The effect of anodic surface treatment on the oxidation of catechols at ultrasmall carbon ring electrodes

Electrochemical anodic treatment at ultrasmall carbon ring electrodes appears to result in the formation of an oxide film that displays charge‐selective and pH‐dependent enhancements following treatment. Voltammetry after treatment in pH 7.4 citrate‐phosphate buffer is more Nernstian for dopamine (DA) and less Nernstian for 3,4‐dihydroxyphenylacetic acid (DOPAC). However, oxidation in pH 2.8 buffer gives rise to voltammetry that is less Nernstian for both DA and DOPAC. Extensive surface oxidation in potassium hydroxide apparently forms a thick layer that acts like a thin layer reservoir for adsorbed analyte. Voltammetry following extensive treatment is attenuated and peak shaped. Minimal surface oxidation in KOH results in more Nernstian sigmoidal voltammetry with only light current attenuation. The data suggest that an oxide layer formed following anodic treatment is non‐uniform and leaves sites of activated carbon exposed on the surface. Furthermore, it appears that this layer has cation‐exchange properties giving rise to charge transfer selectivity. A model of the surface formed following anodic oxidation is consistent with previous models involving both surface cleanliness and carbon structure orientation.