Determination of Δ9-THC, THCA, Δ8-THC, and total Δ9-THC in 53 smokable hemp plant products by liquid chromatography and photodiode array detection

The passage of the 2018 Farm Bill defined hemp as cannabis plant containing 0.3 % or less of Δ⁹-THC, which led to a large increase in hemp production in the United States in 2021. Approximately 76 % of it focused on floral hemp that is used to produce hemp-derived finished products such as smokable hemp (e.g., manicured, roll your own, or cigarettes). As a result, forensic laboratories have seen a significant increase in confiscated cannabis samples, but few reliable analytical methods exist for differentiation between hemp and marijuana. In response to the need for reliable quantitative methods, the National Institute of Standards and Technology (NIST) has developed and evaluated analytical methods to provide forensic scientists the tools necessary. In this manuscript, 53 smokable hemp plant products were analyzed for Δ⁸-THC, Δ⁹-THC, THCA, and total Δ⁹-THC by a previously established liquid chromatography with photodiode array detection (LC-PDA) method using a methanol extraction procedure. Over 90 % of the samples analyzed by NIST were determined to have a total Δ⁹-THC mass fraction above 0.3 % even though samples were being marketed as hemp. Surprisingly, often the associated online documentation reported total Δ⁹-THC mass fractions of ≥ 0.3 %. Mass fractions determined by NIST were compared with manufacturer’s online documentation for 22 samples. Measurements differed by ≈ 55 % for total Δ⁹-THC, ≈ 68 % for THCA, and ≈ 18 % for Δ⁹-THC. Poor agreement may result from method difference, sample inhomogeneity, batch to batch variability, changes due to storage conditions, and/or product labels or online documentation that are not representative of actual products.