Testing for zolpidem in oral fluid by liquid chromatography–tandem mass spectrometry

The purported enhancement of sexuality, coupled with a possible abrupt coma-inducing effect and ease of administration in spiked drinks have resulted in the use of hypnotics to facilitated a sex offence. Among these compounds, zolpidem possesses amnesic properties, is short-acting and can rapidly impair an individual. In order to document zolpidem exposure, we have developed an original analytical method in oral fluid. 500 μl of oral fluid was added to 500 μl pH 7.6 Soerensen buffer was extracted by 2 ml dichloromethane in presence of 5 ng diazepam-d5, used as internal standard. An aliquot of the extract was injected into a 5 μm Novapak C18 column (150 mm × 2.1 mm). Reversed-phase separation was achieved in 6 min, under isocratic conditions (90% acetonitrile, 10% 2 mM ammonium formate pH 3.6) at a flow rate of 150 μl/min. Detection was achieved by tandem mass spectrometry. Molecular ions (m/z 308 and 290 for zolpidem and the IS, respectively) were selected in Q1 and the corresponding daughter ions (m/z 235 and 263 for zolpidem and m/z 154 and 198 for the IS) were detected in Q3 after collision with argon. Linearity was observed for zolpidem concentrations ranging from 0.2 to 100 ng/ml, and the assay was capable of detecting 0.05 ng/ml. Oral fluid was collected for 480 min after oral zolpidem administration of 10 mg to 2 subjects. In both cases, zolpidem was detectable (0.4 ng/ml) after 15 min intake. Peak zolpidem concentrations were obtained at 150 min (53.5 ng/ml) and 180 min (75.7 ng/ml), respectively. Oral fluid tested positive for zolpidem for over 8 h (9–15 ng/ml).