Determination of Bismuth, Cadmium, and Zinc in Pure Iron by Anodic Stripping Polarography
Abstract Generated abstract
This paper develops an anodic stripping polarographic procedure for determining trace bismuth, cadmium, and zinc in pure iron, extending an earlier approach limited by copper interference and possible intermetallic formation. The method dissolves the iron sample, extracts iron with a diethyl and diisopropyl ether mixture, removes copper with sodium diethyldithiocarbamate, re-extracts cadmium with concentrated hydrochloric acid, and measures bismuth, cadmium, and zinc under specified polarographic backgrounds using a film cylindrical electrode. Tests on three pure iron samples are reported, with bismuth found at or near 10^-7 percent levels, cadmium and zinc quantified across the examined samples, and an indicated procedural sensitivity of about 1.10^-7 percent.
Full Text
DETERMINATION OF BISMUTH, CADMIUM, AND ZINC IN PURE IRON BY THE ASV METHOD
Yu. I. IVANOV, A. A. KAPLIN, E. M. MALKOV
(Presented by the Scientific-Methodological Seminar
of the Faculty of Chemical Technology)
The aim of the present work is the further development of methods for determining a number of microimpurities in pure iron by the ASV method. It is known that iron is an exceptionally complex object of analysis in terms of the composition and number of impurities [2, 3, 4, 5]. The formation of intermetallic compounds and the presence of large amounts of copper \((10^{-2}—10^{-3}\%)\) in iron samples limit the application of the procedure described in [1] to the determination of copper and lead. The possibility of further improving the procedure described in [1] has been studied with the aim of determining the microimpurities Bi, Cd, and Zn in pure iron. The essence of the proposed procedure consists in extracting iron with a mixture (1:1) of diethyl and diisopropyl ethers, separating copper from the aqueous phase using sodium diethyldithiocarbamate (DDCNa), and analyzing the aqueous phase for its Bi, Cd, and Zn content by the ASV method.
We investigated the extractability of microimpurities of bismuth, copper, lead, cadmium, and zinc by DDCNa under conditions of optimal separation of iron using a mixture of diethyl and diisopropyl ethers. It was established that copper is extracted practically completely, cadmium—up to 60%, while the remaining elements are not extracted. Conditions were found for the re-extraction of cadmium using 9–10 M HCl.
Analytical procedure
A 0.5 g sample of iron is dissolved in 10 ml of concentrated HCl with heating to 90–95°C in a 25 ml volumetric flask. After dissolution, 1 ml of concentrated HNO₃ is added and the solution is brought to the mark with (3:2) HCl. The contents of the flask are cooled and transferred to a separatory funnel. Approximately the same volume of a mixture of diethyl and diisopropyl ethers (1:1) is added to the funnel, and Fe(3+) is extracted. The extraction is carried out 3–5 times until the aqueous phase is completely decolorized. A 5 ml portion of the aqueous phase is taken for the quantitative determination of Cu and Pb [1]. To the remaining part of the aqueous phase, 0.5 ml of a 10% aqueous solution of DDCNa is added, and copper is extracted. Chloroform is used as the solvent. The extraction is carried out twice. Cadmium is re-extracted from the organic phase using 5 ml of 9–10 M HCl. Then 5 ml portions of the aqueous phase are taken into two quartz beakers of 10 ml capacity each and evaporated to dry salts at 90–95°C. Organic impu-
Table 1
Results of analysis for the content of bismuth, cadmium, and zinc in iron
| Sample | No. of parallel sample | Bismuth content, % | Bismuth content, % | Cadmium content, % | Cadmium content, % | Zinc content, % | Zinc content, % |
|---|---|---|---|---|---|---|---|
| Sample 1 | 1 | $<1\cdot10^{-7}$ | $1\cdot10^{-7}$ | $4.7\cdot10^{-4}$ | $(5.5\pm1)\cdot10^{-4}$ | $6.5\cdot10^{-4}$ | $(6.6\pm0.6)\cdot10^{-4}$ |
| Sample 1 | 2 | $<1\cdot10^{-7}$ | $1\cdot10^{-7}$ | $6.1\cdot10^{-4}$ | $(5.5\pm1)\cdot10^{-4}$ | $7.0\cdot10^{-4}$ | $(6.6\pm0.6)\cdot10^{-4}$ |
| Sample 1 | 3 | $<1\cdot10^{-7}$ | $1\cdot10^{-7}$ | $5.3\cdot10^{-4}$ | $(5.5\pm1)\cdot10^{-4}$ | $6.6\cdot10^{-4}$ | $(6.6\pm0.6)\cdot10^{-4}$ |
| Sample 1 | 4 | $<1\cdot10^{-7}$ | $1\cdot10^{-7}$ | $6.0\cdot10^{-4}$ | $(5.5\pm1)\cdot10^{-4}$ | $6.1\cdot10^{-4}$ | $(6.6\pm0.6)\cdot10^{-4}$ |
| Sample 2 | 1 | $<1\cdot10^{-7}$ | $1\cdot10^{-7}$ | $3.0\cdot10^{-5}$ | $(3.3\pm0.5)\cdot10^{-5}$ | $2.0\cdot10^{-3}$ | $(2.1\pm0.2)\cdot10^{-3}$ |
| Sample 2 | 2 | $<1\cdot10^{-7}$ | $1\cdot10^{-7}$ | $3.7\cdot10^{-5}$ | $(3.3\pm0.5)\cdot10^{-5}$ | $2.3\cdot10^{-3}$ | $(2.1\pm0.2)\cdot10^{-3}$ |
| Sample 2 | 3 | $<1\cdot10^{-7}$ | $1\cdot10^{-7}$ | $3.3\cdot10^{-5}$ | $(3.3\pm0.5)\cdot10^{-5}$ | $2.1\cdot10^{-3}$ | $(2.1\pm0.2)\cdot10^{-3}$ |
| Sample 2 | 4 | $<1\cdot10^{-7}$ | $1\cdot10^{-7}$ | $3.2\cdot10^{-5}$ | $(3.3\pm0.5)\cdot10^{-5}$ | $2.1\cdot10^{-3}$ | $(2.1\pm0.2)\cdot10^{-3}$ |
| Sample 3 | 1 | $3.0\cdot10^{-7}$ | $(3.2\pm0.2)\cdot10^{-7}$ | $4.6\cdot10^{-4}$ | $(4.8\pm0.4)\cdot10^{-4}$ | $5.3\cdot10^{-4}$ | $(5.5\pm0.3)\cdot10^{-4}$ |
| Sample 3 | 2 | $3.3\cdot10^{-7}$ | $(3.2\pm0.2)\cdot10^{-7}$ | $4.4\cdot10^{-4}$ | $(4.8\pm0.4)\cdot10^{-4}$ | $5.5\cdot10^{-4}$ | $(5.5\pm0.3)\cdot10^{-4}$ |
| Sample 3 | 3 | $3.1\cdot10^{-7}$ | $(3.2\pm0.2)\cdot10^{-7}$ | $5.0\cdot10^{-4}$ | $(4.8\pm0.4)\cdot10^{-4}$ | $5.7\cdot10^{-4}$ | $(5.5\pm0.3)\cdot10^{-4}$ |
| Sample 3 | 4 | $3.7\cdot10^{-7}$ | $(3.2\pm0.2)\cdot10^{-7}$ | $5.2\cdot10^{-4}$ | $(4.8\pm0.4)\cdot10^{-4}$ | $5.7\cdot10^{-4}$ | $(5.5\pm0.3)\cdot10^{-4}$ |
the impurities are decomposed with a mixture of 1 ml of concentrated $\mathrm{H_2SO_4}$ + 2 ml of $\mathrm{H_2O_2}$ (33%) with heating.
Bismuth is determined polarographically against a background of 0.5 M HCl. After decomposition of the organic impurities, 5 ml of 0.5 M HCl is added to the beaker and it is placed in the circulating electrolyzer. The solution under study is purged with argon and electrical accumulation is carried out at a potential of $-0.5$ V for 5 min. The sensitivity of the instrument is $S = 1.1^{-8}$ A/mm; the peak potential of Bi against a background of 0.5 M HCl is 0.05 V. Cadmium and zinc are determined against a background of 0.1 M $\mathrm{NH_4F}$. The sensitivity of the instrument is $S = 1.10^{-7}$ A/mm. The peak potentials of cadmium and zinc against a background of 0.1 M $\mathrm{NH_4F}$ are 0.55 V and 0.9 V, respectively. A film cylindrical electrode was used in the work.
All studies were carried out on an OH-101/1 polarograph (Hungary). Table 1 gives the results of the analysis of three samples of pure iron. The sensitivity of the developed procedure is $1.10^{-7}\%$.
Conclusions
A procedure has been developed for the determination of bismuth, copper, lead, cadmium, and zinc in pure iron. The proposed procedure can be used for the analysis of iron for the content of the above-listed impurities with a sensitivity of $1.1^{-7}\%$.
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