STATE STANDARD OF THE UNION OF THE SSR

SOILS

Methods for determining the sulfate ion in water extract

GOST 26426-85

Moscow 1985

DEVELOPED by the Ministry Agriculture USSR

PERFORMERS: L. M. Derzhavin, S.G. Samokhvalov, N.V. Sokolova, V.G. Prizhukova, A.A. Shaimukhametova, A.L. Erinov, L.E. Luchkina, V.L. Konkina, N.G. Pankova, N.V. Vasilevskaya, A.P. Pleshkova, T.A. Yakovleva, T.S. Gruzdeva, N.A. Chebotareva, L.I. Molkanova, O.V. Soboleva, G.K. Kondratiev

INTRODUCED by the Ministry of Agriculture of the USSR

Deputy Minister N.F. Tatarchuk

APPROVED AND INTRODUCED BY Decree State Committee USSR according to the standards of February 8, 1985 No. 283.

STATE STANDARD OF THE UNION OF THE SSR

By the Decree of the USSR State Committee for Standards dated February 8, 1985 No. 283, the validity period was established

c 01.01.86
until 01.01.96

This standard establishes methods for determining the sulfate ion in the water extract from saline soils when conducting soil, agrochemical, reclamation surveys of lands, monitoring the state of the salt regime of soils, as well as during other survey and research work.

The total relative error is:

for the weight method

10% - for the number of equivalents of the sulfate ion St. 1 to 3 mmol in 100 g of soil; 5% - St. 3 mmol in 100 g of soil;

for turbidimetric method

10% - for the number of equivalents of the sulfate ion St. 0.5 yes 3 mmol in 100 g of soil; 7.5% - St. 3 mmol in 100 g of soil.

1. WEIGHT DETERMINATION OF THE SULPHATE ION

The essence of the method is the precipitation of the sulfate ion with a solution of barium chloride and weighing the calcined residue. To prevent the precipitation of carbonate, barium phosphate and other compounds, the analyzed sample is acidified with hydrochloric acid.

1.1. Sampling method

1.1.1. Sampling method - by GOST 26423-85.

1.2. Equipment, materials and reagents

1.2.1. For analysis use:

laboratory scales of the 2nd accuracy class with the highest weighing limit of 200 g according to GOST 24104 -80;

dispensers with a dosing error of not more than 1% or pipettes of the 2nd accuracy class according to GOST 20292-74;

muffle furnace, providing a heating temperature of 700-750ºС;

water bath;

electric stove;

glass funnels according to GOST 25336-82;

desiccator with calcined calcium chloride;

chemical glasses with a capacity of 100 cm 3 according to GOST 25336-82;

porcelain cups;

porcelain crucibles;

watch glasses;

glass sticks;

GOST 1770-74 ;

barium chloride 2-water according to GOST 4108-72, x. h. or h. d. a., solution with mass fraction 10 %;

hydrochloric acid according to GOST 3118-77, x. h. or h. d. a., diluted with distilled water in a ratio of 1:3 and 1:100;

sulfuric acid according to GOST 4204-77, x. h. or h. d. a., solution with a mass fraction of 10%;

methyl red, indicator, analytical grade, solution prepared according to GOST 4919.1-77;

ashless filters "blue tape" with a diameter of 7 cm;

water distilled to GOST 6709-72.

1.3. Conducting an analysis

1.3.1. Preparation of an extract from the soil

GOST 26423-85.

1.3.2. Determination of the sulfate ion

20 cm 3 of the analyzed extract are taken with a dispenser or pipette into a beaker. Distilled water is added to the sample to a total solution volume of 40-50 cm 3, 3 drops of methyl red solution and acidified with hydrochloric acid diluted 1:3 to an acidic reaction, adding an excess of acid in 3-4 drops. If at the same time the solution becomes cloudy, it is filtered through an ash-free filter into a clean beaker. The filter is washed with hydrochloric acid, diluted 1:100, in three portions of 3-5 cm 3 .

When analyzing dark-colored extracts, the sample is placed in a porcelain dish, evaporated to dryness in a water bath, and calcined in muffle furnace for 2 hours at a temperature of 700°C. After cooling, the calcined residue is moistened with 1 cm 3 diluted 1:3 of hydrochloric acid and evaporate the acid to dryness on a water bath. The residue is dissolved by heating in dilute 1:100 hydrochloric acid and the solution is filtered into a clean beaker through an ash-free filter. Wash the dish and filter with dilute 1:100 hydrochloric acid to bring the volume of the filtrate to 40-50 cm 3 .

A glass with a diluted and acidified sample of the extract is heated to a boil. To the hot solution, add dropwise 5 cm 3 of a solution of barium chloride with a mass fraction of 10%, thoroughly mixing the solution with a stick after adding each drop. The beaker is covered with a watch glass and placed in boiling water. water bath for 2-3 hours to settle the sediment.

Then make a test for the completeness of precipitation of barium sulfate. To do this, a few drops of barium chloride solution with a mass fraction of 10% are poured into a transparent settled solution along the glass wall. If turbidity forms near the wall, another 3 cm 3 of barium chloride solution is added to the solution, heated to a boil and the precipitate is allowed to settle. Then start filtering. The precipitate on the filter is washed with hot distilled water, acidified with hydrochloric acid, until the reaction to barium stops (solution of sulfuric acid with a mass fraction of 10%).

The filter with the precipitate is dried on a funnel, placed in a porcelain crucible weighed with an error of not more than 0.001 g, and placed in a cold muffle furnace. The precipitate is calcined for 30 min at a temperature of 700-750°C (at temperatures above 800°C the precipitate decomposes). Then the crucible is cooled in a desiccator and weighed with an error of no more than 0.001 g. To achieve a constant weight, the precipitate is ignited again for 20 minutes at the same temperature.

In the same way, a blank experiment is carried out, taking instead of a sample of the extract 20 cm 3 of distilled water.

It is allowed to increase up to 50 cm 3 or decrease to 5 cm 3 the volume of the extract sample, provided that the mass of the formed precipitate of barium sulfate is 20-200 mg.

1.4. Results processing

1.4.1. The number of sulfate ion equivalents (X), mmol per 100 g of soil, is calculated by the formula:

,

where m- mass of barium sulfate precipitate, mg;

m 1 - the result of a blank determination, mg;

500 - conversion factor per 100 g of soil;

116.7 - molar mass of barium sulfate equivalent, mg/mmol;

V- extract sample volume, cm 3 .

X 1 ) as a percentage is calculated by the formula:

where FROM- the amount of sulfate ion equivalent in the soil, mmol per 100 g;

0.048 - conversion factor to percent.

The result of the analysis is taken as the value of a single determination of the sulfate ion.

The result of the analysis is expressed in millimoles per 100 g of soil and as a percentage rounded to three significant figures.

1.4.2. Permissible relative deviations at a confidence level R\u003d 0.95 of the arithmetic mean of the results of repeated analyzes with selective statistical control are:

14% - for the number of equivalents of the sulfate ion St. 1 to 3 mmol in 100 g of soil; 7% - St. 3 mmol in 100 g of soil.

2. TURBIDIMETRIC DETERMINATION OF THE SULPHATE ION

The essence of the method lies in the precipitation of the sulfate ion with barium chloride and its turbidimetric determination in the form of barium sulfate. Polyvinyl alcohol or glycerin is used as a suspension stabilizer.

The method is not applicable to the analysis of aqueous extracts stained with organic matter.

2.1. Sampling method

2.1.1. Sampling method - by GOST 26423-85.

2.2. Equipment, materials and reagents

2.2.1. For analysis use: photoelectric colorimeter;

laboratory scales of the 2nd class of accuracy with the highest weighing limit of 200 g and of the 4th class of accuracy with the highest weighing limit of 500 g according to GOST 24104 -80;

dispensers with a dosing error of not more than 1% or pipettes and burettes of the 2nd accuracy class according to GOST 20292-74;

glass test tubes with a diameter of 16 mm and a capacity of at least 15 cm 3 according to GOST 25336-82;

measuring laboratory glassware of the 2nd class of accuracy according to GOST 1770-74 ;

barium chloride 2-water according to GOST 4108-72, x. h. or h. d. a .;

hydrochloric acid according to GOST 3118-77, x. h. or h. d. a., concentration solution With( HCl) \u003d 1 mol / dm 3;

polyvinyl alcohol, analytical grade, or glycerin according to GOST 6259-75, analytical grade;

sodium sulfate anhydrous according to GOST 4166-76, x. hours; sodium hydroxide according to GOST 4328-77, analytical grade, solution with a mass fraction of 0.5%;

disodium salt ethylenediamine- N, N, N", N "-tetraacetic acid, 2-aqueous (trilon B) according to GOST 10652-73, analytical grade;

water distilled to GOST 6709-72.

2.3. Preparation for analysis

2.3.1. Preparing a stock precipitating solution with polyvinyl alcohol

5 g of polyvinyl alcohol and 20 g of barium chloride are weighed with an error of not more than 0.1 g and placed in a heat-resistant glass beaker with a capacity of 1000 cm 3 . Pour about 800 cm 3 of distilled water, 60 cm 3 of a solution of hydrochloric acid with a concentration of 1 mol / dm 3 and heat the mixture with stirring until the reagents are completely dissolved. After cooling, the solution is transferred into a volumetric flask with a capacity of 1000 cm 3 , the volume is adjusted to the mark with distilled water, mixed and filtered. The solution is stored in a bottle with a ground stopper for no more than 3 months. In case of turbidity, formation of flakes, sediment, the solution is replaced with a freshly prepared one.

2.3.2. Preparation of a working precipitating solution with polyvinyl alcohol

On the day of analysis, the stock precipitating solution is diluted 2:1 with distilled water.

2.3.3. Preparation of a precipitating solution with glycerol

Weigh 20 g of barium chloride with an error of not more than

0.1 g and placed in a volumetric flask with a capacity of 500 cm 3 . Approximately 300 cm 3 of distilled water and 60 cm 3 of hydrochloric acid with a concentration of 1 mol / dm 3 are poured. After complete dissolution of barium chloride, the volume of the solution is adjusted to the mark with distilled water and mixed. The prepared solution is mixed with glycerol in a ratio of 1:1. The solution is stored for no more than 3 months.

2.3.4.

14.2 g of anhydrous sodium sulfate, dried to constant weight at a temperature of 100-105 ° C, weighed with an error of not more than 0.1 g, placed in a volumetric flask with a capacity of 1000 cm 3 and dissolved in distilled water, bringing the volume of the solution to the mark. The prepared solution is thoroughly mixed. The solution is stored in a flask with a ground stopper, not more than 1 g.

2.3.5. Preparation of reference solutions

In volumetric flasks with a capacity of 100 cm 3, the volumes of the solution prepared according to the table are placed. The volumes of the solutions are adjusted to the mark with distilled water and mixed thoroughly. Solutions are stored in vials with ground stoppers for no more than 1 month.

Reference solutions are used to calibrate the photoelectric colorimeter on the day of analysis.

2.3.6. Preparation of an alkaline solution of Trilon B

30 g of Trilon B, weighed with an error of not more than 0.1 g, is dissolved in 1000 cm 3 of sodium hydroxide solution with a mass fraction of 0.5%.

The solution is used to wash the cuvettes of the photoelectric colorimeter and test tubes in which the determination is carried out. The cuvettes and test tubes are placed in the solution for 1 hour.

2.4. Conducting an analysis

2.4.1. Preparation of an extract from the soil

For analysis, filtrates of extracts prepared according to GOST 26423-85.

2.4.2. Determination of the sulfate ion

1 cm 3 of the analyzed extracts and reference solutions are taken with a dispenser or pipette into test tubes. 10 cm 3 of the working precipitating solution prepared according to or is added to the samples with a dispenser or from a burette and thoroughly mixed. Suspension photometry is carried out no earlier than 10 minutes after the addition of the precipitating solution, in a cuvette with a translucent layer thickness of 10 mm relative to reference solution No. 1, at a wavelength of 520 nm or using a light filter with a maximum transmission in the region of 500-540 nm. Shake the contents of the test tube before placing it into the photoelectric colorimeter cuvette. The suspension is optically stable for 7 hours.

A proportional change in the volumes of the extract sample, reference solutions and precipitating solution is allowed with a dosing error of not more than 1%.

2.5. Results processing

2.5.1. Based on the results of photometry of reference solutions, a calibration graph is built. On the abscissa axis, the concentrations of sulfate ions in reference solutions are plotted in terms of millimoles per 100 g of soil, and on the ordinate axis, the corresponding photoelectrocolorimeter readings are plotted.

The amount of sulfate equivalents in the analyzed soil is determined directly from the calibration curve. If the result of the determination is outside the calibration curve, the determination is repeated after diluting the extract with distilled water. The result found from the graph is increased as many times as the extract was diluted.

Mass fraction of sulfate ion in the analyzed soil (X) as a percentage is calculated by the formula:

where FROM- the number of sulfate ion equivalents in the analyzed soil, mmol per 100 g;

0.048 - conversion factor to percent.

The result of the analysis is taken as the value of a single determination of the sulfate ion.

The result of the analysis is expressed in millimoles per 100 g of soil rounded to the first decimal place and as a percentage rounded to the second decimal place.

2.5.2. Permissible relative deviations at a confidence level R\u003d 0.95 of the arithmetic mean of the results of repeated analyzes with selective statistical control are:

14% - For the number of equivalents of the sulfate ion St. 0.5 to 3 mmol in 100 g of soil;

10% - St. 3 mmol in 100 g of soil.

GOST 26426-85

Group C09

STATE STANDARD OF THE UNION OF THE SSR

Methods for determining the sulfate ion in water extract

soils. Methods for determination of sulphate ion in water extract

Valid from 01.01.86
until 01.01.96*
______________________________
* Expiry date removed
according to protocol N 5-94 of the Interstate Council
for standardization, metrology and certification
(IUS N 11-12, 1994). - Note "CODE".

DEVELOPED by the Ministry of Agriculture of the USSR

PERFORMERS

L.M.Derzhavin, S.G.Samokhvalov, N.V.Sokolova, V.G.Prizhukova, A.A.Shaimukhametova, A.L.Erinov, L.E.Luchkina, V.L.Konkina, N. G. Pankova, N.V. Vasilevskaya, A.P. Pleshkova, T.A. Yakovleva, T.S. Gruzdeva, N.A. Chebotareva, L.I. Molkanova, O.V. Soboleva, G.K. Kondratiev

INTRODUCED by the Ministry of Agriculture of the USSR

Deputy Minister N.F. Tatarchuk

APPROVED AND INTRODUCED BY Decree of the USSR State Committee for Standards of February 8, 1985 N 283


This standard establishes methods for determining the sulfate ion in the water extract from saline soils when conducting soil, agrochemical, reclamation surveys of lands, monitoring the state of the salt regime of soils, as well as during other survey and research work.

The total relative error is:

for the weight method

10% - for the number of equivalents of non sulfate cv. 1 to 3 mmol in 100 g of soil; 5% - St. 3 mmol in 100 g of soil;

for turbidimetric method

10% - for the number of equivalents of sulfate ion St. 0.5 to 3 mmol in 100 g of soil; 7.5% - St. 3 mmol in 100 g of soil.

1. WEIGHT DETERMINATION OF THE SULPHATE ION

The essence of the method is the precipitation of the sulfate ion with a solution of barium chloride and weighing the calcined residue. To prevent the precipitation of carbonate, barium phosphate and other compounds, the analyzed sample is acidified with hydrochloric acid.

1.1. Sampling method

1.1.1. Sampling method - by GOST 26423-85.

1.2. Equipment, materials and reagents

1.2.1. For analysis use:

laboratory scales of the 2nd accuracy class with the highest weighing limit of 200 g according to GOST 24104-80 ;

dispensers with a dosing error of not more than 1% or pipettes of the 2nd accuracy class according to GOST 20292-74;

a muffle furnace providing a heating temperature of 700-750 °C;

water bath;

electric stove;

glass funnels GOST 25336-82 ;

desiccator with calcined calcium chloride;

chemical glasses with a capacity of 100 cm GOST 25336-82 ;

porcelain cups;

porcelain crucibles;

watch glasses;

glass sticks;

GOST 1770-74 ;

barium chloride 2-aqueous GOST 4108-72

hydrochloric acid for GOST 3118-77, h.h. or analytical grade, diluted with distilled water in the ratio of 1:3 and 1:100;

sulfuric acid by GOST 4204-77, h.h. or analytical grade, solution with a mass fraction of 10%;

methyl red, indicator, analytical grade, solution prepared according to GOST 4919.1-77 ;

ashless filters "blue tape" with a diameter of 7 cm;

water distilled to GOST 6709-72.

1.3. Conducting an analysis

1.3.1. Preparation of an extract from the soil

GOST 26423-85.

1.3.2. Determination of the sulfate ion

With a dispenser or pipette, 20 cm3 of the analyzed extract are taken into a beaker. Distilled water is added to the sample to a total solution volume of 40-50 cm 3, 3 drops of methyl red solution and acidified with hydrochloric acid diluted 1:3 to an acidic reaction, adding an excess of acid in 3-4 drops. If at the same time the solution becomes cloudy, it is filtered through an ash-free filter into a clean beaker. The filter is washed with hydrochloric acid, diluted 1:100, in three portions of 3-5 cm.

When analyzing dark-colored extracts, the sample is placed in a porcelain cup, evaporated to dryness in a water bath, and calcined in a muffle furnace for 2 hours at a temperature of 700°C. After cooling, the calcined residue is moistened with 1 ml of dilute 1:3 hydrochloric acid and the acid is evaporated to dryness on a water bath. The residue is dissolved by heating in dilute 1:100 hydrochloric acid and the solution is filtered into a clean beaker through an ash-free filter. The dish and filter are washed with hydrochloric acid diluted 1:100, bringing the volume of the filtrate to 40-50 ml.

A glass with a diluted and acidified sample of the extract is heated to a boil. To the hot solution is added dropwise 5 cm3 of a solution of barium chloride with a mass fraction of 10%, thoroughly mixing the solution with a stick after adding each drop. The glass is covered with a watch glass and placed in a boiling water bath for 2-3 hours to settling the precipitate.

Then make a test for the completeness of precipitation of barium sulfate. To do this, a few drops of a solution of barium chloride with a mass fraction of 10% are poured into a transparent settled solution along the wall of the glass. If turbidity forms near the wall, another 3 cm3 of barium chloride solution is added to the solution, heated to a boil and the precipitate is allowed to settle. Then start filtering. The precipitate on the filter is washed with hot distilled water, acidified with hydrochloric acid, until the reaction to barium stops (solution of sulfuric acid with a mass fraction of 10%).

The filter with the precipitate is dried on a funnel, placed in a porcelain crucible weighed with an error of not more than 0.001 g, and placed in a cold muffle furnace. The precipitate is calcined for 30 minutes at a temperature of 700-750 °C (at temperatures above 800 °C the precipitate decomposes). Then the crucible is cooled in a desiccator and weighed with an error of no more than 0.001 g. To achieve a constant weight, the precipitate is ignited again for 20 minutes at the same temperature.

In the same way, a blank experiment is carried out, taking 20 cm3 of distilled water instead of an extract sample.

It is allowed to increase to 50 cm3 or decrease to 5 cm3 the volume of the extract sample, provided that the mass of the resulting barium sulfate precipitate is 20-200

1.4. Results processing

1.4.1. The number of sulfate ion equivalents (), mmol per 100 g of soil, is calculated by the formula

where is the mass of barium sulfate precipitate, mg;

- the result of a blank determination, mg;

500 - conversion factor per 100 g of soil;

116.7 - molar mass of barium sulfate equivalent, mg/mmol;

- extract sample volume, see

where is the amount of sulfate ion equivalent in the soil, mmol per 100 g;





The result of the analysis is expressed in millimoles per 100 g of soil and as a percentage rounded to three significant figures.

1.4.2. Permissible relative deviations at a confidence probability = 0.95 from the arithmetic mean of the results of repeated analyzes during selective statistical control are:

14% - for the number of equivalents of sulfate ion St. 1 to 3 mmol in 100 g of soil; 7% - St. 3 mmol in 100 g of soil.

2. TURBIDIMETRIC DETERMINATION OF THE SULPHATE ION

The essence of the method lies in the precipitation of the sulfate ion with barium chloride and its turbidimetric determination in the form of barium sulfate. Polyvinyl alcohol or glycerin is used as a suspension stabilizer.

The method is not applicable to the analysis of aqueous extracts stained with organic matter.

2.1. Sampling method

2.1.1. Sampling method - by GOST 26423-85.

2.2. Equipment, materials and reagents

2.2.1. For analysis use:

photoelectric colorimeter;

laboratory scales of the 2nd class of accuracy with the highest weighing limit of 200 g and of the 4th class of accuracy with the highest weighing limit of 500 g according to GOST 24104-80 ;

dispensers with a dosing error of not more than 1% or pipettes and burettes of the 2nd accuracy class according to GOST 20292-74;

glass test tubes with a diameter of 16 mm and a capacity of at least 15 cm GOST 25336-82 ;

measuring laboratory glassware of the 2nd class of accuracy according to GOST 1770-74 ;

barium chloride 2-aqueous GOST 4108-72, h.h. or analytical grade;

hydrochloric acid for GOST 3118-77, h.h. or analytical grade, concentration solution (HCl)=1 mol/dm;

polyvinyl alcohol, analytical grade, or glycerin according to GOST 6259-75, h.d.a.;

sodium sulfate anhydrous GOST 4166-76, chemically pure;

sodium hydroxide by GOST 4328-77, analytical grade, solution with a mass fraction of 0.5%;

disodium salt of ethylenediamine-N,N,N",N"-tetraacetic acid, 2-aqueous (trilon B) according to GOST 10652-73, h.d.a.;

water distilled to GOST 6709-72.

2.3. Preparation for analysis

2.3.1. Preparing a stock precipitating solution with polyvinyl alcohol

5 g of polyvinyl alcohol and 20 g of barium chloride are weighed with an error of not more than 0.1 g and placed in a glass of heat-resistant glass with a capacity of 1000 ml. stirring until complete dissolution of the reagents. After cooling, the solution is transferred into a volumetric flask with a capacity of 1000 ml, the volume is adjusted to the mark with distilled water, mixed and filtered. The solution is stored in a bottle with a ground stopper for no more than 3 months. In case of turbidity, formation of flakes, sediment, the solution is replaced with a freshly prepared one.

2.3.2. Preparation of a working precipitating solution with polyvinyl alcohol

On the day of analysis, the stock precipitating solution is diluted 2:1 with distilled water.

2.3.3. Preparation of a precipitating solution with glycerol

Weigh 20 g of barium chloride with an error of not more than 0.1 g and place in a volumetric flask with a capacity of 500 ml. Approximately 300 ml of distilled water and 60 ml of hydrochloric acid with a concentration of 1 mol / dm are poured. After complete dissolution of barium chloride, the volume of the solution is adjusted to the mark with distilled water and mixed. The prepared solution is mixed with glycerol in a ratio of 1:1. The solution is stored for no more than 3 months.

2.3.4. Preparation of a solution of sodium sulfate concentration (1/2 NaSO) = 0.2 mol / dm (0.2 N.)

14.2 g of anhydrous sodium sulfate, dried to constant weight at a temperature of 100-105 ° C, are weighed with an error of not more than 0.1 g, placed in a volumetric flask with a capacity of 1000 ml and dissolved in distilled water, bringing the volume of the solution to the mark. The prepared solution is thoroughly mixed. The solution is stored in a flask with a ground stopper, not more than 1 g.

2.3.5. Preparation of reference solutions

In volumetric flasks with a capacity of 100 cm3, the volumes of the solution prepared according to clause 2.3.4 indicated in the table are placed. The volumes of the solutions are adjusted to the mark with distilled water and mixed thoroughly. Solutions are stored in vials with ground stoppers for no more than 1 month.

Reference solutions are used to calibrate the photoelectric colorimeter on the day of analysis.

2.3.6. Preparation of an alkaline solution of Trilon B

30 g of Trilon B, weighed with an error of not more than 0.1 g, is dissolved in 1000 ml of sodium hydroxide solution with a mass fraction of 0.5%.

The solution is used to wash the cuvettes of the photoelectric colorimeter and test tubes in which the determination is carried out. The cuvettes and test tubes are placed in the solution for 1 hour.

2.4. Conducting an analysis

2.4.1. Preparation of an extract from the soil

For analysis, filtrates of extracts prepared according to GOST 26423-85.

2.4.2. Determination of the sulfate ion

With a dispenser or pipette, 1 cm3 of the analyzed extracts and reference solutions are taken into test tubes. Add 10 cm of the working precipitating solution prepared according to clause 2.3.2 or clause 2.3.3 to the samples with a dispenser or from a burette and mix thoroughly. Suspension photometry is carried out no earlier than 10 minutes after the addition of the precipitating solution, in a cuvette with a translucent layer thickness of 10 mm relative to reference solution N 1, at a wavelength of 520 nm or using a light filter with a maximum transmission in the region of 500-540 nm. Shake the contents of the test tube before placing it into the photoelectric colorimeter cuvette. The suspension is optically stable for 7 hours.

A proportional change in the volumes of the extract sample, reference solutions and precipitating solution is allowed with a dosing error of not more than 1%.

2.5. Results processing

2.5.1. Based on the results of photometry of reference solutions, a calibration graph is built. On the abscissa axis, the concentrations of sulfate ions in reference solutions are plotted in terms of millimoles per 100 g of soil, and on the ordinate axis, the corresponding photoelectrocolorimeter readings are plotted.

The amount of sulfate equivalents in the analyzed soil is determined directly from the calibration curve. If the result of the determination is outside the calibration curve, the determination is repeated after diluting the extract with distilled water. The result found from the graph is increased as many times as the extract was diluted.

The mass fraction of the sulfate ion in the analyzed soil () as a percentage is calculated by the formula

where is the number of sulfate ion equivalents in the analyzed soil, mmol per 100 g;

0.048 - conversion factor to percent.

The result of the analysis is taken as the value of a single determination of the sulfate ion.

The result of the analysis is expressed in millimoles per 100 g of soil rounded to the first decimal place and as a percentage rounded to the second decimal place.

2.5.2. Permissible relative deviations at a confidence probability = 0.95 from the arithmetic mean of the results of repeated analyzes during selective statistical control are:

14% - for the number of equivalents of sulfate ion St. 0.5 to 3 mmol in 100 g of soil; 10% - St. 3 mmol in 100 g of soil.

The text of the document is verified by:
official publication
Soils. Method for determining cationic-anionic
composition of the water extract: Sat. GOSTs. -
M.: Publishing house of standards, 1985

STATE STANDARD OF THE UNION OF THE SSR

SOILS

METHODS FOR THE DETERMINATION OF THE SULPHATE ION IN WATER EXTRACT

GOST 26426-85

Moscow 1985

DEVELOPED by the Ministry of Agriculture of the USSR

PERFORMERS: L.M. Derzhavin, S.G. Samokhvalov, N.V. Sokolova, V.G. Prizhukova, A.A. Shaimukhametova, A.L. Erinov, L.E. Luchkina, V.L. Konkina, N.G. Pankova, N.V. Vasilevskaya, A.P. Pleshkova, T.A. Yakovleva, T.S. Gruzdeva, N.A. Chebotareva, L.I. Molkanova, O.V. Soboleva, G.K. Kondratiev

INTRODUCED by the Ministry of Agriculture of the USSR

Deputy Minister N.F. Tatarchuk

APPROVED AND INTRODUCED BY Decree of the USSR State Committee for Standards of February 8, 1985 No. 283.

STATE STANDARD OF THE UNION OF THE SSR

By the Decree of the USSR State Committee for Standards dated February 8, 1985 No. 283, the validity period was established

from 01.01.86
until 01.01.96

This standard establishes methods for determining the sulfate ion in the water extract from saline soils when conducting soil, agrochemical, reclamation surveys of lands, monitoring the state of the salt regime of soils, as well as during other survey and research work.

The total relative error is:

for the weight method

10% - for the number of equivalents of the sulfate ion St. 1 to 3 mmol in 100 g of soil; 5% - St. 3 mmol in 100 g of soil;

for turbidimetric method

10% - for the number of equivalents of the sulfate ion St. 0.5 yes 3 mmol in 100 g of soil; 7.5% - St. 3 mmol in 100 g of soil.

1. WEIGHT DETERMINATION OF THE SULPHATE ION

The essence of the method is the precipitation of the sulfate ion with a solution of barium chloride and weighing the calcined residue. To prevent the precipitation of carbonate, barium phosphate and other compounds, the analyzed sample is acidified with hydrochloric acid.

1.1. Sampling method

1.1.1. Sampling method - according to GOST 26423-85.

1.2. Equipment, materials and reagents

1.2.1. For analysis use:

laboratory scales of the 2nd accuracy class with the highest weighing limit of 200 g according to GOST 24104-80;

dispensers with a dosing error of not more than 1% or pipettes of the 2nd accuracy class according to GOST 20292-74;

muffle furnace, providing a heating temperature of 700-750ºС;

water bath;

electric stove;

glass funnels according to GOST 25336-82;

desiccator with calcined calcium chloride;

chemical glasses with a capacity of 100 cm 3 according to GOST 25336-82;

porcelain cups;

porcelain crucibles;

watch glasses;

glass sticks;

measuring laboratory glassware of the 2nd accuracy class according to GOST 1770-74;

barium chloride 2-water according to GOST 4108-72, x. h. or h. d. a., solution with a mass fraction of 10%;

hydrochloric acid according to GOST 3118-77, x. h. or h. d. a., diluted with distilled water in a ratio of 1:3 and 1:100;

sulfuric acid according to GOST 4204-77, x. h. or h. d. a., solution with a mass fraction of 10%;

methyl red, indicator, analytical grade, solution prepared according to GOST 4919.1-77;

ashless filters "blue tape" with a diameter of 7 cm;

distilled water according to GOST 6709-72.

1.3. Conducting an analysis

1.3.1. Preparation of an extract from the soil

For analysis, filtrates of extracts prepared according to GOST 26423-85 are used.

1.3.2. Determination of the sulfate ion

20 cm 3 of the analyzed extract are taken with a dispenser or pipette into a beaker. Distilled water is added to the sample to a total solution volume of 40-50 cm 3, 3 drops of methyl red solution and acidified with hydrochloric acid diluted 1:3 to an acidic reaction, adding an excess of acid in 3-4 drops. If at the same time the solution becomes cloudy, it is filtered through an ash-free filter into a clean beaker. The filter is washed with hydrochloric acid, diluted 1:100, in three portions of 3-5 cm 3 .

When analyzing dark-colored extracts, the sample is placed in a porcelain cup, evaporated to dryness on a water bath, and calcined in a muffle furnace for 2 h at 700°C. After cooling, the calcined residue is moistened with 1 cm 3 of diluted 1:3 hydrochloric acid and the acid is evaporated to dryness on a water bath. The residue is dissolved by heating in dilute 1:100 hydrochloric acid and the solution is filtered into a clean beaker through an ash-free filter. Wash the dish and filter with dilute 1:100 hydrochloric acid to bring the volume of the filtrate to 40-50 cm 3 .

A glass with a diluted and acidified sample of the extract is heated to a boil. To the hot solution, add dropwise 5 cm 3 of a solution of barium chloride with a mass fraction of 10%, thoroughly mixing the solution with a stick after adding each drop. The glass is covered with a watch glass and placed in a boiling water bath for 2-3 hours to settling the precipitate.

Then make a test for the completeness of precipitation of barium sulfate. To do this, a few drops of barium chloride solution with a mass fraction of 10% are poured into a transparent settled solution along the glass wall. If turbidity forms near the wall, another 3 cm 3 of barium chloride solution is added to the solution, heated to a boil and the precipitate is allowed to settle. Then start filtering. The precipitate on the filter is washed with hot distilled water, acidified with hydrochloric acid, until the reaction to barium stops (solution of sulfuric acid with a mass fraction of 10%).

The filter with the precipitate is dried on a funnel, placed in a porcelain crucible weighed with an error of not more than 0.001 g, and placed in a cold muffle furnace. The precipitate is calcined for 30 min at a temperature of 700-750°C (at temperatures above 800°C the precipitate decomposes). Then the crucible is cooled in a desiccator and weighed with an error of no more than 0.001 g. To achieve a constant weight, the precipitate is ignited again for 20 minutes at the same temperature.

In the same way, a blank experiment is carried out, taking instead of a sample of the extract 20 cm 3 of distilled water.

It is allowed to increase up to 50 cm 3 or decrease to 5 cm 3 the volume of the extract sample, provided that the mass of the formed precipitate of barium sulfate is 20-200 mg.

STATE STANDARD OF THE UNION OF THE SSR

Methods for determining the sulfate ion in aqueous

soils. Methods for determination of sulphate ion in water extract

By the Decree of the USSR State Committee for Standards dated February 8, 1985 Ns 283, the validity period was established

from 01.01.86 to 01.01.96

Non-compliance with the standard is punishable by law

This standard establishes methods for determining the sulfate ion in the water extract from saline soils when conducting soil, agrochemical, reclamation surveys of lands, monitoring the state of the salt regime of soils, as well as during other survey and research work.

The total relative error is:

for the weight method

10% - for the number of equivalents of sulfate ion St. 1 to 3 mmol in 100 g of soil; 5% - St. 3 mmol in 100 g of soil;

for turbidimetric method

10% - for the number of equivalents of sulfate ion St. 0.5 to 3 mmol in 100 g of soil; 7.5% - St. 3 mmol in 100 g of soil.

1. WEIGHT DETERMINATION OF THE SULPHATE ION

The essence of the method is the precipitation of the sulfate ion with a solution of barium chloride and weighing the calcined residue. To prevent the precipitation of carbonate, barium phosphate and other compounds, the analyzed sample is acidified with hydrochloric acid.

1.1. Sampling method

1.1.1. Sampling method - according to GOST 26423-85.

Official edition

Reprint prohibited"

1.2. Equipment, materials and reagents

1.2.1. For analysis use:

laboratory scales of the 2nd accuracy class with the highest weighing limit of 200 g according to GOST 24104-80;

dispensers with a dosing error of not more than 1% or pipettes of the 2nd accuracy class according to GOST 20292-74;

a muffle furnace providing a heating temperature of 700-750°C;

water bath; electric stove;

glass funnels according to GOST 25336-82;

desiccator with calcined calcium chloride;

chemical glasses with a capacity of 100 cm 3 according to GOST 25336-82;

porcelain cups;

porcelain crucibles;

watch glasses;

glass sticks;

barium chloride 2-water according to GOST 4108-72, x. h. or h. d. a., solution with a mass fraction of 10%;

hydrochloric acid according to GOST 3118-77, x. h. or h. d. a., diluted with distilled water in a ratio of 1:3 and 1:100;

sulfuric acid according to GOST 4204-77, x. h. or h. d. a., solution with a mass fraction of 10%;

methyl red, indicator, analytical grade, solution prepared according to GOST 4919.1-77;

ashless filters "blue tape" with a diameter of 7 cm; distilled water according to GOST 6709-72.

1.3. Conducting an analysis

1.3.1. Preparation of an extract from the soil

1.3.2. Determination of the sulfate ion

20 cm 3 of the analyzed extract are taken with a dispenser or pipette into a beaker. Distilled water is added to the sample to a total solution volume of 40-50 cm 3, 3 drops of methyl red solution and acidified with hydrochloric acid diluted 1:3 to an acidic reaction, adding an excess of acid in 3-4 drops. If at the same time the solution becomes cloudy, it is filtered through an ash-free filter into a clean beaker. The filter is washed with hydrochloric acid, diluted 1:100, in three portions of 3-5 cm 3 .

When analyzing dark-colored extracts, the sample is placed in a porcelain dish, evaporated to dryness in a water bath, and

poured in a muffle furnace for 2 hours at a temperature of 700°C. After cooling, the calcined residue is moistened with 1 cm 3 of diluted 1:3 hydrochloric acid and the acid is evaporated to dryness on a water bath. The residue is dissolved by heating in dilute 1:100 hydrochloric acid and the solution is filtered into a clean beaker through an ash-free filter. Wash the dish and filter with dilute 1:100 hydrochloric acid to bring the volume of the filtrate to 40-50 cm 3 .

A glass with a diluted and acidified sample of the extract is heated to a boil. To the hot solution is added dropwise 5 cm 3 of a solution of barium chloride with a mass fraction of 10%, thoroughly mixing the solution with a stick after adding each drop. The glass is covered with a watch glass and placed in a boiling water bath for 2-3 hours to settling the precipitate.

Then make a test for the completeness of precipitation of barium sulfate. To do this, a few drops of a solution of barium chloride with a mass fraction of 10% are poured into a transparent settled solution along the wall of the glass. If turbidity forms near the wall, another 3 cm 3 of barium chloride solution is added to the solution, heated to a boil and the precipitate is allowed to settle. Then start filtering. The precipitate on the filter is washed with hot distilled water, acidified with hydrochloric acid, until the reaction to barium stops (solution of sulfuric acid with a mass fraction of 10%).

The filter with the precipitate is dried on a funnel, placed in a porcelain crucible weighed with an error of not more than 0.001 g, and placed in a cold muffle furnace. The precipitate is calcined for 30 min at a temperature of 700-750°C (at temperatures above 800°C the precipitate decomposes). Then the crucible is cooled in a desiccator and weighed with an error of no more than 0.001 g. To achieve a constant weight, the precipitate is ignited again for 20 minutes at the same temperature.

In the same way, a blank experiment is carried out, taking instead of a sample of the extract 20 cm 3 of distilled water.

It is allowed to increase to 50 cm 3 or decrease to 5 cm 3 the volume of the extract sample, provided that the mass of the formed precipitate of barium sulfate is 20-200 mg.

1.4. Results processing

1.4.1. The number of sulfate ion equivalents (X), mmol per 100 g of soil, is calculated by the formula

U_ (t-t-1) 500

where m is the mass of barium sulfate precipitate, mg; rn\ is the result of a blank determination, mg;

500 - conversion factor per 100 g of soil;

116.7 molar mass equivalent of barium sulfate, mg/mmol;

V is the volume of the extract sample, cm 3.

The mass fraction of the sulfate ion in the analyzed soil (Х^) as a percentage is calculated by the formula

where C is the amount of sulfate ion equivalent in the soil, mmol per 100 g;

The result of the analysis is expressed in millimoles per 100 g of soil and as a percentage rounded to three significant figures.

1.4.2. Permissible relative deviations at a confidence level Р=0.95 from the arithmetic mean of the results of repeated analyzes during selective statistical control are:

14% - for the number of equivalents of the sulfate ion St. 1 to 3 mmol in 100 g of soil; 7% - St. 3 mmol in 100 g of soil.

2. TURBIDIMETRIC DETERMINATION OF THE SULPHATE ION

The essence of the method lies in the precipitation of the sulfate ion with barium chloride and its turbidimetric determination in the form of barium sulfate. Polyvinyl alcohol or glycerin is used as a suspension stabilizer.-

The method is not applicable to the analysis of aqueous extracts stained with organic matter.

2.1. Sampling method

2.1.1. Sampling method - according to GOST 26423-85.

2.2. Equipment, materials and reagents

2.2.1. For analysis use:

(hotoelectrocolorimeter;

laboratory scales of the 2nd accuracy class with the highest weighing limit of 200 g and the 4th accuracy class with the highest weighing limit of 500 g according to GOST 24104-80;

dispensers with a dosing error of not more than 1% or pipettes and burettes of the 2nd accuracy class according to GOST 20292-74;

glass test tubes with a diameter of 16 mm and a capacity of at least 15 cm 3 according to GOST 25336-82;

measuring laboratory glassware of the 2nd accuracy class according to GOST 1770-74;

barium chloride 2-water according to GOST 4108-72, x. h. or h. d. a .;

hydrochloric acid according to GOST 3118-77, x. h. or h.d.a., solution of concentration c (HC1) \u003d 1 mol / dm 3;

polyvinyl alcohol, analytical grade, or glycerin according to GOST 6259-75, analytical grade;

sodium sulfate anhydrous according to GOST 4166-76, x. hours; sodium hydroxide according to GOST 4328-77, analytical grade, solution with a mass fraction of 0.5%;

disodium salt of ethylenediamine-^M.Y".N"-tetraacetic acid, 2-aqueous (trilon B) according to GOST 10652-73, analytical grade;

distilled water according to GOST 6709-72.

2.3. Preparation for analysis

2.3.1. Preparing a stock precipitating solution with polyvinyl alcohol

5 g of polyvinyl alcohol and 20 g of barium chloride are weighed with an error of not more than 0.1 g and placed in a heat-resistant glass beaker with a capacity of 1000 cm 3 . Pour about 800 cm 3 of distilled water, 60 cm 3 of a solution of hydrochloric acid with a concentration of 1 mol / dm 3 and heat the mixture with stirring until the reagents are completely dissolved. After cooling, the solution is transferred into a volumetric flask with a capacity of 1000 cm 3 , the volume is adjusted to the mark with distilled water, mixed and filtered. The solution is stored in a bottle with a ground stopper for no more than 3 months. In case of turbidity, formation of flakes, sediment, the solution is replaced with a freshly prepared one.

2.3.2. Preparation of a working precipitating solution with polyvinyl alcohol

On the day of analysis, the stock precipitating solution is diluted 2:1 with distilled water.

2.3.3. Preparation of a precipitating solution with glycerol

Weigh 20 g of barium chloride with an error of not more than

0.1 g and placed in a volumetric flask with a capacity of 500 cm 3 . Pour about 300 cm 3 of distilled water and 60 cm 3 of hydrochloric acid with a concentration of 1 mol/dm 3 . After complete dissolution of barium chloride, the volume of the solution is adjusted to the mark with distilled water and mixed. The prepared solution is mixed with glycerol in a ratio of 1:1. The solution is stored for no more than 3 months.

2.3.4. Preparation of a solution of sodium sulfate concentration cC / 2 Na 2 SO 4) \u003d 0.2 mol! dm b (0.2 n.)

14.2 g of anhydrous sodium sulfate, dried to a constant weight at a temperature of 100-105 ° C, weighed with an error of no more than 0.1 g, placed in a volumetric flask with a capacity of 1000 cm 3 and dissolved in distilled water, bringing the volume of the solution to the mark . The prepared solution is thoroughly mixed. The solution is stored in a flask with a ground stopper, not more than 1 g.

2.3.5. Preparation of reference solutions

In volumetric flasks with a capacity of 100 cm 3, the volumes of the solution prepared according to clause 2.3.4 indicated in the table are placed. Volumes

dilute the solutions to the mark with distilled water and mix thoroughly. Solutions are stored in vials with ground stoppers for no more than 1 month.

Reference solutions are used to calibrate the photoelectric colorimeter on the day of analysis.

2.3.6. Preparation of an alkaline solution of Trilon B

30 g of Trilon B, weighed with an error of not more than OD g, is dissolved in 1000 cm 3 of sodium hydroxide solution with a mass fraction of 0.5%.

The solution is used to wash the cuvettes of the photoelectric colorimeter and test tubes in which the determination is carried out. The cuvettes and test tubes are placed in the solution for 1 hour.

2.4. Conducting an analysis

2.4.1. Preparation of an extract from the soil

For analysis, filtrates of extracts prepared according to GOST 26423-85 are used.

2.4.2. Determination of the sulfate ion

1 cm 3 of the analyzed extracts and reference solutions are taken with a dispenser or pipette into test tubes. 10 cm 3 of the working precipitating solution, according to paragraph 2.3.2 or paragraph 2.3.3, are added to the samples with a dispenser or from a burette and mixed thoroughly. Suspension photometry is carried out no earlier than 10 minutes after the addition of the precipitating solution, in a cuvette with a translucent layer thickness of 10 mm relative to reference solution No. 1, at a wavelength of 520 nm or using a light filter with a maximum transmission in the region of 500-540 nm. Shake the contents of the test tube before placing it into the photoelectric colorimeter cuvette. The suspension is optically stable for 7 hours.

A proportional change in the volumes of the extract sample, reference solutions and precipitating solution is allowed with a dosing error of not more than 1%.

2.5. Results processing

2.5.1. Based on the results of photometry of reference solutions, a calibration graph is built. On the abscissa axis, the concentrations of sulfate ions in reference solutions are plotted in terms of millimoles per 100 g of soil, and on the ordinate axis, the corresponding photoelectrocolorimeter readings are plotted.

The number of sulfate equivalents in the analyzed soil is determined directly from the calibration curve. If the result of the determination is outside the calibration curve, the determination is repeated after diluting the extract with distilled water. The result found from the graph is increased as many times as the extract was diluted.

The mass fraction of the sulfate ion in the analyzed soil (X) as a percentage is calculated by the formula

where C is the number of sulfate ion equivalents in the analyzed soil, mmol per 100 g;

0.048 - conversion factor to percent.

The result of the analysis is taken as the value of a single determination of the sulfate ion.

The result of the analysis is expressed in millimoles per 100 g of soil rounded to the first decimal place and as a percentage rounded to the second decimal place.

2.5.2. Permissible relative deviations at a confidence level Р=0.95 from the arithmetic mean of the results of repeated analyzes during selective statistical control are:

14% - for the number of equivalents of the sulfate ion St. 0.5 to 3 mmol in 100 g of soil; 10% - St. 3 mmol in 100 g of soil.