Purifying your extracted crude is an integral component of your process flow. Two methods, color remediation and chromatography, have similar names and instrumentation (such as N.B.Oler’s Aqua-Tech in Figure 1) but serve different purposes. For this Tech Tuesday, we’ll compare these two techniques and explore their application to the cannabis extraction industry.
Filtration
Filtration, or remediation, uses media (such as activated carbon) and/or size exclusion filters (such as μm-size sintered discs) to remove undesired substances (see Figure 2). Depending on your source biomass and extraction technique, you may want to remove substances such as chlorophyll, heavy metals, and pesticides to both improve your product and to comply with regulatory agencies. Your filter may be known as a Color Remediation Cartridge (CRC) or Color Remediation Column (CRC), and you can use the same filter/media multiple times provided that the media is not saturated and that the filter(s) are not clogged. What is removed (and how much) is determined by the filtration media and filters.
Can: remediate color. Cannot: selectively separate cannabinoids. Chromatography
While, like filtration, chromatography can remove some desired substances from your crude, you can also use chromatography to separate desired substances based on their interaction with the mobile
(solvent) and stationary (media) phases (see Figures 3-4). Depending on the nature of your phases and the length of your chromatography column, your separation may range from very minimal (Figure 5), to separating chemical classes such as terpenes and cannabinoids, to selectively separating individual molecules (ex. THC-A from CBD-A). Be sure to follow an appropriate SOP for fractional collection of elutes!
Can: remediate color and selectively separate cannabinoids. Cannot: media generally cannot be reused multiple time, though filters can be reused after cleaning.
Materials
Filtration and/or chromatography column with appropriate pressure, temperature, and chemical compatibility ratings Typical filtration and chromatography media includes:
-Silica (SiO2, appropriately sized) - Silica gel (ex. 60A from Carbon Chemistry)
-T5 Bentonite Clay -T41 Activated Bleaching Clay (10% Activated Carbon)
Additional Notes
Pay attention to your solvent! Like dissolves like, so be sure to appropriately match your solvent polarity with your media. Be careful with excessive changes in pH, as you may end up degrading your products.
References/Further Reading
Nichols, L. 2: Chromatography. Chemistry LibreTexts (2019). Available at: https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Book:_Organic_Chemistry_Lab_Techniques_(Nichols)/2:_ Chromatography.
Visit nobler.com or contact N.B. Oler at info@nboler.com for products, technical documents, SOPs, and more.
Figure 1. 3D rendering of an Aqua-Tech column built by N.B. Oler.
Figure 5. Remediation (filtration) media (A, B, C, and D; far left) removes undesirable compounds (center two panels), resulting in cleaner product (far right).
Figure 5. Normal chromatography separates using hydrophilic stantionary phase, where hydrophobic molecules elute first.
Figure 5. Reverse-phase chromatography separates using hydrophobic stationary phase, where hydrophilic molecules elute first Since CBD is more hydrophilic than THC, reverse-phase chromatography is ideal for separating CBD from hemp.
Figure 5. Failure to separate. This can occur when there is too much material for the chromatography column to separate the elutes.
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