High-level Density Functional Theory Calculations Reveal a Rapid Approach for Differentiating Marijuana from Hemp by DART-HRMS

The chemical fingerprint obtained by rapidly screening C. sativa plant material using direct analysis in real time – high-resolution mass spectrometry (DART-HRMS) at 350 °C presents a characteristic peak at nominal m/z 315 [C21H30O2 + H+], that is indicative of the presence of Δ9-tetrahydrocannabinol (Δ9-THC) and other isomeric cannabinoids, such as cannabinol (CBD), and cannabicitran (CBTC), among others. Analysis by DART-HRMS of reference standards of these cannabinoids revealed the presence of nominal m/z 629, which is consistent with protonated dimers [C42H60O4 + H+]. To explore the structures and binding energies of various protonated dimer complex combinations (e.g. homodimers: Δ9-THC••Δ9-THC, CBD••CBD, CBTC••CBTC; heterodimers: Δ9-THC••CBD, CBD••CBTC, Δ9-THC••CBTC), high level density functional theory (DFT) calculations were performed. The computational results revealed that the THC••THC protonated homodimer complex formed through the interaction of protonated THC with the O-atom of the pyran ring of the THC molecules is more stable than the other complexes by ~2 – 25 kcal/mol. While this is true at room temperature, population analysis of protonated dimer systems showed that as the temperature increases, the populations of the THC••THC and CBD••THC protonated dimers decrease and become insignificant at ≥200 K, while that of the CBD••CBD protonated dimer increases. Thus, at the DART gas stream temperature at which C. sativa samples were analyzed, the peak at m/z 629 corresponds to the CBD••CBD protonated dimer when CBD levels are high (i.e., in hemp). On the other hand, when THC levels are high, such as in marijuana, no m/z 629 peak should be apparent in the DART mass spectra. Rapid screening of confirmed hemp and marijuana samples proved the prediction to be true. Therefore, these computations support the hypothesis that m/z 629 could be the distinguishing feature to enable rapid differentiation of hemp and marijuana plant material by DART-HRMS analysis.