EVALUATION OF AMPEROMETRIC DETECTORS FOR HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY - ANALYSIS OF BENZODIAZEPINES

The design of amperometric detectors for high-performance liquid chromatography is discussed. A simple flow cell with interchangeable working electrodes made from glassy carbon, carbon paste and mercury is described, and its performance is compared with commercially available cells, using both constant-potential and pulse-measuring techniques. The analysis of nitrazepam, diazepam and chlordiazepoxide was used as a model system; the detectors were used in the reduction mode and the mobile phase was methanol-water (60:40) containing 0.05 M ammonium acetate. The effects of various experimental parameters are reported. The detection limit was found to depend strongly on the reduction potential: at -0.93 V vs. Ag, ng of nitrazepam could be detected, whereas at -1.30 V the detection limit was 30 ng, owing to the high background current at this potential. A potential more negative than -1.1 V must be used for the detection of diazepam and chlordiazepoxide; at -1.30 V the detection limit was 300 ng for these compounds. © 1979.