Study on the Amalgam Polarographic Determination of Trace Amounts of Antimony in Tin with Separation of Antimony by Extraction with Diisopropyl Ether
Abstract Generated abstract
This study examines an amalgam polarographic method for determining trace antimony in tin after separation by extraction with diisopropyl ether from hydrochloric acid solution. The authors evaluate reduction of pentavalent antimony to the trivalent state with hydrazine hydrochloride, extraction behavior in synthetic solutions, and recovery in the presence of dissolved tin, then propose a procedure using dissolution in hydrochloric acid and hydrogen peroxide, ether extraction, reduction, accumulation on a stationary mercury drop, and standard additions. The method gave about 50 to 55 percent recovery from the tin dissolution medium, requiring a correction factor of two, and was applied to tin samples with results comparable to chemical spectral data. Under the stated conditions the reported sensitivity was 1 x 10^-5 percent antimony.
Full Text
STUDY ON THE AMALGAM-POLAROGRAPHIC DETERMINATION OF MICROQUANTITIES OF ANTIMONY IN TIN WITH SEPARATION OF ANTIMONY BY EXTRACTION WITH DIISOPROPYL ETHER
L. F. ZAICHKO, M. S. ZAKHAROV, L. G. SHCHIPKOVA
(Presented by the scientific seminar of the Faculty of Chemical Technology)
Previously [1] we proposed a procedure for determining microconcentrations of antimony in tin by the method of amalgam polarography with accumulation on a stationary mercury drop, according to which dissolution of the tin sample was carried out in a mixture of HCl + Br₂, and separation of antimony from tin and from the impurities Cu and Bi, which interfere with its amalgam-polarographic determination, was effected by extraction from 6 N acid with ethyl acetate.
On the basis of literature data [2, 3], it is of interest to ascertain the possibility of amalgam-polarographic determination of microconcentrations of antimony with its separation from tin and interfering elements (Cu and Bi) by extraction with diisopropyl ether from a hydrochloric-acid medium. The present work is devoted to this question.
Experimental Part
Polarographic measurements were carried out on a self-recording instrument of the OH-101 Orion KTS type with a galvanometer sensitivity of \(1 : 10^{-9}\) A/mm. In the work an electrolyzer with insert cups [1] was used; the stationary electrode was a mercury drop obtained by electrolysis from a saturated mercurous nitrate solution on silver wire sealed into a glass tube. A saturated calomel electrode was used as the anode.
A standard antimony solution (3+) of 500 γ (\(1\gamma = 10^{-6}\) g) was prepared from metallic antimony by dissolving it in concentrated sulfuric acid. A standard Sb (5+) solution was prepared by dissolving a weighed portion of the metal in concentrated hydrochloric acid in the presence of an oxidizing agent—perhydrol. Excess perhydrol was removed by heating at \(t^\circ = 60–70^\circ\).
Solutions with concentrations of 50 γ, 5 γ, and 1 γ were prepared by successive dilution.
Since antimony is extracted in the pentavalent state, whereas it is more convenient to polarograph it in the trivalent state, we carried out investigations to determine the completeness of reduction of \(\mathrm{Sb}^{5+}\) to \(\mathrm{Sb}^{3+}\) by hydrazine hydrochloride in 1 N HCl (background).
For this purpose, a known amount of standard \(\mathrm{Sb}^{5+}\) solution (0.1 γ) was reduced in the presence of an excess of \(\mathrm{Sn}^{4+}\)* \(\sim 50^\circ\) with hydrazine hydrochloride by heating on a water bath (\(\sim 90^\circ\)) for 15 min. In this operation, along with the reduction of \(\mathrm{Sb}^{5+}\) to \(\mathrm{Sb}^{3+}\)
* Tetravalent tin remains with the antimony when it is separated from tin by extraction.
the reduction of $\mathrm{Sn}^{4+}$ to $\mathrm{Sn}^{2+}$ also takes place. After reduction, the solution is cooled, electrolytic accumulation of antimony is carried out, and the anodic polarogram is recorded in the voltage interval from $-0.6$ to $0$ V. On reaching the $\mathrm{Sn}^{2+}$ peak ($-0.48$ V), the potentiometric drum was stopped for a time sufficient for anodic dissolution of tin. After this the drum was switched on again and the anodic wave of antimony was obtained. The resulting wave belonged to trivalent antimony, since pentavalent antimony is not reduced against a background of 1 N HCl. The results of the experiments are given in Table 1.
Table 1
Study of the completeness of reduction of $\mathrm{Sb}^{5+}$ to $\mathrm{Sb}^{3+}$ by hydrochloric-acid hydrazine
| Depth of the Sb wave (mm) after reduction of $\mathrm{Sb}^{5+}$ (0.1 γ) to $\mathrm{Sb}^{3+}$ | Increase in depth of the Sb wave (mm) from addition of $\mathrm{Sb}^{3+}$ (0.1 γ) to the electrolyzer | % reduction |
|---|---|---|
| 25 | 27 | 93 |
| 25 | 25 | 100 |
| 26 | 27 | 96 |
| 25 | 27 | 93 |
| 26 | 26 | 100 |
As is seen from the table, reduction of $\mathrm{Sb}^{5+}$ to $\mathrm{Sb}^{3+}$ occurs quantitatively.
At first, studies were carried out to determine the completeness of the extraction recovery of $\mathrm{Sb}^{5+}$ by diisopropyl ether in synthetic solutions in the absence of tin. For this purpose, a known amount of $\mathrm{Sb}^{5+}$ was taken and its extraction with diisopropyl ether from 7 N HCl was carried out [3]. Polarography was performed against a background of 6 N $\mathrm{NH_4Cl}$ (in this case reduction of $\mathrm{Sb}^{5+}$ to $\mathrm{Sb}^{3+}$ was not carried out).
The results of these studies are given in Table 2.
Table 2
Results of studies on the extraction recovery of $\mathrm{Sb}^{5+}$ with diisopropyl ether from 7 N HCl in synthetic solutions
| After extraction (0.1 γ) $h$, mm, $\mathrm{Sb}^{5+}$ | Increase in $h$ from addition of $\mathrm{Sb}^{5+}$ (0.1 γ) to the electrolyzer | % extraction |
|---|---|---|
| 28 | 30 | 92 |
| 27 | 30 | 90 |
| 26 | 30 | 87 |
| 27 | 30 | 90 |
| 25 | 29 | 86 |
| 25 | 28 | 89 |
Next, the completeness of separation of microconcentrations of antimony from tin was studied. In these studies, a 0.5 g weighed portion of tin was taken and a known amount of $\mathrm{Sb}^{3+}$ (0.1 γ) was added to it. The tin sample was dissolved in a mixture of HCl + $\mathrm{H_2O_2}$. It is of interest to study the extraction separation of antimony from the medium obtained after dissolution of the tin sample and decomposition of the hydrogen peroxide by heating. This will shorten the analysis time (evaporation of the resulting solution at $t \sim 80^\circ$ to dryness requires $\sim 3$ hours) and reduce losses of antimony. The acidity of the solutions after decomposition of $\mathrm{H_2O_2}$ is $\sim 3.5$ N with respect to HCl.
The results of these studies are presented in Table 3.
Table 3
Study of the completeness of the determination of antimony when it is extracted from ~3.5 N solution with diisopropyl ether in the presence of dissolved tin
| \(h\), mm, Sb from the addition before decomposition | Increase in \(h\), mm, Sb from the addition to the electrolyzer | Completeness of determination |
|---|---|---|
| 11 | 22 | 50 |
| 14 | 23 | 51 |
| 13 | 22 | 59 |
| 10 | 20 | 50 |
| 10 | 21 | 48 |
| 12 | 22 | 55 |
| 11 | 20 | 55 |
| 10 | 20 | 50 |
As can be seen from the table, the completeness of determination is 50–55%, and to obtain the true Sb content in tin the result obtained must be multiplied by a constant coefficient—2.
On the basis of the studies performed, the following procedure is proposed for determining microconcentrations of antimony in tin.
0.5 g of powdered metallic tin is dissolved in 4.5 ml of concentrated hydrochloric acid in the presence of 30–35 drops of perhydrol. The perhydrol is added dropwise, and the cups are cooled with tap water. After dissolution of the sample, the perhydrol is decomposed at 60°–70° for 30–40 min in an air bath. After cooling, the contents of the cups are transferred to separatory funnels. The cup is rinsed with 2 portions of 3.5 N HCl, and the volume of the acidic phase is brought to ~7 ml. After this, threefold extraction is carried out with 3-ml portions of ether, vigorously shaking the funnel for 3 minutes each time. The combined extracts are washed twice with 4 N HCl for 2 minutes. The ether is then transferred to a quartz beaker and evaporated to dryness at ~\(t^\circ = 70^\circ\). To the dry residue, 2–3 drops of concentrated HNO\(_3\) are added to destroy traces of organic substances, and it is evaporated to dryness. Next, 2 ml of a 1 N HCl supporting electrolyte is added to the beaker, and reduction is carried out with hydrochloric-acid hydrazine under heating.
After cooling of the solution, the beaker is placed in the electrolyzer, purified N\(_2\) is passed through for 10 min, and electrolysis is carried out on a stationary mercury drop at −0.66 (sat. cal. el.), after which the polarogram is recorded. The Sb content is determined by the method of additions. By this procedure, several tin samples were analyzed.
The results of the analysis of one batch of tin are presented in Table 4.
Table 4
Analysis of tin for antimony content
| Sb content by the method of amalgam polarography | \(2.4 \cdot 10^{-5}\%\) | \(2.3 \cdot 10^{-5}\%\) | \(2.5 \cdot 10^{-5}\%\) | \(2.3 \cdot 10^{-5}\%\) |
| Chemical-spectral data | \(2 \cdot 10^{-5}\%\) | \(2.3 \cdot 10^{-5}\%\) |
The sensitivity of the procedure under the developed conditions, \(\Lambda\) of the solution 2 ml; \(\tau = 7\) min; \(s = 8 \cdot 10^{-9}\) A/mm, is \(1 \cdot 10^{-5}\%\).
REFERENCES
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- Schweizer, Stroms. Analyt. chim. acta, 19, 2, 154, 1958.