Simplified determination of lorazepam and oxazepam in biological fluids by gas chromatography-mass spectrometry.

Lorazepam and oxazepam in plasma and urine were measured by gas chromatography-mass spectrometry. Oxazepam was used as an internal standard in the assay of lorazepam and vice versa. After removal of interfering substances with n-hexane, the drugs were extracted with benzene and converted to N1,O3-bistrimethylsilyl derivatives. Glucuronide forms of the drugs were extracted after hydrolysis with beta-glucuronidase. A common fragment ion at m/e 429 was used to monitor the two drugs. The sensitivity was 2 ng/ml for both drugs, which was sufficient to determine plasma and urine concentrations after therapeutic doses to humans.