Growers Network Staff

February 8, 2018 6 min read
February 8, 2018
6 min read

Variations in Cannabinoid Reporting: Part Six

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In this series of contributor articles, Savino Sguera of Digamma Consulting explores the reasons that laboratories may report different cannabinoid and terpene profiles for similar samples. There are many steps in sample testing and collection that can go wrong or can be intentionally manipulated, and Savino is here to guide us through the process.

Want to read the fifth article? Click here.

The following is an article produced by a contributing author. Growers Network does not endorse nor evaluate the claims of our contributors, nor do they influence our editorial process. We thank our contributors for their time and effort so we can continue our exclusive Growers Spotlight service.

Based on a presentation to the American Chemical Society Fall Conference, 2016

by Savino Sguera


Savino Sguera of Digamma consulting continues his analysis on the reasons why cannabinoid and contaminant reporting can vary heavily in the cannabis industry. Click here to see part five!


A detailed exploration of decarboxylation can be found here. For our purposes, it describes the removal of a CO2 molecule from a cannabinoid acid to yield a cannabinoid base: THCA converts into THC, for instance. This process usually happens via heat, through smoking, vaping, cooking, and sometimes extraction. Decarboxylation can also occur during the analytical testing process if the laboratory employs gas chromatography, which vaporizes a sample on a hot inlet. Liquid chromatography does not require heat. This is why many of the old research papers on cannabis report THC instead of THCA and why THC became the standard to report, as gas chromatography was the standard measurement instrument. But as technology has improved and instrument prices have dropped over the years, liquid chromatography has become the standard measurement instrument, allowing us to know cannabinoid and cannabinoid acid concentrations. A laboratory that only uses gas chromatography will report everything as THC, and we won’t have an accurate idea of how much was THCA and how much was THC. Laboratories that use liquid chromatography will be able to make that distinction.

Figure 10: An illustration of liquid v. gas chromatograms. On the left, liquid chromatograms, which operate near room temperature, show both THCA and THC. On the right, gas chromatograms, because of their very high temperature, show only THC, as all of the THCA has decarboxylated into THC in the instrument.

Since the cannabinoid profile in the typical flower is almost entirely THCA, how do we estimate the amount of THC produced when heated? This is not an easy answer, since that depends on how much heat is used and what the matrix is (flower, wax, shatter, etc); all methods involve some sort of loss of THC. Instead, we can calculate the theoretical maximum amount of THC that can be produced. Some simply add THCA mass and THC mass together to produce one number, but this is wrong, as there is a loss of mass when THCA becomes THC due to carbon dioxide leaving the molecule. The mass of THC produced will always be at least 13% less than the mass of THCA that was heated. This 13% must be accounted-for when translating between THCA and THC on reports and labels, and parties that fail to do this are therefore artificially boosting their numbers. For a full derivation, see the reference posted above.

Figure 11: A graphic depicting how decarboxylation miscalculations may be used to artificially raise potency reports. On the left we see the mass ratio of THCA to THC. On the right, we see three labeling techniques, with the red text being artificially inflated.

Editor’s Note: Learn more about decarboxylation in Digamma’s Treatise on Decarboxylation!

What to Demand from your Lab: Spike Recovery Data and Self-Audit

With all this talk about what labs can do to manipulate data, what can a savvy laboratory client do to protect themselves and vet their laboratory? Beside asking for the laboratory’s ISO 17025 certification, local business license, and state government license or approval, a client can also request a host of data to see that a laboratory is ethical. QA/QC data can be requested, such as matrix reporting limits, calibration ranges, acceptable deviation criteria as written in their QA/QC manual, and annual or quarterly reports showing the labs overall precision for each and every chemical reported. If a lab cannot provide all of this data, they are not satisfying ISO 17025 standards for laboratory QA/QC programs, and should be viewed skeptically. Another item that should be readily available to all cannabis testing lab clients upon request is the spike recovery data.

Figure 12: Results from a matrix spike recovery study. Read below for more details.

A spike recovery study is analytical procedure whereby a lab spikes a known amount of a chemical analyte (in this case, THCA and THC) into a matrix to measure the precision of the analysis in matrix. The results from a spike recovery study done in cannabis flower can be seen in Figure 9. The same quantity of a homogeneous solution of THC and THCA was added to three replicates of prepared cannabis flower (Illustrated in “Flower Spike” 1-3). A fourth preparation of this flower, labeled “Flower MB” was run without any addition to produce a baseline value for the matrix. Precision data is displayed to the right. The values for “Hops Spike” and “Tobacco Spike” represent samples of hops and tobacco, matrix that are negative for cannabinoids, with the same volume of solution added as the cannabis flower spikes. The variation between them helps to illustrate the variation from one matrix to another, and why an analytical method needs to be tailored to a specific matrix in a specific analyte. This is also why all QC data stored needs to be matrix-specific, to illustrate the lab’s precision in the variety of matrices that are accepted as samples.

If you are doubtful about your laboratory’s practices but don’t feel acquainted enough with the technical aspects of chemical testing to vet your lab, contact us below and we can share our self-audit form with you. Our self-audit form is a form that a client gives a laboratory to vet their practices and quality. The laboratory’s management must provide the appropriate answers to each question in written form in a timely manner. A trained chemist can quickly tell you how trustworthy your laboratory is when looking over their answers from a simple self-audit form.


Editor’s Note: That concludes Digamma Consulting’s series on why lab reports on cannabinoids and other compounds in cannabis can vary heavily based on the laboratory in question. Please let us know in the comments below if there is anything else you would like to know about cannabinoid reporting!

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About the Author

Savino Sguera is founder and CSO of Digamma Consulting. Since 2010 he has been an analytical chemist and researcher in the cannabis industry, working with both private and public interests to bring scientific integrity to the business. Savino holds a B.Sci. in Biomedical Engineering from Columbia University.