GOST 20996.4-82

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  ГОСТ 20996.4-82

GOST 20996.4−82 Selenium technical. Method for the determination of arsenic (with Amendments No. 1, 2)

GOST 20996.4−82*

Group B59

INTERSTATE STANDARD

SELENIUM TECHNICAL

Method for the determination of arsenic

Selenium. Method of arsenic 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. VIII

* 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 25.03.2015 N 170th St c 01.10.2015

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


This standard establishes photocolorimetric method for the determination of arsenic (in mass fraction of arsenic 0,002−0,06%).

The method is based on formation of yellow arsenic-molybdenum complex followed by reduction of its sulfate with hydrazine in acidic solution to arsenic-molybdenum blue and the measurement of the optical density of colored solution after prior separation of arsenic transport in the arsenic trichloride or by extraction with organic solvents.

1A. 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 1973−77 Reagents. Arsenious anhydride. Specifications

GOST 2156−76 Sodium bicarbonate. Specifications

GOST 3118−77 Reagents. Hydrochloric acid. Specifications

GOST 3765−78 Reagents. Ammonium molybdate. Specifications

GOST 4160−74 Reagents. Potassium bromide. 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 5841−74 Reagents. Hydrazine sulfate

GOST 6709−72 distilled Water. Specifications

GOST 18300−87 ethyl rectified technical. Specifications

GOST 20288−74 Reagents. The carbon tetrachloride. Specifications

GOST 20996.0−2014 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 5725−6-2003* 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

The accuracy of measuring the mass fraction of arsenic 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 measure of the accuracy, limits of repeatability and reproducibility of measurements of mass fraction of arsenic, at confidence probability P=0,95

Percentage

(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:

installation for the distillation of arsenic trichloride;

— spectrophotometer or photoelectrocolorimeter with all accessories necessary for measurements at a wavelength of 750 nm;

— laboratory drying oven with thermostatic control, ensuring the heating temperature up to 250 °C;

— scale special accuracy class according to GOST 24104;

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

— glasses-1−100 TCS-1−250 TCS according to GOST 25336;

glass hour;

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

— separating funnel VD-1−100 MS, VD-1−1000 TC GOST 25336;

— funnel In-36−80 TC GOST 25336.

When taking measurements, use the following products and solutions:

— sulfuric acid according to GOST 4204, diluted 1:1; 1:3 solution, the molar concentration of 12 mol/DM;

— ammonium molybdate according to GOST 3765, solution mass concentration of 10 g/lin sulfuric acid the molar concentration of 12 mol/DM(store in a plastic container);

— hydrazine sulfate according to GOST 5841, solution mass concentration of 1.5 g/DM;

— distilled water according to GOST 6709;

— nitric acid according to GOST 4461 and diluted 1:1;

recovery mixture;

— arsenious anhydride according to GOST 1973;

— solution of arsenic of known concentration;

— sodium hydroxide (sodium hydroxide) according to GOST 4328, solution mass concentration of 20 g/DM;

— potassium bromide according to GOST 4160;

— hydrochloric acid according to GOST 3118, diluted 3:1 and 1:1 (containing 0.1 mol of potassium iodide in 1 DMof the solution and purified from arsenic);

— carbon tetrachloride according to GOST 20288;

— potassium iodide according to GOST 4232;

— technical rectified ethyl alcohol according to GOST 18300;

— anhydrous sodium bicarbonate according to GOST 2156;

filters obestochennye [1] or similar;

— phenolphthalein [2].

(Changed edition, Rev. N 1, 2).

3A. PREPARATIONS FOR THE MEASUREMENTS

3A.1. When preparing a hydrochloric acid solution containing 0.1 mol of potassium iodide in 1 DMof the solution, arsenic, 500 cmof hydrochloric acid is placed in a separating funnel with a capacity of 1000 cm, add 25 cmof carbon tetrachloride and shaken for 2 min. the Organic layer is separated and discarded. To the aqueous solution add 25 cmof carbon tetrachloride and again shaken for 2 min; the organic layer discarded. Acid clean in a day of application.

3A.2. When preparing a restoration of a mixture to 25 cmof molybdate ammonium solution add 2.5 cmof hydrazine sulfate, the solution was transferred into a measuring flask with a capacity of 50 cm, made up to the mark with water and mix. Use freshly prepared mixture.

3A.3. To construct the calibration curve, prepare solutions of known arsenic concentrations.

In preparing the solution And the mass concentration of arsenic of 0.1 mg/cma portion of the arsenious anhydride weight 0,1320 g dissolved in low heat 2−3 cmof sodium hydroxide solution. Transfer the solution into a volumetric flask with a capacity of 100 cm, add 30 to 40 cmof water, 1−2 drops of phenolphthalein and sulfuric acid, diluted 1:3 prior to the bleaching solution. To the obtained solution are added 1 g of sodium bicarbonate, cooled, made up to the mark with water and mix.

In the preparation of a solution of mass concentration of arsenic is 0.01 mg/cma 10 cm aliquotof solution A is placed in a volumetric flask with a capacity of 100 cm (3), made up to the mark with water and mix. Solution use freshly prepared.

3A.4. Construction of calibration curve

Six glasses with a capacity of 100 cmeach placed 0; 2,0; 4,0; 6,0; 8,0; 10 cmof solution B, which corresponds to 0; 0,02; 0,04; 0,06; 0,08 and 0,1 mg of arsenic, is added from 3 to 5 cmof nitric acid and evaporated to dryness. To the resulting solution was added 35 to 40 cmof water, boil and continue the procedure as specified in 3.2 or 3.3. According to the obtained results build a calibration curve.

As a solution comparison, using a solution of «blank» experience.

Section 3A (Introduced later, Rev. N 2).

3. ANALYSIS

3.1. A portion of the selenium mass 0.5−2 g (depending on the mass fraction of arsenic) is placed in a beaker with a capacity of 250−300 cm, 15−30 cm pour thenitric acid, cover with watch glass (glass plate) and allowed to stand without heating until the cessation of the violent reaction of allocation of oxides of nitrogen.

Remove the glass (plate), wash water over the beaker and heat the resulting solution was evaporated to dryness. The glass with the remainder heated in a tile at a temperature of 280−290 °C to remove the selenium dioxide. For a more complete removal of selenium glass put on 5−7 minutes in the preheated to 300 °C muffle furnace (or in the oven). Pour 10−12 cmof sulphuric acid (1:1) and heated to release vapors of sulfuric acid. After cooling, wash the side of the Cup with water and again evaporate the solution to fumes of sulfuric acid.

To the resulting solution was added 25−30 cmof water and boil it. Cool and carry out the separation of the arsenic.

(Changed edition, Rev. N 1).

3.2. The resulting solution was transferred into a distillation flask (see drawing), wash the side of the Cup with water, transferring the washings to the distillation flask. Then the flask is placed a piece of pumice stone, added 2−2. 5 g of hydrazine, 0.5−1 g of potassium bromide and close the flask cap with the droplet separator. The other end of the nozzle connected to a water refrigerator. Drip through the funnel into the flask is poured 70−75 cmof hydrochloric acid (the volume of liquid should not be more than 120 cm).

In the receiver for the distillate is poured 10 cmof water. The flask with the solution heated to boiling and boil to reduce the liquid volume to 30−40 cm(to 60 cm tognattasolution).

The resulting distillate is transferred to a volumetric flask with a capacity of 100 cm, made up to the mark with water and mix.

3.3. To the solution obtained according to claim 3.1, add 1−1. 5 g of hydrazine, boil and leave for 10−15 minutes to coagulate the precipitate.

Filtered through a loose filter and washed 3−5 times with water. The filtrate is transferred to a separatory funnel with a capacity of 100−150 cm, pour three times the amount of hydrochloric acid containing 0.1 mol of potassium iodide, and 20−25 cmof carbon tetrachloride. Shake the contents of the funnel 2 min. After the separation of the liquids, the organic layer drained into another separatory funnel with a capacity of 100−150 cm.

The first separating funnel hydrochloric acid solution was poured 20−25 cmof solvent and shake for 2 minutes, the Second attached to the first extract to another separating funnel.

The combined extracts are washed twice with portions of 10 cmof hydrochloric acid (3:1), extragerea each time for 1 min. Then the extract is poured 15−20 cmof water and shake the contents of the funnel for 2 minutes the Extract is poured into another separatory funnel and repeat the Stripping of arsenic with 15−20 cmof water. The combined aqueous layers was placed in a volumetric flask with a capacity of 100 cm, made up to the mark with water and mix.

From the solution obtained, as indicated in the claims.3.2. and 3.3, selected aliquot part of 20−50 cmand placing it in a dry glass with a capacity of 100−150 cm, 5−10 cm pourednitric acid and gently evaporated to dryness for the final removal of residual nitric acid. Then the glass is put into an oven and kept at a temperature of 130−135 °C for 1 h.

To the dried residue is poured 35−40 cmof hot water, 4−4. 5 cmrecovery mixture is heated and boiled for 5 min. Solution was cooled and transferred to volumetric flask with a capacity of 50 cm, made up to the mark with water and mix.

Measure the optical density of the solution on the photoelectrocolorimeter, using a filter with maximum transmittance at a wavelength of 750 nm and cuvette thickness of the absorbing layer 30 or 50 mm (depending on the mass fraction of arsenic).

As a solution comparison solution is used in the reference experiment.

The mass of arsenic set by the calibration schedule.

(Changed edition, Rev. N 1).

3.4. (Deleted, Rev. N 2).

4. PROCESSING OF THE RESULTS

4.1. Mass fraction of arsenic , in percent calculated by the formula

,

where the quantity of arsenic 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).

Bibliography

________________
* Operate on the territory of the Russian Federation.

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

(Added, Rev. N 2).