Hair analysis for Δ9-THC, Δ9-THC-COOH, CBN and CBD, by GC/MS-EI: Comparison with GC/MS-NCI for Δ9-THC-COOH

Abstract

A sensitive analytical method was developed for quantitative analysis of Δ9-tetrahydrocannabinol (Δ9-THC), 11-nor-Δ9-tetrahydrocannabinol-carboxylic acid (Δ9-THC-COOH), cannabinol (CBN) and cannabidiol (CBD) in human hair. The identification of Δ9-THC-COOH in hair would document Cannabis use more effectively than the detection of parent drug (Δ9-THC) which might have come from environmental exposure.Ketamine was added to hair samples as internal standard for CBN and CBD. Ketoprofen was added to hair samples as internal standard for the other compounds. Samples were hydrolyzed with β-glucuronidase/arylsulfatase for 2h at 40°C. After cooling, samples were extracted with a liquid–liquid extraction procedure (with chloroform/isopropyl alcohol, after alkalinization, and n-hexane/ethyl acetate, after acidification), which was developed in our laboratory. The extracts were analysed before and after derivatization with pentafluoropropionic anhydride (PFPA) and pentafluoropropanol (PFPOH) using a Hewlett Packard gas chromatographer/mass spectrometer detector, in electron impact mode (GC/MS-EI).Derivatized Δ9-THC-COOH was also analysed using a Hewlett Packard gas chromatographer/mass spectrometer detector, in negative ion chemical ionization mode (GC/MS-NCI) using methane as the reagent gas. Responses were linear ranging from 0.10 to 5.00ng/mg hair for Δ9-THC and CBN, 0.10–10.00ng/mg hair for CBD, 0.01–5.00ng/mg for Δ9-THC-COOH (r2>0.99). The intra-assay precisions ranged from <0.01 to 12.40%. Extraction recoveries ranged from 80.9 to 104.0% for Δ9-THC, 85.9–100.0% for Δ9-THC-COOH, 76.7–95.8% for CBN and 71.0–94.0% for CBD.The analytical method was applied to 87 human hair samples, obtained from individuals who testified in court of having committed drug related crimes.Quantification of Δ9-THC-COOH using GC/MS-NCI was found to be more convenient than GC/MS-EI. The latter may give rise to false negatives due to the detection limit.