For most consumers, cannabis chromatography is a little-known element of the cannabis and hemp purification and testing process. However, it plays an integral role in the quality, look, and taste of the final product. Originally developed in the 1900s, this age-old separation technique is helping cannabis companies clean up crude oil for safe use. 

What Is Chromatography?

First things first, what is chromatography in the most basic sense?

Chromatography is a technique used to separate components of a mixture. In this case, the mixture would be a cannabinoid-based extract. Analytical testing labs use this process to test for potency and purity. Processors use the same scientific concepts to separate the therapeutic compounds and filter out the undesirables.

During the chromatography process, the extract and solvent mixture, the mobile phase, passes through a stationary phase (usually a silica-based media). Essentially, every compound in the extract travels through the stationary phase at a different speed enabling separation of compounds.

How Does Chromatography Work?

This separation technique requires a primary mixture (gas or liquid) moving over the surface of another stationary state of matter (liquid or solid). In this case, a liquid crude oil moves past the solid stationary phase. As the molecules move past the surface of the solid, some temporarily adhere to its surface through a process called adsorption.

Adsorption differs from absorption in that the molecules are not permanently trapped inside the body of a surface. Essentially, each compound handles adsorption in a different way spending different amounts of time in the solid phase. Since the speeds of adsorption vary, the different compounds spread out allowing for separation.

Chromatographic Techniques

As the commercial need for cannabis increases across the world, health agencies and manufacturers are employing a wide variety of analytical techniques. Each technique has its unique pros and cons. Currently, the techniques are being further refined and continue to provide increasingly effective results. 

Centrifugal Partition Chromatography

Generally, the stationary phase is made of silica or another solid state of matter. With CPC, however, the stationary phase is a liquid that is spun around to remain in one place while the liquid mobile phase goes through the column. Compared to other methods, CPC has fast flow rates and uses less solvents than other methods. The lack of solid particles reduces clogs and does not require replacement like traditional silica media and cartridges. It can be used for both testing and purification. 

Flash Chromatography

Flash chromatography is an effective technique in the purification of THC and CBD and the removal of pesticides. It works with pressurized gas to move the mobile phase through the solid stationary phase at a quick rate. As the compounds move through the solid phase, they are eluted from highest to lowest polarity. This technique is perfect for the fast separation of compounds with different polarities.

Reversed Phase Chromatography

Reversed-phase chromatography is another mode of the flash method that uses a unique hydrocarbon-coated silica to reverse the order of polarity. In this case, this method switches the polarities of the mobile and solid phases to elute hydrophilic molecules, such as THC, first. This method is ideal for use when separating compounds with similar polarities, such as CBD and THC, since the traditional method cannot separate the compounds enough.

High Performance Liquid Chromatography

High performance liquid chromatography (HPLC) is another key analytical technique used in the identification of cannabinoid concentrations. HPLC is a type of liquid chromatography for compound identification or sample extraction from crude oil. As the industry standard, it boasts many advantages but can be costly due to its stationery columns and can have slightly longer run times. This is used for testing purposes.

Gas Chromatography

Gas chromatography is a popular analytical tool used in cannabis testing. GC is usually paired with a flame ionization detector (FID) and MS, Mass Spectrometer. GC with FID is helpful in providing information about cannabinoids and terpenes but uses heat, which can cause decarboxylation of acidic compounds altering the original chemical profile. This is used for testing purposes.

Supercritical Fluid Chromatography

In SFC, labs use carbon dioxide in its supercritical state, which has both liquid and gaseous traits, for the mobile phase. When extracted using supercritical CO2, this method boasts high diffusivity, low viscosity, and unparalleled sustainability since it can be quickly recycled and does not release harmful chemicals into the environment. 

Purification & Analysis in the Cannabis Industry

In the cannabis industry, chromatography is used for a lot of important  applications. For one, chromatography is the primary way of testing cannabis. From flower to extracts, tinctures, and also edibles, different forms of chromatography are used to test for different compounds in cannabis related products . In addition, chromatography can also be used to help in the purification of cannabis extracts, which is especially important for medicinal purposes. However, both cannot be performed at the same time.

Analytical Testing

In the commercial sector, third-party analytical testing labs use various methods of chromatography to test for cannabinoid and terpene concentrations, as well as pesticides, heavy metals, and other contaminants from a cannabis sample. Chromatography helps ensure the content of these do not exceed state cutoff levels.

By far, the most common type of chromatography used for testing is HPLC. Many labs use this technique due to its incredible accuracy and lack of heating involved during the process. In the end, testing results are available as certificates of analysis (COA) for consumers.

Purification

In the processing sector, chromatography methods are used to filter out compounds based on the desired end product. Chromatography can help to isolate and capture different cannabinoids in separate collection vessels. 

In order to isolate and separately collect certain compounds, crude oil goes through media, usually silica. The different compounds in the extract will have different absorption rates, meaning they have different levels of “stickiness” to the media causing them to go through it at different rates.

Liquid chromatography can also be used in the complete removal of certain cannabinoids. In a separate column, crude oil is passed through the absorbent media to permanently separate certain compounds from the final product. In most instances, THC is taken out of hemp-derived extracts to remain within the federal and state threshold. 

Chromatography is a crucial step in the supply chain, particularly during extraction and analysis. Its versatility and effectiveness propel the cannabis and hemp industry to new heights in purification and analysis. As the tastes and sensibilities for cannabis products change, old and new chromatographic techniques can enhance the experience of cannabinoid products for all types of users.