Tetrahydrocannabinol, aka THC, is a psychoactive compound found in cannabis and, to a lesser degree, in hemp. Though THC is legal in some locations in the US and Canada, there is a growing market for its non-hallucinogenic cousin, cannabidiol (CBD), which has purported medical benefits.
The problem with isolating CBD from cannabis and hemp is contamination from THC, which is typically present at a moderate to high percentage. In this post, I will provide some insight into rapidly purifying CBD to remove THC.
CBD is shown to provide a cessation of epilepsy episodes, assist with sleep, and anecdotally, reduce pain and inflammation. In fact, GW Pharma’s Epidiolex® (a purified CBD product), was approved by the US FDA in June of 2018 to treat both Dravet’s and Lennox-Gastault syndromes which affect children.
Throughout the Americas and Canada, entrepreneurs see opportunities to establish themselves as premier sources of highly pure CBD. Most utilize at least one extraction procedure followed by winterization or other clarification processes to provide an initial crop clean-up and cannabinoid concentration. However, as with most natural product extractions, many other compounds come along for the ride during extraction and clarification will not remove all of them. That is where flash chromatography comes in.
Reversed-phase flash chromatography separates CBD from THC, and under the right conditions, the separation of peaks (one representing each of these components) can be quite large. A large separation provides for increased sample loads and improved CBD purity (low THC contamination).
Where CBD is legal, THC levels typically need to be less than 0.3%. Other natural products, which are co-extracted, are usually desired providing what is known as an “entourage effect”. These compounds are other non-hallucinogenic cannabinoids along with terpenes and terpenoids.
With the CBD marketplace still evolving, purification methodologies need to as well. Currently, reversed-phase flash chromatography using water-ethanol linear gradients have shown good results but tend to be long and consume a lot of solvent and require significant time, Figure 1.
In this example, 560 mg of a hemp extract is purified on a 12 gram Biotage® SNAP Ultra C18 flash cartridge, a relatively high 4.6% sample load by weight. Although there is separation between CBD (large green peak) and THC+CBC (broad yellow peak), the method is long (13 column volumes = 221 mL), not including column clean-up (another 3-5 column volumes or 50-85 mL). Total solvent consumption is 271-306 mL for this small scale purification so its cost efficiency or throughput is OK but less than ideal (560 mg/290 mL). Increase scale 1000 times to purify 560 grams and ~290 L of solvent would be required.
Since CBD processors need to operate at a high volume (multiple kilos of extract per day), use of a linear gradient, as above, is almost cost prohibitive. Therefore, there is a need for faster, more efficient purification process that minimizes solvent consumption without sacrificing purity and load.
At Biotage, we have experimented with various reversed-phase methods and have found a way to help achieve the hemp and cannabis processor’s THC reduction goals. Rather than use a linear gradient, I have found a step gradient is effective at drastically reducing THC contamination in a hemp extract, Figure 2.
This method (which includes column clean-up) reduces solvent use by more than half vs. the above linear gradient (135 mL vs. 280 mL) and provides substantially higher loading along with excellent recovery using the same size column. The load (800 mg) was 6.7% of the column's media weight and 43% higher than the linear gradient load. This increased loading capacity and reduced solvent consumption improves cost efficiency or throughput to 800 mg/135 mL.
Of the total 800 mg loaded, 780 mg were recovered (97.5%). Of that, fraction 1 accounted for 51% of the total while fractions 5 and 6 (THC + CBC) accounted for 22%.
To determine how well the step gradient worked, I re-purified fraction 1 using the same step gradient, Figure 3.
The results show increased CBD purity in fraction 1. LC-MS analysis (not shown) indicated the original crude hemp extract contained ~75% CBD (similar to the recovery data) and, that after flash chromatography, fraction 1 was 99% pure CBD. The remaining 1% are terpenes and other cannabinoids including CBC, THC, and CBDV.
This data shows the vast improvement that a short step gradient can make in a high-throughput purification environment increasing crude CBD extract purity from 75% to 99%. In the mean time, we will continue to experiment with other optimization techniques.
For more information on THC remediation, please download our Infographic on the topic.
 PharmaTimes, June 26, 2018