Validated gas chromatographic-mass spectrometric analysis of urinary cannabinoids purified with a calcium-hardened β-cyclodextrin polymer

A comprehensive solid-phase extraction (SPE) technique based on the formation of an inclusion complex between β-cyclodextrin (βCD) and cannabinoids including Δ⁹-tetrahydrocannabinol (THC), 11-hydroxy-Δ⁹-tetrahydrocannabinol (11-OH-THC) and 11-nor-9-carboxy-Δ⁹-tetrahydrocannabinol (THC-COOH) was developed in gas chromatographic-mass spectrometric (GC-MS) analysis. A βCD/epichlorohydrin copolymer was prepared and then 'hardened' in aqueous solution with 0.3 M CaCl₂ to yield a stable particulate copolymer, which was used as a novel SPE sorbent. An internal standard THC-COOH-d₉ was added to urine samples containing 3 cannabinoids and then purified with the hardened βCD polymer. The cannabinoids were extracted from the hardened βCD using tetrahydrofuran. Resulting extracts were evaporated and derivatized with MSTFA/NH₄I/dithioerythritol (500:4:2, v/w/w) and analyzed by GC-MS in selected-ion monitoring (SIM) mode. Overall recoveries ranged from 85% to 102%, with a detection limit of 0.2 μg L^-1 for the three cannabinoids tested. The precision (% CV) and accuracy (% bias) of the assay were 1.2-5.1% and 93-111% in 0.2-50 μg L^-1 calibration range, respectively (r² > 0.9997). Twenty actual samples positive by fluorescence polarization immunoassay were also quantitatively analyzed. The devised technique based on the calcium-hardened βCD sorption of cannabinoids and subsequent GC-SIM/MS resulted in better selectivity and extraction efficiency than is possible using the conventional hydrophobicity-based SPE methods.