GOST 20996.11-82

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  ГОСТ 20996.11-82

GOST 20996.11−82 Selenium technical. Method for the determination of mercury (Change No. 1)

GOST 20996.11−82*

Group B59

INTERSTATE STANDARD

SELENIUM TECHNICAL

Method for the determination of mercury

Selenium. Method of mercury 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. VI

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


This standard specifies the extraction-photometric method for the determination of mercury (in mass concentration of mercury of 0.0005−0.06 percent).

The method is based on substitution reactions of copper ions with ions of mercury, copper diethyldithiocarbamate and subsequent measurement of optical density at a wavelength of 410−420 nm.

1. GENERAL REQUIREMENTS

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

2. EQUIPMENT, REAGENTS, SOLUTIONS

Photoelectrocolorimeter.

a pH meter.

Nitric acid GOST 4461−77 and diluted 1:1.

Hydrochloric acid by the GOST 3118−77.

Hydrogen peroxide according to GOST 10929−76.

Ammonia water according to GOST 3760−79.

Hydroxylamine hydrochloride according to GOST 5456−79, a solution of 10 g/DM.

Copper sulfate 5-water according to GOST 4165−78.

Sodium acetate 3-water according to GOST 199−78, a solution of 500 g/DMand a solution of 0.2 mol/DM.

Potassium permanganate according to GOST 20490−75.

Acetic acid GOST 61−75, solution 0,2 mol/DM.

Sodium N, N-diethyldithiocarbamate according to GOST 8864−71, a solution of 10 g/DM.

Acetate buffer solution with a pH of 4.0: mixed 800 cm0.2 mol/DMsolution of acetic acid with 200 cmof 0.2 mol/DMsolution of sodium acetate, the pH of the solution at the set pH-meter.

Carbon tetrachloride according to GOST 20288−74.

Copper diethyldithiocarbamate solution: a sample of copper sulphate with a mass of 40 mg was dissolved in 50 cmof water and transferred to a separatory funnel with a capacity of 100−150 cm. Ammonia is added before the formation of the ammonia complex of copper (the colour change of the solution from blue to dark (blue). Pour 4.5 cmof a solution of sodium diethyldithiocarbamate, 20−25 cmof carbon tetrachloride and extracted 2 min. Extraction is repeated to produce a colorless extract. The organic layer is collected in another separating funnel and washed 2−3 times with water in portions of 30−40 cm, extragerea 1 min. a Solution of copper diethyldithiocarbamate was placed in a volumetric flask with a capacity of 500 cm, made up to the mark with carbon tetrachloride and stirred. The resulting solution was transferred into a bottle made of dark glass.

The working solution of the reagent prepared on the day of use ten-fold dilution of the basic solution by carbon tetrachloride.

Sulfuric acid GOST 4204−77 and diluted 1:1.

Methyl orange, solution 10 g/DM.

Mercury GOST 4658−73.

Standard solutions of mercury.

Solution a: a portion of metallic mercury with a mass of 0.1 g dissolved in 20−25 cmof nitric acid (1:1), boiled for 2−3 min to remove the oxides of nitrogen. Cool, add 20−30 cmof water, boil and cool again, transfer the solution into a measuring flask with volume capacity of 1000 cm, 40−45 cm pourednitric acid (boiled to remove oxides of nitrogen), made up to the mark with water and mix.

1 cmof solution A contains 0.1 mg of mercury.

Solution B: take aliquot part 10 cmof solution A and transfer it into a volumetric flask of 100 cm, made up to the mark with water and mix. The solution is stable for 2 days.

1 cmof a solution contains 0.01 mg of mercury.

(Changed edition, Rev. N 1).

3. ANALYSIS

3.1 a Suspension of selenium by weight of 0.5−2 g (depending on the mass fraction of mercury) is placed in a low glass with a capacity of 200−250 cm, 10−20 cm pour thenitric acid, cover with watch glass (glass plate) and placed in a water bath. Heated for 10 min. Then, opening glass (plate), pour 3−5cmof hydrochloric acid and heating was continued for another 7−10 min.

Remove the glass (plate) wash it with water over a Cup, poured 20−25 cmof hot water kept in a water bath for 5 min and cooled. Filtered in a volumetric flask with a capacity of 50 or 100 cm, made up to the mark with water and mix. Leave for 1 hour

3.2. A portion of the selenium mass 0.5−2 g was placed in a conical flask with a capacity of 250−300 cm, 10−15 cm pour thenitric acid and dissolve in low heat for 5−10 min. Then added 1−1. 5 g of potassium permanganate, 5−10 cmof sulphuric acid (1:1) and heated to release vapors of sulfuric acid. Cool, dilute with water to 30−40 cm, add 3−4 drops of hydrogen peroxide and boiled until the destruction of excess peroxide.

Cool and transfer the solution into volumetric flask with a capacity of 50 or 100 cm, made up to the mark with water and mix.

3.3. Select 5−25 cmof a solution obtained as indicated in claim 3.1 or 3.2, is placed in a separating funnel with a capacity of 100−150 cm. Add 2−3 drops of methyl orange and neutralize with a solution of sodium acetate and 500 g/DMbefore the solution colour from red to yellow. Diluted to 50 cm, acetate buffer solution and a flow of 20−30 cmworking solution of diethyldithiocarbamate copper. Extracted within 2 min. Drained the organic layer into a dry beaker and after 20 minutes, measure the optical density of the solution on the photoelectrocolorimeter, using a filter with maximum transmittance at a wavelength of 413 nm and cuvette thickness of the absorbing layer is 50 mm. Solution comparison the solution serves as the reference experiment.

The amount of mercury found by the calibration schedule.

(Changed edition, Rev. N 1).

3.4. Construction of calibration curve.

In seven separating funnels with a capacity of 100−150 cmis placed 0; 0,5; 1,0; 2,0; 3,0; 4,0; 5,0 cmstandard solution B, which corresponds to 0; 0,005; 0,01; 0,02; 0,03; 0,04; 0,05 mg of mercury and further analysis is carried out as specified in clause 3.3. Solution comparison is the solution, do not contain mercury. The difference of light absorption of a solution of the reagent to be analyzed corresponds to the weakening of the absorption caused by ions of mercury.

4. PROCESSING OF THE RESULTS

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

,

where  — the amount of mercury 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. Discrepancies in the results of two parallel measurements and the two tests should not exceed the values given in the table.