The Canadian government’s decision to legalize the use of cannabis by adults for non-medicinal purposes in October 2018 presents an enormous opportunity for fully-licensed laboratories to establish and expand in support of the testing needs of this growing sector.
While not currently required under the latest quality control regulations issued by Health Canada, terpene profiling of cannabis products is expected to play an important role in helping suppliers meet consumers’ needs and preferences. Here, we consider the importance of cannabis terpene profiling and how laboratories can overcome the analytical challenges specific to this emerging field.
Terpenes in cannabis
Terpenes are non-psychoactive components that give cannabis and its derived products their distinctive smell. Although these compounds are not psychoactive themselves, it is a widely-held belief of many cannabis users, and increasingly some parts of the scientific community, that specific terpenes in cannabis can create distinct or ‘enhanced’ experiences for users (1). These perceived differences are thought to arise from interactions between certain terpenes or terpenoids, phyto cannabinoids, and the endocannabinoid system. This so-called ‘entourage effect’ remains scientifically controversial, yet belief in the phenomenon persists among some groups of users and researchers.
There is anecdotal evidence suggesting that some users associate cannabis chemovars derived from Cannabis indica– one of the two main species of the cannabis plant – with soporific or relaxing effects (2). The other, Cannabis sativa, is believed by some users to have uplifting or energetic effects. While these perceived differences between the two main species of cannabis have not been proven, many users actively seek out specific chemovars of cannabis to produce a particular experience. A more complete understanding of cannabis terpene profiles and their link to users’ sensory experiences by characterizing the terpenes present in specific chemovars could, therefore, help to guide users’ choices.
With the use of cannabis for medicinal purposes in Canada also expected to rise, sourcing material with a specific terpene profile is important for patients too. Research into the collective synergic effect of the terpenes present in cannabis is ongoing (3). However, it may be reassuring for patients to have reliable access to material with a specific terpene profile they are familiar with. For growers and suppliers, there is a commercial advantage in knowing the general terpene profile of the material they provide, whether this is for medicinal or non-medicinal purposes.
The growing market for cannabis products
Characterizing a cannabis product’s terpene profile isn’t just important for those involved in the supply of material that will be inhaled. New Canadian legislation paves the way for an expanding range of medical and non-medicinal products containing cannabis-derived extracts, including concentrates, oils, and edible preparations. For many consumers, the appeal of these products is that they contain the same chemical components that are found in the plant material, and thus may be perceived to offer the same type of experience associated with smoking cannabis.
To obtain these chemical components and include them in concentrates, oils, and edible preparations, terpenes must be isolated and extracted from cannabis. Avoiding contamination with other plant components such as waxes and chlorophyll can be challenging from a production perspective and requires a large amount of method development. Furthermore, the oxidative liability of specific terpenes, and the solvents involved in their re-addition to cannabis materials, can potentially be toxic when consumed through heat-based methods. This highlights the care that must be taken when re-adding terpenes to the final product. For businesses engaged in this sector, terpene profiling allows companies to fine tune their manufacturing processes to optimize the types and levels of terpenes in their products.
Profiling terpenes in cannabis
Profiling terpenes in cannabis is typically undertaken by gas chromatography-mass spectrometry (GC-MS). Many cannabis laboratories screen for 21 different terpenes, while some labs may test for around double this number to include additional terpenes that could play an important role in the proposed entourage effect. However, even with just 21 terpenes to screen for, the diversity of chemical and physical properties these molecules possess presents a significant analytical challenge.
Terpenes commonly associated with cannabis typically fall into three broad families: monoterpenes (containing two isoprenoid units), sesquiterpenes (containing three isoprenoid units), and terpenoids (possessing additional functional groups). This chemical diversity means that these compounds possess very different volatilities. Sesquiterpenes, for example, are typically known to be less volatile than others. Obtaining good recoveries for these analytes can be more difficult when operating headspace analysis due to their low volatility within the autosampler and on the GC-MS column, and the potential for some terpenes to adhere to plant material in the test vial. Sample preparation workflows utilizing extraction can circumvent the latter issue, although careful optimization of solvent and extraction time is necessary.
Monoterpenes, on the other hand, are highly volatile and retaining these analytes in the sample prior to analysis is challenging. This is especially difficult as the grinding technologies used for sample preparation steps can generate a substantial amount of heat which can contribute to pre-analysis volatilization and a subsequent loss of analyte. Consequently, sample preparation steps must be carefully designed to ensure consistent and reliable results. The use of sample grinding equipment with a chilling option, for example, could minimize loss of volatile terpenes. In addition, some laboratories have developed their own solutions to keep samples cold, such as using customized vial trays or headspace vial holders maintained at sub-zero temperatures.
Given the broad range of analytes that must be tested, it is critical to use the same processes when preparing calibration standards as test samples. Furthermore, robust chromatographic separation must be balanced with practical chromatographic run times. As such, the selection of appropriate chromatography conditions, especially columns, is particularly important.
Meeting the challenges of terpene profiling
The current challenges associated with terpene profiling reflect the fact that cannabis testing is a relatively nascent field that will be unfamiliar to many established laboratories. To enable accurate and reliable terpene profiling, cannabis testing laboratories not only require capable technologies, but also the training and familiarity with best practices to ensure these workflows are used in the most effective way.
Instrument manufacturers are already supporting laboratories by bringing GC-MS systems to the market that offer high levels of accuracy, specificity, sensitivity, and operational reliability. In addition to making capable analytical solutions available for terpene profiling, some leading vendors of instruments and consumables, such as Thermo Fisher Scientific, are engaging with fully-licensed testing laboratories to provide educational resources to ensure these technologies are used effectively. The Thermo Fisher seminar series, at which this author was fortunate to speak, aimed to help laboratories in Canada develop optimized methods for cannabis testing through the dissemination of best practices and guidance from industry experts. By supporting laboratories in this way, these valuable training initiatives lay the foundations for higher quality cannabis testing and further growth in this field.
The current challenges in cannabis terpene profiling not only highlight the importance of employing the most capable technologies, but also the need for the cannabis testing community to share and adopt best practice to overcome some of the issues presented here. Vendors of analytical instruments and consumables are engaging with stakeholders across the Canadian cannabis sector to develop complete workflow solutions that provide the terpene profiling and characterization information this growing market needs.
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