Abstract

The development and analytical characterisation of an on-line coupled capillary electrophoresis (CE)-volatile species generation (VSG)-inductively coupled plasma mass spectrometry (ICP-MS) system for the separation and determination of different species of mercury is described. The mercury species studied (inorganic mercury, methylmercury and ethylmercury) are separated as mercury–cysteine complexes by capillary zone electrophoresis (CE) in a 100 cm × 75 µm id fused silica capillary at 25 kV and using a 20 mM sodium tetraborate decahydrate buffer (pH = 9.3). The detection is carried out on-line by both quadrupole (Q) and double focusing (DF) ICP-MS using a VSG system with NaBH₄ reduction as the sample introduction device. The CE-VSG-ICP-MS interface construction provides an electrical connection for stable electrophoretic separations and allows on-line volatile species formation, these being separated from the liquid in a gas–liquid separator, allowing for final transport of the volatile analyte derivatives into the plasma. Characterisation and optimization of operation parameters of this interface are discussed. The analytical performance characteristics of the developed CE-VSG-ICP-MS methodology were evaluated and detection limits in the low µg l⁻¹ range were achieved. The accuracy of the method has also been checked by analysing a certified biological reference material (DOLT-2) with satisfactory results.