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Medical Marijuana Solvent Extraction Efficiency – Potency Determinations with GC-FID

3 August 2011
By
  • Jack Cochran
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Amanda Rigdon and I recently investigated the extraction efficiency of various solvents for medical marijuana potency determinations (although technically we’re not working with medical marijuana; instead we use seized illicit marijuana and did the work under the auspices of the Penn State University Police Department with Randy Hoffman, an Evidence Technician there).

We used an Agilent GC-FID with split injection on a Restek Premium 4mm Precision Liner with Wool and a 15m x 0.25mm x 0.25µm Rxi-5Sil MS.  A cannabinoids standard containing cannabidiol, delta-9-THC, and cannabinol was used for calibration and quantification.  The last eluting compound of interest, cannabinol, had a retention time of about 4.85 min.

One consideration for extraction efficiency in marijuana potency determination is that THCA is the main source for THC determined with GC.  (THCA, or delta-9- tetrahydrocannabinolcarboxylic acid, decarboxylates during smoking, or other heating, including in a hot GC inlet, to delta-9-THC.)  Solvent polarity index (higher value means more polar solvent) was used to assure a range of tested solvents from non-polar (hexane) to highly polar (acetonitrile and methanol) as we tried to achieve maximum extraction efficiency of THCA from marijuana.  Approximately 0.2g ground samples (except in the case of acetonitrile where we ran out of marijuana and only used just over 0.1g) were extracted with 40mL solvent in a precleaned VOA vial.

As seen in the bar graph, methanol was the most efficient extraction solvent for delta-9-THCA (analyzed as THC).  Generally, the delta-9-THCA extraction efficiency correlated with solvent polarity, although not dramatically so.  We had hoped that the non-polar solvent, hexane, would be equally efficient as the polar solvents for THCA extraction for one very important reason that can be seen in the photograph of the extracted samples, and that is, reduced extraction of chlorophyll by the non-polar solvent.  Chlorophyll, a non-volatile substance providing the green color to the extracts quickly degrades GC inlet and column performance and could lead to erroneous potency determinations over time without timely GC inlet maintenance.

More later on the LC analysis of THCA from my colleague Amanda...




Comments

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Sat, Jan 17, 2015

Hi Lisa: You are describing what I would see as the benefits for acetonitrile very well in your comment. I still think more experiments are necessary, but since PA is not a medical cannabis state, we generally will need to rely on experimentalists in states where cannabis is legal to do that work. I don't advise evaporating an extract to dryness and reconstituting as a general practice. Evaporation takes time and equipment and is extra handling, probably more so than is necessary, that will potentially compromise quantification for potency, especially if the reconstitution is inefficient. For example, it is possible that the chlorophyll could hold on to the cannabinoids and the acetonitrile would not be able to redissolve them. Another bad thing about evaporation in this case is that it will almost surely lead to losses of volatile terpenes if you go to dryness (or even if you don't go to complete dryness). We don't have good information about extraction of terpenes with all of these solvent systems, since that was not the focus of the work, but Amanda Rigdon has started to do some work with terpenes in hops and I believe will be publishing some of that work later. In the mean time, if you look on ChromaBLOGraphy you can check out her work using the full evaporation technique with Headspace GC-FID. Better yet, we have an application note on the subject at the link below. http://www.restek.com/Technical-Resources/Technical-Library/Foods-Flavors-Fragrances/fff_FFAN2045-UNV Thanks for reading ChromaBLOGraphy! JC

Sat, Jan 17, 2015

Hi Dustin: No, we have not compared 100% methanol with the solvent mixture chloroform:methanol (10:90). This is a good idea, as I understand this is an industry solvent system that could lead to better extractions of material, but we find it difficult to do these types of experiments as PA is not a medical cannabis State. As such, our experiments have been on illicit marijuana that the police have confiscated, and the experiments are conducted in the presence of the police. Have you compared extraction efficiency of methanol and chloroform:methanol? If so, can you describe your results? Thanks for reading ChromaBLOGraphy! JC

Wed, Jan 14, 2015

Hello, I hope you will get my message. I'm trying to choose 3 solvents in order to perform the extraction of cannabinoids AND terpenes of cannabis. I was wondering : - you don't say anything about ACN which seems to not extract chlorophyll (according to the color). According to the histograms, it appears that it has a good extraction potency. With MeOH leading to high GC maintenance and ethyl acetate which seems to extract chlorophyll relatively well, would you advice working with ACN ? Thaemajor inconvenient that I see is that it is really expensive.. - which leads to my second question. Considering that MeOH shows the best extraction potency, would it be interesting to extract with it, then evaporate to drynesss and then reconstitue in ACN, in which chlorophyll is not soluble ? Or even in hexane... - do you have an idea about the quality of terpenes extraction with these solvents ? Thank you ! Lisa

Thu, Jan 08, 2015

I see that some samples have more solvent than others. Doesn't that have impact of testing results?

Fri, Jun 27, 2014

Hi Josh: I do not have any data for 190 proof ethanol as an extraction solvent for cannabis for potency determinations. Not sure what you mean about water-soluble components, but would expect ethanol to extract polar compounds (which generally have higher water solubilities) relatively efficiently. JC