Speciation of mercury compounds by capillary electrophoresis coupled on-line with quadrupole and double-focusing inductively coupled plasma mass spectrometry

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Abstract
The development and analytical characterization of capillary electrophoresis (CE) coupled on-line with both quadrupole (Q) and double focusing (DF) inductively coupled plasma mass spectrometry (ICP-MS) for the separation and determination of three chemical species of Hg (CH3CH2Hg+, CH3Hg+ and Hg2+) are described. The Hg compounds are separated as mercury–cysteine complexes by capillary zone electrophoresis in a 100 cm × 75 µm id fused silica capillary at 20 kV and using a 20 mM sodium tetraborate decahydrate buffer (pH = 9.3). At relatively high concentrations (parts per million level), the determination of these compounds can be carried out by means of UV detection. However, the determination of low mercury concentrations (parts per billion level) can be achieved only by coupling to ICP-MS detection. To accomplish this coupling a conventional concentric nebulizer has been used. The optimization of the CE-ICP-MS interface operation parameters as well as sample stacking conditions of the analytes are discussed. The analytical performance characteristics of the developed CE-ICP-MS methodology have been evaluated and limits of detection were 4 and 7 µg l−1 (as Hg) for inorganic mercury and methylmercury, respectively. Such low levels for this CE technique are achieved via sample stacking and the use of DF-ICP-MS at low resolution for specific mercury detection.