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A gas chromatographic/electron capture detection procedure was developed for the analysis of 11-nor-delta 9-tetrahydrocannabinol-9-carboxylic acid in urine. Hydrolyzed urine samples (1 mL or less) were extracted by a simple acid-base partitioning step. The extracted metabolite was derivatized with pentafluorobenzyl bromide in a biphasic system using benzyl tributylammonium hydroxide as a phase transfer catalyst. 11-Nor-cannabinol-9-carboxylic acid was used as internal standard. A linear relationship was observed between the peak height ratio of the metabolite/internal standard and the concentration of the metabolite (r = 0.9996), and between the peak height and concentration of the metabolite (r = 0.9995). Concentration of 5 ng/mL of metabolite in urine resulted in a peak-to-noise ratio of 4:1; however, concentrations down to 1 to 2 ng/mL could be determined. The procedure has many advantages over currently available methods, of which sensitivity and speed are the most important.
ElSohly et al. (Sun,) studied this question.