Nanostructured based Electrochemical Sensor for Voltammetric Determination of Ascorbic Acid in Pharmaceutical and Biological Samples

A novel carbon paste electrode modified with carbon nanotubes and 5-amino-2', 4'-dimethoxy-biphenyl-2-ol (5ADMB) was fabricated. The electrochemical study of the modified electrode, as well as its efficiency for electrocatalytic oxidation of ascorbic acid, is described. Cyclic voltammetry was used to investigate the redox properties of this modified electrode at various scan rates. The apparent charge transfer rate constant, k(s), and transfer coefficient, a, for electron transfer between 5ADMB and carbon nanotubes paste electrode were calculated as 7.94 s(-1) and 0.5, respectively. The electrode was also employed to study the electrocatalytic oxidation of ascorbic acid, using cyclic voltammetry, chronoamperometry and square wave voltammetry as diagnostic techniques. It has been found that the oxidation of ascorbic acid at the surface of modified electrode occurs at a potential of about 250 mV less positive than that of an unmodified CPE. The diffusion coefficient, electron transfer coefficient, and heterogeneous rate constant, for oxidation of ascorbic acid at the modified electrode surface were also determined. Square wave voltammetry (SWV) exhibits a linear dynamic range from 1.0x10(-6) to 7.5x10(-4) M and a detection limit of 0.1 mu M for ascorbic acid. Finally this modified electrode was used for determination of ascorbic acid in real samples.