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Publication Title | Don’t Overestimate Cannabidiol During Medical Cannabis Potency Testing by Gas Chromatography

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Technical Article

Don’t Overestimate Cannabidiol During

Medical Cannabis Potency Testing by

Gas Chromatography

By Jack Cochran

Accurate potency testing of medical cannabis with gas chromatography (GC) depends principally on choosing a column with the right selectivity; otherwise, coelutions between cannabinoids of interest may cause error in potency measurements. Cannabidiol is one of the chief cannabinoids with pharmacological value and provides relief against nausea, anxiety, and in ammation. Potency testing for medical marijuana is o en done using “5-type” GC columns since they are commonly available in most labs. However, on 5-type columns cannabidiol can coelute with cannabichromene, a compound that likely also has medical value and is increas- ingly becoming part of potency testing. To identify and report both of these compounds accurately, a GC column with a di erent stationary phase is needed.

Proper Column Choice Results in More Accurate Potency Data

As shown in Figure 1, cannabinoids are aromatic compounds, meaning they will likely be better separated on a column that contains aromatics in the stationary phase because these stationary phases are more selective for aromatic-containing analytes. A fully non-aromatic stationary phase, like a “1-type” (100% dimethyl polysiloxane) column is not appropriate for this analysis since cannabichromene (CBC) and cannabidiol (CBD) will coelute completely. While 5-type columns (5% phenyl) contain some aromatic component, they generally also produce coelutions for cannabichromene and cannabidiol, depending on the conditions used. At best, CBC and CBD can be only partially resolved on 15 m 5% phenyl columns. Much better separations are obtained on higher phenyl-content phases, such as Rxi®-35Sil MS (35% phenyl type) and Rxi®-17Sil MS (50% phenyl type) columns, as they o er excellent selectivity for aromatic cannabinoids. Not only do both columns resolve cannabichromene and cannabidiol, the chromatograms in Figures 2 and 3 demonstrate that they also separate delta-8-tetrahydrocannabinol (d8-THC), delta-9-tetrahy- drocannabinol (d9-THC), cannabigerol (CBG), and cannabinol (CBN). Although both columns perform well, the Rxi®-35Sil MS column is recommended because of the slightly faster analysis time and greater space overall between the peaks of interest.

While stationary phase selectivity is the most important factor in choosing a GC column for cannabinoid analysis, there are some additional aspects of this work that will bene t labs doing medical marijuana potency testing. First, cost savings were achieved by using a 15 m column. When a column with the proper selectivity is used, a 15 m column easily provides the separating power needed for this analysis at about half the cost of a 30 m column. Also, the 0.25 mm x 0.25 μm format has good sample loading capacity and is robust, especially when a proper split injection is used with a Sky® Precision® split liner with wool. Finally, hydrogen carrier gas was used here instead of helium. Using hydrogen provides a faster analysis, increasing sample throughput. Hydrogen carrier gas is a convenient way to speed up run times, increase productivity, and reduce the cost and availability concerns associated with using helium carrier gas.

Pure Chromatography www.restek.com

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