The electrochemical response of the composite electrodes carbon-polyvinyl chloride and carbon-polyvinyl chloride/Nafion was studied in various aqueous electrolytes. Ex situ studies using AFM, SEM and EDS showed that after prolonged electrochemical pretreatment by repetitive potential cycling between - 0.3 and 1.3 V in 0.1 M H2SO4, changes occur to the surface composition, topography and morphology of the electrodes. In situ studies with electrochemical techniques using electrodes pretreated with carbon-polyvinyl chloride and modified with ruthenium-phenanthroline complex exhibited electrochemical activity for redox systems, as well as selectivity in the determination of dopamine in a solution containing excess ascorbic acid.