Identification of marijuana using silver-phosphine ion complexation and a semi-quantitative 1 % decision-point assay

Abstract

Due to the strict federal regulations concerning ∆⁹-tetrahydrocannabinol (∆⁹-THC) content for the differentiation of hemp and marijuana outlined in the 2018 Farm Bill, the ability to quickly and reliably differentiate cannabis as marijuana or hemp is crucial within both the seized drug community and hemp industry. This study provides a novel direct mass spectrometry approach for the identification of marijuana using Ag-phosphine ion complexation and a semi-quantitative 1 % decision-point assay. The main constituents of hemp and marijuana, cannabidiol (CBD) and ∆⁹-THC, are isomeric and cannot be differentiated using soft ionization mass spectrometry techniques alone. However, the incorporation of [Ag(PPh₃)(OTf)]₂ enables the formation of unique MS/MS product ions at m/z 421/423, m/z 353/355, and m/z 231 for CBD due to differences in binding affinity, allowing CBD to be differentiated from ∆⁹-THC. Likewise, the isomeric cannabinoid precursors ∆⁹-tetrahydrocannabinolic acid (∆⁹-THCA) and cannabidiolic acid (CBDA) can be differentiated due to the formation of unique MS/MS product ions at m/z 465/467 and m/z 379/381, which are specific to CBDA. Eight additional cannabinoids were also characterized utilizing the proposed Ag-phosphine ion complexation approach. To reduce the potential for false positives, a more conservative 1 % decision-point assay was developed by fortifying 1 % weight-by-volume ∆⁹-THC-d₉ into methanolic extracts of authentic cannabis plant material, followed by assessing if the total ∆⁹-THC content (composed of ∆⁹-THC and ∆⁹-THCA) was greater than or less than the intensity of the spiked internal standard. When the developed approach was applied to 20 methanolic extracts of authentic cannabis samples with known cannabinoid compositions, 90 % of the samples were correctly identified as marijuana or not marijuana based on the 1 % administrative threshold for the total ∆⁹-THC content. The two lone misidentifications were due to the presence of elevated ∆⁸-THC, which highlights the necessity to explore more selective ligands in the future. This study provides the first application of Ag-ligand ion complexation for the identification of marijuana based on a semi-quantitative 1 % decision-point assay, which shows great promise as an alternative method for the rapid identification of marijuana.