Determination of Δ 1 ‐tetrahydrocannabinol in human fat biopsies from marihuana users by gas chromatography–mass spectrometry

A gas chromatographic–mass spectrometric (GC/MS) method for analysis of Δ 1 ‐tetrahydrocannabinol (Δ 1 ‐THC) in human fat samples is described. The fat sample, obtained from heavy marihuana users 1 week before and 4 weeks after smoking, is homogenized in hexane + 2‐propanol, centrifuged, and the supernatant mixed with Lipidex 5000. The solvent is evaporated and the dried gel is packed in a glass column. Δ 1 ‐THC is eluted from the column with methanol + water + acetic acid, diluted with water and the eluent is passed through a bed of Octadecylsilanebonded silica. After washing and drying, the retained Δ 1 ‐THC is eluted with hexane, derivatized with N‐methyl‐N‐( t ‐butyl‐dimethysilyl)trifluoroacetamide (MTBSTFA) and finally purified by HPLC on an Octadecyl SI 100 column in methanol. The amount of Δ 1 ‐THC is determined by GC/MS, using selected ion monitoring, and a deuterated internal standard. The recovery of Δ 1 ‐THC is about 80%, and the concentration of Δ 1 ‐THC in the fat samples analysed ranged between 0.4 and 193 ng/g wet tissue.