Detection of acid-labile conjugates of ketamine and its metabolites in urine samples collected from pub participants.

The rapid increase of ketamine (K) abuse worldwide has created a need for a sensitive and reliable detection procedure. Ketamine and its major metabolite, norketamine (NK), are usually determined with gas chromatography-mass spectrometry (GC-MS). Phase II metabolism of K has not been fully investigated. In this report, we studied the phase II biotransformation of ketamine. Urine samples were hydrolyzed with concentrated HCl and alkalinized and extracted with organic solvent. GC-MS (electron impact mode) was employed to determine K, NK, and dehydronorketamine (DHNK). Acidic hydrolysis of urine samples resulted in the detection of a significant increase of K, NK, and DHNK. This indicated the presence of acid-labile conjugates of K, NK, and DHNK in positive urine samples. Because we were unable to obtain DHNK reference materials, the determined value of DHNK was only presumptive. The limit of detection of the procedure was 1 ng/mL for K and 5 ng/mL for NK. The limit of quantitation was 5 ng/mL for K and 10 ng/mL for NK. The range of linearity was 5 micro g/mL for K and NK. The within-run precisions (%CV) for K at concentrations of 40, 120, and 360 ng/mL were 1.54%, 3.41%, and 2.08%, respectively. The within-run precisions for NK were 2.09%, 1.08%, and 1.16%, respectively. Between-day precisions for K were 5.04%, 1.99%, and 5.31%, respectively. Between-day precisions for NK were 3.93%, 2.37%, and 4.51%, respectively. The accuracy of the controls was between 93.7% and 102.5% of the target values. The effect of acidic hydrolysis was determined with a group of 50 samples. The median concentration ratios of hydrolyzed to unhydrolyzed K, NK, and DHNK were 1.15, 1.35, and 1.44, respectively.