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

Abstract

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.