Highly sensitive assay of benzodiazepine antagonist in plasma by capillary gas chromatography with nitrogen-selective detection.

A selective and highly sensitive capillary gas chromatographic method was developed for the determination of a benzodiazepine antagonist in human plasma. The analytical procedure involved extraction of the compound and its internal standard from basified plasma with n-butyl chloride-dichloromethane and chromatography of the extract on a DB-5 fused-silica column (30 m X 0.25 mm I.D.), applying automated splitless injection and nitrogen- phosphorus detection. The limit of quantification was about 50 pg/ml, using a 1-ml plasma specimen. The mean inter-assay precision was 2.6% in the concentration range 0.5-10 ng/ml. The method was shown to be specific with respect to various benzodiazepines and their main metabolites. The practicability of the method was demonstrated by the analysis of more than 300 plasma samples from a dose proportionality study performed with human volunteers. Owing to its high sensitivity, the new method can be used to obtain pharmacokinetic parameters of the benzodiazepine antagonist in man after doses near the envisaged therapeutic intravenous dose of less than 1 mg.