On the effect of the stationary phase chemistry and the composition of the mobile phase on retention and selectivity of cannabinoids under normal phase conditions

Due to the progress decriminalization of recreational cannabis and the growing interest in hemp and cannabis products, in the last years much effort has been devoted to investigating the biological and pharmacological activity of cannabinoids in order to ensure consumer safety. However, only 20% of natural occurring cannabinoids (or phytocannabinoids) is currently available as a certified reference material and new cannabinoids are continuously being discovered [1]. The purification of cannabinoids, especially from hemp extracts, could be very challenging due to the presence of a large number of components (such as terpenes, waxes, other cannabinoids, etc.), many of them with similar chemical structure. This points the attention on the need of fast, efficient and cost-effective methods for the isolation and purification of cannabinoids, especially from plant materials [2]. In this field, preparative liquid chromatography (LC) and multicolumn countercurrent chromatography (MCC) are the most employed technique for industrial purification of cannabinoids. However, a deeper understanding of the fundamentals of cannabinoids retention is required for the selection of the optimal combination of mobile phases and column chemistries. In this work, the effect of the stationary phase polarity on retention, separation and selectivity of five different neutral phytocannabinoids, namely CBD, CBC, CBG, CBN D9-THC, has been investigated on four 150x4 mm polar columns packed with 5 μm particles under normal phase (NP) isocratic elution conditions. Results, obtained in an analytical scale, indicate that NP chromatography could be very promising if applied to large scale separations and purifications of cannabinoids, when compared to RP chromatography, due to fast analysis, low backpressure, high selectivity and high sample solubility.