GOST 20996.1-2014

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  ГОСТ 20996.1-2014

GOST 20996.1−2014 Selenium technical. Methods for determination of selenium

GOST 20996.1−2014

INTERSTATE STANDARD

SELENIUM TECHNICAL

Methods for determination of selenium

Selenium technical. Methods of selenium 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 1766-St inter-state standard GOST 20996.1−2014 introduced as the national standard of the Russian Federation from September 1, 2015.

5 REPLACE GOST 20996.1−82


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 methods of measurement of mass fraction of selenium iodometric and gravimetric methods.

The measurement range varies from 97,0% to 99,98%.

2 Normative references

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

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

GOST 3118−77 Reagents. Hydrochloric acid. Specifications

GOST 4204−77 Reagents. Sulphuric acid. Specifications

GOST 4232−74 Reagents. The potassium iodide. Specifications

GOST 4328−77 Reagents. Sodium hydroxide. Specifications

GOST 4461−77 Reagents. Nitric acid. Specifications

GOST 5456−79 Reagents. Of hydroxylamine hydrochloride. Specifications

GOST 6691−77 Reagents. Urea. Specifications

GOST 6709−72 distilled Water. Specifications

GOST 10163−76 Reagents. Starch soluble. Specifications

GOST 10298−79 Selenium technical. Specifications

GOST 12026−76 laboratory filter Paper. Specifications

GOST 18300−87 ethyl rectified technical. 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.


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

GOST 27068−86 Reagents. Chernovetskiy sodium (sodium thiosulfate) 5-water. Specifications

GOST 29169−91 (ISO 648−77) oils. Pipette with one mark

GOST 29227−91 (ISO 835−1-81) oils. Pipettes are graduated. Part 1. General requirements

GOST 29251−91 (ISO 385−1-84) oils. Burette. Part 1. General requirements

GOST ISO 5725−6-2003** Accuracy (trueness and precision) of methods and measurement results. Part 1. General provisions and definitions

__________________

** 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 Characteristics of measurement accuracy

A measure of the accuracy of measuring the mass fraction of selenium 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 General provisions

General requirements for methods of measurements GOST 20996.0.

5 Iodometric method of measuring the mass fraction of selenium

5.1 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;

— drying Cabinet, providing a heating temperature of from 100 °C to 105 °C;

— flasks KN-2−250−19/26 TXC, KN-2−500−19/26 TXC GOST 25336;

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

— burette 1−2-25−01, 1−2-50−01 according to GOST 29251;

pipettes 1−2-2−1, 1−2-2−2, 1−2-2−5, 1−2-2−10 according to GOST and GOST 29169 29227;

— funnel filtering laboratory according to GOST 25336;

— bath water;

— hour glass.

When taking measurements, use the following products and solutions:

— distilled water according to GOST 6709;

— nitric acid according to GOST 4461;

— sulfuric acid according to GOST 4204 or diluted 1:1;

— hydrochloric acid according to GOST 3118 or diluted 1:9;

— hydroxylamine hydrochloride according to GOST 5456;

— urea according to GOST 6691;

— potassium iodide according to GOST 4232, solution mass concentration of 50 g/DM;

— soluble starch according to GOST 10163, solution mass concentration of 5 g/DM;

sodium Chernovetskiy 5-water (sodium thiosulfate) according to GOST 27068, the solution molar concentration of 0.2 mol/DM;

— sodium hydroxide according to GOST 4328, solution mass concentration of 200 g/DM;

— selenium GOST 10298;

— phenolphthalein (indicator) [1]*, an alcoholic solution of the mass concentration of 1 g/DM;
_______________
* See Bibliography. — Note the manufacturer’s database.


the laboratory filter paper according to GOST 12026, brands, f, FS;

paper display [2]*;

filters obestochennye [3]* or similar.
_______________
* See Bibliography, hereinafter. — 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.

5.2 Method of measurement

The method iodometric titration based on the reaction of formation of sodium Selenomethionine in the interaction of selenous acid and sodium thiosulfate. The liberated iodine is titrated with sodium thiosulfate in presence of starch.

5.3 Preparation for measurements

5.3.1 To prepare the solution of the starch mass concentration of 5 g/DMof the starch sample weight of 0.5 g is stirred in 10 cmof water to obtain a homogeneous slurry, the mixture is slowly poured, with stirring, at 90 cmof boiling water and boil for 2−3 minutes, cool. The solution should be used freshly prepared.

5.3.2 in the preparation of a solution of potassium iodide mass concentration of 50 g/DMweighed salts of potassium iodide (pre-dried to constant weight at a temperature not higher than 110°C) with a mass of 5.00 g was dissolved in 90 cmsvejeprokipachenna water. The solution should be used freshly prepared.

5.3.3 in the preparation of the solution servational sodium (sodium thiosulfate) molar concentration of 0.2 mol/DMweighed salt weight 49,6 g is placed in a conical flask with a capacity of 500 cm, 200 cm pourboiled water. The solution was filtered into a measuring flask with volume capacity of 1000 cm, made up to the mark with boiled cooled water and stirred. The solution is kept before eating for 6−7 days.

Allowed to prepare solutions of sodium chernovetskogo from the respective standard titles in accordance with the instructions for their preparation.

5.3.4 establishing a mass concentration of sodium thiosulfate

The mass concentration of sodium thiosulfate set as follows: a portion of selenium with a mass of 0.1 g was placed in a conical flask with a capacity of 250 cm, flow 10 to 12 cmof hydrochloric acid of 1 cmof nitric acid, cover with watch glass and heated to dissolve sample. Remove the glass, wash it over with the flask of water poured from 80 to 100 cmof hot water, add 4−4,5 g of urea and stirred.

After 20 min the solution was cooled in running water and neutralize to phenolphthalein with sodium hydroxide solution until alkaline reaction. To a solution flow of 20 to 25 cmof sulphuric acid diluted 1:1 and cooled.

After cooling, poured gradually with stirring 21 to 23 cmof sodium thiosulfate, 2 to 3 cmof potassium iodide, 2 to 3 cm ofstarch solution, the mass concentration of 5 g/DMand titrate the liberated iodine with sodium thiosulfate until the disappearance of the blue color of the solution.

The mass concentration of sodium thiosulfate With, expressed in grams of selenium per 1 cmof the solution in g/cm, is calculated by the formula

, (1)

where m is the mass of sample selenium, g;

V — volume of sodium thiosulfate consumed for the titration, given the reference experiment, cm.

5.4 performance measurement

5.4.1 Determination of selenium for the mass concentration from 97,0% to 99.5%

A portion of the selenium mass of 0.1 g was placed in a conical flask with a capacity of 250 cm, flow 10 to 15 cmof hydrochloric acid and 1 cmof nitric acid, cover with watch glass or glass plate, and heated until dissolved selenium at a temperature of from 60 °C to 70 °C. Glass (plate) is removed, washed with water, and carefully evaporate the solution on a warm place (a water bath) until a wet residue.

Poured from 30 to 35 cmof hydrochloric acid, add from 60 to 80 cmof water, a little filtrowanie weight and 2−2. 5 g of hydroxylamine hydrochloride. Mix and leave for 2−3 hours in a warm place plate to the coagulation of the precipitate.

The precipitate was filtered off through a filter with filtrowanie ground, washed 2−3 times with hot hydrochloric acid solution, diluted 1:9 and 6−8 times with hot water.

Selenium precipitate with the filter is transferred to a flask in which the precipitation was carried out, add 15 to 20 cmof hydrochloric acid and 1 cmof nitric acid and heated in a water bath to dissolve the residue. To the obtained solution poured from 80 to 100 cmof hot water, add 4−4,5 g of urea and stirred.

After 20 min the solution was cooled and neutralized to phenolphthalein with sodium hydroxide solution until alkaline reaction. To a solution flow of 20 to 25 cmof sulphuric acid diluted 1:1 and cooled.

After cooling, poured gradually with stirring 21 to 23 cmof sodium thiosulfate, 2 to 3 cmof potassium iodide, 2 to 3 cmof a solution of starch mass concentration of 5 g/DMand titrate the liberated iodine with sodium thiosulfate until the disappearance of the blue color of the solution.

5.4.2 Determination of selenium for the mass concentration above 99.5% up to 99.98%

A portion of the selenium mass of 0.1 g was placed in a conical flask with a capacity of 250 cm, flow 10 to 15 cmof hydrochloric acid and 1 cmof nitric acid, cover with watch glass or glass plate, and heated until dissolved selenium at a temperature of from 60 °C to 70 °C.

Glass (plate) is removed, washed with water, add 80 to 100 cmof hot water, add 4−4,5 g of urea and stirred.

After 20 min the solution was cooled and neutralized to phenolphthalein with sodium hydroxide solution until alkaline reaction. To a solution flow of 20 to 25 cmof sulphuric acid diluted 1:1 and cooled.

After cooling, poured gradually with stirring 21 to 23 cmof sodium thiosulfate, 2−3 cmof potassium iodide, 2 to 3 cmof a solution of starch mass concentration of 5 g/DMand titrate the liberated iodine with sodium thiosulfate until the disappearance of the blue color of the solution.

5.5 Processing of measurement results

Mass fraction of selenium, X, %, when using the iodometric method described by the formula

, (2)

where With a mass concentration of sodium thiosulfate on selenium, g/cm;

V — volume of sodium thiosulfate consumed in the titration, cm;

m — weight of selenium,

5.6 the measurement results take the arithmetic mean value of three parallel measurements, provided that the difference between the highest and the lowest results in terms of repeatability with a confidence probability P=0.95 does not exceed the values of the repeatability limit r given 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).

5.7 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.

6 Gravimetric method

6.1 measurement Means, auxiliary devices, materials, solutions

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

— drying oven laboratory;

— the stove is electric with a closed heating element for temperature up to 350 °C;

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

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

— flasks KN-2−250−19/26 KN-2−500−29/32 according to GOST 25336;

— dryer 2−100 according to GOST 25336;

— bath water;

— funnel filtering laboratory 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;

— hydroxylamine hydrochloride according to GOST 5456;

— urea according to GOST 6691;

— technical rectified ethyl alcohol according to GOST 18300;

the filter paper according to GOST 12026, brands, f, FS;

filters obestochennye in [3] or similar.

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.

6.2 Method of measurement

The method is based on the reaction of the deposition of selenium with hydroxylamine hydrochloride and weighing the resulting precipitate of selenium.

6.3 preparing the measurements

6.3.1 in the preparation of the urea solution mass concentration of 300 g/DMthe weight of salt mass of 30.00 g dissolved in 80 cmof water.

6.3.2 During the preparation of the solution of the hydroxylamine of the mass concentration of 100 g/DMthe weight of salt mass of 10.00 g was dissolved in 90 cmof water.

6.4 performance measurement

A portion of selenium with a mass of 0.5 g was placed in a conical flask with a capacity of 250 cm, flow 50 to 55 cmof hydrochloric acid and from 5 to 7 cmof nitric acid, and allowed to stand for 2−3 hours in a warm place, not allowing to boil the solution. To verify the completeness of decomposition after the specified time, pour 1−2 cmof nitric acid. If not there will be a release of oxides of nitrogen, the decomposition is complete. Otherwise, again pour 1−2 cmof nitric acid and incubated the solution for 1−2 hours

Then pour 50 to 60 cmof water, stirred and the insoluble residue is filtered through a dense filter of «blue ribbon» with filtrowanie ground. The filter residue is washed 5−6 times with hot water.

The filtrate with washings collected in a conical flask with a capacity of 500 cm. Bring the volume of the filtrate with water to 180−200 cm, flow from 30 to 35 cmof a solution of urea, heated to boiling, poured from 40 to 50 cmof hydrochloric acid 30−35 cmof a solution of hydroxylamine, mixed and kept on water bath for 1.5−2 h to complete the coagulation of the precipitate.

Check the completeness of the precipitation of selenium, Prilepa in a solution of from 5 to 10 cmof a solution of hydroxylamine. In case of sedimentation of selenium in the solution is weakly boil and repeat the check of completeness of the precipitation.

The precipitate of selenium was filtered through a previously weighed filtering crucible and is washed five to six times with hot water, 2−3 times with alcohol.

The crucible with the precipitate is placed in a drying Cabinet and dried at a temperature of from 105 °C to 110 °C for 1 h. Cool in a desiccator and weighed. Drying and weighing of the precipitate is repeated to obtain a constant weight.

6.5 the Processing of the measurement results

Mass fraction of selenium X, %, when using the gravimetric method calculated by the formula

, (3)

where mis the mass of the crucible with the precipitate of selenium, g;

m — mass of crucible, g;

m — weight of selenium,

6.6 For the results of the measurements taking the arithmetic mean value of three parallel measurements, provided that the difference between the highest and the lowest results in terms of repeatability with a confidence probability P=0.95 does not exceed the values of the 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).

6.7 Discrepancies between the results of measurements obtained in two laboratories, should not exceed the values of the reproducibility limit Rgiven 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.

6.8 the differences in the assessment of mass fraction of selenium used iodometric method.

Bibliography

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UDC 669.776:543.06:006.354 ISS 77.120.99

Key words: selenium technical indicators of accuracy of measurements, means of measurement, processing of measurement results