Oscillo-Potentiometric Titration of Cobalt(Ⅱ) with EDTA Using EDTA-Modified Platinum Electrode as Indicator Electrode

EDTA-modified platinum electrode was prepared and its electrochemical behavior studied by cyclic voltammetry.Two of such modified Pt-electrodes were used as bi-indicator electrode system in the oscillopotentiometric titration of Co(Ⅱ) with EDTA.End point of the titration was determined by an abrupt maximum displacement of the fluorescence spot observed on the screen of the cathodic oscillograph.Repeatability of the modified Pt-electrode was tested for 15 successive determinations using 10.00 mg of Co(Ⅱ),values of end-point potentials obtained were around 45 mV with RSD of 0.01%.The titration was performed in an ammoniacal buffer of pH 10-11,with addition of some appropriate complexing agents,such as fluoride and tartrate.Cobalt was determined in the mass range of 1.2-31.2 mg with recovery in the range of 99.9%-100.3%.The proposed method has been used in the determination of Co2O3 in ceramic pigments,giving results in conformity with the known values,and values of RSD′s (n=7) were less than 0.05%.