Determination of ketamine and metabolites in urine by liquid chromatography–mass spectrometry

We have developed an analytical method by using liquid chromatography–mass spectrometry (LC–MS) to determine ketamine and its metabolites in urine. The ionization efficiency between two ionization modes (ESI and APCI) of LC–MS was compared to each other. An easy and simple sample preparation of urine samples was made by passing samples through a 0.22 μm PVDF syringe filter. The results indicated that the ionization efficiency of positive APCI mode is better than positive ESI mode for determination of trace ketamines. A wide linearity range of the research is from 5 to 250 ng mL−1 and the detection limits for ketamine, norketamine and dehydronorketamine were 0.95, 0.48 and 0.33 ng mL−1, respectively. The proposed method was tested by analyzing ketamine and metabolites in the urines of volunteers. The concentrations of ketamine, norketamine and dehydronorketamine are ranged of 5.4–131.0, 12.5–74.1 and 22.8–278.9 ng mL−1, respectively and the ketamines concentration profiles in human urine were also determined. The results demonstrate the suitability of liquid chromatography–mass spectrometry approach to analyze trace amount of ketamine and its metabolites in urine.