In this work, several contributing factors to the observed mass bias in inductively coupled plasma mass spectrometry (ICP-MS) have been identified. Analyses of the isotopic compositions of B deposited on sampler and skimmer cones demonstrate enrichment of [1][0]B on the former and [1][1]B on the latter. Grounding the capacitive discharge system to enhance sensitivity also magnified the level of [1][1]B enrichment on the skimmer cone more than four-fold. This supersonic expansion of the ion beam behind the sampler is confirmed to be an important source of mass bias. Isotopic analyses of the Fe, Zn and Ti leached from used extraction lenses yielded a linear relationship between the levels of lighter isotope depletion and mass ratio. Although consistent with the space-charge effect, the fact that isotopically-heavy deposits were found demonstrates that the ion beam diverges into a relatively wide solid angle in the field-free region behind the skimmer. This severely impairs transmission of, in particular, the lighter isotopes. For a wide range of elements (Li, B, Fe, Ni, Cu, Sb, Ce, Hf and Re), the magnitude of the mass bias was found to be affected by the sample gas flow rate, as well as the distance between the sampler and the end of the torch, i.e., the sampling depth, employed in the Neptune multi-collector ICP-MS instrument. Mathematical analysis of the profiles of intensity variations as a function of these instrumental parameters revealed that the response peaks closer to the torch for the heavier isotopes of all studied elements. Owing to this spatial non-coincidence, tuning for maximum intensity on either isotope will result in sampling from a region where even slight plasma instabilities will be translated into substantial variations in mass bias. Therefore, in-plasma processes also contribute to the degree and temporal stability of mass bias. In light of these findings, recommendations for optimizing multi-collector ICP-MS with respect to obtaining the highest possible precision are presented.

A model allowing simultaneous determination of the detector dead time and the mass discrimination factor in inductively coupled plasma mass spectrometry (ICP-MS), as well as the corresponding uncertainties, is presented and compared for three representative isotope systems, namely magnesium, indium and thallium. The advantages of using the model presented are firstly that both the detector dead time and the mass discrimination factor can be obtained simultaneously and secondly that the sampling time can be spent entirely on the isotopes of interest.

A comparison of two systems for the quantitation of metal-humic complexes and free metal ions, consisting of the separation by coupled ion exchange columns followed by detection by inductively coupled plasma mass spectrometry or cold vapour atomic fluorescence spectrometry, is presented. The systems evaluated comprised the serially coupled anion and cation exchangers, Sephadex A-25/Chelex 100 and Dowex 1X8/Chelamine Metalfix. Separation and preconcentration of the species studied were accomplished with both systems, elution being carried out using 2 M HNO3. Total concentrations, metal-humic complex fractions and free metal ion fractions of Al, Ba, Cd, Co, Cu, Fe, Hg, Mn, Pb, Sr, U and Zn in nine natural waters were determined. Statistical evaluation of the data from the two cation exchange materials, including results for additional elements, showed better precision (for Al, Ba, Cr, Cu and Mo) and higher recoveries (Al, Ba, Cd, Fe, Sr and Zn) for Chelex 100 than Chelamine Metalfix for free metal ions. On the other hand, Chelamine Metalfix recovered a significantly greater amount of Ni. The amounts of metal-humic complexes were compared with modelled distributions of these species, and one advantage of the preferred Sephadex A-25/Chelex 100 system is that the elements studied are all correctly classified with respect to their binding strengths to humic substances, which is not the case with the Dowex 1X8/Chelamine Metalfix pair. With the preferred system, metal-humic complexes can be reliably determined, as indicated by the results of equilibrium speciation modelling. However, comparison with the total concentrations showed statistically significant, non-quantitative recoveries of Al, Cu, Hg, Mn, U and Zn from some samples. Thus a combination of speciation and total concentration measurements is required to obtain a complete representation of the distribution of trace elements in natural waters.

Performance characteristics of inductively coupled plasma sector field mass spectrometry (ICP-SFMS) were studied with a Pt guard electrode (GE) inserted between the torch and load coil. The importance of the optimisation procedure and the matrix effects caused by a seawater matrix were assessed for 20 elements. Oxide and doubly charged ion formation was also investigated. Use of the GE allows a significant increase in ion transmission, by a factor of three to 20, thus resulting in improved instrumental detection limits. The improvement in sensitivity is mass dependent, with the highest gain observed for lower mass elements. Since, for the majority of analytical applications, actual detection limits depend upon blank levels rather on instrumental sensitivity, the most important factor for the determination of elements at ultra-trace levels is the degree of contamination of reagents and containers used. At the same time, significantly greater oxide formation is observed when operating the GE grounded rather than in the floating mode. For example, the BaO+/Ba+ ratio is ten to twelve times higher in the grounded mode. This calls for compromised instrumental parameters and the potential for severe spectral interferences from oxide species, which are often unresolved, even in high-resolution mode. Furthermore, non-spectral interferences from the seawater matrix appear to be more pronounced with the grounded GE, yielding a recovery of Ni of 55% compared with 93% in the floating GE mode. Hence all possible advantages and limitations of the use of the GE should be carefully considered prior to the analysis of real samples.

A model is presented describing the effects of dead time and mass bias correction factor uncertainties, flicker noise, and counting statistics on isotope ratio measurement precision using inductively coupled plasma mass spectrometry (ICPMS) with a single collector. Noise spectral analysis is exploited to enable estimation of the flicker noise parameters. For the instrument used, the flicker noise component exhibited a fairly weak frequency (f) dependence ( f -0.33±0.12), but was directly proportional to the total number of counts, Q. As white noise, determined by counting statistics, is given by Q0.5, the isotope ratio measurement uncertainties will actually cease to improve when Q exceeds a certain threshold. This would suggest that flicker noise could become the limiting factor for the precision with which isotope ratios can be determined by ICPMS. However, under most experimental conditions, uncertainties associated with mass discrimination and dead time correction factors are decisive. For ratios up to ~22 (115In/113In), optimum major isotope count rates are generally below 0.3 MHz, for which precision in the mass discrimination factor is limiting. The model derived could be used as a starting point for determining optimum conditions and understanding the limitations of single-collector ICPMS for precise isotope ratio measurements.

A procedure was developed for the determination of element distributions in cross-sections of ferromanganese concretions using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The effects of carrier flow rates, rf forward power, ablation energy, ablation spot size, repetition rate and number of shots per point on analyte intensity were studied. It is shown that different carrier gas flow rates are required in order to obtain maximum sensitivities for different groups of elements, thus complicating the optimisation of ICP parameters. On the contrary, LA parameters have very similar effects on almost all elements studied, thus providing a common optimum parameter set for the entire mass range. However, for selected LA parameters, the use of compromise conditions was necessary in order to compensate for relatively slow data acquisition by ICP-MS and maintain high spatial resolution without sacrificing the multielemental capabilities of the technique. Possible variations in ablation efficiency were corrected for mathematically using the sum of Fe and Mn intensities. Quantification by external calibration against matrix-matched standards was successfully used for more than 50 elements. These standards, in the form of pressed pellets (no binder), were prepared in-house using

A method for the determination of methylmercury in plasma and serum samples was developed. The method uses isotope dilution with 198Hg-labelled methylmercury, extraction into dichloromethane, back-extraction into water, aqueous-phase ethylation, purge and trap collection, thermal desorption, separation by gas chromatography, and mercury isotope specific detection by inductively coupled plasma mass spectrometry. By spiking 2 mL sample with 1.2 ng tracer, measurements in a concentration interval of (0.007–2.9) μg L−1 could be performed with uncertainty amplification factors <2. A limit of quantification of 0.03 μg L−1 was estimated at 10 times the standard deviation of concentrations measured in preparation blanks. Within- and between-run relative standard deviations were <10% at added concentration levels of 0.14 μg L−1, 0.35 μg L−1 and 2.8 μg L−1, with recoveries in the range 82% to 110%. Application of the method to 50 plasma/serum samples yielded a median (mean; range) concentration of methylmercury of 0.081 (0.091; <0.03–0.19) μg L−1. This is the first time methylmercury has been directly measured in this kind of specimen, and is therefore the first estimate of a reference range.

An internal standard (IS) can be used to account for moderate, matrix-related shifts in mass bias using multi-collector inductively coupled plasma mass spectrometry through the empirical, linear relationship between measured isotope abundance ratios for different elements in ln-ln space. Unfortunately, erroneous mass bias corrected isotope abundance ratios may be returned by the model, requiring artificial adjustment of the true isotope abundance ratio of the IS. Although inadequate correction for peak tailing has been convincingly used to explain this problem, our analysis of the literature describing the development of the mass bias correction model using an IS reveals the presence of a source of systematic error. The origin of this error is purely mathematical and is eliminated in the revised model presented, in which mass bias corrected isotope abundance ratios are independent of the isotopic composition of the IS. An expression for computing the total combined uncertainty in the corrected ratio, incorporating contributions from the linear model, the isotopic reference material, and measurements of analyte element and IS in the sample, is also derived.

Background: Despite its known toxicity, methylmercury is rarely measured directly in clinical studies; instead, conclusions are based on total mercury measurements. We have developed isotope-dilution-based methods for methylmercury-specific analysis of whole blood by coupled gas chromatography-inductively coupled plasma mass spectrometry (GC-ICPMS). Methods: We analyzed animal and human blood samples after alkaline digestion or extraction of methylmercury into dichloromethane and back extraction into water. Methylmercury was converted to the volatile ethyl derivative, purged, and trapped on a solid-phase collection medium, and then introduced into the GC-ICPMS system. Results: Limits of quantification were 0.4 and 0.03 mu g/L at a signal-to-noise ratio of 10 with the alkaline digestion and extraction methods, respectively. Extraction met our selected acceptable total error criterion, with an SD of 0.58 mu g/L at the critical maternal blood concentration of 5.8 mu g/L.Results obtained with alkaline digestion indicated the need for improved random analytical uncertainty, which was achieved by increasing the enrichment of the isotope dilution. For 37 blood samples, the mean (SD) proportion of total mercury present as methylmercury was 60 (27)%, range 6%-100%.Conclusions: The combination of extraction and isotope-dilution GC-ICPMS meets the requirements for use as a reference method for measuring methylmercury in whole blood.

The impact of variations in peak characteristics on the fidelity of transient signal measurement by inductively coupled plasma-quadrupole mass spectrometry (ICP-QMS) was investigated. Specifically, the question as to whether the multi-element capabilities or the accuracy in determined analyte amounts were deteriorated compared to what has been reported previously when not considering peak variations was addressed. The peak characteristics considered were the time of the signal maximum (tpeak), the standard deviation of the assumed Gaussian input function generated by the sample introduction system (σG), and the time constant for signal decay (τ). Investigations of simulated exponentially-modified Gaussian peaks revealed that, for variations of peak characteristics within reasonable ranges, measurement noise and variations in tpeak, σG and τ all contributed to calibration uncertainty. Electrothermal vaporisation (ETV) and flow injection (FI) systems were used to experimentally generate transient signals of varying peak characteristics. Removing data points from the raw signals simulated the monitoring of up to 100 mass-to-charge ratios, allowing calibration data and analyte amounts to be determined from the processed signals. To obtain calibration graph slopes with relative standard deviations below 1% for the ETV-ICP-QMS system, it was found necessary to acquire 7-24 data points per peak for 50-5 ms dwell times. On this basis, the maximum number of mass-to-charge ratios that could be monitored in a typical ETV-ICP-QMS analysis was 4-10 using dwell times of 50-5 ms. With the FI-ICP-QMS system, variations in the peak characteristics between calibration standards and samples meant that, to obtain less than 3% error in determined analyte amounts, at least 7 or 10 points per peak were required for external and internal standardisation, respectively. It was found that variations in peak characteristics contributed more than measurement noise to the error in determined analyte amounts. In recent studies it has been reported that 3-4 data points per peak are sufficient to accurately monitor a transient if peak variations are not considered, which, for typical ETV signals, would allow the monitoring of 20 mass-to-charge ratios during a single measurement cycle. Thus the results obtained here show that the multi-element capability of ICP-QMS when monitoring transient signals can be severely compromised by such variations.

A method employing supercritical fluid extraction (SFE) and GC coupled with microwave-induced plasma atomic emission spectrometry (MIP–AES) is presented for the determination of methylmercury in sediments. Butylmagnesium chloride was used to derivatize the target compound to butylmethylmercury which is amenable to GC. Using a commercially available reference sediment (PACS-1, National Research Council of Canada) as the model sample, a factorial design was utilized to investigate the effect of three variables; density, temperature and flow rate, on the extraction efficiency. An extraction efficiency of 49 ± 0.5% could be obtained for a 37.5 min dynamic extraction, corresponding to 25 thimble volumes of supercritical CO₂, and using purified support sand. Studies on the efficacy of SFE for another sediment matrix as a function of time have also been undertaken. Repeated pressure reductions in combination with support sand were found to increase the extraction efficiency of methylmercury from PACS-1 but not from a sediment issued by the Community Bureau of Reference (BCR) as part of an interlaboratory comparison. For PACS-1 this resulted in an increase in the average extraction efficiency to 96% for duplicate determinations following 50 thimble volume sweeps. Distillation was used as a reference method for isolation of methylmercury from sediments. Parallel extractions of the BCR sediment, using GC–MIP–AES for the final determination, gave results that were in good agreement and corresponded well with data submitted during the intercomparison exercise. The detection limit for the methylmercury in sediment using the described SFE GC–MIP–AES method is estimated to be 0.1 ng g^–1 based on a 20 µl injection, 0.5 g of sample and three times the blank level. It is proposed that the co-extracted sulfur from the sediment mediates the transport of methylmercury and, to some extent, inorganic mercury from the sediments. This is supported by the strong correlation between the concentrations of butylmethylmercury and dibutylsulfide found in the toluene extract. Using a stable isotope tracer, ¹⁹⁹Hg, and ICP-MS, evidence for the spurious formation of methylmercury during SFE under certain conditions is also presented.

During the last decade, the potential plant impact on the biogeochemical cycle of Si via the large terrestrial biogenic Si reservoir formed by vegetation has attracted considerable interest. It has been concluded that the release of silicic acid from dissolution of soil phytoliths might exceed the Si mobilized by weathering of Si-containing primary minerals, which implies that the biogenic contribution to the total content of Si in the soil profile must be considered in weathering studies. Information about Si isotopes can potentially be used for differentiation between relative contributions from biogenic and mineral sources in natural waters, soil solutions and plants. This would, however, require thorough characterization of the terrestrial biogenic Si reservoir, a task that received somewhat limited attention to date. The aim of the present study was to characterize the Si isotopic composition of a boreal forest, with bedrock consisting of dolomitic limestone, in Northern Sweden. Representative biomass from the forest area exhibited a surprisingly homogenous Si isotopic composition, ranging from δ29Si (-0.14 ± 0.05)‰ (2σ) to (0.13 ± 0.04)‰. Further, a change in the Si isotopic composition of (+0.39 ± 0.04)‰ has been detected in Leymus arenarius, indicating predominant accumulation of heavier isotopes from spring to autumn. Recent studies of Si isotopic composition in plants have been focused on the root uptake of dissolved silicic acid as the only Si accumulation path. Results acquired during the present study provide compelling evidence to suggest that exogenous Si is also incorporated in the surface structure of the plant material. A surface contribution in excess of 5% of the total Si would introduce a significant shift in the bulk isotopic composition (>0.1‰) assuming that the exogenous material differed by 2‰ from the biogenic Si. This strongly suggests that the surface contribution must be carefully considered during in situ uptake studies.

A procedure is described for accurate Si isotope ratio measurements by multicollector inductively coupled plasma mass spectrometry (MC-ICPMS). Dissolved silicon was preconcentrated and separated from other elements present in natural surface waters using anion-exchange chromatography. The optimized procedure provides virtually complete elimination of major inorganic constituents while maintaining Si recovery in excess of 97%. High-resolution capabilities of MC-ICPMS used in this study allow interference-free measurements of 28Si and 29Si isotopes using conventional solution nebulization sample introduction without aerosol desolvation. Owing to the magnitude of polyatomic ion contributions in the region of mass 30, mostly from 14N16O+, measurements of the 30Si isotope can be affected by tailing of the interference signals, making exact matching of analyte and nitric acid concentrations in all measurement solutions mandatory. Isotope abundance ratio measurements were performed using the bracketing standards approach and on-line correction for mass-bias variations using an internal standard (Mg). Uncertainties, expressed as 95% confidence intervals, for replication of the entire procedure are better than ±0.18" for δ29Si and ±0.5" for δ30Si. For the first time with MC-ICPMS, the quality of Si isotope abundance ratio measurements could be verified using a three-isotope plot. All samples studied were isotopically heavier than the IRMM-018 Si isotopic reference material.

It has previously been concluded that the stable Si isotopes are fractionated during geochemical and biogeochemical elemental transfers, such as weathering and precipitation of clays and biogenic Si, which has opened up the possibility of using Si as a tracer in natural terrestrial ecosystems. Furthermore, quantification of the biogenic impact on the biogeochemical Si cycle has attracted significant scientific interest since biological control has been suggested. Previous observations of seasonal variations in the dissolved Si isotopic pattern further imply that high-frequency riverine sampling during main hydrological events might provide important information about natural processes governing the fluvial biogeochemical Si cycle.Therefore, temporal variations in the isotopic composition of riverine dissolved Si were investigated for the Kalix River, Northern Sweden, the largest pristine river system in Europe, based on high-frequency sampling during a period of 25 weeks from early April to early October 2006. Temporal variations spanning 0.4‰ for δ29Si and 0.8‰ for δ30Si of dissolved Si in the Kalix River were observed during the period, suggesting that the riverine dissolved Si input to the oceans cannot be considered to have a constant Si isotopic composition even on a short time scale.The results implicate biogeochemical Si-cycling via formation and dissolution of biogenic silica as processes significantly affecting the dissolved Si transport in boreal systems during April to early October. The Si budget in the river system appeared to be controlled by relative Si enrichment during high discharge events and relative Si depletions in the subarctic mountainous and lake dominated areas. The Si enrichments and depletions were accompanied by decreasing and increasing riverine δ29Si and δ30Si, respectively. These isotope variations can be explained by release of plant derived silica, depleted in heavier Si isotopes, during the spring snowmelt. Further, increased volumetric contribution from the headwater and losses of dissolved Si due to biogenic silica formation by diatoms in the subarctic lakes at a later period are expected to be responsible for the preferential losses of lighter isotopes, as further verified by land cover analysis

Interest in quantifying the biogenic impact on the terrestrial biogeochemical Si cycle has increased significantly since biological control has been suggested. Previous observations of isotopic fractionation of Si during biogeochemical and geochemical processes imply that seasonal dissolved Si isotopic patterns in rivers have the potential for use in extracting information about the riverineand terrestrial biogeochemical Si cycles.Therefore, variations in the isotopic composition of dissolved riverine Si were investigated for the Kalix River, Northern Sweden, one of the largest pristine rivers in Europe, based on high-frequency sampling during a period of 25 weeks from early April to early October 2006. Temporal variations spanning 0.4. for δ29Si and 0.8. for δ30Si of dissolved Si in the Kalix River were observed during the period, suggesting that the riverine Si input to the oceans cannot be considered to have a constant Si isotopic composition even on a short time scale. The results implicate biogeochemical Si-cycling via formation and dissolution of biogenic silica as major processes controlling the Si transport in boreal systems. The Si budget in the river system appeared to be controlled by relative Si accretions during high discharge events and relative Si depletions in the subarctic mountainous and lake dominated areas. There were also temporal variations in Si isotopic composition with accretion (relative Si contribution), accompanied by depletion of the heavier Si isotopes, while the opposite trend was observed during periods of riverine Si depletion. These isotope variations can be explained by release of plant derived silica, depleted in heavier Si isotopes, during the spring snowmelt. Further, increased volumetric contribution from the headwater and losses of Si due to biogenic silica formation by diatoms in the subarctic lakes at a later period are expected to be responsible for the preferential losses of lighter isotopes. These conclusions are further verified by land cover analysis.

Thorough characterization of the Si isotopic composition of the terrestrial biogenic pool could potentially allow Si isotope information to be used when assessing the relative contributions from biogenic and mineral sources to soil water, plants and surface waters. In the present study, the Si isotopic compositions of major biomass components in a boreal forest in Northern Sweden were investigated, along with the relative contributions from exogenous Si incorporated in the plant structure. This was achieved using chemical purification and high-resolution multi-collector inductively coupled mass spectrometry (MC-ICP-MS) for the precise and accurate determination of the Si isotopic composition of plants. The technique, which relies on multi-elemental analysis of plant ashes and sample-specific HF-dissolution followed by strong-anion exchange chromatography, allows efficient separation of Si from matrix and interfering elements, while recovering in excess of 99% Si. The long-term instrumental reproducibility, expressed as two standard deviations (2σ), for the isotopic reference material NBS28 (n=12) was 0.06‰ for δ29Si and 0.12‰ for δ30Si. Results for the analyses of composite plant samples for the eight most prolific species in the boreal forest yielded a surprisingly homogenous Si isotopic composition, expressed as δ29Si (±expanded combined uncertainty) and δ30Si, ranging from (-0.15±0.11)‰ to (0.13±0.06)‰ and (-0.31±0.08)‰ to (0.22±0.13)‰, respectively. Isotopic and elemental analyses of local airborne particulate material suggest that the exogenous Si contribution varies between >1% and >70%, indicating that the potential surface contribution must be considered during Si uptake studies. The present study thus provides evidence that thorough appreciation of the forms of Si in plants is an absolute requirement when assessing the plant impact on the Si cycle via the difference in dissolution kinetics for phytoliths and lithogenic Si.

Soil samples were prepared for multi-element analysis using HNO3 leaching or pseudo-total digestion with HNO3, HCl and HF in a microwave oven, both methods requiring 70 min heating time. Two calibration approaches for the soil characterization were also compared: external calibration, combined with internal standardization, and isotope dilution (ID) after appropriate spiking of the soils with a stable isotope mixture prior to sample preparation. Analyses were performed using inductively coupled plasma sector field mass spectrometry (ICP-SFMS). Accurate total elemental concentrations were only obtained for Cd and P using both sample preparation methods in two certified reference materials, NIST SRM 2709 and CCRMP SO-2, as well as comparable values for a Finnish inter-laboratory soil. The pseudo-total digestion method also provided accurate results for As, Be, Co, Fe, Mn, Ni, Pb, Sb, Ti, V and Zn. For Cu in SO-2 and Cr in both certified reference materials, incomplete recoveries were always obtained. In the case of Cr, this is due to difficulties associated with the complete solubilization of refractory minerals.For a given final dilution factor, external calibration provides better limits of detection (LODs) than ID. As both methods of quantification yield results of essentially equivalent accuracy and precision, external calibration is to be preferred as a greater number of elements are amenable to analysis in a shorter measurement time. On the other hand, ID can be combined with matrix separation (NH3 precipitation was used here), allowing lower dilution factors to be used without deleterious effects on the instrumental performance. In particular, improved LODs could be obtained for Cd, Cu and Hg, primarily as a result of being able to introduce ten-fold more concentrated solutions from which the bulk of the matrix had been removed. For Cu and Ni, matrix separation almost eliminated Ti, and thus the formation of spectrally interfering TiO+ was completely suppressed. Potentially, the combination of ID and matrix separation would allow these elements to be determined without resorting to medium resolution measurement mode, again improving the LODs for the determination by ID-ICP-SFMS.

The performance of double-focusing, sector field ICP-MS (ICP-SFMS) for the multi-elmental analysis of soft tissues following microwave-assisted digestion with nitric acid was eveluated and factors affecting method limits of detection discussed. Accuracy was assessed by replicate analyses of certified reference materials and by participation in performance evaluation programs; the precision was better than 5% relative standard deviation (RSD) for the majority of elements. Cl was the only element for which ICP-SFMS data consistently deviated from certified concentrations in the reference materials tested. Comparison between results obtained by ICP-SFMS and ICP optical emission spectrometry showed good agreement for elements present in tissues at concentrations above 2 μg g-1. The concentrations of 68 elements in different fish and animal soft tissues (muscle, liver, kidney, lung and brain) are presented, and, where possible, compared to previously published data.

Surface complexation of inorganic mercury(II) and monomethyl mercury (CH3Hg+) onto a hydrous goethite (α-FeOOH) surface has been studied. The ph (-log[H+]) has been varied within the range 2.7 < -log[H+] < 9, at 298 K, using a 0.1 mol dm-3 NaNO3 medium. Low total mercury concentrations (≈ 1 μmol dm-3) were used. Inorganic mercury and methyl mercury content in the water phase, in the goethite phase, and adsorbed on the vessel walls was determined by GFAAS and GC-coupled MIP-AES. The inorganic mercury distribution was evaluated, using a previously determined surface complexation model, based on the constant capacitance concept. This model was derived using about 103 times higher total mercury concentrations. In the presence of goethite, approximately 80% of both methyl mercury and inorganic mercury(II) was recovered in the different phases. The extractable fraction adsorbed to the vessel walls was found to be low. About 20% of the inorganic mercury added remained soluble in the presence of goethite. This is close to the predicted value, using a previously determined model derived in the mmol dm-3 range. This implies that the concept of specific high affinity sites is questionable in the case of near trace concentrations of Hg(II). Methyl mercury was found to be weakly coordinated, with about 15% adsorbed on the goethite surface. Furthermore, a model calculation describing the surface complexation of methyl mercury on goethite was performed. The experimental data could best be explained by the formation of the surface complexes ≡FeOHHgCH+3 and ≡FeOHgCH3.

Temporal variations in the iron isotopic composition, δ56Fe between − 0.13‰ and 0.31‰, have been measured in the suspended fraction in a Boreal river. The major mechanism behind these variations is temporal mixing between two types of particles–colloids, Fe-oxyhydroxides and Fe–C colloids. Data in this study indicate that these two types of colloids have different Fe-isotope composition. The Fe–C colloid has a negative δ56Fe value whereas the Fe-oxyhydroxide colloid is enriched in 56Fe. These two types of colloidal matter have different hydrogeochemical origin. The Fe–C colloid reaches the river during storm events when the upper sections of the soil profile (O and E horizons) are flooded by a rising water table. Colloidal Fe-oxyhydroxides reach the river via inflow and subsequent oxidation of groundwater enriched in dissolved Fe(II).

Experiments modeling diffusion of Mo in aqueous solutions have been performed and, using multicollector ICP-MS, the ratios of the diffusivities of Mo isotopes, D97Mo/D95Mo, in aqueous solutions have been determined. Diffusion of MoO42- ions in solution was concomitant with Mo isotopic fractionation with D97Mo/D95Mo = 0.99988 ± 0.00004 (2σ for n = 3). In contrast, during diffusion of Mo polyanions, such as Mo7O246- and Mo8O264-, no measurable isotope fractionation has been found with D97Mo/D95Mo = 1.00000 ± 0.00002 (2σ for n = 3). These results indicate the need for due consideration to Mo speciation when attempting to interpret the role of diffusive fluxes in the formation of Mo isotopic signatures in nature. They also raise the possibility that the various chemical forms of other transition metals may be characterized by species-specific isotopic fractionation effects during physicochemical reactions.

The application of diffusive gradients in thin films (DGT) samplers for measurements of the isotopic composition of soluble Zn by multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS) was tested under laboratory conditions. The effect of diffusion in hydrogels as a possible source of fractionation was investigated by measuring Zn isotope ratios for different fractions of Zn accumulated by DGT and comparing with the bulk isotope composition of the solution. An important finding of this study is that, provided quantitative elution is obtained, no fractionation of Zn isotopes due to the diffusion process is detectable within the reported precision of MC-ICPMS measurements. Consequently, DGT samplers are suitable for studies of the Zn isotopic composition in natural waters.

A technique for the in situ determination of Re and Os in molybdenite samples using direct solid sampling by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) is described. The sample preparation is limited to molybdenite separation followed by grinding and pressing to pellets. For Re determination, the best results were obtained using external calibration in conjunction with internal standardization. Isotopes of both molybdenum and sulphur could be used as internal standards. This quantification approach provides precision levels generally better than 10% the relative standard deviation (RSD) with similar levels of accuracy. Os concentrations were derived from Re concentrations and measured isotopic ratios of intensities measured at masses 187 and 185, using W isotopes for on-line mass bias correction. As a rule, LA-ICP-MS results for Os agree with corresponding isotope dilution ICP-MS data to within 30%. Reproducibility is strongly dependent on the age of the molybdenite as well as on the precision of isotope ratio measurements, which in turn depend on Re and W concentrations. The proposed technique provides a rapid estimation of Re and Os concentrations for subsequent precise analysis by isotope dilution ICP-MS.

An analytical method was developed for Os-Re dating of molybdenite. The method is based on determination of Os and Re concentrations in molybdenite by isotope dilution inductively-coupled plasma mass spectrometry (ID-ICP-MS). Sample digestion and sample/spike equilibration were achieved by a two-stage autoclave-based procedure using a mixture of nitric and sulphuric acids. Os was separated from the sample digest by modified single-stage distillation of osmium tetraoxide (OsO4) using elevated temperature and on-line addition of hydrogen peroxide. OsO4(g) was trapped in a mixture of 0.05% thiourea in 0.05 M sodium hydroxide. An anion-exchange column was used to separate Re from excess Mo in the solution remaining after distillation. Os and Re isotope ratio measurements were performed by single-collector, double focusing inductively-coupled plasma mass spectrometry (ICP-MS) with on-line mass-bias correction. Typical instrumental precision was in the range 0.02-0.2% relative standard deviation (R.S.D.) depending on the analyte concentrations. Notorious Os memory effects in the ICP-MS introduction system were eliminated using 5% ammonia solution, both as matrix for final dilution of the trap mixture as well as for washing between the samples. The reproducibility of the entire analytical procedure was accessed by replicate dating of two molybdenite standards and three molybdenite separates, and was found to be in the range 0.87-1.52% R.S.D. Though accuracy of the method is limited by difficulties in evaluating exact concentration of Os in spike solution, ages obtained in the course of these work agrees well with previously published data.

A method using multiple-collector inductively coupled plasma mass spectrometry (MC-ICPMS) for the precise measurement of Mo isotopic composition in geological samples has been developed. Purification of Mo for isotope ratio measurements was realized by ion-exchange chromatography using the chelating resin Chelex-100. This technique allows an efficient separation of Mo from an excess of Fe in samples and at the same time provides quantitative recovery of Mo. Instrumental mass discrimination is corrected by using Pd spiking and normalization to the 105Pd/104Pd ratio. Mo isotope ratios of samples are expressed in per mil relative to those of the bracketing in-house Mo standard. The long-term reproducibility at the two standard deviation level is 0.04, 0.06, 0.08 and 0.14‰ for 96Mo/95Mo, 97Mo/95Mo, 98Mo/95Mo and 100Mo/95Mo ratio measurements, respectively. The technique has been applied to measurement of the Mo isotopic composition of freshwater sediments and molybdenites. Mass-dependent variations in the isotopic composition of Mo spanning the range of 2.2‰ in terms of the 97Mo/95Mo ratio for two sediment columns from different redox environments have been resolved. These results show that Mo isotope effects induced by geochemical processes operating during weathering and transport of Mo to the oceans should be quantified in order to interpret global Mo isotope budget and make use of stable Mo isotopes as proxy for redox conditions in the geological past.

High resolution MC-ICP-MS is used for the precise measurement of variations in the isotopic composition of Fe in ferromanganese concretions and sediments relative to IRMM-014 standard. The sensitivity for 56Fe in high resolution mode was 3 V per mg lm1 Fe, a figure that is comparable to those from other MC-ICP-MS instruments operated at low resolution. Incorporation of a guard electrode and the efficient ion transmission capabilities of the Neptune MC-ICP-MS instrument are responsible for the high sensitivity. It was observed that the use of HCl resulted in the formation of ClOH+, causing interference with 54Fe in particular. This acid has been preferred in some cases over HNO3 to minimize formation of ArN+, the major interferent for 54Fe. Using the high resolution mode of the Neptune, the nature of spectral interferences is unimportant as all are completely resolved and will not affect the accuracy of the determined Fe isotope ratios. As the instrument also provides flat-topped peaks, high resolution operation does not necessarily result in impaired precision, providing that higher concentrations are used to compensate for the loss in sensitivity compared with the low resolution mode. In the present work, external reproducibilities of 56Fe/54Fe and 57Fe/54Fe isotope ratios were better than 50 ppm (one standard deviation) at a concentration of 5 mg lm1. The level of instrumental mass discrimination observed for raw ratios drifted by as much as 0.09% per mass unit over a measurement session, but could be corrected on-line by simultaneous monitoring of the 62Ni/60Ni isotope ratio. Variations in the Fe concentrations or the acid strength of measurement solutions were found to affect the apparent mass discrimination. Increasing the Fe concentration caused a relative decrease in the raw 56Fe/54Fe and 57Fe/54Fe isotope ratios, thus ruling out the space charge effect as the explanation for this phenomenon. Instead, it is suggested that the larger dry aerosol particles formed at higher Fe concentrations are not completely vaporized until later in the plasma, thus reducing the relative rate of diffusional losses of lighter 54Fe from the central channel. However, application of on-line correction using Ni could adequately account for this effect. From the results for a variety of sedimentary geological materials, analysis of three-isotope data revealed that equilibrium fractionation of Fe occurred during deposition. To be able to distinguish between equilibrium and kinetic fractionation processes, it is imperative to collect accurate and precise data for the 56Fe/54Fe and 57Fe/54Fe isotope ratios. These requirements are readily fulfilled by applying high resolution MC-ICP-MS and on-line correction for instrumental mass discrimination using Ni.

The determination of actinides at low levels using ICP-MS can be interfered by polyatomic ions appearing at the same nominal mass-to-charge ratio. In this work, interferences initially found when analysing plutonium in soil and sediment samples were identified as lanthanide phosphates and the formation of these species examined. It was found that high sample gas flow rates and low rf powers enhanced the formation of lanthanide phosphates. All lanthanides studied (La, Ce, Pr and Nd) formed phosphates, albeit to various extents and of slightly different compositions. Furthermore, the lanthanide phosphate formation was verified by introducing the source of phosphorus, hydroxyethylidene diphosphonic acid (HEDPA), in an [1][8]O enriched water solution. This experiment also revealed that the HEDPA is essentially completely dissociated in the plasma and that the interfering species are most likely formed during ion extraction.

Dead time determinations on a mass spectrometry system with ion counting detection can either be done using an isotope ratio measurement approach or via electronic examination of individual components, e.g., the pulse amplifier. Depending on the dead time of each component in the signal chain, the electronically determined result may not represent the true value for the total system, i.e., there might be a series of hardware related dead times. However, a hardware set artificial dead time in the pulse counting system that is long enough might yield a system dead time that can be represented by this set dead time solely. It is shown in this work that a carefully chosen, artificially introduced set dead time yields a system that may be characterized to a much lower uncertainty than is possible using ratio-based measurement approaches. Ultimately, the impact of the dead time on the combined uncertainty of an isotope abundance ratio measurement may be negligible even at very high count rates, i.e., >1 Mcps. In other words, incorporating the dead time contribution in a combined uncertainty calculation would no longer be necessary.

The purpose of this work was to develop an optimised sample-preparation procedure for the determination of Pu in soil/sediment with ICP-MS. To start with, several different procedures were screened for their ability to separate plutonium and remove uranium. After the screening, two methods were applied on one soil (IAEA Soil6) and two sediment reference materials (IAEA300 and IAEA135). These methods were based on separation of Pu using TEVA and a combination of UTEVA and TRU resins, followed by elution of Pu with 0.1% hydroxylethylidene diphosphonic acid (HEDPA). A comparison was also made between sample preparation based on acid-leaching and complete digestion using lithium borate fusion. The highest yield of Pu (80%) was found with the procedure consisting of fusion followed by TEVA, while the decontamination from U showed large variations (RSD varying from 16–52%) with all procedures. No difference in the recovery of Pu was found between the two sample preparation techniques. The results of the quantitative determination in low resolution of ²³⁹Pu and ²⁴⁰Pu from the UTEVA + TRU-separation were significantly higher than those obtained by the TEVA procedure. An analysis in higher mass resolution displayed interfering peaks in the mass-region of Pu, and lanthanide-containing polyatomic ions were found to be a likely cause for these interferences. The procedure based on lithium borate fusion and separation using the TEVA-resin avoided such interferences and was therefore tested for repeatability over time on IAEA300. The stability of the method was good (RSD = 2.49% (n = 8)), with the exception of one value being significantly higher than the others. This result was confirmed by analysis in higher mass-resolution, which indicates an inhomogeneous distribution of Pu in the reference material, despite a sample intake of about 1 g.

An analytical method allowing multi-element characterization by external calibration, osmium (Os) concentration determination by isotope dilution (ID) and 187Os/188Os isotope abundance ratio measurement from a single sample preparation was developed. The method consists of microwave-assisted, closed-vessel acid digestion of small (0.01-0.4 g dry weight) biological samples spiked with Os solution enriched in a 190Os isotope followed by concentration and Os isotope ratio measurements using double-focusing, sector field inductively coupled plasma mass-spectrometry (ICP-SFMS) operated with methane addition to the plasma and solution nebulization (SN) sample introduction. For samples with Os content below 500 pg, complementary analysis using gas-phase introduction (GPI) on the remaining sample digests was performed. The use of disposable plastic lab ware for sample digestion and analysis by SN ICP-SFMS circumvents Os carry-over effects and improves the sample throughput and cost-efficiency of the method. For a 0.1 g dried sample, Os method limits of detection (MLODs) of 2 pg g -1 and 0.2 pg g-1 were obtained using SN or GPI, respectively. Long-term reproducibility of 187Os/188Os isotope abundance ratio measurements using the GPI approach was better than 1.5% RSD for our in-house control sample (moose kidney) with an Os concentration of approximately 5 pg g-1. Os data for several commercially available reference materials of biological or plant origin (not certified for Os) are presented. The method was used in the large scale bio-monitoring of free-living bank voles from an area affected by anthropogenic Os emissions.

Various stages of an analytical method for high-precision cadmium (Cd) isotope ratio measurements by MC-ICP-MS (sample preparation, matrix separation, instrumental analysis and data evaluation) were critically evaluated and optimized for the processing of carbon-rich environmental samples. Overall reproducibility of the method was assessed by replicate preparation and Cd isotope ratio measurements in various environmental matrices (soil, sediment, Fe-Mn nodules, sludge, kidney, liver, leaves) and was found to be better than 0.1‰ (2σ for δ114Cd/110Cd) for the majority of samples. Cd isotope ratio data for several commercially-available reference materials are presented and compared with previously published results where available. The method was used in a pilot study focusing on the assessment of factors affecting Cd isotope composition in tree leaves. A summary of results obtained for a large number (n > 80) of birch (Betula pubescenes) leaves collected from different locations in Sweden and through the entire growing season is presented and potential reasons for observed variability in Cd isotope composition are discussed. Seasonal dynamics of element concentrations and isotope compositions in leaves were also compared for Os, Pb, Zn and Cd.

Three Si isotope materials have been used for an inter-laboratory comparison exercise to ensure reproducibility between international laboratories investigating natural Si isotope variations using a variety of chemical preparation methods and mass spectrometric techniques. These proposed standard reference materials are (i) IRMM-018 (a SiO2 standard), (ii) Big-Batch (a fractionated SiO2 material prepared at the University of California Santa Barbara), and (iii) Diatomite (a natural diatomite sample originally deposited as marine biogenic opal). All analyses are compared with the international Si standard NBS28 (RM8546) and are in reasonable agreement (<+/- 0.22 parts per thousand. 1 sigma(SD) delta Si-30) given the different measurement techniques involved. These methods include both acid and alkaline dissolution/fusion, Si separation using cation exchange, selective co-precipitation, and gas-source versus plasma-ionization (high and low resolution) mass-spectrometric techniques. The average delta Si-30 for Diatomite, IRMM-018, and Big-Batch are + 1.26 parts per thousand, -1.65 parts per thousand and -10.48 parts per thousand, respectively, with corresponding delta Si-9 values of + 0.64 parts per thousand, -0.85 parts per thousand and -5.35 parts per thousand for the same standards, respectively. For the most fractionated standard (Big-Batch), results demonstrate a kinetic mass-dependent fractionation effect for atomic Si (i.e., delta Si-29 similar to 0.51 x delta Si-30). There is almost no statistical difference between the mean values obtained by each participating laboratory, with the notable exception of the IRMM-018 standard. This effect could be caused by heterogeneity or contamination of this standard. The results for the other two standards indicate that data sets produced using any of the methods employed in this study will have similar precision and differences are limited to 0.2 parts per thousand in mean delta Si-30 values for a given sample between laboratories, or differences of 0.13 parts per thousand. in mean delta Si-29 values.

Changes in the analytical performance of double focusing sector field inductively coupled plasma mass spectrometry (ICP-SFMS) caused by addition of methane to the argon gas ICP were studied for approximately 100 isotopes of 70 elements. The parameters under consideration included instrumental background, analyte sensitivity, precision and formation of spectral interferences as functions of methane flow added to the sample gas. It was shown that for many analytes the capabilities of ICP-SFMS significantly improve by virtue of enhanced sensitivity and reduction of polyatomic interferences. In contrast to quadrupole-based ICP-MS, these gains in instrumental performance do not compromise multi-element capabilities given that the amount of methane is carefully optimized. The accuracy of the results for the determination of 50 elements in water samples was evaluated using the certified reference materials SLRS-4 and SLEW-2.

An analytical procedure allowing multi-elemental analyses and isotope ratio measurements of eight of these (B, Cd, Cu, Fe, Pb, Sr, Tl and Zn) in matrices relevant for bio-monitoring using a single highpressure acid digestion was developed. Method blanks, separation efficiency of matrix elements, repeatability and reproducibility were evaluated using sets of preparation blanks, certified reference materials and duplicate samples prepared and analyzed over a period of several months. The method was used to assess the natural variability of concentrations and isotopic compositions in bio-indicators (tree leaves, needles and mushrooms, over 240 samples) collected mainly from a confined area in North-East Sweden. Ranges found from leaves and needles were compared with data obtained for limited numbers of samples collected in Spain, Italy, France, United Kingdom and Iceland.

Isotope ratios and elemental concentrations were measured in aqueous solutions sampled at varying distances from sources of Fe or Zn ions. The measurements reveal fractionation of isotopes resulting from pure diffusion in solution. Our data demonstrate that diffusion alone can cause changes in 56Fe/54Fe and 66Zn/64Zn isotope ratios in excess of -0.3”. These findings thus confirm previous suspicions that transport processes contribute to observed variations in isotopic compositions. Diffusion must therefore be considered when attempting to make inferences from isotope measurements on samples originating from aqueous systems where concentration gradients may develop.

Elemental response variations as a function of carrier gas flow rate in laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) were studied for a wide range of analytes. The effects of rf power, focus lens settings, thermodynamic properties of analytes and sample matrix were thoroughly examined. It was found that, with the experimental set-up used for this work, processes occurring in the ICP, rather than during ablation and transport, play the decisive role in determining the shapes of flow rate plots observed with LA. Responses for analytes of lower nominal masses and vaporization enthalpies peak at consistently higher flow rates (1.15 1 min-1) than other elements, independent of matrix. On the other hand, the magnitude of the maximum sensitivity is matrix dependent, even for these elements. Involatile elements display much broader maxima at considerably lower flow rates; the more refractory the matrix, the lower the optimum flow rate. This behaviour is consistent with the residence time in the ICP necessary to maximize the efficiency of analyte ion production. The existence of inter-elemental differences in the locations of zones of maximum ion densities formed in the ICP can thus be related to the times required for vaporization of any given analyte from the particles produced by LA. Such differences may be responsible for numerous fractionation effects mentioned in the LA literature. It is also demonstrated that the ion sampling process can affect the shapes of the flow rate plots, potentially shifting the apparent position of the optimum flow rate and confounding the interpretation of inter-element response differences.

Given that laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) has the potential to directly determine the concentrations of some 80 elements in solid samples, the fact that most applications are limited to considerably smaller numbers of analytes is indicative of the inherent problems with calibration. These stem from elemental response variations, both between analytes in any given sample and between matrices for any given analyte. Although response variations are often attributed to differences in ablation or transport efficiencies, there have also been indications that some degree of elemental fractionation may occur in the ICP. The results of the present investigations demonstrate that the ICP is the predominant source of fractionation, and thus response variations are related to the thermodynamic properties of the elements and their host particles. By studying analyte response as a function of carrier gas flow rate (so called flow rate plots) in 16 matrices, patterns in the behaviour of the elements in LA-ICP-MS could be clearly discerned and used for classification. Three groups of elements displaying consistent behavioural patterns over all matrices were identified from these studies: Group A, comprising refractory elements with high oxide bond dissociation enthalpies; Group B, including the rare and heavier alkaline earth (Ca, Sr, Ba) elements; and Group C, consisting of volatile or low mass elements. As each group exhibits decidedly different optimum flow rates and flow rate plot shapes which, with the exception of the group C elements, also depend on the matrix, the utility of LA-ICP-MS for multi-element analyses is severely compromised. In fact, quantitative determination of a wide range of analytes demands that calibration factors be established for at least one element from each group, as well as for all elements that could not be satisfactorily classified. This classification may serve as a guide in the selection of suitable internal standards for LA-ICP-MS, at least for certain groups of analytes. Examples are also given showing how flow rate plots can be employed to predict the adequacy of selected internal standards or solid standard materials for calibration

This chapter presents data on the inorganic components of hazelnuts, walnuts, almonds, pecans, cashews, Brazil nuts, pistachios, pine nuts, peanuts, coconuts, pumpkin seeds, and sunflower seeds. Based on average consumption data for nuts and seeds, their nutritional significance and toxicological relevance in dietary intake are discussed.

Different analytical approaches for origin differentiation between vendace and whitefish caviars from brackish- and freshwaters were tested using inductively coupled plasma double focusing sector field mass spectrometry (ICP-SFMS) and multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). These approaches involve identifying differences in elemental concentrations or sample-specific isotopic composition (Sr and Os) variations. Concentrations of 72 elements were determined by ICP-SFMS following microwave-assisted digestion in vendace and whitefish caviar samples from Sweden (from both brackish and freshwater), Finland and USA, as well as in unprocessed vendace roe and salt used in caviar production. This data set allows identification of elements whose contents in caviar can be affected by salt addition as well as by contamination during production and packaging. Long-term method reproducibility was assessed for all analytes based on replicate caviar preparations/analyses and variations in element concentrations in caviar from different harvests were evaluated. The greatest utility for differentiation was demonstrated for elements with varying concentrations between brackish and freshwaters (e.g. As, Br, Sr). Elemental ratios, specifically Sr/Ca, Sr/Mg and Sr/Ba, are especially useful for authentication of vendace caviar processed from brackish water roe, due to the significant differences between caviar from different sources, limited between-harvest variations and relatively high concentrations in samples, allowing precise determination by modern analytical instrumentation. Variations in the 87Sr/86Sr ratio for vendace caviar from different harvests (on the order of 0.05-0.1%) is at least 10-fold less than differences between caviar processed from brackish and freshwater roe. Hence, Sr isotope ratio measurements (either by ICP-SFMS or by MC-ICP-MS) have great potential for origin differentiation. On the contrary, it was impossible to differentiate between Swedish caviar processed from brackish water roe and Finnish freshwater caviar based solely on 187Os/188Os ratios.

The analytical performance of a hyphenated method for Os isotope ratio measurements by double focusing, sector field ICP-MS (ICP-SFMS) was evaluated. The method is based on several optimised, concurrent processes: Os extraction from samples in hot concentrated nitric acid; separation of Os from the digest solution by formation of volatile osmium tetroxide accelerated by continuous hydrogen peroxide addition; transport of analyte vapour by an oxygen flow into the ICP; and isotopic analysis by ICP-SFMS. Due to the very efficient analyte utilisation (in excess of 0.5‰), isotope ratio measurement can be performed at low pg Os levels. Combined with the ability to process sample sizes up to 2 g (up to 50 g if the organic matrix of biological or botanical samples is eliminated by ashing), materials with Os concentrations in the low, or even sub-pg g-1 range can be analysed by the method. Given that two complete digestion/distillation systems are available for interchangeable use, throughputs of up to 15 samples per 8-hour shift can be achieved. The method precision, evaluated as the long-term reproducibility of 187Os/188Os ratio measurements in a commercial Os standard containing 0.5 ng Os, was 0.16% relative standard deviation (RSD, 1 s). The method has been applied to perform replicate 187Os/188Os ratio measurements in a suite of 50 reference materials of various origins and matrix compositions, with Os concentrations varying from <0.1 pg g-1 to >100 ng g-1, yielding an average precision of 3% RSD. Though none of the materials tested are certified for Os content or Os isotope composition, comparison of the obtained data with published Os isotope information for similar sample types revealed close agreement between the two. The method can also be used for the simultaneous, semi-quantitative approximation of Os concentrations.

In theory, state of the art inductively coupled plasma mass spectrometry (ICP-MS) instrumentation has the prerequisite sensitivity to carry out multi-elemental trace analyses at sub-ng L-1 to sub-pg L-1 levels in solution. In practice, constraints mainly imposed by various sources of contamination in the laboratory and the instrument itself, and the need to dilute sample solutions prior to analysis ultimately limit detection capabilities. Here we review these sources of contamination and, wherever possible, propose remedial strategies that we have found efficacious for ameliorating their impact on the results of multi-elemental trace analyses by ICP-MS. We conclude by providing a list of key points to consider when developing methods and preparing the laboratory to routinely meet the demands of multi-elemental analyses at trace analytical levels by ICP-MS.

A hyphenated method for Os isotope ratio measurements by double focusing, sector field ICP-MS (ICP-SFMS) was developed. The method is based on several optimised, concurrent processes: Os extraction from samples in hot concentrated nitric acid; separation of Os from the digest solution by formation of volatile osmium tetroxide accelerated by continuous hydrogen peroxide addition; transport of analyte vapour by an oxygen flow into the ICP; and isotopic analysis by ICP-SFMS. Due to the very efficient analyte utilisation (in excess of 0.5‰), isotope ratio measurement can be performed at low pg Os levels. Combined with the ability to process sample sizes up to 2 g (up to 50 g if the organic matrix of biological or botanical samples is eliminated by ashing), materials with Os concentrations in the low, or even sub-pg g-1 range can be analysed by the method. This ability was used to measure Os concentrations and isotope ratios in variety of environmental and geological materials. Based on the data, it was possible to trace both long-range and local Os emission sources.

A procedure is described for the determination of Y, Zr, Nb, Ru, Rh, Pd, Ag, SB, Te, Hf, Ta, W, Re, Os, Ir, Pt, An, Tl, Bi, and U in human urine and serum at concentrations relevant to the occupationally unexposed population. Sample preparation was limited to tenfold dilution with 2% HCl. A combination of a sample introduction system designed to provide enhanced sensitivity and the use of water and acids of high-purity has resulted in limits of quantification (LOQ) in the sub-nanogram per liter range for 13 analytes. Instrumental background caused by release of analytes (Y, Zr, Ag, Sb, Au, Tl, Bi, U) from different parts of the sample-introduction system was found to be the major limitation in obtaining better LOQ. Nevertheless, detection capabilities of the proposed procedure were adequate for all elements except Ru, Pd, and Rh. Despite the use of high-resolution mode for these analytes some unresolved spectral interferences might still be present. For 13 elements an external accuracy assessment was accomplished by participating in proficiency testing and inter-comparison programs. Results obtained for pooled urine and serum were compared with concentrations reported for occupationelly unexposed populations in recent publications.

The levels of approximately 70 elements were determined in different culinary nuts (hazelnuts, walnuts, almonds, bitter almonds, pecans, cashews, Brazil nuts, pistachios, pine nuts, peanuts and coconuts) and seeds (pumpkin and sunflower) available on the Swedish market. The study was limited to raw, virtually unprocessed nuts and seeds (both shelled and unshelled) excluding mixed, roasted or salted products. In total, 44 products from different suppliers were analyzed, with the number of samples per nut/seed variety reflecting the availability of unprocessed products in retail outlets, varying from two for bitter almonds and pistachios to six for hazelnuts and walnuts. This selection includes samples from at least 11 different countries of origin. The optimized analytical procedure consists of microwave-assisted sample digestion using a HNO3/HF mixture, followed by multi-elemental analysis by double focusing, sector field inductively coupled plasma mass spectrometry. The analyses were accompanied by rigorous quality control measures including thorough control of potential sample contamination at all analytical stages, participation in inter-laboratory performance assessment schemes, and the analysis of certified reference materials of plant origin. Concentrations thus obtained were compared with data from product labels (where available), food composition tables and other relevant surveys, demonstrating, depending on the elements in question, close agreement as well as considerable differences.

Osmium (Os) concentrations and 187Os/188Os isotope abundance ratios are presented for sedimentary materials, soils, humus, plants, mushrooms, mosses and lichens collected in the vicinity of the town of Luleå, Northeast Sweden, the data for biological specimens being the first reported. Contributions from sampling and varying exposure time to the observed environmental variability were evaluated. Sedimentary materials (from both fresh and brackish water) are most elevated in radiogenic 187Os, followed by inorganic soil horizons, mushrooms and humus. The Os isotopic compositions of plants, mosses and lichens are much less radiogenic, with mean 187Os/188Os lying within a relatively narrow 0.3-0.6 range. Significant temporal variations in Os concentrations and isotopic compositions of plant samples are attributed to integrative uptake of airborne Os with non-radiogenic composition. Measured Os concentrations in biological matrices increase in the order: small shrub leaves (blueberry and lingonberry) ≤ spruce needles ≤ mushrooms ≤ tree leaves ≤ pine needles < mosses lichens. The concentrations found in three different species of plant were used to provide the first estimates of gaseous osmium tetroxide (OsO4) in the environment. Though the Os content of samples from Northeast Sweden does not differ significantly from matrix-matched international reference materials (not certified for Os) of abiotic origin, the estimates of gaseous OsO4 concentrations are roughly an order of magnitude higher than have been reported for particle-bound Os in other studies. The pronounced spatial variations between relatively closely situated sites in mean 187Os/188Os ratios for samples of the same species (presumably with the same dominating uptake mechanism) point to the presence of different local Os sources. This study therefore demonstrates that emissions of Os from automobile catalytic converters are not the only source of contemporary environmental contamination.