Minimization of plasma interferences by liquid chromatography with electrochemical detection after ultraviolet irradiation using chlordiazepoxide as a model substance

Chlordiazepoxide was detected as a model substance in plasma by electrochemistry after separation by reversed-phase liquid chromatography. The method, which incorporates post-column, on-line UV irradiation, exploits the transformation of the molecule both into a phenolic hydroxyl and an oxaziridine by photolysis. For the determination in biological material, the optimization with respect to pH and working potential in combination with solid-phase extraction results in a decrease of plasma interferences. Selectivity and sensitivity can so be significantly improved. The detection limit was 3 ng/ml.