2.4. Procedure
A 25ml of 0.2Mphosphate buffer solution at the desired pH and the necessary standard solutions of BPR and SDS were added into the electrochemical cell. The solution was stirred for 120 s to preconcentration. Following the accumulation period, the stirrer was stopped, and after an equilibrium time of 30 s, the differential pulse voltammograms were recorded from 0.3 to 1.0 V at the optimized value of H step and scan rate. After each experiment the electrode was polished with a white and clean paper. All measurements were made at room temperature.