Detection of THCA in oral fluid by GC-MS-MS.

A major marijuana metabolite, 11-nor-9-carboxy-tetrahydrocannabinol (THCA), has been identified in oral fluids from donors that previously tested positive for Delta(9)-tetrahydrocannabinol (THC). The method consisted of solid-phase extraction of the oral fluid samples followed by gas chromatography-tandem mass spectrometry analysis of the extracts. Testing for THCA was performed on 223 oral fluid samples previously analyzed for THC. The THCA assay was linear from 10 to 240 pg/mL. The mean recovery of spiked THCA in oral fluid was 104%, and precision was 4% at 20 pg/mL using fortified negative samples. This method was rugged and robust, providing detection and quantification of THCA in oral fluids at levels not previously reported. Results of this study showed that THCA was detectable in 21 of 26 oral fluid samples previously reported positive for THC. The range of concentrations from these samples was from 10 pg/mL up to 142 pg/mL THCA.