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Species-specific Hg isotope ratio data has increasingly become an important tool in understanding biogeochemistry of mercury. Among the plethora of analytical techniques capable of separating Hg species to date only gas chromatography has been used to study natural variations in their isotopic composition. Here, we report new methodology for precise and accurate Hg isotope ratio measurements of methylmercury in fish tissues at environmentally relevant levels using high performance liquid chromatography (HPLC) and cold vapour generation multi-collector inductively coupled plasma mass spectrometry (CVG MC-ICPMS). The chromatographic baseline separation of Hg species such as methylmercury (CH3Hg) and inorganic Hg (iHg) was achieved in isocratic mode using reverse phase HPLC with a mobile phase containing L-cysteine as a complexing agent and without the need for species derivatisation. The signal-to-noise ratio of Hg detection by MC-ICP-MS was improved using a cold vapour generation interface with SnCl2 as reducing agent. Challenges driven by the non-reactivity of CH3Hg with SnCl2 and, interferences caused by the presence of L-cysteine in the mobile phase were efficiently overcome through complete oxidation of isolated Hg species prior to cold vapour generation and species-specific Hg isotope ratio measurements. Combined standard uncertainties of δ199/198Hg, δ200/198Hg, δ201/198Hg and δ202/198Hg values determined from replicated measurements of CH3Hg in fish tissue reference materials BCR 463 and NIST SRM 1947 ranged from 0.10‰ to 0.22‰. The obtained δ-values for the Hg isotope ratios are in very good agreement with indicative values of NIST SRM 1947 and those previously reported for BCR 463 material. The developed technique offers a complimentary measurement method to gas chromatography MC-ICPMS in producing isotopically certified species-specific reference materials for Hg. Furthermore, evidence for Hg isotope fractionation induced by dissociation of CH3Hg and interactions with sulphur compounds in solution is provided here as well.

Speciation data for chromium in tobacco products, as obtained by complementary HPLC-ICP-MS and synchrotron-based X-ray Absorption Near-Edge Structure spectroscopy (XANES), are presented for the first time. Non-denaturing extraction conditions were investigated to avoid Cr species redox inter-conversion before analysis of extracts using HPLC-ICP-MS. Methodology based on HPLC-ICP-MS, which is compatible with the extraction conditions, was developed for separation and detection of inorganic Cr species such as Cr(III) and Cr(VI) in aqueous standard solutions. The instrumental limits of detection (3σ criterion) obtained for Cr(III) and Cr(VI) were 0.12 and 0.08 ng g−1 Cr, respectively. The total Cr extracted from 3R4F cut tobacco with water was around 10% of the total Cr in the solid (1949 ± 171 ng g−1 of Cr on a dry weight basis), with 75% of the aqueous Cr associated with species of molecular mass > 3 kDa. Cr(III) was the main identified species in the tobacco extracts using HPLC-ICP-MS, whilst Cr(VI) could not be detected. In situ XANES analysis revealed that the cut tobacco from 3R4F reference cigarettes contained only Cr(III). Following leaching with water, leaching with sodium dodecylsulfate (SDS) on the solid residue led to extraction of a further 10% of the Cr contained in the solid tobacco. The total Cr data obtained by ICP-MS for HNO3 and HNO3/HF acid digests of 3R4F cut tobacco suggested that additional 12% of the total Cr in the solid appears to be associated with silicates, which are known to occur naturally in tobacco products. Although Cr species could not be detected in water leachates from 3R4F smoke condensates using the HPLC-ICP-MS method developed here, XANES measurements identified Cr(III) as the main Cr species present in cigarette smoke condensate, with no detectable Cr(VI). HPLC-ICP-MS data obtained for smoke condensates from cigarettes spiked with Cr(III) before smoke collection revealed that Cr(III) is the main Cr species in present the water soluble fraction of the condensate. Spiking experiments demonstrated that Cr(VI) was highly unstable in trapped smoke condensate. In this work no evidence was observed for the presence of Cr(VI) in mainstream smoke generated from 3R4F cigarettes.

High accuracy procedures for the determination of arsenic are needed for assigning reference values to certified reference materials (CRMs). There are a number of problems associated with the determination of total arsenic by inductively coupled plasma–mass spectrometry. Arsenobetaine (AsB) (the major species in fish) gives an enhanced response (9%) when compared to inorganic arsenic(V) and is very difficult to decompose. Chloride causes interference at m / z 75 by the formation of ArCl + and chloride levels can be significant in marine fish. Also residual carbon in digests can lead to enhancement of arsenic signals by charge transfer effects. This can easily lead to erroneous quantification when compared to standards that do not contain carbon. This newly developed procedure overcomes these issues by complete mineralisation of the matrix leaving insignificant amounts of residual carbon and by removal of chlorine by evaporation. A detection limit of 30 ng/g was achieved. Recoveries for the following CRMs: DORM 2 100.1 ± 4.3%, SRM1548 96.1 ± 4.6%, BCR 422 103.6 ± 6.2% and SRM2976 105.9 ± 6.2% were obtained. The digestion procedure uses open vessel wet digestion with a mixture of sulfuric and nitric acid held at 300 °C. The decomposition of AsB was confirmed by speciation analysis of the digest. Carbon ( m / z 13) was monitored to demonstrate the efficiency of the digestion. Instrumentation for the reduction of ArCl + interference was not required and this view is supported by the recovery data. Measurements were performed by external calibration using tellurium as an internal standard.

Size-exclusion, anion-exchange and reversed-phase ion-pair (RP-IP) HPLC were used in combination with ICP-(Q)MS for selenium (Se)-specific detection and quantitation of Se-compounds in extracts of Se-yeast and Se-methylselenocysteine (SeMC) based supplements. On-line electrospray ionisation (ESI)-MS/MS combined with RP-IP HPLC allowed characterisation of such materials in terms of species identification. Accelerated solvent extraction (ASE) was evaluated for extraction of the Se-compounds from the complex matrices in water. Alternatively, digestion with proteolytic enzymes was used for yeast protein hydrolysis. The use of ultrasonic nebulisation in combination with HPLC-ICP-(Q)MS for Se speciation led to detection limits up to six-fold lower (as low as ng l−1 levels) than those obtained with pneumatic nebulisation. Such enhancement of the ICP-MS capabilities for Se detection, combined with an improved separation using the newly developed RP-IP-HPLC method, allowed quantification of minor Se species such as SeMC in yeast extracts. Identification of the main compounds in yeast and SeleniumMC™ tablet hydrolysates as SeMet and SeMC, respectively, was accomplished by on-line RP-IP HPLC with ESI-MS/MS. Identification of SeMC in yeast digests, on the basis of retention time, molecular mass determination for the [M + H]+ 80Se ions (m/z 184) and detection of its product ions, is reported here for the first time. The mass spectral confirmation for SeMC in yeast is of interest, as this species is believed to be metabolised in animals and humans to methylselenol (CH3SeH), an anti-carcinogenic Se-metabolite.

cited By 12; International audience; Six metrology institutes (NMIs) representing at the Comité International des Poids et Mesures (CIPM) 4 Member States of the Metre Convention and 2 international organisations, and 8 "expert" laboratories selected outside CIPM have compared their capabilities to quantitatively measure methylmercury (MeHg) in a prepared tuna material containing approximately 4.3 mg kg-1 Hg. This comparison was the object of the CIPM-Comité Consultatif pour la Quantité de Matière (CCQM) Pilot Study 39, organised by the Institute for Reference Materials and Measurements (IRMM), from the European Commission - Joint Research Centre. Beside the test material itself, a bottle of the BCR-464 tuna Certified Reference Material (CRM) and an ampoule of IRMM-670, a 202Hg isotope enriched MeHg candidate isotopic CRM, were distributed to all participants, who were free to apply the measurement strategy of their choice. Four, including 1 NMI, relied on external calibration or the method of standard additions, whereas the other 10 implemented an isotope dilution mass spectrometry (IDMS) approach and chose to use the IRMM-670 for their measurements. Alkaline digestion at room temperature (with manual shaking) or high temperature (under sonication, oven or hot plate conditions) was employed by most participants, with hydrochloric acid leaching the second most popular choice. Alkylation (4 phenylations, 4 ethylations and 3 propylations) in the aqueous phase was preferred by a large majority over butylation by the Grignard reaction. All participants were requested to estimate the uncertainty associated with their results and 9 out of 14 stated relative combined uncertainties below 6% (k = 2). Despite this apparent consensus, the perception of which factor caused the largest contribution to this estimation differed among participants because of the differences in the analytical methodologies deployed but also because of wide differences of the concepts of uncertainty estimation. The 'mixture mode' (MM) median, calculated also from the measurement uncertainties stated by the participants, was 1.967 ± 0.204 × 10-5 mol kg -1 (95% confidence). Twelve of the results were re-grouped within a range of less than 0.3 × 10-5 mol kg-1 (MM median = 1.967 ± 0.162 × 10-5 mol kg-1, 95% confidence): they nearly all (1 exception) overlapped with each other within k = 2 stated uncertainties. For the other 2 results the uncertainty seemed to have been particularly underestimated as they lay, respectively, at more than 20% above and less than -40% below the overall average. The relative standard deviation of the results of 9 laboratories out of the 10 that applied IDMS was about 2.6%. It can be assumed from the degree of equivalence shown by 12 out of 14 study participants that, at present, laboratories worldwide are potentially able to supply accurate results for MeHg in fish-type matrices (containing about 2 × 10-5 mol kg-1) within ± 10% uncertainty. This encouraging outcome permitted scheduling of a follow-up CCQM-K43 key comparison for a lower MeHg content level in salmon tissues. © The Royal Society of Chemistry 2005.