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 mum, there were more interactions of the analytes with the stationary phase on the chip than in a 50-mum I.D. capillary. With off-chip injection (20 nl) and UV detection, NO2-, NO3- I-, and thiourea were separated using I mM KCI as the eluent. The linear ranges for NO2- and NO3- are from 5 to 1000 muM with the detection limits of 0.5 muM. (C) 2001 Elsevier Science B.V. All rights reserved.