On-Site Analysis of Cannabis Strength Using FT-IR Spectrosocopy

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Cannabis is increasingly being recognized for its therapeutic value, with many governments reducing its regulation. As cannabis production becomes legalized and regulated, manufacturers have a responsibility to evaluate the chemical content and potency of their plants.

The value of cannabis in controlling spasm, pain, and a range of other diseases, including bipolar disorders and certain type of cancers, is becoming established throughout the medical world.1 Medicinal cannabis is legal, or in the process of being legalized, across 25 states in the United States, and also in nations from Canada, to Italy and the Netherlands.2

While the US FDA is yet to approve the use of raw cannabis, pill forms of cannabinoids are now available to treat some medical conditions.2

In the UK, the legalization of medical cannabis is supported by the ‘End Our Pain campaign,’ which estimates that around one million people across the country rely on cannabis for medical reasons.3 Taking evidence from 623 patients, professionals and experts and over 20,000 scientific and medical reports, a seven-month inquiry from the All Party Parliamentary Group (APPG) for Drug Policy Reform recently confirmed the medicinal value of cannabis and recommended its legalization.3

In the UK, the Cannabis (Legalization and Regulation) Bill 2015-16 received its first reading in March 2016 and it remains to be seen if this bill will eventually become law and permit the medical use of cannabis in the country.4

The Active Compounds in Cannabis

In cannabis, the main psychoactive cannabinoid is tetrahydrocannabinol (THC), which when it enters the body can interact with cannabinoid receptors in the immune system and in the central nervous system.6,7

In addition to its established psychoactive effects - getting ‘stoned’ - THC is imbued with various other valuable effects. THC has been shown to increase appetite and to mitigate nausea, inflammation (redness and swelling), pain, and muscle spasms.

Cannabidiol (CBD) is another major cannabinoid in cannabis with therapeutic value, and has been demonstrated to mitigate inflammation and pain, and help control epileptic seizures. It also has potential to treat mental illnesses.8

THC and CBD have been employed in the treatment of a variety of different, unrelated, conditions, including multiple sclerosis, bipolar disorder, glaucoma, and diabetes. However, they are mostly used in the treatment of chronic pain.9

THC (left) and CBD (right) - the two main phycoactive components of cannabis.

THC (left) and CBD (right) - the two main phycoactive components of cannabis. Image Credit: molekuul_be/Shutterstock.com

Growing Cannabis

In cannabis cultivation, the important factors indicating the value of the crops are the levels of THCA and CBDA, which are acidic forms of THC and CBD. The THCA and CBDA levels vary from 5% to 30% based on the species of the plant crop.5 The plant flowers contain most of the cannabinoids, including CBDA and THCA, and are then harvested.

Cannabis plants are constantly being developed and selectively cross-bred to improve the yield of THCA and CBDA as well as to increase the variety of other cannabinoids found in the plant flowers. A convenient and rapid analytical technique is required to obtain quantitative data on the cannabinoid content of different strains.

The difficulty of analysis lies in throughput and accuracy; there is such a volume of material that traditional gas chromatography is not feasible. Although the most accurate methods are gas chromatography coupled with mass spectrometry (GC-MS) or nuclear magnetic resonance (NMR), the equipment for either method is expensive and needs a skilled operator for a successful analysis.

Alternatively, cannabis growers could deliver samples to a GC-MS analysis laboratory, but this approach is also expensive and can cause delay due to the time between acquiring the samples and obtaining the results.

Spectroscopy is increasingly becoming a method of choice for growers because spectroscopic methods are 5 and 10 times faster than GC-MS and can be carried out by a relatively unskilled operator.

Near infrared spectroscopy (NIR) is suitable for cannabis analysis as this method has already been successfully used to analyze the ‘bulk’ of other agricultural products. NIR has excellent accuracy, does not require solvents for sample extraction (CBD and THC are not water soluble), and is able to provide a much lower cost per analysis compared to GC-MS. It is also rapid and economical, especially when carrying out multiple measurements of heterogeneous samples.6,7

Using FT-IR to Determine the THC and CBD Content of Cannabis

Cannabis producers are especially interested in maximizing the THC and CBD content (potency) of their plants by selectively breeding their plants through optimization of growing conditions, such as water, soil, and light. As growers search for ways to optimize the growing conditions, monitoring plants during their growth is becoming commonplace.

FT-IR is rapidly becoming the technique of choice as it can deliver instant results. FT-IR can be employed to monitor the changes in plant potency over time, as the plant grows, and the effects of the external environment on THC and CBD production.

Due to the presence of a wide variety of cannabinoids, FT-IR analysis of cannabis could be problematic because peaks resulting from THC could be masked by other compounds.7 However, it is easy to employ chemometric methods, which statistically separate overlapping peaks and enable the rapid and accurate, on-site determination of THCA and CBDA in cannabis flowers.

GC-MS and NMR requires sample preparation, sampling, and a specialist analytical lab, causing delays and making these techniques more expensive. As FT-IR monitoring can be performed continuously during plant growth, it is possible to rapidly change the growing conditions to maximize the THC and CBD yield.

FT-IR is an accurate and inexpensive method, providing a viable solution to monitor the levels of THC and CBD in real time.6,7

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Image Credit: photolona/Shutterstock.com

Specac’s FT-IR Accessories for Cannabis Analysis

Specac provides a wide variety of ATR accessories that are compatible with a wide range of spectrometers used in the analysis of solid samples, like cannabis flowers. Specac’s QUEST ATR is suitable for cannabis analysis as:

  • It requires little or no sample preparation, meaning no chemicals are needed and the sample is not destroyed
  • A wide variety of sample shapes and forms can be analyzed with the diamond ATR puck, which is useful when handling dried flowers
  • The diamond top plate enables obtaining the widest range of IR spectrum (400 - 4000 cm-1), meaning a wide range of cannabinoids can be detected

An Atlas autotouch press provided by Specac can be employed to compress cannabis samples into pellets for analysis. Although it is not essential for experiments using the QUEST, which can handle different sample sizes and shapes, it can be useful for further chemical analysis integrated with IR.

The Quest and Atlas autotouch press from Specac for FT-IR analysis.

The Quest and Atlas autotouch press from Specac for FT-IR analysis.

With Specac’s ATR accessories such as Quest, continuous and consistent FT-IR analysis of cannabis can become a viable and inexpensive option for cannabis cultivators.

References and Further Reading

  1. https://www.drugabuse.gov/publications/drugfacts/marijuana-medicine Accessed October 27th 2016
  2. 25 Legal Medical Marijuana States and DC – Medical Marijuana – ProCon.org". procon.org. Retrieved 27th October 2016
  3. http://www.bbc.co.uk/news/uk-37318935 Accessed October 27th 2016
  4. http://services.parliament.uk/bills/2015-16/cannabislegalisationandregulation.html Accessed October 27th 2016
  5. Todd Mikuriya, Introduction from Marijuana: Medical Papers, Medi-Comp Press, 1973, pp. xiii-xxvii
  6. Brian C. Smith, Fundamentals of Fourier Transform Infrared Spectroscopy, CRC Press, Boca Raton, 2011.
  7. M. Giese, M. Lewis, L. Giese, K. Smith, Development and Validation of a Reliable and Robust Method for the Analysis of Cannabinoids and Terpenes in Cannabis.” Journal of AOAC International 98(6):1503-1522, 2015
  8. R.G. Pertwee, The pharmacology of cannabinoid receptors and their ligands: An overview, International Journal of Obesity. 30: S13–S18, 2006
  9. NIDA Research Report series: Marijuana, https://www.drugabuse.gov, Accessed October 27th 2016


This information has been sourced, reviewed and adapted from materials provided by Specac.

For more information on this source, please visit Specac.


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