VOLTAMMETRIC DETECTION FOR CAPILLARY ELECTROPHORESIS

Several approaches to implementing amperometric detection for capillar y electrophoresis have been reported. This report describes the develo pment of a voltammetric detector for CE. The detector is designed to m inimize distortion of the voltammetry due to ohmic potential drop. Thi s was accomplished by using a cast Nafion detection cell at the end of the separation capillary. The cast Nafion detection cell provided a l ow-dead-volume, low-resistance cell that minimized ohmic potential dro p and peak band broadening. The ability to detect the current due to o xidation of analytes superimposed on a large background current was al so improved. A dynamic background subtraction scheme was used in which a second working electrode, positioned in the electrochemical cell bu t outside of the detection cell, was used to compensate for the backgr ound current in realtime. The output of the compensating working elect rode was subtracted from the output of the detecting working electrode prior to analog-to-digital conversion. Postexperimental digital backg round subtraction was also implemented. This approach provided optimal elimination of the background current with maximal detection of the a nalytical signal. The voltammetric detector developed produced high-qu ality voltammetric response of analytes with injected concentrations a s low as 0.20 mu M. The system was evaluated by obtaining CE voltammog rams of a mixture of eight test phenolic acids.