Experimental characterization of end-column electrochemical detection in conjunction with nonaqueous capillary electrophoresis

Abstract

An end-column electrochemical detector arrangement for capillary electrophoresis (CE) based on a 75-microm-i.d. capillary and a 25-microm microdisk electrode is characterized. The investigations were carried out using a nonaqueous (acetonitrile-based) buffer and ferrocene model compounds which offer high reliability for voltammetric measurements. The positioning of the microdisk electrode relative to the capillary outlet is the most important parameter for optimization of detection performance as it determines the characteristics of mass transport toward the electrode and the effect of ohmic potential drop resulting from the electrophoretic current on the actual detection potential. On the basis of spatially resolved studies, it was concluded that for the detection system used the microdisk electrode should be placed in a central position relative to the capillary outlet at a distance within the range of 75-100 microm. The presence of a high-voltage electric field had no negative effect on baseline noise, which was demonstrated by comparison of capillary flow injection based on gravity flow and CE experiments. Even a faster stabilization of the baseline was observed by increasing the separation voltage.