Pseudo-indicator behaviour of platinum electrode explored for the potentiometric estimation of non-redox systems

Abstract

A pseudo-indicator electrode based potentiometric method for estimation of non-redox metal ions is presented. In the proposed method, nature and concentration specific impact of analyte over the redox potential of ideally polarisable Pt/pregenerated-redox-couple interface forms the basis of quantification. Utility of the method in estimation of six non-redox metal ions viz. Zn(2+), Cu(2+), Ni(2+), Cd(2+), Pb(2+), Al(3+) in the concentration range of 10(-1)-10(-3) moldm(-3), individually and as binary mixtures is also presented. Three types of potentiometric behaviours, which we ascribe to the nature specific thermodynamic and kinetic aspects of metal-EDTA binding, were observed. While Cu(2+), Ni(2+), Pb(2+) and Al(3+) were found to bind EDTA efficiently, without exchanging Fe(3+); Zn(2+) and Cd(2+) were observed to replace Fe(3+) from EDTA. In contrast, Ca(2+) and Mg(2+) were found to show no binding affinity to EDTA in the pH range employed in the present work. The proposed method was also used to explore the reversibility and the Nernestian behaviour of ferricyanide/ferrocyanide redox couple through spectroelectrochemical titration of Zn(2+) with ferrocyanide. The presented method is presaged to be a reliable and low cost future replacement for costly and delicate ion selective electrodes (ISE) in the estimation of non-redox species like Zn(2+), Cu(2+), etc.