Octacyanomolybdate-doped-poly(4-vinylpyridine) ionomer film electrode for the electrocatalytic oxidation of L-ascorbic acid

Poly(4-vinylpyridine) (PVP)-based anion exchange polymers are not studied as much as cation exchange polymers Nafion and Eastman Kodak AQ for electroanalytical applications. Similarly, octacyanomolybdate [Mo(CN)(8)(4-)] has not been studied much as a redox mediator. This communication presents results from examinations of the behaviour of Mo(CN)(8)(4-)- doped PVP ionomer film electrode to highlight the opportunities for realization of the application of this composite electrode for L-ascorbic acid (AH(2)) estimation via electrocatalytic mediation in acidic medium. The modified electrodes were characterized by cyclic voltammetry and rotating disc electrode voltammetry. PVP coatings possess strong anion-binding capacity for Mo(CN)(8)(4-) mediator with an extraction coefficient of 990, and electrostatically cross-linked PVP films offer insignificant resistance to permeation of AH(2), facilitating a cross-exchange reaction between the substrate and the mediator in the entire film volume. They show effective electrocatalytic oxidation of AH(2), with the oxidation potential of AH(2) decreased by similar to 200 mV in over-potential compared to that at bare electrode. Mo(CN)(8)(4-)/ PVP composite electrode does not respond to the more common interferents of L-ascorbic acid estimation even at high positive potentials. These and several other attractive potentialities of the modified electrode are demonstrated by direct determination of AH(2) in a commercial vitamin C tablet without any special treatment, with the value closely agreeing (+/- 0.75%) with the reference method.