Degradation mechanism study of fluoroquinolones in UV/Fe2+/peroxydisulfate by on-line mass spectrometry

Antibiotics are of concern due to their prevalent detection in aquatic environment. Sulfate radical based advanced oxidation processes show a great capacity to degrade antibiotics, but the mechanisms are still unclear. In this work, the degradation mechanism of fluoroquinolones (FQs), a major group of antibiotics, in UV/Fe2+/PMS was deeply investigated. The degradation process was in-situ and real-time monitoring by illumination-assisted droplet spray ionization mass spectrometry. A series of reactive intermediates were captured, and further characterized by high-resolution mass spectrometry (HRMS) and tandem MS. About 50 different transformation products have been identified for ciprofioxacin and norfloxacin. More than 15 products were the first time reported. Taking into consideration of the sequential formation and intensity change of intermediates, the feasible and complete transformation pathways of FQs were proposed. Compared with the photolysis process, the defluorination of FQs was not observed in this system. This work provided abundant information of FQs degradation by persulfate advanced oxidation processes (AOPs) and meanwhile demonstrated the importance of HRMS and on-line MS in mechanism research of AOPs. (C) 2019 Elsevier Ltd. All rights reserved.