Characterization and differentiation of positional isomers of fluoro-fentanyl analogs by a combination of instrumental analyses

The isomers of ‰uoro-butyrylfentanyl, ‰uoro-isobutyrylfentanyl, and ‰uoromethoxyacetylfentanyl, in which the position of ‰uorine on the Nphenyl ring varies, were synthesized, characterized, and diŠerentiated by infrared (IR) spectroscopy, liquid chromatography/mass spectrometry (LC/MS), and gas chromatography/mass spectrometry (GC/MS). The isomers could be clearly diŠerentiated by their IR spectra. In the LC/MS chromatograms, the separation of the ‰uoro-butyrylfentanyl and ‰uoro-isobutyrylfentanyl isomers was insuŠicient. However, in the GC/MS extracted ion chromatograms, all compounds were completely separated. The LC/MS and GC/MS mass spectra of the isomers were similar, demonstrating that it is diŠicult to distinguish the positional isomers of ‰uorinated fentanyl analogs by their mass spectra.