EA036947B1 - Method for spectrophotometric determination of aluminum - Google Patents

Abstract

The invention relates to the field of analytical chemistry, in particular, to the spectrophotometric analysis method, and can be used for determination of Al(III) in solutions of its salts containing aluminum in a very low concentration. The objective of the invention is to increase the accuracy, sensitivity, selectivity, to ensure simplicity of work, reduction of the method duration in spectrophotometric determination of Al(III) as a result of replacement of gelatin by a more suitable surfactant - steroidal or triterpenoid saponin with a precisely known chemical composition and with exclusion of the final solution heating process. The essence of the invention is the provision of a method for spectrophotometric determination of Al(III) in solutions of its salts, comprising its transfer to a complex compound with aluminon and saponin as the third component, wherein, in an acid environment, 10-fold quantity of aluminon, 0.5 ml of 1% saponin solution and water up to 10 ml vol. are added to Al(III) solution having pH of 1-2. Spectrophotometric measurement is carried out using a spectrophotometer, =490 nm, l=1 cm.

Description

The invention relates to the field of analytical chemistry, namely to a spectrophotometric method of analysis, and can be used to determine Al (III) in solutions of its salts containing aluminum in very low concentration.

A known method of spectrophotometric determination of aluminum using 2,3,4-trioxyphenylazo-5'-sulfonaphthalene in the presence of cationic surfactants (surfactants) - cetylpyridinium and cetyltrimethylammonium bromide [1]. The disadvantages of this method are low sensitivity, low accuracy, as well as the duration of the method in connection with the synthesis of the azo compound - ligand.

The closest method (prototype) is a method [2] for the photometric determination of Al (III) in solutions of pure salts and artificial mixtures, the essence of which is that the method for determining Al (III) in solutions of pure salts and artificial mixtures, including its transfer in a complex compound with aluminone in an acidic medium, a 100-120-fold amount of aluminone, 0.3-0.5 ml of a surfactant solution containing a 2% gelatin solution, water up to 10 ml volume is added to a solution of Al (III) with a pH of 0-2 followed by heating in a water bath at a temperature of 80-98 ° C.

The disadvantages of the known method (prototype) are:

1. Low accuracy, sensitivity, selectivity due to the use of gelatin as a surfactant, which does not have a specific chemical composition.

2. Insolubility of gelatin in water under normal conditions.

3. Solidification of the gelatin solution when cooled to jelly, which makes further measurement impossible.

4. It is imperative to use the solution only after heating, which cannot ensure the accuracy of measurement on a photometric device due to the formation of steam in the cuvette for measurement;

5. Duration of the method by heating the final solution.

The objective of the invention is to increase the accuracy, sensitivity, selectivity, ensure ease of operation, reduce the duration of the method for spectrophotometric determination of Al (III) as a result of replacing gelatin with a more suitable surfactant - steroid or triterpene saponin with a precisely known chemical composition, and eliminating the process of heating the final solution.

The essence of the invention lies in the fact that in the method of spectrophotometric determination of Al (III) in solutions of its salts, including its transformation into a complex compound with aluminone and the third component of saponin in an acidic medium, to a solution of Al (III) with pH 1-2 is added 10-fold amount of aluminone, 0.5 ml of 1% saponin solution and water up to 10 ml volume. A spectrophotometric measurement is carried out on a spectrophotometer, λ = 490 nm, l = 1 cm.

The advantages of the proposed method for the spectrophotometric determination of Al (III) with aluminone in the presence of saponin are as follows.

1. The accuracy, sensitivity, selectivity of determination of Al (III) sharply increase in comparison with known methods in connection with the use of steroid or triterpene saponin as a surfactant;

The results of parallel determinations of Al (III) in the same volumes of solutions are the same, which indicates a high degree of determination accuracy. In such cases, no statistical processing takes place to establish the relative error.

In comparison with the prototype, one-time determination of Al (III) uses 10 times less test substance, which increases the sensitivity of the method by 10 times.

The study was verified in the presence of ions having the same analytical properties as the aluminum cation. Therefore, the method is much more selective, the determination does not interfere with multiple amounts of zinc (II), chromium (III), lead (II).

2. A stable and transparent solution of the Al (III) intracomplex compound is formed, which facilitates spectrophotometric determination.

3. There is no possibility of formation of jelly, sediment and colloidal particles.

4. Stability of the resulting complex due to the filling of vacant orbitals of the Al (III) ion due to the presence of hydroxyl groups in the saponin molecule in sufficient quantities.

5. The absence of a heating process shortens the duration of the process and simplifies the process.

6. The method is economically profitable: a) various organic solvents are not used; b) the amount of aluminon reagent decreases; c) is used as a surfactant saponin obtained from plant materials in a sufficient amount in a simple way.

7. Successful assay reproducibility.

8. Sufficient provision of method selectivity, since here the presence of cations with similar chemical properties does not interfere.

9. Possibility to study the solution without heating, which does not create vapor formation in the cuvette of the spectrophotometric device.

Various chemically pure salts of Al (III) are used for analysis: AlCl ₃ -6H2O, Al (NO ₃ ) ₃ -9H2O,

- 1 036947

KA1 (SO ₄ ) 2-12H2O, from which 10 ^-5 mol / l solutions are prepared. A certain volume (0.1; 0.3; 0.5; 0.7; 0.9; 1.1 ml) of 10 ^-5 M solution of Al (III) is placed in separate tubes, 2 ml of buffer is added to each of them. solution with pH = 1, 0.5 ml of 10 ^-4 M aluminon solution, 0.5 ml of 1% saponin solution, bring the solution volume to 10 ml with purified water. Measure the optical density on a spectrophotometer (UVVIS spectrophotometer UV 752D), λ = 490 nm, 1 = 1 cm, in comparison with a control solution (indicated components without saponin). The process is repeated three times for each taken separate volume.

In parallel, the optical density of a solution of a standard Al (III) sample, treated similarly to the test solution, is measured. The Bouguer-Lambert-Beer law is observed within the Al (III) concentration of 0.027-0.297 μg / 10 ml. The Al (III) content in the samples is calculated by the formula

D · r ₀ · Y · _about 100 X = ------------ D _Q · t where _an AND D - optical density of the test solution;

D ₀ - optical density of a standard solution;

m is the weight of the test portion of the Al (III) salt, g;

m0 is the mass of Al (III) in the measured standard solution, g;

V _about - the total volume of the Al (III) solution;

VaH is the volume of the measured Al (III) solution.

Example 1. 0.1205 g (accurately weighed) A1C13-6H2O is placed in a volumetric flask with a capacity of 500 ml, dissolved in a small amount of water and the volume is brought to the mark. Take 1 ml of the solution into a volumetric flask with a capacity of 100 ml and bring the volume to the mark with purified water. 0.9 ml is taken from this solution, placed in a test tube and further work is carried out in the same way as above.

The Al (III) content in the samples is calculated by the formula _ 1.17 0.135 10 ~ ⁶ 5 10 ⁴ 100 ^X ~ 0.65-0.1205 -0.9 x = 11.2% (Experimentally) where D - 1.17;

D0 0.65;

m - 0.1205 g;

m0 - 0.135-10 ^-6 g;

V _o6 - 5-10 ⁴ ml;

Van - 0.9 ml.

Theoretical calculation:

241.5g (A1C13-6H2O) -27g (A1)

100% (A1C13-6H ₂ O) -x% (Al)

X = 11.18%

Example 2. 0.1875 g (accurately weighed) A1 (NO ₃ ) ₃ -9H2O is placed in a volumetric flask with a capacity of 500 ml, dissolved in a small amount of water and the volume is brought to the mark. Take 1 ml of the solution into a volumetric flask with a capacity of 100 ml and bring the volume to the mark with purified water. 0.9 ml is taken from this solution, placed in a test tube and further work is carried out in the same way as above.

The Al (III) content in the samples is calculated by the formula _ 1.17 0.135 · 10 ~ ⁶ · 5 · 10 ⁴ -100 ^X “0.65 0.1875 - 0.9 x = 7.2% (Experimental) where D - 1.17;

D0 0.65;

m - 0.1875 g;

m0 - 0.135-10 ^-6 g;

Vo _b - 5-10 ⁴ ml;

Van - 0.9 ml.

Theoretical calculation:

375 g (A1C13-6H ₂ O) -27 g (A1)

100% (A1C13-6H ₂ O) -x% (Al)

X = 7.2%

Example 3. 0.237 g (accurately weighed) KAl (SO ₄ ) ₂ -12H ₂ O is placed in a volumetric flask with a capacity of 500 ml, dissolved in a small amount of water and the volume is brought to the mark. Take 1 ml of the solution into a volumetric flask with a capacity of 100 ml and bring the volume to the mark with purified water. 0.9 ml is taken from this solution, placed in a test tube and further work is carried out in the same way as above.

The Al (III) content in the samples is calculated by the formula:

- 2 036947 _ 1.17 · 0.135 10 ~ ^ϋ 5 · 10 ⁴ -100 ^Χ ~ 0.65 · 0.237 0.9 χ = 5.69% (Experimental) where D - 1.17;

Do 0.65;

m - 0.237 g;

mo - 0.135-10 ^-6 g;

V _o6 - 5-104 ml;

VaH - 0.9 ml.

Theoretical calculation:

474 g (AlCl ₃ -6H2O) -27 g (Al)

100% (А1С1з-6Н2О) -х% (Al)

X = 5.69%

The proposed method makes it possible to determine the Al (III) content in its various salts with a sufficiently high accuracy, which completely coincides with the results of theoretical calculations.

Preparing a standard solution

0.241 g (accurately weighed) of chemically pure AlCl ₃ -6H ₂ O is quantitatively placed in a volumetric flask with a capacity of 1 l, dissolved in a small amount of purified water and the volume is brought to the mark with purified water. Take 1 ml of the solution into a volumetric flask with a capacity of 100 ml and bring the volume to the mark with purified water. 1 ml of solution contains 0.27 μg of Al (III). 0.5 ml is taken from this solution, placed in a test tube and further work is carried out similarly to the test solution.

LITERATURE

1. Nagiyev Kh.V., Kulieva F.V., Suleimanova R.I. Spectrophotometric determination of aluminum in the water of the Caspian Sea using 2,3,4-tri-hydroxyphenylazo-5'-sulfonaphthalene and cationic surfactants // Azerbaijan Chemical Journal, 2006, No. 4, 2006, pp. 97-100.

2. Novopoltseva V.M., Osipov A.K., Nishchev K.N. RF patent, RU 2312339 C1, 2006136349/04, 10.12.2007.

Claims (1)

A method for the spectrophotometric determination of Al (III) in solutions of its various salts, including its conversion into an intracomplex compound with aluminon in an acidic medium with the addition of a surfactant, characterized in that saponin is used as a surfactant, the process proceeds without subsequent heating and ends with spectrophotometric measurement.