Dissolved Organic Matter-Ofloxacin Interaction as Affected by Metal Ions

A dialysis equilibrium system was applied to investigate the roles of Cu(II) and Mg(II) on DOM-ofloxacin (OFL) interaction. The binding behavior of both cations and OFL were studied. The introduction of Cu(II) increased DOM-OFL interaction, while Mg(II) decreased DOM-OFL binding. Cu(II) binding to DOM was also increased by OFL, while Mg(II) binding was decreased by OFL. The change in OFL binding amount in the absence and presence of cations (ΔC b) was calculated and compared with cation binding \( (C_{\mathrm{ b}}^{\mathrm{ m}}) \). \( \varDelta {C_{\mathrm{ b}}}/C_{\mathrm{ b}}^{\mathrm{ m}} \) was in the range of 1–3 for Cu(II), depending on the applied Cu concentration. Two ternary complexes of DOM-OFL-Cu and DOM-Cu-OFL were proposed. For Mg(II), \( \varDelta {C_{\mathrm{ b}}}/C_{\mathrm{ b}}^{\mathrm{ m}} \) was around −1 at Mg(II) concentrations lower than 1 mM but decreased to −5 with increasing Mg(II) concentration. The competitive effect of Mg(II) to OFL was thus proposed.