Hemp Testing Insanity

October 23, 2019
Abstract / Synopsis: 

Federal law sets a strict national limit of 0.3 dry weight percent tetrahydrocannabinol (THC) for hemp to be considered legal. Here, we review concepts from earlier columns on accuracy, precision, and representative samples. Different states are using different sample methods, chromatographic techniques, different levels of THC, and some are even using total THC instead of THC. In light of what we have learned, I discuss why this is crazy and how it is unfair to hemp farmers.

The 2018 Farm Bill legalized the growing of hemp throughout the U.S. so long as the plant material contains less than 0.3% dry weight delta-9-tetrahydrocannabinol (∆9-THC) (1). In my own research, reading of state regulations, and discussions with hemp farmers, I have found that the method of collecting samples, the instrumental technique used to analyze them, and the cannabinoid reading that is being used to determine legality varies from state-to-state. This, along with the problem of inter-laboratory variation in the cannabis analysis industry, has lead to what I call “hemp testing insanity”—the dilemma hemp farmers face trying to legally grow a crop when surrounded by legal confusion.

Hemp Versus Cannabis?

The title of this magazine and this column both contain the word cannabis. So far, my attention has focused on marijuana testing, and in many people’s minds the term cannabis may only mean marijuana. Since the passage of the 2018 Farm Bill (1) the hemp acreage planted in the U.S. has exploded, and cannabidiol (CBD) seems to be on sale practically everywhere, including at Walgreens and in hamburgers at the fast food chain Carl’s Jr. (2,3). Technically, marijuana and hemp are the same plant species, it’s just that the former contains a lot of THC, and the latter very little. Therefore, it is appropriate for this magazine to publish articles about hemp testing, and for this column to address the topic of hemp analysis. Going forward, I will use the term marijuana for high THC plant material, and hemp for low THC plant material.

Review of Analytical Chemistry Concepts

I will not go into detail here, but instead point you towards previous columns of mine that have covered basic topics in analytical chemistry. The topics of error, accuracy, and precision were covered in the November 2018 edition of this column (4). Recall that precision is a measure of reproducibility, accuracy is how far you are off from the true value, and that these two metrics are not the same thing. Precision can, in general, always be determined by running the same sample over and over again and comparing results. Accuracy is not always available unless there exists a standard reference material for an analysis that can provide a legitimate true answer. I have previously lamented the lack of appropriate standard reference materials in this industry (5). Lastly, all measurements contain error, which can be comprised of systematic error, random error, or both. The source of systematic error can frequently be diagnosed and remedied (4). Random error is always with us because we cannot control all the variables in the universe when making a measurement (4).

Representative sampling is another topic I have covered (6). Simply put, in general the whole of which one is trying to analyze will not be homogeneous. It is then important to collect a representative sample of the whole, and analyze multiple aliquots and average the results to get the most representative and accurate picture of a material.

Legal Confusion

Current Federal law in the U.S. limits the amount of THC in ground, dried hemp to 0.3 wt.% (1). Presumably, this low level was set to prevent people from smoking hemp to get high. However, this legal definition is confusing in that it says nothing about tetrahydrocannabinolic acid (THCA), which is found in high quantities in marijuana. The problem is that THCA decarboxylates to THC when heat is applied to smoke the material, via the following reaction:


Additionally, THCA can convert to THC at a known rate at room temperature (7). There exist marijuana strains that contain more than 20% THCA and less than 0.3% THC. A strict interpretation of the law means this material may be legally considered hemp and can be sold and transported throughout the U.S. Of course, when smoked material that contains more than 20% THCA will be highly intoxicating. I doubt it was the intention of the U.S. Congress to allow high THCA marijuana to become legal nationwide. How can a law that states a specific level of a molecule is illegal be enforced if we can’t agree on what molecules we are taking about? We can’t. This is an example of hemp testing insanity.

Because THCA converts to THC, the truest measure of the intoxicating abilities of a marijuana sample is its total available THC, which is calculated using the following equation.

Total THC = THC + (0.877)THCA [1]

In equation 1, the quantities are expressed as weight percent. The 0.877 factor accounts for the fact that THCA molecules are heavier than THC. Most third party cannabis testing laboratories report out the total THC value in addition to the individual THCA and THC readings because the total THC values are useful and important.

It is particularly important for hemp farmers to use the right measurement of THC to manage their crops. For example, imagine a farmer tests a hemp sample and it comes back 0.2% THC and 0.4% THCA. A strict interpretation of the Farm Bill would say this material is legal. However, let’s say the state government comes in, collects samples, and that upon transportation and storage some of the THCA converts to THC and the state’s test results come back 0.4% THC and 0.2% THCA. The state would consider this farmer’s crop noncompliant with the law, with the risk of it being seized and destroyed. This is an example of hemp testing insanity.

To make matters worse, different states are applying different standards to enforce the law. For example, Kentucky uses THC only (8), whereas Oregon uses total THC (9). I recently heard that New York state has switched from using total THC to THC for regulating this year’s hemp crop. This means that hemp farmers in different states are being subjected to different regulations. Thus, a crop in one state may be considered legal whereas the same crop in another state may be considered illegal. This is an example of hemp testing insanity.

HPLC Versus GC

Adding confusion to the matter is that some states, such as Oregon use high performance liquid chromatography (HPLC) (8) to measure cannabinoids in hemp, whereas other states, such as Kentucky, use gas chromatography-flame ionization detection (GC-FID) (9). HPLC measures THC and THCA separately (10), and there is no conversion from THCA to THC during the analysis. However, during GC analysis of cannabinoids, THCA breaks down to THC in the injection port and in the column (11), and what is truly measured is the total THC in the sample. If the GC analysis report says “THC” instead of “total THC,” then comparing GC and HPLC analyses on the same sample can be confusing because the two techniques are measuring different quantities but calling them the same thing!

  1. 115th United States Congress, Senate Bill S.2667, ”Hemp Farming Act of 2018.”
  2. A. LaVito, CNBC, March 27, 2019, https://www.cnbc.com/2019/03/27/walgreens-to-sell-cbd-products-in-some-stores.html.
  3. M. Judkis, The Washington Post, April 17, 2019, https://www.washingtonpost.com/news/voraciously/wp/2019/04/17/carls-jr-is-rolling-out-a-cbd-burger-but-dont-get-your-hopes-too-high/?noredirect=on&utm_term=.4920aef53386.
  4. B.C. Smith, Cannabis Science and Technology 1(4), 12–16 (2018).
  5. B.C. Smith, Cannabis Science and Technology 2(3), 10–14 (2019).
  6. B.C. Smith, Cannabis Science and Technology 2(1), 14–19 (2019).
  7. B.C. Smith, Terpenes and Testing Nov.–Dec., 48 (2017).
  8. Kentucky Dept. of Agriculture, Hemp Program Procedures for Sampling, THC Testing, and Post-Testing Actions, SOP# KDA-HEMP-20190204-1, February 4, 2019.
  9. Oregon Health AuthorityPublic Health Division - Chapter 333, Marijuana Labeling, Concentration Limits, and Testing.
  10. M.W. Giese, M.A. Lewis, L. Giese, and K.M. Smith, J. AOAC Int. 98(6), 1503 (2015).
  11. T. Ruppel and M. Kuffel, “Cannabis Analysis: Potency Testing Identification and Quantification of THC and CBD by GC/FID and GC/MS,” PerkinElmer Application Note (2013).
  12. P. Atkins, Cannabis Science and Technology 2(2), 26–34 (2019).
  13. https://www.oregon.gov/ODA/shared/Documents/Publications/NurseryChristmasTree/SamplingProtocol.pdf.
  14. B.C. Smith, “Quantitation of Cannabinoids in Hemp by Mid-Infrared Spectroscopy,” Cannabis Science and Technology, manuscript submitted.
  15. B.C. Smith, Cannabis Science and Technology 2(2), 12–17 (2019).
  16. B.C. Smith, P. Lessard, and R. Pearson, Cannabis Science and Technology 2(1), 48–53 (2019).
  17. https://en.wikipedia.org/wiki/Equal_Protection_Clause.
  18. https://docs.google.com/spreadsheets/d/1x8doatlR6w1W3W6hA0hlu67qwe9uOSfYoHe3vjcYs6Y/edit#gid=855723386.

Brian C. SmithBrian C. Smith, PhD, is Founder, CEO, and Chief Technical Officer of Big Sur Scientific in Capitola, California. Dr. Smith has more than 40 years of experience as an industrial analytical chemist having worked for such companies as Xeros, IBM, Waters Associates, and Princeton Instruments. For 20 years he ran Spectros Associates, an analytical chemistry training and consulting firm where he improved their chemical analyses. Dr. Smith has written three books on infrared spectroscopy, and earned a PhD in physical chemistry from Dartmouth College.

How to Cite This Article

B.C. Smith, Cannabis Science and Technology 2(5), 10-13 (2019).