Study of the Operating Conditions for a Referenced Contactless Conductivity Detector for Capillary Zone Electrophoresis

The capacitively coupled contactless conductivity detector features a reference channel for the suppression of the signal caused by the background conductivity and high voltage excitation for a good signal-to-noise ratio. It has a built-in high resolution analog-to-digital convertor, and the numerical signal is passed to an attached personal computer via a universal serial bus. There the readings are plotted and can be saved in a file. The operating frequency (200-1000 kHz), as well as the excitation amplitudes (100-350 V) of the signal and reference channels can be set independently by the user. This allowed a detailed evaluation of the influence of the individual sensitivities of the two channels on the electropherograms, and it is demonstrated that corrupt signals may be obtained for a referenced detector unless the working conditions are controlled appropriately. Detection limits of about 5 µM were obtained for small inorganic cations.