Chromatography is sometimes used as an alternative to distillation in the post extraction processing of hemp. The primary advantage of chromatography over distillation is that it does not use heat for separation of the various products in the hemp extract (hemp oil obtained after supercritical fluid extraction).
Distillation separates the various products by boiling the mixture. As every product has a different boiling point, only that product separates out at one particular temperature. Following are the boiling points of various products in cannabis at 1 atmosphere pressure:
- Cannabidiol (CBD): 1600C (3200F) to 1800C (3560F)
- Tetrahydrocannabinol (THC): 1570C (3150F)
- Flavonoids: 1340C (2730F) to 1780C (3520F)
- Terpenes: 1190C (2640F) to 1570C (3150F)
Now, the objectives of post extraction processing of hemp are as follows:
- Maximize CBD content.
- Retain some amount of terpenes and flavonoids which respectively impart a distinctive aroma and flavour to the extract.
- Minimize or even eliminate THC.
- Remove waxes, fats, and lipids.
Because chromatography does not use heat to separate the products, it avoids thermally distorting them i.e. it does not change their chemical composition under the action of heat.
Chromatography dissolves the hemp extract in a fluid (mobile phase) and passes it through a media (stationary phase). Different products pass at different speeds through the media and this enables their separation.
Various types of chromatography used for post extraction processing of hemp include:
- Supercritical Carbon dioxide (sCO2) Chromatography uses sCO2 as the mobile phase.
- Flash Chromatography employs air pressure powered for fast separation. .
- High-Pressure Liquid Chromatography (HPLC) employs pumps to transport the mobile phase at high pressure via carrier gases such as nitrogen or helium.
- Rotary Counter Current Chromatography (CCC) employs a liquid mix as solvent and a liquid stationary phase.
Post extraction processing of hemp is necessary even if an accurate method such as supercritical fluid extraction (SCFE) is used for hemp extraction. SCFE uses a supercritical fluid (SCF) whose capacity to dissolve products from the cannabis raw material depends largely on its pressure. This capacity, called solvent power:
- Rises at elevated pressure; and
- Falls as the pressure declines.
Moreover, at a certain pressure, the SCF extracts:
- One particular product.
- Very little or zero quantities of other products.
This property of the SCF makes the SCFE process a very precise one. Nevertheless, the minor quantities of other products need to be eliminated. And it is the removal of these that requires the application hemp post extraction processing.