Photometric determination of small amounts of titanium in high-purity iron
Abstract Generated abstract
This paper examines photometric determination of trace titanium in high-purity iron using diantipyrylmethane, addressing interference from ferric iron coloration and complex formation. Three analytical variants are developed and compared: extraction-based preliminary separation of iron, direct determination after reduction of iron with ascorbic acid, and direct determination by the method of additions. Tests with titanium additions to high-purity iron and iron oxide were evaluated statistically, with determination times ranging from 5 to 1.5 hours. The additions method without iron separation is recommended for production laboratories as the fastest and most precise of the tested procedures.
Full Text
PHOTOMETRIC DETERMINATION OF TRACE AMOUNTS OF TITANIUM IN HIGH-PURITY IRON
L. L. Skripova, G. A. Chervenchuk
(Presented at the scientific-methodological seminar of the KhTF)
The possibility of photometric determination of trace amounts of titanium in high-purity iron using diantipyrylmethane was studied. This work is a continuation of earlier investigations [1].
The photometric determination of titanium with diantipyrylmethane is hindered by large amounts of iron (3+) because of its own coloration and the formation with the reagent of a complex compound colored reddish-brown.
Large amounts of iron (3+) can be removed by extraction with diethyl ether from a hydrochloric-acid medium, with methyl isobutyl ketone, with a mixture of methyl isobutyl ketone and amyl acetate (1:1), or reduced to the divalent state, which does not react with diantipyrylmethane in an acidic medium. Reduction of iron can be carried out with zinc amalgam, sodium sulfite, sodium hyposulfite, ascorbic acid, etc. [2, 3].
Extraction of iron from the hydrochloric-acid solution of the sample with ether need not be carried out completely, since small amounts of it can readily be reduced with ascorbic acid and do not interfere with the determination.
The extraction operation is associated with a large expenditure of time and unavoidable losses. Therefore, in order to shorten the time of analysis and reduce losses, the possibility was also studied of photometrically determining trace amounts of titanium in high-purity iron with diantipyrylmethane without separating iron.
Three variants of the procedure were developed—with preliminary separation of iron and without separation of iron.
The first variant is with preliminary separation of iron. A 0.5 g sample of iron is dissolved with gentle heating in 15 ml of concentrated hydrochloric acid. Add 1 ml of concentrated nitric acid and continue heating, evaporating almost to dryness. The residue is treated with 5 and 10 ml portions of concentrated hydrochloric acid, evaporating almost to dryness the first time and to a syrup the second time. The residue is dissolved in 10 ml of 6 N hydrochloric acid and transferred to a separatory funnel. Add 20 ml of diethyl ether (free of peroxide) and shake for 5 minutes. The ether layer is separated and washed with 5 ml of 6 N hydrochloric acid. The aqueous portions are combined and evaporated to approximately 10 ml, then transferred to a 25 ml volumetric flask. Add 2 drops of a 5% solution of copper sulfate (catalyst for the reduction of iron), 1 ml of ascorbic acid with \(T = 0.2\ \text{g/ml}\), 3 ml of 5% diantipyrylmethane in 1 N hydrochloric acid, and bring the volume to the mark with 25% sulfuric acid solution. After 30–40 minutes, photometry is carried out on an FEK-N-57.
in a 50 ml cuvette with light filter No. 2 (413 mµ). The comparison solution is water. The amount of titanium is found from a calibration curve constructed under the same conditions under which the sample was decomposed. The procedure was checked by additions of titanium to weighed portions of high-purity iron and iron oxide. One determination requires 5 hours. The results of the analyses were processed by the method of mathematical statistics and are given in Table 1 (first and second rows).
The second variant is without separation of the iron. A 0.5 g weighed portion of iron is dissolved in 10 ml of a 25% sulfuric acid solution with gentle heating. The solution is transferred to a 25 ml volumetric flask. The subsequent operations are carried out analogously to the procedure described above. Ascorbic acid, of the same concentration, is added in an amount of 5 ml. The “blank” test contains all reagents except diantipyrylmethane. The amount of titanium is found from a calibration curve constructed under the same conditions under which the sample is decomposed, i.e., necessarily against an iron background. One determination requires 3 hours. The procedure was checked by additions of titanium to weighed portions of high-purity iron. The results of the analyses were processed by the method of mathematical statistics and are given in Table 1 (third row).
The third variant is without separation of the iron, using the method of additions.
In polarographic and luminescence chemical analyses, the method of additions is widely used for determining small amounts of impurities in high-purity materials.
L. I. Lazarev and V. I. Lazareva [4] successfully used this method for the photometric determination of titanium in steels with the aid of hydrogen peroxide.
We studied the possibility of the photometric determination of titanium in high-purity iron with the aid of diantipyrylmethane, without separating the iron, using the method of additions. A 2.5 g weighed portion of iron is dissolved in 30–40 ml of a 25% sulfuric acid solution with gentle heating. The solution is transferred to a 50 ml volumetric flask and made up to the mark with a 25% sulfuric acid solution. Into four 25 ml volumetric flasks, aliquot portions of this solution of 10 ml each are taken. To the second and third flasks, additions of titanium are made in amounts corresponding to 1 and 2 µg of the latter. To all four flasks are added 1 ml each of 6 N hydrochloric acid, two drops each of a 5% solution of copper sulfate, and 5 ml each of ascorbic acid with \(T = 0.2\ \text{g/ml}\). Then to the first, second, and third flasks are added 5 ml each of a 5% solution of diantipyrylmethane in 1 N hydrochloric acid. The volume in all flasks is brought to the mark with a 25% sulfuric acid solution. After 30–40 minutes, photometry is carried out in the same way as in the preceding procedures. The comparison solution is water. The amount of titanium is found from the formula:
\[ \% \mathrm{Ti} = \frac{C_{\Delta}(D_1 - D_0)} {\text{weighed portion}\,(D_{2(3)} - D_1)\cdot 2000}, \quad \text{where} \]
\(C_{\Delta}\) is the addition of titanium in µg;
\(D_0\) is the optical density of the solution in the fourth flask, i.e., the “blank,” without titanium and diantipyrylmethane;
\(D_1\) is the optical density of the solution in the first flask—the solution under investigation;
\(D_{2,(3)}\) is the optical density of the solution in the second (third) flask with an addition of titanium.
The amount of titanium is calculated for the first and second additions, and the mean value is taken. The time required for one determination is 1.5 hours. The results of the analyses were processed by the method of mathematical statistics and are given in Table 1 (fourth row).
Table 1
Results of titanium determination
| Measured quantity | $n$ | $\overline{X}$ | $S_{\overline{x}}$ | $\tau_{0.95}$ | $\varepsilon$ | $\varepsilon_{\%}$ |
|---|---|---|---|---|---|---|
| % titanium in iron, Kahlbaum grade | 6 | $1.59 \cdot 10^{-3}$ | $0.09137 \cdot 10^{-3}$ | 2.571 | $0.23 \cdot 10^{-3}$ | 14.4 |
| % titanium in $\mathrm{Fe_2O_3}$ | 7 | $2.53 \cdot 10^{-5}$ | $0.1428 \cdot 10^{-5}$ | 2.247 | $0.32 \cdot 10^{-5}$ | 12.6 |
| % titanium in VCh iron | 7 | $1.57 \cdot 10^{-4}$ | $0.07626 \cdot 10^{-4}$ | 2.571 | $0.17 \cdot 10^{-4}$ | 10.8 |
| % titanium in VCh iron | 13 | $1.59 \cdot 10^{-4}$ | $0.05403 \cdot 10^{-4}$ | 2.179 | $0.11 \cdot 10^{-4}$ | 6.9 |
Conclusions
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Three variants of a procedure have been developed for determining small amounts of titanium in high-purity iron using diantipyrylmethane—with preliminary separation of the iron and without separation of the latter.
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A comparative evaluation of the proposed variants has been carried out, and for production laboratories the third variant is recommended—without separation of the iron, using the method of additions—as the most accurate and rapid.
Literature
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L. L. Skripova, G. A. Chervenchuk, A. I. Pokrovskaya. Photometric determination of small amounts of titanium in hydrochloric acid, ammonium and sodium chlorides, and luminophore L-34 using diantipyrylmethane. Izvestiya TII, vol. 174 (in press).
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J. Morrison, G. Freiser. Extraction in Analytical Chemistry. Gos. N.-Tekhizdat Khimliteratury, L., 1960.
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G. B. Sandell. Colorimetric Determination of Traces of Metals. “Mir,” Moscow, 1964.
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L. I. Lazarev and V. I. Lazareva. Colorimetric determination of titanium in alloyed steels by the method of additions. Zavodskaya laboratoriya No. 2, 1958.