This study was funded by the UC Merced Blum Center (to D.M.O. and K.K.H.), Valley Children's Healthcare (to F.

Background Cannabis legalization is expanding rapidly throughout the United States, but there is no reliable means of establishing recent use. Objective To develop and validate a bioanalytical method for determination of Δ9-tetrahydrocannabinol (Δ9-THC), cannabinol, 11-hydroxy-Δ9-THC, 11-nor-9-carboxy-Δ9-THC, and 8β,11-dihydroxy-Δ9-THC in whole blood microsamples by liquid chromatography high-resolution mass spectrometry (LC-HRMS). Methods Cannabinoid extraction from whole blood was performed using a mixture of n-hexane/ethyl acetate (90:10, v/v). Chromatographic separation was performed with a C18 column using a binary mobile phase gradient of water and acetonitrile, each with 0.1% formic acid. Detection was performed by positive ion mode heated electrospray ionization with full scan MS on an Orbitrap mass spectrometer. A clinical study was performed in 30 subjects to identify recent cannabis use based on analysis of cannabinoids in blood samples up to 200 min post-smoking. Results Acceptable linearity of all calibration curves was observed (r2>0.99) for all analytes over a 1–100 ng/mL concentration range, with acceptable accuracy. Limit of detection (LOD) was 0.5 ng/mL. Accuracy and precision met acceptance criteria for all analytes. Repeatability (CV) was <5% at low (3 ng/mL) and high (90 ng/mL) concentrations. In the clinical study, the ratios between 11-nor-9-carboxy-Δ9-THC and Δ9-THC fell immediately after smoking and returned to near baseline levels by 200 min post-smoking, which is consistent with recent use. Conclusions and Highlights The developed LC-HRMS bioanalytical method is suitable for quantification of five key cannabinoids in whole capillary blood microsamples and can be used in conjunction with a test for determining recent cannabis use.

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