Determination of Microconcentrations of Antimony in High-Purity Tin by Amalgam Accumulation Polarography
Abstract Generated abstract
This paper develops a simplified amalgam accumulation polarographic method for determining trace antimony in high-purity tin without the previously used extraction separation. The authors compare the anodic peak behavior of antimony, copper, bismuth, and tin in several supporting electrolytes and identify a mixture of concentrated sulfuric acid and alcohol as suitable, since it gives useful separation of antimony from bismuth and tin while copper is only weakly reduced. The proposed procedure removes most tin by distillation as tin tetrabromide, reduces antimony to the trivalent state, and measures it after electrolysis at a mercury electrode. Application to high-purity tin samples gave antimony contents on the order of 7 to 9 × 10^-6 percent.
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L. F. ZAICHKO, M. S. ZAKHAROV, V. D. MORDVINOVA
DETERMINATION OF MICROCONCENTRATIONS OF ANTIMONY IN HIGH-PURITY TIN BY AMALGAM ACCUMULATION POLAROGRAPHY
(Presented by the scientific seminar of the Department of Physical Chemistry)
Previously [1] we proposed an amalgam-polarographic procedure for determining microconcentrations of antimony in tin, in which the separation of antimony from tin and from impurities interfering with its amalgam-polarographic determination (Cu, Bi) is carried out by extracting it from 6 N HCl with ethyl acetate. The extraction separation of the element is time-consuming and requires the use of additional reagents, high-purity vessels, etc. It is therefore of interest to select a background on which antimony in tin could be determined by amalgam accumulation polarography in the presence of the indicated elements. For this purpose, the amalgam-polarographic behavior of antimony, copper, bismuth, and tin was studied in several electrolytes.
The results of the investigations are summarized in Table 1.
Table 1
Potentials of anodic peaks of Sb$^{3+}$, Cu$^{2+}$, Bi$^{3+}$, and Sn$^{2+}$ on several backgrounds
| No. | Background | Sb$^{3+}$ | Cu$^{2+}$ | Bi$^{3+}$ | Sn$^{2+}$ |
|---|---|---|---|---|---|
| 1 | 1.5 M HCl | −0.15 | −0.25 | −0.15 | −0.5 |
| 2 | 0.25 M HCl | −0.1 | −0.2 | 0 | −0.47 |
| 3 | 5 N H$_2$SO$_4$ + alcohol = 1:1 | −0.1 | weak | 0 | −0.48 |
| 4 | 1 M H$_2$SO$_4$ | −0.1 | 0.2 | 0 | −0.48 |
| 5 | 1 M succinic acid | −0.1 | −0.1 | 0 | −0.4 |
| 6 | 0.36 M H$_2$SO$_4$ + 1 M H$_2$C$_2$O$_4$ | −0.1 | −0.1 | 0 | −0.43 |
| 7 | 1 M H$_2$SO$_4$ + 1 M MnSO$_4$ + 0.1 M HCl | −0.1 | 0 | 0 | −0.47 |
| 8 | 5 N H$_2$SO$_4$ + alcohol = 1:1 + 0.5 M Trilon “B” | −0.1 | weak | 0 | −0.48 |
| 9 | 1 M maleic acid | −0.1 | 0 | 0 | −0.4 |
| 10 | 1 M H$_2$SO$_4$ + malachite green | −0.1 | 0 | 0 | −0.42 |
Dashes in Table 1 mean that, on the given background, no peak of the element is obtained.
On the basis of the investigations presented, the most promising background for determining antimony by amalgam polarography
with accumulation in the presence of Bi, Cu, and a 100-fold excess of Sn is 5 N H₂SO₄ + alcohol = 1:1, on which copper is reduced weakly, and between the peaks of Sb and Bi, Sb and Sn there is a potential difference of 0.1 V and 0.38 V, respectively. We chose this supporting electrolyte for determining microconcentrations of antimony in high-purity tin.
Since the peak potentials of antimony and tin differ by a considerable amount, for the determination of antimony in tin it is sufficient to remove only the bulk of the tin (and not completely).
Because the boiling temperatures of SbBr₅ and SnBr₄ differ appreciably from one another ($T_{\text{boil. SnBr}_4}=202^\circ$, and $T_{\text{boil. SbBr}_5}=280^\circ$) [2], the bulk of the tin can be removed by distilling it in the form of SnBr₄.
On the basis of the results set forth above, the following procedure is proposed for determining microconcentrations of antimony in high-purity tin.
0.5 g of finely divided metallic tin is dissolved in a quartz beaker of 10 ml capacity, previously checked for purity, in a mixture of 4 ml HBr + 1 ml Br₂. The contents of the beaker are evaporated to dryness in a closed glass chamber on an air bath at 170°C. Then, in the beakers, 1 ml of 6 N HCl is added to the dry residue and reduction of Sb⁵⁺ to Sb³⁺ is carried out (simultaneously the residues of Sn⁴⁺ are reduced to Sn²⁺) with sodium hypophosphite (30–40 mg) at 60–70°. To decrease the acidity, after evaporation of HCl, doubly or triply distilled water is added to the beakers 2–3 times and the solution is evaporated to dryness each time. Then the supporting electrolyte (5 N H₂SO₄ + alcohol) is added to the beakers and electrolysis is carried out for 15 minutes at
Table 2
Results of analysis of high-purity tin for antimony content.
Experimental conditions: $\varphi_{\text{e}}=-0.5$ V (sat. cal. el.); $\tau_{\text{e}}=15$ min; $r_{\text{k}}=0.04$ cm; sensitivity $1/3=0.14$ μA/cm; $V_p=2$ ml.
| Depth of the Sb notch in the sample, mm | Depth of the Sb notch from the addition in the electrolyzer, mm | Sb content, % |
|---|---|---|
| 10 | 30 | $7\cdot10^{-6}$ |
| 22 | 23 | $9\cdot10^{-6}$ |
| 11 | 29 | $7.5\cdot10^{-6}$ |
Fig. 1. Polarogram of analysis of tin for antimony content: a) sample of high-purity tin; b) sample of high-purity tin + addition of Sb³⁺ standard, 0.1 μg. Experimental conditions: $\varphi_{\text{e}}=-0.5$ V (sat. cal. el.); $V_p=2$ ml; $r_{\text{k}}=0.04$ cm; $\tau_{\text{e}}=15$ min. Sensitivity 0.14 μA/cm. (PA-1 polarograph).
a potential of −0.5 V (sat. cal. el.). Stirring of the solution during electrolysis is carried out with nitrogen and is maintained constant throughout the series of experiments. After electrolysis is completed, the polaro-
gram. Analyses of high-purity tin were carried out by the proposed procedure. The results of the analysis are given in Table 2.
As an example, Fig. 1 presents polarograms from the analysis of one of the high-purity tin samples.
REFERENCES
- L. F. Zaichko, M. S. Zakharov. Determination of antimony in tin. Methods for the Analysis of Chemical Reagents and Preparations, issue 5–6, p. 79, IREA, Moscow, 1963.
- Chemist’s Handbook, vol. 1, Goskhimizdat, 1962.