Identification of first and second generation ozonation transformation products of niflumic acid by LC-QToF-MS

In this study, the removal of niflumic acid (NA) and the identification of its transformation products (TPs) during ozonation was investigated. The influence of initial ozone concentration and pH value on NA's removal was tested, while suspect and non-target screening approaches were followed for the identification of ozonation TPs. The structure elucidation was based on accurate mass and isotopic pattern criteria and interpretation of the acquired MS/MS spectra. Moreover, an in-house retention time prediction model was used as a supporting tool for their identification. Results indicated the highly reactivity of NA with the molecular ozone, since the reaction was extremely fast and was completed within the first minute of the reaction. A total of thirteen TPs of NA were identified, and their proposed structures show that the oxidation occurred in the heterocyclic ring of the molecule, while the aniline-like part remained intact by ozone attack due to the presence of the three fluoride atoms, which act as electron withdrawing groups. Ozonation experiments were conducted also using the most abundant TP of NA as parent compound. Three second generation TPs of NA were detected and possible structures were proposed.