Portable high-voltage power supply and electrochemical detection circuits for microchip capillary electrophoresis

Miniaturized, battery-powered, high-voltage power supply, electrochemical (EC) detection, and interface circuits designed for microchip capillary electrophoresis (CE) are described. The dual source CE power supply provides +/- 1 kVDC at 380 microA and can operate continuously for 15 h without recharging. The amperometric EC detection circuit provides electrode potentials of +/-2 VDC and gains of 1, 10, and 100 nA/V. The CE power supply power is connected to the microchip through an interface circuit consisting of two miniature relays, diodes, and resistors. The microchip has equal length buffer and separation channels. This geometry allows the microchip to be controlled from only two reservoirs using fixed dc sources while providing a consistent and stable sample injection volume. The interface circuit also maintains the detection reservoir at ground potential and allows channel currents to be measured likewise. Data are recorded, and the circuits are controlled by a National Instruments signal interface card and software installed in a notebook computer. The combined size (4 in. x 6 in. x 1 in.) and weight (0.35 kg) of the circuits make them ideal for lab-on-a-chip applications. The circuits were tested electrically, by performing separations of dopamine and catechol EC and by laser-induced fluorescence visualization.