Choosing Analytical Tools to Assess Complex Cannabis-Infused Matrices

March 1, 2018
Table I
Table I (click to enlarge): List of pertinent biological and chemical contaminants that can arise during the various stages of cannabis cultivation and product management. Detection of any of these above their designated safety level renders the product in question unsafe for consumption.
Table II: The 10 classes of cannabinoids
Table II (click to enlarge): The 10 classes of cannabinoids
Abstract / Synopsis: 

Cannabis is currently one of the most widely studied plants in the world because of the medicinal and pharmaceutical benefits of its natural products. These benefits are primarily attributed to the presence of cannabinoids and terpenes, which can elicit myriad molecular responses. The increased interest in cannabis has led to a deeper knowledge of modern pharmacopeia, not only with respect to the all the possible medical benefits of cannabis constituents and their respective biochemical mechanisms of action, but also in reference to a comprehensive spectrum of its components within the contexts of discovery and quality control. Cannabis products can be found in many shapes and forms ranging from the raw plant material to extracts, which can be consumed directly or incorporated into a variety of products designed for human consumption. Such edible products can encapsulate cannabis constituents in a variety of different matrices, which require different sample preparation considerations because of their variable complexity and profiles of interferences. In many cases, edibles represent a significant challenge because there are many different types that can be prepared, each one of which may require different suitable sample preparation techniques to isolate the cannabinoids for an effective analytical determination. Here, different edibles have been considered based on their composition, and different sample preparation strategies are discussed that may be appropriate for analyzing different products. The choices for different sample preparation methods have been considered based on prior food chemistry literature. This information is adapted to provide recommendations for the targeted determination of cannabinoids within the context of each method, the matrix of interest, and subsequent choice of instrumental determination, such as liquid chromatography or gas chromatography. We focus on the different research approaches used in the past for the comprehensive analysis of cannabis and related products. Challenges and the possible solutions will be highlighted to provide insight into what the future may require in terms of more reliable methods for the characterization of cannabinoids in complex matrices, such as edibles.

As of 2017, 29 states in the United States plus the District of Columbia support the legal use of medicinal Cannabis sativa and Cannabis indica, eight of which also allow recreational use (1). These numbers illustrate the importance of performing proper quality assurance (QA) and quality control (QC) with a comprehensive analysis of all cannabis products that should include the cannabinoids (the main components of the plant that confer its psychoactivity and medical benefits) and terpenes, but also any potential contaminants, such as pesticides, growth regulators, heavy metals, microbes, pests, and residual solvents (Table I) (2-4).

More than 100 different putative cannabinoids have been discovered in cannabis, 10 of which are ubiquitously found in numerous cultivars (Table II lists the more prevalent cannabinoids) (1,5-10). Some of these are well known, such as Δ9-tetrahydrocannabinol (Δ9-THC, the main psychoactive component) and cannabidiol (CBD, has the widest range of reported medical benefits). However, it is believed that the therapeutic effects of cannabis are not exclusively attributable to any single cannabinoid, but rather to their synergistic effects when administered in different combinations and in concert with numerous terpenes (11).

Terpenes are a class of molecules found in cannabis that are primarily responsible for odor and fragrances, while exhibiting antimicrobial, antioxidant, and anti-inflammatory properties. More than 30,000 terpenes exist in the natural world, 100 of which have been detected in cannabis. These molecules all derive from isoprene subunits and can be categorized based on the number of C atoms: hemiterpenes (C5), monoterpenes (C10), sesquiterpenes (C15), diterpenes (C20), and sesteterpenes (C25) (1,12,13). Terpenes from the same categories may be differentiated based on the number of double bonds, but also based on the position of the double bonds or atom connectivity. This compound class is characterized by a large number of isomeric structures, which makes their individual speciation challenging. Another category of terpenes are the so-called “oxygenated terpenoids,” which differ because of the presence of one or more O atoms. Some of the most common terpenes are technically terpenoids, since they contain at least one O atom (for example, linalool belongs to this group) (12).

To satisfy consumers’ different tastes, there are different ways to consume or use cannabis, with the most popular means being through smoking plant material, utilizing sublingual tinctures, and consuming edibles (14). The latter is sometimes preferred because edibles are said to be more discreet for consumers, and the toxins linked to smoking can be avoided (14). Another reason why edibles are becoming so important is because of their longer-lasting psychoactive effects. Edibles usually provide peak effects at 2-4 h after ingestion, in contrast to the peak at 20-30 min following inhalation (14). The reason for this difference is the pathway by which Δ9-THC is metabolized throughout the human body. After consumption and once in the liver, Δ9-THC is hydrolyzed enzymatically (mainly, cytochrome P450) to 11-hydroxy-Δ9-tetrahydrocannabinol (11-OH-Δ9-THC) (14-16). This metabolite confers higher psychoactivity than Δ9-THC, and it is actually believed to be a more active form of the cannabinoid, since it is able to cross the blood-brain barrier more easily (14-16). Analysis performed on blood has shown that 11-OH-Δ9-THC is found at higher levels in the human body after cannabis ingestion compared to inhalation (14). However, this metabolic difference can result in undesirable effects. Because of the delayed onset of Δ9-THC during ingestion, inexperienced consumers can consume greater amounts than what is suggested, leading to adverse effects. As such, properly dosing of cannabis edibles, which is guided by the accurate quantification of the psychotropic cannabinoids, is of paramount importance for individuals who wish to retain the therapeutic benefits of cannabis without the potential pulmonary impacts that can result from smoking.

The scope of this review includes an overview of traditional analytical methods for cannabis natural products and contaminants of concern. Furthermore, different methods for extracting and analyzing cannabis edibles are discussed within the context of matrix complexity. Unfortunately, only a limited amount of literature exists on the topic of cannabis edibles analysis; however, a number of insightful parallels can be drawn from available literature in the food sciences. For a systematic approach, edibles have been classified into different subcategories based on the potential interferences they can contain. For example, gummy bears contain mainly sugars and glycerin, which ought to be well differentiable from cannabinoids, but might cause issues in terms of pesticides analysis. In contrast, cannabis-infused fermented beverages can contain ethanol, which can render the quantification of cannabinoids difficult. Further to this point, baked goods can contain a multitude of fats, proteins, fiber, and other ingredients that can hamper the extraction and analysis of targeted components. Additionally, the inherent hydrophobicity of cannabinoids can drive variable binding to individual compounds of edible products. As such, different matrices—and potential for heterogeneous cannabinoid distribution through an edible product—require different sample preparations and selective analytical platforms can also increase accuracy and precision of determinations. As the scope of products incorporating cannabinoids expands, so too must the analytical methods available to provide reliable quality control of these products.

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How to Cite This Article

A. Leghissa, Z.L. Hildenbrand, and K.A. Schug, Cannabis Science and Technology 1(1), 24-35 (2018).