Detection and quantification of low concentrations of 11-nor-delta-9-tetrahydrocannabinol-9-carboxylic acid from minimal amounts of urine.

A simple liquid-liquid extraction and GC/MS-method for detection and quantification of 11-nor-delta-9-tetrahydrocannabinol-9-carboxylic acid (THC-COOH) from merely 1 ml urine is described. The derivatisation to the methyl ester was carried out using methyl iodide and mefenamic acid was used as internal standard. Experiments with urine spiked with 15 ng THC-COOH/ml resulted in a recovery of 91%. Excellent linearity was obtained over the range 5-100 ng/ml.