Symmetrical electrochemical cell for determination of coextraction constants of metal salts for ion-selective polymeric membranes

A symmetrical electrochemical cell has been developed to perform cyclic voltammetric study of a plasticised poly(vinyl chloride) (PVC) membrane. The plasticised PVC membrane of ca. 100μm thickness was mounted in a specially laboratory-made electrochemical cell for voltammetric analysis on exposure to various sodium salt and metal chloride solutions. Symmetrical cyclic voltammograms were obtained when the sample and internal solutions contained same kind of metal salts. The coextraction constant of a metal salt for the plasticised PVC could be determined from either the positive or negative potential scans of a cyclic voltammetry. In addition, two coextraction constants could also be simultaneously obtained when the membrane was exposed to two different metal salts in the sample and internal solutions, respectively. It was observed that the more lipophilic of the cations or anions, the larger the coextraction constants of these ions for the plasticised PVC membrane. The results followed the Hofmeister sequence of ClO₄^->NO₃^->Br ^->Cl^->OAc^- for anions and the ease of extraction of cations was in the order of Cs⁺>K⁺>Na⁺>Li⁺. The proposed method provides a simpler, faster and more convenient method to obtain the coextraction constants of metal salts for plasticised polymeric membranes.