Photometric Determination of Trace Iron in Hydrofluoric Acid, Antimony Trioxide, and Ammonium Hydrogen Phosphate
Abstract Generated abstract
This paper refines a photometric method for determining trace iron as an alpha,alpha prime-dipyridyl complex and adapts it to hydrofluoric acid, antimony trioxide, and ammonium hydrogen phosphate used in producing the L-34 phosphor. The procedure uses hydrochloric acid treatment, a complexing reducing buffer mixture to control pH and mask interfering metals, reduced dipyridyl reagent consumption, and measurement either by aqueous photometry or extraction color comparison. Addition experiments indicated applicability to the three matrices, with analysis times of about one hour and reported relative errors of up to 5 percent for hydrofluoric acid, 10 to 15 percent for antimony trioxide, and 3 to 5 percent for ammonium hydrogen phosphate.
Full Text
Photometric Determination of Traces of Iron in Hydrofluoric Acid, Antimony Trioxide, and Ammonium Hydrogen Phosphate
Yu. L. Lel’chuk, L. L. Skripova, B. N. Besprozvannykh
(Presented by the scientific seminar of the Chemical-Technological Faculty)
Previously [1] we developed a procedure for the photometric determination of traces of iron in the form of a complex with $\alpha,\alpha'$-dipyridyl in high-purity tin, with a sensitivity of $n \cdot 10^{[[unclear: exponent]]}\%$. In the present work, individual details of the method have been refined and the conditions for its application to the determination of traces of iron in hydrofluoric acid, antimony trioxide, and ammonium hydrogen phosphate, used for the production of the phosphor “L-34,” have been studied.
The experiments carried out showed that, in determining traces of iron in the above-mentioned objects, the consumption of a 2% solution of $\alpha,\alpha'$-dipyridyl can be reduced without detriment to 0.5 ml for each determination; the maturation time of the iron complex with $\alpha,\alpha'$-dipyridyl before photometry, after mixing the reagents, can be reduced to 15 min. The complexing reducing buffer mixture used earlier [1, 2]—consisting of tartaric acid, sodium sulfite, sodium chloride, and caustic soda—for binding tin, antimony, and interfering microimpurities of other metals into stable complexes, for reducing ferric iron to ferrous iron, and for creating and maintaining the optimum pH of the solution of the iron complex with $\alpha,\alpha'$-dipyridyl within the range 3.3–3.5, as well as the method for purifying it from traces of iron, can be successfully applied in the analysis of all the above-mentioned objects. Fluoride and phosphate anions, after treatment of the analyzed weighed portions of hydrofluoric acid and ammonium hydrogen phosphate with hydrochloric acid [1 : 1], do not interfere with the determination of traces of iron. The determination may be completed by photometry of the aqueous solution of the complex on an FEKN-57 photoelectric colorimeter-nephelometer, or by extraction of the complex with 1 ml of a mixture of benzene with meta-cresol and comparison of the color intensity of the extract with a standard scale.
The accuracy of the proposed procedures was checked by the method of additions. The results of the determination of traces of iron in hydrofluoric acid, antimony trioxide, and ammonium hydrogen phosphate, used for the production of the phosphor “L-34,” are given in Table 1.
The work used reagents of “chemically pure” and “analytical grade” qualifications; twice-distilled water; hydrochloric acid, practically completely freed from traces of iron by isothermal distillation and chromatographically with the anion exchanger AN-2F [3]; a complexing reducing buffer mixture prepared by dissolving 7.5 g of sodium chloride, 30 g of tartaric acid, 15 g of sodium sulfite, and 10–11 g of solid caustic sodium hydroxide...
sodium in 500 ml of twice-distilled water. Purification of the mixture from traces of iron was carried out by treating it twice with a 2% solution of α,α′-dipyridyl and subsequently removing the iron complex formed by extraction with a mixture of benzene and meta-cresol.
Table 1
Determination of traces of iron in hydrofluoric acid, antimony trioxide, and ammonium hydrogen phosphate
| Taken for analysis, g | Iron added, μg | Iron found, μg | Iron found, % | Mean value, % | Deviation from the mean, % |
|---|---|---|---|---|---|
| HF | −2.1 | ||||
| 2 | — | 5.46 | \(2.73 \cdot 10^{-4}\) | \(2.79 \cdot 10^{-4}\) | +3.6 |
| 1 | — | 2.89 | \(2.89 \cdot 10^{-4}\) | ||
| 1 | — | 2.76 | \(2.76 \cdot 10^{-4}\) | −1.1 | |
| 1 | 1 | 3.82 | +1.1 | ||
| \(\mathrm{Sb_2O_3}\) | |||||
| 0.5 | — | 7.03 | \(1.41 \cdot 10^{-3}\) | −7.2 | |
| 0.25 | — | 4.33 | \(1.73 \cdot 10^{-3}\) | \(1.52 \cdot 10^{-3}\) | +13.8 |
| 0.25 | — | 3.56 | \(1.42 \cdot 10^{-3}\) | −6.6 | |
| 0.25 | 1 | 4.79 | −0.3 | ||
| \((\mathrm{NH_4})_2\mathrm{HPO_4}\) | |||||
| 0.1 | — | 14.02 | \(1.40 \cdot 10^{-2}\) | +0.7 | |
| 0.1 | — | 14.02 | \(1.40 \cdot 10^{-2}\) | \(1.39 \cdot 10^{-2}\) | +0.7 |
| 0.1 | — | 13.78 | \(1.38 \cdot 10^{-2}\) | −0.7 | |
| 0.1 | 1 | 15.40 | +3.6 |
Determination of traces of iron in hydrofluoric acid
Using a polyethylene pipette with a rubber bulb, 1 or 2 ml of the hydrofluoric acid to be analyzed are taken, transferred to a platinum dish, and evaporated to dryness under an infrared evaporation lamp in an Ergs glass weighing bottle. To the dry residue are added 0.5 ml of especially pure HCl [1 : 1] and 10 ml of the complexing reducing buffer mixture, and the solution is heated to boiling. To the hot solution are added 0.5 ml of a 2% solution of α,α′-dipyridyl; the mixture is stirred, transferred to a 25-ml volumetric flask, allowed to cool, made up to the mark with bidistillate, thoroughly mixed, and left to stand for 10–15 min. The optical density of the solution is measured on an FEKN-57 photoelectric colorimeter-nephelometer with green light filter No. 4, having a transmission maximum at 508 mμ, in cuvettes with a 50-mm layer thickness. Bidistillate serves as the reference solution. From the optical density of the solution, the iron content is found from a calibration graph obtained under the same conditions for a standard iron solution.
At the same time a blank experiment is carried out, in which, instead of hydrofluoric acid, 1 or 2 ml of water are taken and all reagents are added in the same amounts and in the same sequence as for the solution being analyzed. Its optical density is measured and a correction is introduced for the content of traces of iron in the reagents.
The duration of the analysis is 1 hour. The relative error of the determination does not exceed ±5%.
Determination of Traces of Iron in Antimony Trioxide
An accurately weighed sample of antimony trioxide in the range of 0.1–0.25 g is treated in a platinum or quartz dish with 0.5 ml of especially pure HCl [1 : 1]; then 20 ml of complexing reducing buffer mixture is added, the solution is heated to boiling and boiled for 3 minutes, 0.5 ml of a 2% solution of α,α′-dipyridyl is added, the solution is transferred to a 25 ml volumetric flask, and the determination is continued according to the procedure described above for hydrofluoric acid.
The duration of the analysis is 1 hour. The relative error of the determination does not exceed ±10–15%.
Determination of Traces of Iron in Ammonium Hydrogen Phosphate
An accurately weighed sample of ammonium hydrogen phosphate in the range of 0.1–0.5 g is treated in a platinum or quartz dish with 2 ml of especially pure HCl [1 : 1], 10 ml of complexing reducing buffer mixture is added, the solution is heated to boiling, 0.5 ml of a 2% solution of α,α′-dipyridyl is added, and the determination is continued according to the procedure described above for hydrofluoric acid.
The duration of the analysis is 1 hour. The relative error does not exceed ±3–5%.
Student G. N. Dembovskaya took part in carrying out the experimental work.
Conclusions
Methods have been proposed for determining traces of iron with dipyridyl in hydrofluoric acid, in antimony trioxide, and in ammonium hydrogen phosphate used in the production of the phosphor “L-34.”
References
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Yu. L. Lel’chuk, R. D. Glukhovskaya, Izvestiya TPI, vol. 132, 72, 1966.