The detection of Delta9-tetrahydrocannabinol (THC) and 11-nor-9-carboxy-Delta9-tetrahydrocannabinol (THCA) in whole blood using two-dimensional gas chromatography and EI-mass spectrometry.

A method is described for the simultaneous analysis of Delta(9)-tetrahydrocannabinol (THC) and its carboxylic acid metabolite, 11-nor-9-carboxy-Delta(9)-tetrahydrocannabinol (THCA) as their trimethylsiyl derivatives using 2-dimensional chromatography and electron ionization-mass spectrometric detection. The addition of a Deans switch to a standard GC oven allows the use of two chromatographic columns of differing stationary phase to greatly reduce matrix interference. The analytes are extracted from 1 mL of whole blood by first precipitating the blood proteins with the addition of acetonitrile followed by solid-phase extraction. The limit of quantitation for both THC and THCA was determined to be 1.0 ng/mL. The between-run precision at 1.0 ng/mL (N = 30) was 7.7% and 7.4% for THC and THCA, respectively. The method is linear from 1 to 100 ng/mL.