GOST 851.12-93

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  ГОСТ 851.12-93

GOST 851.12−93 Magnesium primary. Method for determination of lead

GOST 851.12−93

Group B59

INTERSTATE STANDARD

MAGNESIUM PRIMARY

Method for determination of lead

Primary magnesium.
Method for determination of lead

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 83 interstate standard GOST 851.12−93 introduced directly as state standard of the Russian Federation from January 1, 1997

4 INTRODUCED FOR THE FIRST TIME

5 REISSUE

INFORMATION DATA

REFERENCE NORMATIVE AND TECHNICAL DOCUMENTS

This standard establishes the atomic absorption method for the determination of lead (with a mass fraction of lead from 0.0005 to 0.01%) in primary magnesium.

The method is based on measuring atomic absorption of lead at a wavelength is 283.3 nm in the electrothermal atomization mode.

The determination is carried out by standard addition.

1 General requirements

1.1 General requirements to the method of analysis according to GOST 25086.

1.2 Mass fraction of lead is determined from the two parallel batches.

2 Equipment, reagents and solutions

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

Microspec with a capacity of 2 µm.

Argon — GOST 10157.

Nitric acid — according to GOST 11125, diluted 1:1.

Ascorbic acid according to the state Pharmacopoeia .

Lead sticks — on the other 6−09−1490.

State standard samples made in accordance with GOST 8.315.

Distilled water — according to GOST 6709.

Standard solutions of lead

Solution a: 0,100 g of lead dissolved in 20 cmof a solution of nitric acid under heating. The solution was cooled to room temperature, 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 lead.

Solution B: 1 cmof solution A is 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 1 µg of lead.

Solution: 10 cmsolution And placed in a volumetric flask with a capacity of 250 cm, made up to the mark with water and mix; prepare before use.

1 cmof solution contains 4 mcg of lead.

3 analysis

3.1 Sample weighing 0.5 g was placed in six beakers with a capacity of 200−300 cm, moistened with water and added in small portions in each Cup at 30 cmof a solution of nitric acid.

Dissolution occurs initially at room temperature and then under heating on an electric stove. After complete dissolution of batches of the solutions were cooled to room temperature and transferred to volumetric flasks with a capacity of 50 or 200 cm(see table 1).

Table 1

In five out of six volumetric flasks, solutions of the sample, add 2,5; 5,0; 7,5; 10,0; 12,5 cmstandard solution B or C (see table 1), which corresponds to the mass concentration of added lead 0,05; 0,10; 0,15; 0,20; 0,25 µg/cm.

To each flask add 0.5 g ascorbic acid, made up to the mark with water and mix.

For the preparation of the reference experiment in a volumetric flask with a capacity of 50 or 200 cm(see table 1) was placed 30 cmof a solution of nitric acid, add 0.5 g ascorbic acid, made up to the mark with water and mix.

Microspace injected into the graphite cuvette sequentially a solution of the reference experiment, the sample solution and in ascending concentrations of lead solutions containing a standard solution of lead.

Measurement of atomic absorption is carried out in the following way:

type of atomization is electro;

the current of the lamp, mA — 7,5;

wavelength, nm — is 283.3;

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

the drying temperature of the first stage, 353−373;

Stage II, 373−473;

the drying time stage I, 10;

Stage II, 10;

the temperature of the ashing stage I, 473−573;

Stage II, 623−693;

time ashing stage I, 10;

Stage II, 10;

the temperature of the atomization, 1473−2273;

the atomization time, s — 7;

cleaning temperature, 2273−2473;

cleaning, C — 3;

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 lead, subtract the value of atomic absorption of the sample solution. According to the obtained results the difference between of atomic absorption and corresponding mass concentrations of added lead in ug/cmbuild a calibration curve, which find mass concentration of lead in solutions of the reference experiment and the sample.

When constructing a calibration chart, each point building on the average result of the three definitions of atomic absorption.

3.2 When the device is in the automatic mode is carried out graduation in four glasses with a capacity of 200−300 cmwill prevent attachment of the sample mass of 0.5 g and then spend the dissolution as specified in 3.1. The solutions were transferred to volumetric flasks with a capacity of 50 or 200 cm(see table 1).

In three of the four volumetric flasks with a solution of the sample add 2,5; 7,5; 12,5 cmstandard solution B or C (see table 1), which corresponds to the mass concentration of added lead 0,05; 0,15; 0,25 µg/cm.

To each flask add 0.5 g ascorbic acid, made up to the mark with water and mix.

The solution in the reference experiment prepared as described in 3.1.

Microspace introduced into a graphite cuvette and the sample solution, and then in ascending concentrations of lead solutions containing additives of a standard solution of lead, and carry out the calibration of an instrument.

Measurement of atomic absorption of lead is carried out in mode 3.1.

Then injected into the graphite cuvette, the solutions in the reference experiment, the sample and hold measurement of atomic absorption of lead in mode 3.1.

After every 4−5 measurements of atomic absorption of lead is carried out the purification of the graphite cuvette: microspace introduce water into it and spend the atomization process in a mode according to 3.1.

4 processing of the results of the analysis

4.1 Mass fraction of lead (a) percentage calculated by the formula

,

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

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

 — the volume of the sample solution, cm;

 — weight of charge, g

.

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

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.

4.4 When placing the results of the analysis make reference to this standard and report the results of accuracy control.