Electrode reactions of 3,4‐dihydroxyphenylacetic acid (DOPAC) at glassy carbon, graphite‐reinforcement carbon, and carbon fiber electrodes

Abstract

AbstractThe voltammetric behavior of 3,4‐dihydroxyphenylacetic acid (DOPAC) in a phosphate buffer solution (pH 7.4) was investigated at untreated and electrochemically treated glassy carbon (GC), graphite reinforcement carbon (GRC), and carbon fiber (CF) electrodes. Except for the pretreated GRC, all of the electrodes exhibit a well‐defined anodic wave (Aa) at approximately 0.25–0.5 V vs. SCE. The untreated and the pretreated GC electrodes yielded irreproducible behavior compared to the GRC electrode. Transfer coefficients and the charge transfer rate constant were evaluated from variations of the peak potential with the potential sweep rate. The peak current was controlled by both diffusion and the sluggish charge transfer process. Similar results were obtained at weakly pretreated CF electrodes. As the level of the pretreatment for the CF electrode was raised up by applying more anodic potential, wave Aa decreased and new anodic and cathodic waves, B and C, appeared at 0.1 and 0.27 V, respectively, versus SCE. Wave B was ascribed to the adsorption of DOPAC. Amounts of the adsorbed species increased with the time the electrode was immersed in the solution and then tended to the steady‐state value. They were subjected to the Langmuir adsorption isotherm. A value of the saturated adsorption was 0.89 × 10−9 mol/cm2 and the adsorption coefficient was 1.63/mmol/dm3.