While column chromatography presents a common method for separating different species in a mixture,the fractionation of different cannabis compounds is sometimes not absolute, despite being both time and financially consuming.
This is where experts believe flash chromatography can offer an all-around more efficient alternative.
What is Flash Chromatography?
Flash chromatography is “a type of rapid preparative column chromatography where 0.1 – 10 g of mixture is separated in less than 15 minutes by using pressurized gas to drive the mobile phase through the column.”
In flash chromatography, gravity or some external source of pressure pushes the mobile phase through the column which is packed with a solid stationary phase. The cannabis compounds interact with the solid stationary phase for differing amounts of time, and are eluted in order of increasing polarity in the column.
What is Reversed-phase Chromatography
Reversed-phase chromatography, in general, is used when cannabis compounds with very different effects and applications, like THC and CBD, have travelled through the silica stationary phase with roughly the same speed and, as a result, haven’t separated enough in the column. When it comes to CBD concentrates which are intended to be non-intoxicating, even a small amount of THC is enough to compromise the final product.
Reversed-phase chromatography employs a special hydrocarbon-coated silica which reverses the elution order.Their ratio of the polar solvents used, like acetonitrile and water, is gradually increased in order to draw the nonpolar compounds through the stationary phase. CBD travels more quickly through the silica since THC has a stronger affinity to the hydrophobic stationary phase, making reversed-phase chromatography great for removing THC from CBD-focused extracts.
Reversed-phase Flash Chromatography with Step Gradient
Reversed-phase flash chromatography tends to achieve higher results of its slower counterpart because if done right, the separation of the respective peaks of THC and CBD can be very tangible. In their efforts to further refine this process, experts tried to use a linear gradient of water and ethanol but deemed the overall process efficient enough – time, money, and solvent-wise.Using a step gradient, however, has been found to do a significantly better job at reducing THC contamination while also being more efficient on all levels, when compared to a linear gradient.
Orthogonal Flash Column Chromatography
This is basically a combination – reversed-phased flash chromatography, followed by normal-phase flash chromatography, in a cycle which ends when the desired purity is achieved.The reason to employ normal-phase chromatography is to remove the terpenes and colored pigments like chlorophyll, which are often found in the reversed-phase fractions. This way, each cycle takes care of the separation of THC and CBD on the one hand, and the separation of THC and CBD from other cannabis compounds on the other.
The takeaway here is that as efficient as flash chromatography might be, the purification of complex mixtures can’t be achieved by any single method. The secret to high purity when it comes to flash chromatography lies in the combination of reverse-phase and normal-phase flash chromatography since the two complement each other.
Overall, flash chromatography isn’t exactly straightforward and might require some experimentation and monitoring to see what works best in your particular case. However, when done right, this method can be highly rewarding and efficient on many levels.