The effects of the electrode system geometry on the properties of contactless conductivity detectors for capillary electrophoresis

The basic analytical parameters of contactless conductivity detectors with planar, semi-tubular and tubular electrodes have been compared. It has been found that the differences in the analytical parameters of the detectors are not significant for analytical use. The mean values of baseline peak-to-peak noise of 0.27, 0.35 and 0.33 mV, sensitivities of 0.97, 2.08 and 2.27 mV/pg (for K+ ion), limits of detection of 0.93, 0.65 and 0.53, and the heights equivalent to a theoretical plate of 2.83, 2.39 and 2.40 mu m were obtained for the detectors with planar, semi/tubular and tubular electrodes, respectively. Modifications of the basic detectors, namely a detector with thinned capillary wall and planar electrodes, and a detector with semi-tubular electrodes placed one against the other on the opposite sides of the capillary were also tested. ne configuration with the electrodes placed one against the other permits detector construction with zero gap between the electrodes without increasing the noise; when the electrodes overlap, the detector begins to operate as a permittivity detector.