Photometric Determination of Aluminum with Xylenol Orange in High-Purity Iron
Abstract Generated abstract
A photometric procedure is described for determining trace aluminum in high-purity iron using xylenol orange, selected for its high sensitivity in aluminum complex formation. The method dissolves the iron sample in hydrochloric acid, oxidizes and extracts iron as chloride complexes with diethyl ether, then develops the aluminum, xylenol orange color reaction at pH 3.0 to 3.3 with heating, ascorbic acid reduction, and Trilon B masking before measurement at 536 nm. Calibration and parallel standard procedures are given, and tests using standard solutions and additions to iron samples indicate a sensitivity of 1 x 10^-4 percent aluminum for a 1 g sample, with reported relative accuracy of about plus or minus 2 to 4 percent and an analysis time of 3 to 4 hours.
Full Text
PHOTOMETRIC DETERMINATION OF ALUMINUM WITH XYLENOL ORANGE IN HIGH-PURITY IRON
V. B. Sokolovich, V. A. Malevannyi, Yu. L. Lelchuk
(Presented by the scientific-methodological seminar of the CTF)
Among photometric reagents for aluminum, xylenol orange is distinguished by its increased specific sensitivity to iron. As Malevannyi and Lelchuk [1] have shown, the specific sensitivity of xylenol orange to iron (III) is 3.3, and to iron (II) 5.0; the specific sensitivity to iron of methylthymol blue is characterized by values of 1.9 and 2.9, respectively, while that of aluminon is 0.9 and 0.8, etc.
Xylenol orange is known as a photometric reagent for many elements. It has been used for the determination of aluminum since 1957 [2]. It has been established that the interaction of aluminum with xylenol orange proceeds slowly at room temperature and is accelerated by heating [3]. The greatest sensitivity is achieved at pH 3.0 [2]. The influence of foreign ions depends on the pH of the solution and can be reduced by masking them with Trilon B.
Xylenol orange was used in order to increase the accuracy of the photometric determination of aluminum in high-purity iron.
The work used triply distilled water and azeotropic hydrochloric acid obtained by isothermal distillation of concentrated hydrochloric acid. The remaining reagents were of chemically pure or analytical-reagent grade.
A 0.1% aqueous solution of xylenol orange was prepared from an imported preparation from “Chemapol.” The initial standard aluminum solution containing 1000 μg in 1 ml was prepared from aluminum sulfate of special purity (grade A₂, VTU 3—334—60).
The working standard solution and the ascorbic acid solution are used freshly prepared.
Construction of the Calibration Curve
From the initial standard aluminum solution containing 1000 μg in 1 ml, a working solution is prepared containing 1 μg of aluminum in 1 ml.
Into a series of 50-ml volumetric flasks are introduced 5 ml each of acetate buffer with pH 3.0–3.3, 1 ml each of 0.1% ascorbic acid solution, and the required volumes of the working standard solution corresponding to contents of 0, 1, 2, 3, etc., up to 10 μg of aluminum. After 3–5 minutes following mixing, 2 ml each of 0.1% xylenol orange solution is added, and the volume is brought with tridistillate approximately to 20 ml.
The flasks are placed on a boiling water bath and heated for three minutes. After rapid cooling, 3 ml of a 0.025 M solution of Trilon B is added, the volume is brought to the mark with acetate buffer, mixed, and 20–25 minutes after the end of heating the optical density of the solutions is measured on an FEK-N-57 in cuvettes with a 30 mm layer thickness, using green light filter No. 5 with a transmission maximum of 536 mμ. The reference solution is tridistillate. From the optical density of each solution, the optical density of the solution with zero aluminum content is subtracted, and a calibration graph is constructed from the data obtained.
The determination may also be completed without a calibration graph, according to the procedure given below.
Course of analysis
An iron sample of about 0.5 g is placed in a quartz beaker, treated with 10 ml of azeotropic hydrochloric acid, approximately 8 N, and heated for 10–15 minutes until complete decomposition. To oxidize the iron to the trivalent state, 15 drops of nitric acid (1:1) are added to the solution. Nitrogen oxides are removed by heating. The solution is cooled, transferred to a separatory funnel, and the beaker is rinsed with 5 ml of azeotropic approximately 8 N hydrochloric acid. From the 6 N hydrochloric-acid solution, iron is extracted with diethyl ether in the form of chloride complexes. Extraction is carried out three times with 20 ml portions of ether, with shaking for three minutes. The aqueous layer is run into a beaker, and traces of ether are removed by gentle heating. The cooled solution is neutralized with ammonium hydroxide to pH ~3.0, transferred to a 50 ml volumetric flask, and diluted to the mark with acetate buffer of pH 3.0–3.3.
The analysis is then continued with an aliquot portion of the solution obtained. The volume of the aliquot depends on the expected amount of aluminum. When the aluminum content is in the range of \(10^{-4}\%\) or lower, the entire solution obtained from decomposition of the sample is subjected to the subsequent analytical operations. When the aluminum content is in the range of \(10^{-3}\)—\(10^{-2}\%\), an aliquot of 10 ml or less is used.
The aliquot is placed in a 50 ml volumetric flask; 1 ml of a 0.1% solution of ascorbic acid is added to reduce traces of iron, and after about 5 minutes, 2 ml of a 0.1% solution of xylenol orange is added. The solution is heated for three minutes on a boiling water bath. After rapid cooling, 3 ml of a 0.025 M solution of Trilon B and acetate buffer to the mark are added to the solution. A blank test is carried through all stages of the analysis (including extraction). When completing the determination without a calibration graph, an exact portion of a standard aluminum solution is also treated in parallel.
Twenty to twenty-five minutes after the end of heating, the optical densities of the solutions are measured on an FEK-N-57 in cuvettes with a layer thickness of 30 mm, using green light filter No. 5 with a transmission maximum of 536 mμ. The reference solution is tridistillate.
The aluminum content is determined from the calibration graph or calculated in weight percent by the formula obtained by us for a 10 ml aliquot:
\[ \%AlK=\frac{C_{\mathrm{Al}}\cdot(D_x-D_0)}{(D_{\mathrm{st.}}-D_0)}\cdot10^{-3}. \tag{4} \]
The accuracy of the proposed method was checked on standard aluminum solutions carried through all stages of the analysis, and by the method of additions on iron samples.
The results of the statistical processing of the experimental data obtained in the analysis are given in Table 1.
Table 1
Results of the photometric determination of aluminum with xylenol orange in high-purity iron
| Measured quantity | $n$ | $\bar{x}\cdot 10^{-3}$ | $S_x\cdot 10^{-3}$ | $S_{\bar{x}}\cdot 10^{-3}$ | $\alpha$ | $\tau$ | $\varepsilon\cdot 10^{-3}$ | Experimental results | Relative error |
|---|---|---|---|---|---|---|---|---|---|
| Al, % | 18 | 4,20 | 0,315 | $\pm 0,073$ | 0,95 | 2,11 | $\pm 0,154$ | $4,35—4,05\cdot 10^{-3}$ | $\pm 3,57$ |
| Al, % | 19 | 4,19 | 0,183 | $\pm 0,043$ | 0,95 | 2,10 | $\pm 0,09$ | $4,28—4,10\cdot 10^{-3}$ | $\pm 2,14$ |
Conclusions
A photometric method has been developed for determining traces of aluminum in high-purity iron with xylenol orange. With a sample weight of the iron being analyzed of 1 g, the sensitivity is $1\cdot 10^{-4}\%$. The accuracy of the determination is $\pm 2—4\%$. The duration of the analysis is 3–4 hours.
LITERATURE
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V. A. Malevannyi, Yu. L. Lel’chuk. On the quantitative evaluation of the interfering action of foreign cations in the spectrophotometric method of analysis. Zh. analit. khim. XXIII, 10, 1558, 1968.
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V. N. Tikhonov. Photometric determination of aluminum using xylenol orange. Zh. analit. khim. XX, 9, 941, 1965.
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A. I. Cherkasov, B. N. Kazakov, V. S. Tonkoshurov. Study of the kinetics of the reaction of aluminum ions with xylenol orange and aluminon. M. analit. khim. XXII, 10, 1464, 1967.
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V. B. Sokolovich, V. A. Malevannyi, Yu. L. Lel’chuk. Photometric determination of aluminum in high-purity iron. Izv. TPI (in press).