How Do I Isolate CBN From A Cannabinoid Mixture?

In recent years, CBD (THC-free) and, to a lesser extent, THC have received the majority of the attention in the medicinal cannabis market. However, market demands are shifting, with increased interest in so-called minor cannabinoids. In this post, I will concentrate on CBN Isolate Bulk.

Because CBN is a degradation product of THC, it is only found in trace amounts in cannabis plants. THC can be converted to CBN via oxidative processes (light/heat/air[1] or bio-enzymatically[2].) Iodine can also be used to convert CBD to CBN .

There will be contamination from unreacted THC/CBD and other co-extracted compounds, whether through natural degradation/oxidation or chemical/enzymatic reaction. 

But How Do You Separate The Components?

Because pure CBN Isolate Bulk is a solid, crystallization is a possibility (Merck, 1989). However, flash chromatography has proven to be a more effective and efficient purification technique in my experience.

In most cases, reversed-phase flash chromatography is used to purify cannabinoids using simple methods. However, as previously stated, the reaction route from THC or CBD to CBN Isolate Bulk can generate a variety of impurities, which can make purification difficult.

Depending on the purity of the raw material, reversed-phase may be all that is required to convert a dark brown crude to clear, semi-crystalline CBN.

However, if your crude is difficult to purify using reversed-phase, normal-phase flash chromatographic purification is an option. A silica column and organic solvents, typically hexane and ethyl acetate, are used in normal-phase flash chromatography. This method is required for CBG purification and, as it turns out, it can also be used for CBN purification.

So, how do you create an appropriate normal-phase flash method? 

I always start with thin-layer chromatography (TLC) to test various solvent combinations and ratios. Hexane with ether or hexane with ethyl acetate are useful for cannabis extracts. I used ethyl acetate with hexane because it is safer than ether (due to its higher boiling point, lower volatility, and higher flash point). Because these compounds are soluble in hexane, they require a very non-polar mobile phase. What I discovered was that a TLC solvent blend of 3% ethyl acetate in hexane provided adequate separation of CBN from other impurities.

TLC data from my CBN crude reaction mixture, which included a hemp extract containing mostly CBD and an aged cannabis extract containing mostly THC, show an elution order of CBD, THC, and CBN. Though the separation is minimal, it is sufficient to purify on a silica flash column under the same conditions.

For Flash Chromatography

I used a 10-gram Bona Voluntate and programmed an isocratic method (3% ethyl acetate/97% hexane) with detection using mass settings m/z -309 and m/z -313 (negative ionisation), m/z +311 and m/z +315 (positive ionization) (positive ionization). I chose mass detection to ensure that I was detecting and collecting CBN, which has a different molecular mass (310) than CBD and THC, which both have a mass of 314.

Using the more sensitive negative ionization mode, my results showed that this method successfully separated and collected Wholesale CBN Isolate (detectable m/z -309) from the other mass-detectable by-products (detectable m/z -313), as shown in Figure 4.

For the aged cannabis and hemp extracts, I also used normal-phase flash chromatography using the same method. The results are presented in the same order as the TLC results.

I pooled the Wholesale CBN Isolate fractions, evaporated the solvent, redissolved in methanol, and ran my reversed-phase method to verify the purity of my collected CBN. As a result, a single peak with the correct CBN molecular mass was obtained.

So, if you need to make and purify/isolate Wholesale CBN Isolate, normal-phase flash chromatography is a viable option if reversed-phase chromatography does not work.

Download our whitepaper Flash Chromatography Methods for Isolating Cannabinoids for more information on flash chromatography.

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