Kinetics and transformation pathways on oxidation of fluoroquinolones with thermally activated persulfate

• Parameters on the degradation of three typical fluoroquinolones were examined.
• Abundant intermediates formed on the piperazine group and quinolone moiety were identified.
• Detailed degradation mechanism for each fluoroquinolone was proposed.

Three typical fluoroquinolones (FQs), ciprofloxacin, norfloxacin and enrofloxacin were degraded using the thermal activation of persulfate (PS). The degradation rates of FQs generally increased with the rise of PS/fluoroquinolone ratio (20:1–80:1) and temperature but decreased with the increase of initial pH values. The major degradation mechanisms of fluoroquinolones by thermally activated PS were proposed. Abundant intermediates identified by liquid chromatography–tandem mass spectrometry (LC–MS/MS) indicated that the oxidation would occur mainly on the C–F bonds (for ciprofloxacin and enrofloxacin) or the C–H (for norfloxacin) bonds on the quinolone groups, causing hydroxyl substitution as well as hydrogen abstraction, and on the piperazine groups following a series of substitutions, additions and eliminations resulting in the final open-loop reactions.