Quantification of cannabinoids in human hair using a modified derivatization procedure and liquid chromatography–tandem mass spectrometry

Abstract

The aim of this work was to develop and validate a liquid chromatography–tandem mass spectrometry method for detecting of the main cannabinoids, cannabinol (CBN) and tetrahydrocannabinol (THC) and the primary metabolite 11-nor-9-carboxy-Δ9-tetrahydrocannabinol (THC-COOH) in hair samples. Extraction of the cannabinoids was carried out by a polymeric strong anion mixed-mode solid-phase extraction cartridge and then employing methanolic HCl followed by 2-fluoro-1-methylpyridinium-p-toluenesulfonate (FMP-TS) as a derivatization procedure of carboxyl and phenolic groups, respectively, offering enhanced sensitivity for the detection of THC-COOH in hair matrices. Formation of a methyl ester increased its lipophilicity and removed the negative charge on the carboxyl group. Calibration curves were prepared over the range of 0.02–4 pg/mg of hair for THC and CBN and 0.2–12 pg/mg of hair for THC-COOH. The extraction recovery was between 81% and 105% for all compounds. The limit of detection (LOD) and limit of quantification (LOQ) were 2 and 20 pg/mg, respectively, for both CBN and THC and 0.1 and 0.2 pg/mg, respectively, for THC-COOH, which met the society of hair testing recommendation. Intra-assay and interassay precision were always lower than 4% and 11%, respectively for these cannabinoids, whereas intra-assay and interassay bias were between +14% and −18% and +15% and −12%, respectively. Twenty-seven hair specimens from cannabis users were investigated. The concentrations of CBN, THC and THC-COOH gave ranges of (0.022–2.562 ng/mg), (0.049–0.431 ng/mg) and (0.222–4.867 pg/mg), respectively. This new method of derivatization improves the LOD to ensure detection of the metabolite.