Capillary column gas chromatography for mercury speciation

The determination of methyl- and ethylmercury halides in environmental and biological samples typically involves gas chromatography with electron-capture detection. However, these organomercury halides are notorious for their poor chromatographic characteristics (severe tailing, decomposition, low column efficiencies) on packed columns. The problems can be temporarily alleviated by column passivation using a concentrated organic solution of mercury(II) chloride. Attempts to use capillary columns instead, to improve the chromatographic behaviour of organomercury halides, have met with mixed success, and the results presented generally show poorer performance than that obtained using packed columns, even after passivation. To eliminate the problem at its source (the polar mercury-halide bond), it is proposed to butylate the mercury species with a Grignard reagent to yield the non-polar dialkyl derivatives. As the electron-capturing halide moiety is absent from these derivatives, mercury-specific detection is necessary, and a microwave-induced plasma emission detector is utilized. In combination with capillary gas chromatography, unprecedented column and separation efficiencies for methyl- and ethylmercury are achieved. The practical utility of the method is illustrated in a preliminary application to the determination of mercury species in a fish tissue reference material after extraction and butylation.