Voltammetric Study of Lomefloxacin Transfer at the Interface between Two Immiscible Electrolyte Solutions: Ionic Partition, Photodegradation, and Sensing Applications

The transfer of ionizable lomefloxacin (LOM) across a polarized interface between two immiscible electrolyte solutions (ITIES) was studied using cyclic and differential pulse voltammetry (DPV). The pH values of water (ionic strength=0.02 M) interfacing with the 1,2-dichloroethane phase were varied to investigate the transfer behavior of differently charged LOM species, including protonated, neutral, and zwitterionic forms of LOM, namely HLOM⁺, LOM⁰, and H⁺LOM⁻. An ionic partition diagram for LOM was drawn with DPV response at various pH values, and the distinctive features of LOM were compared to those of fluoroquinolone antibiotics, which have similar pK_a values. Physical and thermodynamic properties, including the formal transfer potential, lipophilicity, and Gibbs free energy of transfer of LOM were also evaluated. Furthermore, the photodegradation properties of differently charged LOM species and ophthalmic LOM drop samples (pH 5.0) were investigated after exposure to a UV (λ=365 nm) source. Quantitative analysis of HLOM⁺ concentrations in buffer and diluted commercial eye drop solutions containing LOM was finally demonstrated using differential pulse stripping voltammetric responses at pH 3.0 and 5.0 involving the transfer of HLOM⁺ at a polarized microhole-water/polyvinylchloride-2-nitropheyloctylether gel interface.