The Association of Official Agricultural Chemists International (AOAC International) recently recognized a liquid chromatography-diode array detection (LC-DAD) method to analyze cannabinoids in hemp plants. Originally, the LC-DAD method had been approved as an Official Method of Analysis 2018.11 (1) for use in testing for cannabinoids in cannabis plants, oils, and concentrates (2).
Scott Coates, Program Lead for AOAC’s Cannabis Analytical Science Program (CASP), stated, “Until now, no globally recognized method for validating the potency of hemp was available to laboratories” (2).
With its new validation, the LC-DAD method grants laboratories the ability to assess tetrahydrocannabinol (THC) in hemp on a dry-weight basis. This basis is explained further under the United States Department of Agriculture’s Interim Final Rule in the 2018 Agriculture Improvement Act, also called the Farm Bill, which governs over the production of hemp (3). The program’s major requirement is that hemp is tested for THC levels.
The federal government defines plant materials containing no more than 0.3% THC as hemp, often rebuked by critics demanding that the THC level should be increased. With 0.3% THC or lower, these materials can be processed to be used in cannabidiol (CBD) consumer products. At the federal level, marijuana is classified as a Schedule 1 controlled substance. Although this has not been reconsidered, states across the country have begun decriminalizing the consumption and cultivation of low-THC form (hemp) and high-THC form (marijuana).
As stated in the AOAC’s press release (2), the Official Method of Analysis 2018.11 is an LC-DAD technique with optional mass spectrometric detection of Î9-tetrahydrocannabinol (Î9-THC) and tetrahydrocannabinolic acid (THCA) individually, so their concentrations can be reported either individually or as total THC. “Official Method of Analysis 2018.11 is applicable to concentrates, oils, and all plant materials of Cannabis sp., including hemp,” the release stated (2).
The method was modified to also include a sample dry weight determination procedure. “The performance of this method has been demonstrated thoroughly, and laboratories in the hemp industry can confidently implement this straightforward method for determination of total THC on a dry-weight basis,” said Rebecca Phillips, chair of the AOAC Expert Review Panel and a Research Chemist at the U.S. National Institute of Standards and Technology (NIST) (2).
After a stringent review and validation process, the method was judged against requirements from the Standard of Method Performance Requirement (SMPR) Quantitation of Cannabinoids in Plant Materials od Hemp (Low THC Varieties Cannabis sp.) (4). This standard is ascribed in the U.S. Department of Agriculture Hemp Program’s Interim Final Rule and was engineered by AOAC’s Cannabis Analytical Science Program (CASP) in 2019. SMPR is the preferred standard laboratories use to select a method to analyze THC levels.