A comprehensive study on the kinetic aspects and experimental design for the voltammetric response of a Sn(IV)-clinoptilolite carbon paste electrode towards Hg(II)

The Sn(IV) ion exchanged clinoptilolite nanoparticles (Sn(IV)-CNP) were used as a modifier for the modification of carbon paste electrode (CPE). When the modified electrode was immersed in HCl supporting electrolyte, Sn(IV) cations can locate at the Sn(IV)-CNP-CPE electrode surface via an ion exchange process with protons of the supporting electrolyte. These electroactive cations underwent a redox process at the electrode surface. Increased peak current of Sn(IV) reduction by adding Hg(II) analyte into the supporting electrolyte solution was used for the voltammetric determination of Hg(II). Focus of the work was on study of the interaction effects between the influencing variables in square wave voltammetric response of the modified electrode in the presence of Hg(II) cations by designing the experiments (via response surface methodology: RSM) and study of some kinetic aspects of the process in linear sweep voltammetry and chronoamperometry. The optimal run in RSM was obtained in: Csn(IV) in ion exchange solution: 0.37 mol L−1, modifier%: 22.45, amplitude: 60 mV and step potential: 2.9 mV. The response current of the modified electrode was proportion to Hg(II) concentration in the range of 0.1-10 μM (DL: 0.05 μM) in square wave voltammetry and in the range of 0.1-10 μM (DL: 0.01 μM) in chronoamperometry. Using the Tafel plots, the values of α and Ko were determined for the modified electrode as 0.298, 1.91 × 10−3 s−1 and 0.311, 6.62 × 10−3 s−1 in the absence and presence of Hg(II) cations, respectively.