Science & Health Archives – Marijuana Moment
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A federal science agency has released a new report as part of a project designed to help testing laboratories ensure accuracy and precision in testing cannabis products. The report focuses on determining cannabinoid content in plant material samples, following earlier reports on moisture content and certain toxins and heavy metals.
It’s the latest installment of technical guidance from the National Institute of Standards and Technology (NIST), which established its Cannabis Laboratory Quality Assurance Program (CannaQAP) in 2020. The program’s goal is to “help laboratories accurately measure key chemical compounds in marijuana, hemp and other cannabis products including oils,” NIST said at the time of its launch.
The program, created after the 2018 Farm Bill’s federal legalization of hemp, is split into three exercises. The first centered on measuring the concentration of up to 17 different cannabinoids in hemp oil. NIST published a report on that segment in mid-2021.
Exercise 2, the subject of the new report, looked at testing of dried cannabis plant samples rather than hemp oil. In addition to cannabinoid testing, it expanded the scope of the exercise to include testing for moisture content as well as 13 toxic elements.
“Since cannabinoids are increasingly used in over-the-counter supplements, they were included again in this CannaQAP exercise for participants to continue to evaluate their in-house analytical methods in dried hemp plant materials,” Walter Brent Wilson, a research chemist at NIST who served as a co-author of the new report, said in a statement to Marijuana Moment.
Accurate measurement of heavy metals and other toxic elements was a crucial part of the exercise, Wilson explained, “since they are known environmental pollutants that can accumulate in cannabis and significant potential exists for human exposure to toxic elements following hemp consumption.”
As for moisture, that’s important largely because federal law measures cannabinoid content on a dry-weight basis, and, similarly, “many toxic element safety thresholds are on a dry mass basis,” Wilson said.
The exercise’s first report, on determining moisture content in dried plant samples, came out in November 2022, while the toxic elements report was published the following month.
Cannabinoid testing comprises the latest—and longest—report of Exercise 2, which was published late last month. The 304-page document covers sample acquisition and preparation, different analytical methods, various recommendations and other details.
“In areas where few quality control materials have been developed,” the report says, “CannaQAP offers a tool for assessment of the quality of measurements and provides feedback about performance that can assist participants in improving laboratory operations.”
Specific cannabinoids included delta-8 THC, THCA and total delta-9 THC; CBD, CBDA and total CBD; as well as what the study deemed minor cannabinoids: delta-8 THC, CBC and CBCA, CBDV and CBDVA, CBG and CBGA, CBL and CBLA, CBN and CBNA and THCV and THCVA. The exercise saw participation by 226 laboratories.
Notably, the labs used various analytical methods, which meant that cannabinoid testing results weren’t consistently reproducible from lab to lab. As far as within-lab repeatability, however, most met standards set by the international Association of Official Analytical Chemists (AOAC), the report says:
“The majority of within-laboratory (repeatability, %RSDr) variabilities did meet the acceptable repeatability criteria outlined by AOAC International Standard Method Performance Requirements (SMPR) for hemp plant samples (e.g., %RSDr ≤ 5% for THCA). However, almost none of the between-laboratory (reproducibility, %RSDR) variabilities met the AOAC requirements (e.g., %RSDR ≤ 10 % for THCA). The criteria for between-laboratory precision are meant to be applied to variabilities from multiple laboratories using a single analytical method, not variabilities from multiple laboratories using multiple analytical methods, as was the case for this study.”
Among the top-level findings was the importance of calibration. Testing was most reliable when the level of a substance being tested for fell near the middle of the calibration curve; lower levels were less accurate, while higher amounts required dilution.
“To prevent calibration bias, laboratories should use calibration standards that meet ISO [International Organization for Standardization] standards, ensure all purity information is reviewed, independently prepare calibrants routinely, and are traceable to the International System of Units (SI), if possible,” the report says.
A third CannaQAP exercise, already in progress, will combine the two previous exercises “to evaluate if the participants demonstrated improvement,” Wilson at NIST said, adding that final reports are currently in preparation.
Evaluating the precise levels of cannabinoids are especially important as hemp and marijuana markets continue to grow. Often the distinction between legal and illegal products hinges on tiny amounts. To be considered federally legal hemp, for example, a cannabis plant must contain less than 0.3 percent THC on a dry weight basis.
The Drug Enforcement Administration (DEA) also recently clarified that as far as it’s concerned, that threshold includes not only delta-9 THC itself but also the related cannabinoid THCA, which is converted into delta-9 THC when heated—a process known as decarboxylation.
Some experts have disputed DEA’s interpretation of the statute on intoxicating hemp-based cannabinoids, however. And a federal appeals court ruled in 2022 that the way that existing rules are written makes delta-8 THC exempt from control, as the law is “silent” on the minor cannabinoid while clearly legalizing hemp extracts and derivatives.
Lawmakers at the state and federal levels have also begun looking at standards for delta-8 THC, a psychoactive compound commonly derived from hemp products. Some congressional legalization, meanwhile, would ban most consumable hemp-based cannabinoid products entirely.
Some industry stakeholders have said the change could even federally criminalize CBD products because the measure would apply to all ingestible hemp products with any level of THC.
Already many products sold as hemp meet the federal definition of marijuana. A NIST analysis earlier this year found that the vast majority of smokable hemp product samples–about 93 percent—contained more than 0.3 percent THC.
As law enforcement works to better distinguish hemp and marijuana, separate federally funded research published earlier this year detailed two new ways researchers say they’ve discovered to test samples.
Photo courtesy of National Institute of Standards and Technology.
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