Spectropolarimetric determinations of metal ions using D-(-)-1,2-propylenediaminetetraacetic acid

Abstract

A method is presented for the spectropolarimetric determination of scandium (III), titanium (IV), vanadium (IV), chromium (III), manganese (II), iron (III), cobalt (II), nickel (II), copper (II), zinc (II), calcium (II), strontium (II), barium (II), cadmium (II), mercury (II), lead (II), aluminum (Ill), yttrium (Ill), and bismuth (III). The sequential titrations of three mixtures of metal ions are also described. The direct spectropolarimetric titrations of cadmium and copper, cadmium and zinc, and calcium and barium were performed at the same pH. The range of accurate analyses for the spectropolarimetric titrations of the metal ions was from 10⁻¹ to 10⁻⁴ M. The results obtained by spectropolarimetric titrimetry for all the titrations deviated an average of 0.18% from the results obtained from standard wet methods of analysis or primary standards. The analyses of concentrated solutions (10⁻¹ -10⁻² M) deviated an average of 0.15%, while the analyses of the dilute solutions deviated an average of 0.24%. The optical rotation of the solution is monitored during the titration to determine the graphical end point. The titrant used was the disodium salt of D-(-)-1,2-propylenediaminetetraacetic acid, an optically active chelating agent which is stereospecific in its reactions with metal ions. The effects of pH, wavelength, dilution, and temperature on the spectropolarimetric titrations were evaluated to determine the optimum parameters.