At Restek, we’re into
medical marijuana, from an analytical standpoint, as cannabis is one of the most complex (and controversial) natural products.
That complexity can make it very challenging to analyze, especially as the suite of analytes expands beyond the usual
cannabinoids (e.g. delta-9-THC, cannabidiol, cannabinol) to include other cannabinoids (e.g. cannabigerol, cannabichromene,
delta-8-THC, cannabivarin, etc.) and terpenes, sesquiterpenes, oxygenated terpenes, and pesticides.
Except for the pesticides, many of the compounds listed above either have medicinal properties, or contribute to what is called
the “entourage effect”. Simply put, this is where an “extract” of a natural product, which contains many compounds, including
what is normally thought of as the active ingredient, is more effective in treatment than the pure active ingredient alone.
Medical marijuana researchers are especially interested in plants that have higher cannabidiol concentrations, as cannabidiol
possibly has antioxidant, anticonvulsant, anti-anxiety, and anti-nausea properties, as well as having cytotoxic behavior towards
cancer cells. We recently analyzed 100 seized marijuana samples and found that while most had negligible cannabidiol (CBD)
content, four contained CBD that ranged from 0.8 to 4.8%. More later in another blog on that subject.
We had originally hoped that we could do one extraction procedure (QuEChERS) and determine cannabinoids, pesticides,
terpenes, sesquiterpenes, and oxygenated terpenes (using different dilutions and GC and LC runs, of course), but that may be
unrealistic, especially for terpenes, which are relatively volatile. Given that the QuEChERS procedure generates heat when
MgSO4 and water are mixed, some of the terpenes are likely lost during extraction, which would lead to a low-biased
quantification. Static or dynamic headspace analysis, or SPME, may be more appropriate for terpene analysis.
Stay tuned for more information on our new analytical efforts in this field and be sure and review the old stuff by going to
ChromaBLOGraphy
and then using the Search field type in “marijuana” or “cannabis”.
Posted in
Medical Marijuana
,
Pesticides
|
3 Comments »
Medical Marijuana Solvent Extraction Efficiency – Potency Determinations with GC-FID
Wednesday, August 3rd, 2011 by
Jack Cochran
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
Sky
TM
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
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