A capacitively coupled conductivity detector for electroseparations

A conductivity detector providing high-voltage isolation for electroseparations is described. It is based on an oscillator which is capacitively coupled to the measurement electrodes; the conductance between the electrodes determines the output frequency. The detector was evaluated using a small-volume (500 nl) conductivity cell (cell constant 5.1 × 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 conductivity. A novel method was used to determine the cell constant for a pair of microband electrodes (100 μm across on 200 μm centres) with electrolyte confined in a fine channel above them - this was 2615 ± 86 m -1 and the detector has been used with this cell for isotachophoretic separations reported elsewhere.