Experimental and ab initio investigation of the products of reaction from Δ9-tetrahydrocannabinol (Δ9-THC) and the fast blue BB spot reagent in presumptive drug tests for cannabinoids

Cannabis is one of the most abused illicit drugs worldwide while also finding more acceptance for medical and recreational use. Presumptive testing of suspected drug seizures using colorimetric spot tests is an important fast and efficient preliminary step in the identification of drug classes such as the cannabinoids. This study describes the chemical reactions between the Fast Blue BB (FBBB) reagent and three cannabinoids (Δ9-THC, CBD, and CBN) when using a small polymer strip (50 ng LOD) and when using a new capillary microextraction of volatiles (CMV) sorbent device (500 ng LOD). The product chromophore when reacting FBBB and THC was isolated and identified, for the first time, by HNMR and confirmed by accurate mass spectrometry. The coupling of FBBB to the para position (versus the ortho position) relative to the phenolic group of Δ9-THC was expected, and 1H NMR studies and an ab initio reaction coordinate investigation at the B3LYP/3-21g level of theory provide computational support for these findings.