Terpene Analysis: A Higher Level of Cannabis Quality
As cannabis consumers become wiser and more discerning, it is up to producers to ensure their products are up to snuff. Chris Bond explores some of the methods being used to ensure cannabis products on the market meet expectations.
Much has been written about the benefits and features of various terpenes, especially as they relate to cannabis. There are more than 140 of these naturally occurring compounds that are responsible for many of the smells and tastes associated with numerous herbs and plants, both common and rare. Botanically speaking, terpenes are a group of volatile, unsaturated metabolites found in the essential oils of more than 2,000 varieties of different plants, flowers, trees, shrubs, vines, and, of course, cannabis. Pine, citrus, and cannabis aromas, among scores of other familiar scents, all owe their chemical properties to terpenes.
Terpenes are used most often in the creation and preparation of many foods, cosmetics, and medicines, both cannabis-derived and those derived from the pharmaceutical industry. There is a growing body of scholarship and research that attests to the role that terpenes found in cannabis affect the way the body’s endocannabinoid system utilizes tetrahydrocannabinol (THC) and cannabidiol (CBD) compounds. Companies that manufacture both THC- and CBD-containing medicinals as well as recreational cannabis products often conduct terpene analysis, sometimes referred to as flavor profiling, as part of their quality-control measures.
This analysis is a vital step for legitimate producers of cannabis products to verify that their raw materials have been harvested correctly, dried properly, or are even the purported strain they thought they had purchased. Terpenoid content is a heritable trait in plants, including cannabis, so there is a known terpene profile associated with each specific strain of cannabis that a sample can be compared to.
Growers benefit from terpene analysis as well. It can aid them in identifying unique cultivars of cannabis strains as mentioned and serve as an indicator to the grower of when to harvest a specific strain of cannabis. As plants mature through their various stages, terpene levels change. The specific terpenes do not change within each strain, only the amount of each terpene. An analysis at various stages of growth can help to optimize the harvest by doing so when terpenes are at peak or desired levels.
There are several methods that can be undertaken to perform a terpene analysis. Terpenes themselves have a vast range of physical structures and chemical properties. The amount of the sample size as well as the available technology all play a part in deciding which method of terpene analysis can or will be conducted.
Some Methods of Terpene Analysis
In general, all methods of terpene analysis require the same basic steps including:
- Breaking up the plant sample’s cellular structure.
- Extracting the desired sample with an appropriate solvent or via some method of distillation.
- Separating the desired terpene or terpenes from the other contents of the distillate.
- Utilizing the most appropriate method of terpene analysis as is on hand depending on the size and polarity of the desired terpene.
Extraction of any one terpene can require a specific or optimized method to be efficiently and/or economically extracted. Many terpenoids can be volatile. This characteristic serves the sample’s respective plant well in its environmental interaction but can pose unique challenges to the extractor. This volatility can and will inform the method of extraction selection. Sometimes, more traditional methods such as Gas Chromatography (GC) can be used, and other times more unique and specialized techniques must be employed to obtain the desired result.
Gas Chromatography is the most common method of terpene analysis. It generally provides accurate and quick results. It is also a preferred method over some of the other methods described below as terpenes are quite volatile and GC is an adept testing method to account for that volatility. The traditional method for analyzing terpenes is through gas chromatography with a flame ionization detector (GC-FID).
With this method, the first step is to prepare a solvent-based extraction, usually by placing cannabis plant material in some form of liquid solvent (commonly methanol or ethanol) to extract the compounds of interest into the solvent. This extraction liquid is then injected into the GC apparatus where the cannabinoids and terpenes in the solvent extraction are separated as they move through the gas chromatograph column.
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These separated compounds exit the column where they encounter the FID. They are exposed to a hot flame of hydrogen air that allows for the production or conversion of organic ions. The FID’s electrodes then measure the current from the organic ions. This information, along with the retention time of the compound can be used to identify a specific terpene and to quantify the analysis.
Other methods of GC involve the use of a mass spectrometer (MS), which is more sensitive than the FID. This can be problematic, however, as many terpenes are isobars and share some of the same organic ions that cannot be separated for their identification and quantification. The FID has a greater dynamic range than the MS but is not as sensitive or selective.
Many producers and buyers of wholesale cannabis are beginning to perform their own in-house analysis using GC-FID for their terpene analysis. This is less expensive than other equipment and can provide quicker and cheaper results compared to sending samples to labs and waiting on results.
High Performance Liquid Chromatography
High Performance Liquid Chromatography (HPLC) is probably the second-most common method of terpene analysis but is usually better for cannabinoid analysis rather than for terpenes. Terpenes have low ultraviolet (UV) and MS sensitivities.
The cannabinoids present in each sample often interfere or can even essentially “erase” (by coelution) the terpenes in the sample when subjected to this method.
Solid Phase Microextraction of Headspace
Solid Phase Microextraction of Headspace (SPME), or Headspace Sampling (HS), is considered among the more effective methods of terpene analysis. Conventional HS is a method utilizing a concentrator that targets the volatiles in a given sample, including the terpenes. This leaves behind other oils and cannabinoids from the sample. SPME utilizes an autosampler that can be performed by direct immersion with the cannabis sample.
Split/Splitless Injection (SSI) is not as complex a process as HS or SPME, making it an easier analysis to perform, but it is not as efficient for high-output labs to use as the samples need to remain in the columns for an extended period.
As more and more countries legalize some form of cannabis, it is incumbent upon the industry to build and maintain a set of rigorous standards to make sure the products sold to consumers meet or surpass some basic quality-control measures.
The establishment of cannabis testing labs needs to stay ahead of trends and best practices to be able to perform this valuable service to all members of the cannabis supply chain, from grower to buyer, producer to consumer. A terpene analysis is vital to all links in that chain to assure each constituent they have what they think they have and that they were not sold something (or consume something) other than what they thought they were.
The accurate and replicable quantification of cannabis terpenes allows for medicinal and recreational cannabis products to be better characterized and controlled. Each specific strain of cannabis possesses specific psychological and medical characteristics that can be better utilized to its full potential with terpene analysis. Ultimately, the demands of the consumer, at any point on the supply chain, coupled with local, municipal, or federal regulations, the quality and type of equipment, and the efficiency and skill of each respective lab technician will decide how cannabis terpene analysis will be performed.