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

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.