On the electrochemistry of dopamine in aqueous solution. Part I: The role of [SDS] on the voltammetric behavior of dopamine on a carbon paste electrode

From CV and HPLC experiments, the influence of [SDS] on the dopamine electrochemical behavior was determined in aqueous solution. It is shown that in the absence of SDS the dopamine electrochemical oxidation at a carbon paste electrode is a quasi-reversible process, mass transfer controlled that is coupled to a slow chemical reaction (EC mechanism), however, as the [SDS] in solution is increased, the heterogeneous standard rate constant, k0, drastically increases. When [SDS] reaches a value of 5 mM, which is higher than the corresponding critical micellar concentration (CMC), the dopamine electrooxidation reaction becomes adsorption controlled and the chemical reaction is avoided. In all these cases, it was found that, the electrode reaction involves a monoelectronic transfer step. From HPLC experiments it was found that, after imposing a macroelectrolysis (oxidation) of dopamine, two products were detected except when the [SDS] in solution was 5 mM. In this case, just one product was formed corresponding to that having the highest retention time, which can be associated to dopamine semiquinone.