GOST 20996.2-2014

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  ГОСТ 20996.2-2014

GOST 20996.2−2014 Selenium technical. Methods of determining sulphur

GOST 20996.2−2014

INTERSTATE STANDARD

SELENIUM TECHNICAL

Methods of determining sulphur

Selenium technical. Methods of sulphur determination

ISS 77.120.99

Date of introduction 2015−09−01

Preface

Goals, basic principles and main procedure of works on interstate standardization have been established in GOST 1.0−92 «interstate standardization system. Basic provisions» and GOST 1.2−2009 «interstate standardization system. Interstate standards, rules and recommendations on interstate standardization. Rules of development, adoption, application, renewal and cancellation"

Data on standard

1 DEVELOPED by the Technical Committee for standardization TC 368 «Copper"

2 recorded by the Interstate technical Committee for standardization MTK 503 «Copper"

3 ACCEPTED by the Interstate Council for standardization, Metrology and certification (Protocol dated 30 may 2014 No. 67-P)

The adoption voted:

4 by Order of the Federal Agency for technical regulation and Metrology dated 26 November 2014 N 1767-St inter-state standard GOST 20996.2−2014 introduced as the national standard of the Russian Federation from September 1, 2015.

5 REPLACE GOST 20996.2−82


Information about the changes to this standard is published in the annual reference index «National standards», and the text changes and amendments — in monthly information index «National standards». In case of revision (replacement) or cancellation of this standard a notification will be published in the monthly information index «National standards». Relevant information, notification and lyrics are also posted in the information system of General use — on the official website of the Federal Agency for technical regulation and Metrology on the Internet

1 Scope

This standard specifies photojournalistically method of measuring the mass fraction of sulphur (in the range from 0.002% to 0.10%), and titrimetric method of measuring the mass fraction of sulphur (in the range from 0.002% to 0.60%).

2 Normative references

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

GOST 83−79 Reagents. Sodium carbonate. Specifications

GOST 1770−74 laboratory Glassware measuring glass. Cylinders, beakers, flasks, test tubes. General specifications

GOST 3118−77 Reagents. Hydrochloric acid. Specifications

GOST 3640−94 Zinc. Specifications

GOST 3760−79 Reagents. The aqueous ammonia. Specifications

GOST 3773−72 Reagents. The ammonium chloride. Specifications

GOST 4108−72 Reagents. Barium chloride 2-water. Specifications

GOST 4145−74 Reagents. Potassium sulphate. Specifications

GOST 4209−77 Reagents. Magnesium chloride 6-water. Specifications

GOST 4233−77 Reagents. Sodium chloride. Specifications

GOST 4461−77 Reagents. Nitric acid. Specifications

GOST 6259−75 Reagents. Glycerin. Specifications

GOST 6709−72 distilled Water. Specifications

GOST 9147−80 Glassware and equipment lab porcelain. Specifications

GOST 10652−73 Reagents. Salt is the disodium Ethylenediamine-N, N, N', N'-tetraoxane acid 2-water (Trilon B). Specifications

GOST 20996.0−2014 Selenium technical. General requirements for methods of analysis

GOST 24104−2001* laboratory Scales. General technical requirements

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* On the territory of the Russian Federation GOST R 53228.


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

GOST ISO 5725−6-2003* Accuracy (trueness and precision) of methods and measurement results. Part 6. The use of precision values in practice

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* On the territory of the Russian Federation GOST R ISO 5725−6.


Note — When using this standard appropriate to test the effect of reference standards for the sign «National standards» drawn up as of January 1 of the current year and related information signs, 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.

3 General requirements

General requirements GOST 20996.0.

4 Photojournalistically method of measuring the mass fraction of sulfur

4.1 characteristics of the indicators of measurement accuracy

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

The value of the precision, limits of repeatability and reproducibility of the measurement at a confidence probability P=0.95 is given in table 1.


Table 1 — Values of the measure of the accuracy, limits of repeatability and reproducibility of the measurement at a confidence probability P=0,95

Percentage

4.2 measuring instruments, 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 364 nm;

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

— special laboratory scales of accuracy class according to GOST 24104;

— volumetric flasks 2−25−2, 2−50−2, 2−100−2, according GOST 1770;

— glasses-1−100 TCS-1−200 TCS-1−1000 TCS according to GOST 25336;

— crucibles filtering type ТФ32 — ПОР16 according to GOST 25336;

— porcelain Cup according to GOST 9147;

— hour glass.

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;

the anhydrous sodium carbonate according to GOST 83, a solution with a mass concentration of 100 g/DM;

— barium chloride according to GOST 4108, a solution with a mass concentration of 100 g/DM;

— glycerin according to GOST 6259, a solution with a mass concentration of 100 g/DM;

— potassium sulphate according to GOST 4145, recrystallized.

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 methodology/method of measurement.

4.3 Method of measurement

Measurement method based on the reaction of formation of a suspension of barium sulfate in the interaction of barium ions with sulfate ions and measuring the intensity of the turbidity of the solution. As a stabilizer of the slurry using glycerol.

4.4 Preparation for measurements

4.4.1 in the preparation of recrystallized potassium sulfate potassium sulfate sample weight of 100 g was placed in a beaker with a capacity of 1000 cm, 1000 cm pouredwater and dissolved by heating. The undissolved residue is filtered from the hot solution into the filter crucible (or Buchner funnel), the remainder is discarded. The filtrate is evaporated until crystals and cooled. The formed crystals filtered on a filter crucible (or Buchner funnel), transferred to a porcelain Cup and dried at a temperature from 70 °C to 100 °C for 1−1,5 hours the Cup with the crystals cooled and repeat the recrystallization. The resulting salt crystals from the second recrystallization was dried at room temperature.

4.4.2 Preparation of solutions for constructing the calibration curve

For construction of calibration curve prepare solutions of sulfur.

In preparing the solution And the mass concentration of sulphur 0.1 mg/cma sample of potassium sulfate mass 0,0544 g placed in a beaker with a capacity of 100 cm, flow 50 to 60 cmof water was placed in a volumetric flask with a capacity of 100 cm, made up to the mark with water and mix.

In the preparation of a solution of mass concentration of sulphur of 0.01 mg/cm10 cmsolution And placed in a volumetric flask with a capacity of 100 cm, made up to the mark with water and mix.

Solution B is stable for 2 days.

4.4.3 Construction of calibration curve

In six volumetric flasks with a capacity of 25 cmeach are placed 0; 0,5; 2,0; 4,0; 6,0 and 8,0 cmof solution B, which corresponds to 0,00; 0,005; 0,02; 0,04; 0,06; 0,08 mg sulfur, in the seventh volumetric flask with a capacity of 25 cmplaced 1 cmof solution A, which corresponds to 0.10 mg of sulfur. Add to each flask about 3.5−4 cmof hydrochloric acid diluted 1:1, 10 cmwater 10 cmof a solution of glycerine and mix. Then pour 3 to 3.5 cmof barium chloride, made up to the mark with water and mix. After 30−40 min measure the optical density of the solution on the photoelectrocolorimeter (spectrophotometer), using a filter with maximum transmittance at a wavelength of 364 nm in a cuvette with the thickness of the light absorbing layer was 50 mm. In a solution of comparison, using the blank solution experience (solution with zero concentration of sulfur). Graph building given in the reference experiment.

4.5 performance measurement

A portion of selenium from the ground up to 2,0000 0,5000 g (depending on the mass fraction of sulfur) was placed in a beaker with a capacity of 100 or 200 cm, flow from 1 to 2 cmof sodium carbonate solution and 10 to 15 cmof nitric acid. Beaker cover watch glass and leave you without heat until the cessation of the violent reaction. Then boil to remove oxides of nitrogen, remove the glass, wash over the glass, the solution was evaporated to dryness at a moderate heat, avoiding splashing the sample.

To the dry residue add 4 to 4.5 cmof hydrochloric acid, from 10 to 15 cmof water and heat the solution to dissolve the salts. Then incubated the resulting solution for 1 h.

The solution is placed in a volumetric flask with a capacity of 50 cm, made up to the mark with water and mix.

An aliquot of the solution of volume from 1 to 10 cm(or the entire amount depending on the mass fraction of sulfur, in this case, the solution is evaporated to a volume of 10 to 15 cm, then cooled) placed in a volumetric flask with a capacity of 25 cm, add 0.5 to 1 cmof hydrochloric acid diluted 1:1, 10 cmof a solution of glycerine and mix. Then pour 3 to 3.5 cmof a solution of barium chloride, made up to the mark with water and mix.

For 30−40 minutes a solution mix and measure the optical density of the solution on the photoelectrocolorimeter (spectrophotometer), using a filter with maximum transmittance at a wavelength of 364 nm and cuvette thickness of the absorbing layer is 50 mm.

A solution of comparison, using the blank solution experience (solution with zero concentration of sulfur).

The mass of sulphur in the sample solution found by the calibration schedule.

4.6 Processing of measurement results

4.6.1 Mass fraction of sulfur , X, %, is calculated by the formula

, (1)

where mis the mass of sulfur in the solution of the sample, was found in the calibration graphics mg;

mis the mass of sulfur in solution in the reference experiment, was found in the calibration graphics mg;

V — volume of test solution in a volumetric flask, cm;

m — mass of sample selenium, g;

V — volume of the aliquot solution, cm.

4.6.2 the measurement result taking 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, then the procedure set out in GOST ISO 5725−6 (paragraph 5.2.2.1).

4.6.3 Differences between measurements obtained in two laboratories, should not exceed the limit values for the reproducibility given in table 1. In this case, the final result may be decided to their arithmetic mean value. At default of this condition can be used the procedure set out in GOST ISO 5725−6.

5 Titrimetric method of measuring the mass fraction of sulfur

5.1 characteristics of the indicators of measurement accuracy

A measure of the accuracy of measuring the mass fraction of sulfur corresponds to the characteristics given in table 2 (with R=0,95).

The value of the indicator of measurement accuracy, limits of repeatability and reproducibility of the measurement at a confidence probability P=0.95 is shown in table 2.


Table 2 — Values of the measure of the accuracy, limits of repeatability and reproducibility of the measurement at a confidence probability P=0,95

Percentage

5.2 measurement Means, auxiliary devices, materials, solutions

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

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

— special laboratory scales of accuracy class according to GOST 24104;

— volumetric flasks 2−1000−2 according GOST 1770;

— flasks KN-1−250−24/29 TCS GOST 25336;

— glasses-1−250, In-1−1000 GOST 25336;

— funnel In-36−80 TC GOST 25336.

When taking measurements, use the following products and solutions:

— distilled water according to GOST 6709;

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

— nitric acid according to GOST 4461;

— hydrochloric acid according to GOST 3118;

— barium chloride according to GOST 4108, solution mass concentration of 100 g/DM;

— methyl red indicator [1]; solution of the mass concentration of 1 g/DM;

— salt is the disodium Ethylenediamine-N, N, N', N'-tetraoxane acid 2-water (Trilon B, chelating agent III) according to GOST 10652; solution of molar concentration of 0.025 mol/DM;

zinc GOST 3640;

— ammonium chloride according to GOST 3773;

— a buffer solution;

— magnesium chloride 6-water according to GOST 4209, solution of molar concentration of 0.025 mol/DM;

— eriochrome black T indicator mixed with sodium chloride according to GOST 4233 in 1:100 ratio;

filters obestochennye [2]* or similar.
________________
* See Bibliography. — Note the manufacturer’s database.


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 methodology/method of measurement.

5.3 Method of measurement

Method of measurements is based on the deposition of sulfur in the sulfate ion solution of barium chloride, dissolving the resulting precipitate in ammonia solution of Trilon B and titration of the excess magnesium chloride in the presence of an indicator eriochrome black T.

5.4 Preparing to run analysis

5.4.1 When preparing a buffer solution with a pH of 9−9,5 a suspension of ammonium chloride with a mass of 54 g is placed in a measuring flask with volume capacity of 1000 cm, dissolved in a volume of 100 to 150 cmof water, poured 350 cmof ammonia, made up to the mark with water and mix.

5.4.2 in preparing the solution of the disodium salt Ethylenediamine-N, N, N', N'-tetraoxane acid 2-water (Trilon B, chelating agent III) molar concentrations of 0.025 mol/DMweighed salt weight 9,305 g placed in a beaker with a capacity of 1000 cm, and dissolved in a volume of from 500 to 600 cmof hot water. Filtered through the filter «white ribbon», cooled, poured into a measuring flask with volume capacity of 1000 cm, made up to the mark with water and mix. If necessary, the solution was filtered.

5.4.3 the Establishment of the mass concentration of the solution Trilon B sulphur

When establishing the mass concentration of the solution Trilon B sample zinc weight 0,040 g is placed in a conical flask with a capacity of 250 cm, poured from 5 to 6 cmof hydrochloric acid and evaporated to moist condition, flow from 100 to 120 cmof water, heated to boiling the solution is cooled, poured 15 to 20 cmbuffer solution, add a spatula tip of indicator eriochrome black T and titrate the zinc solution of Trilon B molar concentration of 0.025 mol/DMbefore the solution colour to purple-red.

The mass concentration of the solution Trilon B (chelating agent III), expressed in grams of sulfur C1 cmof solution, g/cm, is calculated by the formula

, (2)

where m is the mass of the zinc sample, g;

32,04 — the conversion factor;

V — volume of solution Trilon B, spent on titration, sm.

5.5 performance measurement

Selena weighed weighing from 1 to 3 g (depending on the mass fraction of sulfur) was placed in a flask with a capacity of 250 cm, flow 10 to 20 cmof nitric acid, cover with watch glass and leave you without heat until the cessation of the violent reaction of allocation of oxides of nitrogen, and then removed the glass, washed with water over the flask, the resulting solution was evaporated to dryness.

To the dry residue pour from 3 to 5 cmof nitric acid, from 80 to 10 cmof water and heated to boiling. Poured from 15 to 20 cmof a solution of barium chloride, boil for 8−10 minutes and leave to coagulate the precipitate for 1−6 h (depending on the mass fraction of sulfur).

Filter the precipitate on the filter «blue ribbon» and washed 5−6 times with water. The precipitate is then transferred to a flask in which the precipitation was carried out, poured from 80 to 100 cmof water, from 10 to 25 cm(depending on the amount of sulfur in the sample solution) of the solution Trilon B and 5 to 7 cmof ammonia. Heated to dissolve the precipitate. After cooling, poured from 20 to 25 cmbuffer solution, add a spatula tip of indicator eriochrome black T and mix. Added dropwise methyl red indicator until the color of the solution from blue to green. Then titrated magnesium chloride to change the color of the solution violet-red.

5.6 the Processing of the measurement results

5.6.1 Mass fraction of sulfur , X, %, is calculated by the formula

, (3)

where V — volume of added solution Trilon B, cm;

V — volume of solution of magnesium chloride, used for titration of excess Trilon B, cm;

K — factor is the ratio of molar solutions of Trilon B and magnesium chloride, calculated according to formula 4;

C — mass concentration of the solution Trilon B sulphur, g/cm;

m — weight of selenium,

5.6.2 Calculation of coefficient K ratio of molar solutions of Trilon B and magnesium chloride

To determine the coefficient in a flask with a capacity of 250 cmis placed 10 to 25 cmof the solution Trilon B, pour 100 cmof water, 20 to 25 cmbuffer solution, add a spatula tip of indicator eriochrome black T and mix. Added dropwise methyl red indicator until the color of the solution from blue to green. Then titrated magnesium chloride to change the color of the solution violet-red.

The ratio of molar solutions of Trilon B and magnesium chloride Kis calculated by the formula

, (4)

where V — volume of solution Trilon B, cm;

V — volume of solution of magnesium chloride, used for titration of Trilon B, cm.

5.6.3 For the measurement result taking 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 2.

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

5.6.4 the Differences between measurements obtained in two laboratories, should not exceed the values of the limit of reproducibility shown in table 2. In this case, the final result may be decided to their arithmetic mean value. At default of this condition can be used the procedure set out in GOST ISO 5725−6.

Bibliography

The one mentioned here, are not given. For additional information, please refer to the link. — Note the manufacturer’s database.

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UDC 669.776:546.22:006.354 ISS 77.120.99

Key words: selenium technical, the mass fraction of sulfur, the results of measurement characteristics of indicators of accuracy of measurements, means of measurement, processing of measurement results