Quantification of 9-carboxy-11-nor-delta 9-tetrahydrocannabinol in urine using brominated 9-carboxy-11-nor-delta 9-tetrahydrocannabinol as the internal standard and high-performance liquid chromatography with electrochemical detection.

A method was developed for quantitating 9-carboxy-11-nor-delta 9-tetrahydrocannabinol in human urine as part of the process for validating an automated enzyme immunoassay for marijuana metabolites. Sample cleanup was accomplished using a mixed-mode solid-phase extraction. 9-Carboxy-11-nor-delta 9-tetrahydrocannabinol and the internal standard, brominated 9-carboxy-11-nor-delta 9-tetrahydrocannabinol, were quantified using high-performance liquid chromatography with electrochemical detection (+ 0.85 V). The linear range for this method is 0.012-0.20 microgram/mL. No interference was seen for 22 drugs and metabolites. The pooled relative standard deviation is 4.1% (n = 27) for the quality control samples. This method was compared to gas chromatography with mass spectrometry by linear regression analysis. The slope of the line is 1.00 +/- 0.05 (standard error), the intercept is approximately zero, the coefficient of determination is 0.994, and the standard error of the estimate is 0.006 microgram/mL.