Analysis of 11-nor-9-carboxy-Δ9-tetrahydrocannabinol in urine by LC-MS-MS after stir-bar sorptive extraction and liquid desorption

Stir-bar sorptive extraction (SBSE) is a unique method; a sample solution is stirred with a stir bar covered with polydimethylsiloxane. It generally gives clean extract and high recovery rates and is used for analysis of various compounds. In this study, we established a detailed procedure for analysis of 11-nor-9-carboxy-Δ9-tetrahydrocannabinol (THCA), the main metabolite of Δ9-tetrahydrocannabinol, in human urine by liquid chromatography-tandem mass spectrometry (LC-MS-MS) using SBSE with liquid desorption. For quantitative analysis, an external calibration method was used. A urine sample was fi rst hydrolyzed under strong alkaline conditions, followed by SBSE with a Twister stir bar at about pH 3. The analyte was desorbed from the bar with a small amount of ethyl acetate. After evaporation of the solvent, it was reconstituted in water-methanol mixture for LC-MS-MS analysis in the selected reaction monitoring mode. The calibration curve for THCA was linear in the range of 10–200 ng/ml urine. The lower limit of detection was 1.3 ng/ml. The mean recovery rate was as high as 76.5%. The intraassay accuracy and precision data were satisfactory. The present method established in this study is useful for identifi cation and quantitation of THCA in forensic toxicology, although some improvements of the procedure should be investigated. To our knowledge, this is fi rst report dealing with SBSE for THCA analysis.