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Publication Citation: Consideration and Influence of Complexed forms of Mercury Species on the reactivity Patterns Determined by Speciated Isotope Dilution Model Approaches: A Case for Natural Biological Reference Materials

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Author(s): David Point; J. I. Garcia Alonso; William C. Davis; Steven J. Christopher; Aurore Guichard; O.F. X. Donard; Paul R. Becker; Gregory C. Turk; Stephen A. Wise;
Title: Consideration and Influence of Complexed forms of Mercury Species on the reactivity Patterns Determined by Speciated Isotope Dilution Model Approaches: A Case for Natural Biological Reference Materials
Published: June 01, 2008
Abstract: The origins and the processes driving the inadvertent transformations of inorganic mercury (iHg) and methylmercury (MeHg) in cryogenically stored and homogenized fresh-frozen versus freeze-dried biological Standard Reference Materials (SRM) were investigated using alkaline digestion, derivatization and GC/ICP-MS analysis. Labile enriched 201iHg and 202MeHg isotopic standards together with their cysteine-complexed molecular analogs (201Hg(Cys)2 and 202MeHgCys) were used in a double spike speciated isotope dilution (SID) model to study the role and influence of the complexing ligands/radicals originally associated with mercury species in these materials, on the equilibration, the reactivity and the transformation processes of mercury species. The results revealed that a negligible methylation occurred in both materials, whereas a significant demethylation yield was only detected in the cryogenically stored fresh-frozen materials. Systematic investigation revealed that this apparent demethylation yield, as given by the double-SID model, resulted from the possible influence of demethylating agents, which seem to be inhibited using tetrapropylborate as an alternative derivatizating agent, compared to tetraethylborate. However, a significant fraction of the demethylation yield was found to be potentially biased and resulted from a lack of equilibration between labile spiked iHg species and their endogenous analogs, indicating probable different complexation/lability patterns in the FF material after the extraction step. This effect was not observed in the FD material. A complementary analytical step to account for and to minimize the effect of this competing-ligand complexation process is proposed, which allows the two classes of materials to be denoted as commutable.
Citation: Journal of Analytical Atomic Spectrometry
Volume: 23
Issue: 3
Pages: pp. 385 - 396
Keywords: complexation;demethylation;double spike;GC/ICP-MS;mercury;methylation;methylmercury;speciation;SRM
Research Areas: Organic Analytical Chemistry, Pollution/Indoor Air Quality, Marine Health, Environment/Climate, Chemistry