GOST 20996.3-82
GOST 20996.3−82 Selenium technical. Method for determination of lead (with Change No. 1)
GOST 20996.3−82*
Group B59
INTERSTATE STANDARD
SELENIUM TECHNICAL
Method for determination of lead
Selenium. Method of plumbum 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)
REPLACE GOST 10431−63 in part of sec. V
* PUBLISHING (may 2000) with amendment No. 1, approved in December 1987 (IUS 3−88)
This standard sets the polarographic method for the determination of lead (with a mass fraction of lead 0,001−0,06%).
The method is based on polarography solution containing lead, on the background of the sodium hydroxide solution in the presence of sodium tartrate.
1. GENERAL REQUIREMENTS
1.1. General requirements for method of analysis according to GOST 20996.0−82.
2. EQUIPMENT, REAGENTS, SOLUTIONS
Polarograph brands PPT-1, PU-1.
Nitric acid GOST 4461−77, a solution of 1:3.
Mercury GOST 4658−73.
Hydrochloric acid by the GOST 3118−77, diluted 1:1.
Sodium hydroxide according to GOST 4328−77, a solution of 200 g/DM.
Sodium sanitarily 7-water in ND.
Tartaric acid according to GOST 5817−77, a solution of 100 g/DM.
Lead according to GOST 3778−77*.
_______________
* On the territory of the Russian Federation GOST 3778−98. — Note the manufacturer’s database.
Standard solutions of lead.
Solution a: a sample of lead with a mass of 1 g are dissolved in 20 cmof nitric acid (1:3), the solution was cooled and transferred into a measuring flask with volume capacity of 1000 cm, made up to the mark with water and mix.
1 cmof the solution contains 1 mg lead.
Solution B: take 10 cmof solution A in a volumetric flask with a capacity of 100 cm, made up to the mark with water and mix.
1 cmof a solution contains 0.1 mg of lead.
(Changed edition, Rev. N 1).
3. ANALYSIS
A portion of the selenium mass 1−5 g (depending on the mass fraction of lead) was placed in a beaker with a capacity of 250 cm, 30−35 cm pour thenitric acid, cover with watch glass (glass plate) and allowed to stand until the cessation of the violent reaction. Glass (plate) is removed, washed with water and evaporated the solution to dryness. Then stand on stovetop for 10 minutes.
Add in a glass 7−10 cmof nitric acid and evaporated to dryness. Operation of evaporation of the solution with 3−5 cmof nitric acid is repeated twice.
To the dry residue poured 5−7 cmof a hydrochloric acid solution and evaporated to wet condition. This operation is repeated two times (to remove the smell of nitric acid).
To the obtained solution add 5−7 cmof a hydrochloric acid solution (1:1), heated to dissolve the salts and transferred into the volumetric flask with a capacity of 50 cm. Poured into a flask of 10−12 cmof a solution of tartaric acid, 15−20 cmof sodium hydroxide solution, made up to the mark with water and mix.
Taking away dry in a glass 20 cmof solution, add 1 g of sodium sulfite and leave for 5 minutes, Poured into the cell and polarographic lead in the range of potentials from minus 0.4 to minus 0.75 V relative to a mercury anode.
Lead find by the method of standard additions. To do this, select aliquot part of the standard solution A (0.2 to 0.6 cm) and add it into the solution, stirred for 2 min and polarografic the same as in the case of the analyzed solution. The amount of standard addition is selected so that the height of the peak of lead increased by 2−3 times compared to the peak height of lead in solution.
4. PROCESSING OF THE RESULTS
4.1. Mass fraction of lead in percent is calculated by the formula
,
where is the peak height of the investigated solution;
— the total volume of solution, cm;
— the weight of the portion of selenium, g;
the ratio is ,
where , ,
where , is the height of the peaks obtained in polarographically studied solutions with the addition of a standard solution of lead, mm.
, is the concentration of standard solutions of lead, mg/cm.
4.2. Discrepancies in the results of two parallel measurements and the two tests should not exceed the values given in the table.
Mass fraction of lead, % |
The absolute allowable difference, %, results | |
parallel definitions |
obtained in the laboratories of different enterprises | |
From to 0,0010 0,0030 incl. |
0,0005 |
0,0009 |
SV. 0,003 «to 0,006 « |
0,001 |
0,002 |
«Of 0.006» to 0.015 « |
0,002 |
0,004 |
«0,015» 0,030 « |
0,005 |
0,008 |
«0,03» 0,06 « |
0,01 |
0,02 |
(Changed edition, Rev. N 1).