Study of the degradation process of ofloxacin with free chlorine by using ESI-LCMSMS: Kinetic study, by-products formation pathways and fragmentation mechanisms

•Order 1 Reaction of OFX with Free chlorine.•Seven By-products were observed during reaction.•Different ways of mechanisms have been proposed for identifying structures.•Fragmentation pathways of MSMS spectrum precise the structures of by-products.

This study was conducted to gain a better understanding of the fate of fluoroquinolone antibacterial ofloxacin (OFX) which is the free available chlorine (FAC) in order to determine its effect during water chlorination process. The Direct reactions of FAC with OFX were quite rapid. A half-life of 7.7 s was measured under pseudo-first order conditions in the presence of an excess of total chlorine ([FAC]0 = 13 μM and [OFX]0 = 0.55 μM at pH 7.2 and 20 °C in buffered reagent water. Free chlorine reactions rates were of first-order type in both substrate and oxidant with specific second-order rate constants of 6.8 × 103 M−1 s−1. No induced back reactions or other interference by using thiosulfate to stop the chlorination reaction was shown. The seven products of the reaction were determined by using the LC/MS/MS analysis. Structures were investigated due to the explication of transitions obtained at different CID energies by LC-ESI-MS/MS. Pathways of the formations of these by-products were presented in this study and pathways of the fragmentations of pseudo molecular ions of the structures proposed were presented in supplementary files.