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

PURPOSE: 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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.