On-chip definition of picolitre sample injection plugs for miniaturised liquid chromatography

The fabrication of components for a miniaturised liquid chromatography system on silicon has recently been reported by our research group [J. Cap. Electrophoresis Microchip Technol. 6 (1999) 33; Analyst 125 (2000) 25]. To date, inlet and outlet connection ports, separation micro-channels (20-200 microm in width, 0.5-10 microm in depth, 15-60 cm in length), and an intersection for picolitre injection have been etched on a silicon wafer and then sealed with a Pyrex cover plate on which platinum electrodes for on-chip detection have been patterned. The platinum electrodes have been used for the amperometric detection of phenol, using 20 nl off-chip injection. In this work we present our latest results obtained with on-chip pressure driven picolitre injection, designed to realize the full capabilities of this micro-LC system. The injection volume is dependent on the micro-channel depth, width, and also on the intersection length, allowing injection in the low nanolitre to picolitre range.