GOST 20996.8-82

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  ГОСТ 20996.8-82

GOST 20996.8−82 Selenium technical. Method for the determination of copper (with Amendments No. 1, 2)

GOST 20996.8−82*

Group B59

INTERSTATE STANDARD

SELENIUM TECHNICAL

Method for determination of copper

Selenium. Method of copper 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. IV

* 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 17.02.2015 N 45 St c 01.11.2016

Change No. 2 made by the manufacturer of the database in the text IUS N 5, 2016


This standard sets the photometric method for the determination of copper (at a mass fraction of copper 0,001−0,06%).

The method is based on reaction of formation of colored complex compounds of copper ions with diethyldithiocarbamate lead, and then measure optical density at a wavelength of 420−440 nm.

(Changed edition, Rev. N 1).

1A. NORMATIVE REFERENCES

The present standard features references to the following international standards:

GOST 859−2014 Copper. Brand

GOST 1770−74 (ISO 1042−83, ISO 4788−80) Glassware volumetric laboratory glass. Cylinders, beakers, flasks, test tubes. General specifications

GOST 3118−77 Reagents. Hydrochloric acid. Specifications

GOST 3760−79 Reagents. The aqueous ammonia. Specifications

GOST 4147−74 Reagents. Iron (III) chloride 6-water. Specifications

GOST 4204−77 Reagents. Sulphuric acid. Specifications

GOST 4461−77 Reagents. Nitric acid. Specifications

GOST 6709−72 distilled Water. Specifications

GOST 20015−88 Chloroform. 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 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 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 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.

1B. CHARACTERISTICS OF INDICATORS OF MEASUREMENT ACCURACY

The accuracy of the measurements the mass fraction of copper 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 indicator of measurement accuracy, limits of repeatability and reproducibility of measurements of mass fraction of copper, at confidence probability P=0,95

Percentage

Sections 1A-1B (Introduced later, 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:

— spectrophotometer or photoelectrocolorimeter with all accessories necessary for measurements at a wavelength of from 420 to 440 nm;

— scale special accuracy class according to GOST 24104;

— volumetric flasks 2−50−2, 2−100−2, 2−1000−2 according GOST 1770;

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

glass hour;

slab heating [1], providing temperature up to 400 °C or equivalent;

— separating funnel VD-1−250 TC GOST 25336;

pipettes not lower than 2nd accuracy class according to GOST and GOST 29169 29227.

When taking measurements, use the following products and solutions:

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

— distilled water according to GOST 6709;

— nitric acid according to GOST 4461;

— hydrochloric acid according to GOST 3118, diluted 3:1 and 1:1;

— ammonia water according to GOST 3760;

— iron chloride according to GOST 4147, solution mass concentration of 100 g/lin hydrochloric acid, diluted 3:1;

— chloroform according to GOST 20015;

— copper according to the GOST 859;

— diethyldithiocarbamate, lead (II) by [2], solution mass concentration of 0.5 g/lin chloroform;

paper universal indicator [3].

(Changed edition, Rev. N 1, 2).

3A. PREPARATIONS FOR THE MEASUREMENTS

3A.1. In the preparation of a solution of lead diethyldithiocarbamate (II) the mass concentration of 0.5 g/lin chloroform: 0.5 g of salt is placed in a measuring flask with volume capacity of 1000 cm, add от200 up to 300 cmof chloroform, and stirred to dissolve the sample. Dilute with chloroform to the mark and mix again. The solution was stored in a dark place in the flask of dark glass.

3A.2. For construction of calibration curve prepare solutions of known copper concentration

In preparing the solution And the mass concentration of copper is 0.1 mg/cma sample of copper with a mass 0,1000 g dissolved in 5−8 cmof nitric acid, the solution evaporated to small volume, poured from 20 to 25 cmof sulphuric acid diluted 1:1, the solution is evaporated to release vapors of sulfuric acid. Cooled, poured 40 to 50 cmof water and transfer the solution into a measuring flask with volume capacity of 1000 cm, made up to the mark with water and mix.

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

3A.3. Construction of calibration curve

In seven separating funnels, capacity 250 cmeach, placed 0; 0,5; 1,0; 2,0; 3,0; 4,0; 5,0 cmof solution B, which corresponds to 0; 0,005; 0,01; 0,02; 0,03; 0,04 and 0.05 mg of copper. Add 0.5 cmof ferric chloride, from 50 to 60 cmof water and then spend analysis 3.1. As a solution comparison, using a solution not containing copper.

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

3. ANALYSIS

3.1. A portion of selenium by weight 0.2−1 g (depending on the mass fraction of copper) is placed in a beaker with a capacity of 250−300 cm, add 15−20 cmof nitric 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. It is then heated and evaporated to dryness. Kept dry the rest on the stove for 8−10 minutes, the Operation is repeated two more times adding each time 5−7 cmof nitric acid and evaporating the residue.

To the dry residue add 5−7 cmof hydrochloric acid, heated to dissolve the salts, add 30−40 cmof water, boil, cool and transfer the solution into volumetric flask with a capacity of 100 cm. Top up with water to the mark and mix.

Select aliquot part of the solution is 20−50 cmand transfer it into separating funnel with a capacity of 150−200 cm, neutralized with ammonia until a light turbidity of iron hydroxide, which is dissolved in 3−4 drops of hydrochloric acid (1:1) install the 3−4 pH using universal indicator paper. If in the analyzed solution of iron enough to aliquote parts add 0.5 cmof a solution of ferric chloride and carry out the operation indicated above.

It is neutralized with a separating funnel, the solution is poured 10 cmof a solution of lead diethyldithiocarbamate and shake vigorously 2 min. After the separation of the liquid layer of chloroform is poured into a measuring flask with a capacity of 50 cm, and to the aqueous solution in a separating funnel, poured 10 cmof lead diethyldithiocarbamate and extraction repeated.

If the chloroform layer is yellow in color, the extraction was repeated with 5 cmof the reagent. All extracts collected in a volumetric flask with a capacity of 50 cm, add chloroform to the mark and mix.

The optical density is measured on photoelectrocolorimeter, using a filter with maximum transmittance at a wavelength of 420 nm and cuvette thickness of the absorbing layer is 20 mm.

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

Mass of copper found by the calibration schedule.

(Changed edition, Rev. N 1).

3.2. (Deleted, Rev. N 2).

4. PROCESSING OF THE RESULTS

4.1. Mass fraction of copper in percent is calculated by the formula

,

where the amount of copper 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 (paragraph 5.5.3).

(Added, Rev. N 2).

Bibliography

(Added, Rev. N 2).