GOST 20996.7-82

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  ГОСТ 20996.7-82

GOST 20996.7−82 Selenium technical. Methods for determination of aluminium (with Change No. 1)

GOST 20996.7−82*

Group B59

INTERSTATE STANDARD

SELENIUM TECHNICAL

Methods for determination of aluminium

Selenium.
Method of aluminium determination

AXTU 1709

Date of introduction 1983−07−01

Resolution of the USSR State Committee on standards of 22 June 1982, N 2481 date of introduction is established 01.07.83

Limitation of actions taken by Protocol No. 7−95 Interstate Council for standardization, Metrology and certification (ICS 11−95)

* PUBLISHING (July 2000) with amendment No. 1, approved in December 1987 (IUS 3−88)


This standard establishes photometric methods for determination of aluminium (with a mass fraction of aluminum 0,002−0,06%).

(Changed edition, Rev. N 1).

1. GENERAL REQUIREMENTS

1.1. General requirements for method of analysis according to GOST 20996.0−82.

2A. METHOD OF ALUMINON

2A.1. The essence of the method

The method is based on the reaction of formation of colored compounds of aluminum ions with alumininum at pH 4,5−4,8 after prior separation of selenium by evaporation with bromatological acid and subsequent measurement of optical density at a wavelength of 530 nm.

Sec. 2A. (Added, Rev. N 1).

2. EQUIPMENT, REAGENTS, SOLUTIONS

Photocolorimeter.

Nitric acid GOST 4461−77 and diluted 1:1.

Hydrochloric acid by the GOST 3118−77 and diluted 1:1.

Acetic acid GOST 61−75 and a solution of 0.2 mol/DM.

Ascorbic acid, freshly prepared solution of 20 g/DM.

Benzoic acid technical GOST 6413−77.

Ammonium acetate according to GOST 3117−78.

The technical rectified ethyl alcohol GOST 18300−87.

Aluminon.

Ammonia water according to GOST 3760−79.

Gelatin food according to GOST 11293−89.

Aluminium GOST 11069−74*.
________________
* On the territory of the Russian Federation GOST 11069−2001. Here and hereinafter. — Note the manufacturer’s database.

Standard solutions of aluminium:

Solution a: a sample of aluminum with a mass of 0.1 g dissolved in 10−15 cmof hydrochloric acid (1:1), transfer the resulting solution into a measuring flask with volume capacity of 1000 cm, made up to the mark with water and mix.

1 cmof solution A contains 0.1 mg of aluminium.

Solution B: aliquot part 10 cmof the solution And transferred to a volumetric flask with a capacity of 100 cm, made up to the mark with water and mix.

1 cmof a solution contains 0.01 mg of aluminum.

Composite aluminievy buffer solution: weighed ammonium acetate with a mass of 125 g is placed in a volumetric flask with a capacity of 500 cm, add 200−250 cmof water, 15−20 cmof acetic acid, mix and check the pH value on the pH meter. In a separate bowl dissolve 0.25 g of aluminon 15 cmof water and transferred to a volumetric flask, which was prepared acetic acid solution. Separately dissolve 5 g of benzoic acid in 25 cmof ethanol, transferred into the same volumetric flask and mix. The mixture was diluted to the mark with water and mix.

In a glass with a capacity of 100 cmis placed 2.5 g of gelatin, add 70−80 cmof water and after an hour is heated to dissolve the gelatin. The hot solution is poured into a beaker with 150 cmof water and stirred. After cooling, the solution is mixed with acetate solution (in a volumetric flask) in a beaker with a capacity of 1000 cm.

Pour water to a volume of 950 cmand set the pH of the solution with ammonia (1:1) between 4.5 and 4.8 (on indicator paper or pH-meter). The solution was stirred and transferred into a measuring flask with volume capacity of 1000 cm, cooled, made up to the mark with water and mix. Filter the resulting solution through a double thick filter, collecting the filtrate in a flask made of dark glass with a glass stopper. A clear solution stored in a dark place.

Acid bromide and hydrogen GOST 2062−77.

Thioglycolic acid, 10% solution.

Sec. 2. (Changed edition, Rev. N 1).

3. ANALYSIS

3.1. A portion of selenium depending on the mass fraction of aluminium (tab.1) is placed in a beaker with a capacity of 250−300 cm, 15−30 cm pour thenitric acid, cover with watch glass (glass plate) and allowed to stand without heating until the cessation of the violent reaction of allocation of oxides of nitrogen.

Table 1

Glass (plate) is removed, washed with water on the beaker and heat the solution to dissolve the sample and evaporated to dryness. Pour 8−10 cmof nitric acid and again evaporated to dryness. Evaporation with 5−7 cmof nitric acid is repeated twice.

To the dry residue pour 2−3 cmof hydrochloric acid, evaporated to dryness, poured 2−3 cmbromatological acid and again evaporated to dryness. Evaporation from bromatological acid repeat. Then to the dry residue pour 2−3 cmof hydrochloric acid, evaporated to dryness. Evaporation with hydrochloric acid is repeated twice. The selenium dioxide removal may be performed by heating on the stove at a temperature of 280−290 °C, as described in GOST 20996.4−82.

Pour 2−3 cmof hydrochloric acid, 25−30 cmof water and heated to dissolve the salts. After cooling, transfer the solution into a volumetric flask with a capacity of 100 cm, is diluted to the mark with water and mix.

From the volumetric flask selected aliquot part of the solution according to the table.1 and transfer it into a measuring flask with a capacity of 100 cm. To the solution was added dropwise ascorbic acid or 1−2 drops of a solution of thioglycolic acid for recovery and sequestration of iron in the colorless complex, with a large excess of acid unwanted. If the solution is colorless, then add 1 drop of acid.

To the solution in a volumetric flask poured 15−17 cmaluminievaya buffer solution, heated in water bath for no more than 5 min before the formation of «aluminum Polish». Cool, top up to the mark with water and mix. After 15 min measure the optical density of the solution on the photoelectrocolorimeter, using a filter with maximum transmittance at a wavelength of 530−535 nm and cuvette thickness of the absorbent layer 20 or 30 mm.

As a solution comparison solution is used in the reference experiment.

The mass of aluminum is on the calibration graph

the IR.

3.2. Construction of calibration curve

Eight volumetric flasks with a capacity of 100 cmplaced 0; 0,5; 1,0; 2,0; 3,0; 4,0; 5,0 and 7.0 cmstandard solution B, which corresponds to 0; 0,005; 0,01; 0,02; 0,03; 0,04; 0,05 and 0.07 mg of aluminum, top up with water to 10 cm, add 1−2 drops of ascorbic acid or thioglycolic acid, and further receives, as described in Chapter 3.1.

3.1, 3.2. (Changed edition, Rev. N 1).

4. PROCESSING OF THE RESULTS

4.1. Mass fraction of aluminium () in percent is calculated by the formula

,

where is aluminum found on a calibration schedule, mg;

 — volume aliquote part of the solution, cm;

 — weight of selenium,

4.2. Discrepancies in the results of two parallel measurements and the two tests should not exceed the values given in table.2.

Table 2

(Changed edition, Rev. N 1).

5. METHOD WITH USE OF CHROMAZUROL

5.1. The essence of the method

The method is based on the reaction of formation of colored complex ions of aluminum, chromazurol at a pH of 5.7−5.8 in the presence of thioglycolic acid to mask iron ions and copper and subsequent measurement of optical density at a wavelength of 545 nm.

5.2. Equipment, reagents, solutions

Any spectrophotometer or spectrocolorimeter «Specol».

a pH meter.

Nitric acid GOST 4461−77.

Hydrochloric acid by the GOST 3118−77, solutions of 1:1 and 0.1 mol/DM, made with standard-titre.

Thioglycolic acid, 4% aqueous solution (by volume).

Sodium acetate according to GOST 199−78.

Acetic acid GOST 61−75.

Acetate buffer solution with a pH of 5,8−6,0: a suspension of sodium acetate mass of 75 g dissolved in 150 cmof water, poured 1.5 cmof acetic acid (density of 1.07) and diluted with water to a volume of 250 cm. Control of the pH value on the pH meter.

Chromazurol S, the water-alcohol solution of 0.02 g/DM; dissolve 0.2 g of chromazurol in 30 cmof water, poured in 25 cmof ethyl alcohol and dilute with water to volume of 100 cm. If the solution is turbid, it is filtered.

Phenolphthalein on the other 6−09−5360−87, alcoholic solution of 0.01 g/DM.

Potassium hydroxide according to GOST 24363−80, a solution of 0.8 g/DM.

The technical rectified ethyl alcohol GOST 18300−87.

Primary aluminium GOST 11069−74.

Standard solutions of aluminium according to claim

2.2.

5.3. Analysis

5.3.1. A portion of the selenium mass depending on the mass fraction of aluminium (tab.3) is placed in a beaker with a capacity of 250 cm, pour 15−20 cmof nitric acid, cover the beaker with a cover glass and allowed to stand without heating until the cessation of the violent reaction of allocation of oxides of nitrogen. Remove the glass, wash it with water over the beaker and the solution was evaporated by heating to dryness.

Table 3

Poured another 7−10 cmof nitric acid and again evaporated to dryness.

To the dry residue poured 3−5 cmof hydrochloric acid, 3−5 cmbromatological acid and evaporated to dryness. Again pour 3−5 cmand bromatological hydrochloric acid and evaporation to dryness is repeated. Then add 5 cmof hydrochloric acid, 25−30 cmof water and heat the solution to dissolve the salts. After cooling, placed in a volumetric flask with a capacity of 100 cm, is diluted to the mark with water and mix.

Select aliquot part of the solution according to the table.3 and placing it in a volumetric flask with a capacity of 100 cm, is diluted with water to a volume of 25 cm. The solution is poured in 1−2 drops of phenolphthalein and neutralize with a solution of potassium hydroxide until the appearance of violet colouration of the solution, then add dropwise a solution of hydrochloric acid 0.1 mol/DMto discoloration and 5 cm. Go 0.3 cmof a solution of thioglycolic acid, mix.

After 5 min, dilute with water to volume of 50 cm, add 1 cmof a solution of chromazurol S, 10 cmof ethanol, 5 cmacetate buffer solution, dilute to the mark with water and mix.

After 15 min measure the optical density of the solution on the spectrophotometer or spectrocolorimeter «Specol» at a wavelength of 545 nm in a cuvette with a layer thickness of 10 mm. as a solution comparison solution is used in the reference experiment, carried out through all stages of analysis and containing 1 cmof chromazurol.

The weight of aluminium is determined by graduirovannam

mu schedule.

5.3.2. Construction of calibration curve

In a series of volumetric flasks with a capacity of 100 cmplaced 0; 0,5; 1,0; 1,5; 2,0; 2,5; 3,0 cmstandard solution B, which corresponds to 0; 0,005; 0,01; 0,015; 0,020; 0,025; 0,03 mg of aluminium. Diluted with water to a volume of 15 cm, add 1−2 drops of phenolphthalein and continue the analysis as described in section 3.3.1. According to the obtained results build a calibration curve.

5.4. Processing of the results

5.4.1. Mass fraction of aluminium () in percent is calculated by the formula

,

where is the mass of aluminum was found in the calibration graphics mg;

 — capacity volumetric flasks, cm;

 — volume aliquote part of the solution, cm;

 — weight of selenium,

5.4.2. Discrepancies between the results of two parallel measurements and the two tests should not exceed the values given in table.2.

5.4.3. The differences in the assessment of mass fraction of aluminium used method alumininum (sect.2).

Section 5. (Added, Rev. N 1).