The Development of a Fast and Reliable UV-Visible Spectrophotometric Method for the Quantification of Δ-9-THC and CBD in Plant Material

The 2018 farm bill legalized hemp containing less than 0.3% delta-9 tetrahydrocannabinol (Δ-9-THC) by dry weight, leading to a shift from simple qualitative assessments to more complex quantitative analysis. The legalization of hemp also caused the popularity of cannabis to rise with a high number of cannabis plant seizures by the Drug Enforcement Agency (DEA). A UV-Visible spectrophotometric (UV-VIS) method was developed using Fast Blue B Salt (FBB) to quantify both Δ-9-THC and Cannabidiol (CBD) in plant samples. This method was then compared to Gas Chromatography Mass Spectroscopy (GC-MS), which is currently the standard method for marijuana-hemp concentration determinations in forensic laboratories. Four plant samples were obtained from the National Center for Complementary and Integrative Health (NCCIH) Resource Center for Cannabis and Cannabinoid Research (R3CR) and were analyzed using both UV-VIS and GC-MS instrumentation. Three samples showed variation between instrument techniques with percent differences of 55-119% and 57-173% for Δ-9-THC and CBD, respectively. The fourth sample showed percent difference of 15% and 6% for Δ-9-THC and CBD, respectively. Although there was variation in quantified concentrations, both methods estimated concentrations were consistent with marijuana, as THC levels exceeded 0.6%. This study demonstrates the UV-VIS method may serve as a practical, fast, and cost-efficient tool for presumptive differentiation of marijuana and hemp. This method would be most advantageous to smaller resource-limited laboratories as well as alleviate the caseload pressure on larger forensic labs.