Differentiation of hemp from marijuana using a qualitative decision-point assay

Marijuana and hemp are different cultivars of the species, Cannabis sativa. Trichomes within these genetically distinct forms result in different chemical constituents within the plant matrix. While drug-type cannabis yields higher total Δ9-THC concentrations, industrial or consumer-based hemp products are typically rich in cannabidiol or CBD-rich. Regulatory changes following the passage of agricultural legislation in the United States defines hemp as C. sativa containing no more than 0.3 % Δ9-THC on a dry weight basis. This threshold, which effectively differentiates legal hemp from illegal marijuana, presents a challenge to operational forensic laboratories. In this report we describe a decision-point assay to differentiate hemp from marijuana using a 1 % threshold. Methanolic extracts of C. sativa were analyzed using gas chromatography-mass spectrometry (GC–MS) using a deuterated analog (Δ9-THC-D3). Synchronous selected ion monitoring (SIM) and full scan acquisition was used for targeted analysis of Δ9-THC at the decision-point. Assay performance was evaluated in terms of limit of detection, linearity, carryover, selectivity, precision, accuracy and extract stability. Two analytical approaches are presented. Extraction efficiencies of Δ9-THC from plant matrix were 80–92 %, and decarboxylation of Δ9-tetrahydrocannabinolic acid (THCA) was 67 %. Interferences arising from the cyclization of CBD to produce Δ9-THC in the GC inlet were addressed using concentrations in excess of those typically encountered in plant samples. Accuracy was established across the specified range of the assay using known reference materials containing 0.12 to 10.1 % Δ9-THC. No false positive or negative results were identified (n = 140) using both analytical approaches.