Analytical techniques for the differentiation of hemp and marijuana
Pieslak, Julie Randi
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The passage of the 2018 Farm Bill created a legal distinction between hemp and marijuana, both of which were previously illegal under federal law. The 2018 Farm Bill federally legalized hemp which became defined as any cannabis or cannabis-derived product containing less than 0.3% Δ9-tetrahydrocannabinol (THC) by dry weight. While marijuana has a high concentration of THC, hemp has a high concentration of cannabidiol (CBD), a cannabinoid similar to THC. Aside from the concentration of specific cannabinoids, hemp and marijuana are macroscopically and microscopically indistinguishable and common forensic testing for cannabis, such as the Duquenois-Levine color test, cannot distinguish between the two. Now that the federal law has been changed, new analytical methods are needed to be able to differentiate between what is legal hemp and what is illegal marijuana. This work employs the use of two analytical methods for the differentiation of hemp and marijuana: Ultraviolet-Visible Spectroscopy (UV-Vis) and Direct Analysis in Real Time-Mass Spectrometry (DART-MS). UV-Vis would be useful for quantitating cannabinoids and is a method that is amenable to field use. Previous studies have shown that fast blue BB salt (FBBBS) complexes with THC and CBD, forming unique chromophores, which can be analyzed by UV-Vis. Seven hemp samples and five marijuana samples were analyzed using this method. The hemp samples displayed two absorbances, the first between 285–290 nanometers (nm) and the second between 469–472 nm. The marijuana samples displayed one absorbance between 292–299 nm. The preparation of the hemp samples consistently produced a light to dark orange color in the sample cuvette while the marijuana samples produced a golden yellow color. Calibration curves were prepared using THC and CBD certified reference materials in an effort to quantitate the cannabinoids in each sample. Reproducibility was an issue and r2 values varied greatly. Differences were seen within the UV-Vis spectra of each sample type but further efforts in quantitation are needed. The use of DART-MS to differentiate between hemp and marijuana is still an ongoing effort. Mass spectra were generated of the previously mentioned hemp and marijuana samples. In almost all analyses, the most abundant ion was m/z 315, the [M+H]+ ion for THC and CBD. A 359 ion was also observed within the samples, which is consistent with tetrahydrocannabinolic acid (THCA), cannabidiolic acid (CBDA) and cannabichromenic acid (CBCA). Subtle differences were seen between the two sample types although it’s difficult to determine how significant these differences are upon visual examination of the mass spectral data. Using Analyze IQ Lab chemometric software, predictive models were built using known hemp and marijuana samples. Preliminary data suggests that the methods built are successful and can correctly classify hemp and marijuana based on their mass spectral differences.