A fast screening procedure for ketamine and metabolites in urine samples with tandem mass spectrometry

A screening method based on electrospray tandem mass spectrometry (MS-MS) was developed. Urine samples were spiked with ketamine-d(4) and norketamine-d(4) as internal standard and extracted with 0.5 mL ethyl acetate. Extracted samples were monitored with triple-quadrupole MS-MS. Total analysis time was 1.5 min/sample. Limit of detection was 0.1 ng/mL for ketamine, norketamine, and dehydronorketamine (DHNK). Carryover rate was less than 0.06%. Within-run and between-run precision for ketamine, norketamine, and DHNK at three different concentrations (40, 75, and 125 ng/mL) was between 2.1 and 8.2%. Within-run and between-run accuracy, presented as % bias, was between -5.9 and 2.7%. A group of 76 urine samples were screened with ELISA and gas chromatography-mass spectrometry (GC-MS). With GC-MS as the reference method, when ketamine, norketamine, and DHNK were monitored at cutoff concentration of 100 ng/mL, there were 21 positive, 45 negative, 7 false-negative, and 3 false-positive results. A group of 243 samples was screened with MS-MS and analyzed with GC-MS; there were 74 positive, 163 negative, 6 false-positive, and no false-negative results. In conclusion, the MS-MS procedure is accurate, efficient, and suitable for use as a high-throughput screening method for ketamine and metabolites.