Quantification of 9-Carboxy-11-nor-Δ9-tetrahydrocannabinol in Urine Using Brominated 9-Carboxy-11-nor-Δ9-tetrahydrocannabinol as the Internal Standard and High-Performance Liquid Chromatography with Electrochemical Detection

Abstract

A method was developed for quantitating 9‐carboxy‐11‐nor‐Δ⁹‐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‐Δ⁹‐tetrahydrocannabinol and the internal standard, brominated 9‐carboxy‐11‐nor‐Δ⁹‐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 μg/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 μg/mL.