Identification of common electrochemical oxidation pathways and mass spectrometry fragmentation patterns of the fluoroquinolones difloxacin, norfloxacin, ofloxacin and pefloxacin

Among other fluoroquinolones, difloxacin, norfloxacin, ofloxacin, and pefloxacin are regularly detected in various bodies of water around the world. Advanced oxidation processes such as the electrochemical oxidation are employed to eliminate these micropollutants. Using a microflow cell and a synthesis cell, the four fluoroquinolones were submitted to electrochemical oxidation through a boron-doped electrode. They were subsequently analyzed using high-performance liquid chromatography coupled with high-resolution mass spectrometry. Electrochemical oxidation occurred above 800 mV. Products were formed according to common mechanisms: hydrogen and ethylene elimination, methylene/methyl cleavage, hydroxylation in combination with methyl cleavage. To facilitate future identification of electrochemical oxidation products of the fluoroquinolone class, fragmentation patterns in higher-order mass spectrometry were investigated deriving typical motives. A total of 17 products were identified, 13 of which were novel. Quantitative structure-activity relationship analysis suggested that the electrochemical oxidation products would be less ecotoxic than the initial drugs.