Liquid chromatography on-chip: Progression towards a μ-total analysis system

After a brief introduction to the area of miniaturised analytical separation systems, this paper details the fabrication of components for a miniaturised liquid chromatography system. To date, inlet and outlet connection ports, separation μ-channels (20-200 μm in width, 0.5-10 μm in depth, 15-50 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 machined. In addition the μ-channel walls have been chemically modified with n-octyltriethoxysilane and the reverse phase retention of the drug caffeine was observed using off-chip injection (20 nl) and UV detection (3 nl flow cell). The on-chip platinum electrodes have been used for the amperometric detection of phenol. In addition, using external valving, initial results indicated a successful mode for a partially integrated on-chip injector which should allow further progression towards a μ-chromatographic analysis system.