Article: Characterization of Crystalline Structures in Cannabis Extracts
The Journal of Forensic Sciences recently published a new article by Microtrace Microscopist Otyllia Abraham, entitled “Optical and spectroscopic characterization of crystalline structures in cannabis extracts.” The paper demonstrates optical characterization methods by polarized light microscopy that can assist with screening visually similar samples of marijuana-derived and hemp-derived solvent extracts. These characterizations can then be confirmed by a combination of infrared spectroscopy and X-ray diffraction. Ms. Abraham’s paper is derived from a portion of her Masters research.
“Optical and spectroscopic characterization of crystalline structures in cannabis extracts”
Otyllia R. Abraham MS, Ruth Waddell Smith PhD
Journal of Forensic Sciences, 2021
Marijuana and hemp represent two broad classes of Cannabis sativa plants that are distinguished based on the concentration of the psychoactive cannabinoid delta-9-tetrahydrocannabinol (Δ9-THC). In this work, solvent extracts derived from marijuana and hemp were characterized using optical and spectroscopic techniques. The crystalline components of the solvent extracts were first analyzed using polarized light microscopy to determine optical properties, namely, crystal system, optical sign, and principle refractive indices. Crystals from the marijuana-derived extracts exhibited an orthorhombic crystal system and were optically negative, with nβ between 1.6320 and 1.6330 ± 0.0002. In contrast, crystals from hemp-derived extracts exhibited a monoclinic crystal system and were optically positive, with nβ between 1.600 and 1.6040 ± 0.0002. Crystals were further distinguished through infrared spectroscopy, which highlighted structural differences between the two sample types, primarily based on differences in O-H stretching. Finally, single-crystal X-ray diffraction was used to definitively identify the crystalline components, confirming the presence of tetrahydrocannabinolic acid in marijuana-derived extracts and cannabidiol in hemp-derived extracts. Given the differences in crystal structure identified between marijuana-derived and hemp-derived solvent extracts, optical characterization provides a screening method to differentiate visually similar samples prior to confirmatory analysis.