A thin hydrophilic strip of cellophane is attached to the tip of the separation capillary so that the solution flowing from the capillary passes through the strip to the solution in tbe outlet vial. The conductivity of the strip is measured between a metallic contact to the strip and an auxiliary platinum electrode placed in the outlet vial solution. An interference of the measured signal with a separation electric field coming out from the capillary is eliminated in this arrangement. The detector was employed in determining potassium and sodium ions in mineral waters.