Capillary electrophoresis for trace metal ion analysis in environmental studies

Abstract

A new buffer system consisting of 30 mM hydroxylamine hydrochloride, 0.1 mM 1,10-phenanthroline, 1% methanol and pH 3.7 was optimized for simultaneous determination of water and acid leachable metals from respirable, fine and coarse air particulate matters. A reducing environment was used to resolve metal ions with variable oxidation states. A suitable counteranion was employed to enable acidic pH to be used and methanol was added to improve the resolution of the electropherograms and to achieve simultaneous determination of several metal ions. Compared to existing capillary electrophoresis (CE) buffers, the buffer developed, based on direct UV detection of ion-pair with weak interaction, gives improved resolution and sharper, more stable and well-resolved peaks. It detects total irons and solves interfering problems due to the variable oxidation states of iron in environmental samples. Compared to existing mostly alkaline CE buffers for metal analysis, the acidic nature of the buffer system developed makes the pretreatment step simpler and reduces the risk of reagent contamination. Satisfactory working ranges (15—5500 ppb) and detection limits (0.5—3 ppb) were obtained for leachable Zn, Cu, Co, Fe and Cd. The NIST 1648 urban particulate matters were found to leach out 2.53—42.8% water-extractable and 2.76—71.7% acid-extractable Zn, Cu, Fe and Cd. High iron contents, and lower copper and zinc concentrations were found in respirable suspended particulates (RSP) sampled in Hong Kong.