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 1, 2008

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

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

Pub Type

Journals

Keywords

complexation, demethylation, double spike, GC/ICP-MS, mercury, methylation, methylmercury, speciation, SRM

Citation

Point, D. , Garcia, J. , Davis, W. , Christopher, S. , Guichard, A. , Donard, O. , Becker, P. , Turk, G. and Wise, S. (2008), 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, Journal of Analytical Atomic Spectrometry (Accessed April 19, 2024)