Detection of 11-nor-9-carboxy-tetrahydrocannabinol in the hair of drug abusers by LC–MS/MS analysis

Abstract

Cannabis is the second most commonly abused illicit drug after methamphetamine in South Korea. To prove cannabis consumption, 11-nor-9-carboxy-tetrahydrocannabinol (THC-COOH), the metabolite of tetrahydrocannabinol (THC), was screened for in a hair analysis. In this study, we developed a liquid chromatography–tandem mass spectrometry (LC–MS/MS) analysis method, which was used to analyze authentic hair samples in 2017. Possible contaminants on the surface of hair samples were eliminated by washing twice each with 2mL of methanol and distilled water. After adding an internal standard (THC-COOH-d3), the hair samples (about 20mg each) were digested with 1M NaOH, extracted twice with mixed organic solvents (n-hexane:ethyl acetate), and analyzed by an LC–MS/MS system. Identification and quantification of THC-COOH and THC-COOH-d3 were performed using a multiple reaction monitoring (MRM) mode at m/z 245 and 191 and m/z 248, respectively (quantifier ions are underlined). The following validation parameters were evaluated: selectivity, linearity, limit of detection (LOD), limit of quantification (LOQ), precision, accuracy, matrix effect, and recovery. The LOD and LOQ of the method was 0.1pg/mg. Good linearity was achieved for THC-COOH in the range from 0.1 to 20pg/mg. The method showed an acceptable precision and accuracy, both of which were less than 15% at the three concentrations of THC-COOH (0.2, 1, and 10pg/mg). THC-COOH showed ion suppression at these three concentrations. The concentrations of THC-COOH in the authentic hair samples ranged from 0.10 to 27.30pg/mg (total 586 cases), and its concentrations were classified as low, medium, or high ranges, i.e., 0.10–0.39pg/mg, 0.39–1.99pg/mg, or 1.99–27.30pg/mg, respectively, according to statistical evaluation. This method showed the possibility of replacing the existing gas chromatography-tandem mass spectrometry (GC–MS/MS) analysis. However, further development of our LC–MS/MS method is necessary in order to meet the recommended 0.05pg/mg cut-off.