A sensitive and selective method for the detection of diazepam and its main metabolites in urine by gas chromatography–tandem mass spectrometry

A gas chromatography–tandem mass spectrometry method for detection of diazepam, nordazepam and oxazepam is presented. The method associates electron capture ionization and multiple reaction monitoring (MRM). No derivatization is performed; oxazepam undergoes thermal degradation during chromatographic injection and is thus quantified via its decomposition product. The negative molecular ions are so stable that they do not dissociate when collision is performed under “classical” conditions (i.e. with argon as collision gas). With xenon as collision gas, the energy transfer is sufficient to provide two product ions for diazepam and nordazepam and one product ion for the decomposition product of oxazepam. The sample preparation part involves liquid/liquid extraction with TOXI-TUBES® A extraction tubes; it provides recovery yields between 68 and 95%, depending of the benzodiazepine considered, with coefficients of variation below 6% for 10 samples. The applicability of the method was demonstrated on urine extracts. From 1 mL of urine, the method provides quantitation limits of 0.15 ng/mL for diazepam, 1.0 ng/mL for nordazepam and 1.5 ng/mL for oxazepam. Mechanisms of dissociation of M− ions of benzodiazepines are suggested.