The cannabis industry is booming, thanks to recent and ongoing legalization. Recreational cannabis use is legal in several states, and medical use is legal in 28 states. It was also recently legalized across Canada in 2018. Cannabis has shown promise as a pharmacotherapy for various conditions, including pain and spasticity related to multiple sclerosis, and its use in palliative oncology is well documented. Qualified professionals are in high demand as production escalates, and there are now even Commercial Cannabis Production college programs designed to produce well-trained candidates.
In addition to meeting rapidly increasing demand, producers face increased pressure to complete potency testing, especially following a reported spike in emergency room visits following legalization. Accurate potency testing is challenging, as cannabis products take many forms, ranging from flowers and concentrates for smoking to oils and tinctures, candy, and baked goods, and they consist of thousands of different compounds. Sample preparation is an important consideration to ensure accurate analyses and to protect scientific instruments. In addition to potency, testing for contaminants such as heavy metals, pesticides, and mycotoxins may also be required. Different chromatography techniques are widely used and enable potency and contaminant testing of different cannabis products to ensure consumer safety.
What's in your weed?
Δ9-tetrahydrocannabinol (Δ9-THC or THC) is the primary psychoactive compound in cannabis. It acts on receptors in the brain to alter neurotransmitter release, producing the characteristic sensation of being “high.” Cannabidiol (CBD) is thought to have antagonistic effects that can protect against the adverse effects of THC. THC and CBD are two of more than 100 different cannabinoids and are subject to the most scientific research. Cannabis also contains terpenes, which are volatile unsaturated hydrocarbons that impart the unique aromas associated with different strains.
“Regardless of whether addressing medical cannabis patients or recreational adult use, an accurate understanding of the dosing of primary ingredients is critical in support of the cannabis community and research of the associated clinical science, just as with all other foods and drugs in the US community,” says Reverend Dr. Kymron De Cesare, chief research officer at Steep Hill Inc. Steep Hill began in 2008 and performs regulatory, quality assurance, and R&D testing for cannabis products. For medical cannabis patients, “predictable ‘cause and effect’ through precise dosing is required, along with minimizing unwanted impurities that could do harm, especially to immune-impaired patients.” Potency testing for cannabis produced for recreational use is important in order to meet cultural needs. De Cesare uses alcohol as an example: “Consider the model wherein one shot (43 mL) of 80-proof alcohol, a 12 oz. bottle of five percent beer, and a five oz. glass of 12 percent wine all contain 19 mL of ethyl alcohol.” This model of standardization makes it possible for the consumer to determine their desired dose, and a similar model may also be useful for cannabis. Data from the National Institute on Drug Abuse indicates cannabis potency has increased from 3.7 percent in the 1990s to 9.6 percent by 2013 due to various factors, which could make it difficult for new users to choose a dose without potency data.
Cannabis potency testing and its challenges
As it is available in numerous forms, cannabis is a challenging product to analyze. It consists of hundreds of different compounds, each with known or suspected psychoactive effects, and it can be consumed via smoking, through oils and tinctures, or in food products. De Cesare describes some of the factors that contribute to challenges for potency testing: “This industry evolved out of an illegal black market, wherein set agricultural protocols were never established by the USDA/FDA. Ergo, a wider array of analysis must be done. There are a lot of unusual, nontypical processes used in growing and extracting cannabis, and no other drug-type pharmaceutical is allowed to be adulterated by as large and varied an array of foodstuffs [as] used in the cannabis industry.” There are techniques that can accurately quantify the concentration of active ingredients, and ongoing work is aimed at developing standardized testing protocols.
Gas chromatography (GC) and high-performance liquid chromatography (HPLC) are powerful techniques frequently used for cannabis potency testing. At Steep Hill, De Cesare says that both gas chromatography and high-pressure liquid chromatography—with a variety of different configurations and detectors—are used for cannabis sample testing, along with other methods. Chromatography is often coupled with a detection method such as mass spectrometry. “A variety of different detection methods are used with the primary instruments, including photodiode array, triple quad mass spectrophotometry, etc.,” explains De Cesare.
Each method is best suited for different sample types; HPLC is best suited for liquids and edible materials, and GC is ideal for flowers and concentrates. Samples undergoing HPLC analysis are not heated, and as such, it is possible to detect the THC precursor, tetrahydrocannabinolic acid, and the CBD precursor, cannabidiolic acid (CBDA) to obtain total THC and CBD values. GC is suitable for the detection of THC and CBD that result from the decarboxylation of THCA and CBDA, similar to what occurs when these products are heated for smoking. GC generally provides more rapid analysis. However, the development of a novel liquid chromatography-tandem mass spectrometry method enables analysis in under 10 minutes.
Testing and other compounds and contaminants
In addition to quantifying the active ingredients such as THC and CBD, examining other compounds in cannabis such as terpenes, mycotoxins, heavy metals, and pesticides can ensure consumer safety. Cannabis is a phytoremediation plant and can readily absorb many chemicals present in soil and water. “For instance, soil in northern California predictably has metals associated with mining, whereas southern Californian soil still contains pesticides used in the 1920s to the 1970s that were never designed to break down over time,” explains De Cesare.
Terpenes present in cannabis, such as limonene and myrcene, impart unique aromas. While there is no conclusive evidence, they could contribute to some of the mood effects associated with consumption. Terpenes are also difficult to identify and quantify with confidence using standard methodology. “The wide array of chemical structures means that terpenoids act similar to a great many different chemicals, including pesticides, etc., confusing results. Off-the- shelf protocols for instruments rarely work effectively at differentiating and identifying these similarities. Ergo, a lot more time and energy go into analyzing terpenoid-rich plants like cannabis,” says De Cesare.
There is no single analytical method to assess cannabis potency, terpene, and contaminant content. “The truth is that development is always ongoing,” says De Cesare. “One starts the process by using well-known analysis protocols and evolves and changes them to maximize identification and quantitation of both ingredients and contaminants alike.” Chromatography techniques can be modified by several variables, including mobile and stationary phases, pressure, flow rate, carrier gas, etc. This contributes to their versatility but may also account for the significant variability between protocols for cannabis testing. As laws surrounding cannabis use continue to evolve, so too do the analytical methods used to ensure consumer safety.