As some of you in the medical cannabis analysis community already know, Restek is currently unable to provide our
cannabinoids standard (34014 – CBD, d9-THC, CBN) for potency testing due to raw material unavailability, specifically for
d9-THC. On behalf of our company, I apologize for the impact this might have on your operations. But I have been working
with the materials we do have to try and create an interim solution for you that involves using delta-8-THC, or d9-THCA, the
acid compound found in cannabis that is decarboxylated to d9-THC during vaporizing or cooking or smoking, or injecting it into
a hot GC inlet for potency determination. You can find conversion values in the literature for THCA versus THC, but
I estimated my specific conversion value using the conditions shown under the chromatogram referencing it from analysis of
delta-8-THC (NOT the acid form). I analyzed an equal-concentration (167 ng/µL each), mixed standard that I built from
individual stocks. I’ve listed the part numbers and current availability (as of 1030 EST, Oct 30 2013) below (name, catalog
number, conc in µg/mL, ampules available in Restek stock):
Cannabichromene, 34092, 1000, 13
Cannabidiol, 34010, 1000, 5
delta-8-THC, 34090, 1000, 32
delta-9-THCA, 34093, 1000, 28
Cannabigerol, 34091, 1000, 38
Cannabinol, 34011, 1000, 23
As you can see from the chromatogram below, delta-9-THC from hot GC inlet analysis of THCA is reduced in response versus
all other non-acid cannabinoids, not surprising based on previous scientific literature in this regard. But the thrust of this work is
to try and provide a starting point for estimating delta-9-THC concentrations based on other approaches, since the standard
GC-FID approach may not be available due to the lack of the delta-9-THC standard. Here are some possible approaches:
Use delta-8-THC for GC-FID quantification of delta-9-THC. - In my work, using the d8-THC for d9-THC quantification (from
a retain 34014 standard) resulted in a d9-THC value of 179 when the concentration was at 167 ng/µL, which is approximately
7% high, not bad.
Use delta-9-THC from d9-THCA for quantification of d9-THC by GC-FID. - This results in a relatively high value if you are
currently using d9-THC for quantification. For example, when analyzing the retained 34014 mix (which contains d9-THC) and
quantifying against d9-THC from THCA, instead of 167, I get 256 ng/µL.
Use a “correction factor” for d9-THC quantification if using d9-THCA for GC-FID quantification. In this case, my correction
factor, based on d8-THC response, would be 0.7 (i.e. multiply d9-THC values determined with quantification using d9-THCA by
0.7 to get values more in line with historical values quantified using the non-acid d9-THC).
Use any of the other cannabinoids (e.g. CBC, CBD, CBG, CBN) to estimate GC-FID quantification for d9-THC since the range
of normalized response factors is relatively narrow (97-108, in my example).
I also know that some analysts are determining the acids (e.g. THCA, CBDA, etc.) using LC, which will provide the most
accurate answer for their concentration in cannabis. We have an LC application for THCA here:
Restek Advantage 2011
An interesting discussion for another day is how to tie any cannabinoids in cannabis determination using either GC or LC back to
the actual dosage of THC (and CBD, etc.) delivered to the patient, since that dosage is impacted by partial conversion of acids to
non-acids during vaporization or smoking. Perhaps food could be the most accurate delivery system, since presumably the acid
forms of the compounds of interest are decarboxylated during the cooking process, and with proper sample preparation and
analysis, THC and CBD and other cannabinoid concentrations can be determined directly.
Medical Marijuana « ChromaBLOGraphy: Restek's Chromatography Blog
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02/08/2014 5:38 P
