Electrocatalytic oxidation of ascorbic acid and simultaneous determination of ascorbic acid and dopamine at a bis(4′-(4-pyridyl)-2,2′:6′,2′′-terpyridine)iron(II) thiocyanate carbon past modified electrode

A carbon-paste electrode modified with bis(4′-(4-pyridyl)-2,2′:6′,2′′-terpyridine)iron(II) thiocyanate, [Fe(pyterpy)2](SCN)2, where pyterpy = 4′-(4-pyridyl)-2,2′:6′,2′′-terpyridine, have been applied to the electrocatalytic oxidation of ascorbic acid which reduced the overpotential by about 200 mV with obviously increase the current response. Due to its strong electrocatalytic activity towards ascorbic acid, the modified carbon-paste electrode can resolve the overlapped voltammetric waves of ascorbic acid (AA) and dopamine (DA) into two well-defined voltammetric peaks with peak-to-peak separation in potentials of about 200 mV. This property allows to selective determination of ascorbic acid in the presence of dopamine. Relative standard deviations for AA and DA determinations were less than 3.0% and AA and DA can be determined in the ranges of 8.33 × 10−6–2.92 × 10−3 and 2.00 × 10−6–7.40 × 10−4 M, respectively. The treatment of the voltammetric data of AA showed that it is a pure diffusion-controlled reaction, which involves one electron in the rate-determining step. The transfer coefficient (α) for the electrocatalytic oxidation of AA and diffusion coefficient of this substance under the experimental conditions were also investigated. The modified electrode shows good selectivity, stability and anti-fouling properties. The proposed method was successfully applied to the determination of AA, and DA in vitamin C and dopamine hydrochloride injections samples.