A capacitively coupled conductivity detector for electroseparations

A conductivity detector providing high-voltage isolation for electroseparat ions; is described. It is based on an oscillator which is capacitively coup led to the measurement electrodes: the conductance between the electrodes d etermines the output frequency. The detector was evaluated using a small-vo lume (500 nl) conductivity cell (cell constant 5.1 x 10(3) m(-1)) which is described. It was then characterized using a factorial method and optimized to maximize the sensitivity (absolute change in frequency) to changes in c onductivity. A novel method was used to determine the cell constant for a pair of microb and electrodes (100 mu m across on 200 mu m centres) with electrolyte confi ned in a fine channel above them-this was 2615 +/- 86 m(-1) and the detecto r has been used with this cell for isotachophoretic separations reported el sewhere.