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.
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