Atomic spectrometry update. Environmental analysis
Steve J. Hill*a, Toyin A. Arowolob, Owen T. Butlerc, Simon R. N. Cheneryd, Jennifer M. Cookd, Malcolm S. Cresserb and Douglas L. Milesd
aDepartment of Environmental Sciences, University of Plymouth, Drake Circus, Plymouth, UK PL4 8AA
bEnvironment Department, The University of York, Heslington, York, UK YO10 5DD
cHealth and Safety Laboratory, Broad Lane, Sheffield, UK S3 7HQ
dBritish Geological Survey, Keyworth, Nottingham, UK NG12 5GG
First published on 15th February 2002
Abstract
This is the seventeenth annual review published in JAAS of the application of atomic spectroscopy to the chemical analysis of environmental samples. The review follows on directly from last year's (J. Anal. At. Spectrom., 2001, 16, 194–235), although this year it incorporates a number of changes in structure. The most obvious and perhaps the most important change is the removal of some of the tabulated material. It was recognised by the review group that some of the tables were becoming less comprehensive and that this form of information was better and more easily obtained using electronic searches. We therefore report the most important developments in environmental analysis during the review period, and as such largely tend to focus on improvements to existing techniques to provide more reliable and robust analytical methods. Comments on these changes and possible improvements for future reviews are welcomed by the review coordinator.
1 Air analysis
This section of the Update covers the analysis of aerosols, particulates and gases by atomic spectrometric techniques. Noteworthy areas of research and development are highlighted.1.1 Sample collection and pretreatment
Atmospheric particulate matter is often difficult to dissolve. Microwave assisted dissolution procedures under conditions of elevated temperatures are increasingly being employed. In a detailed paper, researchers optimised a closed vessel digestion procedure.1 Recoveries, in the range 80–110%, were obtained for a wide range of metals in two NIST CRM materials (NIST 1633b Coal Fly Ash and NIST 1648 Urban Particulate Matter) using a mixture of HNO3–H2O2. The addition of HF was required to obtain quantitative recoveries for Cr.1.2 Real-time measurements
Filter based samplers are commonly employed to collect airborne particulate matter. Samples are usually collected over an extended period of time. A disadvantage with this process is that temporal resolution is low and pollution incidences can be missed. A number of researchers are looking at developing instrumentation for real time measurements. The ‘streaker’ sampler, developed at the University of Florida, continues to be used by a number of groups.2–4 This sampler contains a controlled rotating filter assembly with a pre-impactor to remove particles >10 µm and two further stages to sample 2.5–10 µm and <2.5 µm fractions. Analysing by PIXE, these groups are able to produce data with a 1–2 hour resolution. The data were used for source apportionment studies and for tracking specific pollution incidences.The advent of small portable XRF systems has enabled analysts to make on-site measurements. In an original piece of work, researchers at the Woods Hole Oceanographic Institution designed and tested a prototype autonomous aerosol sampler/elemental analyser.5 The system consists of three major components: an air inlet sampling system, a 24-place carousel with each position containing a 25 mm filter, and a measurement station utilising a modified EDXRF system. Filters are rotated into position under the sampling inlet, sealed and air pumped through at 1 m3 h−1. The filters are subsequently rotated to the measurement station and analysed. Commercially available thin-film standards are used for calibration. The temporal resolution of this instrument will depend upon the combination of the aerosol concentration and the instrumental detection limits for particular elements. It is hoped that, in the future, it will be possible to mount the system on a buoy for marine aerosol studies. This instrument could have other applications, e.g. stack sampling. Further work is required to consider size selective sampling characteristics, power consumption and means of remotely downloading stored data.
The development of continuous emission monitoring systems for the rapid and simultaneous detection of metals in stack gases remains high on the agenda. This is especially true in the United States where there are regulatory requirements to measure a number of hazardous metals. Systems utilising the LIP and MIP techniques are in the forefront of these developments. Woskov and co-workers have tested a prototype MIP system at the EPA Rotary Kiln Incinerator Simulator at RTI, North Carolina.6 The system involves sampling an aliquot of stack gas directly into a chamber where microwave power is focused using a waveguide. A fibre optic collection and optical system focuses characteristic emissions onto a detector array covering the range 180–600 nm. Periodic calibration is carried out by nebulising standard solutions using a conventional concentric nebuliser and Scott-type spray chamber. Though further work is required, results obtained suggest that the EPA goal of obtaining results to within ±20% of those obtained by the manual filtration reference method is achievable. Zhang and co-workers in similar field tests evaluated their prototype LIPS system.7 Their system obtained results that were within 22–81% of those obtained using the reference method. Technical difficulties, such as optic damage and drop in laser power due to effect of temperature upon the frequency doubler, hampered their system during the field trials. Both systems suffer from an inability, at present, to measure simultaneously all of the required regulated metals (As, Be, Cd, Cr, Hg and Pb ). Enhancements are planned, including improved optical and detector systems, re-evaluation of calibration protocols and the investigation of signal to background correlation protocols to correct for signal/laser pulse variations. LIPS systems are also under evaluation at the Oak Ridge facility.8,9 These workers have used temporal and spectral resolution, buffering gases and a specially constructed aerosol beam focusing system to enable them to obtain optimal S/N ratios for chromium and mercury test aerosols. A long-term goal of this work is to develop a portable system for ambient air measurements.
1.3 Standardisation and reference materials
The need for harmonisation has led Foster at the Health and Safety Laboratory (HSL) to produce filter standards for XRF instruments.10 Metal aerosols were produced using an ultrasonic nebuliser, desolvated and passed into a test chamber. Air from this chamber was subsequently sampled onto filters using a multiport sampler system. Filters were analysed by XRF to check the intra- and inter-batch precision. Subsets of filters were analysed by ICP-AES to obtain nominal loading values. The remaining filters were distributed to a number of laboratories equipped with a range of XRF instruments (PXRF, benchtop EDXRF and WDXRF) for use as calibration standards. Two welding fume samples were also circulated for analysis. The results obtained were within ±10% of the values determined at HSL, thus demonstrating the transferability of calibrations.Workers at the University of Kentucky applied XAFS spectroscopy to interrogate two NIST particulate reference materials commonly used by analysts working in the air-monitoring field.11 For the NIST 1648 urban reference material they demonstrated that, for example, arsenic and chromium existed predominantly in their less toxic oxidation states, As(III) and Cr(III). Interestingly they found that chromium existed in a highly refractory spinel phase and wondered how such a phase could be so prevalent in the urban environment from which this material was obtained. Their finding upholds a common view that this reference material may not mimic typical urban particulate matter and definitively explains why many laboratories have obtained poor and variable chromium recovery data using this CRM. A vigorous dissolution procedure is necessary. In this author's laboratory acid mixtures involving HF under pressure are used. The group at the University of Kentucky suggested that XAFS spectroscopy could be useful in providing characterisation data to support toxicological and source apportionment studies.
Further details of the production of reference air filter samples under the auspices of the IAEA in Vienna have emerged.12,13 Bulk airborne particulate matter was collected from air intake ducts at a hospital in Vienna and from a ventilation shaft in a road tunnel in Czechoslovakia. The materials were jet milled and homogenised to produce a dust with a bimodal particle size distribution (0.9 µm and 4 µm). Weighed aliquots of each material were suspended in water and continuously stirred using ultrasound and mechanical stirrers. A dosing system was employed to dispense measured volumes onto pre-weighed filters. The filters were subsequently vacuum filtered and dried. Using this procedure batches of 280 filters were produced from each material with average loadings of 867 µg and 810 µg. A battery of techniques, including INAA, PIXE, μ-EDXRF, ICP-AES, ICP-MS and AAS, was used to establish ‘target’ values. The target 20% standard deviation was achieved for many elements but there were inhomogeneity problems for elements such as Br, Cl, Cr, Ni and V. The authors also recognised that by using this approach ‘soluble’ species are lost.
1.4 Speciation
A number of groups are actively involved in the sampling and analysis of volatile metal(loid) species. Workers in Sweden have refined their KCl denuder system reported in previous reviews.14 In this sampling system, gaseous divalent mercury (GDM) is collected on the denuder system which is kept at 20–30 °C above ambient to minimise condensation problems. GDM is thermally desorbed, passed through a heated converter trap to produce elemental mercury and preconcentrated on a gold trap. Based on a 3σ criterion from measured blanks, the detection limit for CVAFS was less than 3 pg.French workers from Pau continue to develop their cryogenic trapping system.15 Air is sampled onto silanised glass wool packed into a glass tube held at −175 °C. Particulate matter and water are removed by using a prefilter and a trap held at −20 °C. Samples are analysed in the laboratory using a GC-ICP-MS system. Field sampling in Bordeaux revealed that tetraalkyllead species and elemental mercury predominated, with average concentrations of 15.5 ng m−3 and 2.7 ng m−3 respectively. A selenium species, thought to be dimethylselenide, was found overlooking a brook and indoors in a nursery suggesting a biomethylation process. Intriguingly, unidentified signals were recorded at masses corresponding to elements such as arsenic, chromium, nickel and vanadium. It would be interesting to replicate this work using a DRC or collision cell and/or high resolution ICP-MS system.
Continuing this theme, the research group in Oviedo determined organolead species in airborne particulate matter using a coupled GC-ICP-MS.16 An effective home-made heated transfer line was used to couple the two instruments. Lead species were extracted from filter samples using 0.5 M acetic acid in methanol and subsequently extracted into hexane using a DDTC–EDTA mixture. Following derivatisation, one microlitre samples were injected to a precision of greater than 4%, using a tetraethyllead internal standard. Method detection limits were determined to be less than 10 fg for all organolead species determined. The accuracy of the proposed methodology was evaluated by the successful determination of tetramethyllead in BCR CRM 605 urban dust. Sampling exercises around the university revealed levels of dimethyllead and diethyllead in air were in the range 1.6–3.8 pg m−3 and 5.5–23.5 pg m−3, respectively.
It is assumed that the advent of commercially available GC/HPLC/CE interface kits, the availability of 'seamless' instrument software packages and the availability of new standards and reference materials will aid the development of speciation methodologies and furthermore facilitate technology transfer to routine laboratories.
1.5 Deposition samplers and global pollution
This last year has seen a renaissance in the use of vegetation as deposition samplers. Mosses,17–19 lichens20 and leaves21 continue to be collected and analysed for metals derived from man-made sources. Careful consideration of data obtained is required as the underlying mineralogical substrate can have a substantial influence. Selective uptake amongst distinct species, localised dust sources arising from human activities and contamination issues need also to be considered. Work by Bellis and co-workers on the use of tree bark as a passive sampling medium has resulted in a number of interesting publications.22–26 This approach has enabled these workers to detect uranium from an enriched source downwind from Tokai-Mura in Japan. The capability of ICP-MS to perform multi-metal screens and isotopic measurements is useful. Biogenic and natural influences can be minimised through the interrogation of isotopic signatures and selective elemental ratios.In a novel application, a research group in the United States used undisturbed attics in houses as dust archives.27 ICP-MS was used to determine a number of metals. Lead levels, for example, correlated well with the age of houses (r2 = 0.87, n = 8).
Atomic spectrometric techniques are to the forefront in research into global/regional pollution studies. A joint Brazilian/American group investigating mercury levels in the Amazon basin has published interesting work.28 In a well-funded project, use was made of airborne sampling platforms. Aircraft were equipped with filtration-based samplers for subsequent analysis by INAA and PIXE techniques. Elemental mercury was sampled through a Teflon line onto gold traps for subsequent analysis by AFS. Mercury levels of up to 14.8 ng m−3 were detected. Further studies apportioned 60% of these releases directly to gold mining activities, in which mercury is used to sequester gold from crushed ore, and 30% from biomass burning due to agricultural activities where mercury is re-released from vegetation and soil.
1.6 Public health
Air pollution is a serious problem in many urbanised areas in the world. A number of epidemiological studies have shown a strong correlation between relative risk of death and levels of suspended particulate matter. Interest is now focusing on the health effects of particles in size ranges lower than 10 µm. Parr and Smodis gave an overview of current IAEA studies in this field where analytical techniques such has INAA, PIXE and EDXRF play an integral role.29 Chemical and toxicological studies conducted on particles smaller than 10 µm relied heavily on measurements made using ICP-AES, ICP-MS and XRF techniques, as demonstrated in a number of papers.30–32These examples exemplify the need to take a multidisciplinary approach to environmental problems and ensure a continuing and exciting role for atomic spectrometry in the field of air analysis.
2 Water analysis
The dominant themes in the application of atomic spectrometry to the analysis of water continue the trends of the last few years. They include many reports of literature on techniques for pre-concentration and matrix separation, apparently driven by the need to achieve detection limits similar to those obtainable by ICP-MS but using cheaper and simpler instrumentation such as AAS. Speciation continues to be a rich vein of research to mine. Here ICP-MS is the pre-eminent technique when coupled with some form of chromatography. Chromium speciation appears to be currently in vogue, perhaps as a result of its increased importance to environmental quality. Interestingly, there is relatively little published work focusing on the development of ICP-AES systems despite its ubiquitous use in the water quality industry. Although the literature reviewed contained much new work, only a disappointingly small proportion was truly novel in terms of analytical chemistry and it is this work that is the focus of this review.2.1 Sample preparation
If aqueous samples are collected and returned to the laboratory for analysis preservation becomes important. Lindemann et al.37 conducted a detailed study of As, Sb, Se and Te species and concluded that aqueous matrices were best stored at 3 °C. They observed that, at −20°C, selenomethionine and Sb(V) were particularly susceptible to transformation. Analytical artefacts are sometimes caused by the “sample” itself. Misund et al.38 determined 66 elements in 56 bottled mineral waters from across Europe. Differences were found in chemical composition due to geological environment or local taste and regulations. However, they found indications that some unwanted elements such as Pb were related to the manufacturers' use of glass bottles rather than plastic containers.
The simplest form of pre-concentration (and sample matrix separation) is co-precipitation, the main disadvantage of this technique being the replacement of one matrix with another. However, it still finds some favour when very rapid pre-concentration from large volumes of liquid is required. Weiss et al.40 used magnesium hydroxide to co-precipitate Pb from seawater, with the aim of measuring lead isotope ratios. The natural occurrence of significant magnesium in seawater meant that blank problems resulting from reagents were minimised, as only vapour purified ammonia was added. Problems caused by high TDS clogging the ICP-MS were encountered because of incomplete separation from other matrix elements. These were solved by repeating the precipitation after dissolution, minimising the amount of precipitate and by long instrument wash periods. Gallium phosphate has been proposed as an alternative precipitation matrix for Pb.41 Trace elements are often co-precipitated from seawater. Chou et al.42 used iron hydroxide to pre-concentrate U, by a derivative of the classical co-precipitation methodology simplified for ICP-MS determination. Perhaps of more general use, Yabutani et al.43 have demonstrated a multi-element co-precipitation method, involving lanthanum, for hydride and oxyanion forming elements (As, Cr, Mn, Mo, Sb, Se, Sn, U, V, W, Y). The seawater sample was mixed with lanthanum nitrate and the pH adjusted to 9.5 with aqueous ammonia, to form the precipitate. After filtration, this was dissolved in nitric acid and the elements determined by ICP-MS.
Liquid–liquid extractions have an honourable history, particularly when associated with colorimetric measurements. Some interest in their use remains. Wang et al.44 demonstrated that the addition of the soft donor atom sulfur into bis(1,1,3,3,-tetramethylbutyl)phosphinic acid (HMBP) to form bis(1,1,3,3,-tetramethylbutyl)monothiophosphinic acid (HMTP) produces a high selectivity towards Cd, allowing it to be quantitatively separated from Zn. The resulting solutions were analysed by AAS. A novel separation scheme for Ag has been proposed by Yu and Shun.45 The Ag+ containing solutions were acidified to pH1 and an emulsion mixture (trioctylamine, N2O5, liquid paraffin and kerosene) added to create a liquid membrane. This was followed by aqueous ammonia as an inner phase desorbtion agent. Centrifugation allowed phase separation and the outer aqueous phase to be discarded. The remaining emulsion was then de-emulsified with a 2–4 kV spark, allowing the resulting aqueous phase to be analysed by AAS for Ag. Enrichment factors of 82 were achieved with full recovery and good precision (2.5% RSD).
Cloud point extraction is an interesting variation on liquid–liquid separation based on micelle formation using surfactants. Chen and Teo46 determined Co and Ni by complexation with 1-(2-thiazolylazo)-2-naphthol (TAN) and using octylphenoxypolyethoxyethanol (Triton X-114) as a surfactant. Optimisation allowed concentration factors of approximately 60 for these elements prior to determination by AAS. In a similar study, da Silva et al.47 complexed Ag, As, Au, Cd, Cu, Pb and Se with ammonium O,O-diethyldithiophosphate in HCl acidified water, also using Triton X-114 as a surfactant. Concentration factors of approximately 40 were achieved for these elements prior to determination by FI-USN-ICP-MS.
The production of new forms of solid phase extraction columns is still a popular occupation, often by linking yet another active organic reagent to a support medium. Frequently, these methodologies are aimed at separating a single element and therefore of minor specialist interest. However, of particular interest has been a comparison by Godlewska-Zylkiewicz et al.48 of three different sorbents for Pt concentration from water. They tested micro-columns of alumina, silica gel with bonded aminopropyl groups and Cellex-T, using respectively ammonia, hydrochloric acid and thiourea as eluents. The best enrichment factor of 400 was found for alumina. Lee et al.49,50 used a chitosan based chelating resin, with iminodiacetate (IDA) based functional groups, to produce a 50-fold enrichment for Ag, Al, Cd, Co, Cu, Fe, Ni, Pb, U and Zn and separation from Ca, K, Mg and Na. The water samples (50 ml at pH 6) were passed through a 1 ml micro-column, the major elements stripped with ammonium acetate and the analytes eluted with 10 ml of 1 M HNO3, giving a pre-concentration factor of 5. The additional factor of 10 was achieved by simple evaporation. The elements were determined by air segmented FI-ICP-MS. Another novel methodology was described by Kuehn and Kriews,51 who used a commercial system consisting of 0.2 µm diameter polymeric beads with IDA functional groups attached. These were added to saline water to bind Cd, Co, Cu, Fe, Mn, Ni, Pb, REE and Zn. Because of their samll size, the beads could then be removed from the matrix and directly analysed suspended in a solution. Enrichment factors of 40–48 were obtained.
The use of fibres as a solid support for ion-exchange or chelating agents has attracted some attention because of their large specific surface areas giving a high adsorption capacity. Wen et al.52 used 8-hydroxyquinoline immobilised on a polyacrylonitrile hollow fibre membrane to pre-concentrate Ag, Be, Bi, Cd, Co, Cu, In, Mn and Pb from seawater. Sample flow rate, pH and eluent volume were optimised prior to element determinations by ICP-MS. Pre-concentration factors of at least 300 were achieved at ng l−1 concentrations, with full recovery and precisions of better than 5% RSD. Bag et al.53 grafted methacrylic acid onto polyethylene terephthalate fibres and separated Cd, Co, Ni and Zn from fresh and saline waters in a batch process. A detailed practical and theoretical study of separation parameters was undertaken. Importantly, separation performance did not degrade over more than 30 cycles. Large scale separation of Zr from seawater was demonstrated by Noriisuye et al.54 Manganese dioxide impregnated fibres were synthesised from polypropylene cartridge filters by the redox reaction of KMnO4 and MnCl2. Full recovery was found when a 200 l sample was continuously circulated at 15 l min−1. The Zr was recovered in a two step elution process. All these studies suggest that separations using fibre based solid supports may have a number of benefits and are thus likely to become increasingly popular.
The use of single fibres for solid phase microextraction (SPME) has become popular in organic analytical chemistry. Fragueiro et al.55 have adopted this technique to separate methylycyclopentadienylmanganese tricarbonyl (MMT) from water. The MMT containing solutions were vigorously stirred in vials for 15 min with the fibre sampling the headspace. The collected MMT was then thermally desorbed into a quartz furnace AAS for determination as Mn. The detection limit of the complete process was 0.71 ng ml−1 as Mn.
An unusual solid phase extraction methodology has been the use of stir-bar sorptive extraction for the determination of traces of organotin compounds at ppt levels.56 The stir bar was coated with µl quantities of poly(dimethylsiloxane) and stirred the samples for 15 min to pre-concentrate tributyltin, triphenyltin and the internal standards tripropyltin and tricyclohexyltin. The bar was then thermally desorbed at 290 °C for 15 min while the compounds were cryo-focused on a pre-column at −40 °C. Once collected, the compounds were flash heated into a GC-ICP-MS system for determination.
Electrochemical pre-concentration methods appear under-represented in this review period. Abdullin et al.57 investigated the use of a variety of electrodes, such as metals (Mo, Pt, Ta and Ti), glassy carbon and spectrographic graphite.
Newcomers to this technique are referred to Moreda-Pineiro et al.,58 who conducted an in-depth optimisation of all factors associated with a HG system coupled to ETV-AAS for the elements As, Cd, Sb and Se. The use of L-cysteine as a pre-reductant for As and Sb is becoming more popular and Chen and He59 have reviewed this (38 references, Chinese).
As the number of techniques available in many laboratories increases, deciding which is the most appropriate is increasingly important. Guerin et al.60 have compared HG coupled to gas chromatography-quartz furnace AAS with HPLC-ICP-MS for arsenic speciation studies of environmental samples. They considered inorganic As(III) and As(V) and methylated species. Good agreement between techniques was found over a wide concentration range for all species. However, detection limits for the HG based technique were up to two orders of magnitude better. Uggerud and Lund,61 tested four introduction techniques for the determination of As by ICP-MS. They concluded that flow-injection with pneumatic nebulisation and ETV gave better detection limits than either hydride generation or hydride generation coupled with ETV, for the simple reason that the blank levels of As in reagents for hydride generation were too high. Thus, the more complicated systems gave no advantage in simple matrices such as natural waters where matrix separation was not required.
One of the most interesting studies in this area has been the development of two cryo-focussing hydride generation techniques for the field-based collection of multi-element alkyl–metal(loid) species. Both involve the simultaneous derivatisation of analytes with sodium borohydride and cryo-trapping the products on columns at −196 °C. The first is a flow-batch technique for large volume samples (0.5–1 l), while the second is an on-line continuous flow system for smaller samples.62 These systems had major advantages for shipboard operation with respect to sample pre-treatment, transport and storage. On returning the columns to the laboratory, cryogenic GC-ICP-MS was used for analyte determinations. Routine detection limits of 0.5–10 pg for 0.5 l samples were found for As, Ge, Hg and Sn species.
Interference by transition metals on hydride generation is a well-known phenomenon. Deng et al.63 determined that 8-hydroxyquinoline can mask out the effects of Co(II), Cu(II), Fe(III), Mn(II), Ni(II) and most importantly Sb(V) when determining Sb(III). They observed that Sb(V) could contribute up to 40% of the signal for Sb(III), depending on Sb(V) concentration and the pH of the matrix.
The generation of lead hydride for atomic spectrometric determination is relatively unusual. Li et al.64 described the use of oxalic acid–ammonium cerium(V) nitrate–sodium tetrahydroborate as a reaction matrix. The claimed the sensitivity of the system was 7.5 times better than that using an ultrasonic nebuliser when coupled to ICP-MS. But somewhat disappointingly, this translated into a detection limit improvement of only a factor of two because of high blank reagent levels (approximately 0.1 µg l−1). The determination of more than one element in an analytical run by hydride generation has obvious productivity implications. Menegario and Gine65 developed a synchronised flow system to sequentially measure As and Se. Prior to addition of sodium borohydride, the sample stream is pre-mixed with either thiourea to promote the reduction of As(V) to As(III) or hot HCl for the reduction of Se(VI) to Se(IV). With ICP-MS being used for analyte measurement LODs of 0.02 µg l−1 As and 0.03 µg l−1 Se were obtained at a rate of 20 samples per hour.
The use of gel permeation chromatography coupled with hydride generation-ICP-MS by O'Driscoll et al.66 has given valuable insights into the binding of MeHg to humic and fulvic acids in aqueous systems. Binding capacities for fulvic acid were 2–14 times higher than humic acid. It was also noted that binding increased as the fulvic acids increased in molecular size and, importantly, that using total S as a proxy for thiol groups (the principal MeHg binding site) is not valid. When coupled to atomic spectrometry in this way, gel permeation technology appears to have a bright future in helping to elucidate the complex role of macro-molecules and organometallic species in the natural environment.
2.2 Speciation
Arsenic speciation continues to attract attention, particularly the organo-metallic species. Jain and Ali69 have provided a general description of arsenic occurrence, toxicity and speciation including an appropriate review of analytical methodologies.Tsalev et al.70 coupled HPLC with HG-AAS and an automated pre-reduction system. This allowed separation of As(III), mono-methyl-arsinate (MMA) and di-methyl-arsinate (DMA) within 7 minutes using their L-cysteine complexes and a strongly acidic cation exchange column. A novel approach by Smichowski et al.71 to the determination of the more toxic As(III) species, was based on As accumulation by baker's yeast (Saccharomyces cerevisiae). When conditions were optimised it was possible to pre-concentrate As(III) by a factor of 7 while leaving behind As(V) in solution.
The determination of As and its species is no longer an academic exercise with human health problems being identified around the world. A number of water quality remediation studies have been made using atomic spectrometry to quantify efficacy. Khan and Rasul72 used ASV, GF-AAS and ICP-AES to determine As and associated elements in water passed through a low-tech chemical filter system. The first filter was a mix of iron chips and sand, and the second wood charcoal and sand. This filter system reduced As(III) to less than 2 ppb (detection limit) and total As to less than 10 ppb. Another more complex system involving chemical reactions was described by Banerjee et al.73 While Hug et al.74 employed HG-AAS to investigate the use of thermal and photochemical oxidation of As(III) to As(V) and its subsequent precipitation using lemon juice (citrate). A statistical link between bladder cancer and As concentration, as determined by HG-AAS, and a significant dose response relationship was demonstrated by Chiou et al.75
Chromium speciation is also of particular current interest. A detailed review (404 refs.) of the literature on chromium speciation has been published by Marques et al.76 Analytical techniques used for liquids samples were summarised, but focussing on atomic spectrometric techniques as these provide most speciation information. Marques et al.77 have also described a simple micro-column separation for AAS using an activated alumina packing. On-line retention was employed with selective elution of anionic Cr(VI) with 2 M ammonium hydroxide and of cationic Cr(III) with 0.2 M nitric acid. The procedure was tested on sewage waters and successfully compared with batch separations. Xue et al.78 used a deacetylated chitosan column to retain Cr(III) and Cr(VI) from waters adjusted to pH 3. The Cr(VI) was then selectively eluted using 0.1 M sodium hydroxide. Total Cr was eluted by pre-oxidation of Cr(III) to Cr(VI) using K2S2O8 and then Cr(III) calculated by difference. In an analogous manner, Hirata et al.79 used a commercially available iminodiacetate resin column to retain Cr(III) from seawater at pH 3, elution was with 0.7 M nitric acid. Total Cr was determined by pre-oxidizing Cr(III) with 2 mM hydroxylamine at pH 1.8. The method was validated with NASS-4 and CASS-3 seawater reference materials. Yeast cells immobilised on sepiolite were used by Bag et al.80 as an active sorbant for chromium speciation.
There has been a relative lack of novel Se speciation studies in this review period. Of note however, is a report by Nickson et al.81 on the use of a quaternary amine anion exchange resin to separate and pre-concentrate selenite and selenate using a flow injection-hydride generation system coupled to ICP-AES. The eluents were 0.08 M and 0.6 M NH4NO3 respectively. The hydride generation and ICP-AES measurement methodologies were relatively conventional. Also of practical interest is the use by Gallignani et al.82 of microwave pre-reduction of selenite to selenate using mild acidic conditions (10% v/v HCl and HBr). The microwave allowed the reduction to be made in a very controlled and reproducible manner. Gomez-Ariza et al.83 went one stage further and put the microwave digestion step on-line with HG-AFS.
By comparison there has been significant interest in Sb speciation. Garbos et al.84 simply removed the Sb(III) species by solvent extraction with N-benzoyl-N-phenylhydroxylamine. An untreated portion of the sample and the treated portion were then analysed by ICP-MS and Sb(III) calculated by difference. The technique was applied to various types of natural water around Warsaw, Poland. Field separation of samples ensured species stability and it was observed that Sb(V) was the dominant chemical form. Kubota et al.85 took the opposite approach and pre-concentrated Sb(III) on activated carbon as the Sb(III)-pyrogallol complex and then determined this directly, by ETV-AAS, as an activated carbon slurry. A more sophisticated study by Krachler and Emons86 used HPLC coupled to ICP-MS via an ultrasonic-desolvating nebuliser to speciate Sb, including trimethylantimony dichloride (Me3SbCl2). They observed many practical problems, including leaching of Sb from glass in the HPLC delivery system and oxidation of Sb(III) to Sb(V) at low concentrations within a few hours. Oxidation was reduced by purging diluent water with helium or diluting with EDTA. After optimisation, low ng l−1 detection limits were found for Sb(III), Sb(V) and Me3SbCl2.
A number of other interesting studies of methodologies, suitable for elemental speciation, have been made in this review period. Körez et al.87 developed a separation and pre-concentration method using a mercapto-modified silica microcolumn for the speciation of Te. The micro-column quantitatively retained Te(IV) and excluded Te(VI) over a wide range of pH. Elution of Te was by KIO3 oxidation, giving a solution amenable to direct determination using hydride generation. Some problems were identified with high concentrations of other elements interfering with recovery from the columns. However, good agreement was found with the values for a drinking water reference material. While developing a micro-volume back-extraction method for the ultra trace determination of Ga, In and Tl, Kawaguchi88 found that Tl speciation was possible. If Tl is extracted into chloroform as the dithizonate complex and back extracted into nitric acid, it may be speciated by either masking Tl(III) with citrate and/or reducing Tl(III) to Tl(I) with ascorbic acid. Detection limits using ETV-AAS for analyte measurement were at the sub ng dm−3 based on a 1000-fold pre-concentration. A fundamental study has been performed by Herrin et al.89 to investigate the suitability of Chelex-100 as a competing ligand in speciation studies of Ag(I). Firstly, a series of batch and column experiments was made and compared to an equilibrium speciation model to determine a conditional stability constant. When the Chelex competed with cyanide and thiosulfate ions for Ag+ the results fitted a model where logKcond equalled 7.2. The effect of pH in the range 6–10 on Ag(I) chelation was found to be minor, as was resin counter ion and total Ag(I) concentration. Minelli et al.90 have extended the range of speciated metals determined in waters. V(IV) was separated from V(V) on a strong anion exchange column loaded with di-sodium ethylene-diamine-tetraacetic acid (Na2EDTA). Both species were captured from 10–100ml of water at pH 3. The V(IV) was then selectively eluted with a mixture of Na2EDTA, tetrabutylammonium hydroxide and iso-propanol. The total and V(IV) were measured by ETV-AAS and V(V) calculated by difference. The method was applied to V speciation in various Italian volcanic waters.
2.3 Instrumental analysis
Isotope dilution is a technique not normally associated with atomic absorption spectrometry. A study by Wizemann95 was therefore one of the most interesting for this instrumentation during the review period. It involved the use of a pair of single mode laser diodes as simultaneous light sources, tuned to the absorption of 85Rb and 87Rb respectively. The beams were modulated in the kHz range by either mechanical choppers or electronically with sinusoidal wavelength modulation before being combined using a beam splitter. The merged beam was then passed into a laboratory modified sealed graphite furnace containing argon buffer gas at 10 hPa. The reduced pressure sample atomisation ensured line broadening was sufficiently small to distinguish the isotopes. The absorption signal was detected using a single photodiode and the individual isotope signals distinguished using two lock-in amplifiers, each referenced to a modulation frequency. The advantage of this optical technique over mass spectrometric techniques for Rb was the lack of Sr isobaric interference at mass 87. The technique was tested by spiking NIST reference water SRM1640 with different quantities of 87Rb. The total Rb content was measured within error of the reference value of 2.00 ng ml−1.
2.3.4.1 ICP-MS analysis. Ke et al.98 coupled a flow injection column separation system in a novel way to an ICP-MS to determine lead in aqueous solutions and seawater, by. The lead was sorbed from the samples onto a C18 bonded silica micro-column as the Pb-DDPA complex. It was then eluted with methanol. Such a volatile organic matrix can frequently prove problematic for an ICP-MS, so an ultrasonic nebuliser was used to remove approximately 66% of solvent vapour. To further reduce this by 50%, a multi-tube Nafion membrane drier was added before the ICP torch. Detection limits of 0.028 ng l−1 were achieved for a 60 s column loading time. This gave a pre-concentration factor of 28 and a sampling frequency of 21 per hour.
The preferred choice of mass spectrometric techniques or radiometric techniques for the determination of radionuclides is based respectively on the mass of analyte available for analysis and on its specific activity. As ICP-MS instrumentation becomes more sensitive the number of radionuclides that may be determined increases. Joannon and Pin99 investigated the determination of 226Ra+ in thermal waters using ultrasonic nebulisation and a quadrupole ICP-MS with a high capacity interface pump for improved sensitivity. An instrumental limit of detection was obtained when the interface pressure was reduced from 2 to 0.85 mbar. To improve the analysis of real samples a number of pre-concentration and matrix separation strategies were tested. A single column cation exchange column was found not to be suitable as the entire Ba and some Ca and Sr remained with the Ra, these then produced a severe signal suppression. A second column separation using a cation exchange resin and perchloric acid eluant helped reduce Ca and Sr, or a specific column material was used to remove Sr and Ba. However, this was time consuming. A better alternative was found to be a commercially available Ra specific solid phase extraction disk designed for radiometric counting. This allowed separation in a single step using a simple filtration device.
Coupling electrochromatography (CEC) to ICP-MS provided a sensitive method for the speciation of As, Cr and Se in the ppb range.100 A bonded phase capillary column of 100 µm i.d. containing macrocyclic polyamine functional groups was used with a −20 kV applied potential. The background electrolyte buffers for the species were: CrO42−/Cr3+ phosphate; HAsO42−/Ph4As+ pyromellitate; SeO42−/SeO32− acetate. The study considered the role of these anions in these buffers as well as the separation efficiency of the bonded phase polyamine compared to bare fused silica and its improved resistance to matrix effects. The problem of maintaining the original Cr(III)/Cr(VI) ratio in samples has been discussed above but this is not the only potential analytical problem in Cr speciation. Accurate quantification using ICP-MS detection may be compromised by interferences. When using HPLC-ICP-MS, Vanhaecke et al.101 considered the problem of 40Ar12,13C+, 37Cl16O+ and 35Cl16OH+ and two potential solutions, the use of high resolution ICP-MS102 and cool plasma conditions.102 On an anion exchange column, HCO3− co-eluted with Cr(VI) and Cl− co-eluted with Cr(VI) respectively. The cool plasma was found to eliminate the ArC+ ions solving the first problem, but did not influence the chloride based interferences. The high resolution ICP-MS removed both problems but at the cost of a 15-fold reduction in sensitivity. However, sub µg l−1 detection limits for both species were obtained, resulting in this being the preferred methodology when using HPLC-ICP-MS.
The advantage of ICP-based techniques is their multi-element capability, although hydride generation has frequently been coupled to ICP-MS as a single element sample introduction technique. Therefore studies such as that by Lee et al.103 on the simultaneous determination of As, Hg, Sb and Se by HG-ICP-MS are welcome. The proposed methodology depended on the pre-oxidation of the analytes using bromate/bromide before their subsequent reduction by sodium borohydride.
The determination of baseline concentrations of many metals in seawater, is one of the most challenging tasks for atomic spectrometry. Ferrarello et al.104 compared the determination of Cd, Cu, Mn, Ni, Pb, U, V, and Zn by quadrupole ICP-MS after matrix separation with dilution and direct determination by high resolution magnetic sector ICP-MS. The pre-concentration method involved the liquid ion-exchanger 8-hydroxyquinoline104 sorbed on either Amberlite XAD-7 or Bondapack C18. The C18 support was better for both on or off column separation. The determination of Hg by ICP-MS is more difficult than many analytes, Ugo et al.105 have combined electrochemical pre-concentration with ICP-MS. The Hg was collected on a gold spiral electrode and then released by electrochemical re-oxidisation in a pure supporting electrolyte. Compared to direct ICP-MS, this approach allowed both pre-concentration and matrix and interference separation, allowing nano-molar determination in process waters from a chlor-alkali plant and lagoon waters from Venice channels.
The simultaneous detection capability of ICP-TOF-MS gives it great advantages when measuring transient signals. Currently its main disadvantage when compared to conventional quadrupole ICP-MS is its poorer sensitivity. Therefore the combination of ICP-TOF-MS with flow injection and pre-concentration has to be advantageous. Benkhedda et al.106 evaluated ICP-TOF-MS with on-line adsorption pre-concentration using a knotted reactor and ultrasonic nebulisation. The analytes (Ag, Cd, Co, Cu, In, Mo, Ni, Pb, Sb) were complexed with ammonium pyrrolidinedithiocarbamate (APDC) from acidic solutions and sorbed into the knotted reactor. After 2 min pre-concentration giving enrichment factors of 5–70, the analytes were desorbed using a small volume of methanol. Coupling an ultrasonic nebuliser with membrane desolvation allowed very efficient sample introduction and minimised the effect of the organic solvent on the ICP.
2.3.4.2 Other MS methods. The historical contamination of the environment in Russia around the Mayak nuclear installation, has been investigated using accelerator mass spectrometry and γ-spectrometry to determine plutonium isotope ratios.107 The matrix separation and pre-concentration although complex allowed the analysis to make use of the unrivalled sensitivity and selectivity of AMS.
3 Analysis of soils, plants and related materials
Continued concern over environmental pollution has led to an excellent review (with 54 refs.) on atomic spectrometry in environmental monitoring and process control from Mermet.108 Sturgeon109 reviewed the current practice and recent developments in analytical methodology for trace element analysis of soils, plants and water. Readers of this update interested in lanthanides may wish to read the review on trace determination of lanthanides in metallurgical, environmental and geological samples.1103.1 Sample preparation
An interesting paper published last year111 described a simplified and fast sample pre-treatment method based on ultrasound-assisted solubilization of metals from plant tissue with ethlenediaminetetraacetic acid in alkaline medium. A similar method for the extraction of Ca, Mg, Mn and Zn from vegetables has been reported.112 The accuracy of the proposed method was assessed by using CRMs as well as wet digestion. Recoveries ranging from 96 to 102% were obtained with different kinds of plant samples and for the majority of the metals studied. Similarly, a procedure using infrared radiation generated by tungsten lamps for fast heating of sample has been described.113 The main advantages of the procedure are its simplicity and low cost.
The direct analysis of samples with strongly interfering matrices has been proposed.114 The sample is thermally pre-treated by using double vaporisation in a two-step atomiser with a purged vaporiser. A porous-graphite capsule or a filter inserted into the vaporizer is used for solid sample analysis. The technique was used for the direct determination of Cd and Pb in potatoes, wheat, milk powder, grass-cereal mixtures, etc. Elik et al.115 advocated the use of a Bio-Collector-Ultrasonic Leaching Method115 for the analysis of heavy metals using plant sprouts for the assessment of environmental pollution. In this study, the bio-collector sprouts were leached using 1% HNO3 solution under ultrasonic treatment and the leachate samples obtained were analysed by AAS.
The oxalic acid-lithium carbonate-lithium tetraborate (1∶1∶1) fusion agent proposed earlier for cement analysis has been applied to determine the composition of various siliceous samples including granite, clay, fly ash, sand and silica fume.116
Speed is an important factor in sample preparation. In a noteworthy paper,117 the routinely used concentrated nitric acid method for digesting plant tissue followed by analysis with ICP-AES has been modified in order to reduce the length of time it takes to complete the digestion. The new method also employs a slightly lower temperature than the old one, thereby preventing boil out of digestion tubes at 125 °C, a characteristic that some plant species exhibit.
It is common knowledge that oil and grease contaminated soils are difficult to digest using the popular HNO3–H2O2 digestion method. Cook et al.118 developed a modified procedure using HNO3–HClO4 for the analysis of total trace metals that can be used on all types of soils including those with oil and grease. Compared to the common HNO3–H2O2 soil digestion method, the proposed method was as effective (no significant difference) in extracting Cu, Pb and Zn and was significantly better at liberating Ni from the soil. Cd concentrations, which are often below the limit of detection by FAAS, were measurable in the proposed method.
As ICP-OES and ICP-MS expand their roles in environmental and earth sciences, the concern about incomplete sample digestion remains. This has resulted in a steady flow of publications exploiting microwave digestion techniques since the publication of the sixteenth environmental Update in JAAS a year ago.119 It is well known that microwave oven digestion of plant materials for the determination of plant nutrient concentrations is an aggressive and effective dissolution procedure. Several papers using microwave-assisted digestion as a routine tool are listed in Table 1. However, many analytical ‘developments’ involved only comparison of various acids and acid mixture ratios and the different type of vessel systems used. For example, microwave-assisted digestion procedures using HNO3, HNO3–H2O2, HNO3–HClO4, HF mixtures and dry ashing + HF were investigated for the determination of 14 metals in pine needle samples by ICP-AES or ICP-MS.120 Reference samples were used to test the dissolution methods. The results showed that the sample digestion procedure is a critical step for obtaining accurate results. Losses of volatile metals were notable in many cases when dry ashing was used. In another study, complete digestion of soils and sediments was achieved121 by using an acid mixture of HF–HCl–HNO3.121 The paper suggested that the microwave-irradiated closed vessel used for the determination of aqua regia-leachable fraction is a viable alternative to the traditional reflux system.
Again this year, a paper appeared reporting on the successful application of microwave assisted extraction for the decomposition and dissolution of plant samples for trace metal determination by ICP-AES using water, and EDTA or HCl (0.01, 0.10 and 1.0 M, respectively) as leaching solutions.122 HCl was found to be very suitable for quantitative extraction of B, Ba, Cd, Cu, Mn, Ni, Pb, Sr and Zn. The use of EDTA led to a complete extraction of B, Cd, Ni, Pb, Sr and Zn. Water was found to be a good leaching solution for B. Also, a flow through microwave digestion device has been developed for the determination of Cd, Cr, Mn, Ni and Pb in soil by aqua regia extraction.123 The device differs from existing commercially available systems as it uses a double pumping action to replace the back-pressure regulator traditionally used to achieve internal pressurisation. The device produced recoveries of metals exceeding 95% of certified levels for a reference soil. In a similar study, a comparison has been made of high-pressure digestion vessel124 and screw top PTFE (STT) jars for digestion.124 The method was applied to the ICP-MS analysis of sediment and soil samples. The results indicate better decomposition of resistant minerals. Good correlation for Nb and Pb, among other elements, was shown between the results from ICP-MS and XRF spectrometry. Barium recovery was, however, relatively low for ICP-MS, possibly due to particle size difference. Also, optimisation of seven factors for a microwave pseudo-digestion procedure has been reported.125 Good accuracy was achieved when the methods were finally applied to several reference materials.
Filgueiras and his team126 compared the ultra sound assisted extraction, based on acid extraction of metals from plant tissue by means of high intensity probe ultrasonication, and microwave-assisted digestion for determination of Mg, Mn, and Zn in plant samples by FAAS. Analytical results for the three metals by both methods showed good agreement, thus confirming again the possibility of using mild conditions for sample preparation instead of intensive treatments inherent with the digestion method. The importance of evaluation of different digestion methods in order to accurately determine elemental concentrations in soils cannot be over emphasised.127 This was confirmed in a study where three commonly used digestion procedures, hot plate aqua regia, microwave aqua regia and microwave aqua regia + HF, were compared for digestion of three standard reference materials and 20 Florida soils. Sixteen elements were determined using either an ICP-OES or GFAAS. In general, the microwave aqua regia + HF digestion was overall the best procedure for determining concentrations of most metals in SRMs and Florida soils. In a similar study, Burnecka et al.128 compared three digestion procedures: high-pressure microwave digestion, conventional wet digestion and dry ashing, for the analysis of vegetables by ICP-AES. Microwave digestion was found to be the most appropriate method of decomposition.
The uses of sealed Teflon vessels and inexpensive microwave ovens were evaluated for their ability to digest batches of six or twelve plant samples and to compare the analyses with those from conventional block heater digestions.129 Recoveries were greater for the block heater digestions than with the microwave digestions for four of the seven elements analysed (p < 0.05). Variability was greater for the microwave oven digestions than the block heater. The authors recommended the use of home made microwave ovens for the digestion of plant material. They concluded by suggesting that domestic ovens may be useful for those requiring occasional analyses or those who analyse samples of similar nature negating the need for frequent method modification.
In a noteworthy paper, Link and Kingston130 evaluated the use of the unique heating mechanisms of the reduced pressure microwave-assisted evaporation apparatus, where losses of determinands due to volatilisation during the evaporation process are minimised, and compared results with those using hot plate evaporation. The authors observed that complete recovery was achieved using microwave-assisted evaporation while losses of several classically volatile determinands occurred using hot plate evaporation.
Some notable papers on sample preparation prior to ICP-MS analysis have been published. The determinations of trace elements in soils and sediments by ICP-MS, following the acid decomposition of samples in a microwave oven, was investigated.131 The use of a HNO3–HCl mixture gave good recoveries for 20–25 determinands; the complete solubilization of materials was achieved by microwave digestion in closed vessels using a mixture of HF–HNO3–HCl. ICP-MS offers excellent possibilities for multielement trace analysis of biological material. Dombovari et al.132 developed an analytical method for the determination of essential elements in small plant tissue samples. Sample preparation was performed with closed vessel microwave digestion. For most analytes, recoveries from the SRM were 95–105%. A simple and effective procedure has been developed by Cao et al.133 to avoid the spectral interference from barium polyatomic ions on some rare earth elements in ICP-MS by combining algebraic correction with AG50W-X8 cation exchange chromatography. Recoveries for REEs are from 96 to 110%. More than 99.5% of Ba in the sample is removed, ensuring that the spectral interferences from barium polyatomic ions on some middle REEs such as Nd, Sm, Eu and Gd are eliminated. The potential of the proposed method was evaluated by analysis of CRMs. Results show that the experimental data are in good agreement with the certified values. The new technique has been successfully employed for the determination of REEs in soil and plant samples.
A procedure based on the use of ion chromatography-ICP-MS has been described136 for the separation of and quantification of Sb(III) and Sb(V) in cell extracts. Another interesting paper this year was on the speciation of Al in tea infusion by ion exchange resins and FAAS.137 It was found that about 30% of aluminium from black tea leaves transfers into the infusion giving 11–12 mg l−1 of Al and that about 10–19% of total aluminium in tea infusion is present as cationic species, while about 28–33% is as hydrolyzable polyphenol-bound Al. A method for speciation and quantitative analysis of inorganic sulfur, sulfate and organic sulfur compounds by using high performance IC with ICP-AES has been developed.138 To achieve a lower detection limit, a hydraulic high-pressure nebulizer was used to connect the ion chromatograph and the ICP. The detection limits were 0.023 mg l−1 and 0.085 mg l−1 of sulfate-S and of organic-S respectively.
Arsenic represents one of the most widely studied elements because of the different toxicological and biological behaviours of its species in living organisms. A procedure to separate and quantify two inorganic species, As(III) and As(V), and two organic arsenic species, monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA), in contaminated soil extracts by HPLC-ICP/MS has been developed.139 The results show that the mobilisation of As depended on the pH value of the extraction solution and the kind of soil extracted. Guerin and co-workers60 carried out a comparative study of HG-GC-QFAAS and HPLC-ICP-MS as methods of analysis for As speciation in environmental samples and confirmed that both methods are suitable for arsenic speciation. An interesting paper on As speciation this year was the evaluation of Saccharomyces cerevisiae as substrate for the biosorption of As(III) in the presence of As(V).71 Optimal analytical conditions for the selective As species in yeast and supernatant solution were carried out by means of ICP-AES with hydride generation.
Interest in the potential link between cancer and some inorganic nickel compounds has drawn attention to the Ni concentration in food and other environmental samples. Yaman140 studied nickel speciation in soils and the relationship with its concentration in fruits. The author has also extended the study to copper141 and with his colleagues, to lead.142
Determination of selenium speciation in plants is important in studying the bioavailability and toxicity of Se in Se-contaminated soil and sediment. Zhang and Frankenberg143 studied the speciation of Se in plant water extracts by ion exchange chromatography-HGAAS. Herbel and co-workers144 used a double spike (82Se and 74Se) TIMS technique to quantify the isotopic fractionation achieved by three different species of anaerobic bacteria capable of accomplishing growth by respiratory reduction of selenate or selenite to Se (IV) or elemental selenium, coupled with the oxidation of lactate.
A modified interface between a GC and a hollow cathode (HC) rf glow discharge (GD) with detection by OES has been developed for elemental speciation studies.145 Solid phase microextraction (SPME) was used for the introduction of the tin and lead species into the injector of the GC after preconcentration of metal species ethylated in situ with sodium tetraethylborate. Various tin and lead species were used as models and separated using a capillary column. Detection was accomplished at 283.9 nm for tin and 283.3 nm for lead. Good detection limits were obtained.
Cao and co-workers studied the assessment of the bioavailability of REE in soils by chemical fractionation and multiple regression analysis.146 The concentrations of the REEs in soils and plants were determined by ICP-MS. The results indicated that the sequential extraction procedure, in conjunction with multiple regression analysis, might be useful for the prediction of plant uptake of REEs from soils. Some workers from Japan studied the multielemental composition of green tea leaves as well as chemical species in tea infusions.147 ICP-AES and ICP-MS were used for elemental analyses and size exclusion chromatography (SEC) was used for elemental speciation. About forty elements were determined in tea samples over a wide concentration range of eight orders of magnitude. Chen and his team148 have developed methods involving an on-line combination of sedimentation field–flow fractionation-ICP-high resolution-MS to study the distribution of extractable heavy metals in a soil contaminated with Cu or Pb from sewage sludge.
The original Tessier sequential extraction method was applied to metal fractionation in sewage sludge samples149 and the results obtained compared with those estimated from direct microwave single extractions. In another study from the same research group, the conventional Tessier and BCR sequential extraction methods were applied to metal partitioning in sewage sludge samples.150 The results obtained by sequential extraction methods for Cr, Cu, Ni, Pb and Zn were compared with those estimated from single extractions using identical operating conditions applied in each individual Tessier and BCR fraction. In a similar study, Scancar and his colleagues151 used the BCR three-step sequential extraction procedure to determine the total concentrations and partitioning of Cd, Cr, Cu, Fe, Ni, and Zn in sewage sludge.
For environmental purposes, new analytical techniques for speciation studies are of great interest. They have to be sensitive and selective because natural matrices are very complex, as well as non- (or less) intrusive in order to keep the image of the real solution. The automated speciation analyser (ASA) is a newly developed instrument for speciation analysis of environmentally and toxicologically interesting elements on a routine basis.152 It is based on a combination of a purge and trap concentrator, an isothermal oven housing a multi-capillary column for the separation of the determinants, and a miniature MIP emission detector. The ASA has the advantage of being small, robust and easy to handle and allows fast analysis. Absolute detection limits of 0.4 and 9 pg for MeHg+ and Hg2+ were obtained. Time-of–flight MS (TOFMS) has recently been introduced as an alternative to scanning-based mass analysers for use in elemental analysis.153 Coupled with an ICP or alternative ion source, TOFMS can produce a complete atomic mass spectrum in less than 50 µs. Because of this high spectral-generation rate, even very brief transient signals can be recorded. In a paper that was published last year, Bings et al.153 highlighted the capabilities of TOFMS in speciation analysis through coupling GC and capillary electrophoresis with ICP-TOFMS. In addition, a novel switched gas sampling glow discharge154 ionisation source was developed.
A very interesting paper on speciation described the development of a thermal-extraction cone penetrometry gas chromatography-MS system (TECP GC-MS) to detect subsurface contaminants in situ.155 The TECP can collect soil-bound organics up to depths of 30 m without bringing the soil to the surface or into a collection chamber. The data obtained are in a remarkable agreement with closed cell thermal desorption (TD) experiments, where no organics are lost to the environment during heating. TECP GC-MS results also compare favourably with those of solvent extracted GC-MS analyses. A flow extraction system with on-line acid off-line flame atomic absorption spectrometric (FAAS) detection was developed to speed up, facilitate and improve the accuracy of sequential extraction for metal speciation in a solid materials.156 The results obtained for five metals of a soil CRM using the proposed system were compared with those of the conventional batch extraction.
3.2 Instrumental methods of analysis
It is well known that the direct determination of Sb in soils by ultrasonic slurry sampling electrothermal atomic absorption spectrometry (USS-ETAAS) in soils and sediments is hampered by spectral interferences that are not completely removed by deuterium background correction. Cal-Prieto et al.164 suggested an accurate and precise method based on peak height evaluation. They found that out of the seven chemical modifiers used for the direct determination of Sb in soils, nitric acid was the most adequate. No significant differences were observed between the experimental and the certified concentrations for three soils CRMs; recoveries ranged from 93 to 110%.
A very simple FAAS method was developed for the indirect determination of ascorbic acid using a FI system based on the redox reaction between chromate and ascorbic acid in acid medium.165 The Cr(III) produced by Cr(VI) being reduced with ascorbic acid is adsorbed on a cation exchange resin microcolumn, then eluted by 3 M HNO3 to the nebuliser of a FAAS instrument. The absorbance of Cr(III) is proportional to the concentration of ascorbic acid in the sample. The method has been applied to the determination of ascorbic acid in vitamin C tablets, vitamin C injections and vegetables.
Milacic and Scancar166, 167 discussed the applicability of an anion-exchange fast protein liquid chromatographic-electrothermal atomic absorption spectrometric procedure for the determination of trace amounts of Cr(VI) in lime-treated sewage sludge.
In a recent study, the use of ultrasonic slurry sampling GFAAS in the determination of Co in sewage sludge has been developed.168 The procedure was validated by analysing CRMs.
Shamsipur and co-workers169 developed a simple and relatively fast method to selectively separate and concentrate trace amounts of lead from aqueous samples for measurement by FAAS. The aqueous sample is passed through an octadecyl-bonded silica membrane disk modified by a recently synthesised bis(anthraquinone)sulfide, Pb2+ ions adsorb quantitatively and almost all matrix elements will pass through the disk to waste. The retained lead ions are then stripped from the disk by a minimal amount of acetic acid as eluent. The detection limit of the proposed method is 50 ng Pb2+ per 1000 ml and the method has been successfully applied to the determination of lead in soil and water samples.
An ultra-sensitive method for the determination of butyltin compounds has been developed by coupling LC with ETAAS by means of a hydride generation in situ trapping system.170 Detection limits of 0.84, 1.66 and 20.4 ng were obtained for mono, di- and tributyltin, respectively. The system has been used for the determination of butyltin species in CRMs of marine materials such as mussel tissues and sediments.
Wang and Hansen171 introduced a novel way of exploiting flow injection/sequential injection (FIA/SIA) on-line ion-exchange pre-concentration with detection by ETAAS and applied it to the determination of trace levels of Ni in environmental and biological samples. The procedure was validated by determining the Ni contents of two CRMs and a human urine sample. In a noteworthy study, Bag and his team172 have developed a method for the determination of Cd, Cu, Fe, Ni and Zn by FAAS after pre-concentration on a column containing Escherichia coli immobilized on sepiolite. The trace metals were determined with relative error lower than 10%.
It is interesting to notice that papers on sample transport efficiency are still appearing once a while. Bernhardt et al.173 used a graphite furnace of the boat-in-tube type as the electrothermal vaporiser (ETV) and an electrostatic precipitator to determine analyte transport efficiencies and dependencies on plant and cereal matrices and on carrier elements. All analyte measurements were carried out with coherent forward scattering using simultaneous multielement determinations. Transport efficiencies of up to 19% for Cu, 21% for Fe and Mn and 36% for Pb from the ETV boat to the L’vov platform were obtained for the SRMs.
For the determination of eight metals in soils and sediments, ICP-AES, ICP-MS and ET-AAS have been compared after acid decomposition of the samples in a microwave oven.177 The authors observed that the use of HNO3–HCl provided good recoveries for Cd, Cu, Ni, Mn and Zn (89–114%), but poorer results for Pb (82–89%). Complete solubilization of the materials was achieved with closed vessel microwave digestion using a mixture of HF–HNO3–HCl.
Schron and co-workers178 have described a method for direct solid sample analysis of sediments, soils, rocks and advanced ceramics by ETV-ICP-AES and GF-AAS. The authors emphasised the need for high-grade homogeneity of the sample powder even at milligram and sub-milligram levels. Precision and accuracy of SS-GF-AAS are improved by application of 3D-calibration plots in comparison to the conventional 2D calibration. In this way, the two methods, SS-ETV-ICP-AES and SS-GF-AAS complement one another's analytical performance. In another study, electrothermal vaporization using a furnace fusion technique was applied to the determination of lead in botanical samples by ICP-AES.179 Calibration was by standard additions from aqueous solutions.
Three interesting papers on applications of AES appeared this year. A paper from Japan180 described how atomic spectrometric methods, specifically ICP-AES and ICP-MS, can be used to distinguish the geographical origin of brown rice samples by their trace element composition. Thirty-four kinds of unhulled rice samples were collected from 27 different locations, digested with HNO3 and HClO4 and analysed by ICP-AES and ICP-MS. The results were analysed using chemometric software, including cluster analysis and principal component analysis to categorise the samples into groups. A paper from Slovakia reported the use of ICP-AES in the determination of trace elements in heroin.181 The nutritional and environmental properties of algal products used in healthy diet have been investigated with the help of INAA and ICP-AES.182
A simple and rapid procedure for extraction of the organometallic species methylmercury from sediment, based on microwave assisted alkaline digestion with methanolic KOH, has been described.186 Organomercury species were extracted with dichloromethane in HCl medium and back-extracted into ultra pure water. The sediment extracts were analysed with HPLC-UV-post-column oxidation-CV-AFS. The detection limit of the proposed method was 12 ng g−1. The method was validated by the analysis of two sediment CRMs and methylmercury concentrations found were in good agreement with the certified values. An important and very noteworthy paper was published during the year. Hempel and his co-workers187 reported the transethylation of an organolead compound to an organomercurial compound in the environment using sodium tetrapropylborate, GC-AED and HPLC-AFS. The importance of their discovery can be seen when it is assumed that this transalkylation takes place at sites where organolead compounds occur and Hg2+ is available. Assessing the risk posed by such sites can therefore not be over emphasised, particularly with organolead compounds still present in our environment as contaminants despite the ban of organolead as a gasoline additive in most countries.
3.2.4.1 ICP-MS. ICP-MS has certainly ‘matured’ and this is reflected in the publication of a number of reviews,188,189 an excellent one being the one entitled ‘ ICP-MS in 2000: a large selection in technological characteristics’ written by Mermet.190 Soil analyses by ICP-MS has been reviewed (60 refs) by Yamazaki.191 Also, recent trends and developments in laser ablation ICP-MS have been reviewed by Gunther et al.192 On a lighter note, Houk193 has written an interesting paper entitled ‘ICP-MS and the European discovery of America‘ where intriguing parallels between the development of the ICP-MS and the voyage of discovery of Christopher Columbus are presented. Environmental Scientists who can read Japanese may wish to consult the review by Yamasaki194 on ‘soil analysis by ICP-MS’.
Monna and co-workers195 studied noise identification and sampling frequency determination for precise Pb isotopic measurements by quadrupole-based ICP-MS. Coupling ICPs with sector field mass spectrometers has led to a remarkable improvement of the analytical capabilities in the field of trace element determinations during the last decade. Moor et al.196 studied the capabilities and limitations of high-resolution ICP-MS.
Recent advances in the coupling of GC and HPLC with ICP-MS and their role in trace element speciation analysis of environmental materials have been excellently discussed in a paper by Szpunar et al.134
A good comparison between the use of INAA and ICP-MS methods for environmental studies has been made by Revel and Ayrault.197 The advantages and drawbacks of using both techniques for soil, sediment, plant and water pollution studies are highlighted in the paper. A comparison of four sample introduction techniques for the determination of As by ICP-MS has been reported.61
Sometimes ICP-MS is preferred to radiometric techniques. Technetium is known to have high mobility in soil–water systems and also high bio-availability for plants because the most stable form of Tc in natural surface environment is thought to be TcO4− which is highly soluble. The chemical form of Tc, however, changes with environmental conditions. 99Tc concentrations in surface soil and plant leaf samples collected from forest sites within the 30-km zone around the Chernobyl reactor were measured198 by ICP-MS after separation of 99Tc using a Tc-selective chromatographic resin. Holmes and Pilvio199 determined thorium in environmental and workplace materials by ICP-MS. They gave the advantages of using ICP-MS over radiometric techniques to measure natural 232Th. Betti et al.200 have demonstrated the suitability of IC-ICP-MS for the simultaneous separation and on-line detection of light fission products such as, Mo, Pd, Rh, Ru, Sb, Tc, Te and Zr. It is well known that as a result of the accident at Chernobyl nuclear power plant (NPP), the environment was contaminated with spent nuclear fuel. The 236U isotope was used to monitor the spent uranium from nuclear fallout in soil samples collected in the vicinity of the Chernobyl NPP.201 The study employed a rapid and sensitive analytical procedure for uranium isotopic ratio measurement based on ICP-quadrupole MS with a hexapole collision cell (HEX-ICP-QMS). Also, in a similar study, the concentrations and isotopic ratios of 239Pu 240Pu in soils collected from the Chernobyl 30 km zone were determined by ICP-MS.202
An analytical method has been developed for the measurement of Mg isotope ratios and determination of Mg concentration in 26Mg spiked plant nutrient solutions by the reverse isotope dilution technique.203 The Mg concentrations were determined by ICP-OES and ICP-MS with external calibration and the measured values were in agreement with the results obtained by the reverse isotope dilution technique. The potential of multiple collector-ICP-MS (MC-ICP-MS) for precise Pb isotopic measurements using admixed Tl for ‘external normalization’ of instrumental mass discrimination has been emphasised. Consequently, the matrix effects for Pb isotope ratio measurements by MC-ICP-MS have been investigated.204 The advantages of the technique were also enumerated.205 Isotopic analysis of uranium in tree bark by ICP–MS has been proposed as a new measurement strategy for monitoring airborne contamination and for discrimination of nuclear and non-nuclear emission sources.206
A method for the determination of trace element concentrations by laser ablation ICP-MS using solution calibration and an internal standard was evaluated by analysing NIST soil and glass samples. In most cases, the measured element concentrations were within ±10% of certified values. For soil samples, Mg was chosen as an internal standard.
An isotope dilution inductively coupled plasma quadrupole mass spectrometric (ID-ICP-QMS) method was developed207 for the simultaneous determination of the platinum group elements Ir, Pd, Pt and Ru in environmental samples. Spiked solutions enriched with the isotopes 191Ir, 104Pd, 194Pt and 94Ru were used for the isotope dilution step. The reliability of the ID-ICP-QMS method was demonstrated by analysing a Canadian geological reference material and by participating in an interlaboratory study for the determination of Pd and Pt in a homogenized road dust sample. Cd and Pb have been determined in six new environmental reference materials (SRMs) using ID-ICP-MS.208
The extraction and pre-concentration capabilities of a new extraction technique, stir bar sorptive extraction, were combined with the separation power of capillary gas chromatography (CGC) and the low detection limits of ICP-MS for the determination of the organo-tin compounds, tributyltin and triphenyltin in aqueous standard solutions, harbour water and mussels (after digestion with tetramethylammonium hydroxide).56
Ultrasonic slurry sampling electrothermal vaporisation ICP-MS (USS-ETV-ICP-MS) has been applied to the determination of Cd, Pb, Tl and Zn in several soil samples.209 A mixture of 1% m/v EDTA and 1.5% m/v of ascorbic acid was used as the modifier to enhance the ion signals. The precision between sample replicates was better than 9% with USS-ETV-ICP-MS method.
3.2.4.2 Thermal ionisation mass spectrometry. TIMS is becoming popular as the technique of choice for the precise determination of isotope ratios. The technique has been used for precise measurement of 37Cl/35Cl isotopic ratios in small amounts of samples,210 isotopes of light rare earth elements in the form of oxide ions,211 the 234U/238U isotopic abundance ratio of three uranium samples separated from a lake sediment and the 87Sr/86Sr isotopic composition of the soil samples of the Bryansk region contaminated by the Chernobyl accident.212 The last study contributed to the understanding of the background levels of these elements in an area contaminated by the Chernobyl accident.
The isotopic and elemental abundance of Cd in five lunar samples has been measured with high precision using TIMS and the stable isotope dilution technique.213 The bombardment of the lunar surface by cosmic rays produces secondary neutrons, some of which are thermalized by the lunar soil and then interact strongly with the isotopes of Cd, Gd and Sm which have high neutron capture cross sections at thermal energies causing changes in their isotopic compositions. Such changes have been measured in samples from the Apollo 14, 16 and 17 missions using TIMS.214 The concentrations of Cd, Gd and Sm in nine lunar samples have also been measured by isotope dilution mass spectrometry, with Cd being measured in lunar samples for the first time by this method.
3.2.4.3 Accelerator mass spectrometry. Accelerator mass spectrometry (AMS), though a specialised technique, is occasionally used in environmental analysis. For example, AMS has been used to determine 129I in environmental materials,215 and the impacts of city traffic on the living environment have been studied by measuring the levels of 14C in tree leaf samples.216 In addition, 236U in soil and sediment reference materials has been measured using the same technique.217
3.2.4.4 ICP-time of flight mass spectrometry. Ultratrace metal determination in samples with a complex matrix such as biological tissues, muscles and natural waters has become one of the challenging areas in trace metal analytical chemistry. ICP-MS is ideal for ultratrace metal analysis because it allows multielemental and isotopic analysis with high sensitivity over a broad dynamic range. Nevertheless, ICP-MS is not readily applicable for all elements in every conceivable sample due to its relatively low tolerance to total dissolved solids (TDS) and polyatomic interferences. ICP-time of flight mass spectrometry has been applied to elemental and speciation analysis of organolead compounds and isotope ratio measurements.218
Total reflection X-ray fluorescence spectrometry (TXRF) has wide applicability in plant analysis. Varga et al.235 studied element distributions between the symplasm and apoplasm of cucumber plants by TXRF spectrometry235 while Wamwangi et al.236 reported the trace element analyses of pollen, bee tissue and honey using the same technique.236 Sobrado and Greaves237 used TXRF to determine the elemental composition and the relative contribution of each element in leaf secretion of the mangrove species Avicennia germinans grown under contrasting salinities.237
| Element | Matrix | Technique; atomization; presentationa | Sample treatment | 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 | Cabbage | AE;ICP;L | Uptake and speciation of various Al species studied; nutrient solution and stem sap analysed | 238 |
| Al | Spices and herbs | AA;ETA;L | Samples mineralised with HNO3 and V2O5 | 239 |
| Al | Tea infusion | AA;F;L | Amberlite XAD-7 resin used to separate the hydrolyzable polyphenols-bound Al species; Chelex-100 resin was used to separate cationic Al species | 137 |
| Al | Tea infusions | AA;F;L | Fluoride-bound Al species determined in tea infusions | 240 |
| Al | Vegetables | AA;ETA;Sl | Acid mineralization with HNO3 and V2O5 | 241 |
| As | Soil extracts | MS;ICP;L | Inorganic and organic As species separated on anion exchange column with NaOH as mobile phase | 139 |
| As | Soils | AA;ETA;L | USEPA Method 3052 (HCl–HNO3–HF, Microwave digestion) | 242 |
| As | Plants, soils and sediments | AA;ETA;Sl | Ultrasonic agitation of the slurry followed by a fast electrothermal program using single and mixed modifiers (Ir/Mg modifier best) | 243 |
| As | Sediment and soils | AA;ETA;Sl | Slurries sonicated for 20 s before delivery to the previously W-Rh (permanent chemical modifier) treated platform | 244 |
| As | Soils | AA;Hy;G | FI—procedure developed; recovery improved; compared with slurry sampling-on-line microwave extraction | 162 |
| As | Environmental samples | AA;ETA;Sl | Plants mineralized by dry ashing and results compared with those by wet digestion with HNO3–HClO4–HF | 245 |
| As | Environmental samples | MS;ICP;L AA;Hy;G | Polluted water, soil extracts and sewage sludge certified by HPLC-ICP-MS and HG-GC-QFAAS | 60 |
| As | Humus, moss | AA;ETA;L | Two sample decomposition methods optimised (HNO3–H2O2 and HNO3–H2O2–HF–H3BO3) | 246 |
| As | Plants | AE;ICP;L | Effect of plant matrices investigated | 247 |
| As | Lichens, plants | MS;ICP;L | Arsenic compounds extracted with two extractants (water or methanol/water (9∶1)) | 248 |
| As | Sea grass | MS;ICP;L | Open-vessel digestion with 4 media, HClO4/H2SO4–HNO3, H2SO4–HNO3, HNO3–H2O2 and HNO3, compared | 249 |
| As | Yeast | AES;Hy, ICP;L | Saccharomyces cerevisiae evaluated as substrate for the biosorption of As(III) in the presence of As(V) | 71 |
| As | Freeze-dried plant samples | AA;-,Hy;L | Six extraction media (acetic acid, EDTA, NaOH, MeOH–H2O, tetrabutylammonium hydroxide, acetonitrile–H2O) tested for ability to extract As and Sb | 250 |
| As | Asparagus | AA;ETA;L | Sample digestion described | 251 |
| As | Medical herbs | MS;ICP;L AA;ETA;L | Plants mineralised in a high-pressure microwave mineralizer; analysed for As, Cd and Pb | 252 |
| As | Soil | AE;Hy;L AE;ICP;L AA;Hy;L | Two commercial microwave digestion systems and epithermal neutron activation analysis evaluated; former yielded poor results | 253 |
| As | Mushrooms | AA;F;L AA;ETA;L MS;ICP;L | Arsenite, dimethylarsinic acid, methylarsonic acid and arsenate separated on anion exchange column | 254 |
| B | Botanical samples | MS;-;L | Sample treatment methods described | 255 |
| Be | Soil | MS;ICP;L | Be, Ni and V extracted from soil samples by aqua regia using microwave-assisted extraction | 256 |
| Be | Soil | MS;ICP;L | Three–step extraction procedure applied to speciate Be, Ni and V | 257 |
| Bi | Environmental samples | AA;ETA;L | FIA on-line two-stage solvent extraction separation/pre-concentration procedure described | 258 |
| 14C | Leaves | MS;-;- | 14C measured in tree-leaf samples to study the impact of city traffic by using accelerator MS | 216 |
| Cd | Lunar soils | TIMS;-;- | Isotopic and elemental abundance of Cd in lunar samples measured using TIMS and stable ID | 213 |
| Cd | Soil, feed, manure | AA;ETA;L | Samples microwave-digested | 259 |
| Cd | Soil | MS;ICP;L | Cd reactivity in metal-contaminated soils investigated using stable ID-sequential extraction over 59-weeks | 260 |
| Cd | Soils | AA;ETA;L AE;ICP;L | The effect of OM addition on solubility and free Cd(II) and Zn(II) speciation studied; soils extracted with ultra pure 0.01 M KNO3 | 261 |
| Cd | Grass-cereal mixtures | AA;ETA;S | Thermal pre-treatment of samples using double vaporisation in a two-step atomizer with a purged vaporizer; porous graphite capsule or a filter inserted into the vaporizer used for direct solid sample analysis | 114 |
| Cd | Soil | MS;ICP;L | Stable 111Cd isotope added to contaminated soil and the column effluents fractionally collected. Contaminant (natural) and tracer 111Cd in effluent determined | 262,263 |
| Cd | Soils | AA;F;L | Parameters influencing extraction efficiency of total water- soluble Cd, Pb and Zn in soil samples investigated | 264 |
| Cd | Lunar samples | MS;-;L | Concentrations of Cd, Gd and Sm in lunar samples measured by IDMS and TIMS | 214 |
| Cd | Environmental SRMs | MS;ICP;L | Certification of Cd and Pb in environmental SRMs | 208 |
| Cd | Soils | XRF;-S | Samples separated into 8 particle-size fractions and their mineral size fractions characterised by X-ray diffractometry; Cd, Cr and Pb determined by XRF | 265 |
| Cd | Sweet corn | MS;ICP;L | Pd, HNO3 and H2O2 modifier used to improve the sensitivities and peak shapes of Cd, Pb and Zn in vegetable oil and sweet corn | 266 |
| Cd | Grain | AE;ICP;L | Sample adjusted to pH 5.5 for injection into dual-channel FI manifold; 1 g sulfhydrylated cotton fibre column used for pre-concentration; Cd, Cu and Pb eluted with 3 ml 2 M HCl | 267 |
| Cd | Sewage sludge | AA;ETA;L | Cd and Pb in ground samples determined by suspending in solution containing 10% (v/v) HF, 1% (v/v) HNO3, 0.5% (m/v) NH4H2PO4 and 0.1% (m/v) sodium hexametaphosphate | 268 |
| Cd | Environmental samples | AA;F;S | Interference problem in determination of Cd, Pb and Zn described; detection limit using D2 lamp background correction improved by 1.05–4.5 times | 269 |
| Cd | Vegetables | AA;F;L AA;ETA;L | Topsoil, unwashed and washed edible green parts of endive and roots of carrot sampled; Cd, Pb and Zn determined | 270 |
| Cd | Herbal plants | MS;ICP;L AA;ETA;L | See As, ref. 252 | 252 |
| Co | Sewage sludge | AA;ETA;L | Slurries prepared by ultrasonic stirring; diluent 5% HNO3; no matrix modifier applied | 168 |
| Cr | Sewage sludge | AA;ETA;L | Samples of sewage sludge and sludge mixed with sawdust (1 + 1, v/v) with a pH of 8.0 and 7.8, respectively, as well as their mixtures with 5% of quicklime analysed | 166 |
| Cr | Spices herbs | AA;ETA;L | Samples mineralised with HNO3 and V2O5 | 271 |
| Cr | Soils | XRF;-;S | See Cd ref. 265 | 265 |
| Cu | Grain | AE;ICP;L | See Cd ref. 267 | 267 |
| Cu | Rice SRMs | AA;-;G | Sample plus 1,10-phenanthroline and 0.1 M HNO3 transferred by 0.1 M HNO3 and merged with sodium tetrahydroborate to produce vapour species of Cu; separated in a G-L separator and detected in a quartz tube atomizer at 1000 °C | 272 |
| Cu | Soils, fruits | AA;F;L | The speciation of Cu in soils based on dissolution in KNO3–H2O2, oxalic acid, acetic acid, EDTA and citric acid as extraction reagents; for fruits, wet and dry ashing methods applied | 141 |
| Cu | Plants | AA;ETA;L | Cu uptake and distribution in plants studied; >99.6% of total Cu in xylem sap was in complexed form | 273 |
| Cu | Plant materials | AA;F;L | Flow system for Cu on-line pre-concentration, employing a tannin resin prepared from Eucalyptus Saligna Sm, proposed | 274 |
| Cu | Soil | MS;ICP;S | Mg used as internal standard; Cu and Ni in soil gave poor results | 275 |
| Cu | Soil | AA;F;L | Total Cu and Zn extracted by acid digestion in Teflon bombs in a microwave oven; available Cu and Zn extracted using DTPA | 276 |
| Cu | Tree bark | AA;F;L | Samples ashed in a muffle furnace and Cu, Pb and Zn determined | 277 |
| Cu | Soils, plants | AE;ICP;L | Soil digested with aqua regia in a microwave closed vessel; plants digested using both microwave and refluxing with H2O2–HNO3 in a heating block | 278 |
| Fe | Soil extracts | AE;ICP;L | Soil (0.1 g) extracted with 0.6 g NH2OH·HCl and 10 ml oxalic acid solution in a PTFE vessel by sealing and heating at 128–130 °C for 1.5 h | 279 |
| Fe | Soil extract | AE;ICP;L | Free iron oxide in soil extract determined; effects of the volume of the loading sample and the concentration of the extractants (NH2OH·HCl, H2C2O4) investigated | 280 |
| Fe | Plants | AA;F;L | ‘Active’ Fe extracted from fresh leaf material of wild plants by 1,10-phenanthroline | 281 |
| Gd | Lunar samples | MS;-;L MS;-;L | See Cd, ref. 214 | 214 |
| Hg | Leaf tissue | AA;CV;G | Samples mineralized in a microwave oven | 282 |
| Hg | Environmental media | AA;F;S | Hg determined by integration of thermal decomposition, amalgamation and AAS (TDA-AAS); solid sample analysed directly | 283 |
| Hg | Plant material | AA;CV;G | Three procedures for the determination of Hg in plant material compared; all used close vessel microwave heating | 284 |
| Hg | Mushrooms | AA;CV;G | Wet digestion of samples with conc. HNO3 in closed PTFE vessels in a microwave oven | 285 |
| Hg | Soil and sediment | AA;CV;G | Total Hg determined in samples using RNAA and CVAAS | 286 |
| Hg | Soil | AA;CV;G | Field screening method with thermal desorption of Hg from the sample onto Au, followed by thermal desorption from the Au to a Au-film Hg vapour analyzer; method compared to CVAAS | 287 |
| Hg | Soil | AF;CV;G MS;ICP;L | Immunoassay and ASV methods evaluated; CVAFS and ICP-MS used for comparison purposes | 288 |
| Hg | Soils | AE;MIP;G | Two methods compared. Hg species extracted into toluene, pre-concentrated by evaporation and methyl Hg butylated with a Grignard reagent followed by determination; methyl Hg also extracted into dichloromethane and back extracted into water followed by in situ ethylation, collection of ethylated Hg species on Tenax and determination | 289 |
| Hg | Environmental samples | AF;-;- | Samples were thermally decomposed and elemental Hg was collected on a gold sand trap and detected by AFS | 290 |
| I | Environmental samples | NAA;-;- | Paper describes how NAA is used to measure 129I/127I ratios | 291 |
| 129I | Environmental materials | NAA;-;- MS;-;- | Two analytical methods (RNAA and AMS) compared | 215 |
| Ir | Environmental samples | MS;ICP;L | Adsorption of Ir on an cw-amino pyridine (AP) resin at very low Ir concentrations was studied using 192Ir radiotracer | 292 |
| Mg | Plant samples | AA;F;L | Acid extraction of Mg, Mn and Zn from plant tissues by high intensity probe ultrasonication described | 126 |
| Mg | Beans and rice | AA;F;L | Sample powder suspended in 1.5 g l−1 agar, <10 drops of dibutyl phthalate and 1 ml 50 g l−1 La (III) as matrix modifier; mixture diluted and, after shaking, suspension sprayed into flame | 293 |
| Mg | Plant nutrient solutions | MS;ICP;L AE;ICP;L | Method developed for the measurement of Mg isotope ratios in 26Mg-spiked nutrient solutions | 203 |
| Mn | Plant samples | AA;F;L | See Mg ref. 126 | 126 |
| Mn | Environmental samples | AA;ETA;L | QC procedures described | 294 |
| Ni | Soil | MS;ICP;L | See Be ref. 257 | 257 |
| Ni | Soil | MS;ICP;L | See Cu ref. 275 | 275 |
| Ni | Soil | MS;ICP;L | See Be ref. 256 | 256 |
| Ni | Environmental samples | AA;ETA;L | Novel way of exploiting FIA/SIA on-line ion-exchange pre-concentration with ETAAS fully described | 171 |
| Ni | Soils, fruits | AA;F;L | Soils extracted with HNO3–H2O2, oxalic acid, EDTA, and acetic acid–citric acid; Ni in fruit pre-concentrated on activated carbon | 140 |
| P | Plant materials | AE;ICP;L | P release from different compounds in the presence and absence of modifiers by ETV- ICP-AES studied | 295 |
| P | Plant leaves | MS;ICP;L | Dry leaf homogenates placed in Teflon vessels with HNO3 and microwave digested | 296 |
| Pb | Soils, fruits | AA;ETA;L AF;F;L | Soils extracted with various chemical reagents; fruits analysed using slotted tube atom trap (STAT) enrichment flame and GFAAS | 142 |
| Pb | Soil | AA;F;L | Pb selectively separated and concentrated by passing the sample through an octadecyl-bonded silica membrane disk modified by a recently synthesized bis (anthraquinone) sulfide | 169 |
| Pb | Soil | AA;F;L | Pb diethyldithiocarbamate complex retained on a miniature column of Chromosorb 102 from buffered sample solutions | 163 |
| Pb | Street dust | AA;F;L | Samples extracted with aqua regia | 297 |
| Pb | Soils | AA;F;L | Significance of playground soil Pb intake to the total daily lead burden in pre-school children evaluated | 298 |
| Pb | Soil | AA;ETA;L | Total Pb determined by refluxing the samples with conc. HNO3 and organic lead by shaking with cold ammoniacal methanol | 299 |
| Pb | Soils | AE;ICP;L | Buffering from secondary minerals studied as a migration limiting factor in Pb-polluted soils | 300 |
| Pb | Soils, dust | AA;F;L | Environmental contamination effect on body burden of Pb studied | 301 |
| Pb | Plant tissue | MS;ICP; Hy;L | HG-ICP-MS explored using oxalic acid-ammonium Ce(IV) nitrate-sodium tetrahydroborate as the reaction matrix and a home made hydride generator | 302,64 |
| Pb | Botanicals | MS;ICP;L | Closed-vessel microwave digestion with FI-ICP-MS | 303 |
| Pb | Botanical samples | AE;ICP;L | Sample ground with diammonium hydrogenphosphate; weighed into a tungsten cuvette which was placed on to the tungsten boat furnace of the vaporizer; tetramethylammonium hydroxide solution added | 179 |
| Pb | Root vegetables | AA;F;L | Pre-concentration achieved with anthranilic acid on activated carbon at pH 5 | 304 |
| Pb | Vegetables | AA;ETA;L | Vegetables dry ashed at 450 °C; soils extracted with 2 M HNO3 and NH4OAc | 305 |
| Pb | Soils, plants | AE;ICP;L | See Cu ref. 278 | 278 |
| Pb | Tree bark | AA;F;L | See Cu ref. 277 | 277 |
| Pb | Herbs | MS;ICP;L AA;ETA;L | See As ref. 252 | 252 |
| Pb | Vegetables | AA;F ETA;L | See Cd ref. 270 | 270 |
| Pb | Environmental samples | AA;F;L | See Cd ref. 269 | 269 |
| Pb | Soils | XRF;-;S | See Cd ref. 265 | 265 |
| Pb | Sewage sludge | AA;ETA;L | See Cd ref. 268 | 268 |
| Pb | Sweet corn | MS;ICP;L | See Cd ref. 266 | 266 |
| Pb | Grain | AE;ICP;L | See Cd ref. 267 | 267 |
| Pb | Environmental SRMs | MS;ICP;L | See Cd ref. 208 | 208 |
| Pb | Grass cereal mixtures | AA;ETA;L | See Cd ref. 114 | 114 |
| Pb | Soils | AA;F;L | See Cd ref. 264 | 264 |
| Pd | Road sediments | MS;ICP;S | Good agreement between LA-ICP-MS and HR-ICP-MS analysis was obtained for Pt and Rh whereas the determination of Pd remains subject to interferences | 306 |
| Pd | Soil | AA;ETA;L | Prior separation and enrichment of the metal as Pd(II)–SnCl3-N-butylacetamide (BAA) complex into 1-pentanol by solvent extraction | 307 |
| Pt | Road sediments | MS;ICP;L | See Pd ref. 306 | 306 |
| Pt | Dust | MS;ICP;L | Samples taken with medium volume PM-10 collectors for 48 h | 308 |
| Pt | Environmental materials | MS;ICP;L | Accumulation of Pt on the soil surface studied | 309 |
| Pt | Soil | MS;ICP;L | Samples ignited, spiked by 198Pt and decomposed by acid digestion (H–HClO4, HCl–HNO3); Pt separated from the matrix by tellurium co-precipitation | 310 |
| Pu | Soil and vegetation | AMS;-;- | Ashed samples digested with aqua regia and filtered; filtrate separated by IEC and eluate evaporated to dryness; to the residue, 2 mg Fe(NO3)2 was added and the mixture ashed at 800 °C | 107 |
| Pu | Environmental samples | MS;ICP;L TIMS;-;- | Isotope ratios of U and/or Pu in each particle measured by SIMS | 311 |
| Pu | Soils | MS;ICP;L | Samples from forest sites within 30 km of the Chernobyl reactor analysed for 239Pu and 240Pu | 202 |
| REE | Soils | MS;ICP;L | Bioavailability of REEs in soils evaluated, based on the combination of chemical fractionation and multiple regression analysis; REEs partitioned by a sequential extraction procedure into five fractions | 146 |
| REE | Wheat seeds | MS;ICP;L | Contents of 15 REEs in the seeds of sixty breeds of wheat collected from the seed bank measured | 312,313 |
| REE | Soil | MS;ICP;S TIMS;-;- | Characterisation, fractionation and migration of REE in a granite-derived soil system studied | 314 |
| REE | Soils, plants | MS;ICP;L | The spectroscopic overlap interference of BaO+ and BaOH+ on some middle REEs are overcome by separation of REEs from Ba with AG50W-X 8 cation exchange chromatography | 133 |
| Rh | Road dust | MS;ICP;L | See Pt ref. 308 | 308 |
| Rh | Road sediments | MC;ICP;S | See Pd ref. 306 | 306 |
| S | Soils | MS;ICP;L | Sulfur oxidised by bromine into sulfate with achievement of isotope equilibrium between the sample and spike | 315 |
| S | Plant extracts | AE;ICP;L | Speciation and quantitative analysis of inorganic sulfur form, sulfate and organic sulfur compounds by using high performance IC with ICP-AES described | 138 |
| Sb | Soil | MS;ICP;L | Conventional single and sequential extraction procedures used to speciate Sb in soil | 135 |
| Sb | Soils and vegetables | AF;Hy; F;L AA;ETA;L | Soils digested with HNO3–HC–HF mixture; plants digested with HNO3–H2SO4–H2O2 or HNO3–H2O2 mixtures; microwave oven digestion procedures allowed the total dissolution of the matrices | 184 |
| Sb | Soils | AA;ETA;L | Nitric acid164 found to be best modifier for Sb | 164 |
| Sb | Environmental samples | AA;F;G | Extraction efficiency 0.7–37% for most samples | 316 |
| Sb | Plant cell extracts | MS;ICP;L | Sb species separated using 15 mmol L−1 nitric acid (pH 6) as eluent on a PRP-X100 column | 136 |
| Sb | Plant samples | AA;-,Hy;L | See As ref. 250 | 250 |
| Se | Soils | AA;-,Hy;L | Efficiency of four acid-based closed vessel decomposition procedures checked with CRMs, pressurised microwave sample preparation using (1+1) HNO3∶ H2SO4 recommended | 317 |
| Se | Plant tissue samples | QMS;ICP;L | Samples decomposed with HNO3, HF and H2O2 using closed-vessel microwave digestion | 318 |
| Se | Cereal samples | MS;ICP;L | Anion exchange chromatographic system coupled to ICP-MS used for the identification and quantification of Se compounds | 319 |
| Se | Plants | AA;-,Hy;L | Anion exchange resin143 used to separate Se into non-amino acid organic Se, Se-amino acids, selenite and selenate | 143 |
| Se | Garlic | MS;ICP;L | Sample leached with water and the aqueous extract fractionated by preparative size-exclusion chromatography | 320 |
| Se | Mushrooms | AF;F;L | Se compounds in edible, selenium-accumulating mushrooms characterised using various chromatographic techniques combined with several detectors | 321 |
| Se | Tea | AF;-,Hy;G | Sample decomposed with HNO3 and HClO4 and boiled with conc. HCl to convert Se(VI) to Se(IV); portion of the solution injected into a carrier stream of KBH4 containing NaOH in FI manifold | 183 |
| Se | Environmental samples | AA;ETA;Sl | See As ref. 245 | 245 |
| Sm | Soil | MS;-;S | Isotopic compositions of Sm and Yb analysed using LA-ion trap MS | 322 |
| Sm | Lunar samples | MS;-;L | See Cd ref. 214 | 214 |
| Tc | Soil | MS;ICP;L | Three extraction techniques used; 1. Acid leaching of Tc from ashed soil. 2. Acid leaching of Tc from raw dry soil. 3. Tc volatilisation from ashed soil using a combustion apparatus | 323 |
| Tc | Soil, plant samples | MS;ICP;L | Soils volatilized and Tc trapped in a combustion apparatus and purified by passing through a chromatographic resin; wet digestion in combination with the resin used for plant | 198 |
| Th | Environmental samples | MS;ICP;L | Experimental parameters that must be accounted for in sample digestion and preparation described | 199 |
| Th | Tree bark | MS;ICP;L | Bark analysed by nebulisation of bark digests | 25 |
| Tl | Soil | MS;ICP;L | Two isotopes, 203Tl and 205Tl used; lutetium used as an internal standard; soil extracts measured after dilution | 324 |
| 236U | Environmental media | AMS;-;- | Sample preparation procedures described | 217 |
| U | Environmental samples | QMS;ICP;L | Good agreement between isotopic ratio measurements by ICP-QMS with hexapole collision cell and double-focussing sector field ICP-MS | 201 |
| U | Tree bark | MS;ICP;L | Quadrupole-MS equipped with a microconcentric nebulizer and membrane desolvator used | 206 |
| U | Tree bark | MS;ICP;L | See Th ref. 25 | 25 |
| V | Soil | MS;ICP;L | See Be ref. 257 | 257 |
| V | Soil | MS;ICP;L | See Be ref. 256 | 256 |
| Yb | Soil | MS;IT;S | See Sm ref. 322 | 322 |
| Zn | Soils | AA;F;L | See Cu ref. 276 | 276 |
| Zn | Soils | AA;ETA;L AE;ICP;L | See Cd ref. 261 | 261 |
| Zn | Plant samples | AA;F;L | See Mg ref. 126 | 126 |
| Zn | Soils | AA;F;L | See Cd ref. 264 | 264 |
| Zn | Sweet corn | MS;ICP;L | See Cd ref. 266 | 266 |
| Zn | Soils, plants | AA;F;L | See Cd ref. 269 | 269 |
| Zn | Vegetables | AA;F;L AA;ETA;L | See Cd ref. 270 | 270 |
| Zn | Tree bark | AA;F;L | See Cu ref. 277 | 277 |
| Zn | Soil | AE;ICP;L | See Cu ref. 278 | 278 |
| Various | Soil | MS;ICP;L AE;ICP;L | Samples extracted for 2 h with a 0.01 M CaCl2 solution at a 1∶10 extraction ratio | 159 |
| Various | Soil | AA;F;L AA;ETA;L | Sample digested with HNO3–HClO4. Metals in saturation extracts and 0.43 M HNO3 extracts analysed for Cd, Cu, Pb and Zn | 325 |
| Various | Soil | MS;ICP;L | Flow through microwave digestion device for the determination of Cd, Cr, Mn, Ni and Pb in soil by aqua regia extraction developed | 123 |
| Various | Soil | AA;F;L AE;ICP;L | Samples extracted with boiling aqua regia | 326 |
| Various | Soils | AES;ICP;L AA;ETA;L | Samples digested using a mixture of HClO4–HF | 327 |
| Various | Soils | MS;ICP;L | Samples digested with HF–HNO3 | 328 |
| Various | Soils | XRF;-;S | Trace element enrichments and depletions in soils studied | 329 |
| Various | Contaminated soils | MS;ICP;L | Colloidal fraction from the soil obtained by repeated gravitational sedimentation and extracted with 0.11 M acetic acid, 0.1 M NH2OH·HCl, 0.05 M EDTA or aqua regia | 148 |
| Various | Soils | AA;ETA;S | Results from the SS-GFASS compared with those obtained by Zeeman-GFAAS or FAAS after microwave aqua regia extraction and/or aqua regia/HF digestion; generally good agreement achieved | 330 |
| Various | Soils | AA;F;L | Determination of metals in soils and sediments of the coastal zone of Louisiana described | 331 |
| Various | Soils | AE;ICP;L | Soil extracted with 1 M NH4Cl solution | 332 |
| Various | Soils | AE;ICP;L | Chemical decomposition using microwave acid digestion for the rapid determination of multi-elements proposed | 333 |
| Various | Soils | AE;ICP;L | Samples were with lithium metaborate and dissolved in HNO3 | 334 |
| Various | Soils | AA;ETA;L | Samples extracted with sodium diethyldithio-carbamate into MIBK and Co, Cu, Pb and Ni determined using Zeeman BG correction | 335 |
| Various | Contaminated soils | AA;F;L AA;ETA;L | Column leaching and sorption experiments to assess the mobility of potentially toxic elements in industrially contaminated land described | 336 |
| Various | Soils | AE;ICP;L AA;ETA;L | Three commonly used digestion procedures, hotplate aqua regia, microwave aqua regia, and microwave aqua regia + HF, compared | 127 |
| Various | Soils | MS;ICP;L | High pressure digestion vessels124 fabricated and use compared with screw top PTFE (STT) jars | 124 |
| Various | Soils, sediments | AE;ICP;L | Complete digestion achieved using HF–HCl–HNO3.121 The microwave irradiated closed vessel system used for the determination of aqua regia leachable heavy metals proved to be a viable alternative to the traditional reflux system | 121 |
| Various | Soils | AA;F;L AE;ICP;L | HNO3–HClO4 mixture used for the analysis of trace metals in oil and grease contaminated soils | 118 |
| Various | Soils | MS;ICP,Hy;L | Improved speciation technique described for the identification and quantification of species of 12 elements by HG/LT-GC/ICP-MS. | 337 |
| Various | Soils | AA;F;L | Flow extraction system with on-line acid and off-line FAAS detection developed; extraction performed in a closed extraction chamber where extractants were running through sequentially | 156 |
| Various | Soils | AE;ICP;L AA;ETA;L | Samples extracted with 1 M NH4NO3, according to DIN19730 | 338 |
| Various | Soils | AE;ICP;L | Determination of heavy metals in Arctic soils described | 339 |
| Various | Soils | XRF;-;- | Pseudototal contents of soil samples extracted with aqua regia; extractable contents estimated by extraction with EDTA solution | 340 |
| Various | Soils | XRF;-;- | Procedure for the determination of total concentrations of major and selected trace elements in arable soils from 10 countries around the Baltic sea described | 341 |
| Various | Soils | MS;ICP;L | Metal(loid)organic compounds in contaminated soil determined | 342 |
| Various | Soils | MS;ICP;L | Potential of ICP-sector field-MS for trace element analysis in complex environmental matrices such as soil solutions investigated | 189 |
| Various | Soils | MS;ICP;L | A mixture of 1% m/v EDTA and 1.5% m/v ascorbic acid used as modifier in the ultrasonic slurry sampling ETV-ICP–MS analysis of Cd, Tl, Pb and Zn | 209 |
| Various | Soils | AE;ICP;S AA;ETA;S | Methods for the direct solid sample trace element determination of six heavy metals in soils described. | 178 |
| Various | Soils | MS;ICP;L | Speciation analysis of soil extracts solution for As, Se, Sb and Te performed by on-line coupling of anion exchange HPLC with ICP-MS | 37 |
| Various | Soils | AE;ICP;S | Samples pressed into pellets with a binder and an internal standard; silver and aluminium powders found adequate binders for the pellet preparation | 343 |
| Various | Soils | AE;ICP;L | Mobility of the constituents of chromated copper arsenate in a shallow sandy soil described | 344 |
| Various | Soils | AE;ICP;S | Simultaneous trace analysis of solid soil samples by AES using an arc argon two-jet plasmatron as the source of spectrum excitation described | 345 |
| Various | Soils | AE;ICP;L | New HNO3–H2O2 wet digestion method for total concentrations of elements in soils developed | 346 |
| Various | Soils | MS;ICP;L | Soil analyses by ICP-MS reviewed | 191 |
| Various | Soils | AA;F;L XRF;-;L | Procedure for the determination of Ce, La, Nd, Pr and Y in soils evaluated | 347 |
| Various | Soils | MS;ICP;L MS;-;L | ICP-MS determination of REE, thorium and uranium in soils and CRMs evaluated | 212 |
| Various | Soils | MS;ICP;L AE;ICP;L AA;ETA;L | Complete solubilization of the samples achieved with closed vessel microwave digestion using a mixture of HF–HNO3–HCl | 131,177 |
| Various | Soils | MS;ICP;L | For the determination of lanthanides and some toxic and essential elements, accurate results obtained only after an overnight period with mixture of HF–HNO3 and afterwards stepwise microwave digestion with HF–H3BO3 | 348 |
| Various | Soils | AE;ICP;L MS;ICP;L | Changes in solution concentrations of 60 mineral elements following CaCO3 addition to a moderately acid semi-natural soil reported | 349 |
| Various | Soils | AE;ICP;L AA;F;L | ICP-AES optimized for the determination of six metals in Mehlich III soil extracts | 350 |
| Various | Soils | AE;ICP;L AA;F;L | Samples extracted with 0.5 M HCl | 351 |
| Various | Soils, dust | MS;ICP;L | Attic dust and soil samples analysed for 17 trace elements | 27 |
| Various | Road sediment, soils | AE;ICP;L NAA;-;- | 0.5 M HCl partial leach used for the road deposited sediment and background soils | 352 |
| Various | Dust, soils | AA;CV;G MS;ICP;L | Mercury concentrations were determined using nitric-sulfuric acid digestion and cold vapour AAS; concentrations of 31 other elements determined after HNO3–HF digestion | 353 |
| Various | Road sediments | MS;ICP;S | Road sediment surfaces ablated, followed by multi-elemental analysis by ICP-MS | 354 |
| Various | Soils | AA;F;L | Samples digested with a mixture of nitric-perchloric acids | 355 |
| Various | Soil, sediments, plants | AE;ICP;L | Samples mixed with 4 ml HNO3–HClO4 (4∶1) and 0.2–2 ml 40% HF for microwave digestion; digest diluted with water to a known volume | 356 |
| Various | Soil, sorghum | AA;F;L XRF;-;- | EDXRF, AAS and ASV methods compared for the evaluation of heavy metals in soil and sorghum | 357 |
| Various | Soil, wheat | AA;F;L NAA;-;- | Samples extracted with EDTA and DTPA | 358 |
| Various | Soils, plants | MS;ICP;L | Procedure used for determination of 37 trace elements in soils and plants described | 359 |
| Various | Soil, plants | XRF;-;S | Metal concentrations in soils and plants were analysed in a stochastic manner | 360 |
| Various | Plants, soils | AA;ETA;L | Conventional extraction and microwave mineralization techniques applied | 361 |
| Various | Soil, mushroom | AA;F;L AE;F;L | Cd, Cs, Hg, Ni, Pb and Se taken up by cultivated mushroom from soil assessed | 362 |
| Various | Plants, soils | MS;ICP;L | Concentrations of REE, Th and U determined | 363 |
| Various | Compost | AA;F;L | Three-stage sequential extraction procedure recommended by BCR applied to compost | 160 |
| Various | Plant materials | AE;-;S | NIST standard reference materials dried, powdered using a ball-mill, and applied to double-sided tape on a glass slide for analysis by plasma spectometry | 364 |
| Various | Plant leaves | MS;ICP;L | Dry leaf homogenates placed in 7 ml teflon vessels with HNO3 (1 ml), and microwave digested | 296 |
| Various | Vegetables | AE;ICP;L | Three digestion procedures: high pressure microwave digestion, conventional wet digestion, and dry ashing applied for sample preparation | 128 |
| Various | Plants | AA;ETA;L | An off-line HPLC-GF-AAS method using size exclusion chromatography (SEC) column developed to investigate heavy metal ions in xylem sap samples of cucumber plants | 365 |
| Various | Plant samples | AA;ETA;L | Application of a fast program combined with advantages of the iridium permanent modifier proposed for trace element analysis by ETAAS | 366 |
| Various | Plants | AE;ICP;L | Analyses performed after chemical mineralisation of samples | 367 |
| Various. | Plant materials | PIGE;-;- | Plant materials dry ashed at 550 °C and analysed for Al, Mg, Mn, Na and P using PIGE | 221 |
| Various | Moss | AE;ICP;L MS;ICP;L | Regional distribution of 16 metals in terrestrial moss reported | 368 |
| Various | Mushrooms | AE;ICP;L MS;ICP;L | Dried samples wet digested with conc. HNO3 in closed PTFE vessels using a microwave oven | 369 |
| Various | Moss | AA;F;L; AF;F;L | Comparison made between two moss species collected from 75 sites | 17 |
| Various | Mushrooms | AA;F;L | Concentrations of 8 trace elements determined in seven species of edible mushrooms | 370 |
| Various | Leaf extract | AA;F;L | Ca, Fe, K, Na andP determined | 371 |
| Various | Soils | XRF;-;- AE;ICP;L | Soil formation under two moss species in sandy materials investigated | 372 |
| Various | Plant, cereal materials | AA;ETA;S | Graphite furnace of the boat-in-tube type used for ETV and electrostatic precipitator used for determining analyte transport efficiencies and dependencies on plant and cereal matrices and on carrier elements | 173 |
| Various | Pollen, bee tissue and honey | XRF;-S | Dried pollen and bee tissues pelletized for TXRF; honey samples analysed directly; samples digested and concentrated for EDXFR | 236 |
| Various | Vegetables | MS;ICP;L AE;ICP;L | Samples digested with HNO3 and HF in Teflon beaker on a hot plate; decomposed samples dissolved in a 1M HNO3 solution containing internal standard elements; 40 elements determined | 373 |
| Various | Green tea leaves | MS;ICP;L AE;ICP;L | See ref. 373 | 147 |
| Various | Soil | MS;L;- | Laser mass spectrometer developed for rapid qualitative and quantitative elemental and isotopic analyses of soil samples for ecological screening and mapping of heavy metal pollution | 374 |
| Various | Marine algae | AA;F;L NAA;-;- | Concentrations of 9 trace metals determined | 375 |
| Various | NIST peach leaves | AE;ICP;L | Three microwave ovens and 2 teflon vessels evaluated for their ability to digest batches of 6 or 12 plant samples and to compare their analyses with those from conventional block-heater digestions | 129 |
| Various | Pine needles | AE;ICP;L MS;ICP;L | Microwave digestion procedures using HNO3, HNO3– H2O2, HNO3– HClO4, HF mixtures and dry ashing + HF investigated for the determination of 14 metals | 120 |
| Various | Plant sprouts | AA;F;L | Bio-collector sprouts leached with 1% HNO3 under ultrasonic effect and the leachate obtained analysed | 115 |
| Various | Plant tissue | AA;F;L AA;ETA;L | Powdered plant samples slurried in the solubilization medium and subjected to high intensity ultrasonication by a probe ultrasonic processor (20 kHz, 100 W); metal solubilization accomplished within 3 min using a 30% vibrational amplitude and 0.1 M EDTA at pH 10 | 111 |
| Various | Apple leaves | -;-;L | Sample preparation investigated using infra-red radiation generated by tungsten lamps for fast heating of sample in a glass flask; determination of Cu, Fe, Mn and Zn described | 113 |
| Various | Leaves | AE;ICP;L | Element transference characteristics and element speciation in the extract of leaves studied using C18 bonded silica gel column separation and microwave digestion/extraction for sample treatment | 376 |
| Various | Spruce needles | AE;ICP;L NAA;-;L | Multivariate interpretation of the foliar chemical composition of Norway spruce described | 377 |
| Various | Mushrooms | AE;ICP;L | Samples dried, milled and digested; 17 metals were determined | 378 |
| Various | Soils, plants | AE;ICP;L MS;ICP;L | Soil solutions obtained by high speed centrifugation and ultra-filtration of samples at 60% water-holding capacity | 379 |
| Various | Teas | AA;ETA;L | Ground sample of commercially available leafy material was prepared and three 0.5 g sub-samples were run in parallel; infusions also analysed | 380 |
| Various | Plants | AA;F;L; AE;F;L | A microwave digestion procedure used to prepare the herbal plants | 381 |
| Various | Vegetables | -;-;L | Fast and accurate method for the extraction of Ca, Mg, Mn and Zn from vegetables using ultrasonic energy and dilute acid described | 112 |
| Various | Plant materials | AE;ICP;L | Application of microwave assisted extraction examined; water, EDTA and HCl (0.01, 0.10 and 1.0 M, respectively) used as leaching solutions | 122 |
| Various | Soils | AE;ICP;L NAA;-;L | Samples were extracted with DTPA, 2M HNO3, HCl–HNO3–H2SO4 and HClO4; bio-available B extracted with hot water | 382 |
| Various | Mushrooms | MS;ICP;L AE;ICP;L AA;ETA;L | 11 mineral elements determined | 383 |
| Various | Black tea leaves | AE;ICP;L MS;ICP;L | Multi-element determination of major-to trace elements in tea and tea infusions carried out; about 40 elements in tea leaves and tea infusions were determined over a wide concentration range of 8 orders of magnitude | 384 |
| Various | Rice | AE;ICP;L MS;ICP;L AA;F;L | Vietnamese rice samples analysed for 14 elements | 385 |
| Various | Mosses | AA;F;L | Cd, Cu, Mn, Pb, and Zn extracted with multi acid digestion | 386 |
| Various | Moss | MS;ICP;L AE;ICP;L AA;CV;G | Duplicate samples of the two terrestrial moss species collected from 8 catchments spread over northern Europe analysed for 38 elements | 387 |
| Various | Plant CRMs | MS;ICP;L | Determination of heavy and toxic elements in plants discussed | 388 |
| Various | Leaves | MS;ICP;L | LA-ICP-MS applied to the spatially resolved determination of 9 elements in green leaves of oak trees | 389 |
| Various | Plant samples | MS;ICP;L | Capability of pine needles to be used as bio-indicators of trace metals in the environment discussed | 390 |
| Various | Crops | MS;ICP;L | Concentrations of major and trace elements in organic and conventional crops compared | 391 |
| Various | Mosses | MS;ICP;L | Digestion of samples was performed in PTFE vessels using the mixture of HNO3–H2O2–HF | 392 |
| Various | Moss | MS;ICP;L | NIST archival leaf standards used as matrix matched standards for reliable quantitative elemental analysis of moss samples by LA-ICP-MS | 19 |
| Various | Mushroom | MS;ICP;L | Microwave digestion used | 393 |
| Various | Brown rice | AE;ICP;L MS;ICP;L | Rice samples were digested with HNO3–HClO4 | 180 |
| Various | Tea leaves | AE;ICP;L MS;ICP;L | Systematic errors observed in acid digests of tea leaves evaluated | 174,175 |
| Various | Plant RMs | AE;ICP;L MS;ICP;L | Samples decomposed with HNO3–HF in Teflon beaker on a hot plate; digest dissolved in a 1 M HNO3 solution | 394 |
| Various | Pine needles | MS;ICP;L NAA;-;L | 43 composite samples of several years of needle growth analysed for major and trace elements | 395 |
| Various | Plant materials | PIGE;-;- | Plant materials dry ashed at 550 °C; analysis performed with an external beam of 3 MeV protons incident on the target | 221 |
| Various | Plant ash | AE;-;- | Determination of micro- and macro-elements using an arc argon two-jet plasmatron as the source of spectrum excitation developed | 396 |
| Various | Otoliths, plankton | PIXE;-;- | Otoliths cleaned, sectioned and ground to the core prior to analysis using a thick absorber (Mylar plus Al); phytoplankton cultured using low, medium and high levels of nutrient; culture liquor freeze-dried onto foil and kept in a dessicator until analysis | 219 |
| Various | Trees | AA;F;L | Be, Cd, Cu, Mn, and Zn determined in leaves from an area with large coal-fired plants | 397 |
| Various | Environmental samples | MS;ICP;L NAA;-;- | Advantages and draw backs of INAA and ICP-MS for soil, sediment, plant and water pollution studies discussed | 398 |
| Various | Environmental samples | AA;F;L | A FI on-line co-precipitation system with DDTC nickel(II) as a carrier coupled to FAAS for the determination of trace Cu, Cd, Fe and Pb | 399 |
| Various | Environmental samples | MS;ICP;L | On-line solid phase extraction method developed for determination of actinide elements in environmental samples using a column containing TRU-Spec(TM) resin coupled with sector-field ICP-MS | 400 |
| Various | Environmental samples | MS;ICP;L | Suitability of IC-ICP-MS for simultaneous separation and on-line detection of 8 light fission products studied | 200 |
| Various | Environmental RMs | MS;ICP;L | Samples digested with HNO3–H2O2–HF using closed-vessel microwave digestion | 401 |
| Various | Road dust samples | MS;ICP;L | Samples dissolved with aqua regia in a high pressure asher; interfering elements eliminated by chromatographic separation using an anion-exchange resin | 207 |
| Various | Soils | AA;F;L | The effects of the application of sewage sludge and petrochemical residue in maize culture as source of micro-nutrients on soils evaluated; samples digested with HNO3–HClO4 | 402 |
| Various | Sewage sludge | AA;ETA;L | Slurry technique applied for Cd, Cr, Ni and Pb in sewage sludge by ETAAS; suspensions prepared in 0.5 and 5.0% (v/v) HNO3 and 0.5 and 5.0 HNO3 with 0.5% (m/v) glycerol introduced directly into furnace | 403 |
4 Analysis of geological materials
4.1 Reference materials
Reference materials (RMs), whether certified or not, are the corner stone of geoanalytical science. Depending on the practices in any particular laboratory, they are used for method validation, calibration, establishing measurement traceability and assigning values to in-house reference materials and quality control samples. Every geoanalyst is therefore encouraged to read Kane's tutorial review on the use of reference materials.404 It contains pertinent remarks about the correct use of RMs, particularly in terms of their fitness for purpose, homogeneity and their use in calibration. It highlights problems such as the paucity of suitable RMs with sufficiently well-defined reference values for many important analytes, and the lack of standard methods for geoanalysis generally. She also discusses the quandary facing geoanalysts that flows from the lack of constancy of reference values throughout the history of many RMs.New analytical data and new compilations of “recommended” values for RMs are published regularly. Rocholl and co-workers405 give new concentration data for 24 lithophile trace elements in NIST certified reference material glasses SRMs 610 and 611, in support of their use in microanalytical techniques. The individual wafers were deemed to be homogeneous and representative of the entire batch of the SRM 610 and 611 glasses, with the possible exception of the alkali metals and a few volatile or non-lithophile trace elements. On the basis of their new data and other recently published data, the authors proposed “preferred average” values for the elements studied; these were, within a few percent, identical to those proposed by other workers. Wieser and DeLaeter406 measured Mo concentrations in eleven USGS geochemical RMs by isotope dilution (ID) TIMS. In every case except one, the values determined were significantly lower than the current consensus values. Their lower values probably reflect the absence of contamination in ID-TIMS compared to other analytical methods. Isotope dilution TIMS and multi-ion counting spark source mass spectrometry were used to compare the elemental composition of five new RMs issued by the US Geological Survey (USGS) with five original USGS RMs, including K, Rb, Sr, Ba and the REEs.407 Dulski408 reported the abundances of 24 trace elements, including the REEs, in 86 geochemical RMs and proficiency testing samples to demonstrate the reliability of his routine ICP-MS procedures, as well as provide new data for some poorly characterised RMs.
With the volume of new data on RMs being published each year, there is a clear need for the geochemical reference sample bibliography for 1999 compiled by Roelandts.409
There has been much activity in the production of new reference materials. Given the current interest in the determination of the PGEs in road dust, the European Union has identified the need for a road dust RM certified for its Pt, Pd and Rh content.410 The first part of the project consisted of an interlaboratory study to test the feasibility of preparing such a RM and to evaluate and minimise most of the pitfalls observed in PGE measurements. The main results of this interlaboratory study reflected the state-of-the-art for the determination of these elements and were encouraging enough to prompt the decision to proceed with the certification campaign. The Chinese Institute of Geophysical and Geochemical Exploration have produced four new high-grade gold ore reference materials, GAu 19–22, to complement their other gold RMs.411 A unique opportunity for the preparation of a new RM was afforded by the collapse of a cliff section at Stevns Klint in Denmark, which resulted in the collection of about 50 kg of Fish Clay that presents the Cretaceous–Tertiary boundary layer.412,413 Preliminary analytical data support the development of this material as a RM, especially for the determination of Ir and other PGEs.
4.2 Sample treatment
4.2.1.1 Laser ablation. It is evident that laser ablation ICP-MS has become a well-established technique for both elemental and isotopic analysis of geological and similar materials. The reader is directed to an authoritative review by Gunther and co-workers192 of recent trends and developments in the use of laser ablation coupled to ICP-MS. The move towards shorter wavelengths, i.e. from 1064 to 157 nm, has been made possible by the availability of high quality optical materials, and has led to the incorporation of UV gas lasers such as eximer lasers into analytical systems. There is now considerable flexibility in the laser wavelength, output energy, repetition rate and spatial resolution available. However, the ablation process will vary with the solid substrate and the authors concluded that no one laser wavelength was suitable for all types of solid samples.
The technique has progressed to such an extent that a procedure for the automated determination of trace elements in silicate materials by LA-ICP-MS, akin to solution analysis using an autosampler, has been published.414 Each measurement at a defined point included a 60 s pre-ablation delay, a 60 s ablation and a 90 s flush delay. Each analytical cycle consisted of four standards, one reference material for quality control and 15 samples, and took approximately 70 min to complete. Either of the NIST reference glasses 610 or 613 was used as an external calibration standard and Ca used as an internal standard to correct for drift, differences in transport efficiency and sampling yield.
Although laser ablation is employed in bulk analysis, its main strength lies in applications requiring spatially resolved analysis, depth profiling or surface mapping. Quantification can be particularly tricky when naturally heterogeneous samples are tackled. For this reason, LA-ICP-MS is often employed in conjunction with electron probe microanalysis (EPMA), as the latter technique can provide independent major element concentrations at virtually the same location; one or more of these elements can then be used as internal standards during laser ablation. This approach was used in the determination of major and trace element compositions of natural glasses415 and volcanic glass shards,416 trace element partitioning between biotite and muscovite417 and the hydrothermal alteration of monazite.418
There is much interest in the distribution of PGEs both in mineral grains as an indicator of processes involved in their formation, and on a larger scale as a consequence of their use in catalytic converters in cars. LA-ICP-MS was used to characterise sulfides, silicates and chromites for PGEs, Re and Au, using synthetic pyrrhotite standards annealed with known quantities of noble metals, to understand noble metal enrichment processes within the Merensky Reef.419 The distribution of siderophile elements, including the PGEs, in zoned metal grains of a metal-rich chondrite was determined by LA-ICP-MS with a spatial resolution of about 30 µm, to ascertain its mode of formation.420 On a different scale, LA-ICP-MS has been employed to characterise road dusts for PGEs and other trace elements.306,354 Rauch and co-workers354 inferred that the PGEs, through their association with Ce, remained bound to autocatalyst particles in road sediments. Motelica-Heino et al.306 were able to determine Pd, Pt and Rh in road sediments at sub µg g−1 levels with a relative standard deviation of 10% and estimated detection limits in the lower ng g−1 range. They used uncontaminated road sediments spiked with PGEs in both solid and liquid form, to assess the analytical performance of the technique and as calibration standards. They obtained good agreement between LA-ICP-MS and solution high resolution ICP-MS for Pt and Rh, but the determination of Pd was still subject to interferences.
The chemical composition of fluid inclusions may allow the detailed reconstruction of the fluid evolution associated with hydrothermal ore-forming systems.421 Laser ablation is a particularly elegant method of sampling individual fluid inclusions, especially where several generations of inclusion may co-exist. Recent studies include several centred round hydrothermal ore deposits in New South Wales, Australia.422–424 Various calibration strategies applicable to the analysis of fluid inclusions have been devised over the years and several new methods of producing synthetic inclusions have been reported recently. BoueBigne and colleagues425 employed aqueous standards whose absorption coefficients were modified by the addition of a chromophore to produce the desired ablation yield. Dubessy and co-workers426 prepared synthetic fluid inclusions to study a H2O–CH4–NaCl system in fluorite and quartz. A Nd-YAG laser was focussed through a Cassegrain objective to form ablation cavities of at least 10 µm diameter inside the crystals. Experimental fluids were allowed to migrate into these cavities via microcracks over a four-week period at elevated temperatures. The ablation cavities then acted as large synthetic inclusions and the microcracks as smaller ones. Schafer et al.427 produced synthetic fluid inclusions in glass by equilibrating a granitic melt with included vesicles containing an aqueous chloride fluid phase at 850 °C and 2 kbar. They reported that rapid isobaric quenching of the system preserved the host phase as an unfractured granitic glass, which typically contains more than a hundred individual two-phase fluid inclusions.
Fundamental studies on the processes taking place during laser ablation of synthetic glassy materials, both vitreous and crystallised, at 266 and 1064 nm were conducted by Motelica-Heino and colleagues.428 They collected the products of ablation on filters and examined, with an SEM fitted with an X-ray energy dispersive spectrometer detector for chemical analysis, both this material and the craters formed. They concluded that quantitative analysis of simple glassy materials like minerals or glasses could be achieved using external calibration without a matrix-matched standard, provided an internal standard that is not prone to fractionation, e.g. a refractory element, is used. However, enhancement or depletion in concentrations of volatile analytes are still likely to occur even at 266 nm. A similar study using a frequency-quadrupled Nd:YAG laser to sample the silicate minerals acmite, albite, augite, diopside, forsterite and labradorite and deposit them as films on graphite substrates has been reported.429 These minerals could be easily distinguished by their film compositions despite the fractionation effects observed, making it possible that laser ablation could be employed to sample such materials in remote terrestrial and extraterrestrial locations.
Many more geochemists now have access to high precision isotope ratios and zircon U-Pb ages, at relatively low cost and with minimal sample preparation, through the use of laser ablation sampling coupled to magnetic sector ICP-MS, particularly multicollector (MC) instruments.430–435 As a consequence, geochemists are seeking to apply the technique to a wider range of applications than hitherto. Griffin and co-workers436 determined the Hf isotopic composition of 124 mantle-derived zircon megacrysts, ranging in age from 90 to 2500 Ma, as a means of measuring indirectly the concentration of Hf in the mantle over a long interval of time. Hirata437 used LA-MC-ICP-MS to determine Zr isotope ratios and U-Pb ages of terrestrial and extraterrestrial Zr-bearing minerals. The combination of these data permitted him to make a more accurate estimate of the initial abundance of 92Nb∶93Nb at the formation of the solar system.
Stable isotope compositions of diagenetic minerals can provide valuable information on their source and mechanism of formation. Laser-based stable isotope methods offer several advantages for these types of minerals, which may only be available in situ in small quantities.438,439 McConville and colleagues440 studied the S isotope content of diagenetic pyrite using LA and an ion microprobe, as well as bulk analysis. Laser sampling at the scale of 100–500 µm seemed to be adequate to characterise the S isotope variations in this material.
4.2.1.2 Slurry sampling. There are very few developments in the analysis of geological materials as slurries to report, and it is evident that this mode of sample introduction is most favoured coupled with ETV-AAS.243,244 The inherent difficulties in achieving total recoveries of Cr when dissolving geological materials makes it a suitable element for quantification using slurry sampling. Hou and Chang441 demonstrated that Cr could be determined by slurry sampling and probe atomisation in graphite furnace AAS, using aqueous calibration standards, with RSDs of 3.0–6.5% and a detection limit of 5.1 pg (10−12).
Solutions containing HF must be either evaporated prior to analysis or quenched using boric acid. Traditional evaporation methods may pose recovery problems, as some elements may be lost as volatile chloride or fluoride species. Link and Kingston130 evaluated the use of a newly developed reduced pressure microwave-assisted evaporation apparatus to minimise the loss of several volatile analytes known to be vulnerable to volatilisation during evaporation on a hot plate.
Alkaline fusions are still favoured for some applications, although not employed generally because of the increased total dissolved salt content of the final solution. Tourmaline is a highly refractory mineral with a high B content but can be broken down effectively by fusion with a mixture of sodium carbonate and zinc oxide prior to determination of B by ICP-AES.443 Alternatively, AAS can be employed to analyse dissolutions of siliceous materials prepared from alkaline fusions.116,444
For many types of sediment, an important consideration may be the grain size fraction to be analysed in relation to the chemical information sought. Sutherland445 compared the results obtained from 121 stream sediment samples that were split into two grain-size fractions, less than 63 µm and 63–125 µm, acid digested and analysed by ICP-AES and FAAS for Al, Ba, Cu, Fe, Mn, Ni, Pb, Ti and Zn. The data indicated statistically significant differences between the two fractions for all elements except Mn, but the environmental interpretations obtained were essentially equivalent. However, in the case of fine-grained material originating from a former uranium mine, it proved important to separate the material into different particle sizes because a correlation was found between particle size and the concentration of elements such as Cu, Fe, Mn and Zn; high amounts of U were sorbed on the particle surfaces.446
Tsimbalist and colleagues447 proposed a series of sample preparation techniques for the determination of Au, Ag and PGEs in different types of geochemical sample, such as chromites, molybdenites and ultrabasic ores. The methods studied included acid digestion, fusion with sodium peroxide, cold sintering with an oxidising mixture of sodium peroxide and sodium carbonate, and also oxidising fluorination with bromine trifluoride. Their use of a high-energy centrifugal epicyclic mill to reduce the particle size, from 3–5 mm to 0.2–5 µm in 5 to 10 min, accelerated sample dissolution by mineral acids as well as reducing the sampling uncertainty. The PGEs contents were determined by AAS after extraction and preconcentration in an organic phase.
Various strategies for separating and preconcentrating the noble metals have been reported. Anion exchange resins have been used to improve the recovery of trace amounts of Au, Pd and Pt from large amounts of associated base metals.452 Dilute thiourea was used as the eluant to quantitatively recover as little as 1 µg of the target elements from about 10 mg of base metals. Activated carbon was used to separate Ag, Au and Pd from aqua regia digests of geological samples.453 The novel feature of the method was that the analytes were recovered from the activated carbon by oxidising and dissolving it in concentrated nitric and perchloric acids. A new silica gel based chelating agent with thiourea as a functional group has been employed for on-line preconcentration and separation of trace levels of Ag, Au, Pd and Pt.454,455 In the method to determine Ag, Au and Pd together, the selected metal ions were adsorbed on a column packed with the modified silica gel at a sampling flow rate of 5.0 ml min−1, eluted with 5% thiourea at 2.5 ml min−1 and determined by FAAS.454 More widely recognised procedures for determining gold in rocks by ETV-AAS after aqua regia digest and extraction into IBMK456 and by fire assay methods457,458 are still employed and should not be discounted.
To avoid interferences, including matrix suppression, from calcium when determining Th and U in apatite minerals by ICP-AES, Fujino and co-workers459 treated the mineral with hot concentrated nitric acid followed by solvent extraction. The extraction reagent was 1-phenyl-3-methyl-4-trifluoroacetyl-5-pyrazolone and diisobutyl ketone was selected as the organic solvent. After quantitative extraction of Th and U above pH 2, the organic phase was injected directly into the ICP. An alternative approach, applicable to Ce and La as well as Th and U, involved the use of o-vanillinsemicarbazone on a polymer support prior to determination by ICP-AES or ETV-AAS.460
Isotopic analysis by TIMS requires efficient chemical separation of the element of interest. This is particularly true for NdO+ measurements where isobaric interferences must be minimised. Griselin461 devised a new HPLC procedure to separate Nd from other light REEs using Aminex (Bio-Rad C) resin and a CH3OH–Hac–HNO3 eluent. Deniel and Pin462 reported a new scheme for the simultaneous separation of Pb and Sr from silicate rocks for isotopic measurements, using the selectivity of the chromatographic material referred to as Sr.Spec. The column volume of only 150 µl required small quantities of nitric and hydrochloric acids, which were easy to purify by sub-boiling distillation, resulting in satisfactory blank levels, high Pb yields and good purity. Le Fevre and Pin463 explored the use of a solid-phase extraction material, commercially known as U-TEVA.Spec, to isolate Hf and Zr in a single separation step, prior to determination by multiple collector ICP-MS.
Highly sensitive and selective techniques are required to determine organotin species. Solid-phase microextraction gas chromatography (SPME-GC) is currently finding much favour, because of the high preconcentration factors it offers, attached to element-specific detection systems. The performance of four specific detection systems, namely flame photometry, pulsed flame photometry, MIP-AES and ICP-MS, were evaluated by Aguerre and co-workers for this specific purpose.466 As expected, ICP-MS was the most sensitive but required the construction of a dedicated transfer line. Pulsed flame photometry was considered to be the best choice for routine use because of its low cost combined with good sensitivity and selectivity. Other systems described for Sn speciation employing solid phase extraction include: SPME-GC glow discharge-optical emission detection,145 headspace SPME GC-MS,467 SPME-GC with flame ionisation detection468 and solid phase extraction-capillary GC-MS.469
In a notable development, Wu and colleagues470 coupled automated in-tube SPME and HPLC to a quadrupole mass spectrometer, using electrospray as an ionisation source. They evaluated the performance of their system by measuring the content of tributyltin in a marine sediment CRM.
Alternative methods of determining organotin compounds in sediments published since the last Update include: capillary GC coupled to ICP-MS after solvent extraction and ethylation;471 coupling of HPLC with ETV-AAS by means of a hydride generation in situ trapping system;170 HPLC and hydride generation ICP-AES;472 GC coupled to a microwave-induced helium plasma atomic emission detector;473 and HY-GC-ETV-quartz furnace AAS.474
Atomic fluorescence spectrometry (AFS) can be employed to speciate a number of environmentally important elements. The most obvious candidate is Hg. Cai and co-workers475 determined both methylmercury and ethylmercury in sediment samples using GC-AFS following aqueous phenylation with sodium tetraphenylborate; the merits of using phenylation with sodium tetraphenylborate over ethylation with sodium tetraethylborate were discussed. In another approach, methylmercury was leached from sediments using a microwave-assisted alkaline digestion with methanolic potassium hydroxide, before extraction with dichloromethane in HCl and back-extraction into high purity water.186 The sediment extracts were then injected into a HPLC system with UV post column oxidation before quantification by AFS. A recent review on the analysis of Hg species by HPLC covers articles published from 1986 to 1999.476
All too often, scant regard is paid to the preservation of elemental species during sampling and preparation prior to analysis. The reader’s attention is drawn to an interesting paper on the transformations which may occur between Cr(VI) and Cr(III) during the analysis of solid samples using isotope dilution mass spectrometry.477 The authors developed a method capable of monitoring and correcting for species transformations in both directions during the determination of Cr(VI). A study of changes in concentrations of methylmercury during storage emphasised the need for its prompt analysis following extraction, but found that the storage temperature was not a significant factor.478
Various difficulties are inherent in the quantification of Se in sediments by ICP-MS. Not only do most of the important Se isotopes suffer from isobaric and polyatomic interferences, but it has a relatively high first ionisation potential and the abundance distribution between the six isotopes results in poor sensitivity compared to most other elements. Moor and Kobler481 employed a double loop FI-HG system with a short reaction time of 100 ms to increase the sensitivity, coupled to a quadrupole ICP-MS instrument. The high boron load and the necessary prereduction of Se(VI) were clear disadvantages, so they also examined the direct determination of Se using sector field ICP-MS. Although promising results were obtained using the 78Se and 82Se isotopes, the uncertainty was larger than that obtained by HG.
4.3 Instrumental analysis
A review targeted at a specific field of analysis is always welcome. Stafilov483 has compiled such a review for the determination of trace elements in minerals by ETV-AAS. The same research group has published methods based on ETV-AAS for the quantification of Co, Cu, Pb and Ni in gypsum335 and Tl in some sulfide minerals.484
Arambarri and colleagues485 sought to improve the determination of Sn in aqua regia-HF digests of sediments by ETV-AAS with palladium as the chemical modifier. They estimated the influence of various parameters and optimised the significant ones, i.e. pyrolysis temperature, atomisation temperature and concentration of the modifier, and achieved a detection limit of 48 µg l−1. Palladium was also used as the chemical modifier in the determination of In and Te in geological RMs by solvent extraction and ETV-AAS486 but large amounts of Bi, Cu, Pb and Sn still suppressed the signal. An unusual chemical modifier, lithium tetraborate, was used to quantify the Cd content of a river sediment.487
The element most commonly determined by AFS is mercury and its organometallic species. The reader is referred to sections 3.2.3 and 4.2.4 of this Update, which both contain pertinent information on this subject.
ICP-AES is used routinely in the multi-elemental analysis of geochemical samples for geochemical exploration, pollution studies and the like, either after a partial leach with aqua regia491 or total digestion with an HF-based acid mixture.333 The technique is also regularly employed for the determination of REE in silicate rocks.492–494 Separation of the REE can now be achieved on-line493 and interference effects from matrix elements have been reassessed.492
A procedure has been developed for the determination of trace amounts of Mo in geological samples by ICP-AES, based on the complexation of Mo(VI) ions by calmagite and its sorption onto activated carbon.495 After heating the activated carbon with concentrated nitric acid at 120 °C and treating the residue with 20% (v/v) nitric acid, an enrichment factor of 100 was achieved. Solid phase extraction of the Mo(V) ion as a thiocyanate complex on polyurethane foam has been used to separate and preconcentrate Mo from iron-rich matrices, prior to quantification by ICP-AES.496
ICP-MS has become the preferred technique for the determination of REE in most geological samples, particularly as part of a wider suite of elements acquired for petrogenetic studies. However, for certain mantle-derived materials containing low natural concentrations of REE, i.e. generally less than 1 ng g−1, the detection limits normally obtained by ICP-MS may not be adequate. Jain and co-workers499 looked at two alternative instrumental strategies to improve the REE detection limits without resorting to separation and preconcentration. Two USGS RMs, DTS-1 and PCC-1, containing low abundances of the REE, were analysed using both an ultrasonic nebuliser coupled to a quadrupole ICP-MS instrument and a sector field ICP-MS instrument with a microconcentric desolvating nebuliser. The data obtained from the two techniques agreed to better than ±5% and formed smooth, coherent chondrite-normalised REE patterns. Although improved precision was obtained using the sector field instrument because of its inherent lower background intensities, greater stability and slightly better sensitivity, both methods were generally precise to better than ±5% at sub-µg g−1 levels.
Geoanalysts still need to be aware of potential interferences arising from polyatomic ions, which can lead to inaccuracies. In a noteworthy paper, Aries and colleagues500 propose a method to systematically correct for oxide and hydroxide interferences, with reference to the REE and first row transition elements. The corrections are based on the calculation of the oxide and hydroxide ratio for a specific element from the raw data. This is then used to calculate the oxide and hydroxide interference contributions of all other interfering elements by reference to a set of oxide and hydroxide ratios measured on standard solutions under constant plasma operating conditions.
Studies of the platinum group elements (PGE) have benefited greatly from the relative ease of access and sensitivity of detection that ICP-MS affords. Rao and Reddi501 in a overview of the occurrence of the PGE, their use and recent trends in their determination, emphasise the leading role currently assumed by ICP-MS. Kollensperger and colleagues502 investigated the capabilities and limitations of sector field ICP-MS for the quantification of Pd, Pt and Rh in road dust. Sample preparation involved microwave-assisted HF-based mixed acid digestion and the samples were introduced into the ICP via an ultrasonic nebuliser incorporating a membrane desolvation unit. Reliable results were obtained by utilising high mass resolution and eliminating significant oxide levels by membrane desolvation. However, not all interferences could be separated even at high mass resolution and these had to be evaluated carefully. Limits of detection were 0.5, 0.4 and 0.1 ng g−1 for Pd, Pt and Rh, respectively.
A novel approach has been developed in the determination of Pd by ICP-MS for the on-line removal of potential interferents, such as yttrium and copper, which cannot be resolved using high resolution ICP-MS.503 A strong cation exchanger, 2-(4-chlorosulfonylphenyl)ethyltrichlorosilane, was covalently bound to a silica capillary directly coupled to a microconcentric nebuliser or a direct injection nebuliser. The modified surface of the capillary had the ability to remove Y and Cu during the measurement of 105Pd and was easily flushed by several injections of 0.01 M HCl.
Isotope dilution mass spectrometry is considered to be a definitive method of analysis because the chemical manipulations are performed on a direct mass basis and the spectrometric determinations involve only isotope mass ratio measurements. Pin and colleagues504 have reviewed the advantages of combining isotope dilution with ICP-MS, rather than TIMS, which allows the ID method to be used more routinely. ID-ICP-MS is particularly suitable in the determination of Os to overcome possible loss of volatile OsO4 during sample preparation and analysis.448,505,506 An interesting application of ID coupled to high resolution ICP-MS was the determination of 241Am in sediments.507 After isolation from major elements by selective precipitations, Am was separated from other transuranic elements and purified by anion exchange and extraction chromatography, prior to the mass spectrometric measurements.
The analytical technique that has attracted most attention recently in the earth sciences is probably multiple collector ICP-MS. An extensive review with 53 references covering instrumentation, measurement techniques and analytical capabilities is therefore very timely.508 When these instruments were first built, the immediate goal was the precise determination of isotope ratios of elements that were difficult to determine by TIMS because of their high ionisation potentials. Over the last few years MC-ICP-MS has been undergoing a rapid evolution and this review is an ideal vehicle to appreciate the relevance of technique to present and future research in the earth sciences. Prior to the advent of MC-ICP-MS, routine analysis of the Lu-Hf isotope system developed slowly because of the difficulty of measuring Hf isotope ratios by TIMS. Anyone interested in the Lu-Hf isotope geochemistry of silicate rocks should read Blichert-Toft's509 account of the development of suitable analytical techniques and the current uncertainties surrounding this system. Useful studies on Pb isotope measurements by MC-ICP-MS have been reported.204,205
A number of improved methods for isotopic measurements in geological materials by TIMS have been published. Deyhle512 improved the precision and accuracy of B isotope measurements by positive TIMS using static multicollection of Cs2BO2 ions. Similarly, the conversion of chlorine to CsCl prior to the detection of Cs2Cl+ ions with an array of Faraday cup collectors in static mode improved the precision of 37Cl∶35Cl ratios.210 Modifications to an existing method for the determination of Cl isotopes in fluid inclusions allowed real differences between samples to be measured with greater certainty.513 A neat approach to reduce 17O and 18O related isobaric interferences when determining isotope ratios of the light REE by TIMS has been developed.211 This involved the introduction of 16O-enriched oxygen into the ion source chamber via a specially designed gas inlet system and enabled isotope ratios of La, Ce and Nd to be measured without isobaric interference corrections.
Accelerator mass spectrometry (AMS) is regularly used for radiocarbon dating of sediment sequences. The steady evolution of both the technique and hardware of 14C AMS has resulted in substantial improvements in precision, throughput and background over the last few years.514 Sediments in prehistoric caves and flints have been dated by developing a method to extract 10Be and 26Al atoms from their quartz content, and monitoring the production rates of these isotopes by cosmic rays at the Earth's surface.515 Published procedures for processing samples for the determination of 10Be, 26Al and 36Cl have been adapted and improved where necessary for earth science studies.516 Developments in AMS have enabled Pb and S isotopes to be measured with a precision of better than 1 per mil.517 The aim of this research was to provide in situ microanalysis of geological samples for radiogenic and stable isotope data free from molecular and isobaric interferences. AMS is now capable of determining very low concentrations of the actinide nuclides, and has been applied to the measurement of 236U in soils and sediment RMs, intertidal sediment cores, minerals and U standards.217,518,519
For a wider review of developments in mass spectrometric techniques, the reader is referred to the recent JAAS Update on atomic mass spectrometry.520
A range of X-ray analytical techniques is often employed to fully characterize geological materials. In a study of cobalt-rich oceanic crusts, XRF was used to provide the bulk chemical analysis and XRD to identify the minerals present.523 It is hoped that a combined XRF/XRD instrument, presently under development, will be able to carry out in situ investigations to provide definitive evidence as to whether ice and hydrous minerals exist just below the surface of the Moon.524 A combination of microanalytical techniques, including XRD, EPMA and synchrotron-based micro-XRF, was used to investigate the spatial distribution of Pu sorbed on geological materials.525
Synchrotron X-ray fluorescence (SXRF) has been used to map both major and trace element distributions in fluid inclusions.526–528 Phedorin and his many collaborators529,530 sought to identify the most suitable analytical technique for the elemental analysis of sedimentary cores from Lake Baikal and an organic-rich rock formation. They found that synchrotron XRF was superior to INAA, ICP-MS, AAS and WD-XRF in this application because of its speed, cost, non-destructive nature of the measurements and sensitivity, combined with the small sample size required. The low backgrounds permitted quantification of elements such as Br, Cd, I and Te, which are difficult to determine by other techniques.
Emeralds have been characterized by particle-induced X-ray emission (PIXE) to provide criteria for discriminating between natural and synthetic emeralds531 and to deduce the source of natural emeralds from an established database.532 Because PIXE can provide elemental maps of sample material in a non-destructive fashion, it has been used to analyse samples from geological and archaeological sites533,534 and to map the Au content of arsenopyrite and pyrite minerals, as a means of quantifying the invisible gold in ore and mineral concentrates.535
For a wider review of developments in X-ray techniques, the reader is referred to the recent JAAS Update on X-ray fluorescence spectrometry.536
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