Differentiation of cannabinoid isomers via Cu‐mediated molecular ion formation and electrospray ionization–tandem mass spectrometry

Gas chromatography-electron ionization-mass spectrometry (GC-EI-MS) remains the primary analytical technique used for cannabis analysis in seized drug laboratories. Electron ionization (EI) mass spectra exhibit extensive fragmentation, enabling the identification of cannabinoids by comparison with reference EI mass spectral libraries. However, limitations such as thermal degradation and potential cannabinoid conversion can occur due to the elevated temperatures of the GC inlet. In contrast, liquid chromatography-mass spectrometry (LC-MS) uses a soft ionization technique, such as electrospray ionization (ESI), which predominantly yields the protonated molecule with minimal fragmentation. Even with collisional activation using tandem mass spectrometry (MS/MS) analysis, the product ion spectra are nearly identical for cannabinoid isomers, reducing the effectiveness of this technique for cannabinoid identification. In this study, copper (Cu) salts are used to induce cannabinoid molecular ion formation under ESI conditions, enabling cannabinoid isomer differentiation. Thirteen cannabinoids were analyzed in the presence of Cu, and the resulting MS/MS product ion spectra exhibited fragmentation analogous to cannabinoid EI mass spectra. To evaluate forensic applicability, the EI-like product ion spectra were searched against the NIST 20 EI-MS mass spectral library using NIST MS Search software. Spectral matches confirmed that this alternative approach can generate EI-like data under ESI-MS/MS conditions, improving cannabinoid isomer identification. Additionally, this method was applied to methanolic extracts of authentic cannabis plant material to ensure cannabinoid molecular ion formation in real-world samples. The developed method offers an alternative approach to traditional workflows, while providing spectral data consistent with those routinely interpreted by seized drug analysts.