Determination of flunitrazepam, desmethylflunitrazepam and clonazepam in plasma by gas liquid chromatography with an internal standard.

A method is developed for gas-chromatographic determination of flunitrazepam, desmethylflunitrazepam and clonazepam in plasma, using methylclonazepam as internal standard. Following extraction of the benzodiazepines and their hydrolysis, the benzophenones are analyzed by gas-chromatography, with a glass column filled with 3% OV-225 on Gas Chrom Q and a 63Ni electron capture detector. The technique has a good selectivity. Its limit of sensitivity is about 0.5 ng/ml of plasma. It is suitable for investigations on pharmacokinetics and bioavailability as well as for monitoring the correlation between plasma level and therapeutic efficacy and toxicology.