HEXADEUTERO-11-NOR-DELTA-9-TETRAHYDROCANNABINOL-9-CARBOXYLIC ACID - A SUPERIOR INTERNAL STANDARD FOR THE GC MS ANALYSIS OF DELTA-9-THC ACID METABOLITE IN BIOLOGICAL SPECIMENS

GC/MS analysis of biological specimens is believed to be the most forensically accepted method for confirming the presence of abused drugs. 11-Nor-△S-tetrahydrocannabinol-9-carboxylic acid (△B-THC-COOH) is the major metabolite of △9-tetrahydrocannabinol (△g-THC) for which testing (including GC/MS) is directed as an indication of marijuana use. The currently available internal standard for △9-THC-COOH is d3-△9-THC-COOH, which has the deuterium atoms located on the side chain. In addition to the high cost of this compound, it suffers from a limited dynamic range of analysis, especially when the methyl derivative is used. This is because of a contribution to one of the internal standard ions (m/z 316) from a fragmentation of the natural drug which involves loss of the side chain. The new internal standard, d6-11-nor-△9-tetrahydrocannabinol-9-carboxylic acid (d6-△9-THC-COOH), avoids these disadvantages. The six deuterium atoms are located on the two methyl groups of Carbon 6 in the dibenzopyran structure. The dynamic range of analysis with the new internal standard was tested between 6.25 to 1, 000 ng/mL with a correlation coefficient of 0.998. Analysis of several urine specimens for △9-THC metabolite using both d3- and d6- internal standards showed a correlation coefficient of 0.9987. © 1992, Oxford University Press. All rights reserved.