A spectropolarimetric titrimetric method for the determination of cadmium, mercury, lead and bismuth

Abstract

Spectropolarimetric methods of analyses for cadmium(II), mercury(II), lead(II) and bismuth (III) were developed, based on the stereospecific ligand, D-(—) -1,2-propylenediaminetetraacetic acid (D(—)PDTA). The optical rotation of the solution was monitored with a photoelectric polarimeter to determine the end-point of the titration. The titrant and metal complexes formed are optically active and serve as self-indicators. Since D(—)PDTA is stereospecific in its reaction with these metals, maximum utilization of the optical rotation of these complexes is achieved. The observed optical rotation is linear with respect to concentration of the metal complexes, hence straight-line extrapolations to the end-point are possible. The effects of pH, wavelength, and dilution are discussed and the optimum conditions for the determination of each metal are established. The range of accurate spectropolarimetric analyses at 365 nm with the Perkin-Elmer 141 spectropolarimeter was 10 -1–10 -3 M for cadmium(II), and 10 -1–10 -4 M for lead(II), mercury(II) and bismuth(III). The range of the average deviations from visual chelometry for the four metals titrated was 0.05–0.29%.