Discrimination of hemp and marijuana using a fieldable, combined, colorimetric/spectrophotometric approach
Bernstein, Alexis Ryan
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The passage of the 2018 Farm Bill, which included the legalization of regulated hemp production, is causing identification concerns within the forensic science community. Cannabis has two legal constructs, hemp and marijuana, which are macroscopically and microscopically indistinguishable. Hemp and marijuana both contain Δ9-tetrahydrocannabinol (THC), however, the difference between them is based on the percentage of THC by dry weight. Per Section 7606 of the Agricultural Act, hemp is defined as containing less than 0.3% THC by dry weight. This project aims to create a commercially available, off the shelf, fieldable test kit to discriminate between hemp and marijuana. To be able to discriminate between the two categories, it will be important to be able to quantitate the percentage of THC. Fast Blue BB salt (FBBBS) has been shown in previous studies to produce distinct color changes with cannabidiol (CBD) and THC. Eight hemp varieties were obtained, as well as five varieties of marijuana. Cannabinoids were extracted from the plant material with the use of acetonitrile. The colorimetric reaction with FBBBS uses sodium hydroxide as the catalyst. Following the reaction, the samples were analyzed using one of two spectrophotometers, a commercially available handheld device and the other a larger bench-top style spectrophotometer. Qualitative results to date indicate that FBBBS produces a different color change with hemp and marijuana. Hemp produces a dark orange, whereas marijuana produces a golden yellow. Additionally, Ultraviolet–Visible Spectroscopy results show that there are differences in the peak patterns between hemp and marijuana. There are commonalities of absorbances at particular wavelengths between different varieties of hemp, as well as the different varieties of marijuana. This study is to be further expanded on with some of the steps listed as Future Directions. Quantitative data has not yet been obtained, which is an important aspect of the field-test kit to differentiate between the two categories of cannabis. Furthermore, calibration curves will need to be created and used to quantitate the amount of THC and CBD present in purchased samples. A prototype kit has been constructed, consisting of a ruggedized Pelican™ case, a handheld visible spectrophotometer, a sample homogenizer, solvents, transfer pipettes and cuvettes. Another spectrophotometer will be obtained that scans a wider wavelength range.