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-d4 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.