Direct amperometric determination of l-ascorbic acid (Vitamin C) at octacyanomolybdate-doped-poly(4-vinylpyridine) modified electrode in fruit juice and pharmaceuticals

The glassy carbon electrode (GCE) modified with Mo(CN)84−-incorporated-poly(4-vinylpyridine) (PVP/Mo(CN)84−), which has been recently shown to possess several attractive attributes as an efficient electrocatalytic electrode for l-ascorbic acid oxidation and its estimation, is used for l-ascorbic acid estimation directly in orange fruit juice and Celin tablet in a 0.1 M H2SO4 acid solution without any special treatment. Constant potential amperometry at 570 mV (saturated calomel electrode, SCE) in stirred solutions is used for this purpose. A good correlation is attained with the official titrametric method. To understand the possible electrocatalytic reaction mechanism for the electro-oxidation of l-ascorbic acid, calibration graphs over the range 1 × 10−5 to 1 × 10−2 mol dm−3 l-ascorbic acid are compared for the three electrodes, ca. PVP/Mo(CN)84−, undoped PVP, and GCE; the curvature at high ascorbic acid concentration for the PVP/Mo(CN)84− electrode is explained in terms of Michaelis–Menten (MM) saturation kinetics. The apparent MM constant (KM), the maximum catalytic current (iM), the complex decomposition rate constant (kc), and the heterogeneous modified electrode rate constant ( k ′ ME ) are calculated from three different approaches. A reasonably high value of ≈1 × 10−2 cm s−1 is obtained for k ′ ME , indicating efficient l-ascorbic acid mediation at the PVP/Mo(CN)84− electrode, thus accounting for quite a high sensitivity of this modified film electrode compared to several other modified electrodes.