صدیقه هاشم نیا

Dopamine (DA), uric acid (UA) and Ascorbic acid (AA) are important human body compounds that play determining role in metabolism; therefore monitoring their concentration in biological fluids is important. They are electrochemically active compounds and electrochemical techniques can be used to investigate them. The main goal of this study was to design of a new carbon paste electrode modified with silver nanoparticles to use in an electrochemical study of dopamine in the absence and presence of ascorbic acid and uric acid. After the synthesis of the nanosized silver colloids by a chemical reduction process in aqueous solution in the presence of polyvinylpyrrolidone (PVP) as a stabilizing agent, a silver nanoparticle modified carbon paste electrode was prepared. Then the modified electrode was used to study electrochemical properties of DA using cyclic and differential-pulse voltammetric techniques. The cyclic voltammetric results indicate that the modified electrode can remarkably enhance electrocatalytic activity toward the oxidation and reduction of dopamine in pH3 asetate buffer solution than carbon paste electrode. The electrochemical process was observed to be diffusion-controlled, quasi-reversible and involving two-electron oxidation. Under optimal conditions, the anodic peak current was proportional to DA concentration in the range of 5.0 to 430.0 ?M with a detection limit of 1.0 ?M using differential pulse voltammetry. The linear range of DA in the presence of UA and AA was from 5.0 to 70.0 and 15.0 to 170.0 µ M with a detection limit of 1.68 and 7.6 respectively. The electrode can also use for selective determination of DA in the presence of a mixture of AA and UA in phosphate buffer solution (pH 7.0). Results showed a linear dynamic range of DA extended from 12.5 to 300.0 µM and a detection limit of 1.1µM.