Cd(Ⅱ) modified Pt-electrode was prepared and the adsorption character of Cd(Ⅱ) on the electrode was studied by cyclic voltammetry. The mechanism of electrode response was discussed. A new method using oscillo-potentiometry for the titration of Cd(Ⅱ) was described by optimizing the testing conditions. In 0.1 mol/L hexamethylene tetramine solution (pH 6.0), Cd(Ⅱ) was titrated with EDTA, and two modified Pt-electrodes were used as bi-indicator electrode system. The end point of titration was determined by an abrupt maximum displacement of the fluorescence spot observed on the screen of the cathodic oscillograph. When Cd(Ⅱ) content was in the range of 9.0×10^－4～3.5×10^－3 mol/L, the recovery was in the range of 99.8%～100.3%. Furthermore, the modified electrode showed excellent stability and reproducibility. In 1.0×10^－3 mol/L Cd(Ⅱ) solution, the values of end point potentials obtained from 13 continuous determinations were all around 37 mV, and the relative standard deviation (RSD) was 0.02%. Moreover, the proposed method has been used in the determination of Cd(Ⅱ) contained in samples with recoveries of 99.71%～100.09% and RSD (n＝7) less than 0.81%, which are in accordance with the indicator method.

Key words: oscillography analysis, double potentiometric titration, modified Pt-electrode, Cd(Ⅱ), EDTA