GOST 20996.1-82
GOST 20996.1−82 Selenium technical. Methods for the determination of selenium (with Change No. 1)
GOST 20996.1−82*
Group B59
INTERSTATE STANDARD
SELENIUM TECHNICAL
Methods for determination of selenium
Selenium. Methods of selenium 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 20996.1−75
* PUBLISHING (may 2000) with amendment No. 1, approved in December 1987 (IUS 3−88)
This standard establishes titrimetric and gravimetric methods for the determination of selenium (at a mass fraction of selenium from 97.0% and above).
1. GENERAL REQUIREMENTS
1.1. General requirements for methods of analysis GOST 20996.0−82.
2. TITRIMETRIC METHOD FOR THE DETERMINATION OF SELENIUM
2.1. The essence of the method
The method is based on the reaction of formation of sodium Selenomethionine in the interaction of selenous acid and sodium thiosulfate. Determination of selenium is conducted in the presence of a small amount of potassium iodide, fixing the end point of titration by the iodine-starch reaction.
2.2. Reagents and solutions
Nitric acid GOST 4461−77.
Hydrochloric acid by the GOST 3118−77 and diluted 1:9.
Sulfuric acid GOST 4204−77 and diluted 1:1.
Sodium hydroxide according to GOST 4328−77, a solution of 200 g/DM.
Sodium thiosulfate crystal according to GOST 244−76, 0.2 mol/DMthe solution of 49.6 g of sodium thiosulfate dissolved in 1000 cm
of water and filtered into a vessel made of dark glass. The titer of the solution set after 5−6 days.
The titer determination of sodium thiosulfate: a sample selenium of high purity with a mass of 0.1 g was placed in a conical flask with a capacity of 250 cm, add 10−12 cm
of hydrochloric acid of 1 cm
of nitric acid, cover with watch glass and slightly heated to dissolve the sample. Remove the glass, wash with water, add 80−100 cm
of hot water, 4−4,5 g of urea and then do as described in claim
Titer of sodium thiosulfate (), expressed in grams of selenium per 1 cm
of a solution, calculated by the formula
where is the mass of sample selenium, g;
— the volume of sodium thiosulfate consumed in the titration, sm
.
Potassium iodide according to GOST 4232−74, a solution of 50 g/DM.
The soluble starch according to GOST 10163−76, a solution of 5 g/DM.
Selenium of high purity.
Phenolphthalein according to SD, solution in alcohol 1 g/DM.
Hydroxylamine hydrochloride according to GOST 5456−79.
Urea according to GOST 6691−77.
The technical rectified ethyl alcohol GOST 18300−87.
(Changed edition, Rev. N 1).
2.3. Analysis
2.3.1. 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, add 10−15 cm
of hydrochloric acid and 1 cm
of nitric acid, cover with watch glass or glass plate and slightly heated to dissolve the selenium. Glass (plate) is removed, washed with water, and carefully evaporate the solution in a warm place until the wet residue (preferably a water bath).
Pour 30−35 cmof hydrochloric acid, 60−80 cm
of 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 (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 15−20 cmof hydrochloric acid and 1 cm
of nitric acid and heated in a water bath to dissolve the residue. To the obtained solution poured 80−100 cm
of hot water and add 4−4,5 g of urea, then do as mentioned in paragraph 2.3.
2.
2.3.2. Determination of selenium with the mass fraction of over 99.5% of
A portion of the selenium mass of 0.1 g was placed in a conical flask with a capacity of 250 cm, add 10−15 cm
of hydrochloric acid and 1 cm
of nitric acid, cover with watch glass or glass plate and slightly heated to dissolve the selenium.
Glass (plate) is removed, washed with water, add 80−100 cmof hot water, 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. The solution was poured 20−25 cmof sulfuric acid solution (1:1) and cooled.
Titrated with sodium thiosulfate, adding it while mixing, gradually, in small portions to 21−23 cm. Then pour 2−3 cm
of potassium iodide, 2 to 3 cm of
starch solution and continue the titration (from microburette) liberated iodine with sodium thiosulfate until the disappearance of blue colors
I.
2.4. Processing of the results
2.4.1. Mass fraction of selenium () in percent is calculated by the formula
where is the titre of sodium thiosulfate on selenium, g/cm
;
— the volume of sodium thiosulfate consumed in the titration, cm
;
— weight of selenium,
2.4.2. The discrepancy between the largest and smallest results of the three parallel determinations should not exceed 0.4%; the results of two analyses obtained in different laboratories is 0.5%.
(Changed edition, Rev. N 1).
3. GRAVIMETRIC METHOD FOR THE DETERMINATION OF SELENIUM
3.1. The essence of the method
The method is based on the reaction of the deposition of selenium in hydrochloric acid hydroxylamine and weighing the resulting precipitate elemental selenium.
3.2. Equipment, reagents
Drying oven laboratory.
Crucibles filter type ТФ32-PORT 16 according to GOST 25336−82.
Nitric acid GOST 4461−77.
Hydrochloric acid by the GOST 3118−77 and a solution of 1:8.
Hydroxylamine hydrochloride according to GOST 5456−79.
The technical rectified ethyl alcohol GOST 18300−87.
Urea according to GOST 6691−77, a solution of 300 g/DM.
(Changed edition, Rev. N 1).
3.3. Analysis
A portion of selenium with a mass of 0.5 g was placed in a conical flask with a capacity of 250 cm, 50−55 cm poured
hydrochloric acid, 5−7 cm
of 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 a specified time add 1−2 cm
of nitric acid. If not there will be a release of gaseous nitrogen, the decomposition is complete. Otherwise, the newly added 1−2 cm
of nitric acid and incubated the solution for 1−2 hours
Then pour the 50−60 cmof water, stirred and the insoluble residue is filtered through a dense filter with filtrowanie ground. Washed 5−6 times with hot water.
The filtrate with washings collected in a conical flask with a capacity of 500 cm.
Bring the filtrate volume to 180−200 cm, 30−35 cm add
urea solution, heated to boiling and poured 40−50 cm
of hydrochloric acid 30−35 cm
of 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 by adding to the solution 5−10 cmof 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 5−6 times with hot water, 2−3 times with alcohol.
The crucible with the precipitate is placed in a drying Cabinet and dried at 105−110 °C for 1 h. Cool in a desiccator and weighed. Drying and weighing of the precipitate is repeated to produce a constant
mass.
3.4. Processing of the results
3.4.1. Mass fraction of selenium () in percent is calculated by the formula
where is the mass of the crucible with the precipitate of selenium, g;
— weight of crucible, g;
— weight of selenium,
3.4.2. Discrepancies in the results of analysis according to claim
(Changed edition, Rev. N 1).
3.4.3. The differences in the assessment of mass fraction of selenium used titrimetric method (sect.2).
(Added, Rev. N 1).
