DEVELOPMENT OF AN AMPEROMETRIC DETECTOR FOR PACKED CAPILLARY COLUMN SUPERCRITICAL-FLUID CHROMATOGRAPHY

Amperometric detection at a naked platinum microelectrode is shown to be compatible with pressure-programmed packed capillary column supercr itical fluid chromatography (SFC) using carbon dioxide modified with a s little as 1% acetonitrile, Amperometric detection in modified carbon dioxide is, hence, possible without addition of salts, which otherwis e may limit the stability of the chromatographic system. The detection , which can been based on either oxidations or reductions, is also com patible with the use of methanol as a sole modifier, Picogram amounts of ferrocene could be detected after separations both at a constant pr essure and under pressure-programmed conditions. The detection limit f or ferrocene, at a constant pressure of 200 atm, was found to be appro ximately 20 pg, The response of the amperometric detector was observed to increase with decreased mobile phase density and increased amount of added modifier. The injection of increasing amounts of analytes res ulted in increased peak tailing, most likely due to the limited solubi lity of the oxidation products in the mobile phase. The influence of t his effect was, however, small for the amounts of analytes relevent in capillary column SFC.