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

Abstract

A comprehensive solid-phase extraction (SPE) technique based on the formation of an inclusion complex between beta-cyclodextrin (beta CD) 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 beta CD/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-d(9) was added to urine samples containing 3 cannabinoids and then Purified with the hardened beta CD polymer. The cannabinoids were extracted from the hardened beta CD using tetrahydrofuran. Resulting extracts were evaporated and derivatized with MSTFA/NH4 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 mu g 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 mu g 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 beta CD 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. (c) 2008 Elsevier B.V. All rights reserved.