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Determination of 11 Cannabinoids in Hemp Plant and Oils by Liquid Chromatography and Photodiode Array Detection



Walter Brent Wilson, MARYAM ABDUL-RAHMAN


Drug scheduling has directed the testing approaches for forensic laboratories since the 1970s when Cannabis (marijuana and hemp) and its psychoactive constituent, Δ9-tetrahydrocannabinol (Δ9-THC), were classified as Schedule 1 controlled substances. Seized evidence is tested by federal, state, and local crime laboratories following a qualitative test scheme that includes macro- and microscopic identification of plant features, colorimetric test for presence of Δ9-THC or its acidic precursor Δ9-tetrahydrocannabinolic acid (THCA), and gas chromatography – mass spectrometry for confirmation of their presence. However, the 2018 Farm Bill defined hemp as Cannabis containing 0.3 % or less of decarboxylated-Δ9-THC (total THC) and removed hemp from the controlled substance list requiring forensic laboratories are to quantify the level of total THC to distinguish Cannabis is marijuana (an illegal controlled substance) or hemp (a legal commodity). GC-MS and liquid chromatography coupled to a photodiode array detector (LC-PDA) are popular analytical techniques for Cannabis; however, GC is limited because THCA decarboxylates to Δ9-THC in the high temperatures of the GC inlet with conversion rates typically ranging from 50 % to 70 %. The National Institute of Standards and Technology (NIST) has recently established an integrated Cannabis measurement services program for forensic and Cannabis testing laboratories to help ensure the quality of analytical measurements through the development of a Cannabis Quality Assurance Program (CannaQAP) and Reference Materials (RMs). To support these efforts NIST are developing, implementing, and/or validating analytical methods for screening bulk hemp and/or marijuana samples. In addition, while also permitting their potential implementation of these methods in forensic laboratories. In this article, an LC-PDA method is evaluated for the determination of 11 cannabinoids in 4 hemp plant reference samples from the University of Kentucky Proficiency Testing Program and 15 commercially available hemp oils. Samples are extracted following a previously approved methanol (MeOH) extraction method by an AOAC Expert Review Panel. The results summarized here demonstrate the accuracy and precision of the LC-PDA method for the screening of future RMs and/or CannaQAP samples.


Hemp, Cannabis, Marijuana, Cannabinoids, Δ-9-Tetrahydrocannabinol, Liquid Chromatography


Wilson, W. and ABDUL-RAHMAN, M. (2022), Determination of 11 Cannabinoids in Hemp Plant and Oils by Liquid Chromatography and Photodiode Array Detection, Chromatographia, [online],, (Accessed May 29, 2024)


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Created January 21, 2022, Updated November 29, 2022