DETERMINATION OF Ca⁺⁺, Ba⁺⁺, Mg⁺⁺, Al⁺⁺⁺, Cr⁺⁺⁺, Zn⁺⁺, Fe⁺⁺⁺, Pb⁺⁺, Bi⁺⁺⁺, Hg⁺⁺, Cu⁺⁺ BY EDTA TITRATION USING Cu-PAN SYSTEM

The application of Cu-Pan system EDTA titration of some cations was reinves-tigated systematically. The influence of various factors such as pH, temperature, quantity of indicator used, was studied in some detail. The stability constants of Cu-PAN complex were found to be 1.4×10⁶, at pH 2; 1.9×10⁶, at pH 4; 1×10⁵, at pH 6; 7.5×10⁴, at pH 8; and 2.1×10⁵, at pH 10. Based upon the above observations an improved method was suggested as follows: Dissolve a certain amount of salt sample in distilled water or dilute hydrochloric acid to make a solution of about 0.02 M. in concentration. Pipette 10 ml. of this solution accurately into a beaker. Add 5 ml. of acetate buffer or other suitable buffer as required for the specified sample. About 20% excess of standard disodium EDTA solution is added and then 10—15 ml. of alcohol. Titrate with 0.02 M. standard Cu⁺⁺ solution until the color of the solution changes from yellow to orange red, using 5—10 drops of 0.1% of methanolic solution of PAN as indicator. The method gave a more distinct end point in determination of Ba⁺⁺ and Cr⁺⁺⁺ in comparison with the method using Eriochrome black T as indicator.