The testing of whole blood samples for tetrahydrocannabinol (Δ-9-THC) consumption is routine and has been around for many decades. Δ-9-THC is metabolized into 11-Hydroxy-Δ9-tetrahydrocannabinol (11-OH-Δ-9-THC) and further into 11-nor-9-carboxy-Δ-9-THC (Δ-9-THC-COOH). It is important to test for the parent and both metabolites to properly monitor for THC usage.
As more isomers of Δ-9-THC become available on the market, testing becomes more complicated and novel methods are needed to achieve isomeric resolution. One such isomer, Δ-8-THC, is federally unregulated in the United States and readily available for purchase in many stores. This compound forms its own hydroxylated and carboxylated metabolites, (11-OH-Δ-8-THC and Δ-8-THC-COOH), that must be chromatographically resolved from their isomeric metabolites. The resolution of isomeric metabolites is key in reporting accurate specimen findings and poor resolution, especially when one isomer is in much greater abundance than the other, can result in quantitation issues and invalid data.
In this study, an LC-MS/MS method was successfully developed for reliable and accurate testing of Δ-8/9-THC isomers and isomer metabolites in whole blood. The method was determined to be quick, rugged, and sensitive enough to meet reporting guidelines for clinical and forensic toxicology laboratories. While C18 phase columns may show some selectivity for the three isomer pairs, full resolution of the isomers is needed for accurate quantitation. To achieve this resolution on a C18 phase would likely result in a lengthy analytical runtime. The FluoroPhenyl ligand shows selectivity for all three isomer pairs, allowing for adequate separation of the analytes in a reasonable analytical runtime.
