SPECIATION OF MERCURY IN NATURAL-WATERS BY CAPILLARY GAS-CHROMATOGRAPHY WITH A MICROWAVE-INDUCED PLASMA EMISSION DETECTOR FOLLOWING PRECONCENTRATION USING A DITHIOCARBAMATE RESIN MICROCOLUMN INSTALLED IN A CLOSED FLOW-INJECTION SYSTEM

A method for the simultaneous determination of mercury species at sub-ng l-1 levels in natural waters is described. The detection limits are 0.05 ng l-1 for methyl- and ethylmercury and 0.15 ng l-1 for inorganic mercury. Methyl-, ethyl- and inorganic mercury are first preconcentrated on a dithiocarbamate resin packed in a miniature 60 mul column incorporated in a closed and semi-automated flow injection system. The mercury species, which are quantitatively enriched on the resin, are completely eluted with an acidic thiourea solution, extracted into toluene as diethyldithiocarbamate complexes and butylated with a Grignard reagent. The butylated forms (2-40 mul) are injected into a gas chromatograph equipped with a retention gap, linked to a non-polar analytical column, and detected at 253.7 nm with an atomic emission detector after excitation in a microwave-induced plasma.