2 REGULATORY REFERENCES

This standard uses references to the following standards:

4 POTENTIOMETRIC METHOD

The method is based on the oxidation reaction of divalent manganese with a solution of potassium permanganate to trivalent in a neutral medium in the presence of sodium pyrophosphate.

The influence of iron, titanium, aluminum, chromium and other elements is eliminated by binding them into soluble pyrophosphate complex compounds.

Potassium carbonate - sodium carbonate according to GOST 4332.

sodium peroxide.

Hydrogen peroxide according to GOST 10929.

Sodium carbonate according to GOST 83, solution 50 g / dm 3.

Sodium diphosphate 10-water according to GOST 342, solution 120 g / dm 3. The solution is prepared 24 hours before use.

Bromothymol blue (indicator), solution 0.4 g / dm 3.

Metal manganese according to GOST 6008, purity not less than 99.9%; 10 g of metallic manganese are placed in a glass with a capacity of 400 cm 3, processed for several minutes surface layer with a mixture of 50 cm 3 of water and 5 cm 3 of nitric acid until a shiny surface is obtained. The manganese is washed six times with water, then with acetone, and dried at 100°C for 10 min.

A standard solution of manganese 1 g/dm 3 prepared as follows: 1.0000 g of metallic manganese is placed in a beaker with a capacity of 400 cm 3 , 20 cm 3 diluted 1:1 sulfuric acid and 100 cm 3 water are added. The solution is boiled for several minutes, cooled, poured into a volumetric flask with a capacity of 1000 cm 3, topped up to the mark with water and mixed. 1 cm 3 solution contains 0.001 g of manganese.

Potassium permanganate according to GOST 20490, a purity of at least 99.5% and recrystallized as follows: 250 g of potassium permanganate are placed in a glass with a capacity of 1 dm 3 and 800 cm 3 of water heated to 90 ° C are poured. The solution is filtered under vacuum through a crucible with a filter glass plate No. 3. The filtered solution is quickly cooled in ice water to 10 ° C with vigorous stirring and the finely crystalline precipitate is allowed to settle. Then the solution is drained, the crystalline mass is transferred into a crucible with a filter glass plate No. 3 and sucked off. The recrystallization is repeated one more time. The resulting crystalline mass is transferred onto glass or into a wide porcelain cup and dried in air in a place protected from light, protecting from dust. When the crystalline mass ceases to stick together when crushed with a glass rod, it is dried at 80 - 100° C for 2 - 3 hours in an oven. Then transferred to a dark glass jar with a ground stopper. Purified in this way, potassium permanganate is completely non-hygroscopic.

A titrated solution of potassium permanganate 1.8 g / dm 3 prepared as follows: 1.8 g of potassium permanganate is dissolved in 1 dm 3 of water and left for 6 days, then the solution is poured through a siphon into a dark glass bottle.

The mass concentration of a titrated solution of potassium permanganate according to a standard solution of manganese is set as follows: an aliquot of a standard solution of manganese with a volume of 100 cm 3 is taken into a beaker with a capacity of 400 - 500 cm 3 containing 150 cm 3 of a solution of sodium pyrophosphate. Set the pH of the solution to 7, as indicated in, and titrate with a solution of potassium permanganate in accordance with. In parallel, a control experiment is carried out without adding a standard solution of manganese.

Mass concentration FROM titrated solution of potassium permanganate in grams of manganese per cubic centimeter, established by the standard solution, is calculated by the formula

FROM = ,

where t is the mass of manganese in an aliquot of the standard solution, g;

Mass concentration FROM titrated solution of potassium permanganate in grams of manganese per cubic centimeter, established by potassium permanganate, is calculated by the formula

FROM = ,

where t - weight of potassium permanganate sample, g;

Mass concentration FROM titrated solution of potassium permanganate in grams of manganese per cubic centimeter, established according to a standard sample, is calculated by the formula

FROM = ,

where BUT - mass fraction of manganese in a standard sample, %;

t -weight of a standard sample sample, g;

V 1 - volume of potassium permanganate solution used for titration of standard manganese solution, cm3;

V 2 - volume of potassium permanganate solution used for titration of the control experiment solution, cm 3 .

5.11.2 Standardization for potassium permanganate ( )

Place 1.5 g of potassium permanganate () in a fluoroplastic or Teflon glass with a capacity of 250 - 300 cm 3, add 30 - 40 cm 3 of water and mix thoroughly. Pour 20 cm 3 of hydrochloric acid (), cover with a watch glass and heat. At the end of the reaction, the watch glass is removed and washed with water. To the cooled solution add 10 cm 3 of perchloric acid () and 20 cm 3 of hydrofluoric acid (

Foreword

The goals, basic principles and procedure for carrying out work on interstate standardization are established by GOST 1.0-92 "Interstate standardization system. Basic provisions" and GOST 1.2-2009 "Interstate standardization system. Interstate standards, rules and recommendations for interstate standardization. Rules for the development, adoption, application , updates and cancellations"

About the standard

1 Prepared by Protector Limited Liability Company jointly with Lumex-Marketing Limited Liability Company

2 Introduced by the Federal Agency for Technical Regulation and Metrology, technical committee according to standardization TC 343 "Water quality"

3 Adopted by the Interstate Council for Standardization, Metrology and Certification (Minutes of October 20, 2014 N 71-P)

4 This standard has been developed taking into account the main regulatory provisions international standard ISO 6333:1986 Water quality - Determination of manganese - Formaldoxime spectrometric method

Degree of conformity - non-equivalent (NEQ)

NOTE When using this standard, it is advisable to check the validity of the referenced standards in information system common use- on the official site federal agency on technical regulation and metrology on the Internet or according to the annual information index "National Standards", which was published as of January 1 of the current year, and according to the issues of the monthly information index "National Standards" for the current year. If the reference standard is replaced (modified), then when using this standard, you should be guided by the replacing (modified) standard. If the referenced standard is canceled without replacement, the provision in which the reference to it is given applies to the extent that this reference is not affected.

3 Sampling

3.2 If the determination of manganese according to method A is supposed to be carried out no earlier than 12 hours after sampling, then the selected sample is preserved by adding concentrated nitric acid at the rate of 5 acid per 1000 samples. If the pH of the canned sample is above 2, then nitric acid is added until the pH is less than 2 (control by universal indicator paper).

3.3 If method B is used, preserve the sample by adding 10% sulfuric acid solution according to 7.3.6. If the pH of the preserved sample is above 2, then add a solution of sulfuric acid until the pH is less than 2 (control by universal indicator paper).

4 Requirements for measurement conditions

4.1 When preparing for measurements and during their conduct, it is necessary to comply with the conditions established in the operation manuals or in the passports of measuring instruments and auxiliary equipment.

4.2 Measurements of the volumes of water and solutions are carried out at a temperature environment from 15°С to 25°С.

4.3 All solutions, unless otherwise noted, should be stored at ambient temperature between 15°C and 25°C in closed containers.

4.4 Laboratories conducting tests shall comply with the requirements of GOST ISO/IEC 17025.

5 Measuring instruments, auxiliary equipment, reagents, materials

Photometer, spectrophotometer, photoelectric colorimeter, photometric analyzer (hereinafter referred to as the device), which allow measuring the optical density of a solution in the wavelength range from 400 to 700 nm with an allowable absolute measurement error of the spectral transmittance of no more than 2% in optical cuvettes with a thickness of the light-absorbing layer from 1 up to 10 cm.

Interstate reference standard for the composition of aqueous solutions of manganese (II) ions mass concentration 1 with a permissible relative error of the certified value of not more than 2% at a confidence level P = 0.95.

Non-automatic scales in accordance with GOST OIML R 76-1 with limits of permissible absolute error of not more than 0.001 g.

Volumetric flasks 2-50-2, 2-100-2, 2-200-2, 2-1000-2 according to GOST 1770.

Measuring cylinders 2-10-2, 2-25-2, 2-50-2, 2-100-2, 2-200-2, 2-500-2, 2-1000-2 according to GOST 1770.

Graduated pipettes 1-1-2-1, 1-1-2-2, 1-1-2-5, 1-1-2-10 or other types and designs according to GOST 29227.

Household electric stove according to GOST 14919.

Bath water of any type.

Mechanical or electronic stopwatch or mechanical clock in accordance with GOST 10733, or electronic clock in accordance with GOST 23350, or electronic-mechanical quartz clock in accordance with GOST 26272 of any brand or timer.

Any type of centrifuge capable of centrifuging liquid volumes up to 100 and providing a rotation speed of at least 85 (5000 rpm)

Household refrigerator of any type, providing temperature from 2°С to 8°С.

Heat-resistant conical flasks with a capacity of 50, 100, 250, 500, 1000, 1500 according to GOST 25336.

Chemical glasses with a capacity of 1000 in accordance with GOST 25336.

Porcelain evaporating bowls according to GOST 9147 or quartz according to GOST 19908.

Glass sticks

Ashless filters "red tape"

Ammonium persulphate (persulfate) according to GOST 20478, analytical grade.

Magnesium sulfate 7-water according to GOST 4523, chemically pure. or h.d.a.

Sodium hydroxide (sodium hydroxide) according to GOST 4328, chemically pure. or h.d.a.

Silver nitrate according to GOST 1277, analytical grade.

Mercury sulfate oxide, analytical grade, mass fraction of the main substance is not less than 98%

Potassium persulphate (persulfate) according to GOST 4146 or sodium persulphate (persulfate), analytical grade.

Sodium sulphate (sodium sulfate) according to GOST 195, anhydrous, analytical grade.

Water ammonia according to GOST 3760, chemically pure or in accordance with GOST 24147, os.ch.

Salt of iron oxide and ammonium double sulphate (Mohr's salt) according to GOST 4208.

Phenolphthalein (indicator), alcohol solution with mass fraction 0.1% according to GOST 4919.1.

Paper indicator universal.

Note - It is allowed to use other measuring instruments, equipment, auxiliary devices and materials with metrological and technical specifications not worse than those specified in this standard, as well as chemical reagents of a higher qualification.

6 Determination of manganese content using oxidation to permanganate ions (method A)

6.1 Essence of the method

The essence of the method lies in the catalytic oxidation of manganese compounds with potassium persulfate or sodium persulfate to permanganate ions, followed by measurement of the optical density of the solution and calculation of the mass concentration of manganese in the water sample. When using a device equipped with a monochromator, the working wavelength is set to 525 nm, when using filter devices, a light filter is selected that has an absorption maximum in the (53020) nm region.

Depending on the method of eliminating the interfering effect of chloride ions, the following method options are established:

1 - using codeposition with magnesium hydroxide;

2 - with evaporation with sulfuric acid;

3 - using complex formation with mercury (II).

6.2 Interfering influences

Interfering influences are eliminated during sample preparation. Elimination of interfering influences in option 3 is effective if the content of chloride ions in the sample aliquot taken for analysis does not exceed 0.1 g.

6.3 Determination of manganese content with elimination of the interfering effect of chloride ions by co-precipitation with magnesium hydroxide (option 1)

6.3.1 Preparing for measurements

6.3.1.1 Preparation of stock solution of manganese, mass concentration 10

Pipette 1 into a volumetric flask with a capacity of 100 standard sample the composition of the solution of manganese (II) ions, mass concentration 1, diluted with distilled water to about half the volume of the flask, add 0.5 concentrated nitric acid and bring to the mark with distilled water.

The shelf life of the solution is no more than 1 month.

6.3.1.2 Preparation of 10% magnesium sulfate solution

In a conical flask (or glass) with a capacity of 100 add 10 g of 7-aqueous magnesium sulfate and dissolve in 90 distilled water.

The shelf life of the solution is no more than 6 months.

6.3.1.3 Preparation of 20% phosphoric acid solution by volume

In a glass with a capacity of 1000, 800 of distilled water are placed and 200 of phosphoric acid are poured carefully with stirring and, if necessary, with external cooling.

6.3.1.4 Preparation of 4% sodium hydroxide solution

In a conical flask with a capacity of 100, 96 distilled water is placed and 4 g of sodium hydroxide are added. After the sodium hydroxide is dissolved, the solution is transferred to a vessel from polymer material.

The shelf life of the solution is no more than 2 months.

6.3.1.5 Preparation of 1% silver nitrate solution

In a volumetric flask with a capacity of 100 add 1 g of silver nitrate, dissolve in distilled water and then make up to the mark with distilled water.

6.3.1.6 Preparation of calibration solutions

Pipette 0.00 into conical heat-resistant flasks with a capacity of 50 or 100; 0.25; 0.50; 1.00; 2.00; 3.00; 4.00; 5,00 stock solution of manganese (6.3.1.1). To each flask add 10 solutions of orthophosphoric acid, 20% by volume (see 6.3.1.3), 10 solutions of silver nitrate (see 6.3.1.5), and 0.3 g of potassium persulfate or sodium persulfate. The contents of the flasks are diluted with distilled water to about 40, brought to a boil on a hotplate and boiled for 3 minutes.

Solutions are cooled in a current cold water, transferred to 50 volumetric flasks, diluted to the mark with distilled water and mixed. The mass concentration of manganese in the prepared calibration solutions is 0.00, respectively; 0.05; 0.10; 0.20; 0.40; 0.60; 0.80; 1.00 .

The manganese-free calibration solution is a calibration blank.

6.3.1.7 Preparing the instrument

6.3.1.8 Instrument calibration

Measure the optical density of all the calibration solutions and the calibration blank (6.3.1.6) three times at the wavelength specified in 6.1 in an optical cuvette with a light-absorbing layer between 2 and 4 cm thick, using distilled water as a reference solution.

For each calibration solution, the arithmetic mean value is calculated from the obtained optical density values.

A calibration characteristic is established in the form of a dependence of the arithmetic mean values ​​of the optical density of the calibration solutions minus the arithmetic mean value of the blank sample optical density on the mass concentration of manganese in the corresponding solution. Wherein:

If the device is equipped with a computer (microprocessor) system for collecting and processing information, then the calibration characteristic is set in accordance with the manual (instruction) for the operation of the device;

If the device does not provide for automated calibration, then the obtained calibration characteristics are processed by the linear regression method using the software. In the absence of such a possibility, the angular coefficient of the calibration characteristic b, (units of optical density), is calculated using the formula

where is the mass concentration of manganese in i-th calibration solution, ;

The arithmetic mean value of the optical density of the i-th calibration solution minus the optical density of a blank sample for calibration, units of optical density;

Number of calibration solutions.

Note - The software for some devices allows you to calculate the calibration coefficient K, equal to 1/b.

6.3.1.9 Checking the acceptability of the calibration characteristic

The verification of the acceptability of the calibration characteristic using a computer (microprocessor) system for collecting and processing information is carried out in accordance with the manual (instruction) for operating the device.

If the device does not have software that provides for automated calibration, then for each calibration solution calculate the value of the slope of the calibration characteristic , (units of optical density), according to the formula

where and - see 6.3.1.8.

The calibration characteristic is recognized as acceptable if the condition is met at each calibration point

where b is the value of the slope of the calibration characteristic, calculated by the formula (1) , (units of optical density).

If this condition is not met, then the establishment of the calibration characteristic is repeated.

6.3.1.10 Checking the stability of the calibration characteristic

The stability of the calibration characteristic is controlled at least once a quarter, as well as when replacing reagents, after repair or long downtime device. For control, use one or two newly prepared calibration solutions according to 6.3.1.6 (hereinafter referred to as control solutions).

Measure the optical density of the control solutions in the same way as in 6.3.1.8 and, using the calibration characteristic, calculate the value of the mass concentration of manganese in the control solutions from the obtained optical density values.

The calibration characteristic is considered stable when the condition

where is the mass concentration of manganese in the calibration solution obtained during the control measurement, ;

The actual value of the mass concentration of manganese in the calibration solution, .

If condition (4) is not met for only one control solution, then prepare this control solution again and repeat measurements. The results of the repeated control are considered final. In this case, if the condition of stability of the calibration characteristic is not met, then the calibration of the device is carried out again.

6.3.1.11 Preparing water samples for analysis

6.3.1.11.1 If the water sample has been preserved (3.2), determine the volume of 4% sodium hydroxide solution required to neutralize the acid.

To do this, take an aliquot of water with a volume of \u003d 100, add from 3 to 5 drops of a 1% alcoholic solution of phenolphthalein and pour 4% sodium hydroxide solution (6.3.1.4) from a graduated pipette until a pink color that does not disappear for 30 s appears. Record the volume of sodium hydroxide solution used and, if necessary, recalculate it to the volume of an aliquot of the sample taken for the determination in 6.3.1.11.2. The aliquot used to find the volume of the sodium hydroxide solution is discarded.

6.3.1.11.2 If the water sample was not preserved at the time of sampling, then add 2 4% sodium hydroxide solution (6.3.1.4) to an aliquot of 100 samples, mix, add 2 10% magnesium sulfate solution (6.3.1.2) , mix again and leave until the precipitate of magnesium hydroxide, with which co-precipitation of manganese occurs, settles to the bottom of the glass. Depending on the expected value of the mass concentration of manganese, the volume of the aliquot can be increased up to 500. At the same time, the volume of added solutions of sodium hydroxide and magnesium sulfate is changed proportionally.

If the water sample was preserved during sampling, then the volume of sodium hydroxide solution determined according to 6.3.1.11.1 is added to the sample aliquot and then all operations provided for an unpreserved sample are carried out, starting with the addition of magnesium sulfate solution.

6.3.1.11.3 After settling, most of the solution above the precipitate is decanted, and the residue is filtered through an ashless red tape filter. The filter cake is washed two or three times with distilled water and dissolved in 10 phosphoric acid solution (6.3.1.3), collecting the filtrate in a volumetric flask with a capacity of = 50.

Wash the filter with distilled water two or three times so that the total volume of the filtrate and washings in the flask is approximately 35. Then add 10 1% silver nitrate solution (6.3.1.5) and mix. In this case, no turbidity of the solution due to the formation of silver chloride should be observed. Approximately 0.3 g of ammonium persulfate or potassium persulfate is added to the solution, brought to a boil on a hot plate and kept in a boiling water bath for 10 minutes.

After cooling, the solution is brought to the mark with distilled water and the optical density is measured according to 6.3.2.

6.3.1.11.4 If after the addition of the silver nitrate solution (6.3.1.5) a white precipitate or cloudiness develops, shake the solution flask vigorously until the precipitate clumps and the solution clears. Then the solution is centrifuged or filtered through a dry "red tape" filter into another 50 volumetric flask, the precipitate is washed 2-3 times with a small amount of distilled water and discarded. To the filtrate wash water add 0.3 g of ammonium persulfate or potassium persulfate (section 5), bring to a boil on a hot plate and keep in a boiling water bath for 10 minutes. After cooling, the solution is brought to the mark with distilled water and the optical density is measured according to 6.3.2.

6.3.1.11.5 Prepare a blank sample in the same way, replacing the test water sample with distilled water. If the water sample was preserved (see 3.2), then before analyzing the blank sample, nitric acid is added to it in the same volume as when preserving the water sample.

6.3.2 Taking measurements

Carry out at least three measurements of the optical density of the sample and the blank prepared according to 6.3.1.11 against distilled water under the same conditions under which the calibration solutions were measured (see 6.3.1.8).

Calculate the arithmetic mean of the obtained values.

If the value of the optical density of the prepared sample is outside upper limit range of the calibration characteristic, then the sample analysis is repeated, taking a smaller aliquot, or the water sample is diluted with distilled water before analysis and all operations according to 6.3.1.11.1 - 6.3.1.11.4 are carried out with the diluted sample.

The dilution factor f is calculated by the formula

where is the volume of the volumetric flask used to dilute the sample, ;

The volume of the sample aliquot taken for dilution, .

6.3.3 Processing measurement results

6.3.3.1 If there is a computer (microprocessor) system for collecting and processing information, the procedure for processing the results is determined by the manual (instruction) for operating the device.

6.3.3.2 In the absence of a computer (microprocessor) system for collecting and processing information, the mass concentration of manganese in a water sample X, , is calculated by the formula

where A is the optical density of the prepared water sample (6.3.2

Optical density of a blank water sample (6.3.2), units of optical density;

The volume of the sample prepared according to 6.3.1.11.3, ;

f is the dilution factor [formula (5)].

b is the slope of the calibration characteristic [formula (1) ], (optical density units);

The volume of an aliquot of the sample (stock or diluted according to 6.3.2) taken for the determination according to 6.3.1.11.1 or 6.3.1.11.2 , ;

6.3.3.3 The result of measurements of the mass concentration of manganese is taken as the arithmetic mean of the results of two measurements and obtained under repeatability conditions, provided that the condition

where r is the value of the repeatability limit according to table 1.

6.3.6 Registration of measurement results

The measurement results are recorded in a test report, which is drawn up in accordance with the requirements of GOST ISO / IEC 17025. In this case, the test report must contain a reference to this standard indicating the measurement method.

The results of measurements of the mass concentration of manganese, , are presented as

At P = 0.95 or at k = 2,

where - confidence limits of the relative error of measurements of the mass concentration of manganese according to table 1,%;

Relative expanded uncertainty, %, at coverage factor k = 2 according to table 1 .

The numerical value of the measurement result must end with a digit of the same digit as the absolute value of the measurement accuracy indicator, expressed in milligrams per cubic decimeter. The absolute value of the measurement accuracy indicator is represented by two significant figures, if the first digit is less than three. In other cases, one significant digit is left.

6.4 Determination of manganese content with elimination of the interfering effect of chloride ions by evaporation with sulfuric acid (option 2)

6.4.1 Preparation for measurements - according to 6.3.1

6.4.1.1 Preparation of a solution of silver nitrate with a molar concentration of 0.1

In a conical flask with a capacity of 1500, 17 g of silver nitrate are dissolved in 1000 of distilled water.

The shelf life of the solution in a dark glass container is no more than 1 month.

Note - It is allowed to prepare a smaller volume of the solution, based on the need.

6.4.1.2 Preparation of a sulfuric acid solution, 33.3% by volume

In a heat-resistant glass with a capacity of 1000, 500 distilled water is placed and 250 concentrated sulfuric acid is poured carefully with stirring and external cooling.

The shelf life of the solution is not limited.

6.4.1.3 Preparing water samples for analysis

Introduce an aliquot of the water sample measured with a cylinder into a porcelain bowl, carefully add 5 ml of sulfuric acid solution (6.4.1.2) and evaporate first on a water bath and then on an electric hotplate to complete removal acids.

Moisten the dry residue with a small amount of distilled water, add 5 concentrated nitric acid (section 5), 10 hot distilled water and heat until the precipitate dissolves. Transfer the solution to a heat-resistant 50 ml conical flask, add 3 solutions of 0.1 molar concentration of silver nitrate (see 6.4.1.1), add 0.2 g of ammonium persulfate (Section 5), heat to boiling and boil on the hotplate for 3 minutes .

The flask is cooled under running cold water, its contents are quantitatively transferred into a volumetric flask with a capacity of 50 and its volume is adjusted to the mark with distilled water, then measurements are made according to 6.4.2.

6.4.2 Carrying out measurements - according to 6.3.2 using the calibration characteristic according to 6.3.1.8. Distilled water is used as a reference solution.

6.5 Determination of manganese content with the elimination of the interfering effect of chloride ions by adding mercury sulfate (option 3)

6.5.1 Preparation for measurements - according to 6.3.1 with the following clarifications below.

6.5.1.1 Preparation of mixed reagent

In a heat-resistant conical flask with a capacity of 1000, 200 distilled water, 400 concentrated nitric acid and 75 g of oxide mercury sulfate are added, then 200 phosphoric acid (section 5) and (351) mg of silver nitrate (section 5) are added. After cooling, the contents of the flask are transferred to a 1000 volumetric flask and made up to the mark with distilled water.

The shelf life of the mixed reagent is no more than 6 months.

Note - It is possible to prepare a smaller volume of the mixed reagent, depending on the need.

6.5.1.2 Preparation of calibration solutions

In heat-resistant conical flasks with a capacity of 100 pipettes make 0.00; 0.50; 1.00; 2.00; 4.00; 6.0; 8.0 and 10.0 manganese stock solution (6.3.1.1).

The contents of the flasks are diluted with distilled water to a volume of 80 - 90, and 5 mixed reagent (6.5.1.1), 1.0 g of ammonium persulfate (section 5) are added to each flask, the solution is brought to a boil and boiled on an electric stove for 3 minutes.

The flasks are rapidly cooled under running cold water, their contents are transferred into volumetric flasks with a capacity of 100, brought to the mark with distilled water and mixed.

A manganese-free calibration solution (with mass concentration of manganese equal to zero) is a blank sample for calibration. The mass concentration of manganese in the remaining calibration solutions is 0.05, respectively; 0.10; 0.20; 0.40; 0.60; 0.80; 1.00 .

Calibration solutions are prepared on the day of use.

6.5.1.3 Preparing the instrument

Preparation of the device for operation is carried out in accordance with the manual (instruction) for the operation of the device.

6.5.1.5 Preparing water samples for analysis

Into a heat-resistant 100, 250, or 500 capacity conical flask, add an aliquot of the water sample by cylinder, add 1 drop of hydrogen peroxide (Section 5), 5 mixed reagents (6.5.1.1) and concentrate the sample by hot plate evaporation to 90 or dilute with distilled water to the same volume. . Then add 1.0 g of ammonium persulfate (section 5) and bring the solution to a boil on an electric stove and boil for 3 minutes.

The flask is cooled under running cold water, its contents are transferred to a 100 volumetric flask, made up to the mark with distilled water and mixed.

NOTE The recommended sample size is 100 aliquots, with an expected mass concentration of manganese in the sample between 0.05 and 1 . At a lower manganese content (from 0.01 to 0.05) the volume of the aliquot should be increased to 250-500, and at a higher content (over 1) it should be reduced to 20 or 25.

6.5.2 Carrying out measurements - according to 6.3.2 using the calibration characteristic according to 6.5.1.4. Distilled water is used as a reference solution.

7 Determination of manganese content using formaldoxime (method B)

7.1 Essence of the method

The essence of the method lies in the formation of a complex compound of manganese with formaldoxime in an alkaline medium, followed by measurement of the optical density of the solution and calculation of the mass concentration of manganese in the water sample. When using a device equipped with a monochromator, the working wavelength is set to 455 nm, when using filter devices, a light filter is selected that has an absorption maximum in the (44020) nm region.

7.2 Interfering influences

Iron(II) ions form a violet complex with formaldoxime, which interferes with the determination of manganese. This influence is eliminated during sample preparation by adding solutions of sodium ethylenediaminetetraacetate (7.3.1), a mixed solution of hydroxylamine hydrochloride and ammonia (7.3.5), and Mohr's salt (7.3.7) containing iron (II) ions to all calibration solutions, a blank sample and an aliquot of the water sample.

The presence of 1 cobalt (which is unlikely for water within the scope of this standard) gives a response equivalent to 40 manganese.

In the presence of calcium, orthophosphate ions above 2 (calculated as phosphorus) may underestimate the results. The combined presence of calcium and magnesium at a total mass concentration value above 300 causes an overestimation of the results. These interfering influences are eliminated when preparing a water sample according to 7.3.13.

7.3 Preparing for measurements

7.3.1 Preparation of a solution of sodium ethylenediaminetetraacetate, molar concentration 0.24

In a volumetric flask with a capacity of 1000, half-filled with water, add 90 g of Trilon B, add 19 g of sodium hydroxide and, after complete dissolution, bring to the mark with distilled water.

The shelf life of the solution in a container made of polymeric material is no more than 2 months.

Note - Similarly, you can get the specified solution by dissolving in distilled water 109 g of tetrahydrate () or 100 g of dihydrate () tetrasodium salt of ethylenediaminetetraacetic acid in distilled water and bring to the mark with distilled water.

7.3.2 Preparation of formaldoxime solution

In a volumetric flask with a capacity of 100 add 50 of distilled water, add 10 g of hydroxylamine hydrochloride and after its dissolution add 5 aqueous solution formaldehyde (formalin) and dilute to the mark with distilled water.

7.3.3 Preparation of a solution of hydroxylamine hydrochloride, molar concentration 6

Add 42 g of hydroxylamine hydrochloride to a 100 volumetric flask, dissolve in distilled water and then make up to the mark with distilled water.

Shelf life of the solution at a temperature of 2°C to 8°C - no more than 1 month.

7.3.4 Preparation of 4.7 molar ammonia solution

Add 50% of distilled water to a 200 volumetric flask, add 70% of concentrated aqueous ammonia solution (section 5) and make up to the mark with distilled water.

The shelf life of the solution in a tightly closed container made of polymer material is no more than 2 months.

7.3.5 Preparation of a mixed solution of hydroxylamine hydrochloride and ammonia

Mix equal volumes of ammonia (7.3.4) and hydroxylamine hydrochloride (7.3.3) solutions.

The shelf life of the solution at a temperature of 2°C to 8°C in a tightly closed container made of polymer material is no more than 7 days.

7.3.6 Preparation of a solution of sulfuric acid with a molar concentration of approximately 3

In a heat-resistant glass with a capacity of 1000, 750 of distilled water is added, 170 of concentrated sulfuric acid is added carefully with stirring and, if necessary, cooling. Allow the contents of the beaker to cool, transfer to a 1000 volumetric flask and make up to the mark with distilled water.

The shelf life of the solution is no more than 1 year.

7.3.7 Preparation of Mohr's salt solution, mass concentration 700

500 distilled water is added to a volumetric flask with a capacity of 1000, 700 mg of Mohr's salt are added, after dissolution, 1 solution of sulfuric acid is added (

GOST 4974-72

Group H09

INTERSTATE STANDARD

DRINKING WATER

Methods for determining the content of manganese

drinking water. Methods for determination of manganese content

For the text of Comparison of GOST 4974-72 with GOST 4974-2014, see the link.
- Database manufacturer's note.
____________________________________________________________________

Introduction date 1974-01-01

INFORMATION DATA

1. APPROVED AND INTRODUCED BY Decree State Committee standards of the Council of Ministers of the USSR dated 25.12.72 N 2320

2. REPLACE GOST 4974-49

3. REFERENCE REGULATIONS AND TECHNICAL DOCUMENTS

4. The limitation of the validity period was removed by the Decree of the State Standard of the USSR of December 25, 1991 N 2121

5. RE-ISSUE


This standard applies to drinking water and establishes colorimetric methods for the determination of manganese content.

The methods are based on the oxidation of manganese compounds to an ion. Oxidation occurs in an acidic environment with ammonium or potassium persulfate in the presence of silver as a catalyst, and a pink color appears. The sensitivity of the method is (the volume of the studied water is 500 cm3) 10 µg/dm.

1. SAMPLING METHODS

1. SAMPLING METHODS

1.1. Water samples are taken according to GOST 2874* and GOST 24481 **.
____________________
* Within the territory of Russian Federation GOST R 51232-98 applies.
** On the territory of the Russian Federation, GOST R 51593-2000 applies.

1.2. The volume of a water sample for determining the manganese content should not be less than 1 dm3.

1.3. In cases where manganese cannot be determined immediately after sampling, the latter is preserved by adding 5 ml of concentrated nitric acid per 1 dm of the sample.

2. EQUIPMENT, MATERIALS, REAGENTS

Photoelectrocolorimeter; cuvettes with = 20-50 mm.

Electric stove.

Bath water.

Muffle furnace.

Measured glass laboratory glassware in accordance with GOST 1770, GOST 29227 and GOST 29251, with a capacity of: volumetric flasks 50, 100 and 1000 cm 3, a burette with a tap 25 and 50 cm, pipettes 1 and 10 cm with divisions of 0.01 and 0.1 cm, cylinders measuring with a flat bottom with a mark of 100 cm; measuring cylinders 25 and 50 cm.

Evaporating cups with a diameter of 9 cm.

Glass funnels for filtration according to GOST 25336.

Glass laboratory glasses in accordance with GOST 25336.

Flat-bottom flasks with a capacity of 500 and 250 cm3 according to GOST 1770.

Laboratory filter paper according to GOST 12026.

Potassium permanganate according to GOST 20490.

Ammonium persulphate (persulfate) according to GOST 20478.

Magnesium sulfate according to GOST 4523.

Sodium hydroxide according to GOST 4328, 4% solution.

Manganese sulfate according to GOST 435.

Orthophosphoric acid 85% according to GOST 6552.

Nitric acid according to GOST 4461.

Sulfuric acid according to GOST 4204.

Phenolphthalein.

Silver nitrate according to GOST 1277.

Mercury sulfate oxide.

Distilled water according to GOST 6709.

All reagents must be of analytical grade.

3. DETERMINATION OF MANGANESE CONTENT WITH SEPARATION OF CHLORIDE ION WITH CO-precipitation WITH MAGNESIUM OXIDE HYDRATE (Method A)

3.1. Preparation for analysis

3.1.1. Preparation of a standard solution of potassium permanganate

3.1.2. Preparation of the basic standard solution of manganese sulfate

0.2748 g, calcined at 500 ° C, is dissolved in about 10 cm 3 of dilute (1: 4) hot sulfuric acid and the volume is adjusted to 1 dm with distilled water. 1 cm of solution contains 0.10 mg.

3.1.3. Preparation of a working standard solution of manganese sulfate

The solution is prepared by diluting 100 ml of the stock solution to 1 dm with distilled water. 1 cm of solution contains 0.01 mg.

The solution is prepared on the day of the analysis.

3.1.4. Preparation of a 10% solution of magnesium sulfate

10 g is dissolved in 90 ml of distilled water. Commercially available magnesium sulphate often contains an admixture of manganese salts, so it must be checked for purity before use. To do this, 5 cm 10% magnesium sulfate solution, about 10 cm distilled water, 10 cm 20% phosphoric acid solution, 1 cm 1% silver nitrate solution, 0.2 g persulfate are added to a 50 cm volumetric flask. ammonium or potassium in crystals and kept in a boiling water bath for 5 minutes. The solution is cooled and topped up with distilled water to the mark. If the solution is colored pink color, which means that magnesium sulfate is contaminated with manganese. In this case, to 1 dm of a 10% solution of magnesium sulphate, add 20 cm of a 1% alkali solution dropwise in the cold with thorough mixing of the solution. The precipitate of magnesium oxide hydrate adsorbs manganese. The precipitate is allowed to settle and the clear solution is siphoned or filtered.

3.1.5. Preparation of a 20% solution of phosphoric acid

20 g of analytical grade. dissolved in 80 ml of distilled water.

3.2. Conducting an analysis

To 500 cm 3 of the investigated water, not acidified during sampling, add 5 cm 4% sodium hydroxide solution, mix, add 5 cm 10% magnesium sulfate solution, mix again and leave. In this case, the precipitate settles to the bottom of the glass. (When determining, 1 cm 4% sodium hydroxide solution and 1 cm 10% magnesium sulfate solution are added to 50 cm 3 of water).

If the test water was acidified during sampling, then before determining manganese in the test water with a volume of 50 cm 3, the acid is neutralized with a 4% sodium hydroxide solution from a graduated pipette for phenolphthalein (1% alcohol solution). The amount of spent alkali is recalculated for the volume of the investigated water, and this amount is added to the investigated water before the beginning of the determination. Manganese coprecipitation is then carried out as described above.

After settling, most of the solution above the precipitate is drained by a siphon, and the residue is filtered through a loose filter. The precipitate is dissolved on the filter in 10 ml of 20% phosphoric acid, collecting the filtrate in a 50 ml volumetric flask.

The filter is washed two or three times so that the total volume of the filtrate and washings in the flask is about 35 cm3. Then 10 cm3 of a 1% silver nitrate solution is added and mixed. In this case, there should not be a strong turbidity of the solution due to the formation of silver chloride. About 0.3 g of ammonium or potassium persulfate is added to the solution, heated to a boil and kept in a water bath for 5 minutes. After cooling, the solution is brought to the mark with distilled water and its color is compared with an exemplary standard scale or measured on a photoelectrocolorimeter with a green light filter (= 530 nm) in cuvettes with a working layer thickness of 20-50 mm.

When analyzing test water with a high content of chlorine ions, the filter cake is washed two or three times with distilled water and then dissolved in phosphoric acid. If, after adding silver nitrate, a white precipitate or turbidity still forms, then the flask with the solution is shaken sharply until the precipitate collects in clods and the solution becomes clear. Otherwise, add another 5 ml of silver nitrate solution and check again if there is an excess of silver ion. After that, the solution is separated from the precipitate by filtration through a dry filter into another volumetric flask, the precipitate is washed 2-3 times with a small amount of distilled water and discarded. 0.3 g of ammonium or potassium persulfate is added to the filtrate with washings and the analysis is continued as described above.

3.2.1. Preparation of the standard scale

The following quantities of a standard solution of manganese sulfate are added to a flask with a capacity of 50 cm 3 (1 cm solution contains 0.01 mg): 0.0; 0.5; 1.0; 2.0; 3.0; 4.0; 5.0; 6.0; 8.0; 10.0 cm.

Then, 10 cm3 of a 20% solution of phosphoric acid, 10 cm3 of a 1% solution of silver nitrate and about 0.3 g of ammonium or potassium persulfate are added to each flask, then distilled water is added to a volume of about 40 cm3, heated to a boil and kept in a water bath for 10 minutes. After cooling, dilute the volume of the solution with water to the mark and mix.

Get a standard scale with a content of 0.0; 0.005; 0.01; 0.02; 0.03; 0.04; 0.05; 0.06; 0.08; 0.1 mg.

The scale is unstable and discolors the next day, but it can be restored. To do this, 0.2 g of ammonium or potassium persulfate is added to each flask, heated to a boil and kept in a water bath or not too hot sand bath for 10 minutes.

To prepare a standard scale using a standard solution of potassium permanganate, the same quantities and the same concentration of manganese are taken into volumetric flasks with a capacity of 50 cm3 and the volume is adjusted to 50 cm3 with distilled water.

optical density standard solutions are measured on an electrophotocolorimeter with a green light filter (= 530 nm) using cuvettes with a working layer thickness of 20-50 mm. Based on the data obtained, a calibration graph is built, according to which the content is determined.

3.3. Results processing

The content of manganese (), mg / dm, is determined by the formula

where is the manganese content found on a standard scale or calibration graph, mg;

- the volume of the investigated water, taken for determination, see.

4. DETERMINATION OF MANGANESE CONTENT WITH REMOVAL OF CHLORIDE ION BY EVAPORATION WITH SULFURIC ACID (Method B)

4.1. Preparation for analysis

4.1.1. Preparation of a standard solution of potassium permanganate

9 cm exactly 0.01 n. The solution is added to a volumetric flask with a capacity of 100 ml, diluted with distilled water to the mark and mixed. 1 cm of solution contains 0.01 mg.

4.1.2. Preparation of 0.1 n. silver nitrate solution

17 g are dissolved in 1 dm of distilled water.

4.2. Conducting an analysis

Add 5 cm of sulfuric acid (1:2) to 100-500 cm3 of the test water in a porcelain cup and evaporate first in a water bath and then on a hot plate to completely remove the acid.

The dry residue is moistened with a small amount of distilled water, 5 ml of concentrated nitric acid, 10 ml of hot distilled water, 3 ml of 0.1 N. , 0.2 g of ammonium persulfate and heat the solution until the color intensity stops increasing.

After cooling the solution, bring its volume with distilled water in a volumetric flask with a capacity of 50 cm to the mark and compare its color with a standard scale or measure the optical density on a photoelectrocolorimeter with a green light filter (= 530 nm). The content is determined according to the calibration graph in the same way as in method A. The calculation of the test results is carried out according to clause 3.3.

When analyzing water with a high manganese content, the colorimetric titration method is also used. To do this, 50 cm 3 of the test water containing is transferred to a glass with a capacity of 100 cm 3, and distilled water is added to another glass of the same capacity in a volume equal to the volume of the test solution. Putting both glasses side by side on white paper, pour into a glass of distilled water from a burette standard solution potassium permanganate until the color in both glasses is the same. According to the volume of the spent solution of potassium permanganate, the content of manganese in the test water is calculated.

MINISTRY OF ENVIRONMENT AND NATURAL PROTECTION
RESOURCES OF THE RUSSIAN FEDERATION

QUANTITATIVE CHEMICAL ANALYSIS OF WATER

METHOD OF MEASUREMENTS OF MASS
MANGANESE CONCENTRATIONS IN NATURAL AND WASTE
IN WATER BY THE PHOTOMETRIC METHOD USING
AMMONIUM PERSULFATE.

If the mass concentration of manganese ions in the analyzed sample exceeds the upper limit of the range, then the sample can be diluted so that the concentration of manganese ions corresponds to the regulated range.

If the mass concentration of manganese ions in the analyzed sample is below the minimum concentration determined by the method, concentration by evaporation is allowed.

Interfering influences due to the presence in the sample organic matter, chloride ions and iron are eliminated by special sample preparation for analysis (item 9).

1. PRINCIPLE OF THE METHOD

The photometric method for determining the mass concentration of manganese ions is based on the oxidation of manganese (2+) ions to permanganate ions in a nitric acid medium by the action of ammonium persulfate in the presence of a catalyst - silver ions, followed by measuring the optical density of the solution at? = 540 nm.

2. ASSIGNED CHARACTERISTICS OF THE MEASUREMENT ERROR AND ITS COMPONENTS

This method provides the results of the analysis with an error not exceeding the values ​​given in Table 1.

Table 1

Values ​​of indicators of accuracy, repeatability and reproducibility of the technique

The values ​​of the accuracy index of the methodology are used for:

Registration of the results of the analysis issued by the laboratory;

A spectrophotometer or photocolorimeter that measures absorbance at wavelength? = 540 nm.

*Cuvettes with an absorbing layer thickness of 50 mm.

Scales laboratory, 2 classes of accuracy, GOST 24104.

Electric drying cabinet, OST 16.0.801.397.

Pipettes measured with divisions of 0.1 cm 3, 4(5)-2-1(2);

3-1-50, GOST 29227.*

*Supplements and amendments have been made in accordance with the protocol No. 23 of the meeting of the STC FP "CECA" of the Ministry of Natural Resources of Russia dated May 30, 2001.

Glasses N-1-150 TLC, GOST 25336.

Cylinders 3-25 (50, 100), GOST 1770.

Porcelain cups for steaming.

Glass or polyethylene bottles with ground or screw caps with a capacity of 500 - 1000 cm 3 for sampling and storage of samples and reagents.

3.3. Reagents

Distilled water, GOST 6779.

Nitric acid, GOST 4461.

Orthophosphoric acid, GOST 6552.

Mercury (II) nitrate 1-water, GOST 4520.

Silver nitrate, GOST 1277.

Ammonium persulphate, GOST 20478.

Sulfuric acid, GOST 4204.

Hydrochloric acid, GOST 3118.

Chloroform, TU 6-09-4263.

All reagents used for analysis should be of analytical or chemical grade.

4. SAFETY REQUIREMENTS

4.1. When performing analyzes, it is necessary to comply with safety requirements when working with chemical reagents in accordance with GOST 12.1.007.

4.2. Electrical safety when working with electrical installations in accordance with GOST 12.1.019.

4.3. Organization of training of workers in labor safety in accordance with GOST 12.0.004.

4.4. The laboratory room must comply with fire safety requirements in accordance with GOST 12.1.004 and have fire extinguishing equipment in accordance with GOST 12.4.009

5. OPERATOR QUALIFICATION REQUIREMENTS

Measurements can be made by an analytical chemist who is proficient in the technique of photometric analysis and who has studied the instructions for use of the spectrophotometer or photocolorimeter.

6. MEASUREMENT CONDITIONS

Measurements are carried out under the following conditions:

ambient air temperature (20 ± 5) °С;

atmospheric pressure (84.0 - 106.7) kPa (630 - 800 mm Hg);

relative humidity (80 ± 5)%;

mains voltage (220 ± 10) V;

AC frequency (50 ± 1) Hz.

7. WATER SAMPLING AND STORAGE

Sampling is carried out in accordance with the requirements of GOST R 51592-2000 “Water. General requirements to sampling.”*

*Supplements and amendments have been made in accordance with the protocol No. 23 of the meeting of the STC FP "CECA" of the Ministry of Natural Resources of Russia dated May 30, 2001.

7.1. Water samples are taken in glass or polyethylene bottles, pre-rinsed with selected water. The volume of the sample to be taken must be at least 200 cm 3 .

7.2. * Samples are analyzed no later than two hours after sampling or preserved by adding 5 cm 3 of concentrated nitric acid per 1 dm 3 of water.

*If it is required to determine manganese in dissolved form, the sample is filtered through a blue tape filter paper before canning.

7.3. When sampling, an accompanying document is drawn up in the approved form, which indicates:

purpose of analysis, suspected contaminants;

place, time of selection;

sample number;

position, name of the person taking the sample, date.

*Supplements and amendments have been made in accordance with the protocol No. 23 of the meeting of the STC FP "CECA" of the Ministry of Natural Resources of Russia dated May 30, 2001.

8. PREPARATION FOR MEASUREMENTS

8.1. Instrument preparation

The preparation of the spectrophotometer or photoelectric colorimeter for operation is carried out in accordance with work instruction for the operation of the device.

8.2. Preparation of solutions

8.2.1. Preparation of a solution of mercury (II) nitrate.

Dissolve 17.131 g of Hg(NO 3) 2 H 2 O in distilled water, first moistening with 1 cm 3 of concentrated nitric acid and diluted to 1 dm 3 .

1 cm 3 of the resulting solution is equivalent to 3.54 mg of chloride ions.

8.2.2. Preparation of ammonium persulfate solution.

Dissolve 20 g of ammonium persulfate (NH 4) 2 S 2 O 8 in 80 cm 3 of distilled water.

8.2.3. Preparation of silver nitrate solution.

Dissolve 16.9874 g of AgNO 3 in distilled water and dilute to 1 dm 3 .

8.2.4. Preparation of the basic solution of manganese from GSO with certified manganese content.

The solution is prepared in accordance with the instructions attached to the sample.

1 cm 3 of the solution should contain 0.01 mg of manganese.

The solution is good for a month.

8.3. Construction of a calibration graph

To build a calibration graph, it is necessary to prepare samples for calibration With mass concentration of manganese ions from 0.05 to 0.5 mg / dm 3. The conditions of the analysis, its conduct must comply with paragraphs 6 and 10.

The composition and number of samples for calibration for the construction of a calibration graph are given in Table 2. The error due to the procedure for preparing samples for calibration does not exceed 2.5%.

table 2

Composition and number of samples for calibration in the analysis of manganese ions

Samples for calibration are analyzed in ascending order of their concentration. To build a calibration graph, each artificial mixture must be photometered 3 times in order to eliminate random results and average the data. When constructing a calibration graph, the optical density values ​​are plotted along the ordinate axis, and the value of the substance concentration in mg / dm 3 is plotted along the abscissa axis.

8.4. Controlling the stability of the calibration characteristic

The stability control of the calibration characteristics is carried out at least once a month or when changing the batch of reagents. The means of control are newly prepared samples for calibration (at least 3 samples from those given in Table 2).

The calibration characteristic is considered stable if the following condition is met for each sample for calibration:

where X - result control measurement mass concentration of manganese ions in the calibration sample;

FROM- certified value of the mass concentration of manganese ions in the sample for calibration;

The standard deviation of within-laboratory precision, as determined by the implementation of the method in the laboratory.

Note . It is permissible to establish the standard deviation of intralaboratory precision when implementing the methodology in the laboratory on the basis of the expression: with subsequent refinement as information accumulates in the process of monitoring the stability of the analysis results.

The values ​​are given in table 1.

If the stability condition for the calibration characteristic is not met for only one calibration sample, it is necessary to re-measure this sample in order to eliminate the result containing a gross error.

If the calibration characteristic is unstable, find out the reasons and repeat the control using other calibration samples provided by the procedure. When the instability of the calibration characteristic is detected again, a new calibration curve is built.

9. REMOVAL OF INTERFERING EFFECTS

9.1. To eliminate the interfering effect of chloride ions, if their concentration does not exceed 300 mg / dm 3, it is proposed to introduce a solution of a mercury (II) salt, which forms a slightly dissociated compound with chloride ions. At a higher content of chloride ions, pre-processing nitric and sulfuric acids.

9.2. Organic substances interfere with the determination at their high concentration (COD exceeds 16 mg / dm 3). With a high content of organic substances, 5 cm 3 of concentrated nitric and concentrated sulfuric acid should be added to the sample, evaporated in a porcelain cup until sulfuric acid vapor appears, and after cooling, dissolve the residue in 5 cm 3 of nitric acid, adding distilled water to 100 cm 3. With a lower content of organic substances, one can limit oneself to boiling the sample for 5–10 minutes with the addition of 10 cm 3 of concentrated nitric acid per 100 cm 3 .

9.3. The interfering effect of iron is eliminated by adding 1 cm 3 of concentrated phosphoric acid to the sample, before oxidation with persulfate.

10. MEASUREMENTS

When measuring the mass concentration of manganese ions in samples of natural and waste water, the following operations are performed:

To 100 cm 3 of a sample, if it is necessary to pre-diluted or evaporated, add 3 cm 3 of concentrated nitric acid and such a volume of mercury nitrate solution (clause 8.2.1) that it is equivalent to the content of chloride ions in the sample taken, and in addition another 2 cm 3. Add, if necessary, phosphoric acid (d \u003d 1.7 g / cm 3), heat to a boil, add 5 cm 3 of ammonium persulfate solution (clause 8.2.2), 2 drops of silver nitrate solution (clause 8.2.3) and boil 5 min.

After cooling the solution, it is transferred to a volumetric flask with a capacity of 200 cm 3, diluted with distilled water to the mark and mixed. Optical density is measured at? = 540 nm with respect to a blank run in a cuvette with a layer thickness of 50 mm.

11. PROCESSING OF MEASUREMENT RESULTS

where FROM- the concentration of manganese ions, found on the calibration curve, mg/DM 3 ;

To- dilution or concentration factor.*

*Supplements and amendments have been made in accordance with the protocol No. 23 of the meeting of the STC FP "CECA" of the Ministry of Natural Resources of Russia dated May 30, 2001.

For the result of the analysis X cf take the arithmetic mean of two parallel definitions x1 and X 2

for which the following condition is satisfied:

where r- repeatability limit, the values ​​of which are given in table 3.

Table 3

Values ​​of the probability repeatability limit P = 0.95

If condition (1) is not met, methods for checking the acceptability of the results of parallel determinations and establishing the final result can be used in accordance with Section 5 of GOST R ISO 5725-6.

The discrepancy between the results of the analysis obtained in the two laboratories should not exceed the limit of reproducibility. If this condition is met, both results of the analysis are acceptable, and their arithmetic mean value can be used as the final one. Reproducibility limit values ​​are shown in Table 4.

Table 4

Reproducibility limit values ​​at probability P = 0.95

If the reproducibility limit is exceeded, methods for assessing the acceptability of the analysis results can be used in accordance with Section 5 of GOST R ISO 5725-6.

12. PRESENTING THE RESULTS OF THE ANALYSIS

12.1. Analysis result Xcp in documents providing for its use, it can be represented as:

where? - an indicator of the accuracy of the method.

Meaning? calculated by the formula:

Meaning? shown in table 1.

It is permissible to present the result of the analysis in the documents issued by the laboratory in the form: on condition

where X cf- the result of the analysis obtained in accordance with the prescription of the methodology;

± ? R- the value of the characteristic of the error of the results of the analysis, established during the implementation of the methodology in the laboratory and provided by the control of the stability of the results of dialysis.

Note . When presenting the result of the analysis, the documents issued by the laboratory indicate:

The number of results of parallel determinations used to calculate the result of the analysis;

Method for determining the result of the analysis (arithmetic mean or median of the results of parallel determinations).

12.2. In the event that the mass concentration of manganese ions in the analyzed sample exceeds the upper limit of the range, then it is allowed to dilute the sample so that the mass concentration of manganese ions corresponds to the regulated range.

Analysis result X cf in documents providing for its use, it can be represented as:

where ±?" is the value of the error characteristic of the results of the analysis, corrected by the value of the error of taking an aliquot.

12.3. If the mass concentration of manganese ions in the analyzed sample is below the minimum concentration determined by the method, concentration by evaporation is allowed. In this case, simultaneously with the analyzed sample, a control analysis of a certified solution containing manganese ions or corresponding to their content in the initial working sample is carried out.

The result of the analysis of the initial working sample is considered satisfactory if the following condition is met:

where X- the result of the control measurement of the mass concentration of manganese ions in the control sample (certified solution);

FROM- certified value of the mass concentration of manganese ions in the control sample (certified solution);

To- standard operational control analysis procedures.

- the value of the characteristic of the error of the results of the analysis, corrected for the value of the concentration of the sample.

13. QUALITY CONTROL OF THE RESULTS OF THE ANALYSIS DURING THE IMPLEMENTATION OF THE METHOD IN THE LABORATORY

Quality control of the analysis results when implementing the methodology in the laboratory provides for:

Operational control of the analysis procedure (based on the assessment of the error in the implementation of a single control procedure);

Control of the stability of the results of the analysis (based on the control of the stability of the standard deviation of repeatability, standard deviation of intralaboratory precision, error).

13.1 Algorithm for operational control of the analysis procedure using the addition method

K to with control standard TO.

The result of the control procedure K to calculated according to the formula

where X" cp- the result of the analysis of the mass concentration of manganese ions in a sample with a known additive is the arithmetic mean of two results of parallel determinations, the discrepancy between which satisfies condition (1) of section 11.

X cp - the result of the analysis of the mass concentration of manganese ions in the original sample is the arithmetic mean of two results of parallel determinations, the discrepancy between which satisfies the condition (1) of section 11.

Control standard K calculated according to the formula

where - values ​​of the error characteristic of the analysis results, established in the laboratory when implementing the method, corresponding to the mass concentration of manganese ions in the sample with a known additive and in the original sample, respectively.

Note .

If condition (2) is not met, the control procedure is repeated. If condition (2) is not met again, the reasons leading to unsatisfactory results are found out and measures are taken to eliminate them.

13.2 Algorithm for online control of the analysis procedure using control samples

Operational control of the analysis procedure is carried out by comparing the result of a single control procedure K to with control standard TO.

The result of the control procedure K to calculated according to the formula

where cp- the result of the analysis of the mass concentration of manganese ions in the control sample is the arithmetic mean of two results of parallel determinations, the discrepancy between which satisfies the condition (1) of section 11;

FROM- certified value of the control sample.

Control standard To calculated by the formula:

where ±? l - characteristic of the error of the results of the analysis, corresponding to the certified value of the sample for control.

Note . It is permissible to establish the error characteristic of the analysis results when implementing the methodology in the laboratory on the basis of the expression: with subsequent refinement as information accumulates in the process of monitoring the stability of the analysis results.

The analysis procedure is considered satisfactory if the following condition is met:

If condition (3) is not met, the control procedure is repeated. If condition (3) is not met again, the reasons leading to unsatisfactory results are found out and measures are taken to eliminate them.

The frequency of operational control of the analysis procedure, as well as the ongoing procedures for monitoring the stability of the analysis results, are regulated in the Laboratory Quality Manual.

STATE COMMITTEE OF THE RUSSIAN FEDERATION ON STANDARDIZATION AND METROLOGY

CERTIFICATE No. 224.0103.032/2004

CERTIFICATE

on the certification of the measurement technique

Measurement technique mass concentration of manganese in natural and sewage photometric method using ammonium persulfate.

Developed FGU "Center environmental control and Analysis” Ministry of Natural Resources of Russia (Moscow).

certified in accordance with GOST R 8.563-96.

Certification was carried out based on the results metrological examination of materials for the development of measurement methods.

As a result of the testing, it was found that the method meets the metrological requirements for it and has the following main metrological characteristics:

1. Range of measurements, values ​​of indicators of accuracy, repeatability, reproducibility

2. Range of measurements, values ​​of limits of repeatability and reproducibility at probability P = 0.95

3. When implementing the methodology in the laboratory, provide:

Operational control of the measurement procedure (based on the assessment of the error in the implementation of a single control procedure);

Monitoring the stability of measurement results (based on the stability control of the standard deviation of repeatability, standard deviation of intralaboratory precision, error).

The algorithm for operational control of the measurement procedure is given in the document on the measurement procedure.

The procedures for monitoring the stability of the results of the measurements performed are regulated in the Quality Manual of the laboratory.

4. Date of issue of the certificate, 02.02.2004

Deputy Directors for scientific work I.E. Dobrovinsky

* and GOST 24481 **.

* On the territory of the Russian Federation, GOST R 51232-98 applies.

** On the territory of the Russian Federation, GOST R 51593-2000 applies.

Glass laboratory glasses in accordance with GOST 25336.

Flat-bottom flasks with a capacity of 500 and 250 cm3 according to GOST 1770.

Laboratory filter paper according to GOST 12026.

Ammonium persulphate (persulfate) according to GOST 20478.

Sodium hydroxide (caustic soda) according to GOST 4328, 4% solution.

Orthophosphoric acid 85% according to GOST 6552.

Phenolphthalein.

Mercury sulfate oxide.

All reagents must be of analytical grade.

3. DETERMINATION OF MANGANESE CONTENT WITH THE SEPARATION OF CHLORIDE ION
CO-precipitation with magnesium oxide hydrate (Method A)

When analyzing water with a high manganese content, the colorimetric titration method is also used. To do this, 50 cm3 of the test water containing is transferred into a glass with a capacity of 100 cm3, and distilled water is added to another glass of the same capacity in a volume equal to the volume of the test solution. Putting both glasses side by side on white paper, pour a standard solution of potassium permanganate into a glass with distilled water from a burette until the color in both glasses is the same. According to the volume of the spent solution of potassium permanganate, the content of manganese in the test water is calculated.

. DETERMINATION OF MANGANESE CONTENT WITH THE REMOVAL OF CHLORIDE ION
BY ADDING MERCURY SULPHATE (Method B)

5.1 . Preparation for analysis

5.1.1. Preparation of the basic standard solution of manganese sulfate

2748 g of MnSO4, calcined at 500 °C, are dissolved in approximately 10 cm3 of dilute hot sulfuric acid (1:4) and the volume is adjusted to 1 dm3 with distilled water. 1 cm3 of solution contains 0.10 mg Mn2+.

5.1.2. Preparation of a working standard solution of manganese sulfate

The solution is prepared by diluting 100 cm3 of the stock solution to 1 dm3 with distilled water. 1 cm3 of solution contains 0.01 mg Mn2+.

The solution is prepared on the day of the analysis.

5.1.3. Preparation of a special reagent

G of mercury sulfate (HgSO4) is dissolved in 400 cm3 of concentrated nitric acid (HNO3) and 200 cm3 of distilled water. Then 200 cm3 of 85% phosphoric acid and 0.035 g of silver nitrate (AgNO3) are added. After cooling the solution, its volume is adjusted to 1 dm3 with distilled water.

5.2 . Conducting an analysis

The influence of chlorides is eliminated if their content in the test water is not more than 0.1 g.

Add 5 cm3 of a special reagent to an aliquot of the test water, and the sample is concentrated by boiling or diluted with distilled water to 90 cm3. Then add 1.0 g of ammonium persulfate and bring the solution to a boil on an electric stove and boil for 1 minute. Remove from the plate and after 1 min quickly cool under running water, dilute the solution with distilled water to 100 cm3, mix.

The color intensity is determined visually or photometrically using a standard scale prepared under the same conditions as the test water.

To prepare the standard scale, a working standard solution of manganese sulfate is used. The standard solutions of the scale contain from 0.005 to 0.1 mg of manganese. The color of the scale is stable for 24 hours. Optical density is measured with a green light filter (l = 530 - 525 nm).

Distilled water is used as a control liquid.

5.3 . Results processing

where a- manganese content found on a standard scale or on a calibration graph, mg;

V- the volume of the investigated water taken for determination, cm3.

The allowable discrepancy between repeated determinations is 15% (rel.).

INFORMATION DATA

1. APPROVED AND INTRODUCED BY Decree of the State Committee for Standards of the Council of Ministers of the USSR of December 25, 1972 No. 2320