Improved and validated method for the determination of Δ9-tetrahydrocannabinol (THC), 11-hydroxy-THC and 11-nor-9-carboxy-THC in serum, and in human liver microsomal preparations using gas chromatography–mass spectrometry

A validated method for the quantification of Δ9-tetrahydrocannabinol (THC) and its main metabolites 11-hydroxy-tetrahydrocannabinol (OH-THC) and 11-nor-9-carboxy-tetrahydrocannabinol (THC-COOH) in serum is presented. The substances were isolated by solid-phase extraction, derivatised by methylation, and analysed by means of GC–MS in the selected ion monitoring mode. Quantitation was achieved by the addition of deuterated analogues as internal standards. The method was linear up to 10 ng/ml for THC and OH-THC, and up to 50 ng/ml for THC-COOH. The limits of quantification were 0.62 ng/ml for THC, 0.68 ng/ml for OH-THC and 3.35 ng/ml for THC-COOH. The limits of detection for the least intensive ions were 0.52 ng/ml for THC, 0.49 ng/ml for OH-THC and 0.65 ng/ml for THC-COOH. The method was validated according to the requirements of the Journal of Chromatography B. The method has been routinely used on samples from drivers suspected of “driving under the influence”. In addition to the forensic application, a cross-validation was carried out by applying the method developed for serum to human liver microsomal preparation samples.