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Mercury speciation analysis of both inorganic and methyl Hg in ultrapure and natural waters by purge-and-trap gas chromatography pyrolysis atomic florescence spectrometry (PT-GC-Pyr-AFS, MERX-M, Brooks Rand) was performed. This automated analytical setup was also compared with gas chromatography inductively coupled plasma mass spectrometry (GC-ICPMS, X Serie 2 ThermoFisher). In addition, a reagent cleaning step of the buffer solution and derivatizing reagents (NaBEt4 and NaBPr4) was evaluated to improve the detection limit of the method. PT-GC-Pyr-AFS experiments analyzing Milli-Q and Deionized water (Millipore) using cleaned reagents and quantifying by external calibration led to MeHg+ and Hg2+ concentration values significantly lower than those obtained using uncleaned reagents. The limit of detections (LODs) after cleaning was found significantly low using both NaBEt4 and NaBPr4. However, the lowest LODs were obtained when using cleaned NaBPr4 (range: 1–2 pgL–1 for MeHg+ and 9-10 pgL–1 for Hg2+). Matrix effects have been finally investigated using both PT-GC-Pyr-AFS and GC-ICPMS to characterize and quantify potential interferences in natural water samples with different salinities and organic matter contents, including coastal water reference material (CRM) certified for total mercury concentration (IRMMBCR-579).

A rapid, accurate, sensitive, and simple method for simultaneous speciation analysis of mercury and tin in biological samples has been developed. Integrated simultaneous sample preparation for tin and mercury species includes open focused microwave extraction and derivatization via ethylation. Capillary gas chromatography-inductively plasma mass spectrometry (CGC-ICPMS) conditions and parameters affecting the analytical performance were carefully optimized both for species-specific isotope dilution analysis of MMHg and TBT and for conventional analysis of MBT and DBT. [sup.201]Hg-enriched monomethylmercury and [sup.117]Sn-enriched tributyltin were used for species-specific isotope dilution mass spectrometry (SIDMS) analysis. As important, accurate isotope dilution analysis requires equilibration between the spike and the analyte to achieve successful analytical procedures. Since the spike stabilization and solubilization are the most critical and time-consuming steps in isotope dilution analysis, different spiking procedures were tested. Simultaneous microwave-assisted spike stabilization and solubidization can be achieved within less than 5 min. This study originally introduces a method for the simultaneous speciation and isotope dilution of mercury and tin in biological tissues. The sample throughput of the procedure was drastically reduced by fastening sample preparation and GC separation steps. The accuracy of the method was tested by both external calibration analysis and species-specific isotope dilution analysis using the first biological reference material certified for multielemental speciation (oyster tissue, CRM 710, IRMM). The results obtained demonstrate that isotope dilution analysis is a powerful method allowing the simultaneous speciation of TBT and MMHg with high precision and excellent accuracy. Analytical problems related to low recovery during sample preparation are thus minimized by SIDMS. In addition, a rapid procedure allows us to establish a performant routine method using CGC-ICPMS technique.

Speciated isotope-dilution mass spectrometry (SID-MS) is claimed to be an absolute method; however, it has been found to be affected by artifact monomethylmercury (MMHg) formation in sediments. The determination of MMHg in sediments was carried out by SID-MS after open-focused microwave extraction. The extracted mercury species were then ethylated and separated by capillary gas chromatography (CGC). Isotope ratios (peak area ratios at different masses) were measured by on-line ICPMS detection of the CGC-separated compounds. Reproducibility of [sup.202]Hg/[sup.201]Hg isotope ratio measurements were 0.60% for MeEtHg and 0.69% for [Et.sub.2]Hg; for [sup.202]Hg/[sup.199.Hg], 0.43 and 0.46%, respectively, were determined. The absolute detection limits for CGC-ICPMS measurements were better than 26 fg for [sup.202]Hg, 20 fg for [sup.201]Hg, and 24 fg for [sup.199]Hg. For the direct determination of MMHg in sediment reference materials (CRM 580, IAEA 356, and IAEA 405), higher values than the certified were always found. Systematic experiments were carried out to localize the sources of the unintentional abiotic methylmercury formation during analysis. Different spiking and derivatization procedures (either ethylation, propylation, or derivatization by Grignard reagents) were tested. In addition, isotopically enriched inorganic mercury was spiked. The amount of inorganic mercury initially present in the sample was found to be the critical factor that should be known and carefully controlled. A simple solvent extraction technique involving no critical cleanup steps was applied in order to reduce high [Hg.sup.2+] amounts. The method was applied to the determination of MMHg in sediment reference material IAEA-405 with satisfactory results after organic solvent extraction. The limitations of applicability of the proposed method are evaluated as related to inorganic mercury, organic carbon, and sulfur contents. The results obtained confirmed that available sediment reference materials are adequate to achieve traceable mercury speciation analysis and to detect potential sources of MMHg artifact formation.

Methylation and demethylation represent major transformation pathways regulating the net production of methylmercury (MMHg). Very few studies have documented Hg reactivity and transformation in extreme high-altitude lake ecosystems. Mercury (Hg) species concentrations (IHg, MMHg, Hg°, and DMHg) and in situ Hg methylation (M) and MMHg demethylation (D) potentials were determined in water, sediment, floating organic aggregates, and periphyton compartments of a shallow productive Lake of the Bolivian Altiplano (Uru Uru Lake, 3686 m). Samples were collected during late dry season (October 2010) and late wet season (May 2011) at a north (NS) and a south (SS) site of the lake, respectively. Mercury species concentrations exhibited significant diurnal variability as influenced by the strong diurnal biogeochemical gradients. Particularly high methylated mercury concentrations (0.2 to 4.5 ng L for MMHg) were determined in the water column evidencing important Hg methylation in this ecosystem. Methylation and D potentials range were, respectively, <0.1-16.5 and <0.2-68.3 % day and were highly variable among compartments of the lake, but always higher during the dry season. Net Hg M indicates that the influence of urban and mining effluent (NS) promotes MMHg production in both water (up to 0.45 ng MMHg L day) and sediment compartments (2.0 to 19.7 ng MMHg g day). While the sediment compartment appears to represent a major source of MMHg in this shallow ecosystem, floating organic aggregates (dry season, SS) and Totora's periphyton (wet season, NS) were found to act as a significant source (5.8 ng MMHg g day) and a sink (−2.1 ng MMHg g day) of MMHg, respectively. This work demonstrates that high-altitude productive lake ecosystems can promote MMHg formation in various compartments supporting recent observations of high Hg contents in fish and water birds. [ABSTRACT FROM AUTHOR]