Solid-phase extraction, identification, and quantitation of 11-nor-delta-9-tetrahydrocannabinol-9-carboxylic acid.

A procedure has been developed to extract and recover minute amounts of delta-9-carboxytetrahydrocannabinol (THC-COOH) from urine. A new non-isotopic internal standard is introduced to permit a chromatographic assay of the metabolite. The method affords a 91% recovery of 20 ng/mL of the THC-COOH acid from spiked urine with the assurance of a 3.8% coefficient of variation.