STUDIES ON THE COMPILATION OF SPECTRA OF A SERIES OF ELEMENTS IN VARIOUS ELECTROLYTES BY AMALGAM ACCUMULATION POLAROGRAPHY

A. A. KAPLIN, V. M. PICHUGINA, R. F. ZARUBINA

(Presented by the scientific seminar of the Department of Physical Chemistry)

In developing methods for determining microquantities of a number of elements, the polarographic experimenter often does a great deal of work in order to select the necessary background for the separation and determination of the elements under study. As is known, on different backgrounds, with other conditions being the same, the peak potentials of one and the same element have different values because of complex formation and the differing reversibility of electrode processes. Therefore, obtaining spectra of elements subjected to polarographic analysis is an important task. Spectra of elements on one and the same background make it possible to assess the possibility of determining some elements in the presence of excess amounts of other elements equivalent to them, and the relative sensitivity of the determination. The first report on obtaining spectra of anodic peaks was made by Stromberg and Zakharov [1].

The aim of the present work is to obtain spectra of the elements Zn, Cd, Pb, Cu, Bi, Sb, Sn, In, Tl on the most commonly used backgrounds.

On the basis of practical and theoretical considerations, the following constant conditions were selected: an electrolyzer, the design of which is described in [2]; a silver film electrode, 0.5 cm long, 0.05 cm in diameter, with an area of 0.078 cm²; Hg-film thickness 7.8 μ. The electrolysis potential (relative to the saturated calomel electrode) for all elements was −1.5 V, the electrolyte volume was 5 ml. The concentration of the element added to the cell was \(3 \cdot 10^{-8}\) g/ml. In some cases, if at this concentration the relative sensitivity of the element was low, concentrations of \(1 \cdot 10^{-7}\) g/ml and \(3 \cdot 10^{-7}\) g/ml were used. In all experiments, purging (5 min) and stirring of the solution during electrolysis (3 min) were carried out with purified nitrogen at a constant pressure of the latter. The experiments were performed on an LP-60 polarograph. The rate of potential change was 0.4 V/min. The speed of the paper tape was 0.4 cm/min. The sensitivity of the instrument was \(1 \cdot 10^{-8}\) A/mm. Standard solutions with a concentration of 5γ were prepared monthly by diluting more concentrated metal standards. Background solutions of 0.5 N concentration were prepared from “chemically pure” grade reagents. The electrolyte concentration in the cell was made 0.02 N; 0.1 N; 0.5 N.

Measured quantities:

\(\varphi_{\text{p}}\) — peak potential of the element (V);

Analytical-polarographic characteristics of a series of elements for various backgrounds

Table 1

Continuation of Table 1

Table 1 (continued)

\(I_a\)—depth of the anodic peak, \((a)\), converted to a monovalent metal;

\(\delta\)—half-peak width, mV, converted to a monovalent metal.

The data obtained are summarized in Table 1.

Conclusion

Values of \(\varphi_n\), \(I_a\), and \(\delta\) were obtained for the elements Zn, Cd, Pb, Cu, In, Tl, Sb, Bi, and Sn in NH\(_4\)F, NaCl, KOH, LiOH, HCl, HNO\(_3\), H\(_2\)SO\(_4\), and HClO\(_4\) supporting electrolytes at concentrations of 0.02 N, 0.1 N, and 0.5 N.

References

1. A. G. Stromberg, M. S. Zakharov. Zav. lab. 27, 517, 1961.
2. V. I. Kuleshov. In: Methods for the Analysis of Chemical Reagents and Preparations, issues 5–6, IREA, Moscow, 1963.