Determination of Cannabinoids in Human Hair by GC/MS

Abstract

An analytical method for the determination of the three most important components of cannabis [viz., Δ⁹ tetrahydrocannabinol (THC), cannabidiol (CBD), and cannabinol (CBN)] and the main metabolite of THC (11‐nor‐Δ⁹ tetrahydrocannabinol‐9‐carboxylic acid [THC‐COOH]) in human hair, using gas chromatography/mass spectrometry (GC/MS), is proposed. Hair samples were washed and hydrolyzed with 2.5 M NaOH to complete dissolution. Extraction was done with 9:1 (v/v) n‐hexane/ethyl acetate and separated basic and neutral cannabinoids (viz. CBD, THC, and CBN) first, and acid cannabinoids (THC‐COOH) after addition of 6 N HCl to pH 2–3. The first extract was analyzed using THC‐d3 as internal standard. The second extract was derivatized with bistrimethylsilyltrifluoroacetamide (BSTFA) + 1% trimethylchlorosilane (TMCS) and analyzed using THC‐COOH‐d3 as internal standard. Calibration curves run over the concentration range 0.1–5.0 ng/mg for each compound exhibited good correlation coefficients and excellent sensitivity. The coefficients of variation were less than 8% and the relative errors laid in the range ±7%. Thirty‐five hair samples were studied, obtaining concentrations in the ranges 0.01–15.26 ng/mg for CBD, 0.04–0.29 ng/mg for THC, 0.03–6.66 ng/mg for CBN, and 0.05–0.80 ng/mg for THC‐COOH.

Keywords:

• Cannabinoids
• Hair
• GC–MS
• THC