A rapid and sensitive ESI-MS screening procedure for ketamine and norketamine in urine samples

Traditionally, ketamine was analyzed with gas chromatography (GC) equipped with nitrogen-phosphorus detection, flame-ionization detection, and mass selective detection (MSD) or with liquid chromatography-mass spectrometry (LC-MS). These procedures are sensitive but tedious and slow. There is no commercial immunoassay for ketamine. We have developed a simple and rapid electrospray ionization MS (ESI-MS) procedure to screen ketamine and norketamine (NK) in urine samples. Samples were spiked with ketamine-d(4) (K-d(4)) as internal standard and extracted with 0.2 mL of hexane. An experienced technician can prepare a batch of 60 samples in 1 h. An Agilent LC-MSD trap system with autosampler was employed to inject 10-microL extracted samples directly for mass analysis without chromatographic separation. Total analysis time was 1.3 min per sample. The ESI-MS was operated in scan mode. The ion pairs (m/z 238/242 for K/K-d(4) and m/z 224/242 for NK/K-d(4)) extracted from the full scan mass spectrum were used for quantification. Because of the nature of the ion trap mass detector employed, the presence of other compounds at high concentration could cause the suppression of target analyte ion intensity determined. Limits of detection were 3 ng/mL for ketamine and 15 ng/mL for NK. Carryover was 0.28% for ketamine and 0.39% for norketamine. Within-run precision (%CV) for K and NK at 3 different concentrations (80, 200, and 600 ng/mL) was 4.0% to 14.7%. A group of 168 urine samples collected from disco-dancing club participants were screened with ESI-MS and confirmed with GC-MS. The sensitivity was 97.1% and specificity was 85.7%. These results indicated that the ESI-MS screening procedure is rapid, sensitive, accurate, and reliable.