CONTACTLESS CONDUCTIVITY DETECTION FOR CAPILLARY ELECTROPHORESIS

A contactless capacitively coupled conductivity detector for capillary electrophoresis is introduced. The detector consists of two electrode s which are placed cylindrically around the outer polyimide coating of the fused-silica capillary with a detection gap of 2 mm. The electrod es form a cylindrical capacitor, and the electric conductivity of the solution in the gap between the electrodes is measured. A high audio o r low ultrasonic frequency for coupling of the ac voltage is used in o rder to minimize the influence of reactance of the liquid. For an impr oved version of the detector, two syringe cannulas are used as the ele ctrodes and the capillary is simply assembled into the tubing. This al lows an easy placement of the detector on various positions along the capillary. The limit of detection of inorganic cations and anions is 2 00 ppb, as determined for sodium and chloride, respectively.