Simultaneous determination of Δ9-tetrahydrocannabinol, cannabidiol, cannabinol and 11-nor-Δ9-tetrahydrocannabinol-9-carboxylic acid in hair using liquid chromatography–tandem mass spectrometry

Abstract

For several years, hair analyses have become a powerful tool to investigate past exposure towards xenobiotics. In the case of illicit drugs and more precisely of cannabis exposure, four compounds are usually investigated: Δ9-tetrahydrocannabinol (THC), the main active compound of cannabis, one of its metabolites [11-nor-Δ9-tetrahydrocannabinol-9-carboxylic acid (THC-COOH)] and two cannabinoids (cannabinol and cannabidiol). Up until now, the hair determination of the carboxylic metabolite of THC, which has been described as the only marker allowing distinguishing consumption and passive exposure, has been performed using a gas chromatography–tandem mass spectrometry method. The aim of this study was to develop a liquid chromatography–tandem mass spectrometry (LC–MS/MS) method for the simultaneous quantitative determination of the four markers. The sample preparation was based on an alkaline hydrolysis of hair samples followed by a liquid–liquid extraction of compounds in acidic conditions using a hexane/ethyl acetate mixture. The method was validated and the results were satisfactory: intra- and inter-assay accuracies below 9% and relative standard deviation below 15% for the four compounds. Moreover, the limit of quantification for THC-COOH, the most challenging compound, was validated at 0.2pg/mg. This concentration is in accordance with the recommendations made by a scientific society which specializes in hair testing. It makes it possible to distinguish the kind of exposure to cannabis.