SPECIATION OF MERCURY AT NG ML CONCENTRATION LEVELS BY CAPILLARY ELECTROPHORESIS WITH AMPEROMETRIC DETECTION/

A technique based on capillary electrophoresis and amperometric detect ion (CE-AD) has been developed for the speciation of mercury. This tec hnique has the unique capability to detect only cationic mercury speci es that are electrochemically active. Capillary electrophoresis with e lectrokinetic injection allows efficient separation of inorganic mercu ry and organomercury cations in 8 min. Selective detection of these el ectrochemically active species is attained by controlling the reductio n potential applied on the micro-electrode. For Hg2+, an optimal poten tial of -0.2 V can be used to prevent interference by less electroacti ve toxic metals and other substances found in complex environmental sa mples. The amperometric signal is linearly proportional to the Hg2+ co ncentration over three orders of magnitude, with a detection limit of 0.2 ng/ml. The mass detection limit corresponds to 8 fg of Hg2+ in an injection volume of 40 nl. For CH3Hg+, the detection limit is 3 ng/ml when a potential of -0.5 V is used. These detection sensitivities are attractive for environmental monitoring of contaminated sediments in e cosystems. Steam distillation is evaluated for the extraction of CH3Hg + from the sediment matrix. It yields an unknown mercury species which is unsuitable for CE-AD determination under the specified conditions. (C) 1998 Elsevier Science B.V.