GOST 851.5-93

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  ГОСТ 851.5-93

GOST 851.5−93 Magnesium primary. Methods for determination of aluminium

GOST 851.5−93

Group B59

INTERSTATE STANDARD

MAGNESIUM PRIMARY

Methods for determination of aluminium

Primary magnesium.
Methods for determination of aluminium

ISS 77.120.20
AXTU 1709

Date of introduction 1997−01−01

Preface

1 DEVELOPED by the Ukrainian scientific-research and design Institute of titanium

INTRODUCED by Gosstandart of Ukraine

2 ADOPTED by the Interstate Council for standardization, Metrology and certification (Protocol No. 3 dated February 17, 1993)

The adoption voted:

3 Decree of the Russian Federation Committee on standardization, Metrology and certification from February, 20th, 1996 N 76 inter-state standard GOST 851.5−93 introduced directly as state standard of the Russian Federation from January 1, 1997

4 REPLACE GOST 851.5−87

5 REISSUE

INFORMATION DATA

REFERENCE NORMATIVE AND TECHNICAL DOCUMENTS

This standard establishes photometric (at a mass fraction of aluminum from 0,0002 to 0,060%) and atomic absorption (at a mass fraction of aluminum from 0,001 to 0,060%) methods for determination of aluminum in the primary magnesium.

If there are differences in the analysis carried out by the photometric method.

1 General requirements

1.1 General requirements for methods of analysis GOST 25086.

1.2 Mass fraction of aluminum determined from two parallel batches.

1.3 When building a calibration curve each point build on the average result of the three definitions of optical density of the atomic absorption.

1.4 Permitted discrepancies in the results of the analysis of the same samples obtained by the two methods, calculated according to GOST 25086.

1.5 When placing the results of the analysis make reference to this standard, specify the method of determining, and method and results of control of accuracy of analysis results.

2 the Photometric method for the determination of aluminium

2.1 the essence of the method

The method is based on the formation of complex compounds of aluminum, chromazurol and chloride -cetylpyridinium and measuring the optical density of the solution.

2.2 the Instrument, reagents and solutions

The spectrophotometer or photoelectric colorimeter.

Ion meter or pH meter.

Hydrochloric acid — according to GOST 3118, diluted 1:1 and 1:99.

Acetic acid — according to GOST 61, solution with molar concentration of 2 mol/DM.

Sodium acetate 3-water — GOST 199.

Magnesium chloride 6-water — GOST 4209.

Chromazurol  — on the other 6−05−1175, a solution with a mass concentration of 1 g/DM.

-cetylpyridinium chloride on the other 6−09−15−121, a solution with a mass concentration of 2 g/DM.

Ascorbic acid according to the State Pharmacopoeia , a freshly prepared solution with a mass concentration of 50 g/DM.

Aluminum brand A99 — according to GOST 11069.

Buffer solution, pH 6.2 and 6.3:

250 g sodium acetate dissolved in 500 cmof water, add 30−40 cmof acetic acid, add water to 1000 cmand stirred; the pH of the solution is controlled by the ionomer.

A solution of magnesium chloride:

5 g magnesium chloride were placed in a glass with a capacity of 200 cm, add 10 cmof hydrochloric acid and after complete dissolution of the sample solution was evaporated until beginning crystallization of salts. The residue is dissolved in 40−50 cmof water, transferred to a volumetric flask with a capacity of 100 cm, made up to the mark with water and mix.

Standard solutions of aluminium:

Solution a: 0,10 g of aluminium is dissolved in 20 cmof a hydrochloric acid solution. The solution was transferred into a measuring flask with volume capacity of 1000 cm, made up to the mark with water and mix; fit for use for 6 months.

1 cmof solution A contains 0.1 mg of aluminium.

Solution B: 1 cmof solution A is placed in a volumetric flask with a capacity of 100 cm, is poured a solution of hydrochloric acid (1:99) to the mark and mix; prepare before use.

1 cmof the solution contains 0.001 mg of aluminium.

State standard samples made in accordance

with GOST 8.315.

2.3 analysis

2.3.1 Sample weighing 1.0 g was placed in a beaker with a capacity of 200 cm, pour small portions of 10−20 cmof hydrochloric acid. After the violent reaction of the wall of the beaker is washed with water and evaporated until beginning crystallization of salts. The solution in the reference experiment was evaporated to dryness. The residue is dissolved in 40−50 cmof water, transferred to a volumetric flask with a capacity of 100 or 200 cm(see table 1), made up to the mark with water and mix.

Table 1

In a volumetric flask with a capacity of 50 cmis placed 10 cmbuffer solution, 3 cmof a solution of chromazurol 5 cmchloride -cetylpyridinium, 5 cmof a solution of ascorbic acid and, in accordance with table 1, aliquote part of the analyzed solution. Then topped to the mark with water, mix and after 10 min measure the absorbance at a wavelength of from 590 to 597 nm. Solution comparison is the solution of the reference experiment

.

2.3.2 Construction of calibration curve

To build a calibration curve in seven volumetric flasks with a capacity of 50 cmis placed 10 cmbuffer solution, 3 cmof a solution of chromazurol 5 cmchloride -cetylpyridinium, 5 cmof ascorbic acid solution and 5 cmof a solution of magnesium chloride. After addition of each reagent solutions are mixed. Then, in six of the seven flasks is added 0,5; 1,0; 1,5; 2,0; 2,5; 3,0 cmstandard solution B, which corresponds to 0,0005; 0,0010; 0,0015; 0,0020; 0,0025; 0,0030 mg of aluminium. A seventh solution of the flask is a solution of the reference experiment. The solutions in all flasks is poured to the mark with water and then do as described in 2.3.1.

Solution comparison is the solution of the reference experiment.

According to the obtained values of optical density calibration curve built in accordance with GOST 250

86.

2.4 Processing of results of analysis

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

, (1)

where is the mass of aluminium in the sample solution found by the calibration schedule g;

 — total volume of sample solution, cm;

 — the mass of sample, g;

 — volume aliquote parts of a solution of the sample, cm.

2.4.2 Standards of accuracy of analysis results

The values of the characteristics of error definitions: permitted discrepancies in the results of parallel measurements (the rate of convergence) and the results of the analysis of the same samples obtained in two laboratories or in the same, but in different conditions (a measure of reproducibility), and the margins of error definitions ( — accuracy rate) at a confidence level =0.95 is shown in table 2.

Table 2

2.4.3 Control of accuracy of analysis results

Control of accuracy of analysis results is carried out according to state standard sample in accordance with GOST 25086.

It is allowed to conduct control of accuracy by the method of additives in accordance with GOST 25086.

Additives is a standard solution A.

3 Atomic absorption method for the determination of aluminium

3.1 the essence of the method

The method is based on measuring atomic absorption of aluminum at a wavelength of 309,3 nm in the electrothermal atomization mode. The determination is carried out by standard addition.

3.2 Equipment, reagents and solutions

Spectrophotometer atomic absorption equipped with graphite atomizer, a source of excitation of spectral lines of aluminium.

Microspec with a capacity of 20 µm.

Argon — GOST 10157.

Hydrochloric acid — according to GOST 14261, diluted 1:1.

Aluminum brand A99 — according to GOST 11069.

State standard samples made in accordance with GOST 8.315.

Distilled water — according to GOST 6709.

Standard solutions of aluminium:

Solution a: prepared in accordance with 2.2.

Solution B: 10 cmsolution And placed in a volumetric flask with a capacity of 100 cm, made up to the mark with water and mix; prepare before use.

1 cmof a solution contains 0.01 mg of aluminum.

Solution: 25 cmsolution And placed in a volumetric flask with a capacity of 100 cm, made up to the mark with water and mix; prepare before use.

1 cmof the solution contains 0.025 mg of aluminium

.

3.3 analysis

3.3.1 Sample the sample weight of 0.25 or 0.5 g (see table 3) is placed into the seven cups with a capacity of 300 cm. Moisten with water, add in each glass a small portions at 5 or 10 cmof hydrochloric acid (see table 3) and are dissolving at room temperature. After complete dissolution of batches of the solutions were transferred to volumetric flasks with a capacity of 100 or 250 cm(see table 3).

Table 3

In six of the seven volumetric flasks with a solution of the sample add 0,5; 1,0; 2,0; 3,0; 4,0; 5,0; 6,0 cmstandard solution B or C (see table 3), which corresponds to the mass concentration of added aluminum 0,05; 0,1; 0,2; 0,3; 0,4; 0,5; 0,6 µg/cm. The solutions in all flasks is poured to the mark with water and mix.

To prepare the solution in the reference experiment in a volumetric flask with a capacity of 100 or 250 cmis placed 10 or 5 cmof hydrochloric acid, made up to the mark with water and mix (see table 3).

Microspace injected into the graphite cuvette sequentially a solution of the reference experiment, the sample solution and, in order of increasing aluminium concentrations, solutions containing additives of a standard solution of aluminum.

Measurement of atomic absorption of aluminium is carried out in the mode:

type of atomization is electro;

the lamp current, mA 10;

wavelength nm 309,3;

the slot width of the device, nm — 1,3;

the drying temperature of the first stage, 353−423;

Stage II, 423−473;

the drying time stage I, 5;

II stage — 5;

temperature ashing, stage I, 773−1473;

Stage II, 1473−2273;

time ashing stage I, 5;

II stage — 5;

the temperature of the atomization, K — 2973;

the atomization time, s — 7;

cleaning temperature, K — 2973;

cleaning — 2;

the speed of the argon cm/min — 200.

At the stage of atomization, the argon flow is stopped.

From the values of atomic absorption solutions containing additives of a standard solution of aluminium, subtract the value of atomic absorption of the sample solution. According to the obtained values of the difference between of atomic absorption and corresponding mass concentrations of added aluminium in µg/cmbuild a calibration curve, which find mass concentration of aluminum in solutions of the reference experiment and the sample.

3.3.2 In the case when the instrument is in automatic mode and held its graduations, hinge carat weight of 0.25 or 0.5 g (see table 3) are placed in four glasses with a capacity of 300 cmand then spend the dissolution as specified in 3.3.1. The solutions were transferred to volumetric flasks with a capacity of 100 or 250 cm(see table 3).

In three of the four volumetric flasks with the solutions of the sample is added to 0.5; 3,0; 6,0 cmstandard solution B or C (see table 3), which corresponds to the mass concentration of added aluminum 0,05; 0,30; 0,60 µg/cm.

The solutions in all flasks is poured to the mark with water and mix.

The solution in the reference experiment prepared as described in 3.3.1.

Microspace introduced into a graphite cuvette and the sample solution, and then, in order of increasing aluminium concentrations, solutions containing additives of a standard solution of aluminium, carried out the calibration of an instrument.

Measurement of atomic absorption of aluminium is carried out in a mode according to 3.3.1.

Then injected into the graphite cuvette, the solutions in the reference experiment and the sample and hold measurement of atomic absorption of aluminum in the regime 3.3.1.

After every 4−5 measurements of atomic absorption of aluminium refining the graphite cuvette: microspace it enters the water and is carried out the atomization process mode on 3.3.1.

3.4 Processing of analysis results

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

, (2)

where is the mass concentration of aluminium in sample solution, µg/cm;

mass concentration of aluminum in solution in the reference experiment, µ g/cm;

 — the volume of the sample solution, cm;

 — weight of charge, g

.

3.4.2 Standards of accuracy of analysis results

The values of the characteristics of error definitions: permitted discrepancies in the results of parallel measurements (the rate of convergence) and the results of the analysis of the same samples obtained in two laboratories or in the same, but in different conditions (a measure of reproducibility), and the margins of error definitions ( — accuracy rate) at a confidence level =0.95 is shown in table 4.

Table 4

3.4.3 Control of accuracy of analysis results

Control of accuracy of analysis results is carried out according to state standard sample in accordance with GOST 25086.