Ion chromatography on-chip

On-chip separation of inorganic anions by ion-exchange chromatography was realized. Micro separation channels were fabricated on a silicon wafer and sealed with a Pyrex cover plate using standard photolithography, wet and dry chemical etching, and anodic bonding techniques. Quaternary ammonium latex particles were employed for the first time to coat the separation channels on-chip. Owing to the narrow depths of the channels on the chip, 0.5–10 μm, there were more interactions of the analytes with the stationary phase on the chip than in a 50-μm I.D. capillary. With off-chip injection (20 nl) and UV detection, NO₂⁻, NO₃⁻, I⁻, and thiourea were separated using 1 mM KCl as the eluent. The linear ranges for NO₂⁻ and NO₃⁻ are from 5 to 1000 μM with the detection limits of 0.5 μM.