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 inorgani c mercury. Methyl-, ethyl- and inorganic mercury are first preconcentr ated on a dithiocarbamate resin packed in a miniature 60 mul column in corporated in a closed and semi-automated flow injection system. The m ercury species, which are quantitatively enriched on the resin, are co mpletely eluted with an acidic thiourea solution, extracted into tolue ne as diethyldithiocarbamate complexes and butylated with a Grignard r eagent. The butylated forms (2-40 mul) are injected into a gas chromat ograph equipped with a retention gap, linked to a non-polar analytical column, and detected at 253.7 nm with an atomic emission detector aft er excitation in a microwave-induced plasma.