Detection and quantitation of urinary 11-nor-delta-9-tetrahydrocannabinol-9-carboxylic acid, a metabolite of tetrahydrocannabinol, by capillary gas chromatography and electron impact mass fragmentography.

ABSTRACT

A procedure for detection and quantitation of 11-nor-delta-9-tetrahydrocannabinol-9-carboxylic acid, a major metabolite of delta-9-tetrahydrocannabinol in urine, has been described. Since the metabolite is present in both conjugated and unconjugated forms, hydrolysis of urine was carried out to increase the sensitivity of detection. The acidic metabolite was isolated by strongly basic anion exchange resin, and subsequently derivatized to methyl 1-dehydroxy-1-methoxy-11-nor-delta-9-tetrahydrocannabinol-9-carbox ylate (1a) by methyliodide in the presence of tetramethylammonium hydroxide. The derivatized product was separated in a capillary column gas chromatograph, and finally detected by a mass spectrometer under electron impact mode. Confirmation of the product was carried out by monitoring three ions that represent the major portions of the molecule and comparing their relative abundances to that of a standard. Quantitation was based on 5'-2H3-11-nor-delta-9-tetrahydrocannabinol-9-carboxylic acid as internal standard. Excellent linearity was obtained over the range of 2 to 1000 ng/mL. The overall yield of extraction using the anion exchange resin was 50 to 60%. This extraction process is rapid and suitable for a large number of sample analyses. The methylated product (1a) is stable for at least 72 hr at room temperature.