GC-FID Used to Analyze Cannabis Hemp Components

Purple green marijuana plant on black background. Colored neon large leaves and buds of cannabis hemp. Hemp bush and empty space for text | Image Credit: © Tsareva.pro - stock.adobe.com

In a recent study out of the Connecticut Agricultural Experiment Station in New Haven, Connecticut, gas chromatography with flame ionization detection (GC-FID) was used to measure total Delta-9 tetrahydrocannabinol (THC) and total cannabidiol in hemp samples. Their findings were published in Plants (1).

Cannabis sativa growth has been cultivated worldwide for centuries, predominantly for fiber, though it has also been used medicinally for ailments like rheumatic pain, constipation and malaria. Previous evidence shows that psychotropic use of cannabis began in the early 1600s in North America, with medicinal use following in the 1800s for treating tetanus, epilepsy, rabies, and as a muscle relaxant.

In December 2018, Cannabis sativa growth was legalized in the United States with the United States Agriculture Improvement Act. This allowed the growth of Cannabis sativa that does not contain more than 0.3% total Delta-9 tetrahydrocannabinol (THC) in the country. However, the plant’s illegal status in the United States and elsewhere has hindered the development of plant cultivars that meet this legal definition.

Read More: GC–MS Used to Profile Cannabis Samples

In this study, the scientists assessed sampling strategies and conformance to the THC limit. As such, 14 cultivars of hemp were grown and tested by using gas chromatography with flame ionization detection (GC-FID) for total Delta-9 THC and total cannabidiol (CBD) from 2020 to 2022. Each year, samples of fresh plant material were collected from the cultivars on a weekly basis, starting in mid-August and ending in late October. From there, the scientists examined the rate of increase in THC and CBD for different cultivars and select individual plants. The sampling showed that both CBD and THC rapidly increased over a 1–2-week time frame with maximum concentrations (approximately 16% and 0.6%, respectively). To better represent small lots of hemp, the scientists suggest that sampling agents collect more than the minimum number of plants required per the United States Department of Agriculture (USDA) Agricultural Marketing Service (AMS) guidelines. Testing individual plants on the same day for select cultivars showed that while the CBD to THC ratio largely remains constant (approximately 20:1 in compliant hemp) during the growing season, individual plants are highly variable in concentration.

According to the scientists, the final rule of AMS guidelines says the range of the test result is calculated based on the measurement uncertainty and that a field lot passes if the lower range of the test result is < 0.3% total Delta-9 THC. However, this does not provide guidance on what sources of uncertainty are included in the calculation, making it difficult for laboratories to estimate uncertainty due to field sampling. This study shows that this may be a significant issue, based on observed within-cultivar plant-to-plant viability. Given interlaboratory comparison data, plant heterogeneity, and field sampling issues, the measurement uncertainty applied to THC test results for compliance levels is probably in the 30% to 50% range. This is worth discussing amongst laboratories and their regulatory partners, along with how measurement uncertainty is applied to test results for compliance purposes. Consumers should know that the ratio of CBD to THC in hemp cultivars is approximately 20:1, with that ratio likely being maintained in the end products. Though previous studies show THC and CBD production being almost entirely controlled via genetics, this study’s findings show the difficulty in defining a hemp crop based on a test result versus plant genetics, especially given uncertainties around sample collection, laboratory variability and plant-to-plant maturity.

Reference

(1) Arsenault, T. L.; Prapayotin-Riveros, K.; Ammirata, M. A.; White, J. C.; Dimkpa, C. O. Compliance Testing of Hemp (Cannabis sativa L.) Cultivars for Total Delta-9 THC and Total CBD Using Gas Chromatography with Flame Ionization Detection. Plants 2024, 13 (4), 519. DOI: 10.3390/plants13040519