Design of an electronic interface for capacitively coupled four-electrode conductivity detection in capillary electrophoresis microchip

In this paper, we present an electronic interface dedicated to capacitively coupled four-electrode liquid conductivity detection in micro capillary electrophoresis devices. Due to the small dimensions of the detector (106 μm×170 μm), it is necessary to adapt the read-out interface. Our study focuses on two major aspects of the four-electrode setup: First, the current which flows between the two outer electrodes must be known. Second, the two inner electrodes must be connected to a high input impedance and high common mode rejection ratio (CMRR) differential amplifier. The results obtained in a miniaturized CE channel show a linear response with liquid impedances within a range of 250 kΩ to 3.45 MΩ (for a MES/His buffer, this compares to a concentration range of 0.2–20 mM).