GOST 19251.2-79

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  ГОСТ 19251.2-79

GOST 19251.2−79 (ISO 713−75, ISO 1054−75) Zinc. Method for the determination of lead and cadmium (with Amendments No. 1, 2, 3)

GOST 19251.2−79
(ISO 713−75,
ISO 1054−75)

Group B59

STATE STANDARD OF THE USSR

ZINC

Method for the determination of lead and cadmium

Zinc. Method of cadmium and lead determination

AXTU 1709

Date of introduction 1980−01−01

INFORMATION DATA

1. DEVELOPED AND INTRODUCED by the Ministry of nonferrous metallurgy of the USSR

DEVELOPERS

V. I. Lysenko, L. I. Maksay, R. D. Cohen, V. A. Kolesnikov, N. Romanenko, R. A. Pestova

2. APPROVED AND put INTO EFFECT by Decision of the USSR State Committee for standards from 09.08.79 N 3077

3. Change No. 3 adopted by the Interstate Council for standardization, Metrology and certification (Protocol № 7 from 26.04.95)

The adoption voted:

4. The standard fully conforms to the ISO standards 713−75, ISO 1054−75

5. INSTEAD 19251.2 GOST-73

6. REFERENCE NORMATIVE AND TECHNICAL DOCUMENTS

7. Limitation of actions taken by Protocol No. 4−93 of the Interstate Council for standardization, Metrology and certification (ICS 4−94)

8. REPRINT (February 1998) with Amendments No. 1, 2, 3, approved in October 1984, April 1989, June 1996 (ICS 1−85, 7−89, 9−96)


This standard sets the polarographic method for the determination of lead (with a mass fraction of lead from 0.001 to 2.5%) and cadmium (at a mass fraction of cadmium from 0.0005 to 0.3%).

The method is based on the simultaneous polarographic determination of lead and cadmium in the acidic sodium chloride solution respectively at the potentials of half-minus and minus 0,47 0,67 versus the saturated calomel electrode.

The sensitivity of the method for determination of lead on the oscilloscope polarography 0.08 mg/DM, variable-current — 0.04 mg/DM, the sensitivity of the detection of cadmium on the oscilloscope polarography 0.05 mg/DM, variable-current — 0.02 mg/DM.

For the mass concentration of cadmium in excess of 0.01% is allowed polarographically cadmium chloride-ammonia background at the half-wave potential of minus 0.85 and In relation to the saturated calomel electrode.

The standard fully conforms to the ISO standards and ISO 713−75 1054−75.

(Changed edition, Rev. N 2).

1. GENERAL REQUIREMENTS

1.1. General requirements for method of analysis and security requirements — according to GOST 19251.0.

(Changed edition, Rev. N 1).

2. APPARATUS, REAGENTS AND SOLUTIONS

Polarography oscillographic or polarograph AC.

Nitric acid according to GOST 4461, diluted 1:3.

Hydrochloric acid according to GOST 3118 and diluted 2:1.

Hydrogen peroxide according to GOST 10929.

Hydrazine dihydrochloride according to GOST 22159 or sodium posterolaterally according to GOST 200.

Sodium chloride according to GOST 4233, does not contain lead and a solution of 200 g/DM, in a flask with a capacity of 2 DMare placed 400 g of sodium chloride, add 10 cmof hydrochloric acid, adjusted to a volume of 2 DMwater and stirred.

Background electrolyte: in a flask with a capacity of 2 DMare placed 400 g of sodium chloride, 10 g of hydrazine dihydrochloride, poured 10 cmof hydrochloric acid, dilute with water to volume of 2 DMand mixed.

Allowed the use of a background electrolyte of the following composition: a bottle with a capacity of 2 DMwas placed 500 g of sodium chloride, 10 g of sodium phosphonoacetate, pour 7 cmof hydrochloric acid, dilute with water to volume of 2 DMand mixed.

Lead of C1 grade according to GOST 3778*.
_______________
* Valid GOST 3778−98. — Note the CODE.

Cadmium brand Кд0 according to GOST 1467.

Standard solutions of lead and cadmium.

Solution a: a sample of finely chopped lead weight 1,0000 g of cadmium of 0.2000 g placed in a beaker with a capacity of 1 DM, is dissolved by heating in 30 cmof nitric acid, diluted 1:3, and evaporated to dryness; pour 10 cmof hydrochloric acid and evaporated to dryness. Evaporation with 10 cmof hydrochloric acid repeated two more times. To the residue is added 600 cmof a solution of sodium chloride, heated to dissolve the salt, cooled, transferred to a volumetric flask with a capacity of 1 DM, adjusted to the mark with this same solution and mix.

1 cmstandard solution contains 1 mg lead and 0.2 mg of cadmium.

Solution B: sample of finely chopped lead mass 0,1000 g of 0.0500 g of cadmium is placed in a beaker with a capacity of 1 DM, is dissolved by heating in 30 cmof nitric acid, diluted 1:3, and further analysis is carried out as specified in the methodology preparation of standard solution A.

1 cmstandard solution B contains 0.1 mg of lead and 0.05 mg of cadmium.

Ammonia water according to GOST 3760.

Sodium sanitarily according to GOST 195.

Gelatin food according to GOST 11293, solution 5 g/DM.

A standard solution of cadmium: a portion of the cadmium mass 0,2500 g dissolved in 20 cmof nitric acid 1:3. Transferred to a volumetric flask with a capacity of 500 cm, was adjusted to the mark with water and mix.

1 cmof a standard solution of cadmium contains 0.5 mg of cadmium.

Calibration solutions of cadmium: in six conical flasks with a capacity of 100 cmis placed 2.5 cmof solution zinc chloride, 0; 0,2; 0,5; 1,0; 2,0 3.0 cm anda standard solution of cadmium 20 cmof hydrochloric acid and 0.5 cmof nitric acid, heat, add 15 cmof water and boil to remove oxides of nitrogen. Cooled and transferred to volumetric flasks with a capacity of 100 cm. Add 40 cmof ammonia, 0.5 g of sodium sulfite, 2.5 cmgelatin solution. Bring to mark with water and mix.

Calibration solutions of cadmium contain 0; 1,0; 2,5; 5; 10 and 15 mg/lof cadmium.

Zinc chloride according to GOST 4529 anhydrous.

Zinc purity 99.99%, metal powder or thin shavings.

The salt solution of zinc chloride containing 200 g/lof zinc prepared from zinc chloride or zinc.

Preparation of the solution of zinc chloride salt: 800 g of zinc chloride was placed in a flask with a capacity of 3 DMand dissolved with stirring in 500 cmof water, being careful (the solution is strongly heated). Add 20 cmof hydrochloric acid, 35−40 g of metallic zinc and stirred for 30 min. (cleaning of impurities of lead and cadmium). The solution was filtered through a glass filter No. 2 (the filter add about 2 g of zinc powder) without creating a vacuum. The filtrate collected in a flask with a capacity of 1 DM. 5 cmof the filtrate was evaporated and determine the lead and cadmium. When these elements are present in the solution, the filtrate is poured into a flask, which carried out the purification from impurities, add 10 cmof hydrochloric acid and treated with zinc again. After cleaning and filtering the zinc solution is diluted with water to a volume of 2 DMand mixed.

Preparation of the solution of zinc chloride from zinc metal: 400 g of zinc powder (shavings) is placed in a flask with a capacity of 3 DMand dissolved in 50 cmof hydrochloric acid, diluted 2:1, and then (at least reduce the rate of dissolution of zinc) is added in portions of 25−30 cmof concentrated hydrochloric acid with frequent stirring. On the dissolution of zinc consumed, about 1.2 DMhydrochloric acid. Once on the bottom of the flask will have about 25−30 grams of zinc, add 25−30 g of zinc powder, 20 cmof hydrochloric acid and continue cleaning until dissolved, approximately half of the zinc powder. The solution is filtered and checked for purity as described above. The filtrate was diluted to a volume of 2 DMwater.

Calibration solutions of lead and cadmium: 13 conical flasks with a capacity of 100 cmmeasured in accordance with the table.1 standard solutions A or B, a solution of zinc chloride and evaporated to a moist residue. Poured at 45−50 cm, background electrolyte, heated to dissolve the salts, cooled, transferred to volumetric flasks with a capacity of 200 cm, is diluted to the mark and the background electrolyte and stirred.

The contents of lead and cadmium in the calibration solutions are shown in table.1.

Table 1

Solutions 1−7 are used in the analysis of zinc, containing 0,02% or less of lead, 0.01% and less cadmium and solutions 8−13 — for the analysis of zinc with a high content of impurities. Calibration solutions of 1, 4 and 8 are control experiments with the reagents.

(Changed edition, Rev. N 2, 3).

3. ANALYSIS

3.1. The weight of zinc, selected depending on the mass fraction of lead and cadmium at the table.2, was placed in a conical flask with a capacity of 100−250 cm, is added in small portions appropriate amount of hydrochloric acid, diluted 2:1, and are dissolving at first without heating and then with heating. After dissolution of the sample add about 0.5 cmof hydrogen peroxide and evaporated to a moist residue.

Table 2

To the residue poured 25 or 50 cmbackground electrolyte, heated to dissolve the salts, cooled, transferred to a volumetric flask with a capacity of 50 or 100 cm(table.2), adjusted to labels of background electrolyte and stirred.

Simultaneously hold the control samples used reagents: in a conical flask with a capacity of 100 cmplaced at 12.5 cmof a solution of zinc chloride (for attachment 2,5000 g), 5 cm(for attachment 1,0000 g) or 2.5 cm(for attachment 0,5000 g) are poured, respectively, 60, 20 and 15 cmof hydrochloric acid, diluted 2:1, then 0.5 cmof hydrogen peroxide and evaporated until beginning crystallization of zinc chloride. To the residue poured 25 or 50 cmbackground electrolyte; heat to dissolve the salt, cooled, transferred to a volumetric flask with a capacity of 50 or 100 cm, as described above.

A portion of sample solution (similar to the control experiment) is poured into the polarographic cell and conduct polarography of lead and cadmium respectively at the potentials of half-minus and minus 0,67 0,47 In a relatively saturated calomel electrode and the optimal values of the current range. In similar conditions polarographic appropriate calibration solutions. Polarographically using polarography AC is carried out at a dripping period of mercury from the capillary of 1−2. 5 s and the optimal values of the current range.

From the values of the wave heights of the element is subtracted the value of the wave heights in the reference experiment and calculate the content of lead and cadmium.

(Changed edition, Rev. N 2,

3).

3.2. For the mass concentration of cadmium is less than 0.01% is allowed polarographically cadmium chloride-ammonia background. Suspension zinc weight 0,5000 g is placed in a conical flask with a capacity of 100 cm, carefully, in small portions, add 20 cmof hydrochloric acid and 0.5 cmof nitric acid and lead dissolution at first without heating and then with heating. After complete dissolution of the sample add 15 cmof water and boil to remove oxides of nitrogen. Cooled and transferred to volumetric flask with a capacity of 100 cm. Add 40 cmof ammonia, 0.5 g of sodium sulfite, 2.5 cmgelatin solution. Bring to mark with water and mix. The obtained solution was allowed to stand until precipitation of the hydroxide.

Part of the sample solution (control experience) is poured into the polarographic cell and polarographic cadmium in the minus half-wave potential of 0.85 In a relatively saturated calomel electrode at optimum values of current range. In similar conditions polarographic appropriate calibration solutions of cadmium. Polarographically using polarography AC is carried out at a dripping period of mercury from the capillary of 1−2. 5 s and the optimal values of the current range.

From the values of the wave heights of cadmium subtract the values of the wave heights in the reference experiment and calculate the content of cadmium.

(Added, Rev. N 2).

4. PROCESSING OF THE RESULTS

4.1. Mass fraction of lead or cadmium (), %, is calculated by the formula

,

where the wave height of the element in the sample solution, mm;

 — volume of the volumetric flask, cm;

 — the concentration of the element in the calibration solution, mg/DM;

 — wave height of the element in the calibration solution, mm;

 — weight of charge, g

.

4.2. The absolute values of the differences between the results of two parallel measurements (rate of convergence) and test results (a measure of reproducibility) with confidence probability of 0.95 does not exceed values of allowable differences specified in table.3.

Table 3

(Changed edition, Rev. N 2).