Validated gas chromatographic-mass spectrometric analysis of urinary cannabinoids purified with a calcium-hardened...

A comprehensive solid-phase extraction (SPE) technique based on the formation of an inclusion complex between beta-cyclodextrin (betaCD) and cannabinoids including Delta(9)-tetrahydrocannabinol (THC), 11-hydroxy-Delta(9)-tetrahydrocannabinol (11-OH-THC) and 11-nor-9-carboxy-Delta(9)-tetrahydrocannabinol (THC-COOH) was developed in gas chromatographic-mass spectrometric (GC-MS) analysis. A betaCD/epichlorohydrin copolymer was prepared and then 'hardened' in aqueous solution with 0.3M CaCl(2) to yield a stable particulate copolymer, which was used as a novel SPE sorbent. An internal standard THC-COOH-d(9) was added to urine samples containing 3 cannabinoids and then purified with the hardened betaCD polymer. The cannabinoids were extracted from the hardened betaCD using tetrahydrofuran. Resulting extracts were evaporated and derivatized with MSTFA/NH(4)I/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 microg 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 microg L(-1) calibration range, respectively (r(2)>0.9997). Twenty actual samples positive by fluorescence polarization immunoassay were also quantitatively analyzed. The devised technique based on the calcium-hardened betaCD 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.