On-chip electrochromatography using sol–gel immobilized stationary phase with UV absorbance detection

A chromatography column on a chip was fabricated by immobilizing reversed-phase stationary phase particles (5 μm, C4) using sol–gel technology. Channels were fabricated in quartz using photolithography and wet etching. Localization of the stationary phase was achieved by immobilizing the stationary phase at the desired location in the separation channel prior to bonding of the cover plate. Cross channel design was employed for gated injection. An optical fiber setup was developed for carrying out on-chip UV absorbance detection. The effective optical path length was theoretically determined for the trapezoidal shaped channel and the result was shown to match closely with the experimentally determined value. The effect of applied voltage on velocity was evaluated using thiourea as an unretained marker. Separation performance of the stationary phase was demonstrated by separation of three peptides (Trp–Ala, Leu–Trp and Trp–Trp) under isocratic chromatographic conditions.