Confirmation of a Tetrahydrocannabinol Metabolite in Urine by Gas Chromatography

A new method for confirming urinary 11-nor-Δ9-tetrahydrocannabinol-9-carboxylic acid, the major metabolite of tetrahydrocannabinol, has been developed. The metabolite is extracted, derivatized to the methyl ester, methyl ether, and analyzed on a gas chromatograph equipped with a flame ionization detector. In spiked urine specimens, metabolite concentrations as low as 20 ng/mL have been detected by this procedure. In a random sampling of urines, greater than 95% correlation was obtained between confirmation by this method and confirmation by gas chromatography/mass spectrometry in those specimens producing an immunological response greater than 75 ng/mL.