Determination of ketamine and its major metabolite, norketamine, in urine and plasma samples using microextraction by packed sorbent and gas chromatography-tandem mass spectrometry

• First MEPS-GC–MS/MS method for K and NK determination in urine and plasma samples.
• Excellent quantitation limits using only 0.25 mL of sample.
• High recoveries for K and NK.
• Suitable for regular urine and plasma analysis in the field of forensic toxicology.

Ketamine is a club drug widely abused for its hallucinogenic effects, being also used as a “date-rape” drug in recent years. We have developed an analytical method using gas chromatography-tandem mass spectrometry (GC–MS/MS) for the identification and quantification of ketamine and its major metabolite in urine and plasma. No derivatization step is needed to accomplish analysis. The compounds were extracted from 0.25 mL of sample using microextraction by packed sorbent on mixed mode (M1) cartridges. Calibration curves were linear in the range of 10–250 ng/mL for urine and 10–500 ng/mL for plasma, with determination coefficients higher than 0.99. The limit of detection (LOD) was 5 ng/mL for both compounds in both specimens. Recoveries ranged from 63 to 101%, while precision and accuracy were below 14% and 15%, respectively. These low limits of detection and the quite high recoveries obtained, in very low sample amounts, allow detecting small quantities of the compounds, making this procedure suitable for those laboratories performing routine analysis in the field of forensic toxicology. Compared with existing methods, the herein described procedure is fast, since no derivatization step is required, and cost effective for the quantification of ketamine and norketamine in biological specimens by gas chromatography.