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Cannabinoid Crystallization from CO2 extract (Thank you to Confidence Analytics.)

At Confidence Analytics, we strive to understand more about Cannabis every day. Not only do we perform experiments to improve our procedures and data quality, but we have the opportunity to try new and exciting techniques in the laboratory.

This week, Molecular Biologist Levi Boss and Chemist Zachary Iszard bring you some preliminary results on a project that fascinates them: crystallization and isolation of cannabinoids.

In much of the chemical industry, recrystallization is used to achieve very high purity on a large scale without complex equipment. The target compound of interest, is dissolved in a specific solvent to form a solution. Low pressure and heat are applied so that the target compound crashes out of solution, or precipitates out as a solid. The target compound will prefer to stick to other molecules like itself, and will do so in an ordered fashion – forming a crystal. When a substance crystallizes, any impurities – which have different chemical structures – are excluded from the crystal lattice, simply because the impurities interfere with the tightly ordered structure and prefer to either remain in solution or self-associate. Examples of this process are the formation of rock salt and rock candy by evaporation. A Cannabis-specific example most readers are likely familiar with would be the winterization of concentrates by low temperature. In this example, the plant waxes and lipids are the target compounds. Evaporation and cooling are two different ways to make the target compound less soluble in the chosen solvent, and thus precipitate out.

We found that a semi-solid CO­2 oil (75% total cannabinoids) will form localized crystals at the bottom of a small glass beaker over several days under slight heat. The experiment was repeated and controlled using an ethanol solution highly saturated with CO2 oil, filtered through a 0.2 um nylon filter, and winterized. The results were pleasing: much larger and more numerous crystals!

We let these beakers heat at about 40°C (104°F) for another few days, and the crystals had indeed grown. We also noticed that the crystals had piled up higher than the surrounding layer of concentrate, and that bubbles had formed underneath these crystals. With a careful eye and a magnifying glass, it is easy to see that some of the crystals are colorless – a very general indicator of purity. We hypothesized that these bubbles were tell-tale indicators of decarboxylation of THC-A, since they increased in size over an extended period of time under testing conditions – hinting at a chemical reaction proceeding toward completion.

Samples were taken for HPLC potency analysis, and the results were promising. The crystal sample, though lower in total cannabinoid content, was enriched in THC-A compared to the surrounding material, which had a higher percentage of every other minor cannabinoid. This supports our hypothesis that THC-A is the material that is observed crystallizing. Since THC-A was the majority compound in the concentrate sample, none of this is terribly surprising. Because the crystals themselves were small, we couldn’t pick out only crystals for analysis, so our results are indeed imperfect.

The next task is to improve the crystallization method, and to form larger isolated crystals more quickly.


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