Monitoring of chronic Cannabis abuse: An LC–MS/MS method for hair analysis

An advanced analytical method based on liquid chromatography–tandem mass spectrometry (LC–MS/MS), has been developed for the identification and determination in hair of Δ9- tetrahydrocannabinol together with its major metabolite 11-nor-9-carboxy-Δ9-tetrahydrocannabinol. Since the latter is formed endogenously, it allows the assessment of chronic use excluding passive exposure to Cannabis. The sample pre-treatment procedure is based on a feasible incubative extrac- tion followed by a liquid–liquid extraction step. Chromatographic separation was performed using a reversed-phase column and gradient elution with a formic acid/acetonitrile/water mobile phase. The lim- its of quantitation and of detection were 3 pg/mg and 1 pg/mg, respectively, for both analytes. The method was successfully applied to the analysis of hair samples from Cannabis abusers; the analyte concentrations found ranged from 55 to 100 pg/mg for Δ9 -tetrahydrocannabinol and from 5 to 10 pg/mg for 11-nor-9- carboxy-Δ9 -tetrahydrocannabinol. Accuracy studies also gave satisfactory results (recovery > 87%), thus confirming the suitability of the assay for chronic consumption monitoring.