Improved gas chromatography–negative ion chemical ionization tandem mass spectrometric method for determination of 11-nor-Δ9-tetrahydrocannabinol-9-carboxylic acid in hair using mechanical pulverization and bead-assisted liquid–liquid extraction

A gas chromatography–negative ion chemical ionization tandem mass spectrometric (GC–NCI-MS/MS) method was developed and validated for the determination of 11-nor-Δ9-tetrahydrocannabinol-9-carboxylic acid (THC-COOH) in human hair. After decontamination, hair samples were weighed (25 mg), mechanically pulverized with a bead mill, and incubated in 0.7 mL of 1.0 M sodium hydroxide at 95 °C for 30 min. Bead-assisted liquid–liquid extraction was performed with n-hexane:ethyl acetate (9:1, v/v), a method developed in our laboratory. The extract was evaporated to dryness, derivatized with pentafluoropropanol and pentafluoropropionic anhydride, and analyzed by GC–MS/MS in the negative ion chemical ionization mode using methane as the reagent gas. The linear ranges were 0.05–10.0 pg/mg for THC-COOH with the coefficient of determination (r2 = 0.9976). The intra-day and inter-day precisions were within 1.7 and 13.8%, respectively. The intra-day and inter-day accuracies were −4.8 to 10.0% and −3.9 to 3.8%, respectively. The limit of detection and quantification were 0.015 and 0.05 pg/mg, respectively. The recoveries were in the range of 79.4–87.1%. The results indicate that the proposed method is simple, rapid, accurate, and precise for determination of THC-COOH in hair. The method identified THC-COOH in hair specimens from suspected marijuana abusers.