Increasing the concentration of SDS in the phosphate buffer solution led to an increase in the oxidation peak current due to increase the adsorbed surfactant molecules. The maximum peak current was obtained at 0.24mMSDS. However, with further increasing concentration of SDS, the oxidation peak current remains unchanged. The reason for this behavior probably lies on the surface saturation at 0.24 mM SDS. Therefore, this value of SDS was chosen for next experiments.