Abstract:

Bi(Ⅲ) modified Pt-electrode was prepared and the adsorption character of Bi(Ⅲ) on the electrode was studied by cyclic voltammetry. The mechanism of electrode response was discussed. A method using oscillo-potentiometry for the titration of Bi(Ⅲ) was described. In 0.1 mol/L nitric acid solution(pH=1.0), Bi(Ⅲ) 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 Bi(Ⅲ) content was in the range of 1.19×10-4～1.44×10-2 mol/L, the recovery was in the range of 99.8%～100.1% and the detection limit was 1.0×10-4 mol/L(S/N=3). Furthermore, the modified electrode showed excellent stability and reproducibility. In 1.0×10-2 mol/L Bi(Ⅲ) solution, the values of end point potentials obtained from 7 continuous determinations were all around 100 mV, and the relative standard deviation(RSD) was 0.04%. Moreover, the proposed method has been used in the determination of Bi(Ⅲ) contained in samples with recoveries of 99.5%～100.5% and RSD(n=7) less than 0.25%, which are in accordance with the indicator method.

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