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Important Medical Marijuana Cannabinoids Analyzed by GC-FID on Rxi-35Sil MS and Rtx-35

24 Apr 2014

In a previous post, “Don’t overestimate cannabidiol during medical cannabis potency determinations with gas chromatography. Use stationary phase selectivity for accuracy and hydrogen for fast analysis.”, I recommended a 15m x 0.25mm x 0.25µm Rxi-35Sil MS GC column for fast separations of CBC, CBD, delta-8-THC, delta-9-THC, CBG, and CBN with hydrogen carrier gas. This same separation can be done on a 15m x 0.53mm x 0.50µm Rxi-35Sil MS, a column format that has additional sample loading capacity and ruggedness, at the cost of slightly longer run times. We also have a 15m x 0.53mm x 0.50µm Rtx-35, a 35% pendant phenyl-type column that doesn’t have the arylene-modification that the 35Sil MS uses for increased thermal stability. (The 35 has a 300°C maximum operating temperature and the 35Sil MS can go to 360°C!) Sometimes the arylene-modified columns and the pendant-only columns can differ in selectivity, but in this case the chromatograms are very close to each other.

One novel twist I put on this work was to prepare a standard that had different relative concentrations of cannabinoids. Although the variation of concentrations in medical cannabis can range somewhat widely based on strain, I decided to stagger the concentrations from high to low as delta-9-THC, cannabidiol, cannabigerol, cannabichromene, delta-8-THC, cannabinol. This potentially allows more accurate determination of cannabinoids versus using a standard that is equal in concentration for all compounds, even while considering that the flame ionization detector probably has the widest linear dynamic range for GC. This variable-concentration-standard also allows elution order mapping/confirmation of cannabinoids for GC columns (and LC columns).  You can build your own “JC Mix” with individual cannabinoid standards located on our Medical Marijuana web page.


35Sil MS Smart Mix

 

 


35 Smart Mix 5