Potential interferences generated during mercury species determination using acid leaching, aqueous ethylation, cryogenic gas chromatography and atomic spectrometry detection techniques

A careful search for formation of methylmercury (MeHg+) as an artefact and for potential interferences has been carried out using an analytical procedure involving aqueous phase ethylation, cryogenic trapping, low temperature gas chromatography and quartz furnace atomic absorption spectrometry (Eth-CT-GC-QFAAS) for mercury speciation, after open-focused microwave extraction. The results show that spurious MeHg+ formation from Hg2+ can occur mainly in the chromatographic column during the determination step rather than during the extraction step. The silanizing agent, dimethyldisilazane, acting as a methyl donor, appears to be responsible for the EtMeHg formation when high concentrations of Hg2+ (>1 ppm) are present in the solution during the analysis. On the other hand, the production of several unknown peaks, closely corresponding to Me2Hg, Et2Hg etc. in the chromatogram, is the result of impurities in the derivatizing agent, NaBEt4. The magnitude of these interferences varies with different lots of reagent. The derivatization and determination steps must always be checked following standard QA/QC procedures. Once interference problems are taken into account, reliable understanding of Hg cycling and behaviour in aquatic environments will be achieved.