Investigation of Mexiletine Hydrochloride Binding on Transition Metal Oxide Nanoparticles by Capillary Electrophoresis

<title>Abstract</title> The binding affinity of pharmaceutical salts to metal oxide nanoparticles is a fundamental environmental process that determines their transport and bioavailability. Mexiletine hydrochloride (MEX.HCl) interactions with different transition metal oxide nanoparticles (TMONPs) in aqueous dispersion were evaluated by capillary electrophoresis to determine their binding affinities. The results indicated that MEX.HCl bound onto TiO₂, Co₃O₄ and ZnO nanoparticles in alkaline, neutral and acidic pH levels. Interestingly, TiO₂ manifested the highest binding affinity of 81 ± 1% at pH 9.4. It was shown that higher initial concentrations of MEX.HCl in an aqueous solution, increasing from 15 to 75 µg/mL, yielded higher binding affinities for TiO₂ than Co₃O₄ and ZnO nanoparticles. The binding rate followed pseudo-second-order kinetics and the binding data were better modeled by the Freundlich isotherm than the Langmuir isotherm. These findings revealed that MEX.HCl binding occurred on the heterogeneous binding sites on TMONPs mainly by the physisorption mechanism via electrostatic attraction and hydrogen bonding.