Determination of zolpidem in human hair by micropulverized extraction based on the evaluation of relative extraction efficiency of seven psychoactive drugs from an incurred human hair specimen

A micropulverization method for rapid extraction of psychoactive drugs from hair was developed. A hair sample (10 mg) was micropulverized for 10 min at 42 Hz with 0.2 mL of 45% (w/v) aqueous ammonium phosphate (pH 8.4). Liquid–liquid extraction was carried out in the same tube using acetonitrile, and the organic layer was removed and filtered. Conventional methods, including solid–liquid extraction with an ammonium phosphate solution or methanol, were also employed, and the relative extraction efficiencies of amitriptyline, nortriptyline, norfludiazepam, flunitrazepam, 7-aminoflunitrazepam, mianserin and zolpidem with these methods from an incurred human hair specimen were compared using liquid chromatography/tandem mass spectrometry. The highest extraction efficiencies for all the analytes were achieved using the method developed here, even though the extraction time (10 min) was short. Overnight methanol extraction has frequently been used for hair analysis; however, the extraction efficiency was not sufficient for amines. The method was successfully applied to the quantification of zolpidem in human hair. The range of quantification was 1–25,000 pg/mg, and interday accuracy and precision (n = 5) at three concentrations were 1.8–8.8% and 3.3–8.1%, respectively. The developed method was applied to three actual (incurred) samples, for which the concentrations of zolpidem were determined to be 78.9–18,300 (pg/mg).