[Validation of a method for detecting benzodiazepines in the urine by acid extraction of their benzophenones and thin layer chromatography].

The authors confirm the validity of a method of detection for 18 benzodiazepines. Its original feature consists of the extraction in an acid medium. Between 70 and 100 per cent of the drug is recovered, except for the benzophenones which are strongly basic. The yield of hydrolysis is between 70 and 95 per cent, except for diazepam and lormetazepam, for which the yield is about 50 per cent. Depending on the nature of the benzodiazepines, the limit of detection of the process described is between 5 and 20 micrograms/l of urine. Following a single therapeutic dose in non-dependent volunteers, the benzodiazepines were detectable for at least 36 to 48 hours.