Micro- scale preparation of isotopically enriched monomethylmercury (MM201Hg)

Abstract

A simple and fast synthesis method for the micro-scale laboratory preparation of
isotopically enriched monomethylmercury (MMHg) which is not commercially available has
been evaluated and established successfully. This enriched solution is an important standard
for species-specific isotope dilution mass spectrometry analysis (SSIDMS) for determination
of the true concentration of methylmerury in biological (hair) and environmental samples
(soil and sediment). The isotopically enriched MMHg has been synthesised from inorganic
standard solution prepared from commercially available mercury oxide (201HgO) using
methylcobalamin co-enzyme as methylation agent. The synthesis time required is 1 h at
37°C. The product is highly pure, yielded more than 95% as201Hg in MMHg. The proposed
method is allows control of unintentional formation of health hazard dimethylmercury. It is
also allows work on a micro-scale to control the use of expensive enriched isotope standard.
The synthesised product was analysed using capillary gas chromatography (CGC) coupled
with inductively coupled plasma mass spectrometry (ICP-MS) after derivatisation with
sodium tetraethylborate (NaBPr4). The concentration, purity, isotopic composition and
stability of synthesized, enriched MMHg have been investigated in order to establish standard
protocols for MMHg isotope dilution analysis.