DETERMINATION OF METHYLMERCURY IN FISH AND RIVER WATER SAMPLES USING IN-SITU SODIUM TETRAETHYLBORATE DERIVATIZATION FOLLOWING BY SOLID-PHASE MICROEXTRACTION AND GAS-CHROMATOGRAPHY MASS-SPECTROMETRY

A solid-phase microextraction (SPME) analytical procedure is described for the quantitative determination of methylmercury and labile Hg2+ in fish and river water matrices. The analytical procedure involves aqueous-phase derivatization of ionic mercury species with sodium tetraethylborate in a sample vial and subsequent extraction with a silica fiber coated with poly(dimethylsiloxane). The mercury derivatives are desorbed in the splitless injection port of a gas chromatograph and subsequently analyzed by electron impact mass spectrometry. Both headspace SPME and aqueous-phase SPME are studied, and the linear range of the method spans several orders of magnitude for both procedures. The detection limits of the headspace SPME procedure for a 20-ml sample are 7.5 and 3.5 ng/l as Hg for CH3Hg+ and Hg2+, respectively. The detection limits of aqueous-phase SPME for a 1.5-ml sample are 6.7 and 8.7 ng/l as Hg for CH3Hg+ and Hg2+, respectively. Analyses of standard reference materials and river water sample demonstrate the suitability of this method for the determination of methylmercury and labile Hg2+.