Preparation of Polypyrrole/Nuclear Fast Red Films on Gold Electrode and Its Application on the Electrocatalytic Determination of Methyl-dopa and Ascorbic Acid

Anovel voltammetric method using the Ppyox/NFR/Au (poly pyrrole– nuclear fast red– gold) modified electrode was developed for simultaneous measurement of various combinations of ascorbic acid (AA) and methyldopa (MDA). Poly pyrrole film was prepared by incorporation of nuclear fast red (NFR) as doping anion, during the
electro polymerization of pyrrole onto a gold (Au) electrode in aqueous solution using cyclic voltammetric (CV)
method, and then it was overoxidized at constant potential. Differential pulse voltammetry was utilized for the
measurement of both analytes using modified electrode. Well-separated voltammetric peaks were observed for
ascorbic acid (AA) and methyldopa at the Ppyox/NFR/Au modified electrodes with peak separation of 0.210 V. It has
been found that under optimum condition (pH 3.0), the oxidation of AA and MDA at the surface of the electrode
occurs at a potential about 260 and 50 mV less positive than unmodified Au electrode respectively. The current
catalytic oxidation peaks showed a linear dependent on the concentration of AA and MDA in the range of 9.0 10 6
to 1.0 10 3 and 1.0 10 7 to 2.0 10 5 mol L1 respectively. The detection limit of 5.8 10 6 and 5.0 10 8 mol L1
(S/N¼3) were obtained for AA and MDA respectively. The modified electrode was used for determination of AA
and MDA in some real samples such as human serum and tablet.