Evaluation of decarboxylation efficiency of Δ9-tetrahydrocannabinolic acid and cannabidiolic acid by UNODC method.

Purpose: Decarboxylation of Δ⁹-tetrahydrocannabinolic acid (Δ⁹-THCA) to Δ⁹-tetrahydrocannabinol (Δ⁹-THC) by heating is a common method for determining total Δ⁹-THC. In the manual for cannabis identification and analysis, the United Nations Office on Drugs and Crime (UNODC) proposed decarboxylation conditions. Although the manual's primary analytical target is Δ⁹-THC, some reports also quantified cannabidiol (CBD). The authors assessed the efficiency of decarboxylation of Δ⁹-THCA and cannabidiolic acid (CBDA), a carboxylated form of CBD, under four decarboxylation conditions, including the UNODC condition.

Methods: Δ⁹-THCA and CBDA were heated in 2-mL glass vials at 150 °C for 12 min after the following treatment: condition A involves the addition of ethanol without capping, condition B involves non addition of solvent without capping, condition C involves non addition of solvent with capping, and condition D (UNODC condition) involves the addition of 0.5 mg/mL tribenzylamine (TBA) in ethanol without capping. The residue after heating was dissolved in methanol and then analyzed by high-performance liquid chromatography.

Results: The production of Δ⁹-THC and CBD was low (≤ 10.1%) under conditions A and B. Under condition C, Δ⁹-THC production was increased (53.4%), but CBD production was hardly improved (11.7%). Under condition D, Δ⁹-THC and CBD production dramatically increased to 83.2 and 71.0%, respectively.

Conclusions: These findings indicated that TBA improved the production of Δ⁹-THC and CBD from their carboxylated forms; however, even in the presence of TBA, their production did not reach 100%. Forensic toxicologists should understand the effectiveness and limitations of decarboxylation under the UNODC condition.