Simultaneous electrochemical determination of dopamine and ascorbic acid using poly (l-serine) modified carbon paste electrode

A polymerized film of l-serine was prepared on the surface of a carbon paste electrode by electropolymerization using cyclic voltammetry. The polymer film-modified electrode was successfully used for the simultaneous determination of dopamine and ascorbic acid. It enhanced the redox peak currents of dopamine and ascorbic acid conspicuously and could determine them sensitively and separately at their low concentrations in 0.1 M acetate buffer solution (pH 5.5). The negative electrocatalytic activity of the poly-l-serine on the electrochemical oxidation of ascorbic acid reduced its oxidation potential to a more negative potential. It results in the separation of the overlapping voltammogram of dopamine and ascorbic acid at the carbon paste electrode in a mixture. The separation of anodic peak potentials of dopamine and ascorbic acid reached 180 mV by cyclic voltammetry. Using differential pulse voltammetry the calibration curves of dopamine and ascorbic acid were obtained in the range of 50 × 10−6-3 × 10−4 M and 0.1-0.3 × 10−4 M respectively. The detection limit of dopamine was 5 × 10−8 M in the presence of 1 mM ascorbic acid. The effect of pH and scan rate on the electrode process was investigated. High sensitivity and selectivity, sub-micro molar detection limit, high reproducibility together with ease of preparation and regeneration of the electrode surface make the electrode very suitable for the determination of dopamine in the presence of ascorbic acid in pharmaceutical and clinical preparations.