Determination of Trace Amounts of Zinc, Cadmium, Lead, and Copper in High-Purity Mercury by Anodic Stripping Polarography
Abstract Generated abstract
An amalgam polarographic procedure is developed for determining trace zinc, cadmium, lead, and copper in high purity mercury, where direct analysis is hindered by the mercury matrix. The authors compare electrochemical separation of mercury with removal by conversion to mercury chloride and sublimation, finding that incomplete electrochemical removal leaves mercury at levels that interfere with measurement. A method is proposed in which mercury is dissolved, converted to chloride, sublimed, and the residue is analyzed in ammonium fluoride background after electrochemical accumulation at a fixed potential, with concentrations evaluated by standard additions. Recovery tests and analyses of mercury samples are reported, supporting the applicability of the procedure for microquantity impurity determination.
Full Text
PROCEEDINGS
of the Tomsk Order of the October Revolution and Order of the Red Banner of Labor
S. M. Kirov Polytechnic Institute
Volume 302 1976
DETERMINATION OF MICROQUANTITIES OF ZINC, CADMIUM, LEAD, AND COPPER IN HIGH-PURITY MERCURY BY THE APN METHOD
V. F. SLIPCHENKO, V. M. PICHUGINA, A. A. KAPLIN
(Submitted by the scientific seminar of the Department of Physical and Colloid Chemistry)
At present there are a number of works in the literature on the determination of certain impurities in mercury [1—3]. All of them are based on separating mercury and the impurities by various methods.
Amalgam-polarographic determination of impurities that are more electronegative than the base element is impossible without their mutual separation. This problem can be solved by separating the base from the impurities to be determined, or vice versa. For routine analyses the first variant is the most acceptable. Therefore the principal studies were carried out precisely in this direction.
Mercury can be separated by distillation, extraction, sublimation of the corresponding chlorides, etc. In our studies mercury was separated electrochemically and by sublimation in the form of mercury chloride.
Electrochemical separation of mercury was carried out from an acidified solution of mercurous nitrate at a current density of 100 mA for 2.5—3 h on a silver spiral cathode with an area of 30 mm².
Table 1
Results of estimating losses of Zn, Cd, Pb, Cu during analysis (“introduced—found”).
(Experimental conditions: background—0.1 N NH₄F; solution volume = 3 ml; sensitivity = \(3 \cdot 10^{-8}\) A/mm)
| Zinc | Zinc | Zinc | Cadmium | Cadmium | Cadmium | Lead | Lead | Lead | Copper | Copper | Copper |
|---|---|---|---|---|---|---|---|---|---|---|---|
| introduced, \( \times 10^{-7}\) g/ml | found, \( \times 10^{-7}\) g/ml | % | introduced, \( \times 10^{-8}\) g/ml | found, \( \times 10^{-8}\) g/ml | % | introduced, \( \times 10^{-8}\) g/ml | found, \( \times 10^{-8}\) g/ml | % | introduced, \( \times 10^{-8}\) g/ml | found, \( \times 10^{-8}\) g/ml | % |
| 1.5 | 1.7 | — | 7.5 | 7.5 | 100 | 7.5 | 7.7 | — | 7.5 | 6.0 | 93 |
| 1.5 | 1.5 | 100 | 7.5 | 8.0 | — | 7.5 | 8.0 | — | 7.5 | 6.0 | 93 |
| 1.5 | 1.7 | — | 7.5 | 6.0 | 93 | 7.5 | 7.6 | 100 | 7.5 | 7.5 | 100 |
| 1.5 | 1.5 | 100 | 7.5 | 5.4 | 72 | 7.5 | 7.3 | 97 | 7.5 | 8.0 | — |
As a result of the studies carried out, it was established that mercury cannot be completely separated by this method, and the presence of mercury in the analyzed solution in an amount of \(10^{-3}\)—\(10^{-2}\) ml/l interferes with the determination of the indicated elements.
Therefore, subsequent studies were carried out in the direction of distilling mercury in the form of chlorides. To determine the losses of the impurities being determined that are possible in the course of the analysis, measured additions of these elements were introduced into a mercury sample and all operations required for the analysis were performed. The experimental results are given in Table 1. On the basis of the studies carried out, an amalgam-polarographic procedure is proposed for determining zinc, lead, cadmium, and copper in mercury.
Course of the Analysis
A weighed portion of mercury (0.2–0.5 g) is dissolved in 3 ml of concentrated nitric acid; the solution is evaporated to dryness. To the beaker are added 2 ml of 8 N hydrochloric acid. The solution is evaporated to dryness at a temperature of 70–80°C, and the salt obtained is sublimed at 160°C. After distillation of the salt, 3 ml of 0.1 N ammonium fluoride solution are added to the beaker, and electrochemical accumulation of zinc, cadmium, lead, and copper is carried out at an electrolysis potential of −1.7 V (relative to the saturated calomel electrode) for 3 min. The impurity content in the sample is evaluated by the method of additions.
The results of the analysis are given in Table 2.
Table 2
Results of analysis of mercury for the content of Zn, Cd, Pb, and Cu. Experimental conditions in the text
| Object | Determined element | n | $\overline{x}\cdot 10^5$ | $t_\alpha$ | $E = S_{\overline{x}}\cdot t_\alpha$ | $E$, % |
|---|---|---|---|---|---|---|
| Mercury sample No. 1 | Zn | 4 | 3.2 | 2.8 | 2.1 | 66 |
| Mercury sample No. 1 | Cd | 6 | 0.35 | 2.5 | 1.9 | 54 |
| Mercury sample No. 1 | Pb | 4 | 0.5 | 2.8 | 1.12 | 22.4 |
| Mercury sample No. 1 | Cu | 4 | 0.27 | 2.8 | 0.358 | 13 |
| Mercury sample No. 4 | Zn | 3 | 0.6 | 3.2 | 0.896 | 15 |
| Mercury sample No. 4 | Cd | 3 | 0.43 | 3.2 | 2.62 | 61 |
| Mercury sample No. 4 | Pb | 3 | 1.2 | 2.8 | 0.392 | 32.6 |
| Mercury sample No. 4 | Cu | 2 | 0.06 | 4.3 | 3.87 | 65 |
References
- E. Jackwerth, Z. Anal. Chemie, 206, 269 (1964).
- E. Ya. Neiman, E. D. Belova. “Zavod. labor.,” 3, 1969.
- V. G. Tipsova, A. G. Dvorzhak, E. I. Malkina. ZhAKh, 23, 1968.