Solid-phase extraction and gas chromatography-mass spectrometry analysis of 11-nor-9-carboxy-δ9-tetrahydrocannabinol in urine for monitoring marijuana abuse


A specimen pretreatment procedure, combining solid-phase extraction and methylation, was developed for the analysis of 11-nor-9-carboxy-Δ9- tetrahydrocannabinol (9-THC-COOH) in urine for monitoring marijuana exposure. d3-11-Nor-9-carboxy-Δ9-tetrahydrocannabinol (d3-9-THC-COOH) was used as an internal standard, while the now universal selected ion monitoring gas chromatography-mass spectrometry approach was used for detection (m/z 313, 357, 372 and 316, 360, 375 for 9-THC-COOH and d3-9-THC-COOH, respectively) and quantitation (m/z 372 and 375 for 9-THC-COOH and d3-9-THC-COOH, respectively). The effectiveness of the overall procedure was evaluated. One of the extraction columns evaluated achieved > 90% recovery of the analyte in 5-mL drug-free urine fortified with 15 ng/mL 9-THC-COOH. Using the one-point calibration approach, the overall protocol achieved the following analytical parameters: detection limit: 2.09 ng/mL; limit of quantitation: 4.18 ng/mL; upper end of linear range: 376 ng/mL (or better); interday precision: 1.49- 8.03% CV in the 4.18-376 ng/mL concentration range studied.

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