Quantitative and qualitative spectroscopic parameters determination of major cannabinoids

Cannabis based products are widely used for various medicinal conditions. Currently, the most common method to identify and quantify cannabinoids are liquid chromatographic methods coupled to UV-VIS or mass spectrometric detectors. As cannabinoids are fluorescent compounds, fluorescent-based detection methods are gaining increasing interest. Consequently, a comprehensive qualitative and quantitative determination of fluorescence characteristics of major cannabinoids is warranted. In the present study we have determined the fluorescent excitation-emission-spectrum of 13 major cannabinoid standards and calculated their molar extinction coefficient (epsilon) and quantum yield (Phi) values. Furthermore, we examined the correlation between epsilon and Phi to available physico-chemical substance descriptors, namely, octanol/water partitioning coefficient, molar weight and boiling point. The cannabinoids displayed a characteristic fluorescence excitation (225-400 nm)-emission (300-525 nm) signal. Neutral and acid cannabinoids could be distinguished based on their characteristic excitation-emission spectrum, namely neutral cannabinoids exhibited maximal intensities at 280 nm excitation and 300 nm emission, while acidic cannabinoids displayed maximal intensity at 300 nm excitation and 400 nm emission. Moreover, cannabinoids with overlapping UV spectrum (such as Delta 9-trans-tetrahydrocannabinolic acid, cannabidiolic acid and Cannabigerolic acid) were found to have overlapping fluorescence excitation-emission spectrum, due to the same number of conjugated double bonds and the presence or absence of a carboxylic group. The calculated epsilon and Phi values were found to negatively correlate with each other. The spectral data provided hereby could assist to develop tools for initial screening of extracted samples for the presence of cannabinoids.