A sensitive analytical method for simultaneous quantification of cannabidiol (CBD), Δ9-tetrahydrocannabinol (THC), 11-hydroxy-THC (11-OH-THC), and 11-nor-9-carboxy-THC (THCCOOH) in plasma is presented for monitoring cannabinoid pharmacotherapy and illicit cannabis use. Analytes were extracted from 1 mL plasma by solid phase extraction, derivatized with N, O,-bis(trimethylsilyl) trifluoroacetamide with 1% trimethylchlorosilane, and analyzed by two-dimensional gas chromatography mass spectrometry (2D-GCMS) with cryofocusing. The lower calibration curve was linear from 0.25–25 ng/mL for CBD and THC, 0.125–25 ng/mL for 11-OH-THC and 0.25–50 ng/mL for THCCOOH. A second higher linear range from 5–100 ng/mL, achieved through modification of injection parameters, was validated for THC, 11-OH-THC and THCCOOH and was only implemented if concentrations exceeded the lower curve upper limit of linearity. This procedure prevented laborious re-extraction by allowing the same specimen to be re-injected for quantification on the high calibration curve. Intra- and inter-assay imprecision, determined at four quality control concentrations, were <7.8% CV. Analytical bias was within ±9.2% of target and extraction efficiencies were >72.9% for all analytes. Analytes were stable when stored at 22°C for 16h, 4°C for 48h, after three freeze-thaw cycles at −20°C and when stored on the autosampler for 48h. This sensitive and specific 2D-GCMS assay provides a new means of simultaneously quantifying CBD, THC and metabolite biomarkers in clinical medicine, forensic toxicology, workplace drug testing, and driving under the influence of drugs programs.
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