Electronic protection methods for conductivity detectors in micro capillary electrophoresis devices

Two level shifting methods are presented to protect the contactless conductivity detector in a micro capillary electrophoresis (CE) device. In the separation channel of a micro CE device an electrical potential is present at the detector area. The conductivity detector with read-out electronics is referenced to ground potential. The potential difference between separation channel and detector causes, at a high enough value (here 2 V), breakthrough of the insulating layer on the detector. By shifting the potential of either the conductivity detector or the separation voltage-supply the difference between the detector electrode potential and the channel potential at the detector area is cancelled. For this compensation system an electrode is integrated in the channel, near the detector, to measure the channel potential. By compensating for the potential difference between the channel and the contactless detector, lower requirements are put on the breakthrough voltage of the insulating layer. This enables thinning of the insulating film on the conductivity detector, which improves the performance of the contactless conductivity detector and, hence, the overall system performance. Measurement results of the voltage probe are presented as well as breakthrough voltage measurements of the SiC insulating film covering the conductivity detector. (C) 2002 Elsevier Science B.V. All rights reserved.