Development of a novel isolation method for Δ⁹-tetrahydrocannabinolic acid-A from cannabis suitable for forensic...

Δ⁹-Tetrahydrocannabinolic acid-A (Δ⁹-THCA-A) is a precursor of Δ⁹-tetrahydrocannabinol in cannabis. Here, considering applicability to ordinary forensic laboratories, we developed a novel isolation method for Δ⁹-THCA-A without the need for special equipment.

Dried pulverized cannabis inflorescence (2 g) was extracted with acetonitrile. After the extract was treated with graphite carbon powder to remove chlorophyll, the solvent was replaced with methanol. The methanol solution was diluted with aqueous sodium hydroxide solution and then washed with a mixture of n-hexane/ethyl acetate (7:1, v/v). The remaining aqueous layer was acidified with acetic acid and extracted with the n-hexane/ethyl acetate mixture. The extract was purified by silver nitrate-impregnated silica gel column chromatography.

The isolation procedure gave a pale beige solid as the final product. The final product was identified as Δ⁹-THCA-A by comparison of the analytical results of gas chromatography/mass spectrometry (GC/MS) after trimethylsilylation and high-performance liquid chromatography with ultraviolet detection (HPLC-UV) with an authentic standard. The final product was confirmed to be highly pure by ¹H-nuclear magnetic resonance spectroscopy in addition to GC/MS and HPLC-UV.

This novel isolation method gave highly pure Δ⁹-THCA-A without using special purification equipment, such as a flash chromatography system or an HPLC system with a fraction collector, which are uncommon in forensic laboratories. This method will be useful for many forensic laboratories that find it difficult to obtain commercial Δ⁹-THCA-A as a standard.