GOST 20996.6-82

• gost-209966-82.pdf (118.58 KiB)
  ГОСТ 20996.6-82

GOST 20996.6−82 Selenium technical. Method for determination of iron (with Amendments No. 1, 2)

GOST 20996.6−82*

Group B59

INTERSTATE STANDARD

SELENIUM TECHNICAL

Method for determination of iron

Selenium. Method of iron 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 sect. III

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


The Change N 2, approved and promulgated by the Order of Rosstandart on 09.04.2015 N 249-St c 01.09.2015

Change No. 2 made by the manufacturer of the database in the text ICS N 7, 2015


This standard establishes photocolorimetric method for determination of iron (at mass fraction of iron 0,003−0,6%).

The method is based on reaction of formation of colored complex compounds of iron ions with sulfosalicylic acid and the measurement of its optical density at a wavelength of 400−450 nm.

1A. NORMATIVE REFERENCES

This standard uses the regulatory references to the following international standards:

GOST 1770−74 (1042−83 ISO, ISO 4788−80) Glassware volumetric laboratory glass. Cylinders, beakers, flasks, test tubes. General specifications

GOST 3118−77 Reagents. Hydrochloric acid. Specifications

GOST 3760−79 Reagents. The aqueous ammonia. Specifications

GOST 4461−77 Reagents. Nitric acid. Specifications

GOST 4478−78 Reagents. Sulfosalicylic acid 2-water. Specifications

GOST 6709−72 distilled Water. Specifications

GOST 9849−86 iron Powder. Specifications

GOST 20996.0−82 Selenium technical. General requirements for methods of analysis

GOST 24104−2001* laboratory Scales. General technical requirements
______________
* On the territory of the Russian Federation GOST R 53228−2008 «Scales non-automatic actions. Part 1. Metrological and technical requirements. Test».


GOST 25336−82 Glassware and equipment laboratory glass. The types, basic parameters and dimensions

GOST ISO 5725−6-2002* Accuracy (trueness and precision) of methods and measurement results. Part 6. The use of precision values in practice
________________
* On the territory of the Russian Federation GOST R ISO 5725−6-2002 «Accuracy (trueness and precision) of methods and measurement results. Part 6. The use of precision values in practice».


Note — When using this standard appropriate to test the effect of reference standards in the information system of General use — on the official website of the Federal Agency for technical regulation and Metrology on the Internet or published annually by the information sign «National standards» published as on January 1 of the current year and related information published monthly indexes published in the current year. If the reference standard is replaced (changed), when using this standard should be guided by replacing (amended) standard. If the reference standard is cancelled without replacement, then the situation in which the given link applies to the extent that does not affect this link.


(Added, Rev. N 2).

1B. CHARACTERISTICS OF INDICATORS OF MEASUREMENT ACCURACY

A measure of the accuracy of measuring the mass fraction of iron corresponds to the characteristics given in table 1 (with R=0,95).

Limit values of repeatability and reproducibility of measurements for a confidence probability P=0.95 is given in table 1.


Table 1 — values of the indicator of measurement accuracy, limits of repeatability and reproducibility of measurements of mass fraction of iron

Percentage

Section 1B. (Added, Rev. N 2).

1. GENERAL REQUIREMENTS

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

2. MEASUREMENT MEANS, AUXILIARY DEVICES, MATERIALS, SOLUTIONS

When performing measurements using the following measuring instruments and auxiliary devices:

— spectrophotometer or photoelectrocolorimeter with all accessories necessary for measurements at a wavelength of 400−450 nm;

— scale special accuracy class according to GOST 24104;

— the stove is electric with a closed heating element for temperature up to 400 °C;

— volumetric flasks 2−50−2, 2−100−2, 2−1000−2 according GOST 1770;

— glasses-1−250 TCS according to GOST 25336.

When taking measurements, use the following products and solutions:

— distilled water according to GOST 6709;

— nitric acid according to GOST 4461;

— hydrochloric acid according to GOST 3118, diluted 1:1 and 1:4;

— ammonia water according to GOST 3760, diluted 1:1;

— sulfosalicylic acid 2-water according to GOST 4478, solution mass concentration of 100 g/DM;

— iron according to GOST 9849.

Notes

1. Allowed the use of other measuring instruments of the approved type, auxiliary devices and materials, technical and metrological characteristics are not inferior to mentioned above.

2. Allowed the use of reagents produced by other normative documents, provided that their metrological characteristics of the measurement results given in the measurement technique.


(Changed edition, Rev. N 2).

3A. PREPARATIONS FOR THE MEASUREMENTS

3A.1. To construct the calibration curve, prepare solutions of known iron concentration.

In preparing the solution And the mass concentration of iron to 0.1 mg/cma sample of iron with a mass of 0.1 g was placed in a beaker with a capacity of 250 cm, flow from 30 to 35 cmof a mixture of hydrochloric and nitric acids (3:1) to heat and evaporate the solution to dry salts. Poured from 100 to 120 cmof hydrochloric acid diluted 1:1 was placed in a volumetric flask with a capacity of 1000 cm, made up to the mark with water and mix.

In the preparation of a solution of mass concentration of iron is 0.01 mg/cma 10 cm aliquotof solution A is placed in a volumetric flask with a capacity of 100 cm, made up to the mark with water and mix.

3A.2. Construction of calibration curve

Nine volumetric flasks with a capacity of 50 cmeach are placed 0; 1,0; 2,0; 4,0; 6,0; 8,0; 10,0; 15,0; 20,0 cm (3) solution B, which corresponds to 0; 0,01; 0,02; 0,04; 0,06; 0,08; 0,1; 0,15; 0,2 mg of iron, made up to 30 cmof water, 5 to 6 cmsulfosalicylic acid solution and neutralized with ammonia until you see a red-yellow staining. Add 2 to 2.5 cm (3) ammonia solution, made up to the mark with water and mix.

After 10 minutes measure the optical density of the solution at a wavelength of 400−450 nm in a cuvette with the thickness of the light absorbing layer was 50 mm. In a solution of comparison used water. Calibration curve built with consideration of the idle experience (reference solution with zero concentration of iron)

Section 3A. (Added, Rev. N 2).

3. ANALYSIS

3.1. A portion of selenium with a weight of 1 or 2 g (depending on the mass fraction of iron) were placed in a glass with a capacity of 250−300 cm, pour 15−20 cmof nitric acid and evaporated to dryness. The dry residue is kept for 8−10 minutes on the stove. The operation is repeated twice, adding each time 5−7 cmof nitric acid and evaporating to dryness each time.

Then to the dry residue pour 3−4 cmof hydrochloric acid and heated to dissolve the residue. Add 40−50 cmof water, boil and transferred to a volumetric flask with a capacity of 100 cm, is poured a solution of hydrochloric acid (1:4) to the mark and mix.

Select aliquot part of the solution 2−25 cm(depending on the mass fraction of iron) and transfer it into a measuring flask with a capacity of 50 cm. Top up with water to 30 cm, poured 5−6 cmsulfosalicylic acid solution and neutralized with ammonia until you see a red-yellow staining. Add 2−2. 5 cmof ammonia solution, made up to the mark with water and mix.

After 10 minutes measure the optical density of the solution on the photoelectrocolorimeter, using a filter with maximum transmittance at a wavelength of 430 nm and cuvette thickness of the light absorbing layer was 50 mm.

Solution comparison is the solution of the reference experiment.

Weight of iron set calibration schedule.

(Changed edition, Rev. N 1).

3.2. (Deleted, Rev. N 2).

4. PROCESSING OF THE RESULTS

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

,

where  — the amount of iron was found in the calibration graphics mg;

 — volume of the volumetric flask, cm;

 — volume aliquote part of the solution, cm;

 — weight of selenium,

4.2. The measurement results take the arithmetic mean of two parallel definitions, provided that the absolute difference between them in terms of repeatability does not exceed the value (at confidence probability P=0,95) repeatability limit rgiven in table 1.

If the difference between the highest and lowest results of parallel measurements exceeds the limit value of the frequency of occurrence, perform the procedure described in GOST ISO 5725−6 (paragraph 5.2.2.1).

(Changed edition, Rev. N 1, 2).

4.3. The absolute value allowable discrepancies between the two measurement results obtained in different laboratories, should not exceed the limit values for the reproducibility given in table 1 (at confidence probability P=0,95). At default of this condition can be used the procedure set out in GOST ISO 5725−6.

(Added, Rev. N 2).