Thin-layer chromatography on silver nitrate-impregnated silica gel for analysis of homemade tetrahydrocannabinol...

Various forms of cannabidiol (CBD)-containing products are sold in Japan. CBD is easily converted to mixtures of ∆⁹-tetrahydrocannabinol (∆⁹-THC) and its isomer, ∆⁸-THC, using household chemicals like diluted hydrochloric acid. This ease of production increases concerns regarding production of homemade THC mixtures. It is difficult to separate ∆⁹-THC, ∆⁸-THC, and CBD using thin-layer chromatography (TLC) on conventional silica gel. The selectivity of TLC on silver nitrate-impregnated silica gel (AgNO₃-silica gel) differs from that of conventional silica gel. This study thus aimed to evaluate the separation ability of AgNO₃-silica gel TLC.

To evaluate potential separation ability, standards of five THC isomers (∆⁹-THC, ∆⁸-THC, a pair of diastereomers of ∆¹⁰-THC, and ∆^6a,10a-THC), CBD, CBN, and ∆⁹-THCA were analyzed by 10% AgNO₃-silica gel TLC (developed using toluene, system A) and silica gel TLC [developed using n-hexane/diethyl ether (8:2, v/v), system B]. Then, mock homemade THC mixtures, prepared by heating crystalline CBD in acidic ethanol, were analyzed using systems A and B.

System A showed clear separation between the five THC isomers and between ∆⁹-THC, ∆⁸-THC, CBD, and their by-products in the mock homemade THC mixture. However, system B did not separate some combinations of THC isomers and gave a single group-like spot to the THC mixture.

AgNO₃-silica gel TLC shows high separation ability between THC isomers and among ∆⁹-THC, ∆⁸-THC, and CBD. It will thus be useful for analyzing homemade THC mixtures.