GC-MS Method Overcomes Matrix Interference Challenges in Cannabis Analysis

A new method has been developed to enhance the detection of the cannabinoids present in cannabis-based consumer products. This has been achieved by a team at the United States Food and Drug Administration’s (FDA’s) Forensic Chemistry Centre (FCC), who have adapted existing gas chromatography-mass spectrometry (GC-MS) methods to help overcome some of the key challenges analysts face when tackling highly heterogenous cannabis samples. It is hoped that this will pave the way for consumers to know exactly which cannabinoids are in the cannabis products they buy.

A surge in consumer cannabis products

In their recent publication in Forensic Science International, the team of FDA scientists describes a new method that can detect and identify individual cannabinoids in the huge range of legal cannabis products now available in 30 US states and countries around the world. This is the first time that some cannabinoids have been identified in certain consumables - particularly products containing glycerin, sugar, and lactose, that can mask the presence of some cannabinoids.

This new adapted GC-MS method can identify different cannabinoids in products at very low concentrations, which could help ensure that consumers are accurately informed about they are consuming. 

Difficulty in detecting cannabis in consumer products 

Cannabis plants contain over 100 different cannabinoid compounds. When added to consumer products, these cannabinoids can be present in very varied amounts, from minute trace quantities to concentrations nearing 40%. They are also added to chemically challenging matrices, like lactose and sugar, that can make them hard to detect using traditional tried-and-tested analytical techniques.

GC-MS has been used to qualitatively analyze cannabinoids in plants, and plant extracts and preparations, for many years. Here, to avoid the cannabinoids becoming acidic, they are derivatized to TMS-cannabinoids prior to analysis. This ensures they show up on the GC-MS chromatogram. However, analyzing cannabinoids in consumer products is not as straightforward. 

Consumer cannabis products often contain chemical species that can cause matrix interference and make it difficult to effectively identify the cannabinoids present in them. This occurs as these matrix chemicals are co-extracted with the cannabinoids and then interfere with the cannabinoid derivatization process. If this occurs, the GC-MS chromatogram does not correctly represent the cannabinoids present. 

Adapting methods to isolate cannabinoids 

To tackle this problem, the FDA FCC team adapted GC-MS methods to detect cannabinoids in a range of cannabis-containing substances. Using both ethanol- and acetonitrile-based extractants, they were able to extract cannabinoids from commercial products such as oils, vapes, food and drink and beauty products.  Once extracted, the team used GC-MS to identify 11 acidic and neutral target cannabinoids.

In products with a high content of glycerin, sugar or lactose, various interferences were encountered, and the team struggled to identify certain cannabinoids through GC-MS analysis. Glycerin is present in many oral cannabis supplements and vape products, sugar is in cannabis foods such as candies and preserves, and lactose is in milk containing cannabis products. So, to ensure that cannabinoids can be successfully identified in products containing these substances, the team looked at how using different extractants can reduce the interference they cause. 

Their results have enabled them to establish protocols which dictate the best way to extract cannabinoids from glycerin, sugar or lactose-containing substances to avoid the presence of interfering co-extractants. Here, they advise that extractants are should be acetonitrile-based, rather than ethanol-based, as the interfering matrix chemicals are less soluble in acetonitrile. In the case of products containing lactose, pretreatment with lactase prior to extraction is generally also required. The FCC team hope that these protocols will be widely adopted by those investigating cannabinoids in consumer products in the future.

Transparency for cannabis consumables

Overall, the team has successfully isolated 11 target cannabinoids in approximately 60 products. They can use their adapted extraction techniques and GC-MS method to detect individual cannabinoids present in concentrations as low as 1.0 µg/g. Their method can be applied to any cannabis-based sample, except hemp seeds.

In follow up work, the FCC team have developed a technique to quantify the different cannabinoids present in commercially available consumables. Together, these two techniques may help increase transparency, and ensure that consumers are correctly informed about both the type and quantity of cannabinoids present in commercially available cannabis-based products.