Color determination method and evaluation of methods for the detection of cannabinoids by thin-layer chromatography (TLC).

Cannabis sativa is the drug of abuse most cultivated, trafficked, and consumed worldwide. One of several techniques used to detect cannabinoids is based on the thin-layer chromatography (TLC). However, the designation of the colors observed can be inaccurate and not reproducible. The designation of colors goes beyond physical and physiological aspects, because what is conventionally called color is a socio-cultural construction. Thus, the objective of this paper was to evaluate the different TLC methods to detection of cannabinoids, and apply standardization method in naming of colors. TLC analysis performed using silica gel 60 F254 as a stationary phase. Three mobile phase compositions [hexane:chloroform (8:2 v:v), hexane:ethyl ether (8:2 v:v), and chloroform:hexane (8:2 v:v)], as well as, two different solutions of Fast Blue B salt (FBBS, Azoic Diazo No. 48) and Fast Blue RR (FBRR, Azoic Diazo No. 24) were evaluated. Determination of colors names was realized through the Sci-Chromus® software. The best resolution was obtained using hexane:ethyl ether (8:2 v:v) as a mobile phase. It was observed that although the cannabidiol (CBD), delta-9-tetrahydrocannabinol (Δ -THC), cannabinol (CBN), and cannabigerol (CBG) were detect using both the FBBS- and FBRR-acidified solutions, the best visualization was achieved using the latter reagent. To the best of our knowledge, this is the first study that applied and demonstrated a method for standardization and denomination of colors in the TLC analysis of cannabinoids. This method was able to reduce the subjectivity in naming the colors observed and presented several application possibilities.