Enhanced selectivity in the determination of delta9-tetrahydrocannabinol and two major metabolites in serum using ion-trap GC-MS-MS.

Cannabinoids were extracted from serum with C18 SPE cartridges and analyzed as their trimethylsilyl (TMS) derivatives. A benchtop gas chromatography-tandem mass spectrometry (GC-MS-MS) system based on an ion trap with external ionization was used. Quantitation was done in relation to trideuterated internal standards in dual MS-MS mode. Confirmation of the identity for the three compounds of interest, delta9-tetrahydrocannabinol (THC), 11-hydroxy-delta9-tetrahydrocannabinol (11-OH-THC), and 11-nor-9-carboxy-delta9-tetrahydrocannabinol (THCCOOH), was achieved by registering the daughter spectra in full scan mode. It was possible to identify the three compounds at concentrations down to 0.25 microg/L for THC, 0.5 microg/L for 11-OH-THC, and < 2.5 microg/L for THCCOOH by comparison with reference spectra. The limits of quantitation are better than 2 microg/L for THC, 5 microg/L for 11-OH-THC, and 8 microg/L for THCCOOH. The within-run and day-to-day precision for the three analytes were very similar and ranged from 4.2 to 10.4%.