As new and exciting products enter Colorado’s regulated cannabis industry, the scope of cannabis testing must continuously evolve. Labs must get creative in adjusting and re-validating their methods for these new products as they can present different challenges during sampling, extraction, and data analysis. This is especially true for cannabis infused products, a classification for a range of infused products including topicals, edibles, tinctures, beverages, and any other products not generally consumed via inhalation of products of combustion or vaporization. These cannabis products require a homogeneity test to be performed on them before they can be sold to the public.
The basic method of a homogeneity test is to perform multiple potency tests from different parts of the product and ensure that these potency values are within a given statistical range dependent on the amount of active cannabinoid present in the product. Once the test results have been compared, the product is considered “homogenous” if the cannabinoids are distributed evenly throughout the individual pieces, but also throughout the package the product is sold in. The requirements for this test have changed to better comply with the safety standards and best practices of model industries, including the food manufacturing and pharmaceutical industries.
As of January 2021, the Marijuana Enforcement Division (MED) mandated that all marijuana products be tested in at least four replicates with a relative standard deviation (RSD) threshold of 10%. The RSD is a concept in analytical chemistry often used to examine assay repeatability, the number itself being a percentage reflecting the average percent deviation from the mean between all replicates. Originally, there was no such standard requirement for the number of replicates or an acceptable RSD threshold. These loopholes were often exploited by labs without rigorous attention to scientific detail, allowing some products to make it to store shelves that should not have otherwise.
Locally, when a representative sample package is submitted for homogeneity testing to a regulated testing facility, the result obtained must be within a certain percentage of the labelled, or claim, value. Previously, this was a standard +/- 15% of the claim value on the label. This has since been updated and can now vary from +/- 5% for products containing high amounts of cannabinoids, to +/- 40% for cannabinoids in extremely low amounts, typically either for micro-dosed major cannabinoids or minor cannabinoids such as cannabigerol (CBG) or tetrahydrocannabivarin (THCV) that do not usually occur naturally in large amounts. These cannabinoids must be on the product label if they are in quantities above 0.5 mg. The number of containers required to be submitted for testing has also been updated to account for production batch sizes up to 25,000 containers, a limit that was previously capped at 10,000 containers.
Though these are most of the basics of a homogeneity test, the specifics of this test can change dramatically depending on the matrix type of the product being analyzed as well as the concentration of cannabinoids present in the product.
Even within the same type of product, there can be fairly significant differences that require changes to a “standard method”, a requirement not explicitly spelled out in the MED’s rules. For instance, a gelatin edible is going to vary slightly from a pectin edible and would therefore require at least a minor modification of the method to produce an accurate result. Significant method changes may be something like making a small change in the amount of heat used to melt the gummy before the addition of a solvent for cannabinoid extraction.
Even within a broad category such as “edible”, there will be differences in sample preparation and analysis for a specialty-baked good, such as a cookie or brownie, versus the gummy edibles described above, and even between the cookie and brownie themselves depending on the composition of these baked goods. Other infused edible products that have been submitted have included popcorn, frozen pizza, and barbecue sauce, all different matrices requiring special attention to detail. As stated previously, not all infused products are edible. Some are topically applied, some are transdermal patches, and in a few cases, there are even suppositories! As one could imagine, the types of ingredients in each of these products can vary drastically, and an analyst would not be able to obtain accurate results using the same method for all these products.
Certain matrices can also create instrument interferences, which, if not accounted for, can affect the accuracy of results. Chocolates or certain salves, for example, contain molecules like phenols or coloring agents that can elute during chromatographic analysis. If the responses to these are high enough at the wavelength the method uses for detection, interfering peaks can skew final results. Matrix blanks, a version of the product without added cannabinoids, are often needed from the companies in these situations. The blanks are run alongside the dosed product and recovery calculations can ensure accurate results.
Differences in solubilization between products can present problems as well. A sugar-based edible cannot be melted and extracted in only organic solvent, as polarity differences prevent proper mixture. For these products like cookies and gummies, water and heat are necessary as a first step to solubilize the product. Once the product is fully solubilized, then extraction solvent can be added, and a full cannabinoid recovery is possible.
Some products such as medical topicals can have large amounts of cannabinoids in the container, even if there are still relatively few per “serving” (or application). Especially from a medical perspective, it is equally important, if not more so, to ensure that each application has the same cannabinoid content so that it can be properly dosed and applied. One of the ways a lab addresses these varying cannabinoid concentrations is by adjusting dilution schemes to stay within the validation parameters of the instrument. An analyst cannot use the same dilution for a 50 milligram per fluid ounce tincture, a liquid suspension of cannabinoids often dosed with a dropper, as they would for one dosed at 3,000 milligram per fluid ounce, or else the test would fall outside the linear range of the instrument set up by the calibration curve. Most solid edibles have a large enough mass to cannabinoid ratio that lower dilution factors can be used. Tinctures and other liquid edibles, however, can present problems if dosed at higher levels. Though recreational products cannot exceed 100 mg per package, there is currently no such limit for high delta-9-tetrahydrocannabinol (THC)-containing medical products or cannabidiol (CBD) products.
Homogeneity test results have caused some previous methods for edible production to fall out of use due to their inherent inconsistencies. Some manufacturers of infused products are spraying cannabinoids onto the surface of their edible products. This practice has been shown through experimentation in our laboratories to yield inconsistent cannabinoid distributions, so the “10 milligram” dose you are ingesting may have much more or much less than the label states (maybe none at all!).
This inconsistent distribution has also been shown using cannabinoid sources that have been absorbed in an oil or butter. Disregarding calculation errors in the production process, even when using the same cultivar to produce the oil, there will be input material discrepancies due to varying growing conditions. So, it is easy to see how an infused product, especially an edible, could have varying cannabinoid concentrations.
Another method that has become less utilized is injection of doses. While the total cannabinoids per piece should be accurate, as well as the total cannabinoids per package, the fact that the dose would be injected into one part of the edible means that an individual piece would not be homogeneous throughout. If a patient were trying to split a dose in half, or into quarters, which dose would they take, and would it be in the amount they are expecting? This has led most reputable infused product manufacturers to use distillate as the cannabinoid source and homogenizing their product in the process.
Regulators will continue to update and provide clarity on ever changing grey areas in the cannabis space. Manufacturers will improve and hone their infusion methods and get more creative with their product development, and laboratories will need to be open to adapting their homogeneity practices to compensate for these changes. One recent example is the metered dose inhaler. To test this product, Kaycha Colorado developed an apparatus involving suction and filter papers. This is a process completely outside of the original standard operating procedure and was added in after development. The more creative and innovative edible manufacturers become, the more adaptable labs often need to become to properly analyze the product. If they do not, they could be left in the wake of the fast paced, constantly evolving cannabis product market.