11-nor-Delta9-tetrahydrocannabinol-9-carboxylic acid ethyl ester (THC-COOEt) unsuccessful search for a marker of combined cannabis and alcohol consumption.
11-Nor-Delta(9)-tetrahydrocannabinol-9-carboxylic acid ethyl ester (THC-COOEt) can be presumed to be a mixed metabolite formed during combined consumption of cannabinoids and alcohol. In order to examine this hypothesis, THC-COOEt and its deuterated analogue D(3)-THC-COOEt were synthesized as reference substance and internal standard from the corresponding carboxylic acids and diazoethane and methods were developed for the sensitive detection of THC-COOEt in plasma and hair based on gas chromatography-electron impact mass spectrometry after silylation with N-methyl-N-tert-butyldimethylsilyl-trifluoroacetamide and gas chromatography-negative chemical ionization mass spectrometry (GC-NCI-MS) as well as tandem mass spectrometry (GC-NCI-MS-MS) after derivatization with pentafluoropropionyl anhydride. The methods were applied for THC-COOEt determination to plasma samples from 22 drunk driving cases which contained both ethanol (0.30-2.16 mgg) and THC-COOH (15-252 ngmL) as well as to 12 hair samples from drug fatalities which were both positive for THC (0.09-2.04 ngmg) and fatty acid ethyl esters as markers of chronic alcohol abuse (0.70-6.3 ngmg). In none of these samples THC-COOEt could be found with limits of detection of 0.3 ngmL in plasma and 2 pgmg in hair in 11 samples using GC-NCI-MS and 0.2 pgmg in one sample using GC-NCI-MS. Therefore, the use of this compound as a marker for combined cannabis and alcohol consumption could not be achieved.