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 proced ure 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 extractio n. The results show that spurious MeHg+ formation from Hg2+ can occur mainl y in the chromatographic column during the determination step rather than d uring 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 th e analysis. On the other hand, the production of several unknown peaks, clo sely corresponding to Me2Hg, Et2Hg etc. in the chromatogram, is the result of impurities in the derivatizing agent, NaBEt4. The magnitude of these int erferences varies with different lots of reagent. The derivatization and de termination steps must always be checked following standard QA/QC procedure s. Once interference problems are taken into account, reliable understandin g of Hg cycling and behaviour in aquatic environments will be achieved. (C) 1999 Elsevier Science Ltd. All rights reserved.