Conductivity Detection In Capillary Electrophoresis Research Articles

Contactless Conductivity Detection for Capillary Electrophoresis

A contactless capacitively coupled conductivity detector for capillary electrophoresis is introduced. The detector consists of two electrodes which are placed cylindrically around the outer polyimide coating of the fused-silica capillary with a detection gap of 2 mm. The electrodes form a cylindrical capacitor, and the electric conductivity of the solution in the gap between the electrodes is measured. A high audio or low ultrasonic frequency for coupling of the ac voltage is used in order to minimize the influence of reactance of the liquid. For an improved version of the detector, two syringe cannulas are used as the electrodes and the capillary is simply assembled into the tubing. This allows an easy placement of the detector on various positions along the capillary. The limit of detection of inorganic cations and anions is 200 ppb, as determined for sodium and chloride, respectively.

Characteristics and Calibration of Conductivity Detection in Capillary Electrophoresis

The characteristics of end-column conductivity detection in capillary electrophoresis are investigated using solutes and background electrolytes that possess a range of mobilities. Indirect detection is most sensitive for low- to medium-mobility solutes. Detection limits are 1 × 10 -6 M for hexane sulfonate, and the response is linear for over two orders of magnitude. A generalized response expression is developed for conductivity detection based on the similarities in conductivity and electrophoretic mobility.