Detection of inorganic ions on a capillary electrophoresis microchip using a conductivity technique

Microchip-based electrophoretic separation systems are essential components in the development of fully integrated micro total analysis systems. In this paper, a miniaturized analytical system for separating and detecting inorganic ions is described. The system was based on a polycarbonate (PC) capillary electrophoresis (CE) chip and a contactless conductivity detector, both being developed at CSIRO Microfluidics and Microfabrication Laboratories, Melbourne, Australia. The PC chip was fabricated using the soft lithography technique in conjunction with nickel plating and hot embossing. The detector electrodes were fabricated from a PCB board and attached on the separation chip bottom surface. The thin capping layer (20 micron) of the chip allowed for sensitive detection of conductivity change. The system was demonstrated to separate reliably the potassium, sodium and lithium ions in a 20mM MES/His buffer within a minute at an electrical field of 28.5kV/m. The detection limit for the current design is around 100μM. Such a system offers great promise to be integrated into robust hand-held devices for in-situ monitoring of chemical and biological samples with high speed, reliability and low costs.