × 10^−4 µg l^−1	294
Cd	Environmental water	AA;ETA;L	Separation and preconcentration using anion ion chromatography	295
Cd	Drinking water	AA;ETA;L	Custom made W coil atomiser used. LOD 0.2 l^−1	206
Cd	Drinking water	AA;F;L	Buffered samples complexed with ammonium diethyldithiophosphate and separated on C18 silica column. Eluted with ethanol	130
Cd	Snow	MS;ICP;L	Magnetic sector spectrometer used in low resolution mode for best sensitivity	242
Cd	Environmental water	AA;ETA;L	Speciation using multiple column system and flow injection	197
Cd	Saline water	AA;ETA;L	(NH4)2HPO4 and NH4NO3 chemical modifiers used with 20 µl sample injection. LOD 0.005 µg l^−1	214
Cd	Waste water	MS;ICP;L	See Ag, ref. 280	280
Cd	Environmental and saline water	AA;ETA;L	Co-precipitation with Ni–diethyldithiocarbamate from buffered sample. Precipitate dissolved in HNO3 + acetone	296
Cd	Environmental water	AE;ICP;L	Sample pre-concentrated by evaporation	297
Cd	Saline water	AA;ETA;L	On-line preconcentration used by sorption of Cd-APDC complex onto C18 micro-column and elution with ethanol. LOD 0.5 ng l^−1	132
Cl	Environmental water	AMS;-;L	δ^36Cl ratios measured for atmospheric tracer studies	277
Cl	Water	AE;ICP;L	Use of far UV (134–136 nm) lines made sub-ppm detection possible	298
Co	Saline water	AA;ETA;L	See Cd, ref. 294	294
Co	Environmental water	AA;ETA;L	Preconcentration carried out using sorption in knotted reactor precoated with 1-phenyl-3-methylbenzoylpyrazol-5-one	119
Co	Environmental water	AA;F;L	Sample solution mixed with Nitroso-R salt + cetyltrimethylammonium bromide and buffered. Benzophenone added and solid collected. Solid dissolved in ethanol for analysis. LOD 3.9 ng ml^−1	299
Co	Saline water	AA;ETA;L	Preconcentration using 8-quininol and Ni co-precipitation carrier with 1-nitroso-2-naphthol auxiliary complexation. Direct solid analysis used. LOD 1 ng l^−1	139
Cr	Drinking water	AA;F;L	Simultaneous preconcentration of Cr^VI and Cr^III species on C18 column and sorption loop. Separated carried out at elution stage.	300
Cr	Water	MS;ICP;L	Automated column chelation system for speciation described	171
Cr	Environmental water	AA;F;L	Speciation carried out using melamine–urea resin. Cr^VI eluted with sodium acetate. Cr^III determined by difference after oxidation	165
Cr	Water	MS;ICP;L	Solid phase chelation column technique used for speciation	172
Cr	Water	MS;ICP;L	Dual membrane on-line system for simultaneous extraction of Cr^III and Cr^VI species	301
Cr	Drinking water	AA;ETA;L	Transverse atomiser used	302
Cr	Waste and saline water	AA;ETA;L	Selective flow injection of Cr^VI using solvent extraction IBMK + APDC	303
Cr	Drinking and environmental water	MS;ICP;L	Ion chromatography used to speciate Cr^III from Cr^VI	173
Cr	Saline water	AA;F;L	Species separated into different chelating agents, then removed from the matrix by micelle formation of surfactants	168
Cr	Environmental water	AA;ETA;L	Speciation performed using acidic activated alumina columns	170
Cr	Environmental and saline water	AA;ETA;L	Samples pre-concentrated by precipitation with quinolin-8-ol, Pd and tannic acid. LOD 20 ng l^−1	138
Cr	Environmental water	AA;ETA;L	Speciation study using chelation/extraction of Cr^VI with APDC	169
Cr	Water	MS;ICP;L	See As, ref. 187	187
Cr	Waste water	AA;-;L	Preconcentration and speciation carried out using complexation with EDTA and separation on SAX resin followed by elution with aqueous NaCl	166
Cu	Environmental water	AA;ETA;L	Novel atomisation source used which allowed sequential metal vapour elution into a gas stream	203
Cu	Water	AA;ETA;L	See Cd, ref. 129	129
Cu	Drinking water	AA;ETA;L	See Cr, ref. 302	302
Cu	Drinking water	AA;ETA;L	See Cd, ref. 206	206
Cu	Environmental water	AA;F;L	Separation and preconcentration performed using XAD-2 column loaded with calmagite	114
Cu	Drinking water	AA;F;L	See Cd, ref. 130	130
Cu	Saline water	AA;F;L	Separation performed on-line using XAD-2 resin followed by elution with HCl	117
Cu	Saline water	AA;ETA;L	Ammonium nitrate as chemical modifer. Injection 20 µl aliquot. LOD 0.06 µg l^−1.	214
Cu	Environmental water	AA;F;L	See Co, ref. 299	299
Cu	Saline water	AA;F;L	Buffered sample complexed with 1-nitroso-2-naphthol with separation on RP-C18 micro-column and eluted with ethanol. LOD 2 µg l^−1	131
Fe	Environmental water	AA;-;L	Relationship between Fe and Mn concentrations and turbidity investigated	304
Fe	Environmental water	AA;F;L	See Co, ref. 299	299
Fe	Drinking and environmental water	MS;ICP;L	Selective determination of Fe^III by on-line formation and sorption of pyrrolidine carbodithionate complex in knotted reactor followed by elution with HNO3	201
Hg	Water	AE;ICP;L	Separation and preconcentration carried out using quinine impregnated cation exchange resin. Gas phase analysis performed using HG	305
Hg	Drinking water	MS;ICP;L	Use of Au as a routine long term preservative investigated	104
Hg	Saline water	MS;ICP;L	See Cd, ref. 247	247
Hg	Saline water	AA;-;L	FI and HG sample introduction. Air segmentation used to reduce reagent consumption. LOD 0.1 µg l^−1	146
Hg	Environmental water	AA;CV;L	Separation and preconcentration of species using 2-mercaptobenzothiazole loaded onto Bio-Beads. LOD 10 ng l^−1	123
Hg	Water	AF;ETA;L	Miniature system for field use described	306
Hg	Environmental water	AA;CV;L	Extraction using dithizone in CHCl3. Various pretreatments for speciation investigated	198
Hg	Environmental water	AA;CV;L	Separation from HCl acidified water carried out using polyamide resins and elution with thiourea	124
Hg	Saline water	MS;ICP;L	ID coupled with vapour generation to minimise interferences while maximising sensitivity and accuracy	307
Hg	Saline and drinking water	AA;CV;L	Various dithioacetal derivitives synthesised and immobilised on silica gel. Hg^II sorption properties evaluated	125
Hg	Water	AA;ETA;L	Separation and preconcentration carried out prior to analysis	308
I	Water	AA;ETA;L	Separated as ion pair followed by indirect determination of I^− through quantification of Hg	208
I	Water	AE;ICP;L	Speciation study using chemical separation and vapour generation	184
I	Rain water	AMS;-;-	^129I determined	278
I	Saline water	AMS;-;-	See C, ref. 276	276
In	Saline water	AA;ETA;L	See Bi, ref. 290	290
In	Environmental water	AA;ETA;L	Solvent extraction used with buffered 5-sulfo-8-quinolinol and zephiramine	309
Mn	Saline water	AA;ETA;L	Separation and preconcentration carried out on Chelex-100 resin. Interference correction performed using multiple linear regression techniques	213
Mn	Environmental water	AA;ETA;L	See Cu, ref. 203	203
Mn	Environmental water	AA;-;L	See Fe, ref. 304	304
Mo	Environmental and saline water	MS;MIP;L	ID determination used after 8-hydroxyquinoline separation	266
Ni	Saline water	AA;ETA;L	Optimisation carried out on-line micro-column separation using chelation on 1-(di-2-pyridyl)methylene thiocarbonohydrazide modified silica gel. LOD 0.06 ng ml^−1	111
Ni	Environmental and saline water	MS;ICP;L	ID and separation from matrix as volatile metal carbonyl used to maximise accuracy and minimise interference	258
Ni	Saline water	AA;ETA;L	See Cd, ref. 294	294
Ni	Saline water	AA;F;L	Complexation using dimethylglyoxime and separation on C18 column. Elution using ethanol containing HNO3	310
O	Soil water	MS;-; L	Samples equilibrated with CO2 prior to analysis	273
P	Environmental water	MS;ICP;L	Coupled capillary zone electrophoresis methods developed for speciation	199
Pb	Saline water	AA;ETA;L	See Cd, ref. 212	212
Pb	Drinking water	AE;ICP;L	Dithiocarbamate complex collected in PTFE knotted reactor and desorbed with HCl. Ultrasonic nebulisation used to increase sensitivity. LOD 0.2 ng ml^−1	128
Pb	Environmental water	AA;ETA;L	Electrochemical preconcentration used with W coil for subsequent ETA sample introduction	215
Pb	Saline water	MS;ICP;L	See Cd, ref. 247	247
Pb	Saline water	AA;ETA;L	See Bi, ref. 290	290
Pb	Environmental water	MS;ICP;L	Isotope ratios directly measured using ultrasonic nebulisation for improved sensitivity and magnetic sector instrument for best precision	256
Pb	Water	AA;ETA;L	See Cd, ref. 129	129
Pb	Environmental water	AA;F;L	See Cd, ref. 295	295
Pb	Drinking water	AA;ETA;L	See Cd, ref. 206	206
Pb	Drinking water	AA;F;L	See Cd, ref. 130	130
Pb	Drinking water	AA;ETA;L	Comparison of drinking water Pb with that found in bone	311
Pb	Water	AA;F;L	Speciation study carried out using complexation with diethyldithiocarbamate and separation on C60 column	194
Pb	Snow	MS;ICP;L	See Cd, ref. 242	242
Pb	Environmental water	AA;-;L	Samples treated with acetic media, sorbed onto C60 columns as dithiocarbamate complexes and eluted with IBMK	195
Pb	Water	MS;ES;L	Coupled separation of species using in-tube solid phase micro-extraction and HPLC.	196
Pb	Water	AA; ETA;L	Thermal desorption of tetraethyl species from solid phase micro-extraction fibres described	118
Pb	Environmental water	MS;ICP;L	Improved isotope ratio measurements made through the use of a hot–cold tandem spray chamber arrangement	255
Pb	Waste water	MS;ICP;L	See Ag, ref. 280	280
Pb	Saline water	MS;ICP;L	Mg(OH)2 co-precipitation used for separation and preconcentration	260
Pd	Snow	MS;ICP;L	Double focusing magnetic sector instrument allowed exceptional sensitivity	241
Pt	Snow	MS;ICP;L	See Pd, ref. 241	241
REE	Environmental water	MS;ICP;L	Ultrasonic nebulisation used for sensitivity.	312
Rh	Snow	MS;ICP;L	See Pd, ref. 241	241
Ru	Environmental and waste water	AA;ETA;L	Co-precipitation with chitosan at pH 8 for preconcentration followed by re-dissolution in acetic acid	136
S	Saline water	MS;ICP;L	Collision/reaction cell used to reduce polyatomic interferences. Isotope ratios determined	313
Sb	Saline water	AA;ETA;L	See As, ref. 148	148
Sb	Water	AA;F;L	See As, ref. 145	145
Sb	Water	AF;Hy;L	Speciation using HPLC and hydride generation	192
Sb	Drinking water	MS;ICP;L	On-line HPLC used to separate Sb^III and Sb^V using a phthalic acid–EDTA mobile phase on a silica based anion exchange column. LOD Sb^III 30 pg for 100 µl and Sb^III 10 pg for 100 µl	72
Sb	Environmental water	MS;ICP;L	Speciation study performed using HG sample introduction and magnetic sector instrument for improved sensitivity. LOD Sb^III 4.2 ng l^−1 and Sb^V 17 ng l^−1	191
Sb	Environmental water	MS;ICP;L	Speciation carried out using HPLC separation	193
Se	Saline water	AA;ETA;L	See As, ref 148	148
Se	Saline water	AA;ETA;L	See As, ref. 149	149
Se	Environmental water	AA;-;L	Se speciation performed using chemical pre-treatment and HG. LOD 0.5 µg l^−1	178
Se	Environmental water	MS;ICP;L	See As, ref. 161	161
Se	Saline water	MS;ICP;L	See As, ref. 158	158
Se	Water	AA;F;L	See As, ref. 145	145
Se	Water	AF;Hy;L	A LC-UV-HG coupled system for speciation described	181
Se	Water	AA;ETA;L	Speciation study with complexation by pyrrolidine dithiocarbamate and sorbtion onto C18 micro-column followed by elution using ethanol. LOD 4.5 ng l^−1	314
Se	Saline water	AA;ETA;L	Chemical interference study carried out	211
Se	Water	AA;ETA;L	Analysis performed using standard additions method.	315
Se	Waste water	AF;Hy;L	Speciation study using coupled FIA and HG, both on and off-line, described	182
Se	Water	MS;ICP;L	ID and ETA sample introduction used for improved accuracy and sensitivity and for removal of interferences	316
Se	Environmental water	MS;ICP;L	See As, ref. 150	150
Se	Waste water	MS;ICP;L	Anion exchange columns tested for suitability in speciation studies.	317
Se	Water	MS;ICP;L	See As, ref. 250	250
Sn	Saline water	AA;ETA;L	Sn separated from matrix by hydride generation. LOD 130 ng l^−1	147
Sn	Environmental and waste water	AA;ETA;L	Organo species separated with toluene in presence of acetic acid and NaCl. Hot injection and chemical modification used for analysis.	318
Sn	Water	AA;-;L	Organic species ethylated and extracted into hexane. Speciation performed using coupled gas chromatography	175
Sn	Environmental, waste and saline water	AA;ETA;L	Speciation study carried out by chemical separation	174
Sn	Environmental water	AA;ETA;L	Separation and preconcentration of tributyl species, using tropolone sorbed onto XAD-2 resin, described	176
Te	Environmental and drinking water	AA;F;L	Pulsed flame system with quartz tube atom trapping described	319
Tl	Saline water	MS;ICP;L	ID and HG used for improved accuracy and minimisation of matrix effects	257
Tl	Saline water	MS;ETA;L	ID used to demonstrate existence of dimethyl species	200
U	Environmental water	MS;ICP;L	Cellulose based chelating resin used for separation and preconcentration of the determinand. Problems of organic complexation in the sample considered	320
V	Snow	MS;ICP;L	See Cd, ref. 242	242
Zn	Environmental water	AA;F;L	Preconcentration carried out from acidic media (pH 3) as thiocyanate complex onto polyurethane foam. Determinand eluted using acetone + HNO3. LOD 0.85 µg l^−1	140
Various	Saline water	MS;ICP;L	Sample mixed with buffered bis(2-hydroxyethyl)dithiocarbamate and complexes sorbed onto C18 resin. Metals eluted with methanolic HNO3. LODs typically pM	127
Various	Environmental water	MS;ICP;L AF;-;L	On-line serially coupled Sephadex A-25, Chelex 100 and Dowex 1X8/Chelamine Metalfix used to separate and pre-concentrate and determine metal–humic complexes and free metal ions	321
Various	Saline water	AA;ETA;L	Elements electroplated onto graphite probes at various pH and voltage conditions. Cr^III and Cr^VI speciation performed. LOD Cr^III 14 ng l^−1 and Cr^VI 17 ng l^−1	134
Various	Saline water	MS;ICP;L	Normal sample introduction used but spectrometer fitted with high sensitivity interface	261
Various	Water	AE;ICP;L	Separation and preconcentration using iminoacetate–agarose absorbent	322
Various	Environmental water	XRF;-;L AE;ICP;L	Amidoxime chelating groups bound to poly (acrylnitrile) textile, used to separate various traces. Elemental determination carried out by either direct XRF analysis or after extraction in 1% HNO3 for ICP-AES	141
Various	Environmental water	AE;ICP;L	Low TDS samples allowed the use of ultrasonic nebulisation. Array detector spectrometer gave simultaneous spectral background correction	323
Various	Environmental water	MS;ICP;L	Field flow fractionation used to study colloid size fractions.	324
Various	Saline water	MS;ICP;L	Dithiocarbamate complexation and separation on phenyl column described with elution of determinands with HNO3	126
Various	Environmental water	MS;ICP;L	Multi-element standard additions methodology described	262
Various	Water	MS;ICP;L	Review covering detection and speciation of metals presented	325
Various	Drinking water	MS;ICP;L	Performance test of technique using NS-30 protocol.	326
Various	Environmental and drinking water	AA;ETA;L	System for simultaneous elemental determinations described	205
Various	Saline water	MS;ICP;L	Batch separation and preconcentration using Chelex 100 resin performed	105
Various	Water	MS;ICP;L	FIA system for on-line dilution described	327
Various	Environmental water	MS;ICP;L	Method for producing semi-quantitative data using chemometrics described	328
Various	Water	MS;ICP;L	Evaluation of an axial TOF type instrument described	329
Various	Saline water	MS;ICP;L	A comparison of imminodiacetate and 8-hydroxyquinoline micro-columns for matrix separation and analyte preconcentration was made	107
Various	Environmental water	MS;ICP;L	Evaluation of TOF spectrometer for transient signals, in particular when coupled to GC, described	330
Various	Environmental water	AA;F;L AA;ETA;L AE;ICP;L	National water quality survey presented	331
Various	Environmental water	AE;GC;L	Solid phase microextraction used to collect and separate organometallic species	332
Various	Environmental water	AE;ICP;L AA;ETA;L AA;F;L	Well water quality assessment study carried out	333
Various	Saline water	MS;ICP;L	Multivariate calibration technique developed to correct for interferences	248
Various	Saline water	MS;ICP;L	Strategies for coping with saline matrices described	245
Various	Water	MS;ICP;L	Capillary electrophoresis used to study metal–humic substance binding	334
Various	Water	MS;ICP;L	Advantages of magnetic sector instruments over quadrupole instrument discussed	253
Various	Environmental water	MS;ICP;L	Influence of filtration on the analysis of crystalline bedrock groundwater tested	102
Various	Environmental water	AA;F;L	Functionalization of XAD-2 resin with chromotropic acid for preconcentration of metals described	120
Various	Saline water	MS;ICP;L	Description of on-line separation and preconcentration using buffered samples and Metpac-CC1 column given	106
Various	Ultra-pure water	MS;ICP;L AA;F;L AA;ETA;L	Review of blank optimisation for elemental analysis presented	98
Various	Water	AE;ICP;L	Tedlar bags tested and found suitable for sampling and storing water. Minimal absorption of six trace elements found over a wide pH range	100
Various	Water	MS;ICP;L	Coupled ion chromatography to used to separate anions. Ultrasonic nebuliser with desolvation improved sensitivity	185
Various	Environmental and waste water	AA;F;L	Determinands pre-concentrated on 5-amino-1,3,4-thiadiazole-2-thiol modified silica gel and eluted with HCl	121
Various	Environmental water	MS;ICP;L	Influence of bottle type and acid washing on trace element analysis investigated	101
Various	Saline water	XRF;-;L	Electro-deposition of analytes on pure Nb disk carried out prior to analysis	231
Various	Saline water	TXRF;-;L	Samples pre-concentrated by precipitation as dithiocarbamates. Precipitate deposited on filter for direct analysis	237
Various	Environmental water	-;ICP;L	Isocratic separation of cations and anions performed on CS12 and AS14 columns using methanesulfonic acid and NaHCO3	335
Various	Environmental water	AA;F;L	Chemical modification used to reduce interferences	336
Various	Environmental water	MS;ICP;L	Magnetic sector instrument used to avoid interferences	254
Various	Environmental water	XRF;-;L	PIXE analysis of freeze dried water residues used for characterisation of pollution	337
Various	Drinking water	XRF;-;L	Total reflectance form of technique used.	228
Various	Water	XRF;-;L	Micro-analysis using ultra-thin droplets on low scattering substrate described	232
Various	Ultra-pure water	MS;ICP;L	Routine analysis used standard additions method	99
Various	Water	MS;ICP;L	Water quality testing application described	338
Various	Water	MS;ICP;L	Separation and preconcentration carried out with iminodiacetate chelation. Improved sample throughput achieved using air-segmented FI sample introduction	339
Various	Saline water	MS;ICP;L	FI and chelating resin columns used for matrix removal and preconcentration	340
Various	Saline water	MS;ICP;L	La co-precipitation used for separation and preconcentration of hydride and oxyanion forming elements	341
Various	Saline water	AA;ETA;L	Coupled HG used for simultaneous determination of As, Bi, Se and Sn	342
Various	Environmental water	MS;ICP;L	Ultrasonic nebulisation and magnetic sector instrument used for high sensitivity determinations	243
Various	Environmental water	MS;ICP;L	Comparison of Norwegian groundwater concentrations with health limits made	264
Various	Saline water	MS;ICP;L	Evaluation of interferences, internal standardisation and standard addition analysis reported	244
Various	Water	XRF;-;L	Asymmetric flow field flow fractionation used to separate collodial humic substances prior to analysis	343
Various	Water	MS;ICP;L	Separation carried out using TRU-SPEC resin	110
Various	Saline water	MS;ICP;L	Evaluation of three column materials; basic alumina, iminodiacetate and nitrotriacetate carried out. On the basis of throughput, matrix elimination and recovery	108
Various	Snow water	MS;ICP;L	Cold plasma conditions used to avoid interferences and sensitivity of microconcentric nebuliser allowed determination of major elements	240
Various	Environmental water	XRF;-;L	Droplet of water evaporated onto polymer film for analysis	233
Various	Environmental water	TXRF;-;L	Samples evaporated onto siliconized quartz carrier with internal standard	227
Various	Waste water	AE;MIP;L	Analytical system developed for on-site monitoring	226
Various	Water	AE;ICP;L	Matrix effects from Ca and Na studied in an axial plasma	221
Various	Water	AA;ETA;L	Review of the application of Zeeman graphite furnace AA in chemical laboratories and toxicology applications presented	344

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The other main area of work, for which there is a clearly defined need, and which is producing an ever increasing number of publications is that of speciation. There have been some significant advances in producing more robust methods for speciation and the variety of metal/non-metal species that have been identified and quantified has shown a marked increase over the period of this review.

ICP-MS continues to be the dominant instrumentation used for water analysis. More emphasis has been put on understanding and removing isobaric interferences from molecular ions by the use of techniques such as matrix removal, collision cells and the use of high resolution instruments.

Conspicuous by their absence have been the lack of papers addressing the area of data quality. Although there are many water CRMs certified for total element concentrations, the lack of RMs for speciation studies has not been addressed in the literature covered in this review.

2.1 Sample preparation

2.1.1 Reagents. For ultra-trace analysis of water samples it is essential that ultra-pure water is used for the preparation of standards and blanks. Dabouret et al.^96–98 describe the operation of the latest Milli-Q™ ultra-pure water system, the methods used for the removal of difficult impurities such as B and Si, and have reviewed methods for analysis ultra-pure water. Hoelzl et al.⁹⁹ have outlined how ICP MS can be used to routinely check the quality of ultra-pure water.

2.1.2 Sample collection and preservation. The collection and storage of water samples must be designed so that modifications of their chemical composition through contamination or loss of analytes are minimised. The use of Tedlar bags for the collection of water samples was investigated.¹⁰⁰ Under low pH conditions the bags showed no measurable adsorption from 100 ppb solutions over 24 h. The effect of bottle type and acid washing on trace element analyses of water samples by ICP-MS was investigated.¹⁰¹ Four bottle types and 62 elements were covered by the study. Final recommendations suggested that the best procedure was to use factory new, unwashed HDPE bottles. The same author¹⁰² investigated the influence of filtration on the concentrations of 62 elements analysed by ICP-MS in groundwater samples from 15 selected wells in crystalline bedrock. Analysis of unfiltered and filtered samples was compared (<0.45 µg and <0.1 µg). Differences between filtered and unfiltered samples were noticeable but generally small. Results for Sn, however, suggested that filtration was introducing significant contamination. Differences between <0.45 µm and <0.1 µm filtered samples were generally negligible.

The chemical stability of large organic molecule metal complexes dissolved in natural water were investigated by on-line size exclusion chromatography ICP-MS. Acidification of the samples with HNO₃ was found to have a marked effect on the size exclusion chromatograms. The partitioning of major to ultra-trace elements in coastal sea-water sequentially filtered to 0.45 µg and subsequently ultra-filtered to a molecular weight permeation limit of 10 000 Da was investigated by analysing the particulates and filtrates obtained at each stage using a combination of ICP-AES and ICP-MS.¹⁰³ A detailed account of the fractionation of a wide range of metals is given. Hg is well known for its ability to ‘plate-out’ onto the walls of sample storage containers. Fateman et al.¹⁰⁴ carried out a study in which they found that the addition of AuCl was an effective preservative reagent for Hg in potable water up to a concentration of 1 µg l⁻¹ when using either glass or poly(ethylene terephthalate) containers. Although this preservative reagent is acceptable for ICP-MS determination, AuCl is known to cause a severe suppressive interference when used with CVAFS, a widely used methodology for Hg determination.

2.1.3 Preconcentration and separation procedures. As previously discussed, preconcentration of the analyte prior to atomic spectrometry measurement is a preoccupation of many research groups working in water analysis. Apart from reasons expressed earlier in this review, this may be explained by the fact that the preconcentration step is often accompanied by separation of the analyte from the sample matrix, which is often more important, in terms of the reduction in interference effects, than the increase in sensitivity from the preconcentration.

Solid phase microextraction methods (SPME) are one of the most popular preconcentration techniques. This relates to the ready availability of proprietary solid phase adsorbents and the ease with which the technique can be interfaced to on-line, automated systems. This methodology divides into two areas: direct methods, in which the target analyte or species is reversibly adsorbed or complexed onto the solid substrate which is designed to be element/species specific; and indirect methods, where the target analyte is complexed in solution (often with an organic reagent) and adsorbed onto a solid substrate designed for adsorption of organic compounds e.g., C₁₈ silica columns.

A wide range of direct SPME preconcentration methods have been reported. In a batch adsorption approach for multi-element preconcentration,¹⁰⁵ sea-water was mixed with Bio-Rad Chelex 100 resin and, following filtration and washing of the resin, the analytes were eluted with 2 M HNO₃. Thirty-three elements were determined by ICP-MS with a preconcentration factor of 41.7. Using an on-line method, chelation ion chromatography¹⁰⁶ was used to preconcentrate 17 trace elements using an iminodiacetate (IDA) chelating resin. A comparison of mini-columns¹⁰⁷ prepared from IDA resin and 8-hydroxyquinoline immobilised on a microporous silica frit showed that both types were suitable for on-line ICP-MS preconcentration, although the latter gave slightly shorter analysis times. Other work using preconcentration with IDA resin followed by ICP-MS analysis include a comparison with basic alumina and nitrotriacetate adsorbents¹⁰⁸ and a FI on-line system with an IDA-agarose column. Tetsushi et al.¹⁰⁹ used an on-line nitrilo-triacetate resin adsorbent and Truscott et al.¹¹⁰ used an actinide specific resin for actinides in their ICP-MS applications. In applications using AES, Hg was preconcentrated on a new quinine impregnated cation exchange resin before elution and HG introduction into the ICP. Chlorinated organic compounds were collected on an organic-specific solid phase extraction cartridge prior to GC separation and MIP AES determination. A number of ET-AAS methods with SPME have also been published. Co and Ni were preconcentrated from a sea-water matrix with a Muromac A-1 micro-column built into the tip of the auto-sampler. A similar idea was used by Siles Cordero et al.¹¹¹ who used a silica gel chelating resin functionalised with 1-(di-2-pyridyl)methylene thiocarbonohydrazide in the auto-sampler head to separate and preconcentrate Ni from sea-water. SIMPLEX optimisation was used to obtain the best furnace operating conditions. Slurried chelating resin (N,N-diethylaminoepoxypropyl-crosslinked chitin) bound to Ag extracted from tap water was directly injected into the graphite furnace prior to determination.¹¹² Filter discs (3 mm diameter) supporting finely pulverised anion-exchange resin with Bromopyrogallol Red as the chelating resin were used to preconcentrate Sb from river water. The discs were analysed directly in the specially designed graphite furnace with Zeeman background correction.¹¹³ FAAS, although less fashionable, has not been ignored. Element/species specific applications have used solid phase adsorbents for Cu,^114,115 Pb^116,117 and tetraethyllead.¹¹⁸ The performances of APDC, 8-hydroxyquinoline, 1-phenyl-3-methyl-4-benzoylpyrazol-5-one and 2-nitroso-1-naphthol-4-sulfonic acid were compared as chelating reagents for Co. The chelates were pre-coated onto the walls of a PTFE knotted reactor in a FI manifold. The best chelating reagent was found to be 1-phenyl-3-methyl-4-benzoylpyrazol-5-one, giving a 28-fold enrichment.¹¹⁹ Other FAAS applications have developed multi-element preconcentration methods: Cd, Co, Cu, Fe, Ni and Zn;¹²⁰ Cu^II, Fe^III, Hg^II, Ni^II, Pb^II and Zn^II;¹²¹ and Cd, Co, Fe, Ni and Zn.¹²² CVAAS methods for Hg include the use of 2-mercaptobenzothiazole loaded Bio-Beads SM-7 to separate and preconcentrate inorganic and alkylmercury species¹²³ and polyamide resin for inorganic Hg;¹²⁴ silica gel immobilised dithioacetal derivatives have been used for for Hg^II.¹²⁵

Indirect SPME preconcentration methods have also been reported but are not as numerous as their indirect counterparts. Preconcentration of metals from sea-water has been used in a number of applications. Klemm et al.¹²⁶ preconcentrated 10 metals (Cd, Co, Cu, Fe, Mn, Ni, Pb, Tl, U and Zn) by the addition of NaDDC and APDC to form an organic complex which was adsorbed onto a phenyl column. HNO₃ was used to elute the metals prior to ICP-MS analysis. Wells et al.¹²⁷ used bis-(2-hydroxyethyl)dithiocarbamate as their complexing reagent and a polystyrene based hydrophobic C₁₈ resin as the solid phase extractant. They obtained pM detection limits for Cd, Co, Cu, Fe, Ni and Zn using high resolution ICP-MS for the final determination. Arsenic was preconcentrated from sea-water using quinolin-8-ol-5-sulfonic acid as the complexing reagent and activated alumina as the adsorbent with final As quantification by HGAAS. Various combinations of complexing reagents, solid phase adsorbents and As method have been used for Cd, Cu and Pb.^128–132 Ni has been determined using a dimethylglyoxime complexing reagent in a FI manifold with a C₁₈ column for preconcentration and FAAS for quantification. Peng et al.¹³³ preconcentrated Be from drinking water as its acetylacetone complex prior to ETAAS determination.

In ETAAS applications the graphite atomisation cell can be used as a suitable substrate for direct preconcentration. Electrodeposition onto a graphite ridge probe was used to pre-concentrate Cd, Cr, Cu, Ni and Pb from sea-water¹³⁴. Oreshkin et al.¹³⁵ preconcentrated metals onto a micro-column crucible that was subsequently used as the ET atomiser.

Hydride and oxoanion forming elements were coprecipitated from sea-water with La and, after separation and dissolution, were determined by ICP-MS. In applications using ETAAS determinations of dissolved co-precipitates, Minamisawa et al.¹³⁶ used chitosan to co-precipitate Ru, and Oh et al.¹³⁷ reacted Co and Cu with Nitroso-R and cetyltrimethylammonium bromide and co-precipitated the resultant complexes with benzophenone. Other workers^138,139 used direct solid sampling of the co-precipitate to determine Cr and Co respectively, by ETAAS.

A number of less conventional preconcentration methods and substrates have also been reported. Zn was preconcentrated from acidic medium as its thiocyanate complex onto a foam mini-column placed in the loop of a four-way valve and eluted with 30% acetone in 2% HNO₃ into a FAAS system for quantification.¹⁴⁰ McComb and Gesser¹⁴¹ used amidoxime chelating groups covalently bound to the surface of a textile encased in a 35 mm XRF slide holder. The slide holder was placed in the water to be analysed to complex the metals of interest and removed for XRF determination. Comparisons of the results with ICP-AES showed good correlations with those elements having a high complex stability constant (e.g., Pb) and poor agreement for low stability constant complexes (e.g., Mg). They concluded that the method could be used for fast semi-quantitative analysis of trace metals in water. Romero-Gonzalez et al.¹⁴² used a micro-column packed with dealginated seaweed biomass to carry out on-line preconcentration of Cd^II, Cr^III, Cu^II, Pb^II and chemical speciation of Cr^III and Cr^VI. The method was validated using two Lake Ontario reference waters, TMDA 51.2 and TMDA 54.2. Microwave assisted distillation was used in conjunction with HG-AAS to separate inorganic As species from natural waters from Chile.¹⁴³ It was shown that the method was statistically indistinguishable from an ion-exchange HG-AAS method and provided a simple and inexpensive method for preconcentrating As from water samples. A novel liquid–liquid extraction methodology for organotin compounds has been described by Eberhardt et al.¹⁴⁴. A 5 µl volume of sample was successfully processed in a containerless environment, using acoustic levitation.

2.1.4 Hydride generation methods. HG as a method for sample introduction, continues to be used widely in AS applications involving the analysis of waters. A number of these have been reported in other parts of this review. This section brings together new developments in the HG process and other HG applications that have not been reviewed elsewhere.

Laborda et al.¹⁴⁵ described a new electolytic process of producing hydrides using a low dead volume flow through cell. Coupled to a flame heated quartz tube, As, Se and Sb were determined by AAS with low ng ml⁻¹ detection limits.

Other HG applications involving AAS determination have also been reported. A low-consumption air-segmented sequential-injection HG method for Hg determination has been designed.¹⁴⁶ The method reduced the NaBH₄ reductant consumption by a factor of 25 compared with conventional methods and allowed 90 samples h⁻¹ to be analysed with a LOD of 0.1 µg l⁻¹. Sn was determined in sea-water using a heated quartz furnace atomiser with Zeeman background correction.¹⁴⁷ Moreno Camero et al.¹⁴⁸ generated hydrides of As, Sb and Se which were passed over a negatively charged W or Pt electrode inserted into the graphite furnace producing a 40-fold concentration factor. In another ETAAS application, the operating conditions for simultaneous HG of Sb, As, Bi, and Se were optimised. The hydrides were preconcentrated directly on the graphite furnace prior to determination.

On-line FI methods coupled to ICP-MS have been described for As and Se in sea-water and reference waters.^149,150

A study of the effect of six different reaction media on the determination of Bi by HG-ICP-AES was carried out.¹⁵¹ Tartaric acid was found to be the most efficient reaction medium in terms of efficient HG and control of interferences; a sub-µg l⁻¹ LOD was obtained.

2.2 Speciation

Determination and quantification of the chemical form of a number of analyte elements in water samples continues to be a fertile area for research.

The differential sensitivity of As species when reacting with reducing agents to form As hydrides and hence allow their speciation to be quantified, has been well known for many years and has continued to be exploited in a number of novel applications. Using the relative differences in sensitivity of As^III, As^V, monomethylarsenic acid (MMA) and dimethylarsenic acid (DMA), FIA-HG-AAS¹⁵² combined with chemometric data processing was successfully used to identify the number and quantity of As species in solutions containing different amounts of the aforementioned forms of As. Shraim et al.,¹⁵³ using HG-AAS, varied the concentrations of the HCl acid matrix, the L-cysteine pre-reducing agent, the NaBH₄ reducing agent and the pre-reduction time to obtain conditions that were selective for total As, As^III, As^V, DMA, and MMA. The same authors¹⁵⁴ carried out a similar study in which they replaced the HCl reaction matrix with HClO₄ and, using the same pre-reduction and reducing agents, arrived at conditions that were not only selective for the previously described As species but also found one set of conditions that gave total inorganic As. In a similar approach,¹⁵⁵ but this time only varying the concentration of the NaBH₄ reducing reagent, conditions where As^III, and As^V could be selectively determined were found. ICP-AES was used for determination.

A number of researchers have used chromatography combined with on-line atomic spectrometry for As speciation. In a study of AFS and ICP-MS detectors for HPLC-HG speciation of As¹⁵⁶ both methods were found to be comparable and were able to determine As^III, As^V, DMA and TMA directly whilst, with the addition of on-line UV photo-oxidation, arsenobetaine could also be quantified. Ion chromatography ICP-MS has been successfully used^157–159 for As^III and As^V speciation. In one such application involving mine tailings waters¹⁵⁷ an iron arsenate species was identified. Cation exchange chromatography ICP-MS¹⁶⁰ was used to determine As^III, As^V, MMA, TMA, trimethlylarsine oxide, tetramethylarsonium ion and arsenobetaine. The determination of all species was carried out in 20 min using a sulfonic acid type cation exchange resin column with HNO₃, NH₄NO₃, and pyridinecarboxylic acid eluent. Arsenic anionic species were also investigated by CE-ICP-MS.¹⁶¹

ETAAS based methods for As speciation have also been reported. As^III was separated with a 2,3-dimercaptopropane-1-sulfonate reagent¹⁶² which specifically complexed with As^III. Total As was determined by reduction of As^V to As^III with L-cysteine prior to complexation. As^V was determined by difference. The complex was concentrated on a Sep-Pak C₁₈ column, eluted with methanol, and determined by ETAAS using a Ni matrix modifier and Zeeman background correction. In a similar approach using different complexation media,¹⁶³ As^III was complexed with APDC and adsorbed onto Dianion PA316 anion exchange resin in the presence of sodium perchlorate. The resin was filtered from the mixture and ultrasonically mixed with a Ni matrix modifier solution prior to the resulting suspension being directly injected into the ETAAS. Again As^V was obtained by difference by determining total As by pre-reduction of the As^V to As^III before the complexation step.

Latva et al.¹⁶⁴ describe a sequential extraction technique where As^III, As^V, DMA and phenylarsonic acid were sequentially collected from one sample solution by adsorbing the different As species on metal loaded activated charcoal. The As concentration in activated charcoal fractions was directly determined by EDXRF.

A number of different methods for Cr^III/Cr^VI speciation with FAAS detection have been described. Cr^VI was preconcentrated and separated from Cr^III by absorption on melamine–urea resin and eluted with 0.1 M sodium acetate.¹⁶⁵ If the Cr concentration was high enough, total Cr could be determined directly; for low concentrations, Cr^III was converted to Cr^VI by oxidation with H₂O₂ and preconcentrated on the resin. Cr^III was calculated as the difference between total Cr and Cr^VI. Adria-Cerezo et al.¹⁶⁶ formed an anionic complex of Cr^III with EDTA. Cr^III and Cr^VI were then retained on a strong anionic resin and sequentially eluted with 0.5 M NaCl. The method gave low µg l⁻¹ detection limits and was tested on waste water samples. Gaspar et al.¹⁶⁷ preconcentrated and separated Cr^VI in a FI manifold by complexation with 0.1 M APDC which was sorbed onto the internal walls of a PEEK sample loop. The loop was washed with water and eluted with IBMK before passing into the FAAS. With the addition of potassium hydrogenphthalate to the sample, complexed Cr^III was collected on a C₁₈ column and eluted into the flame with methanol. This arrangement gave sub-µg l⁻¹ detection limits for both forms of Cr. A micelle-mediated method for Cr^III/Cr^VI speciation has been described by Paleologos et al.¹⁶⁸ Triton X-114 was used as a surfactant and APDC and 8-hydroxyquinoline were used to form hydrophobic complexes with Cr^III and Cr^VI, respectively, again giving low µg l⁻¹ detection limits for both species.

Chromium speciation with ETAAS detection has also been reported. An on-line FI manifold was used to complex Cr^VI with APDC and to extract the resulting complex into IBMK with a PTFE knotted reactor using an air-flow to deliver the organic concentrate to the graphite tube. A detection limit of 3.3 µg l⁻¹ was achieved. An off-line method¹⁶⁹ using the same complexing reagent and organic solvent used multiple injections achieved a detection limit of 0.057 µg l⁻¹ Cr. In another approach,¹⁷⁰ activated alumina packed in a mini-column was used to adsorb both Cr^V and Cr^VI, which were eluted separately with 1 M HNO₃ and 1 M NH₄OH, respectively. Using Zeeman background correction and a MgNO₃ matrix modifier, ppt detection limits were obtained.

An on-line automated liquid handling system^171,172 was used with ICP-MS for Cr^III/Cr^VI speciation. A solid phase chelation resin column with an iminodiacetic acid functional group retained Cr^III, Cr^VI was determined directly; Cr^III was eluted with 1 M HNO₃. Using IC-ICP-MS, Sacher et al.¹⁷³ determined both Cr^III and Cr^VI using Rh^III as an internal standard. Stability of the samples was found to be a particular problem and minimum storage time in the dark at 4 °C with a neutral pH was recommended.

The speciation of organic and inorganic Sn using ETAAS¹⁷⁴ was determined in two steps. First, the total Sn content of water samples was quantified by GFAAS with direct injection into a Zr-coated graphite tube. Secondly, after adjustment of the sample to pH 5.5 and the addition of KBH₄, organic Sn was extracted from the sample by solvent extraction with dichloromethane. The Sn content of the organic extract was determined by ETAAS. Inorganic Sn was determined by difference. In another approach using solvent extraction,¹⁷⁵ the sample, with the NaBEt₄ added and adjusted to pH 5.5, was extracted into hexane. Using GC connected on-line to a quartz furnace FAAS system, mono-, di- and tri-alkyltin compounds were measured in the hexane extract. Tributyltin (TBT) was selectively retained as a chelate on tropolene immobilised on a non-ionic polymeric adsorbent.¹⁷⁶ The TBT chelate was eluted with IBMK and determined by ETAAS on a Zr-coated graphite tube.

Procedures were developed for the speciation of Al in waters percolating through forest soil using on-line HPLC-ICP-MS.¹⁷⁷ Inorganic and organic Al were separated on a cation exchange column. Polymeric Al hydroxides were complexed with Pyrocatechol Violet prior to cation exchange chromatography. Size fractionation of the organic Al species was obtained by size exclusion chromatography.

The dual role of Se as either an essential or toxic element, depending on its concentration and chemical form, continues to drive the need for methods for Se speciation. The majority of methods are based on the gaseous introduction of the hydride into the AS system. Zang et al.¹⁷⁸ determined Se^IV, Se^VI and organic Se in agricultural drainage waters by HG-AAS. Se^IV was determined on an untreated sample, total Se was measured by digestion with H₂O₂ followed by acid reduction to Se^VI and organic Se were determined after the sample was oxidised to Se^VI with persulfate under alkaline conditions. Se^VI was measured by difference. Both As and Se species were determined in contaminated groundwater¹⁷⁹ by HPLC separation and fraction collection prior to HG-AAS. The less commonly studied trimethylselenonium ion was determined by conventional HG-AAS; although recoveries in tap water were low and Se^IV gave a strong positive interference. Methods for speciation by AAS have also been reviewed by Farkasovska.¹⁸⁰

AF methods when combined with HG are found to have high sensitivity for Se and have been found suitable for speciation studies. Vilano and Rubio¹⁸¹ developed an on-line HPLC-UV irradiation system that allowed Se^IV, Se^VI, selenocystine and selenomethionine to be separated and determined. Moreno et al.¹⁸² describe a FI manifold utilising on-line reduction of Se^VI to Se^IV in a microwave oven for inorganic Se speciation.

In a study to investigate the use of microbes for Se reduction in industrial waste water, Kristof et al.¹⁸³ used on-line ion chromatography ICP-MS to determine selenate and selenite. The addition of 2% v/v methanol gave a five-fold enhancement in sensitivity.

The ability of ICP-MS to determine Br and I sensitively has lead to the development of ICP-MS methods for the speciation of halides. Using on-line vapour generation of I by oxidation with NaNO₂ in concentrated H₂SO₄, iodine, iodide and iodate were determined in saline and fresh-water matrices.¹⁸⁴ Disinfection of potable water by UV irradiation can lead to trace bromate contamination. A popular choice for this application has been the use of ion chromatography ICP-MS.^185–188 In addition to bromate determination, Divjak et al.¹⁸⁵ also determined halogens, oxyhalogens, sulfate, phosphate, selenite, selenate, and arsenate in a single 4 min chromatogram and Panstar et al.¹⁸⁷ to speciate As and Cr. Bromate analysis has also been carried out¹⁸⁹ using IC separation followed by collection of the bromate fraction onto a quartz reflector; after drying, bromate was determined by TXRF.

As with As and Se, the ability of Sb to form a gaseous hydride from its reduced oxidation state forms the basis of a powerful method for speciating and determining Sb in water samples. HG-ICP-MS^190,191 and HG-AFS¹⁹² were used for Sb^III and Sb^V speciation. Other workers^72,193 used HPLC combined with ICP-MS to carry out the species separation and determination.

The widespread use of the toxic trialkyllead compounds as an anti-knocking agent in fuels continues to leave a legacy that requires sensitive methods for determining triethyllead (TEL) and trimethyllead (TML) in environmental waters. Baena et al.¹⁹⁴ developed a continuous preconcentration technique to determine inorganic Pb, TML and TEL in water. Inorganic Pb was precipitated as PbCrO₄, which was redissolved in acid, TEL and TML were complexed with NaDDC and adsorbed onto a C₆₀ fullerene column and desorbed sequentially with n-hexane and IBMK. The separated and preconcentrated species were determined by FAAS. The same author¹⁹⁵ developed a screening technique for rainwaters using the C₆₀ column to trap TEL and TML and to measure their combined concentration by FAAS. If the compounds were found to be present above a certain threshold then further investigation was carried out using derivatisation and GC-MS determination. Zoltan et al.¹⁹⁶ describe a solid-phase micro-extraction methodology combined with HPLC and ESMS that allowed elemental Pb (²⁰⁸Pb⁺) and the molecular ions of TEL and TML (m/z 253 and 295, respectively) to be monitored simultaneously.

Metal humic complexes in water have been studied by ion exchange column separation and determination by ICP-MS and AFS, whereas Stewart et al.³³⁴ approached the problem using capillary electrophoresis ICP-MS. Cd complexes in natural water¹⁹⁷ were divided into methodologically defined fractions according to the adsorption media used for preconcentration and separation; Chelex 100 labile fraction (Cd ions and weak Cd complexes) and silica C₁₈ fraction (stable Cd organic complexes). The fractions were determined with a FI-ETAAS system.

Other noteworthy speciation studies include an investigation of the forms of Hg carried in river streams¹⁹⁸ where a sequential extraction scheme was devised to measure Hg in suspended particulates, organic complexes and as dissolved inorganic Hg. CVAAS was used for quantification. P compounds in natural aquatic systems were studied by capillary zone electrophoresis ICP-MS.¹⁹⁹ Schedlbauer et al.²⁰⁰ showed the presence of dimethylthallium in ocean water using ID-MS. An ICP-MS method for Fe^II/Fe^III speciation²⁰¹ has been reported, although it is suggested that this is an over complicated approach as there are good colorimetric methods with equally good performance for carrying out this determination.

2.3 Instrumental analysis

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

2.3.1 Atomic absorption spectrometry. A third edition of Welz's excellent book on all aspects of AA has recently been published.²⁰² FAA continues to be used widely in many laboratories but there seem to be very few advances in the field. Many of the papers being published are mainly routine where there is more emphasis on the application than the methodology. A few unusual AAS methodologies and applications have been reported. Ohta et al.²⁰³ used sequential metal vapour elution for the determination of Cu and Mn. Metals vaporised from the sample at 1950 °C are passed into a Mo 1.22 mm id column heated to 1900 °C. Interaction of the metal chlorides with the column causes different elements to pass through at different rates before being quantified by AAS. Cu and Mn were successfully separated from the matrix elements, allowing interference free determination. Ag and Cd were measured in waste water²⁰⁴ using ETV introduction into an argon MIP, which was used as an atomiser for AAS.

In the past, the major justification for ETAAS analysis has been its very low detection limits. This was balanced, however, by the method being inherently slow and subject to many interferences. The detection limit advantage of ETAAS has now been superseded by the routine use of ICP-MS in many laboratories. Despite this, the relatively low cost and the richness of areas for research in the use of ETAAS continues to produce a wide range of publications in water analysis. The introduction of simultaneous AA instruments with multi-element light sources and array detectors has led to improvements in sample throughput. A method for the simultaneous measurement of Pb, Cd, Cr, Cu and Ni in potable water²⁰⁵ has been described which produces LODs that meet the most stringent international regulations for surface and groundwaters. A W-coil AAS instrument has been used for the simultaneous determination of Cu, Cd and Pb in drinking water.²⁰⁶ Murphy et al.²⁰⁷ have used a simultaneous instrument to measure various combinations of the hydride forming elements As, Bi, Sb, Se and Te after in-atomiser trapping of the hydrides on an Ir coated graphite tube.

Bermejo-Barrera et al.²⁰⁸ used an indirect ETAAS method for the determination of I. An ion pair between 1,10-phenanthroline, Hg^II and I⁻ was selectively extracted into IBMK. The determination of Hg in the extract gave an indirect measurement of I⁻ in solution. Cl was measured by monitoring the absorbance of diatomic AlCl molecules using a Pb HCL at 216.4 nm.²⁰⁹ Calibration graphs were linear over the range 0.03–3 mg l⁻¹. Pesticides, thiuram, disulfiram and ziram in water²¹⁰ were determined by reaction with CuSO₄ and adsorption of their Cu complex on a cellulose ester membrane which was then subsequently dissolved in 2-methoxyethanol prior to ETAAS determination of Cu content.

Studies of methods for reducing interference effects in ETAAS have been carried out by a number of researchers. Cabon et al.²¹¹ have made a very detailed study of the effects of Na, Mg, Ca and Sr in their nitrate, chloride and sulfate forms and of sea salt on the determination of Se. Under optimised conditions in a sea-water matrix, with a Pd matrix modifier, they obtained an LOD of 0.8 µg l⁻¹ for a 10 µl sample, using a two step atomiser²¹² consisting of an end heated graphite atomiser and a transverse heated graphite tube vaporiser connected together to form a T-joint. Samples were vaporised in the vaporiser tube and swept through with an Ar flow into the atomiser for measurement. The device reduced background interference in the determination of Cd and Pb in sea-water. A mathematical approach to reducing interferences has been described by Grotti et al.²¹³ A multiple linear regression model was successfully used to correct for the effects of Na, K, Mg and Ca on the Mn calibration. For this approach to be successful, however, the major element composition of each sample must be known. The success of ETAAS analysis is illustrated in the determination of Cd and Cu in sea-water.²¹⁴ Under optimised conditions with a transversely heated graphite atomiser with longitudinal Zeeman effect background correction, interferences were negligible and LODs of 0.06 µg l⁻¹ and 0.005 µg l⁻¹ were obtained for Cu and Cd respectively.

Preconcentration of the analyte prior to ETAAS has been described by Barbosa.²¹⁵ The standard graphite furnace was replaced by a W coil which, in conjunction with a FI system, was used to electrochemically preconcentrate Pb from natural water samples prior to ETAAS determination.

2.3.2 Atomic emission and atomic fluorescence. ICP AES has reached the stage of a mature technique that is used widely in many laboratory environments. Recently, however, the instrumentation for this technique has changed significantly. With the introduction of reliable and sensitive array technology a number of manufacturers are adopting a combination of echelle spectrometers with array detectors. This instrumentation has overcome old arguments as to whether users should choose scanning sequential analysis systems or simultaneous direct reader type systems by combining the advantages of both in one instrument. Olesik²¹⁶ has produced a tutorial article on the basic principles of echelle systems with charge transfer detectors. Manufacturers^217–219 have published applications showing the suitability of this type of instrumentation for carrying out environmental analysis to the US Environmental Protection Agency specifications. The spectrometers of these systems allow users access to many more emission lines than on older systems, giving a greater emphasis on the necessity for reliable atomic spectral libraries. To help satisfy this need Wiese et al.²²⁰ have produced a review of databases currently available on the World Wide Web.

Many ICP-AES systems now have the ability to view the plasma axially as well as radially. The advantage of axial viewing is that it allows better detection limits for many transition metals, but it is generally not as robust as radial viewing and suffers more from ionisation effects from matrix elements such as EIEs and Ca, as discussed by Brenner et al.²²¹. Some manufacturers advocate the use of both axial and radial viewing as described Mitko et al.²²² in their study of the analysis of salinated water. Others²¹⁹ suggest that this ‘dual viewing’ option compromises the true simultaneous nature of signal measurement and that axial viewing alone under the correct conditions with an ionisation suppressing buffer, such as Cs, is a more superior ‘modus operandi’.

A number of AE applications on the analysis of halides have been reported. Tyler²²³ describes an ICP-AES system that used CaF₂ and MgF₂ optics, allowing far UV lines of Cl and Br to be used for the quantification of halides in oils. A survey of available halide emission lines from the far UV to the IR was carried out using a DCP system with a CID Echelle Spectrometer.²²⁴ Leo et al.²²⁵ used a GC-MIP-AE system to identify chlorinated compounds in municipal waste-water.

Duan et al.²²⁶ have described a low powered MIP-AE system designed to be a field portable system for on-line liquid stream monitoring. The instrument was shown to have pg ml⁻¹ LODs for As, Be, Cu, Hg, Mg, Mn and Zn.

2.3.3 X-ray fluorescence spectrometry. XRF techniques are usually associated with the analysis of solids but reports of methods for water analysis are increasing. TXRF has been used for the analysis of As and other heavy metals in groundwaters of the Argentine Pampas Plain²²⁷ and the determination of heavy metals in Damascus drinking water.²²⁸ Colloidal humic substances have been investigated by a combination of field-flow fractionation and TXRF.²²⁹ Yasuko et al.²³⁰ used synchrotron TXRF to obtain fg detection limits for As in river water. Electrochemical preconcentration of trace metals on a Nb disc substrate was used in combination with TXRF²³¹ to reduce matrix effects and produce pg⁻¹ LODs.

Micro-sample analysis using XRF techniques has been addressed in a number of publications. A 50 µl sample was deposited on an ultra-thin (0.15 µm) polyimide film support²³² prior to XRF analysis. A similar approach²³³ gave results comparable to ICP and AA techniques. Cheburkin et al.²³⁴ used an energy-dispersive miniprobe multielement analyser, originally designed for the analysis of single mineral grains, for the analysis of 150 µl water samples.

The technique of grazing emission XRF has been applied to mineral water²³⁵ and marine aerosols.⁸⁶

Other XRF applications include the determination of As and Se in drinking water with a solvent extraction preconcentration step,²³⁶ the characterisation of estuarine waters²³⁷ and a fast method (5 min per sample) for the determination of major and minor ions in marine pore-water.²³⁸

2.3.4 Mass spectrometry.
2.3.4.1 ICP-MS analysis. The introduction of second and third generation of instrumentation with improved detection limits, reliability and decreasing costs has allowed many laboratories to adopt ICP-MS as the method of choice for water analysis. Ying et al.²³⁹ have developed warning diagnostics for ICP-MS to indicate abnormal operation of the instrumentation. The method uses a decision tree approach based on monitoring Ar-based signals during normal operation and partial least squares modelling of the signals from a solution containing Ba, Bi, In, and Li during the instrument warm up stage.

The very low detection limits of ICP MS are ideally suited for the analysis of low total dissolved solids samples that would require preconcentration of the analytes before analysis by other less sensitive techniques. Examples of this are a number of studies involving ICP-MS for the determination of metals in snow. Major metals (Na, Mg, Al, K, Ca and Fe) were determined in arctic snow²⁴⁰ using a cool plasma and microconcentric nebulisation. Barbante et al.²⁴¹ determined Pd, Pt and Rh in polar and alpine snow using a double focusing ICP-MS. High resolution ICP-MS was also used for Cd, Pb and V in Antarctic snow.²⁴² Using a combination of ICP sector field MS and ultrasonic nebulisation the ultra-trace elements Mn, Ni, Cu and U were determined.²⁴³

A number of research groups are addressing the problems presented by high salinity matrices in the analysis of sea-water samples by ICP-MS. Masanao et al.²⁴⁴ used internal standardisation and standard addition as appropriate methods to overcome spectral interferences. Wilbur²⁴⁵ suggested that there is no single approach for all analytes and a combination of methods including vapour generation sample introduction and standard addition are required to overcome matrix effects. For As determination in sea-water, Shakra²⁴⁶ used a combination of cation exchange to remove Na and Ca prior to analysis and hexapole technology in the instrumentation to remove ArCl⁺ interferences. A two stage process for the determination of As and Se¹⁴⁹ used a FI-HG manifold to separate and preconcentrate the As and Se hydrides on a Pd coated graphite furnace followed by ETV into the ICP-MS. Liu et al.²⁴⁷ combined ETV sample introduction with ID to determine Cd, Hg and Pb. Danzer et al.²⁴⁸ adopted a very different approach by using multivariate calibration techniques. They advocate the use of a partial least squares algorithm, which includes data from both analytes and the interfering species, to produce a calibration model to reduce spectral interferences. They suggest that this methodology has the potential to rival high resolution ICP-MS.

Reaction cell technology of different designs for the reduction of polyatomic isobaric interferences in ICP-MS are now being supplied on commercial instruments. Two manufacturers have published results of the figures of merit obtained when using these devices. Feldman et al.²⁴⁹ describe an ion-guiding hydrogen-filled hexapole which substantially reduces interferences on elements such as As, Ca, Cr, Fe, K and Se. Tanner et al.²⁵⁰ discuss the practical use of their rf/dc quadrupole dynamic reaction cell.

The issue of isobaric interferences in ICP-MS can also be alleviated by the use of high resolution (HR) mass spectrometers. Sector field instruments are now more widely available and this is reflected in the number of published applications for water analysis.^251–255 Poitrasson and Dundas²⁵⁶ used a combination of HR ICP-MS with an ultrasonic nebuliser to measure ²⁰⁶Pb/²⁰⁷Pb, ²⁰⁶Pb/²⁰⁸Pb and ²⁰⁷Pb/²⁰⁸Pb in synthetic and riverine waters at Pb concentrations from 1–1000 ng l⁻¹ with precisions ranging from 0.3 to 3% RSD.

ID ICP MS is considered to be a definitive analytical technique capable of providing improved accuracy and precision over alternative methods and has shown an increase in publications over the period of this review. ²³⁹Pu/²⁴⁰Pu and ²⁴⁰Pu/²³⁹Pu ratios were measured using on-line separation with a combination of Sr-Spec^™ and TEVA-Spec^™ resins and a micro-concentric glass nebuliser. Vapour generation methods were used for Te (hydride generation),²⁵⁷ Ni (carbonyl vapour generation)²⁵⁸ and Hg in sea-water by CV generation.²⁵⁹ ETV sample introduction methods were used for the determination of Hg and Pb in sea-water and Se in rain, soft and hard drinking water reference materials.

The ability of isotopic ratios to provide information on the age and source of water samples has provided the impetus for researchers to use ICP-MS for isotopic ratio measurements. Pb isotopic ratios have been measured in water,²⁵⁶ sea-water²⁶⁰ after coprecipitation with Mg(OH)₂ and rainwater.³³ Sulfur isotope ratios were determined in waters using an instrument with hexapole ion optics to reduce the interferences from O₂⁺ and NO⁺ molecular ions.

The variety of other applications of ICP-MS to water analysis clearly shows that the technique is becoming established in the analytical community. The analytical characteristics of a high efficiency ion transmission (S mode) ICP-MS for reference waters has been described.²⁶¹ The determination of size and trace element distribution of colloidal material in natural water by on-line field-flow fractionation ICP-MS has been reported. Macro and trace elements in lake Baikal water have been determined.^262,263 A survey of trace elements in 476 crystalline bedrock groundwaters in Norway has been published.²⁶⁴ Barwick et al.²⁶⁵ have applied a rigorous cause and effect approach, from the preparation of standards and samples to the final ICP-MS measurement, to the determination of uncertainty in the determination of ⁶⁰Ni in aqueous samples. Unsurprisingly, the dominant components to the overall uncertainty were method precision, instrument drift and bias.

2.3.4.2 Other MS methods. ID-MIP-MS has been used for the determination of Mo in water samples after extraction as the 8-hydroxyquinoline complex.²⁶⁶

The measurement of the stable O and H isotopes ratios of water is important in many areas of science from geochemistry to biology for determining mechanisms of water transport through physico-chemical processes such as evaporation or equilibration with other O and H containing compounds. Begley and Scrimgour²⁶⁷ describe a fast on-line flow system for converting the water sample to gaseous H and O before quantification by isotope ratio MS. The method can be used on samples as small as 1 µl. A new method for accurate determination of δ¹⁷O and δ¹⁸O using electrolysis from CuSO₄ solution to produce O gas prior to isotope ratio MS quantification has been reported.²⁶⁸ Ward et al.²⁶⁹ present a rapid and inexpensive method for the production of H gas from water using LiAlH₄. Standardisation problems in O isotope measurements has been discussed by Kornexl.²⁷⁰ Other O and H stable isotopic measurements in a wide range of applications have been reported.^66,271–275

Tandem accelerator MS is an important technique for a number of environmentally important isotopes including ¹⁴C, ³⁶Cl and ¹²⁹I. Mizushima et al.²⁷⁶ describe the processes in setting up a new facility; measurement of ³⁶Cl in South American rainwater has been reported²⁷⁷ and ¹²⁹I determinations in environmental waters have also been presented.^278,279

3 Analysis of soils, plants and related materials

Since the publication of the 15th environmental update in JAAS a year ago,⁸⁴ ongoing concerns over environmental pollution have resulted in a further steady flow of publications and conference papers exploiting the capabilities of atomic spectrometry. This is reflected in Table 3. However, real progress with methodology for soil and plant analysis has, as last year, been less dramatically obvious. Also as last year, many analytical “developments” have often involved only minor tinkering with existing methods, although improvements are sometimes claimed.

Table 3 Summary of applications of atomic spectrometry to the analysis of soils, plants and related materials

Element	Matrix	Technique; atomization; presentation^a	Sample treatment/comments	Ref.
a Hy indicates hydride and S, L, G and Sl signify solid, liquid, gaseous or slurry atomization, respectively. Other abbreviations are listed elsewhere.
Al	Soil	AA;F, air-C2H2;L	Al supposedly determined after Na2CO3 fusion with 94–104% recovery	417
Al	Forest soil water	MS;ICP;L	System described for on-line speciation	177
Al	Vicia faba root cells	XRF;-;S	SIMS and electron microprobe used to study Al distribution	405
As	Soil	MS;ICP;G	GC used to separate volatile As species evolved from soils prior to determination	361
As	Kelp extracts	MS;Hy, ICP;L	Arsenosugars separated by chromatography prior to detection	359
As	Contaminated soil	XRF;-;S	As contamination at a German military site studied with mobile XRF system	418
As	Seaweeds	MS;ICP;L	Anion exchange HPLC tested for As speciation but size-exclusion HPLC preferred for organoarsenic species fractionation and matrix removal	357
As	Plant leaves	AE;Hy, ICP;L	FIA system described for simultaneous determination of As and Hg. RSD at 10 µg l^−1 was 1.4 and 1.3% for As and Hg, respectively	382
As	Algae	MS;ICP;L	As species separated by cation exchange chromatography	160
As	Soils, plants	MS;ICP;L	Ion chromatography used to separate As species	159
As	Kelp powder extract	MS;ICP;L	As species separated by narrow bore HPLC prior to on-line detection	360
As	Algal extracts	MS;ICP;L	Arsenosugars separated by HPLC	358
As	Plant digests	MS;Hy, ICP;L	System described for rapid sequential determination of As and Se; sample mixed alternately with thiourea or HCl for As or Se determinations	150
As	Seagrass	MS;ICP;L	Digestion with HNO3 + H2O2	419
As	Soils	XRF;-;S	Pollution near Cornish mine workings studied	420
As	Soils	AF;Hy;L	Microwave-assisted distillation procedure described to pre-concentrate As as AsCl3	392
B	Brown rice, soil extracts	MS;ICP;L	B concentrations and isotope ratios measured; B separated from matrix elements by ion exchange	421
Be	Soil	AE;ICP;L AA;ETA;L	3 digestion methods compared, and gave slightly different results	422
Ca	Wheat flour	AA;F;Sl	Ca and Mg determined in agar and dibutyl phthalate containing La	423
Ca	Rice, beans	AE;F;Sl	Slurry prepared in La and agar solution; Ca and K measured	424
Cd	Plants	MS;ICP;L	Size-exclusion chromatography used for Cd speciation in cytosols of plant tissues and cell cultures	369
Cd	Tomato leaf	AA;ETA;Sl	Slurry prepared in PTFE–plant glue–HNO3 matrix	387
Cd	Soil	AA;ETA;L	Matrix modifiers compared	425
Cd	Soils, vegetables	AA;F;L	Soil soaked with aqua regia + HClO4 prior to digestion; 3 different acid digestions all worked for Cd	426
Cd	Crops	AE;ICP;L AA;ETA;L	Effect of soil additives on Cd uptake studied	427
Cd	Plant extracts	MS;ICP;L	Cd complexes separated by size exclusion chromatography	368
Cd	Soil	AA;ETA;Sl	Ammonium oxalate used as dispersant, and Pd as modifier; LOD 0.15 pg	428
Cd	Soil, apple leaves	AA;CV;L	Cold vapour determination described in detail	390
Cd	Soil solution	AA;F;L	Circulating dialysis system described for studying organic complex species of Cd, Cu and Pb	429
Cd	Plant materials	AA;F;L	Cd and Pb separated at diethyldithiophosphate complexes on C18 column at pH 1 in FIA system; oxalic acid and thiourea used to mask Fe and Cu	317
Cd	Soils	AE;ICP;L AA;ETA;L	Interference found from As in both techniques	378
Cr	Tomato plants	MS;-;S	SIMS used to study Cr distribution	430
Cr	Tobacco	AA;F;L	On-line preconcentration procedure described for Cr speciation	431
Cu	Humic acids	AA;-;-	Generation of hydroxyl radicals in soils loaded with Cu^II and Fe^III examined	432
Cu	Soil solution	AA;F;L	See Cd, ref. 429	429
Fe	Maize flour	AA;F;Sl	Fe and Zn determined using flour slurry in agar	433
Fe	Humic acids	AA;-;-	See Cu, ref. 432	432
Hg	Soil	AA;CV;L	Different acid extraction systems compared for a CRM	434
Hg	Soils	AA;Hy;G	Organomercury compounds separated by capillary GC coupled via hydride generation system to spectrometer	435
Hg	Aquatic plants	AA;CV;Sl	Slurry prepared in 15% m/m HNO3 with 0.02% v/v Triton X-100; mixture subjected to ultrasonic treatment prior to injection into FI manifold	436
Hg	Contaminated soil	AE;MIP;G	Organometallic compounds of Hg, Pb and Sn converted to volatile derivatives with NaBEt4; compounds purged with He, and preconcentrated onto Chromosorb 102; trapped compounds thermally desorbed and passed to GC with MIP detector	383
Hg	Soils	AA;-;-	Soil sequentially extracted with ammonium acetate, hydroxylamine hydrochloride in acetic acid, dilute HCl, NaOH and finally 8 mol l^−1 HNO3	375
Hg	Lichens	AA;CV;G	3 digestion procedures compared; open tubes gave low results	353
Hg	Plant leaves	AE;Hy, ICP;L	See As, ref. 382	382
Hg	Environmental samples	AA;CV;G	Use of Au amalgamation preconcentration critically evaluated	437
K	Plant parts	MS;TI;-	Application of ^26Mg and ^41K and TIMS to the assessment of K and Mg uptake by Scots pine	406
K	Beans, rice	AE;F;Sl	See Ca, ref. 424	424
Mg	Plant parts	MS;TI;-	See K, ref. 406	406
Mg	Wheat flour	AA;F;Sl	See Ca, ref. 423	423
Mn	Tea	AE;MIP;L	Sample digested with HNO3, then HClO4; Mn and P determined	384
Mo	Grass, clover	AA;ETA;L	Pt-group metals studied as modifiers. Characteristic mass 3.1 pg with Ir modifier	388
Mo	Soil	AA;ETA;L	Metal preconcentrated by extraction of thiocyanate complex into IBMK	355
P	Tea	AE;MIP;L	See Mn, ref. 438	438
Pb	Contaminated soils	XRF;-;S	SEM and XRF used to study Pb speciation in soil solid phase	439
Pb	Contaminated soils	XRA;-;S	XRA fine structure spectroscopy used to identify Pb solid compounds in soils	370
Pb	Polytrichum formosum	MS;ICP;L	Pb isotope ratios measured in attempt to identify sources of Pb pollution	399
Pb	Contaminated soil	AE;MIP;G	See Hg, ref. 383	383
Pb	Algae	AF;Hy;L	KBH4 used as reductant, and HCl + K3Fe(CN)6 as carrier	393
Pb	Humic and fulvic acid complexes	MS;ICP;S	LA used to study ^206Pb complex position on gel plates after gel electrophoretic separation of complexes	366
Pb	Pine needles	MS;ICP;L	Factors influencing isotope ratios critically discussed.	33
Pb	Environmental samples	AA;F;L	Microcolumn preconcentration procedure described and evaluated in detail for Pb	356
Pb	Soil	MS;ICP;L	Isotope ratios used to elucidate anthropogenic contributions to soil Pb	400
Pb	Soil	XRF;-;S	Cone penetrometer XRF tool described for quantifying sub-surface heavy metal contamination	415
Pb	Grapes	AA;ETA;L	NH4H2PO4 and MgNO3 used as modifier; temperature raised in series of steps	440
Pb	Soil solution	AA;F;L	See Cd, ref. 429	429
Pb	Plant materials	AA;F;L	See Cd, ref. 317	317
Pb	Soil, house dust	AA;F;L	Hot acid leaching used	69
Pt	Plant material	MS;-;-	Speciation methods reviewed	363
Pu	Soil, dust	MS;ICP;L	Procedure described to separate Pu from U to prevent interference from ^238UH^+ in ^239Pu determination	441
Ra	Soil	MS;ICP;L	^226Ra pre-concentrated from acid digest by co-precipitation with Pb	252
REE	Soils	MS;ICP;L	Microwave-assisted digestion using HF + HCl + HNO3 and EDTA	361
REE	Soils	MS;ICP;L	Microwave-assisted digestion with HNO3–HF–HCl; digest mixed with EDTA, and mixture digested with HClO4. Re used as internal standard; 14 REE determined	442
REE	Soils	AE;ICP;L	Soluble REE studied after preconcentration with MgCl2 as carrier, by adjusting to pH 10–11	354
Sb	Plants	AA;furnace;G	Quartz furnace used for atomization after NaBH4 used to volatilise methylantimony species	364
Sb	Soil	MS;ICP;L	Open vessel wet digestion evaluated for soil near mining area	193
Se	Cereals	AA;Hy;L	Varietal and geographic differences studied	443
Se	Soil drainage water, soil sediment	AA;Hy;L	Procedure described for oxidation of organic Se compounds; detection limit was 0.008 mg kg^−1 for soil	178
Se	Spirulina	AA;Hy;L	Sample decomposed with HNO3 + HClO4; residue taken up in 6 mol l^−1 HCl plus FeCl3 prior to FIA; LOD 17 ng g^−1	444
Se	Soils	AA;Hy;L	Relationship between bioavailable Se in soils and Se in blood serum studied	445
Se	Plants	MS;ICP;L	Samples extracted with hot water or using enzymatic extraction for speciation. HPLC conditions described. 75% of eluted Se in identified compounds	365
Se	Plant digests	MS;Hy, ICP;L	See As, ref. 150	150
Sn	Contaminated soil	AE;MIP;G	See Hg, ref. 383	383
Tc	Soils	MS;ICP;L	Trapping system described to preconcentrate ^99Tc	446
Th	Soil, plants	MS;ICP;L	Determination of Th and U by ICP-MS and gamma counting compared in high natural radiation area; ICP-MS was more accurate and precise	447
Tl	Plant materials, soil	MS;ICP;L	ID used with ^203Tl spike; good results obtained for 3 CRMs; external calibration with Rh as internal standard also gave good recovery	401
Zn	Maize flour	AA;F;Sl	See Fe, ref. 433	433
Zn	Grey mangrove leaves	XRF;-;S	SEM and microanalysis used to study distribution of Zn in different forms	448
Various	Soils	MS;ICP;Sl	1 mol l^−1 HNO3 leaching was used in an attempt to improve recoveries of elements using slurry nebulisation	449
Various	Tea leaves	AE;ETV, ICP;L	Various fluorine-containing compounds tested as modifiers for ETV; 6% PTFE was best	381
Various	Algae	XRF;-;S	Heterogeneity problems associated with single cell analysis assessed	450
Various	Wood pulp	AE;ICP;S	Solid samples analysed directly on graphite probe introduced to plasma, after in situ pre-treatment and ashing	379
Various	Macrofungi	AA;F, air-C2H2;L AA;CV;L	Sliced samples digested with 4 + 1 + 1HNO3 + H2SO4 + H2O; residue taken up in water; Cd, Co, Cu, Fe, Mn, Pd and Zn determined in digest. Hg determined in separate digest	451
Various	Plants	AE;ICP;L	Five digestion procedures, dry ashing, ashing + alkali fusion, HNO3 + H2SO4 + HClO4, HNO3 + H2SO4 + HClO4 + HF and H2SO4 + H2O2 compared	452
Various	Leaves, soils	AA;Hy, ETA;G	System described for trapping hydrides of As, Sb and Se in Ir-lined furnace	389
Various	Soils	AE;-;S	System described for producing thin film of particles for determination of 15 elements by PIXE	407
Various	Apple leaves	XRF;-;-	Instrument adjusted to detect selected trace elements only	453
Various	Rice	AA;F;L MS;ICP;L AE;ICP;L	14 elements determined in Vietnamese rice survey	454
Various	Agricultural crops	MS;ICP;L	Microwave-assisted digestion with HNO3 described	455
Various	Wild berries	AE;ICP;L MS;ICP;L	Trace element distributions studied in northern Sweden; effects of mining activities and roads were confirmed	456
Various	Soils	MS;ICP;L	Stable isotope exchange used to identify labile pools of elements in soils	457
Various	Tea, coffee	AA;ETA;Sl	Slurries prepared in HNO3 and Triton X-100; RSD ca. 8%	458
Various	Ponderosa Pine phloem	AE;ICP;L	15 elements determined in samples from 149 trees in study of selective herbivory	459
Various	Humic acids	MS;ICP;L	Samples digested with HNO3; Al, As, Cu, Mn, Pb and Zn determined	460
Various	Soils	AE;ICP;L	Soil contamination studied in urban New Orleans; Cd, Mn, Ni, Pb and Zn determined	461
Various	Soils	MS;ICP;L AE;ICP;L XRF;-;- AA;-;L	Precision, accuracy, detection limits and recovery compared between different techniques and different laboratories	462
Various	Plant species in parks	AE;ICP;L	11 elements determined in urban park pollution study	463
Various	Soils	XRF;-;S	Portable spectrometer used to analyse contaminated soils	464
Various	Industrial soils	AA;-;L AE;ICP;L XRF;-;S	Different methods critically compared	347
Various	Plants	AA;ETA;L	Tetrabutylammonium hydroxide used at 90 °C for 2 h; digest diluted with water and analysed for Cd, Cr, Cu, Mn, Ni and Pb	350
Various	Soils, cane plants	AA;F;L	Sugar and soil compositions compared in Egypt	465
Various	Vegetables	AA;F;L	Samples digested with 10 + 1 + 1 HNO3 + H2SO4 + HClO4	466
Various	Vegetables	AA;-;L	Very high concentrations of Cu and Zn found in red beets	467
Various	Mushrooms	AE;ICP;L	15 elements determined in 92 specimens to look for bioaccumulation	468
Various	Plant tissues	AA;ETA;Sl	Slurry formed in 1% HNO3; Cd, Cu, Cr, Mo, Ni and Pb determined	469
Various	Sludge-treated soils	AE;ICP;L	Redistribution of heavy metals between species studied after sludge applied to soil	470
Various	Soils	AA;-;L AE;-;-	Results of inter-laboratory comparison showed up problems for Cd, Co, Cr, Cu, Mn, Ni, Pb, V and Zn	471
Various	Plants, soil	AA;-;-	10 elements measured in parts of Oenothera biennis plants	472
Various	Plants, soil	AA;-;-	10 elements measured in Oenothera biennis and underlying soil	473
Various	Algae	AA;-;-	Binding of Cd, Cu, Ni, Pb and Zn by Chlorella vulgaris studied	474
Various	Soil	AA;-;-	Samples digested with HNO3 + HCl; soils near motorway studied	475
Various	Soils	XRF;-;S	Sample preparation for use with portable XRF spectrometer described	414
Various	Celastrus paniculatus seeds	AA;-;L	Samples were ashed	476
Various	Vine leaves	AE;ICP;L	Microwave-assisted digestion with HNO3 + HF + H2O2 or dry ashing used; Cu, Pb and Zn from industrial pollution studied	477
Various	Putranjiva roxburghii seeds	AA;-;-	Samples ashed; Co, Cu, Fe, K, Na, Ni, Pb and Zn determined	478
Various	Soils	-;-;-	Significance of difference in spatial heterogeneity of pollutant and background element distributions discussed for assessment of polluted sites	479
Various	Soils	AA;F;L	Results of pseudo-total analysis using HNO3 + H2O2 and HCl + HNO3 digestions compared; silicates were more soluble in aqua regia	480
Various	Tree bark	MS;ICP;S	LA used to study Al, Ca, Cd, Ce, Cr, Cu, Fe, Mn, P, Pb, S, Ti and Zn in bark	403
Various	Tree rings	MS;-;S	SIMS used to study As, Cd, Cr and Pb in tree rings	481
Various	Cucumber plants	TXRF;-;L	Roots dissolved using microwave-assisted digestion; sap analysed directly; heavy metal effects on nutrient uptake and transport studied	482
Various	Scots pine fine roots	XRF;-;L	Samples digested with HNO3 and Ga used as internal standard for TXRF analysis	416
Various	Peat	TXRF;-;L	TXRF applied to solutions from operationally defined fractionation procedure	483
Various	Soils, sediment	XRF;-;S	Samples simply dried at 105 °C	484
Various	Plants	MS;ICP;L	Magnetic sector instrument used to overcome polyatomic interferences associated with transition metal isotopes	397
Various	Spruce wood	XRF;-;S	A synchroton radiation microbeam system used to study element distributions	485
Various	Soils on waste sites	XRF;-;S	Use of mobile ED-XRF system described	486
Various	Plants	AE;ICP;L	Interference problems due to lowering of plasma temperature when using axially viewed plasma assessed	377
Various	Barley leaves	XRF;-;S	Ca, Cl and K determined for rapid screening	487
Various	Vegetation, soil	XRF;-;S	Polygonal graphic representations applied to semi-quantitative analysis for 3 and 4 elements	488
Various	Soil	XRF;-;S	Portable spectrometer evaluated	26
Various	Soil, sediment	MS;ICP;L	Microwave assisted digestion; 14 elements determined	328
Various	Soils, rocks	AE;ETV, ICP;S AA;ETA;S	ETA used for Cd, Pb and Zn; ETV-ICP-AES with high-temperature halogenation suitable for Cr, Cu, Ni. Pb and Zn	380
Various	Libyan soils	XRF;-;S INAA;-;S	Results obtained by two methods compared	489
Various	Soils	MS;-;S	SIMS used to characterise U and Pu particles in soils; samples transferred to conductive graphite support	404
Various	Soils	XRF;-;S	Computer program described that corrects for matrix effects in trace element determinations	413
Various	Soil humic acids	MS;ICP;L	Complexing properties of humic acids studied using size exclusion chromatography	367
Various	Rice, soils	AA;ETA;L	Cd, Cu and Zn concentrations compared in rice and soil samples from Japan, Indonesia and China; samples acid digested	490
Various	Algae, cabbage	AA;ETA;L	Open and microwave digestion compared for Cd, Cr, Cu and Pb; results were in agreement at 95% confidence level	491
Various	Soils	AA;F, air-C2H2;L	Potentially toxic elements extracted with dilute HCl, and preconcentrated prior to determination of Cd, Cu, Pb and Zn	492
Various	Plant samples	MS;ICP;L	Described procedure gave 95–105% recovery for SRM analyses	493
Various	Soils	XRF;-;S	Pollution from highways studied in Moscow	494
Various	Tea	AE;ICP;L MS;ICP;L	Report of use of pattern recognition to trace tea origins	495
Various	Soils	AA;-;L	Sequential extraction procedure assessed for operational speciation of Cd, Cr, Ni, Pb and Zn	496
Various	Plants, soils	MS;ICP;L	Microwave-assisted digestion with HCl + HNO3 + HF; precision typically better than 6 and 10% RSD for soil and plant samples, respectively	497
Various	Soil	AE;ICP;L	PCA used to identify polluted areas	498
Various	Spruce seeds, plant CRMs	AA;ETA;Sl	Slurries prepared in 0.14 mol l^−1 HNO3. CRM data confirmed accuracy for Al, Cu, Li and Mn	386
Various	Wild mushrooms	AA;-;L	Samples homogenized and sub-samples ashed	499
Various	Soils	LIBS;-;-	Effect of plasma temperature discussed	500

---

Once real progress attains a near-plateau, well-written reviews become quite useful. Haraguchi³⁴⁵ has reviewed recent progress in applications of atomic spectrometry for multi-element profiling of environmental and geochemical samples. Another review, but in Chinese, covered the analysis of agricultural samples³⁴⁶ in China between 1994 and 1998.

Several analytical techniques for analysis of industrial soils have been critically compared by Anderson et al.³⁴⁷ The techniques covered included XRF, ICP-AES and AAS; the portable XRF spectrometer gave results within a factor of two of those for certified standards for most elements, but for V gave very high (7-fold) results compared with those from ICP-AES. Cave, both individually³⁴⁸ and with co-workers,³⁴⁹ has stressed the importance of assessment of bioavailability and of speciation of toxic elements in surveys of contaminated soils. This is especially true as a growing body of legislation forces local authorities to make proper and appropriate risk assessments of contaminated sites.

3.1 Sample preparation

3.1.1 Sample dissolution procedures. Sample preparation and dissolution are the most time consuming and labour intensive stages of soil and plant analyses. Silva and colleagues³⁵⁰ have advocated the use of solubilisation of plant materials with 25% tetramethylammonium hydroxide by heating at 90 °C for 2 h before analysis by AAS using ETA. Digests could be stored for up to 3 years without changes being detected in determinant concentrations.

Several papers using microwave-assisted digestion as a routine tool are listed in Table 3, but there have been fewer claims of exciting advantages this year than there were last year. In one possibly noteworthy paper, a focused microwave digestion procedure was described for plant materials which used a new-generation state-of-the-art system prior to determination by ICP-MS.³⁵¹ Lavilla et al.³⁵² compared low and medium pressure microwave-assisted digestion of plant samples with high pressure digestion of the same samples; for the 5 elements studied, the three methods gave similar results.

A comparison has been made of digestion methods for determination of Hg in lichen.³⁵³ Digestion in open tubes in an Al block gave lower (50–61%) recoveries than either digestion in a glass reflux apparatus or microwave-assisted digestion in teflon containers, whereas these two methods yielded similar results.

3.1.2 Preconcentration. As sensitivities of analytical techniques have improved over the past decade or two, there has perhaps been less need for preconcentration methods than hitherto. Nevertheless, new or improved methods worth noting still appear from time to time. A procedure has been described, for example, for concentration of REE, using MgCl₂ as a carrier, at pH 10–11.³⁵⁴ A solvent extraction procedure has been suggested for extraction of Mo from soil digests as its thiocyanate complex into IBMK;³⁵⁵ subsequent determination was by ETAAS. Automation of preconcentration steps using FIA methodology has been a focus of interest for several years now. An example of this interest is a paper on the use of a macrocycle immobilized silica gel sorbent for microcolumn preconcentration and separation in the determination of Pb by FAAS.³⁵⁶ Lead was retained on the column over a wide range of sample acidities, and then was eluted from the column with dilute EDTA at pH 10.5.

3.1.3 Speciation. Interest in speciation of toxic elements in soils and sediments was highlighted in last year's review⁸⁴ and has shown no sign of abating over the past year. Arsenic speciation again has continued to figure prominently, as indicated in Table 3. Noteworthy studies this year include one using bidimensional size-exclusion anion exchange HPLC for quantification of arsenosugars in seaweeds by ICP-MS.³⁵⁷ Some problems with retention time matching and spiking experiments were initially encountered in anion exchange HPLC-ICP-MS because of co-elution with other arsenic species. Size exclusion HPLC was therefore proposed for a preliminary fractionation step. In another study, of brown alga (Fucus serratus) extracts, HPLC-ICP-MS and LC-ES-MS were used together to identify arsenosugars.³⁵⁸ For the same group of compounds in kelp extracts, IC-ES ionization-MS-MS was used along with IC-membrane- hydride generation ICP-MS.³⁵⁹ The use of the hydride system indicated that three unknown arsenosugar peaks were not hydride active, which simplified the chromatographic resolution needed to quantify more toxicologically important As compounds. Another study of kelp extracts used narrow-bore HPLC on line with ICP-MS to speciate four arsenosugars.³⁶⁰ In other reports, diverse As species in water, soils and plants have apparently been successfully quantified by ion chromatography-ICP-MS.^159,160 Finally, for As, a procedure based on LC and GC-ICP-MS has been described for characterisation of gaseous As compound emissions from soil microcosms.³⁶¹

An interesting speciation paper this year was on the determination of organomercury compounds in soils from orchards and wheat fields by capillary GC coupled with an AA spectrometer via an in-situ hydride generation system.³⁶² The polar organomercuric halides in 0.1 mol l⁻¹ ethanoic acid–sodium ethanoate buffer at pH 4 were reacted with KBH₄ and the volatile derivatives in the headspace were determined.

Because of the risks associated with environmental contamination from continued use of catalytic converters, methods for preconcentration and speciation of Pt are currently of particular interest. The past year saw the publication of a short but useful review of the characterisation of Pt species and possible species transformations in grass extracts.³⁶³

Craig et al.³⁶⁴ have described a procedure for the detection of methylantimony species in environmental samples; the system used NaBH₄ as a derivatizing reagent and purge and trap quartz-furnace AAS. For the generation of trimethylantimony, rigorous exclusion of air and rapid purging of the derivative into the cold trap was found to be important.

Selenium speciation has been performed on hot water and enzymatic extracts from Se-enriched plants, using HPLC-ICP-MS and HPLC-electrospray ionization-MS.³⁶⁵ The HPLC was mostly carried out with 0.1% heptafluorobutanoic acid as ion-pairing agent in methanol–water solution, but for some compounds trifluoroethanoic acid was necessary. The authors were able to identify around three quarters of the compounds eluted.

Use of atomic spectrometry for characterization of organic complexing properties of natural compounds seems to have been attracting more attention over the review year. For example, gel electrophoresis was used with LA-ICP-MS to measure the binding of Pb to various molecular size fractions of humic and fulvic acids;³⁶⁶ this study used ²⁰⁶Pb as a stable isotope tracer. Similarly, HP size exclusion chromatography coupled to ICP-MS has also been used to study the metal complexing properties of molecular size fractions of soil-derived humic acid.³⁶⁷ Size exclusion chromatography-ICP-MS has been used to study Cd complexation in plants, both with³⁶⁸ and without³⁶⁹ electrospray tandem mass spectrometry (ES-MS-MS).

3.1.4 Selective extraction methods. In the previous section, speciation of elements either in soil or plant solution phases or in the gas phase was considered. Identification of elements in different chemical forms in the solid phase is also of interest, however. Welter et al.³⁷⁰ have used X-ray absorption fine structure to establish the presence of PbCO₃, PbSO₄, PbO and basic PbCO₃ as key components in Pb-contaminated soil. Dharmasri and Hudnall³⁷¹ have described an ICP-OES-based method for the determination of pyrites in coastal soils in Louisiana and acid sulfate soil from Sri Lanka.

Operationally defined element fractionation procedures are still attracting attention in the soils area, both through application of tried and tested methods, and as new and hopefully improved methodology.³⁷² Davidson and Délevoye³⁷³ found ultrasonic treatment useful for speeding up soil extraction steps. Cave et al.³⁷⁴ have described a novel stepwise (concentration gradient-based) extraction system using leaching with HNO₃ + H₂O₂ from soil samples supported on a porous membrane in a centrifuge tube. Initial results using the system, developed at the British Geological Survey, were encouraging. A 4-stage sequential extraction for Hg in soils has been recommended, based upon NH₂OH.HCl in 25% ethanoic acid, HCl, NaOH and HNO₃.³⁷⁵

3.2 Reference materials

New research on reference materials in environmental atomic spectrometry research is nearly always worthy of attention. An interesting concept being developed over the past year for candidate reference materials was that of an uncertainty budget.³⁷⁶ Uncertainty budgets allowed all the most significant sources of potential error to be identified, and facilitated more meaningful comparison of results between laboratories. The approach was tested on an algae reference material.

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. Many additional but more routine 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. Axially viewed ICPs are also now in regular use, and following our report last year of systematic studies of matrix element interferences when they are employed for plant analysis,⁸⁴ further work on this topic has now appeared.³⁷⁷ Again plasma temperature shifts seemed to pose a problem. Another noteworthy interference study is one by Lambkin and Alloway³⁷⁸ on the problem of determination of Cd in As-contaminated soils.

Direct analysis of solid samples by ICP spectrometric methods still has a select collection of devotees, and laser ablation methodology can be a powerful auxiliary tool in some specialised applications.⁹⁴ However, direct insertion of solid wood pulp samples into an ICP via a pyrolytically coated graphite sample probe has also been suggested;³⁷⁹ drying and ashing were performed by inductive heating in the plasma prior to plasma ignition.

Some researchers prefer to use electrothermal vaporisation for solid sample analysis. High temperature vapour halogenation is often recommended for improved precision and accuracy when employing ETV in ICP-OES.³⁸⁰ In one such study it was reported that best results were obtained using 6% PTFE as a modifier added to the sample.³⁸¹

Hydride generation and cold vapour sample introduction are sometimes used to enhance sensitivity in ICP-OES. For example, this approach has been adopted for the determination of low concentrations of As and Hg in plant samples.³⁸²

As mentioned in last year's update,⁸⁴plasmas other than the ICP are not widely used in AES. However a MIP has been used as emission source in a GC detector in the determination of organometallic forms of Hg, Pb and Sn in contaminated soil.³⁸³ A MIP has also been used for the determination of P and Mn at concentrations down to 8 and 95 ng ml⁻¹ in acid digests of tea leaves.³⁸⁴

3.3.2 Atomic absorption spectrometry. Atomic absorption spectrometry, even using electrothermal atomisation, is widely regarded as a mature and reliable technique. However, results from round robin tests analysing solid samples by ETAAS seem to suggest that optimism still outweighs achievable skill at times.³⁸⁵ Inspired by RSDs of 1.7–7% for Al, Cu, Li and Mn in plant CRMs, authors of one recent paper nevertheless suggested a slurry-based ETA method for spruce seeds.³⁸⁶ A slurry method, using PTFE as modifer, has also apparently been successfully applied to the determination of Cd in tomato leaves.³⁸⁷ The importance of using an appropriate modifier was highlighted in a recent study of the determination of Mo in grass and clover.³⁸⁸ For the hydride-forming elements As, Sb and Se, hydride generation has been advocated as a method for introducing the determinands from soil, sediment and leaf samples to an Ir-lined graphite furnace atomiser.³⁸⁹

In flame atomic absorption spectrometry, little should be expected in the way of exciting innovation. Some may still be interested in further reports of the determination of Cd by cold vapour sample introduction, now using FIA.³⁹⁰ Those excited by a report of determination of Ca, Mg and Sr by FIA-AAS, unless known to be addicted to Sr chemistry, might be regarded as bordering on the eccentric. Nevertheless, a useful and thorough report on this topic has just been published.³⁹¹

3.3.3 Atomic fluorescence spectrometry. In last year's update, the point was made that atomic fluorescence spectrometry is seen largely as a bit of an academic curiosity, which has great potential for a handful of elements, but not enough to ever make it commercially viable. Applications still appear in the literature, however. Over the past 12 months, for example, it has been used to determine Hg in soil after microwave-assisted distillation,³⁹² and algal Pb concentrations using hydride generation.³⁹³

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 in other recent years.⁸⁴ 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. Newcomers and seasoned practitioners alike still may benefit from reading good current reviews of the technique, however, be they comprehensive reviews³⁹⁴ or short overviews.³⁹⁵

MS techniques are also currently attracting considerable attention in the environmental sphere because of the information that may be gleaned by exploiting biologically or physico-chemically driven isotope discrimination processes. Interest centres around ¹⁸O/¹⁶O discrimination^272,274 and ¹⁴N/¹⁵N ratios,³⁹⁶ although Sr isotopes are also important.

3.3.4.1 Inductively coupled plasma-mass spectrometry. Isobaric interferences may pose problems in ICP-MS analysis of real samples. Townsend³⁹⁷ has therefore pointed out the merits of sector-field ICP-MS over quadrupole MS in this context.

Much of the interest in ICP-MS still seems to be arising as a consequence of its capability for measuring isotope ratios. For example, stable isotope exchange now seems to be being seriously considered for quantifying labile pools of elements in soils.³⁹⁸ Isotope ratios are of course also now being considered as a fingerprinting tool for identifying origins of both products and pollutants: for example for Pb in mosses,³⁹⁹ soils⁴⁰⁰ or pine needles.³³ For elements such as Tl, the potential to use isotope dilution techniques is also very attractive.⁴⁰¹

In terms of instrumental development, there seems to be little major to report. Papers have appeared on hydride generation for As and Se,¹⁵⁰ an FIA system for on-line dilution,³²⁷ and LA for soil⁴⁰² and bark⁴⁰³ samples.

3.3.4.2 Secondary ionisation mass spectrometry. Secondary ionisation mass spectrometry has proved to be a valuable technique for the characterisation of U- and Pu-containing particulates in Russian top soils, swipes and forensic samples.⁴⁰⁴ Isotopic composition was typically measured with an accuracy of 0.5%. SIMS has also been used in a study of the subcellular localization of Al in Vicia faba root cells.⁴⁰⁵
3.3.4.3 Thermal ionisation mass spectrometry. Thermal ionisation mass spectrometry has been exploited in a study of nutrient uptake by Scots Pine, using ²⁶Mg and ⁴¹K as tracers.⁴⁰⁶

3.3.5 Laser ionisation breakdown spectrometry. An atomic spectrometric method of analysis probably regarded by many as being in the “rather exotic” league is laser ionisation breakdown spectrometry. This reputation does not detract from its potential to analyse soils directly in the field, however. Recently reported studies using LIBS in a simulated Martian atmosphere (5–7 torr pressure of CO₂) suggest that it would not even matter if the field was on Mars! This will do nothing to bring its rather exotic image more down to earth.

3.3.6 Particle-induced X-ray emission spectrometry. Particle-induced X-ray emission spectrometry has been used by a number of researchers over the past year. Examples in the soil and plant analysis field include: analysis of agricultural soil samples for 15 elements;⁴⁰⁷ the study of Cd distribution in Cd accumulating Brassica juncea L;⁴⁰⁸ and mapping of elemental distribution in arbuscular mycorrhizal roots of the grass Cynodon dactylon from the vicinity of gold and uranium mine tailings.⁴⁰⁹ The same technique has been used to study element distributions in seeds of Silene vulgaris.⁴¹⁰ The full potential of micro-PIXE for element mapping has yet to be recognised.

3.3.7 X-ray fluorescence spectrometry. Applications of X-ray fluorescence spectrometry in general,⁴¹¹ and in the analysis of vegetation in particular, have recently been reviewed.⁴¹² Attempts are still being made to improve software used to correct for matrix effects,⁴¹³ and to improve calibration methodology for portable field instruments.⁴¹⁴ Whereas such systems are usually used to analyse surface soils, a system has now been developed in the USA based upon a cone penetrometer to allow sub-surface metal contamination to be investigated.⁴¹⁵

Total reflection XRF spectrometry has been used for the analysis of fine roots of Scots Pine.⁴¹⁶ Dried samples were digested with HNO₃ and Ga added as an internal standard. The mixture was placed on a quartz plate and allowed to dry for analysis for 14 major and trace nutrient/potentially toxic elements. Detection limits were mostly in the range 0.5–23 µg g⁻¹.

4 Analysis of geological materials

This section considers the trends and advances made in the application of atomic spectrometry to the understanding of the composition of geological materials in the widest sense. Judged solely from the volume of published literature in the period under review, it would appear that the most active areas of instrumental research are ICP-MS, often combined with laser ablation sample introduction, and X-ray techniques.

However, the geochemist has a large array of analytical techniques at his disposal, particularly for microanalysis. Ottolini⁵⁰¹ published a useful review of the characteristics and limitations of various microprobe techniques including EMPA, PIXE, SIMS and ASM. Any assessment of the comparability of data obtained by these different techniques relies on the availability of certified reference materials that are homogeneous on a micrometre scale. To this end, Hinton⁵⁰² used an ion probe to check the homogeneity of the range of the NIST multi-element SRM 600 series of glass standards, which are used extensively as microprobe standards. He concluded that although the absolute concentrations of analytes are significantly lower than the nominal values, these differences were due to difficulties encountered in the manufacture of the glasses and unlikely to be due to inhomogeneities in the material itself. The consistency between the ratios of random samples of glasses (SRM 610/612 and SRM 611/613) was supporting evidence for a high degree of homogeneity on all scales.

Reference materials are the cornerstone of much geochemical analysis. Over 300 such materials are available to date, but only relatively few satisfy the more stringent criteria for certified reference materials as defined by ISO. Kane and Potts⁵⁰² present a valuable interpretation of these ISO guidelines and advocate that all new reference materials should be prepared with the guidelines in mind. The Geological Survey of Japan has published a compilation of analytical data received by October 1998 for five reference materials, giving recommended and preferred values for 65 elements.⁵⁰³ It is good to see that this information is also published on the Internet.

4.1 Sample treatment

4.1.1 Solid sample introduction.
4.1.1.1 Laser ablation. The current generation of UV laser ablation systems possess characteristics such as a flat beam energy profile to produce flat-bottomed craters, dynamic focusing to maintain the focus at the sample surface during ablation and stage reposition accuracies of <1 µm.⁵⁰⁴ All these features are valuable assets when the laser system is employed as a microprobe.

Although none of these applications is particularly novel, laser ablation ICP-MS has recently provided data on the chemical composition of a variety of geological materials, from basalts,⁵⁰⁵ tephras,⁵⁰⁶ apatite⁵⁰⁷ and coal⁵⁰⁸ to Egyptian artefacts⁵⁰⁹ and molluscs.⁵¹⁰ Strictly speaking, the last material should only be deemed to be geological if it is fossilised, but many geochemists are aware that growth structures in shells and other biogenic carbonates contain chemical information which can be related to the environmental conditions under which they grew. In this work the ICP-MS instrument was optimised on ⁸⁸Sr, using a piece of natural calcite, and calibrated using BCS CRM 393 prepared as a pressed limestone powder.

Craig et al.⁵¹¹ have assessed alternative calibration strategies for the analysis of carbonate-rich materials by LA-ICP-MS. They compared commercially available glass RMs, geological RMs and high purity calcium carbonate powder spiked with the analytes of interest. Their preferred strategy was to use geological RMs, with calcium as the internal standard as it proved more reliable than indium. Ødegård⁵¹² has developed a method of preparing synthetic calibration materials for mineral analysis by LA-ICP-MS and other microtechniques. It is based on direct fusion in high-purity graphite electrodes and has been tested on quartz and rutile (TiO₂) spiked with a relatively large range of elements including the REE. Promising results have been obtained so far and it is hoped to extend the method to other oxide minerals.

As reported in last year's Update, there is still much interest in the bulk analysis of geological materials by ablating lithium borate/metaborate glass disks to determine a wide range of trace elements, and even a few major elements as well.^513–515 Günther and co-workers⁵¹⁵ used the glass standard NIST 612 as an external calibration standard and silica as an internal standard to correct for the different masses of material ablated. Although the precision was not as good as XRF, they were able to determine 40 isotopes with a reproducibility of better than 5% for the major and minor elements. A method to determine Zr and Hf in a flux-free fusion of whole rocks by LA-ICP-MS using isotope dilution calibration has been proposed by Reid et al.⁵¹⁶ The samples were prepared by adding a known amount of Zr/Hf spike solution to the rock powder, drying, grinding to homogenise the spike with the sample and then fusing on an iridium strip heater at 1600 °C for 2 min before cooling quickly. By using isotope dilution, the need for external calibration using a CRM is eliminated.

There is increasing interest in the use of laser sampling coupled to magnetic sector ICP-MS, particularly multiple collector (MC) instruments, to perform high precision isotopic measurements with the minimum of sample preparation. This has opened the door to much more rapid methods for U–Pb and Pb–Pb age determinations of single zircon crystals^517–521 with precisions comparable to those obtained by the SHRIMP technique for homogeneous zircons. Griffin et al.⁵²² determined the Hf isotope composition in zircon megacrysts by MC-ICP-MS using a fixed detector array of 12 Faraday cups and 3 ion counters.

The detection limits offered by laser-induced breakdown spectroscopy (LIBS) are in the range 30–300 mg kg⁻¹, considerably higher than those obtained with laboratory techniques such ICP or XRF. However, LIBS comes into its own in real-time applications that require less precise analyses without the time and cost of sample preparation. Bolger⁵²³ investigated its use for rapid on-line determination of major and minor constituents of mineral drill core samples. A novel normalization scheme based on integrating the total plasma emission was demonstrated as a method for correcting signal variations caused by the uneven surface of the rock. LIBS has also been used for the rapid identification of the origin of particulate geological material by comparison of the data obtained against an electronic library of spectra.⁵²⁴

Laser-based techniques have been assessed for their potential use in space exploration.^525,526 Brinckerhoff and co-workers⁵²⁵ describe a prototype miniature reflection time-of-flight mass spectrometer with a mass of about 2 kg and volume < 2 × 10³ cm³ that could be used in-situ to measure the elemental and isotopic composition of regolith materials on other planets. Microscopic surface samples are obtained with a short-pulse laser and repeated pulses could be used to access unweathered subsurface materials. LIBS has also been evaluated with a view to its potential application in space exploration.⁵²⁶ Two instrumental systems are described, one for close range (175 mm) analysis at reduced pressure and the other for measurements at distances up to 19 m. Detection limits were generally in the range 1.2–88 mg kg⁻¹ for close range work and 1.9–95 mg kg⁻¹ for greater distances.

4.1.1.2 Slurry nebulisation. This is still an attractive approach to the analysis of geological materials as it significantly reduces sample preparation time and minimises the risk of contamination or loss of analyte. Many of the recent advances centre on the introduction of slurries into electrothermal atomisers. Direct solid sampling for the analysis of soils and sediments for Cr, Cu, Ni, Pb and Zn by ETAAS and ETV-ICP-AES have been systematically investigated.³⁸⁰ Two Brazilian groups independently optimised the experimental conditions for the determination of trace elements in coal using ETAAS⁵²⁷ and ETV-ICP-MS.⁵²⁸

A third group of workers from Brazil concluded that the use of a tungsten–rhodium chemical modifier offered improvements over existing methods for the determination of Pb in sediment slurries by ETV-AAS.⁵²⁹ The permanent W–Rh modifier remained stable for approximately 250 firings when 20 µl of a 0.5% m/v sediment slurry were delivered to the atomiser.

In ETV-ICP-MS, significant analyte signal suppression is observed if microgram quantities of silicate materials are vaporised directly into the plasma. A Canadian team⁵³⁰ has determined the optimum conditions for the removal of silica by the addition of HF as a matrix modifier to drive off the silica as the tetrafluoride at temperatures below 480 °C. They concluded that 20 µl of 50% HF, and a reaction hold time of 150 s for the digestion to occur, was effective in completely removing 0.125 g of silica while maintaining the integrity of the graphite tube for over 200 firings. It will be interesting to see whether this method is widely adopted.

An ultrasound-assisted extraction procedure has been proposed as an alternative to slurry sampling and sample digestion for the determination of Cd in sediments.⁵³¹ Slurries were sonicated in nitric acid for 2–5 min using a titanium probe, centrifuged and 20 µl of the liquid phase introduced into a graphite tube previously treated with a W–Rh permanent modifier. Although good agreement with reference values was demonstrated, it is clear that the technique was really designed for the analysis of biological samples. A method employing slurry sampling combined with ultrasonic pretreatment for the determination of mercury by FI-CV-AAS has also been reported.⁴³⁶

4.1.2 Sample dissolution. An HF-based mixture of acids is normally required if microwave-assisted digestion procedures are to be successful in the total dissolution of silicate minerals.^532–535 Whilst such sample digestion procedures can minimise contamination and lower the analytical blank, there seems to be little mention of the problems posed by the analysis of the resulting solutions which may contain significant amounts of HF even after dilution. A novel application of microwave-assisted digestion has been a sequential extraction scheme for the direct determination of sulfate-S, pyritic-S and organic-S concentrations in bituminous or sub-bituminous coal.⁵³⁶ The initial extraction using 5 M HCl was analysed for sulfate-S. The residue from the initial digestion was treated with 2 M HNO₃ to obtain a solution containing pyritic-S, and the organic-S content was determined on a solution obtained by an HF-based acid mixture attack on the second residue and quenching with boric acid.

The use of xenon difluoride as a reagent for the digestion of sediments has been investigated.⁵³⁷ Although the authors report an improvement in detection limits for many elements compared with an HF vapour phase digestion, its use does have severe limitations in that it should only be handled under dry gas conditions.

Sequential extraction schemes are often used to obtain information about the distribution of trace elements between different physico-chemical phases. In such cases where the results are operationally defined, it is difficult to ensure comparability between laboratories. Therefore data on elemental concentrations derived from partial and sequential extractions of commonly available reference materials are welcome. Lynch⁵³⁸ has compiled a set of provisional elemental concentrations derived from partial extractions (dilute HNO₃–dilute HCl; concentrated HNO₃–concentrated HCl; concentrated HNO₃–concentrated HClO₄) and a five-step sequential extraction of eight CCRMP sediment reference materials. Twenty North American laboratories contributed data to this study, most of which were obtained by ICP-AES. Workers from the Geological Survey of Japan⁵³⁹ used a five-step extraction scheme with ETAAS to determine the partitioning of Au in geological reference materials. Values for Cd distributions in three coal fly ash, soil and sediment reference materials by ETAAS following sequential extractions has also been reported.⁵⁴⁰

4.1.3 Separation and preconcentration. Yang and Pin have investigated new methods for the separation of trace amounts of Zr and Hf from the major constituents of silicate rocks based on extraction chromatography.^541,542 They used a single stage extraction with a tertiary amine or quaternary ammonium salt as the stationary phase.⁵⁴¹ Although they successfully separated Zr and Hf from matrix elements such as Al, Fe, Ti, Ca, etc., it was found that trace amounts of fluoride introduced by acid digestion of the rock samples had a detrimental effect on the separation. Further work with N-benzoyl-N-phenylhydroxylamine (BPHA) yielded a superior method capable of producing detection limits of 0.02 and 0.07 µg g⁻¹ for Zr and Hf, respectively, from a LiBO₂ fusion rather than dissolution with HF.⁵⁴²

The determination of precious metals almost invariably involves preconcentration and separation of the analytes of interest because of their low abundance in most silicate phases. In a detailed review containing 116 references, Reddi and Rao⁵⁴³ summarise the main advantages and disadvantages of the methods in current use for the quantification of Au and the platinum group elements (PGE). A shorter review by Hoffman et al.⁵⁴⁴ examines the alternatives to fire assay for the determination of Au. They conclude that although fire assay remains the reference method for Au it is not foolproof for recovering 100% of the gold present. Akatsuka and McLaren⁵⁴⁵ discuss preconcentration and separation methods for the determination of trace Pt in environmental samples by ICP-MS.

Several groups of workers have been seeking to make improvements on published procedures. The method to determine Au, Ir, Pd, Pt, Rh, and Ru by ICP-MS after fusion with sodium peroxide and separation with tellurium co-precipitation has been modified by Jin and Zhu.⁵⁴⁶ They claim enhanced recoveries of Ru and Au, with detection limits of 1–9 pg g⁻¹ using 20 g of sample. The chlorination technique using a Carius tube has been developed by a group at Durham University to incorporate solvent extraction and anion exchange separation for the determination of the PGE including Os and Re–Os isotopes in geological samples by isotope dilution ICP-MS.^547,548

4.1.4 Speciation studies. A combination of cation exchange chromatography and ICP-MS has been employed for the simultaneous measurement of arsenic species in various matrices including river sediments;¹⁶⁰ a detection limit of 0.14 µg l⁻¹ As was reported. In a comparison of the performance of ICP-MS and AFS detection, based on the use of HPLC and hydride generation, comparable detection limits of the order of 0.1–0.3 µg l⁻¹ As were obtained.¹⁵⁶ The chemical stability and oxidation behaviour of cationic arsenic compounds in a microwave sample preparation system using nitric acid and hydrogen peroxide have also been investigated.⁵⁴⁹

A novel piece of research has looked at the possibility of using a low pressure (LP) ICP ion source for organomercury speciation in sediments.⁵⁵⁰ Atomic mass spectra for methylmercury were obtained when the plasma was sustained in pure helium between 9 and 12 W power. Molecular spectra were obtained under soft ionisation conditions at 5 W power in the presence of a reagent gas; ammonia was found to yield the best stability and sensitivity when employed to modify the ionization conditions in the LP-ICP.

There is still much interest in methods for the measurement of organotin species. HPLC coupled with ICP-MS is an attractive solution, but problematical because of matrix effects and potential changes in the chemical form of the analyte during sample extraction. The latter difficulty has been tackled by spiking the sample with tributyltin iodide enriched in ¹¹⁶Sn prior to extraction⁵⁵¹ and optimising a microwave-assisted acid extraction.⁵⁵² Alternative approaches using multicapillary GC with ICP-AES⁵⁵³ or ICP-MS detection⁵⁵⁴ have been reported recently.

4.1.5 Vapour generation. A multi-element approach based on atom-trapping ETAAS for As, Sb and Se has been developed for a range of materials including soils and sediments.³⁸⁹ Gaseous hydrides of the elements of interest formed by reaction with sodium tetrahydroborate are introduced into a graphite tube coated with iridium. The hydrides are preconcentrated at 300 °C in the tube before measurement. Murphy and co-workers²⁰⁷ adopted a similar approach; they included an off-line reduction process to ensure that the analyte was in its most sensitive and favourable oxidation state. However, so far, they have only applied their method to waters. The use of hydride generation for the determination of bismuth at trace levels is an attractive alternative to conventional modes of sample introduction to ICP-AES in order to improve sensitivity. However, relatively strong interferences have been observed in the generation of BiH₃ in comparison with other hydride-forming elements. A comprehensive study of the effect of hydrochloric, tartaric, oxalic, citric, sulfosalicylic and acetic acids on the efficiency of BiH₃ formation and the interfering effect of transition metals and other hydride-forming elements concluded that tartaric acid was the most suitable reaction medium.¹⁵¹

4.2 Instrumental analysis

4.2.1 Atomic absorption spectrometry. For an up-to-date text on atomic absorption spectrometry the reader need look no further than the third edition of Welz's book on the subject,²⁰² which contains chapters on its application to the analysis of a multitude of sample types including rocks, minerals and ores. Although AAS is still widely employed for geochemical analysis, as witnessed by the papers in Table 4, it is hard to divine much that is new. The method of co-precipitating Ag from sea-water with cobalt (II) pyrrolidinedithiocarbamate, prior to measurement by ETAAS, has been applied to the determination of Ag at pg g⁻¹ levels in road salt samples.⁵⁵⁵ A procedure claiming to be new and rapid for the determination of Hg, involving pyrolysis of the sample in a combustion tube at 750 °C under an oxygen atmosphere, collection on a gold amalgamator and detection by AAS using a silicon UV dioxide detector, has been reported recently.⁴³⁷

Table 4 Summary of the analyses of geological materials

Element	Matrix	Technique; atomization; presentation^a	Sample treatment/comments	Ref.
a Hy indicates hydride and S, L, G and Sl signify solid, liquid, gaseous or slurry atomization, respectively. Other abbreviations are listed elsewhere.
Ag	Lead ore	AA;-;L	Dissolved in HNO3 and HClO4	632
Ag	Sediment	AA;ETV;L	Digested with aqua regia. Ru deposited on platform as permanent modifier	559
Al	Sediment	AE;arc;S	Ground to ca. 3.8 µm. Slurried with H2SO4 and La as internal standard	633
As	Environmental material	AA;-;Hy	Stability of cationic As compounds during microwave assisted digestion studied	549
As	Sediment	MS;ICP;L	Species eluted from sulfonic acid type cation exchange column	160
As	Coal	AF;-;G	Continuous on-line extraction with subcritical water	560
As	Soil and sediment	AA;ETA;Hy	Automated hydride generation followed by preconcentration on Ir coated walls of furnace at 300 °C	389
As	Environmental material	AA;-;Hy	Reaction conditions for speciation examined	153
As	Sediment	MS;ICP;- AF;-;-	Comparison of ICP-MS and AFS detection for speciation studies	156
Au	Geological material	-;-;-	Review with 9 refs. of fire assay and other techniques	544
Au	Geological material	AE;ICP;L	10 g calcined at 650 °C for 1 h. Digested with 30 ml 50% aqua regia, followed by on-line FI preconcentration	634
Au	Geological RMs	AA;ETA;L	Five-step sequential extraction	539
Au	Sulfides	MS;-;S XRF;-;S	Comparison between SIMS and synchrotron XRF	635
B	Tourmaline	MS;-;S	Matrix effects on the determination of B, H and Li investigated	636
Bi	Geological material	AE;ICP;Hy	Six reaction media compared	151
C	Graphite	MS;-;S	SIMS used to measure C isotopic ratios in study of crustal fluids	598
C	Geological materials	MS;-;S	Impure CO2 reduced to graphite, re-oxidised at 500 °C to pure CO2 and reduced to amorphous carbon. ^14C∶^12C ratio determined by AMS	637
C	Diamond	MS;-;S	SIMS study of variations C isotope composition and N abundance	599
C	Geological material	MS;-;S	Description of the geological, archaeological and environmental applications of the Erlangen, Germany, AMS system	606
Ca	Carbonates	MS;ICP;L	Dissolved in 3 M HCl, centrifuged, supernatant evaporated to dryness and dissolved in 2 M HNO3. Isotope ratios measured with high precision using multiple collector ICP-MS	586
Ca	Halite	MS;ICP;L	Nd∶YAG laser (266 nm) used to ablate single fluid inclusions	638
Cd	Fly ash, soil and sediment	AA;ETA;L	Microwave assisted digestion with HNO3, HCl and HF	425
Cd	Coal	AA;ETA;S	Slurried with a mixture of 5% v/v HNO3, 0.05% Triton X-100 and 10% ethanol	527
Cd	Sediment RMs	MS;ICP;L	Microwave assisted digestion with HF and HNO3. Isotope dilution and mass bias corrections used with sector field ICP-MS	577
Cd	Sediment	AA;ETA;L	W–Rh permanent chemical modifier used	557
Cd	Fly ash, soil and sediment	AA;ETA;L	Forms of Cd studied using sequential extraction	540
Cd	Sediment	AA;ETA;L	Comparison of ultrasound-assisted extraction, microwave-assisted digestion and slurry sampling	531
Cu	Geological material	MS;ICP;L	Dissolved in 5 M HNO3. Isotope ratios measured using multiple collector ICP-MS	585
Cu	Sediment	AA;ETA;L	See Cd, ref. 531	531
Eu	Environmental material	AE;ICP;G	Separated and preconcentrated on micro-column of immobilized 1-phenyl-3-methyl-4-benzoyl-5-pyrene. ETV sample introduction	639
F	Humite-group minerals	EMPA;-;S	Comparison of accuracy of EMPA, SIMS and SREF in the determination of high concentrations of F	640
Fe	Geological material	MS;ICP;L	Dissolved in 6 M HCl, purified by double precipitation with aqueous NH3. Isotope ratios measured with high precision using double focusing multiple collector ICP-MS	584
Fe	NIST SRMs	MS;ICP;L	See Pb, ref. 589	589
Ga	Geological material	XRF;-;S	Analytes preconcentrated onto macroporous resins loaded with 5-phenylazoquinolin-8-ol. Resins deposited on Millipore filters, covered with Mylar film and analyzed by WDXRF	610
H	Tourmaline	MS;-;S	See B, ref. 636	636
Hf	Iron rich geological material	MS;ICP;L AE;ICP;L	Digested with HNO3, HF and HClO4. Hf, Zr and Fe separated from major elements on anion exchange column	541
Hf	Rock	MS;ICP;S	Powder mixed with enriched spike solution, dried and ground. Fused twice without flux. Hf and Zr determined by LA-ICP-MS using Nd∶YAG (266 nm) and ArF (193 nm) excimer lasers	516
Hf	Basalt	AE;ICP;L	Two chromatographic separation techniques are compared	542
Hf	Zircon	MS;ICP;S	Ablated with frequency quadrupled Nd∶YAG laser at 266 nm. Isotope composition determined by multicollector ICP-MS	522
Hg	Environmental material	XRF;-;S	Amalgam formed with thin layer of gold deposited on quartz reflector. TXRF data processed to resolve overlapping Hg and Au peaks	623
Hg	Coal	AF;-;G	See As, ref. 560	560
Hg	Sediment	AA;-;G	Slurried with 9 + 1 mixture of 15% HNO3 and 15% HCl containing 0.02% v/v Triton X-100. Ultrasonic treatment prior to FI sample introduction	436
Hg	Sediment	AE;-;-	Comparison of GC and detection techniques for speciation studies	641
Hg	Sediment	MS;ICP;-	Comparison of extraction methods and use of a low pressure He plasma for the determination of organomercury species	550
Hg	Environmental material	MS;ICP;-	Species separated by microcolumn multicapillary GC	554
Hg	Sediment	AA;-;G	Reduction with stannous chloride	642
Hg	Zinc ore	AAS;-;CV	0.1–0.2 g dried and powdered sample wetted with H2O, mixed with 10 ml HCl, heated on a hotplate for 10 min to remove H2S, mixed with 10 ml HCl and 4 ml HNO3, heated for 30 min and diluted to 100 ml with H2O	643
Hg	Environmental material	AA;-;G	Pyrolysed in a combustion tube at 750 °C under O. Hg collected on Au	437
Hg	Environmental material	-;-;-	Review with 57 refs. of Chinese work	61
In	Geological material	XRF;-;S	See Ga, ref. 610	610
La	Environmental material	AE;ICP;G	See Eu, ref. 639	639
Li	Basalt	MS;ICP;L	Digested with concentrated HF∶HNO3 (3∶1). Isotopic composition measured using multi-collector ICP-MS	582
Li	Tourmaline	MS;-;S	See B, ref. 636	636
Li	Basalt	MS;ICP;L	Isotopic composition measured using multicollector sector ICP-MS	583
Mo	Geological material	MS;ICP;L	Digestion with HF and mixed Mo, Sb and W spike. Measurement involved ID-FI-ICP-MS	576
Mo	Molybdenite	MS;-;L	Mo isotopes determined by TIMS	596
Nb	Geological material	MS;-;S	60 mg mixed with 30 mg graphite spiked with ^91Zr, milled and pressed into electrodes. Nb, Y and Zr determined by spark source MS with multiple ion counting	603
Nb	Geological RMs	XRF;-;S	Comparison of direct WDXRF analysis of pressed powder pellets with separation and collection of analyte on anion-exchange membranes	611
Nb	Meteorites	MS;-;S	Nb, Y and Ta determined by spark source MS with multiple ion counting	602
O	Emerald	MS;-;S	SIMS used to measure O isotopic ratios to identify origin of gems	644
Os	Geological material	MS;ICP;L	Isotope dilution used with three different nebulisers	590
Os	Molybdenite	MS;ICP;-	Os-Os dating method studied using ICP-MS and negative ion TIMS	591
Os	Geological material	MS;ICP;G	OsO4 introduced directly into the plasma of a multicollector ICP-MS. Picogram levels of Os and Re determined by isotope dilution	592
Pb	Sediment	AA;ETV;L	W–Rh permanent chemical modifier used	558
Pb	Sediment	AA;ETV;L	See Ag, ref. 559	559
Pb	Zircon	MS;ICP;S	Instrumental conditions and calibration strategies for Pb–Pb age determination by LA-ICP-MS discussed	518
Pb	Ore	AA;-;L	Decomposed with HCl and HNO3	645
Pb	Geological material	MS;ICP;S	Discussion of errors in LA-ICP-MS and other techniques of U–Pb age determination	519
Pb	Sediment	AA;ETA;S	Slurried with 0.5% v/v HNO3 containing 0.04% Triton X-100. W–Rh permanent chemical modifier used	529
Pb	Sediment	AA;ETA;L	Microwave assisted digestion with aqua regia and HF	556
Pb	Coal	AA;ETA;S	See Cd, ref. 527	527
Pb	Zircon	MS;ICP;S	Single grains pressed into epoxy disc and polished. U–Pb age determined by LA-ICP-MS	520
Pb	Zircon	MS;ICP;S	U–Pb age determined by LA-ICP-MS	521
Pb	NIST SRMs	MS;ICP;L	Precision of isotope ratio measurements improved by collisional damping in a dynamic reaction cell. See Fe, ref. 589	589
Pb	Sediment	AA;ETA;L	See Cd, ref. 531	531
Pd	Dust and sediment	MS;ICP;L	Microwave assisted digestion with aqua regia. Ultrasonic nebulisation used with sector field ICP-MS	579
Pd	Copper-nickel ores	AAS;-;L	Pd adsorbed on silica treated with N-allyl-N′-propylthiourea. Eluted with thiourea solutions in HCl	646
Pt	Dust and sediment	MS;ICP;L	See ref. 579	579
Pt	Geological and environmental material	MS;ICP;-	Discussion of preconcentration and separation methods presented	545
Pu	Environmental materials	MS;ICP;L	Low-flow microconcentric nebuliser	587
Pu	Environmental RMs	MS;ICP;L	On-line separation of ^238U with two extraction resins. Measurement involving isotope dilution and HR-ICP-MS	441
Rb	Halite	MS;ICP;L	See Ca, ref. 638	638
Rb	Geological material	AA;-;S	Ablated with Nd∶YAG laser. Isotope spectrum obtained by scanning plasma with narrow band Ti∶sapphire laser	647
Rh	Dust and sediment	MS;ICP;L	See Pd, ref. 579	579
REE	Rock	MS;ICP;L	Decomposed in a mixture of HF + HClO4 at 150 °C	568
REE	Geological material	MS;ICP;L	Direct injection nebuliser used with sector field instrument	648
S	Coal	MS;-;S	Chemical form of sulfur investigated by SIMS	649
S	Coal	AE;ICP;L	Forms of S determined following sequential microwave assisted acid extraction	536
Sb	Soil and sediment	AA;ETA;Hy	See As, ref. 389	389
Sb	Geological material	MS;ICP;L	See Mo, ref. 576	576
Se	Coal	AF;-;G	See As, ref. 560	560
Se	Soil and sediment	AA;ETA;Hy	See As, ref. 389	389
Se	Sediment	AA;-;Hy	Six different extraction solutions compared	650
Se	Rock	AA;-;Hy	Digested with HF, HClO4 and HNO3 at 140 °C for 2 h	651
Se	Environmental material	AA;-;-	Review in Czech with 130 refs.	180
Sn	Sediment	AA;ETV;L	See Ag, ref. 559	559
Sn	Sediment	MS;-;-	Extracted with 1 M HCl in methanol and ethyl acetate (1∶1). Organotin compounds detected by GC-MS	652
Sn	Sediment	AE;-;-	Microwave assisted digestion with acetic acid followed by solvent extraction and derivatization. Organotin compounds separated by multicapillary GC	653
Sr	Silicate rock	MS;ICP;L	Dissolved in a mixture of 28 M HF and 14 M HNO3 in a PTFE vessel, evaporated to dryness and dissolved in 2 M HCl. Sr separated on Dowex 50W-X8 cation exchange column. Precision of isotope ratios measured by quadrupole instrument shown to be adequate where variations are large	654
Sr	Halite	MS;ICP;L	See Ca, ref. 638	638
Ta	Meteorites	MS;-;S	See Nb, ref. 602	602
Th	Environmental materials	MS;ICP;L	See Pu, ref. 587	587
Th	Geological material	MS;-;L	Improved chromatographic procedure for the separation of Th and U using TRU^SPEC resins in acidic media	594
Th	Ore	MS;ICP;L	On-line matrix separation with 2,6-pyridinedicarboxylic acid. Isotopes measured by sector field ICP-MS	580
Ti	Silicate RMs	MS;ICP;L	Digested with HF. ID and FI used with sector field instrument	575
Tl	Geological material	MS;ICP;L	Two-stage anion exchange separation. Isotopic data obtained by multiple collector instrument. Method claimed to be an improvement over that from TIMS	581
U	Environmental materials	MS;ICP;L	See Pu, ref. 587	587
U	Geological material	MS;ICP;S	See Pb, ref. 519	519
U	Zircon	MS;ICP;S	See Pb, ref. 520	520
U	Uranium ore	MS;-;L	High precision measurement of natural U isotope ratios resulting in proposed IUPAC reference values	655
U	Geological material	MS;-;L	See Th, ref. 594	594
U	Environmental material	MS;ICP;L	Digested with HF + HNO3 + HClO4. Pt used as internal standard	566
U	Zircon	MS;ICP;S	See Pb, ref. 521	521
U	Ore	MS;ICP;L	See Th, ref. 580	580
U	Phosphogypsum	MS;ICP;L	Refluxed with HNO3 for 2 h at 120–140 °C. U separated by column chromatography	588
U	Minerals	-;-;-	Review of spectroscopic techniques	656
W	Geological material	AE;ICP;L	Fused with KHSO4. Comparison made with derivative spectrophotometry	564
W	Geological material	MS;ICP;L	See Mo, ref. 576	576
Y	Geological material	MS;-;S	See Nb, ref. 603	603
Y	Meteorites	MS;-;S	See Nb, ref. 602	602
Zn	Ore	AA;-;L	See Pb, ref. 645	645
Zr	Geological material	MS;-;S	See Nb, ref. 603	603
Zr	Iron rich geological material	MS;ICP;L AE;ICP;L	See Hf, ref. 541	541
Zr	Basalt	AE;ICP;L	See Hf, ref. 542	542
Various	Geological material	-;-;-	Review with 134 refs. of techniques for multi-element analysis, emphasizing ICP-MS and ICP-AES	345
Various	Zircon	MS;ICP;S	U–Pb and Pb–Pb ages and 25 trace elements determined by LA-ICP-MS	517
Various	Geological and environmental samples	MS;-;S	Examples of recent developments and applications of RIMS	600
Various	Geological material	-;-;-	Review with 97 refs. of advances in the determination of Au and the PGEs from 1990–1998	657
Various	Environmental materials	AA;ETA;Hy	As, Bi, Sb, Se and Te determined by in-atomiser trapping in Ir-coated graphite tube	207
Various	Geological material	MS;-;-	Review of atomic mass spectrometry	394
Various	Rock, ore and concentrates	AE;ICP;L	Digestion in aqua regia followed by fusion with Na2O2. Au, Pd, Pt and Rh determined after reductive co-precipitation using Se as collector	658
Various	Feldspar	AE;ICP;L	Decomposed with HF + H2SO4 + HNO3. Fused with Na2CO3 and Na2B4O7 at 1000 °C for 15 min, cooled and dissolved in HCl (1∶1). Al, Ca, Fe, Mg and Ti determined	659
Various	Geological material	AA;-;-	Book reviewing AAS, 964 pp.	202
Various	Geological material	MS;ICP;S	Study of the use of HF to remove Si in ETV slurry sample introduction	530
Various	Geological and environmental materials	XRF;-;S	Annual review of XRF spectrometry with 537 refs.	411
Various	Sepiolites	AE;ICP;L	Microwave assisted digestion with HNO3, HCl and HF	532
Various	Niobium–tantalum ore	XRF;-;S	Pelletised with cellulose binder	616
Various	Obsidian artefacts	XRF;-;S	Diamond polished, mounted in epoxy-resin and subjected to PIXE analysis and fission track dating	660
Various	Rubies	XRF;-;S	Provenance examined using trace element fingerprinting of PIXE data	625
Various	Geological materials	EPMA;-;S	Interactive program used to choose matrix correction model for data from a CAMECA SX50 microprobe	661
Various	Geological and environmental material	XRF;-;S	Novel method of EDXRF signal deconvolution for gas-filled proportional counters described	662
Various	Sediment	AE;ICP;L MS;ICP;L	Major and trace elements determined after fusion with LiBO2	663
Various	Basalt	MS;ICP;S	28 trace elements determined by LA-ICP-MS to fingerprint ancient Egyptian quarries	509
Various	Geological material	MS;-;S	Fused into glass, powdered, pressed into electrodes and 18 elements determined by spark source MS with multiple ion counting	664
Various	Soil	AA;F;L AA;ETA;L	Rapid partial dissolution proposed for geochemical exploration	665
Various	Geological materials	XRF;-;S	Principles and applications of micro-XANES and micro-XRF using synchrotron radiation explained	666
Various	Platinum group minerals	XRF;-;S	PIXE and EPMA trace element data from cooperite and braggite compared	628
Various	Gold ore	XRF;-;S	PIXE microanalysis used to examine Au–pyrite associations in the Kimberley reefs	629
Various	Sulfides	XRF;-;S	Micro-PIXE evaluated for the identification of chemical signatures and textural types	630
Various	Zircons	XRF;-;S	PIXE analysis used to discriminate zircons from S-, I- and A-type granites	627
Various	Coral and sediment	XRF;-;S	Various EDXRF methods, including TRXRF, discussed for the determination of marine pollution indicators	615
Various	Soil gas	MS;ICP;L	Use of trace metals sorbed onto activated carbon collectors over ca. 100 d as an exploration tool for buried mineralization	667
Various	Geological material	-;-;-	Discussion of techniques for the determination of Au, Ir, Os, Pd, Pt, Rh and Ru presented	543
Various	Geological RMs	MS;-;L	Figures of merit for ICP-TOF-MS discussed	330
Various	Geological RMs	MS;ICP;S	Fused with Li2B4O7. Minor and trace elements determined by LA sample introduction using NIST 612 glass for calibration and Si as internal standard	515
Various	Coal	AE;GD;S	Ashed and pressed into pellets without binder	668
Various	Phosphate rock	AE;-;S	Ground and pressed into pellets. LIBS used in near-line process monitoring	669
Various	Sediment	XRF;-;S	0.3 g mixed with 3 drops of organic solvent and pelletised. Trace elements determined by EDXRF using 925 MBq ^109Cd source	670
Various	Ore	XRF;-;S	Ground to <300 mesh and pelletised with cellulose binder. Ba, I, In, Mo, Sb, Sn and Sr determined by EDXRF using ^241Am source	617
Various	Sediment	AA;F;L	Microwave assisted digestion with HNO3. Cr, Cu, Pb and Zn determined by EPA methods	671
Various	Soil and sediment	AE;ICP;L	Study of spectral interferences in the determination of trace elements	562
Various	Trapiche rubies	XRF;-;S	Spatial variability of Al, Ca, Cr, Fe, Si and Ti examined	626
Various	Martian rock	XRF;-;S	Direct analysis by alpha proton X-ray spectrometry at Pathfinder landing site	613
Various	Coal	MS;ICP;S	Trace elements determined by LA-ICP-MS	508
Various	Geological material	MS;ICP;L	REEs determined by isotope dilution	574
Various	Geological material	MS;ICP;-	Review with 13 refs. of geochemical applications of sector based ICP-MS	672
Various	Geological material	-;-;-	Review with 859 refs.	84
Various	Clinopyroxene	MS;ICP;S	Comparison of LA-ICP-MS with other techniques for the determination of incompatible trace elements	673
Various	Synthetic glasses	MS;ICP;S	Synthetic calibration glasses for LA-ICP-MS prepared by fusion of spiked TiO2 and SiO2 in high purity graphite electrodes	512
Various	Geological RMs	-;-;-	An interpretation of ISO guidelines for certification presented	502
Various	Coal	MS;ICP;L	Microwave assisted digestion in concentrated HNO3	571
Various	Geological material	MS;-;S	Compact benchtop SIMS instrument described	597
Various	Geological material	MS;-;S	Description of the AUSTRALIS AMS system incorporating a 30 µm Cs beam source and its applications for trace element and isotopic measurement given	608
Various	Foraminifera	MS;ICP;L	Element-calcium ratios measured precisely on single shells using sector field instrument	674
Various	Sediment	AE;ICP;L, XRF;-;S	Samples dried, homogenized and leached sequentially with ammonium nitrate, ammonium acetate, hydroxylamine hydrochloride, ascorbic acid and HNO3 + H2O2. Ba, Ca, Fe, Mn, and Sr determined by ICP-AES. Undissolved residue filtered off, dried and pellitized. Ca, Fe, K, Mn, Rb, Si, Sr, Ti, Y, Zn and Zr determined by EDXRF	614
Various	Sediment	TXRF;-;S	200 mg microwave-digested in PTFE bomb with HNO3, HF, H2O and Ga as internal standard, diluted with water and 10 µl pipetted onto a quartz sample carrier	237
Various	Geological material	MS;ICP;S	Fused with Li2B4O7 and LiBO2 (9∶1) at 1050 °C. Trace elements determined by LA-ICP-MS	513
Various	Soil and sediment	XRF;-;S	Dried at 105 °C. Reasons for not fusing discussed. Matrix correction based on α-coefficients calculated for homogeneous materials	484
Various	Geological RMs	MS;ICP;L	100 mg samples microwave digested with 2 ml HF and 0.5 ml HNO3 at 130 °C for 48 h	397
Various	Silicates	XRF;-;S	Comparison of software packages for processing data from analysis of fusion disks	675
Various	Moon rock	XRF;-;S	Description of the CCD-based X-ray spectrometer to be launched in 2003 aboard the SELENE orbiter given	612
Various	Monazite	XRF;-;S	Evaluation of WDXRF operating parameters for the determination of 32 elements including the REEs	619
Various	Sediment	XRF;-;S	Various X-ray techniques compared in pollution studies	624
Various	Black shale	MS;ICP;L	Digested with HNO3 + HF in a PTFE bomb at 190 °C for 3 h. Cd, Ga, Ge, In, Re, Se, Te and Ti determined	573
Various	Sediment	MS;ICP;L	0.1 g dried at 120 °C and digested with 1.5 g XeF2 in the vapour phase at 190 °C and 9 × 10^6 Pa, followed aqua regia digestion	537
Various	Extra terrestrial regolith	MS;-;S	Description of compact (ca. 2 kg) laser ablation TOFMS for direct analysis of planetary surfaces	525
Various	Granite	MS;ICP;L	100 mg digested with 1 ml HF and 0.5 ml HNO3 in PTFE-lined stainless steel bombs at 190 °C for 12 h. Insoluble residue dissolved in 40% HNO3 at 110 °C for 3 h. Rh used as internal standard	567
Various	Silicate RMs	XRF;-;S	Figures of merit given for the analysis of six RMs using synchrotron-XRF with a standard-free fundamental parameter approach to quantification	676
Various	Soil and sediment	MS;ICP;L	Microwave assisted digestion with HF + HNO3	535
Various	Geological material	AA;F;L	Cd, Cu, Fe, Ni and Zn preconcentrated on columns of Aspergillus niger immobilized on sepiolite	677
Various	Rock, soil and sediment	AA;ETV;S	Cr, Cu, Ni, Pb, and Zn determined using direct solid sample introduction	380
Various	Geological material	AE;-;S	Use of LIBS for the direct determination of Cr, Cu, Fe, Mn and Ni in drill core	523
Various	Rock RMs	MS;ICP;L	Microwave assisted digestion. REEs separated on Dowex AG-50WX-12 cation exchange column	569
Various	Lignite	MS;ICP;-	38 elements determined along with mineralogical studies	678
Various	Geological material	MS;ICP;S	Fused with Li2B4O7. 35 elements determined by LA-ICP-MS	514
Various	Coal and fly ash	MS;ICP;L	1-Methylpyrrolidin-2-one used to extract organically associated trace elements	572
Various	Iron ore	AE;-;S	LIBS used for the rapid identification of particles	524
Various	Rock	TXRF;-;S	Ablated under Ar with Nd∶YAG laser directly onto sample carrier	622
Various	Geological material	MS;ICP;L	Au and the PGEs determined after fusion with Na2O2 and co-precipitation with Te	546
Various	Rock, soil and sediment	XRF;-;S	0.25 g powder mixed with 1 g H3BO3 and pellitised. Ba, Fe, Sr and Zr determined using 3.7 GBq ^241Am source and Si(Li) detector	679
Various	Colemanite ore	XRF;-;S	As, Ba, Cs, I, In, Sb, Sn and Sr determined by EDXRF using 100 mCi ^241Am source	618
Various	Soil and sediment	AE;-;S	Two LIBS systems evaluated for space exploration	526
Various	Sediment	MS;ICP;-	Four methods used: microwave digestion, NiS fire assay, acid leaching and Carius tube digestion. Os and the PGEs determined	593
Various	Geological and environmental materials	MS;-;S	Recent advances in AMS reviewed	605
Various	Rock	MS;ICP;L	High pressure digestion with HF + HNO3 in a Teflon bomb. 43 trace elements determined using double focusing instrument	578
Various	Meteorites	MS;-;S	Au, Ir, Os and Pt determined by SIMS	680
Various	Geological material	-;-;-	Use of chemometric techniques to maximise information from multi-element measurements	348
Various	Fluid inclusions	XRF;-;S	Ca, Cl, K, Mg and SO4 ions determined on frozen samples by EDXRF attached to a scanning electron microscope	620
Various	Rock and soil	XRF;-;S	Samples dried, ashed at 1000 °C, ground in agate and Pd–C powder added as internal standard. Mixture deposited on 4 µm thick polypropylene sheet and fixed with 10% collodion solution. A 2.9 MeV proton beam provided by a small cyclotron. Correction for self-absorption examined	681
Various	Garnet	TXRF;-;S	Sample digested. Results compared with those obtained directly on the minerals by EMPA	621
Various	Geological material	XRF;-;S	Review with 37 refs. of micro-PIXE and Rutherford backscattering spectrometry capabilities	631
Various	Sulfide minerals	AA;F;L	Decomposed with HCl, H2SO4 and HNO3	682
Various	Carbonates	MS;ICP;S	Calibration strategies for the determination of Ba, Cd, Fe, Mg, Mn, Pb, Sr, U and V by LA discussed	511
Various	Coal	AA;ETA;S	As, Mn, Pb and Se determined in 5% v/v HNO3 slurries	528

---

Chemical modifiers still provide a fruitful area of research in ETAAS.^425,556 As noted in Section 4.2.1.2, a tungsten carbide–rhodium coating has been advocated as a permanent chemical modifier for the determination of Cd and Pb in dissolved sediments as well as slurries.^557,558 Ruthenium has also been proposed as a permanent modifier for the analysis of Ag, Pb and Sn in aqua regia extracts.⁵⁵⁹

4.2.2 Atomic fluorescence spectrometry. Atomic fluorescence spectrometry has excellent detection limits for As, Hg and Se and is routinely used for their detection in geological samples including coal.^560,561 In their search for an alternative to the standard methods of sample preparation, Fernández-Pérez and co-workers⁵⁶⁰ used subcritical water extraction, at temperatures of 100–374 °C and pressures high enough to maintain the liquid state, as the basis of a rapid, clean and efficient method for the extraction of trace metals from coal prior to measurement by AFS.

4.2.3 Atomic emission spectrometry. A review of multielemental analysis with 134 references,³⁴⁵ which includes the application of both ICP-AES and ICP-MS to geochemistry, as well as environmental and biological materials, has been published recently. Although tables of spectral lines with an assessment of possible interferences in inductively coupled plasma atomic emission spectrometry have been available for decades, Daskalova and Boevski⁵⁶² have compiled a table of interferences from Al, Ca, Fe, Mg and Ti specifically for soils and sediments. It is available on the Internet.

Although other techniques may have superior detection limits, ICP-AES has many attributes that make it well suited to the rapid analysis of geochemical exploration samples.⁵⁶³ An ICP-AES method has been developed to determine W in niobate–tantalate and tin slag samples.⁵⁶⁴ The steps involved in the sample dissolution depend on the exact nature of the sample but essentially they are fused with KHSO₄ and dissolved in citric acid, except when high levels of Nb and Ta are present. In this case the KHSO₄ fusion is dissolved in ammonium oxalate solution, Nb and Ta precipitated as the hydroxides and then the solution boiled to destroy the oxalate before aspiration into the plasma.

4.2.4 Inductively coupled plasma mass spectrometry. Quadrupole ICP-MS is in routine use world-wide for the determination of trace elements in silicate rocks,^565–567 particularly the REE.^568–570 Potential pitfalls for the unwary lie in the choice of a method of dissolution appropriate to the sample type and the elements of interest. Thirty-eight elements including the REE were determined in granite after a HF–HNO₃ acid digest in PTFE-lined stainless steel bombs at 190 °C for 12 h.⁵⁶⁷ Sample types as diverse as wood and coal,^571,572 black shale⁵⁷³ and benthic material from estuaries³⁴⁰ are all amenable to analysis by ICP-MS once they have been digested by appropriate means.

Separation of the REE may be necessary if very low detection limits are required.^569,574 To this end, Griselin and co-workers⁵⁷⁴ developed a relatively simple isotope dilution ICP-MS method for the analysis of geological samples containing between 1 and 10 ng g⁻¹ REE; any variation in yield from the chromatography step was accounted for by the isotope dilution spikes. Makishima and Nakamura have successfully employed isotope dilution with FI-ICP-MS to tackle the challenging tasks of determining Ti at µg g⁻¹ levels⁵⁷⁵ and Mo, Sb and W at ng g⁻¹ concentrations⁵⁷⁶ in a range of silicate rocks. In both methods a spike solution is added during sample decomposition and the final solution stabilised with HF before direct introduction into the ICP-MS instrument via a FI manifold. To avoid the isobaric interferences on ⁴⁷Ti⁺, a high resolution ICP-MS instrument with a mass resolution of >3000 was used to determine Ti.⁵⁷⁵ Park and co-workers⁵⁷⁷ employed ID-ICP-MS for their very accurate measurement of Cd in sediment reference materials.⁵⁷⁷

When operated in high resolution (HR) mode, magnetic sector ICP-MS is often able to resolve isotopes of interest from various polyatomic ions that are known to interfere in quadrupole ICP-MS. Thus, the ArCl interferences on ⁷⁵As and ⁷⁷Se can be separated with a resolution of m/Δm of 7500.²⁵¹ Many of the polyatomic interferences associated with the isotopes of the first row transition metals can be overcome using medium resolution (ca. 3000), with improved accuracy as a consequence.³⁹⁷ A Chinese group claim to have devised a simple method to determine 43 trace elements in rock samples by HR-ICP-MS⁵⁷⁸ but it remains to be seen whether this will be the method of choice for routine work of this type. Rauch and co-workers⁵⁷⁹ demonstrated that ultrasonic nebulisation combined with HR-ICP-MS provides sufficient sensitivity for the determination of PGEs at ng g⁻¹ levels in road dusts and river sediments. Interferences on Pt were resolved at a resolution of 10 100, Hf being the main interferent, but interferences on Pd from oxides of Rb, Sr, Zr and Y remain, even in HR-ICP-MS, so that reported values of Pd should be treated with caution unless a separation has been performed first. HR-ICP-MS, combined with on-line sample pre-treatment, has also been applied to the determination of trace quantities of ²³⁹Pu, ²⁴⁰Pu, ²⁴²Pu and ²³⁸U in soil and sediment RMs.⁴⁴¹ Separation of ²³⁸U and preconcentration of Pu were performed sequentially on two extraction resins, Sr-Spec™ and TEVA-Spec™, using a fully automated liquid handling system. In addition, the use of a microconcentric nebuliser was found to reduce the UH⁺/U⁺ ratio by about 5-fold over a conventional pneumatic nebuliser. Detection limits reported for ²³⁹Pu, ²⁴⁰Pu and ²⁴²Pu by this method were 4, 3 and 6 fg ml⁻¹, respectively. High performance ion chromatography (HPIC) combined with HR-ICP-MS has been employed in the measurement of U isotopes and Th in industrial ores containing high levels of REE⁵⁸⁰ using 2,6-pyridinedicarboxylic acid as a complexing agent.

The wider availability of magnetic sector (MS) ICP-MS instruments, particularly those fitted with multiple collectors (MC), is reflected in recent developments in the measurement of isotopes by HC-ICP-MS. As indicated in last year's Update on atomic mass spectrometry,³⁹⁴ MC-ICP-MS now equals or surpasses the precision of TIMS for some applications, such as the measurement of Tl isotopic compositions of geological materials and meteorites.⁵⁸¹ Lithium isotopic ratios in basalts from island arcs^582,583 have been determined with a throughput of 8 min per sample and a precision of ±1.1 parts per thousand, similar to the precision of other methods in current use. High precision measurement of ⁵⁷Fe∶⁵⁴Fe ratios in meteoritic iron, haematite and siderite by MC-ICP-MS⁵⁸⁴ were achieved by matching the Fe concentrations in the sample and standard solutions to minimise the influence of the ⁴⁰Ar¹⁴N⁺ polyatomic ion on ⁵⁴Fe. The isobaric interference from ⁵⁴Cr⁺ was corrected for by monitoring ⁵²Cr⁺; the IRMM-14 Fe isotope standard was used to correct for mass bias. The same group of workers from Oxford has also explored the possibility of using Cu stable isotope ratios as tracers in geological and planetary processes.⁵⁸⁵ They ascertained that the natural variation in ⁶⁵Cu∶⁶³Cu is more than 30 times the 2σ analytical uncertainty of the technique employed. The performance of MC-ICP-MS has also been evaluated for Ca isotope ratio measurement.⁵⁸⁶ With suitable precautions and correction for potential isobaric interferences on ⁴²Ca, ⁴³Ca and ⁴⁴Ca, it was shown to equal the precision and accuracy of the best results obtained by TIMS but with a throughput of 12–15 samples per day compared to 2–3 for TIMS.

In spite of improved access to magnetic sector ICP-MS instruments, isotope measurements by quadrupole ICP-MS are still of interest, particularly in environmental applications.^587,588 It would appear that internal precisions limited only by the error in counting statistics can be achieved by judicious optimisation of the parameters in quadrupole instruments fitted with a dynamic reaction cell (DRC).⁵⁸⁹ The usual polyatomic interferences on the isotopes of Fe were removed by the ion–molecule reaction induced by adding ammonia to the reaction cell, whereas neon was used to pressurise the cell when measuring Ag and Pb.

Various strategies have been devised to improve the determination of osmium isotopic ratios by ICP-MS.^590–593 Pearson and co-workers⁵⁹⁰ evaluated three different nebulisers in terms of their memory for Os and concluded that a direct injection nebuliser (DIN) was superior to conventional or desolvating nebulisers. Other workers^592,593 also introduced OsO₄ directly into their magnetic sector ICP-MS instruments.

4.2.5 Other mass spectrometric techniques. The spate of activity in magnetic sector ICP-MS has probably deflected attention from thermal ionisation mass spectrometry (TIMS); developments in this and other mass spectrometric techniques are described in the recent Update on this subject.³⁹⁴ The advantages of using Tru-SPEC resins in acidic media for the separation of U and Th from geological matrices prior to measurement by TIMS have been recognised by You and Bickle.⁵⁹⁴ James and Palmer⁵⁹⁵ have discussed the use of TIMS for the determination of Li isotope ratios in low concentration samples and potential modifications to sample preparation methods, and Wieser and Laeter⁵⁹⁶ have described their sample preparation procedures for the determination of Mo isotopes by TIMS.

An important application of secondary ion mass spectrometry (SIMS) is the production of two-dimensional chemical maps of the surface of a sample or an investigation of sub-surface atomic layers. With this in mind, a compact benchtop imaging SIMS instrument has been developed⁵⁹⁷ which is fully automated and designed for operation by a laboratory technician. Because of the reduced costs associated with this instrument, compared to a full SIMS system, it could represent a breakthrough in terms of ease of access to the technique in many disciplines, including geochemistry. Determination of ¹²C∶¹³C in graphite by SIMS has been used in conjunction with other information to fingerprint graphite precipitation mechanisms and carbon chemistry of crustal fluids.⁵⁹⁸ Similarly, a SIMS study of carbon isotopes and nitrogen abundance within complex diamonds from Colorado, USA, has revealed in single stones large variations of a magnitude normally found in entire diamond suites elsewhere.⁵⁹⁹

Recent developments in and applications of resonance ionisation mass spectrometry (RIMS) have been reviewed by Wendt and co-workers.⁶⁰⁰ They consider that the technique, with experimental detection limits as low as 10⁶ atoms per sample, has reached the status of a routine method for fast and sensitive detection of ultra-trace amounts of long-lived radioactive isotopes. They provide experimental details for the determination of radiotoxic isotopes such as ^236–244Pu, ^89,90Sr and ⁹⁹Tc in environmental samples and the very rare radioisotope ⁴¹Ca for cosmochemical and radiodating purposes. The high sensitivity and selectivity of RIMS makes it well suited for the detection of many heavy elements in solar material collected by NASA space missions.⁶⁰¹

A recently developed spark source mass spectrometric (SSMS) technique using multiple ion counting has been used to determine Nb, Y and Ta in carbonaceous chondrites⁶⁰² and Y, Zr and ultra-low concentrations of Nb in geological materials.⁶⁰³ The latter application⁶⁰³ had an analytical precision of 2–5% for concentrations down to 0.020 µg g⁻¹ and 10% for lower concentrations. The accuracy of the method is influenced by the interference corrections made on ⁹¹Zr and ⁹³Nb, with Al-rich samples being particularly problematical. A comparison showed that ICP-MS gave systematically lower values than SSMS; the authors had no explanation for this and speculated that there may have been loss of Nb during the chemical dissolution of the samples prior to ICP-MS measurement.

Accelerator mass spectrometry (AMS) is the analytical method of choice for the detection of long-lived radionuclides that cannot be practically analysed with decay counting or conventional mass spectrometry. Merchel and Herpers⁶⁰⁴ have provided an update on the radiochemical separation techniques required prior to the determination of such radionuclides by AMS, with improved procedures for the separation of nuclides such as ⁵³Mn, ⁵⁹Ni and ⁶⁰Fe. Recent advances in AMS have been reviewed⁶⁰⁵ in terms of its sensitivity, precision and standardisation. The use of AMS for the analysis of nuclides of heavy mass, such as actinides, with important applications in the field of nuclear waste disposal is also discussed. One of the most frequent uses of AMS is for radiocarbon analysis; the method and its application to the dating of sediment samples, macrofossils, humic acids and archaeological samples has been addressed by Kretschmer.⁶⁰⁶

Rucklidge and co-workers⁶⁰⁷ have reviewed, with 14 references, the application of AMS to the in situ analysis of trace elements in solids such as electrically conducting mineral phases with a minimum grain size of 0.5 mm, including graphite, sulfides, oxides, native copper and nickel–iron alloys. Their emphasis was on the analysis of precious metals with practical detection limits ranging from 0.005 to 50 ppb using Cs⁺ sputter sources of negative ions. The current programme of research into in situ microanalysis in support of mineral exploration on the AUSTRALIS system includes the determination of stable isotopes such as ³⁴S.⁶⁰⁸ This high-energy system features a novel isotope switching method that circumvents source instabilities. The source for this instrument currently produces a 30 µm Cs beam routinely, but the authors hope to achieve 1 µm resolution ultimately.

4.2.6 X-ray techniques. As indicated in previous updates in this series, XRF is employed as a routine method of analysis of geological materials and the maturity of the technique is such that relatively few advances are reported compared to its widespread usage. As with any analytical technique, there has been a drive to improve detection limits. Various separation procedures have been developed to preconcentrate the elements of interest onto a filter or membrane prior to analysis by XRF.^609–611 Inevitably this requires the analyst to dissolve the sample first, which would seem to negate much of the advantage of using XRF, rather than ICP or other solution techniques, in the first place.

Some of the biggest challenges for XRF lie in the arena of solar exploration. A CCD-based XRF instrument, due for launch in 2003, has been designed with the aim of mapping the major element composition of 90% the Moon's crust.⁶¹² Interpretation of some of the data from the Mars Pathfinder site obtained by alpha-proton XRF have been published.⁶¹³ The linear chemical trends in the rock compositions were interpreted as mixing lines between rock and adhering dust.

A number of applications of energy dispersive XRF (EDXRF) are given in Table 4, including lake sediments,⁶¹⁴ marine corals and sediments⁶¹⁵ and ores.^616–618 From the varied locations of the authors, it is tempting to conclude that this technique is now more affordable and more widely used.

Willis and McNew⁶¹⁹ took on the challenge of evaluating WDXRF for the analysis of monazite and other REE compounds. They examined line selection, X-ray tubes and their operating voltage, as well as problems of infinite thickness, mineralogical and particle size effects, spectral line overlap, crossing of major element absorption edges, lack of suitable standards and lack of influence coefficient software to handle up to 32 elements in a single run.

An improved method for the determination of the major element composition of individual fluid inclusions in halite using a scanning electron microscope (SEM) with an attached EDXRF has been described.⁶²⁰ The improvements include a newly designed brass sample holder and modified methods for the preparation and freezing of saline standard solutions. Because of the low-vacuum environment in the SEM the sample does not need a conductive coating, thus permitting direct observation of the inclusion surface to be analysed.

The reader is referred to another Update in this series⁴¹¹ for a comprehensive review of recent developments in all aspects of XRF, including total reflection XRF (TRXRF) spectrometry. Ebert and co-workers⁶²¹ have obtained results by EMPA and TRXRF on single crystals of garnet, which were in good agreement. One of the more novel pieces of work published in the year under review was use of laser ablation as a sampling technique for the analysis of solids by TRXRF.⁶²² Previous work suggested that several practical difficulties needed to be solved. These include the likelihood of fractional vaporization during ablation and the removal, by shock waves of the laser plume from successive laser shots, of material already collected on the carrier. An improved configuration of the sample and quartz glass or Plexiglas® carrier, together with careful control over the laser ablation process, was used to analyse both metallic and non-metallic materials. Although the technique was less sensitive than LA-ICP-MS, the authors claimed that its easy and reliable quantification by internal standardization was important in certain circumstances.

The usual sample preparation procedures are not suitable for the determination of Hg by TRXRF. Bennun and co-workers⁶²³ developed a method whereby a thin layer of gold fixed to a quartz reflector was dipped into an ionic solution of mercury, thereby forming an amalgam that was then amenable to traditional TRXRF analysis. Since the Hg and gold peaks overlap, it was necessary to develop a data processing scheme to improve the precision. Sample preparation techniques are also discussed in relation to the analysis of estuarine sediments by TRXRF.^237,624

Although access to particle-induced X-ray emission (PIXE) instrumentation is relatively limited, a number of varied geological applications are noted in Table 4. These include the elemental mapping and fingerprinting of rubies,^625,626 analyses of zircons as indicators of granite type,⁶²⁷ distribution of trace elements in minerals in platinum ores⁶²⁸ and analyses of sulfides from gold deposits.^629,630 The performance characteristics of PIXE, and other nuclear spectrometric techniques for the study of multilayered solids, is the subject of a recent review with 37 references.⁶³¹

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110. J. B. Truscott, P. Jones, B. Fairman and E. H. Evans, presented at Tenth Biennial National Atomic Spectroscopy Symposium, Sheffield, UK, July 17–20, 2000..
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217. M. Sousa Bispo, B. Ferreira Dos Santos, M. G. A. Korn and S. L. C. Ferreira, presented at Pittcon.'99, Orlando, FL, USA, March 7–12, 1999..
218. Z. A. Grosser, L. Davidowski, J. Latino and D. Sears, presented at Pittcon.'99, Orlando, FL, USA, March 7–12, 1999..
219. S. Bridger and M. Knowles, Varian Australia Pty Ltd, Mulgrave, Victoria, Australia 3170., 2000..
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252. Y. J. Kim, C. K. Kim, C. S. Kim, J. Y. Yun and B. H. Rho, J. Radioanal. Nucl. Chem., 1999, 240, 613.
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284. S. M. Talebi, presented at Instrumental Methods of Analysis. Modern Trends and Applications (IMA '99), Chalkidiki, Greece, 19–22 September, 1999..
285. N. Molenat, A. Astruc, M. Holeman, G. Maury and R. Pinel, Analusis, 1999, 27, 795.
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291. L. Paama and P. Peramaki, presented at Instrumental Methods of Analysis. Modern Trends and Applications (IMA '99), Chalkidiki, Greece, 19–22 September, 1999..
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319. J. G. Miao, X. H. Wu and J. R. Chen, Fenxi Shiyanshi, 1999, 18, 27.
320. E. R. Unsworth, P. Jones, S. J. Hill and J. Cook, presented at Tenth Biennial National Atomic Spectroscopy Symposium, Sheffield, UK, July 17–20, 2000..
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330. F. C. Adams, H. Emteborg, M. Heisterkamp and X. Tian, presented at Instrumental Methods of Analysis. Modern Trends and Applications (IMA '99), Chalkidiki, Greece, 19–22 September, 1999..
331. D. Voutsa, G. Zachariades, A. Kouras, A. Anthemides and C. Samara, presented at Instrumental Methods of Analysis. Modern Trends and Applications (IMA '99), Chalkidi, Greece, 19–22 September, 1999..
332. S. Mothes, S. Tutschku and R. Wennrich, presented at Instrumental Methods of Analysis. Modern Trends and Applications (IMA '99), Chalkidiki, Greece, 19–22 September, 1999..
333. T. Devine and J. Ratliff, presented at Pittcon.'99, Orlando, FL, USA, March 7–12, 1999..
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