EVALUATION OF ULTRAMICROELECTRODES FOR THE DETECTION OF METAL-IONS SEPARATED BY CAPILLARY ELECTROPHORESIS

Carbon-fiber, platinum, gold, and mercury films deposited on a gold substrate were evaluated for amperometric detection of metal ions under constant- and pulsed-voltage conditions. The carbon electrodes were rods 10 mum X 250 mum long, and the other electrodes were disks 10-25 mum in diameter. Detector response was not reproducible for solid electrodes operated under constant voltage, but was considerably improved for mercury film electrodes. Detection of 14 test metal ions separated in a 25-mum capillary gave detection limits in the range of 10 amol to 50 fmol without removal of background signal from oxygen. Long-term reproducibility of the mercury electrodes was limited to the reproducibility of the procedures used for renewal of the mercury film, approximately 5%. An evaluation of pulsed stripping at gold and carbon-fiber electrodes showed that the solid electrode surfaces were reproducibly (<2% variation) conditioned by the pulse train, even when operated continuously in relatively high concentrations (10(-4) mol/L).