Th(IV)-hexacyanoferrate modified carbon paste electrode as a new electrocatalytic probe for simultaneous determination of ascorbic acid and dopamine from acidic media

A stable carbon paste electrode (CPE) was prepared with Th(IV)-hexacyanoferrate (Th-HCF) ion pair and its electrochemical behavior was investigated by cyclic voltammetry. The apparent heterogeneous rate constant, k(s), and transfer coefficient, a, for electron transfer between Th-HCF ion-pair and CPE were calculated as 3.1 +/- 0.1 s(-1) and 0.47, respectively. The surface coverage (G) of the proposed electrode was calculated as 7.06 x 10(-10) mol cm(-2). The proposed Th-HCF modified carbon paste electrode (THMCPE) showed a good electrocatalytic behavior with a significant shift toward negative potentials in oxidation of ascorbic acid (AA) and dopamine (DA) in acidic media (phosphate buffer solution, pH 3). The THMCPE exhibited excellent characteristics for simultaneous determination of AA and DA. Amperometric curves using the catalytic currents are linear for DA and AA concentrations in the ranges 8 x 10(-6) - 2 x 10(-3) and 1 x 10(-5) - 2 x 10(-3) mol L-1 with detection limits 5.6 x 10(-6) mol L-1 and 4.7 x 10(-6) mol L-1, respectively. Diffusion coefficients of AA and DA in electrocatalaytic oxidation were calculated from chronoamperometric data.