A spectropolarimetric method of analysis was developed utilizing the stereospecific ligand, D-(-)-l,2propylenediaminetetraacetic acid, D(-)PDTA. The optical rotation of the solution was monitored with a photoelectric polarimeter to determine the end point of the titration. The metal complexes and the titrant are optically active and self-indicators; therefore, it is possible to utilize the maximum quantitative pH range for the determination of each metal. All the metals were analyzed using three buffers. Because D(-)-PDTA is a stereospecific ligand, it ensures maximum utilization of the rotations of the metal complexes. The observed optical rotation is linear with respect to concentration of the metal complexes; consequently, it was possible to perform straight line extrapolations to the end point. The effects of pH, wavelength, dilution, and diverse ions were investigated and the optimum conditions for the determination of each metal were established. The average deviation for all the metal ion titrations was 0.19%.
Recent developmentsin the construction of photoelectric spectropolarimeters (7) and in the availability of commercial spectropolarimeters (2, 3) have resulted in a renewal of interest in extending the range of spectropolarimetric titrimetry in analysis. These instrumental developments make use of electronic polarimeters and spectropolarimeters as practical detectors in titrimetry with dissymmetric substances.Spectropolarimetric titrimetry is a new analytical technique, first described by Kirschner and Bhatnagar (4). Basic to the technique is the use of photoelectric polarimeter to monitor the change in optical rotation of a solution upon the addition of titrant. The system must be chosen such that a recognizable change in optical rotation occurs at the titration end point. Applications to both acid-base titrimetry and the determination of metal ions have been described (5).Only three metal ion ligand titrations have been described to date: the titration of L-(+)-histidine monohydrochloride with copper(II) chloride (4), the titration of disodium EDTA with zinc(II) nitrate using L-(+)-histidine as an asymmetric indicator (5), and the titration of d-(-)-1,2-propylenediamine with nickel(II) perchlorate (5).A simple spectropolarimetric method for the determination of the 3d transition metals was developed. This method is uncomplicated, sensitive, rapid, and versatile. In order to obtain this simple spectropolarimetric method, a strong stereospecific chelating agent, d-(-)-1,2-propylenediaminetetraacetic acid, d(-)PDTA, was selected as the titrant. In this paper a spec-(
Ki[Zn]2' KiX2[Zn] 2 /(3) where bracketed concentrations refer to amalgam concentrations and CuZn appeared to form. Its slope of Kap/K\K2 gave K2 = 7.6 X 10-2 and its intercept gave K:i = 2.1. Several other combinations of species and stoichiometry were attempted and several sets of solubility expressions like Equation 3 were formulated. These gave much larger variabilities in calculated solubility products and instability constants than the assumed stoichiometry. Kap = [Cu][Zn]3, K3 = ([Zn][CuZn2])/[CuZn3], K2 = ([Zn][CuZn])/[CuZn2],Ki = ([Zn][Cu])/[CuZn],
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