MASS CONCENTRATION OF CALCIUM IN WATERS.
MEASUREMENT PROCEDURE
TITRIMETRIC METHOD WITH TRILON B

Rostov-on-Don

2007

Preface

1 DEVELOPED BY SI “Hydrochemical Institute”

2 DEVELOPERS L.V. Boeva, Ph.D. chem. Sciences, T.S. Evdokimova

3 AGREED with UMZA and NPO Typhoon of Roshydromet

4 APPROVED AND ENTERED INTO EFFECT by the Deputy Head of Roshydromet on March 13, 2007.

5 CERTIFIED BY GU "Hydrochemical Institute" certificate of certification No. 55.24-2006 dated 16.05. 2006

6 REGISTERED BY GU "NPO "Typhoon" under the number RD 52.24.403-2007 dated March 30, 2007.

7 INSTEAD RD 52.24.403-95 “Methodological instructions. Methodology for measuring the mass concentration of calcium in waters using the titrimetric method with Trilon B"

Introduction

Calcium is one of the most abundant elements in the earth's crust. Due to its high chemical activity in nature, calcium is found only in the form of compounds. Calcium carbonate CaCO 3 is one of the most common compounds on earth. It is found in the form of many minerals - calcite, chalk, marble, limestone, dolomite, etc.

The main sources of calcium entering natural waters are the processes of chemical weathering and dissolution of calcium-containing minerals, primarily limestones, dolomites, gypsum and other sedimentary and metamorphic rocks. Dissolution is promoted by microbial processes of decomposition of organic substances, accompanied by a decrease in pH. Large amounts of calcium are carried out with wastewater from the silicate, metallurgical, glass, chemical industries and runoff from agricultural land, especially when calcium-containing mineral fertilizers are used.

Under natural conditions, changes in the concentration of dissolved calcium are caused mainly by the equilibrium of carbon dioxide salts and carbon dioxide. In mineralized waters containing a significant amount of sulfates, the concentration of dissolved calcium decreases due to the formation of poorly soluble CaSO 4 .

In water bodies, calcium in noticeable quantities can precipitate in the form of CaCO 3 during water evaporation, as well as under conditions of activated photosynthesis, accompanied by an increase in water pH. A characteristic feature of calcium is its tendency to form fairly stable supersaturated solutions of CaCO 3 in surface waters. The ionic form of calcium is characteristic only of low-mineralized waters. With increasing mineralization, calcium ions form neutral (CaSO 4 and CaCO 3) or charged (CaHCO 3 +) ion pairs. Calcium forms fairly stable complex compounds with organic substances contained in water.

In river and lake waters, the calcium content in most cases ranges from 10 to 100 mg/dm3. When water comes into contact with minerals containing calcium, its content can increase to several hundred milligrams per cubic decimeter.

The maximum permissible concentration (MPC) of calcium in the water of fishery water bodies is 180 mg/dm 3; the MAC has not been established for drinking water bodies.

GUIDANCE DOCUMENT

MASS CONCENTRATION OF CALCIUM IN WATERS.

METHOD FOR PERFORMING MEASUREMENTS USING THE TITRIMETRIAL METHOD WITH TRILON B

Date of introduction

3 Assigned measurement error characteristics

3.1 Subject to all measurement conditions regulated by the methodology, the error characteristics of the measurement result with a probability of 0.95 should not exceed the values ​​​​given in Table 1.

Table 2 - Measurement range, values ​​of error characteristics and its components (P = 0.95)

	Repeatability index (standard deviation of repeatability) s g, mg/dm 3	Reproducibility index (standard deviation of reproducibility) s R, mg/dm3	Correctness index (limit of systematic error at probability P = 0.95) ± D s, mg/dm 3	Accuracy indicator (error limits at probability P = 0.95) ± D, mg/dm 3
From 1.0 to 200.0 incl.	0.1 + 0.004× X	0.1 + 0.031× X	0.1 + 0.018× X	0.2 + 0.063× X

When performing measurements in samples with a mass concentration of calcium over 200 mg/dm 3 after appropriate dilution, the measurement error does not exceed D×h, where D - error in measuring calcium concentration in a diluted sample; h - degree of dilution.

The detection limit for calcium is 0.6 mg/dm3.

The accuracy indicator values ​​of the method are used when:

Registration of measurement results issued by the laboratory;

Assessing the activities of laboratories for the quality of measurements;

Assessing the possibility of using measurement results when implementing the technique in a specific laboratory.

4 Measuring instruments, auxiliary devices, reagents, materials

When performing measurements, the following measuring instruments and other technical means are used:

4.1.1 High-quality laboratory balances (II) accuracy class according to GOST 24104-2001.

4.1.2 Medium laboratory scales ( III)accuracy class according to GOST 24104-2001 with a weighing limit of 200 g.

4.1.3 State standard sample of the composition of an aqueous solution of calcium GSO 8065-95 (hereinafter referred to as GSO).

4.1.4 Measuring flasks 2 accuracy classes 2, 2a according to GOST 1770-74 with capacity: 250 cm 3 - 4 pcs.

500 cm 3 - 2 pcs.

4.1.5 Graduated pipettes, 2 accuracy classes 1, 2 according to GOST 29227-91, capacity: 1 cm 3 - 5 pcs.

2 cm 3 - 3 pcs.

5 cm 3 - 1 pc.

10 cm 3 - 1 pc.

4.1.6 Pipettes with one mark, accuracy class 2, execution 2 according to GOST 29169-91, capacity: 10 cm 3 - 2 pcs.

25 cm 3 - 2 pcs.

50 cm 3 - 2 pcs.

100 cm 3 - 2 pcs.

4.1.7 Burettes 2 accuracy classes 1, 3 according to GOST 29251-91 with capacity:

5 cm - 1 pc.

10 cm 3 - 1 pc.

25 cm 3 - 1 pc.

4.1.8 Dimensional cylinders 1, 3 according to GOST 1770-74 with capacity:

25 cm 3 - 1 pc.

50 cm 3 - 1 pc.

100 cm 3 - 2 pcs.

500 cm 3 - 1 pc.

1000 cm 3 - 1 pc.

4.1.9 Conical test tubes, version 1 according to GOST 1770-74, capacity

10 cm 3 - 2 pcs.

4.1.10 Conical flasks Kn version 2, THS, according to GOST 25336-82 capacity

250 cm 3 - 10 pcs.

500 cm 3 - 2 pcs.

4.1.11 Glasses V-1, THS according to GOST 25336-82 with a capacity of:

100 cm 3 - 3 pcs.

250 cm 3 - 2 pcs.

400 cm 3 - 2 pcs.

600 cm 3 - 2 pcs.

1000 cm 3 - 2 pcs.

4.1.12 Polypropylene glass 250 cm 3 - 1 pc.

4.1.13 Laboratory funnels according to GOST 25336-82 with diameter:

56 mm - 1 pc.

75 mm - 4 pcs.

4.1.14 Weighing cups (bugs) according to GOST 25336-82:

SV-19/9 - 2 pcs.

SV-24/10 - 1 pc.

SV-34/12 - 1 pc.

4.1.15 Mortar No. 3 or 4 according to GOST 9147-80 - 1 pc.

4.1.16 Chromatographic column with a diameter of 1.5 - 2.0 cm and

length 25 - 30 cm - 1 pc.

4.1.17 Watch glass - 1 pc.

4.1.18 Glass rods - 2 pcs.

4.1.19 Bottles for storing samples and solutions made of light and dark glass with screw-on or ground-in caps with a capacity of 100 cm3, 250 cm3, 500 cm3, 1000 cm3.

4.1.20 Polyethylene (polypropylene) containers for storing samples and solutions with a capacity of 100 cm3, 250 cm3, 500 cm3, 1000 cm3.

4.1.21 Household refrigerator.

4.1.22 Drying cabinet for general laboratory purposes.

4.1.23 Electric stove with a closed spiral according to GOST 14919-83.

4.1.24 Device for filtering samples using membrane or paper filters.

It is allowed to use other types of measuring instruments, utensils and auxiliary equipment, including imported ones, with characteristics no worse than those given in.

When performing measurements, the following reagents and materials are used:

4.2.1 Calcium carbonate (calcium carbonate) according to GOST 4530-76, chemically pure.

4.2.2 Disodium salt ethylenediamine -N,N ,N,N-tetraacetic acid 2-water (trilon B) according to GOST 10652-73, analytical grade.

4.2.3 Granulated zinc according to TU 6-09-5294-86, analytical grade.

4.2.4 Ammonium chloride (ammonium chloride) according to GOST 3773-72, analytical grade.

4.2.5 Aqueous ammonia according to GOST 3760-79, analytical grade.

4.2.6 Sodium chloride (sodium chloride) according to GOST 4233-77, analytical grade.

4.2.7 Sodium hydroxide (sodium hydroxide) according to GOST 4328-77, analytical grade.

4.2.8 Sodium sulphide 9-water (sodium sulfide) according to GOST 2053-77, analytical grade, or sodium N,N -diethyldithiocarbamate 3-water (sodium diethyldithiocarbamate) according to GOST 8864-71, analytical grade.

4.2.9 Hydrochloric acid according to GOST 3118-77, analytical grade.

4.2.10 Ammonium purpurate (murexide) according to TU 6-09-1657-72, analytical grade.

4.2.11 Naphthol green B.

4.2.12 Eriochrome black T (chromogen black ET).

4.2.13 Hydroxylamine hydrochloride according to GOST 5456-79, analytical grade.

4.2.14 Active carbon.

4.2.15 Potassium alum according to GOST 4329-77, analytical grade.

4.2.16 Barium chloride 2-water (barium chloride) according to GOST 4108-72, analytical grade.

4.2.17 Distilled water according to GOST 6709-72.

4.2.17 Universal indicator paper (pH 1-10) according to TU 6-09-1181-76.

4.2.18 Membrane filters “Vladipor MFAS-OS-2”, 0.45 microns, according to TU 6-55-221-1-29-89 or another type, equivalent in characteristics or ash-free paper filters “blue tape” according to TU 6-09-1678-86.

4.2.19 Ash-free paper filters “white tape” according to TU 6-09-1678-86.

It is allowed to use reagents manufactured according to other regulatory and technical documentation, including imported ones, with qualifications not lower than those specified in.

5 Measurement method

The measurements are based on the ability of calcium ions to form a slightly dissociated compound that is stable in an alkaline environment with Trilon B. The end point of the titration is determined by the color change of the indicator (murexide) from pink to red-violet. To increase the clarity of the color transition, it is preferable to use a mixed indicator (murexide + naphthol green B). At the same time, at the end point of titration, the color changes from dirty green to blue.

Under analytical conditions, magnesium precipitates in the form of hydroxide and does not interfere with the determination.

6 Safety and environmental requirements

6.1 When performing measurements of the mass concentration of calcium in samples of natural and treated wastewater, comply with the safety requirements established in national standards and relevant regulatory documents.

6.2 According to the degree of impact on the body, harmful substances used when performing measurements belong to hazard classes 2 and 3 according to GOST 12.1.007.

6.4 There are no additional requirements for environmental safety.

7 Operator qualification requirements

Persons with secondary vocational education or without vocational education, but who have worked in the laboratory for at least a year and have mastered the technique, are allowed to perform measurements and process their results.

8 Measurement conditions

When performing measurements in the laboratory, the following conditions must be met:

Ambient air temperature (22 ± 5) °C;

Atmospheric pressure from 84.0 to 106.7 kPa (from 630 to 800 mm Hg);

Air humidity no more than 80% at 25 °C;

Mains voltage (220 ± 10) V;

AC power frequency (50 ± 1) Hz.

9 Sampling and storage

Sampling for measurements of calcium mass concentration is carried out in accordance with GOST 17.1.5.05 and GOST R 51592. Sampling equipment must comply with GOST 17.1.5.04 and GOST R 51592. Turbid samples are filtered through a 0.45 µm membrane filter or blue ribbon paper filter. The first portion of the filtrate should be discarded. Samples are stored in glass or polyethylene containers for no more than 6 months.

10 Preparing to take measurements

10.1 Preparation of solutions and reagents

10.1.1 Trilon B solution with a molar concentration of 0.02 mol/dm 3 amount of substance equivalent (hereinafter referred to as EQE).

Dissolve 3.72 g of Trilon B in 1 dm 3 of distilled water. The exact concentration of the solution is determined using a solution of zinc chloride in accordance with at least 1 time per month.

The solution is stored in a tightly closed container.

Weigh out about 0.35 g of metallic zinc, moisten it with a small amount of concentrated hydrochloric acid and immediately wash it with distilled water. Zinc is dried in an oven at a temperature of 105 ° C for 1 hour, then cooled and weighed on a laboratory balance accurate to the fourth decimal place.

A sample of zinc is transferred quantitatively into a volumetric flask with a capacity of 500 cm 3, into which 10 - 15 cm 3 of bidistilled water and 1.5 cm 3 of concentrated hydrochloric acid are first added. Zinc is dissolved. After dissolution, the volume of the solution is brought to the mark on the flask with distilled water and mixed.

Calculate the molar concentration of zinc chloride C Zn , mol/dm 3 KVE, in the resulting solution according to the formula

(1)

where q - weighed amount of metallic zinc, g;

32.69 - molar mass of zinc equivalent (1/2 Zn 2+ ), g/mol;

V is the capacity of the volumetric flask, dm 3.

When calculating the value of C Zn rounded so that it contains 4 significant figures.

10.1.3 Ammonium-ammonia buffer solution

In a volumetric flask with a capacity of 500 cm 3, 7.0 g of ammonium chloride is dissolved in 100 cm 3 of distilled water and 75 cm 3 of concentrated ammonia solution is added. The volume of the solution is adjusted to the mark on the flask with distilled water and mixed thoroughly. The buffer solution is stored in a plastic container for no more than 2 months.

10.1.4 Eriochrome black T indicator

In a mortar with 50 g of sodium chloride, carefully grind 0.5 g of eriochrome black T. Store in a dark glass bottle for no more than 6 months.

In a mortar with 100 g of sodium chloride, thoroughly grind 0.2 g of murexide. Store in a dark glass bottle for no more than 6 months.

In a mortar with 100 g of sodium chloride, carefully grind 0.2 g of murexide and 0.4 g of naphthol green B. Store in a dark glass bottle for no more than 6 months.

10.1.7 Naphthol green solution B, 0.8%

0.4 g of naphthol green B is dissolved in 50 cm 3 of distilled water. The solution is stored in a dark bottle for 3 months.

To 5 cm 3 of a 0.8% solution of naphthol green B, add 45 cm 3 of distilled water and mix. The solution is stored for no more than 3 days.

10.1.9 Sodium hydroxide solution, 20%

Dissolve 20 g of sodium hydroxide in 80 cm 3 of distilled water.

10.1.10 Sodium hydroxide solution, 8%

Dissolve 40 g of sodium hydroxide in 460 cm 3 of distilled water.

10.1.11 Sodium hydroxide solution, 0.4%

Dissolve 2 g of sodium hydroxide in 500 cm 3 of distilled water.

Sodium hydroxide solutions are stable when stored in tightly closed plastic containers.

10.1.12 Sodium sulfide solution

2 g of sodium sulfide are dissolved in 50 cm 3 of distilled water. Store in a tightly closed plastic container in the refrigerator for no more than a week.

10.1.13 Sodium diethyldithiocarbamate solution

5 g of sodium diethyldithiocarbamate are dissolved in 50 cm 3 of distilled water. Store for no more than 2 weeks in the refrigerator.

10.1.14 Hydroxylamine hydrochloride solution

5 g of hydroxylamine hydrochloride are dissolved in 100 cm 3 of distilled water. Store in a tightly closed dark bottle in the refrigerator for a month.

10.1.15 Hydrochloric acid solution, 1:3

Mix 200 cm 3 of concentrated hydrochloric acid with 600 cm 3 of distilled water.

10.1.16 Activated carbon

The preparation of activated carbon is given in the Appendix.

10.1.17 Aluminum hydroxide suspension

The preparation of a suspension of aluminum hydroxide is given in the Appendix.

In a conical flask with a capacity of 250 cm 3, using a pipette with one mark, add 10.0 cm 3 of zinc chloride solution (), add 90 cm 3 of distilled water, 5 cm 3 of ammonium-ammonia buffer solution and 70 - 100 mg of eriochrome black T indicator. The contents of the flask are thoroughly mixed and titrated from a 25 cm 3 burette with a solution of Trilon B until the color changes from violet-red to blue (blue).

The molar concentration of a solution of Trilon B C Tr, mol/dm 3 KVE, is calculated using the formula

(2)

where C Zn - molar concentration of zinc chloride solution, mol/dm 3 KVE;

V Zn is the volume of zinc chloride solution, cm 3.

V Zn is the volume of Trilon B solution used for titration, cm 3.

11 Taking measurements

11.1 Selection of titration conditions

The volume of an aliquot of a water sample for measuring the mass concentration of calcium is selected based on the known value of water hardness or based on the results of an evaluative titration.

For evaluation titration, take 10 cm 3 of water, add 0.2 cm 3 of 8% sodium hydroxide solution, 20 - 30 mg of murexide indicator and titrate with Trilon B solution until the color changes from pink to red-violet. Based on the volume of Trilon B solution consumed for titration, select from the table the appropriate volume of an aliquot of the water sample to measure the mass concentration of calcium.

Table 2 - Volume of water sample recommended for measuring the mass concentration of calcium

Depending on the calcium concentration, the titration should be carried out using a burette of suitable capacity. If, according to the results of the evaluation titration, the volume of Trilon B is less than 0.4 cm 3 or the hardness value is less than 1 mmol/dm 3 KVE, use a burette with a capacity of 5 cm 3; when the volume of Trilon is less than 0.8 cm 3 or the hardness value is from 1 to 2 mmol/dm 3 KVE - a burette with a capacity of 10 cm 3; at a higher calcium concentration or hardness value - a burette with a capacity of 25 cm 3. If you do not have a burette with a capacity of 10 cm 3, you can use a burette with a capacity of 25 cm 3; It is permissible to replace a burette with a capacity of 5 cm3 with a burette with a capacity of 10 cm3, but replacing a microburette with a capacity of 5 cm3 with a burette with a capacity of 25 cm3 is unacceptable.

Up to 3 incl.

St. 3 to 8 inclusive.

St. 8 to 12 incl.

Permissible discrepancy in Trilon B volumes, cm 3

11.2.3 To obtain a sufficiently clear color transition during titration with a mixed indicator, the ratio of murexide and naphthol green in the mixture is important. For different batches of indicators, this ratio may be different. If, when using a dry mixed indicator, it is not possible to obtain a clear color transition at the end point of the titration, naphthol green should be used in the form of a 0.08% solution (see). Titration is carried out as follows. Take an aliquot of water into a conical flask, add 2 cm 3 of 8% sodium hydroxide solution, 0.2 - 0.3 g of murexide indicator (see), mix and add a solution of naphthol green B until the solution becomes dirty. green color (in total there is approximately 0.9 - 1.2 cm 3 of solution). After this, the sample is titrated in accordance with.

11.3 Elimination of interfering influences

11.3.1 Measurements of the mass concentration of calcium are interfered with by iron ions (more than 10 mg/dm 3), cobalt, nickel (more than 0.1 mg/dm 3), aluminum (more than 10 mg/dm 3), copper (> 0.05 mg/dm 3), causing an unclear color change at the equivalence point, or completely eliminating the possibility of indicating the end point of the titration.

Other cations, such as lead, cadmium, manganese ( II ), zinc, strontium, barium at high concentrations (usually not found in natural waters) can be partially titrated together with calcium and magnesium and increase the consumption of Trilon B. To eliminate or reduce the interfering effect of metal cations, add 0.5 cm to the sample before titration 3 solutions of sodium sulfide or diethyldithiocarbamate and 0.5 cm 3 solution of hydroxylamine hydrochloride.

11.3.2 Titration results may be distorted in the presence of significant amounts of anions (HCO 3 -, CO 3 -, PO 4 -, SiO 3 2-). To reduce their influence, the sample should be titrated immediately after adding sodium hydroxide and indicator.

11.3.3 The interfering influence of suspended substances is eliminated by filtering the sample.

11.3.4 If the water sample is noticeably colored due to the presence of substances of natural or anthropogenic origin, it becomes difficult to fix the titration end point. In this case, before performing measurements, the sample should be passed at a speed of 3 - 5 cm 3 /min through a chromatographic column filled with active carbon (layer height 15 - 20 cm). The first 25 - 30 cm 3 of the sample passing through the column is discarded.

As a rule, colored compounds of anthropogenic origin are sorbed by active carbon almost completely, while natural ones (humic substances) are only partially sorbed. If the color of the sample, caused by humic substances, cannot be eliminated by activated carbon, determining the end point of titration is greatly facilitated by using a slightly overtitrated sample of the same water (witness sample) for comparison.

The precipitate in the beaker and the filter are washed 2-3 times with small portions of distilled water, collecting the washing water in the same flask. After this, bring the solution in the flask to the mark, mix, take the required aliquot from the flask and titrate it in accordance with.

11.3.6 If the calcium concentration is sufficiently high, interfering influences can be eliminated by diluting the sample with distilled water.

12 Calculation and presentation of measurement results

12.1 Mass X, mg/dm 3, and molar X m, mmol/dm 3 KVE, calcium concentration in the analyzed water sample is determined by the formulas

(3)

where 20.04 is the mass of a mole of calcium CE (1/2 Ca 2+), g/mol;

WITH m r- molar concentration of Trilon B solution, mol/dm 3 KVE;

V m R- volume of Trilon B solution used for sample titration, cm 3;

V is the volume of water sample taken for titration, cm3.

If the color of the sample was removed using a suspension of aluminum hydroxide (see), the result obtained is multiplied by 1.25.

12.2 The measurement result in documents providing for its use is presented in the form:

(4)

Where - the arithmetic mean of two results, the difference between which does not exceed the repeatability limit r(2.77 s r ). Values ​​of s r are given in the table;

±D - limits of the error characteristics of the measurement results for a given mass concentration of calcium (table).

The numerical values ​​of the measurement result must end with a digit of the same digit as the values ​​of the error characteristic; the latter should not contain more than two significant figures.

12.3 It is acceptable to present the result in the form

(4)

where ± D l - the limits of the error characteristics of the measurement results, established during the implementation of the methodology in the laboratory and ensured by monitoring the stability of the measurement results.

Note - It is permissible to establish the characteristic of the error of measurement results when introducing a technique in a laboratory on the basis of the expression D l = 0.84 × D with subsequent clarification as information is accumulated in the process of monitoring the stability of measurement results.

12.4 The measurement results are documented in a protocol or journal entry according to the forms given in the Laboratory Quality Manual.

13 Quality control of measurement results when implementing the technique in the laboratory

13.1 General provisions

13.1.1 Quality control of measurement results when implementing the methodology in the laboratory includes:

Operational control by the performer of the measurement procedure (based on an assessment of repeatability, error in the implementation of a separate control procedure);

13.1.2 The frequency of operational control and procedures for monitoring the stability of measurement results are regulated in the Laboratory Quality Manual.

13.2 Algorithm for operational control of repeatability

13.2.1 Repeatability control is carried out for each of the measurement results obtained in accordance with the procedure. To do this, the selected water sample is divided into two parts, and measurements are performed in accordance with section.

13.2.2 Result of the control procedure r To , mg/dm 3, calculated by the formula

r k = |X 1 - X 2 |, (6)

where X 1, X 2 are the results of measurements of the mass concentration of calcium in the sample, mg/dm 3.

13.2.3 Repeatability limit rn, mg/dm 3, calculated by the formula

r n = 2.77 × s r , (7)

where s r - repeatability indicator, mg/dm 3 (table).

13.2.4 The result of the control procedure must satisfy the condition

13.3 Algorithm for operational control of the measurement procedure using the additive method together with the sample dilution method

13.3.1 Operational control of the measurement procedure using the additive method together with the sample dilution method is carried out if the mass concentration of calcium in the working sample is 10 mg/dm3 or more. Otherwise, operational control is carried out using the additive method according to. To introduce additives, use GSO or a certified calcium solution (Appendix).

13.3.2 Operational control by the performer of the measurement procedure is carried out by comparing the results of a separate control procedure K to with the control standard K.

13.3.3 The result of the control procedure K k, mg/dm 3, is calculated using the formula

(9)

where is the result of a control measurement of the mass concentration of calcium in a sample diluted in h times, with a known additive, mg/dm 3 ;

The result of a control measurement of the mass concentration of calcium in a sample diluted in h times, mg/dm 3 ;

13.3.4 Control standard K, mg/dm3, is calculated using the formula

(10)

where D lx ² ( D lx ¢ and D lx ) - values ​​of the error characteristics of the measurement results, established during the implementation of the method in the laboratory, corresponding to the mass concentration of calcium in a diluted sample with an additive (diluted sample, working sample), mg/dm 3 .

Note - To calculate the control standard, it is permissible to use the values ​​of the error characteristics obtained by calculation using the formulas D lx ¢

13.3.5 If the result of the control procedure satisfies the condition:

13.4.1 The performer’s control of the measurement procedure is carried out by comparing the results of a separate control procedure K to with the control standard K.

13.4.2 The result of the control procedure K k, mg/dm 3, is calculated using the formula

(12)

where is the result of a control measurement of the mass concentration of calcium in a sample with a known additive, mg/dm 3 ;

The result of measuring the mass concentration of calcium in the working sample, mg/dm 3 ;

C is the concentration of the additive, mg/dm3.

13.4.3 Error control standard K, mg/dm3, is calculated using the formula

(13)

where D lx ¢ (D lx ) - values ​​of the error characteristic of the measurement results, established during the implementation of the method in the laboratory, corresponding to the mass concentration of calcium in the sample with the additive (working sample), mg/dm 3.

Note - To calculate the control standard, it is permissible to use the values ​​of the error characteristics obtained by calculation using the formulas D lx ¢ = 0.84× D x ¢ and D ls = 0.84× D x.

3.4.4 If the result of the control procedure satisfies the condition

B.5 Procedure for preparing certified solutions

B.5.1 Preparation of a certified calcium solution AP1-Ca

Using high-precision scales, 31.216 g of calcium carbonate is weighed in a polypropylene glass with a capacity of 250 cm 3 to the fourth decimal place. The sample is moistened with distilled water and 120 cm 3 of hydrochloric acid (1:1) is gradually added with stirring. Cover the glass with a clean watch glass and leave until dissolved.

After dissolution, carefully, using a stick, transfer the solution through a funnel into a volumetric flask with a capacity of 250 cm 3 . Rinse the glass and funnel three or four times with distilled water and transfer the washes into the same flask. Bring the solution in the flask to the mark with distilled water and mix.

The resulting solution is assigned a calcium mass concentration of 50.0 mg/cm 3 .

B.5.2 Preparation of a certified AP2-Ca solution

25.0 cm 3 of AP1-Ca calcium solution is added to a volumetric flask with a capacity of 250 cm 3 using a pipette with one mark with a capacity of 5 cm 3. The volume of the solution is adjusted to the mark on the flask with distilled water and mixed.

The resulting solution is assigned a calcium mass concentration of 5.00 mg/cm 3 .

B.6 Calculation of metrological characteristics of certified solutions

B.6.1 Calculation of metrological characteristics of the certified AP1-Ca solution

The certified value of the mass concentration of calcium C1, mg/cm3, is calculated using the formula

(IN 1)

where m - mass of calcium carbonate sample, g;

V is the capacity of the volumetric flask, cm 3;

40.08 and 100.09 are the mass of a mole of calcium and calcium carbonate, respectively, g/mol.

Calculation of the limit of possible error values ​​for establishing the mass concentration of calcium in the AP1-Ca solution D 1

, (AT 2)

where C 1 is the value of the mass concentration of calcium assigned to the solution, mg/cm 3 ;

D m - the limiting value of the possible deviation of the mass fraction of the main substance in the reagent from the assigned value m, %;

m - mass fraction of the main substance in the reagent assigned to the chemically pure reagent, %;

D m - maximum possible weighing error, g;

m is the mass of a sample of calcium carbonate, g;

D V - the limit value of the possible deviation of the volume of the volumetric flask from the nominal value, cm 3;

V is the nominal volume of the volumetric flask used, cm 3.

The error in establishing the mass concentration of calcium in the AP1-Ca solution is equal to

B.6.2 Calculation of metrological characteristics of the certified AP2-Ca solution

The certified value of the mass concentration of calcium C 2, mg/cm 3, is calculated using the formula

(AT 3)

where C 1 is the value of the mass concentration of calcium assigned to the AP1-Ca solution, mg/cm 3 ;

V 1

V 2 - volumetric flask capacity, cm3.

Calculation of the error in establishing the mass concentration of calcium in the AP2-Ca solution D 2 , mg/cm 3, is carried out according to the formula:

(AT 4)

where C 2 is the value of the mass concentration of calcium assigned to the AP2-Ca solution, mg/cm 3 ;

D 1 - error in preparing the certified AP1-Ca solution, mg/cm 3 ;

C 1 - the value of the mass concentration of calcium assigned to the AP1-Ca solution, mg/dm 3 ;

D V 1 - limit value of possible volume deviation V 1 from the nominal value, cm 3;

V 1 - volume of AP1-Ca solution taken with a pipette, cm 3;

D V 2 - the limit value of the possible deviation of the capacity of the volumetric flask from the nominal value, cm 3;

V 2 - volumetric flask capacity, cm 3.

The error in establishing the mass concentration of calcium in the AP2-Ca solution is equal to

AT 7 Safety requirements

General safety requirements when working in chemical laboratories must be observed.

B.8 Requirements for the qualifications of performers

Certified solutions can be prepared by an engineer or laboratory technician with secondary vocational education, who has undergone special training and has worked in a chemical laboratory for at least 6 months.

B.9 Labeling requirements

Flasks with certified solutions must be labeled with the symbol indicating the certified solution, the mass concentration of calcium in the solution, the error in its determination and the date of preparation.

B.10 Storage conditions

The certified AP1-Ca solution is stored in a tightly closed bottle for a year.

The certified AP2-Ca solution is stored in a tightly closed bottle for no more than 3 months.

Federal Service for Hydrometeorology and Monitoring
environment

GOVERNMENT INSTITUTION
"HYDROCHEMICAL INSTITUTE"

CERTIFICATE No. 55.24-2006
about MVI certification

Measurement procedure mass concentration of calcium in water using the titrimetric method with Trilon B.

developed GU "Hydrochemical Institute" (GU GHI)

and regulated RD 52.24.403-2007

certified in accordance with GOST R 8.563-96 as amended in 2002.

Certification was carried out based on the results experimental research

As a result of the MVI certification, it was established:

1. The MVI meets the metrological requirements imposed on it and has the following basic metrological characteristics:

Measurement range, values ​​of error characteristics and its components (P = 0.95)

Measuring range of calcium mass concentration X, mg/dm 3	Repeatability index (standard deviation of repeatability) s r, mg/dm 3	Reproducibility index (standard deviation of reproducibility) s R, mg/dm3	Correctness index (limit of systematic error at probability P = 0.95) ± D s, mg/dm 3	Accuracy indicator (error limits at probability P = 0.95) ±D, mg/dm 3
From 1.0 to 200.0 incl.	0.1 + 0.004× X	0.1 + 0.031× X	0.1 + 0.018× X	0.2 + 0.063× X

2. Measurement range, values ​​of repeatability and reproducibility limits at confidence level P = 0.95

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

Operational control by the performer of the measurement procedure (based on the assessment of repeatability and error when implementing a separate control procedure);

Monitoring the stability of measurement results (based on monitoring the stability of standard deviation of repeatability, standard deviation of intra-laboratory precision, error).

The frequency of operational monitoring and procedures for monitoring the stability of measurement results are regulated in the Laboratory Quality Manual.

Chief metrologist of the State Chemical Institute A. A. Nazarova

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Hydrochemistry

Methodology for determining calcium and magnesium ions in natural waters (determining total water hardness)

D.Yu. Kovalev

1. Brief theory

2. Preparation of solutions

3. Taking measurements

3.1 Titrimetric method

3.2 Ion exchange chromatography method

1. Brief theory

Chemical analysis of natural and drinking water shows that any water is not a pure substance with the formula H 2 O, but a mixture of a large number of substances.

Numerous analyzes of natural waters have shown that among the large number of components dissolved in them, 90% of the salt content consists of carbonates, bicarbonates, chlorides and sulfates of calcium, magnesium and sodium. O.A. Alekin proposed a classification of natural waters based on the results of their chemical analysis. Based on the predominant anion, waters are divided into three classes: carbonate (hydrocarbonate), chloride and sulfate. Based on the predominant cation, waters are divided into three groups: calcium, magnesium and sodium.

Natural waters constantly contain calcium and magnesium ions, which ensure water hardness. The source of their entry into water is the dissolution of gypsum, limestone and dolomites that are part of the rocks. In sanitary and hygienic terms, calcium and magnesium ions do not pose a great danger, but excessive hardness of water makes it unsuitable for domestic purposes, because the resulting scale damages the heating elements of electrical water heating systems. Optimal water hardness is up to 7 mEq/l.

Two methods are used to determine calcium and magnesium ions:

1. titrimetric

2. ion exchange chromatography method

1. The most accurate and widespread method for determining total hardness is complexometric, based on the formation of strong intra-complex compounds with Trilon B by Ca 2+ and Mg 2+ ions. Eriochrome black is used as an indicator when determining total hardness. Depending on the overall hardness, the concentration of the Trilon B working solution and the volume of the water sample may be different.

To determine calcium in natural waters, the trilonometric method with the indicator murexide is mainly used.

2. Preparation of solutions

Trilon B solution with a concentration of 0.02 mol/dm 3 equivalents.

Weight 3.72 g. Trilon B is dissolved in 1 dm 3 of distilled water. The exact concentration is determined using a standard zinc chloride solution. The solution is stored in a plastic container, its concentration is checked at least once a month.

A solution of zinc chloride with a concentration of 0.02 mol/dm 3 equivalents.

Weigh out about 0.35 g of metallic zinc on a technical scale, moisten it with a small amount of concentrated hydrochloric acid and immediately wash it with distilled water. The zinc is dried in an oven at 105 for 1 hour, then cooled and weighed on an analytical balance.

A sample of zinc is placed in a volumetric flask with a capacity of 500 cm 3, into which 10-15 cm 3 of distilled water and 1.5 cm 3 of concentrated hydrochloric acid are first added. Zinc is dissolved. After dissolving the zinc, the volume of the solution is adjusted to the mark on the flask with distilled water. Calculate the molar concentration of the equivalent of a solution of zinc chloride C Zn (1/2 ZnCl 2), mol/dm 3, using the formula:

where m is the weight of metallic zinc, g; 32.69 - molar mass of Zn 2+ equivalent, g/mol; V is the volume of the volumetric flask, cm 3.

Buffer solution NH 4 Cl + NH 4 OH.

7.0 g of ammonium chloride is dissolved in a 500 cm 3 volumetric flask in 100 cm 3 of distilled water and 75 cm 3 of concentrated ammonia solution is added. The volume of the solution is adjusted to the mark with distilled water and mixed thoroughly. The buffer solution is stored in glass or polyethylene containers for no more than 2 months. Sodium hydroxide, 2 mol/dm3.

40 g of sodium hydroxide are dissolved in a 500 cm 3 volumetric flask and the solution is brought to the mark with distilled water.

Indicator eriochrome black T.

Grind 0.25 g of eriochrome black T with 50 g of sodium chloride in a mortar.

Murexide indicator.

Grind 0.5 g of murexide with 100 g of sodium chloride. It is better not to prepare an aqueous solution, because Murexide is unstable in solution.

Sodium sulfide solution, 4%.

2 g of sodium sulfide are dissolved in 50 cm 3 of distilled water. Store in a tightly sealed plastic container for no more than a week.

Hydroxylamine hydrochloride solution.

5 g of hydroxylamine hydrochloride is dissolved in 100 cm 3 of distilled water. Store for no more than 2 months.

Establishing the exact concentration of Trilon B solution.

Add 10 cm 3 of zinc chloride solution to a conical flask with a capacity of 250 cm 3, add distilled water to approximately 100 cm 3, 5 cm 3 of a buffer solution and 10-15 mg of the indicator eriochrome black T. The contents of the conical flask are thoroughly mixed and titrated from a burette with a Trilon solution B until the color changes from red to blue. The concentration of Trilon B solution is calculated using the formula:

3. Taking measurements

3.1 Titrimetric method

Determination of calcium and magnesium ions

Elimination of Interfering Ions

To eliminate the interfering influence of iron, zinc, copper and tin cations, add 0.5 ml of sodium sulfide solution to the sample.

To eliminate the interfering effect of manganese, add 0.5 ml of hydroxylamine hydrochloric acid solution to the sample.

Progress of analysis

v Evaluative titration

Before analyzing a water sample with an unknown hardness value, an evaluative titration is carried out. To do this, take 10 cm 3 of water, add 0.5 cm 3 of a buffer solution, an indicator (eriochrome black T) and titrate until the color changes from red to blue. Based on the amount of Trilon B consumed, the corresponding volume of water sample is selected from Table 1.

ion exchange chromatography water magnesium

v Determination of the amount of calcium and magnesium

To a sample of the required volume (see Evaluative titration) 100 cm 3 add 5 cm 3 buffer, indicator (eriochrome black T) on a spatula. Titrate immediately with stirring until the color changes from wine red to blue.

v Determination of calcium

To a sample of the required volume (see Evaluative titration) 100 cm 3 add 2 cm 3 NaOH (2N) and an indicator (murexide) on a spatula. Titrate until the color changes from red to purple. The color of the solution should be compared with the color of the titrated solution.

where Str is the molar concentration of the equivalent of Trilon B, mol/dm 3 ; V"tr is the volume of Trilon B used for titration with murexide, cm 3 (see Determination of calcium); 20.04 is the equivalent mass of Ca 2+; Vsample is the volume of the sample taken for analysis, cm 3.

where Str is the molar concentration of the equivalent of Trilon B, mol/dm 3 ; V tr - volume of Trilon B used for titration with eriochrome black T, cm 3 (see Determination of the amount of calcium and magnesium); V"tr - volume of Trilon B used for titration with murexide, cm 3 (see Determination of calcium); 12.15 - equivalent mass of Mg 2+; Vsample - volume of sample taken for analysis, cm 3.

v Determination of total water hardness

The total hardness is found using the formula:

where C tr is the molar concentration of the equivalent of Trilon B, mol/dm 3 ; Vtr is the volume of Trilon B solution used for sample titration, cm 3 ; Vsample - sample volume taken for analysis, cm3.

Additive method. To determine this method, an additive equal to 50-150% (preferably 100%) of water hardness is introduced into the sample (see Determination of total water hardness) GSO 8206-2002.

Then the total hardness of the water with the additive is calculated.

a. Results of measurements obtained under reproducibility conditions for sample 1.

Sample 1: lake Average, s. Ozernoe, 85 km from the coast, date: 10/1/13, time: 16.55, t = +3.

The exact concentration of Trilon B has been established: Trilon C = 0.002226 (mol/dm 3). When performing an evaluative titration, the volume of the required sample corresponds to 100 (ml).

V (?Ca 2+ -Mg 2+), (ml)	V (Ca 2+), (ml)

a. Measurement results using the sample addition method 1. Total water hardness: .

Additive volume:

V (?Ca 2+ -Mg 2+), (ml)	V (Ca 2+), (ml)

Total water hardness with additive: .

Additive check:

3.2 Ion exchange chromatography method

The eluent is methanesulfonic acid. The method is based on the chromatographic separation of cations due to their different mobility during migration through an ion chromatography column, followed by recording the electrical conductivity of the eluate.

The chromatograph is prepared for operation in accordance with the operating manual (instructions) so that when measuring calibration solutions, separation of the peaks of the analyzed cations is achieved with a separation coefficient of at least 1 (Appendix B to GOST R 51392).

Injection of the sample into the chromatograph and further measurements of the electrical conductivity of the eluate are carried out in accordance with the operating manual (instructions). In the resulting chromatograms, the cations contained in the sample are identified by the retention time of the peaks, and the peak areas of each cation are determined. Based on the obtained calibration characteristics, the concentration of each cation in the sample is determined.

Results of the ion exchange chromatography method

Sample without additive			Sample with additive

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The determination method is based on the precipitation of magnesium ions in the form

When calcined, magnesium pyrophosphate is formed (weight form):

To prevent formation, precipitation is carried out in the presence of ammonium salts. But a large excess of them should be avoided, since it leads to the formation of a precipitate corresponding to the composition; this precipitate after calcination forms not only but also:

When washed with water, the precipitate is partially hydrolyzed:

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Conditions for carrying out the precipitation reaction - see book 1, chapter. IV, § 10.

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Washing is completed when the test for completeness of precipitation shows the absence of chlorine ions (sample with). The funnel with the washed sediment is placed in an oven for drying.

The dried sediment is poured out of the filter onto glossy paper and covered with an inverted funnel. The filter is placed in a crucible brought to a constant mass and ashed, then the sediment from the paper is poured into the same place and carefully calcined in a muffle furnace at 1000-1100 ° C to a constant mass. Weighing and calcination are repeated until the mass becomes constant.

If the precipitate is not separated from the filter, it becomes dark in color. The formation of a dark, carbon-containing precipitate can be avoided by carbonizing the filter at a low temperature. It is not recommended to treat magnesium ammonium phosphate sediment containing dark coal particles with nitric acid, as this does not give good results.

The calculation of the analysis results is carried out using the previously given formulas (see § 3).

MASS CONCENTRATION OF CALCIUM IN WATERS.
MEASUREMENT PROCEDURE
TITRIMETRIC METHOD WITH TRILON B

Rostov-on-Don

2007

Preface

1 DEVELOPED BY SI “Hydrochemical Institute”

2 DEVELOPERS L.V. Boeva, Ph.D. chem. Sciences, T.S. Evdokimova

3 AGREED with UMZA and NPO Typhoon of Roshydromet

4 APPROVED AND ENTERED INTO EFFECT by the Deputy Head of Roshydromet on March 13, 2007.

5 CERTIFIED BY GU "Hydrochemical Institute" certificate of certification No. 55.24-2006 dated 16.05. 2006

6 REGISTERED BY GU "NPO "Typhoon" under the number RD 52.24.403-2007 dated March 30, 2007.

7 INSTEAD RD 52.24.403-95 “Methodological instructions. Methodology for measuring the mass concentration of calcium in waters using the titrimetric method with Trilon B"

Introduction

Calcium is one of the most abundant elements in the earth's crust. Due to its high chemical activity in nature, calcium is found only in the form of compounds. Calcium carbonate CaCO 3 is one of the most common compounds on earth. It is found in the form of many minerals - calcite, chalk, marble, limestone, dolomite, etc.

The main sources of calcium entering natural waters are the processes of chemical weathering and dissolution of calcium-containing minerals, primarily limestones, dolomites, gypsum and other sedimentary and metamorphic rocks. Dissolution is promoted by microbial processes of decomposition of organic substances, accompanied by a decrease in pH. Large amounts of calcium are carried out with wastewater from the silicate, metallurgical, glass, chemical industries and runoff from agricultural land, especially when calcium-containing mineral fertilizers are used.

Under natural conditions, changes in the concentration of dissolved calcium are caused mainly by the equilibrium of carbon dioxide salts and carbon dioxide. In mineralized waters containing a significant amount of sulfates, the concentration of dissolved calcium decreases due to the formation of poorly soluble CaSO 4 .

In water bodies, calcium in noticeable quantities can precipitate in the form of CaCO 3 during water evaporation, as well as under conditions of activated photosynthesis, accompanied by an increase in water pH. A characteristic feature of calcium is its tendency to form fairly stable supersaturated solutions of CaCO 3 in surface waters. The ionic form of calcium is characteristic only of low-mineralized waters. With increasing mineralization, calcium ions form neutral (CaSO 4 and CaCO 3) or charged (CaHCO 3 +) ion pairs. Calcium forms fairly stable complex compounds with organic substances contained in water.

In river and lake waters, the calcium content in most cases ranges from 10 to 100 mg/dm3. When water comes into contact with minerals containing calcium, its content can increase to several hundred milligrams per cubic decimeter.

The maximum permissible concentration (MPC) of calcium in the water of fishery water bodies is 180 mg/dm 3; the MAC has not been established for drinking water bodies.

GUIDANCE DOCUMENT

MASS CONCENTRATION OF CALCIUM IN WATERS.

METHOD FOR PERFORMING MEASUREMENTS USING THE TITRIMETRIAL METHOD WITH TRILON B

Date of introduction

3 Assigned measurement error characteristics

3.1 Subject to all measurement conditions regulated by the methodology, the error characteristics of the measurement result with a probability of 0.95 should not exceed the values ​​​​given in Table 1.

Table 2 - Measurement range, values ​​of error characteristics and its components (P = 0.95)

	Repeatability index (standard deviation of repeatability) s g, mg/dm 3	Reproducibility index (standard deviation of reproducibility) s R, mg/dm3	Correctness index (limit of systematic error at probability P = 0.95) ± D s, mg/dm 3	Accuracy indicator (error limits at probability P = 0.95) ± D, mg/dm 3
From 1.0 to 200.0 incl.	0.1 + 0.004× X	0.1 + 0.031× X	0.1 + 0.018× X	0.2 + 0.063× X

When performing measurements in samples with a mass concentration of calcium over 200 mg/dm 3 after appropriate dilution, the measurement error does not exceed D×h, where D - error in measuring calcium concentration in a diluted sample; h - degree of dilution.

The detection limit for calcium is 0.6 mg/dm3.

The accuracy indicator values ​​of the method are used when:

Registration of measurement results issued by the laboratory;

Assessing the activities of laboratories for the quality of measurements;

Assessing the possibility of using measurement results when implementing the technique in a specific laboratory.

4 Measuring instruments, auxiliary devices, reagents, materials

When performing measurements, the following measuring instruments and other technical means are used:

4.1.1 High-quality laboratory balances (II) accuracy class according to GOST 24104-2001.

4.1.2 Medium laboratory scales ( III)accuracy class according to GOST 24104-2001 with a weighing limit of 200 g.

4.1.3 State standard sample of the composition of an aqueous solution of calcium GSO 8065-95 (hereinafter referred to as GSO).

4.1.4 Measuring flasks 2 accuracy classes 2, 2a according to GOST 1770-74 with capacity: 250 cm 3 - 4 pcs.

500 cm 3 - 2 pcs.

4.1.5 Graduated pipettes, 2 accuracy classes 1, 2 according to GOST 29227-91, capacity: 1 cm 3 - 5 pcs.

2 cm 3 - 3 pcs.

5 cm 3 - 1 pc.

10 cm 3 - 1 pc.

4.1.6 Pipettes with one mark, accuracy class 2, execution 2 according to GOST 29169-91, capacity: 10 cm 3 - 2 pcs.

25 cm 3 - 2 pcs.

50 cm 3 - 2 pcs.

100 cm 3 - 2 pcs.

4.1.7 Burettes 2 accuracy classes 1, 3 according to GOST 29251-91 with capacity:

5 cm - 1 pc.

10 cm 3 - 1 pc.

25 cm 3 - 1 pc.

4.1.8 Dimensional cylinders 1, 3 according to GOST 1770-74 with capacity:

25 cm 3 - 1 pc.

50 cm 3 - 1 pc.

100 cm 3 - 2 pcs.

500 cm 3 - 1 pc.

1000 cm 3 - 1 pc.

4.1.9 Conical test tubes, version 1 according to GOST 1770-74, capacity

10 cm 3 - 2 pcs.

4.1.10 Conical flasks Kn version 2, THS, according to GOST 25336-82 capacity

250 cm 3 - 10 pcs.

500 cm 3 - 2 pcs.

4.1.11 Glasses V-1, THS according to GOST 25336-82 with a capacity of:

100 cm 3 - 3 pcs.

250 cm 3 - 2 pcs.

400 cm 3 - 2 pcs.

600 cm 3 - 2 pcs.

1000 cm 3 - 2 pcs.

4.1.12 Polypropylene glass 250 cm 3 - 1 pc.

4.1.13 Laboratory funnels according to GOST 25336-82 with diameter:

56 mm - 1 pc.

75 mm - 4 pcs.

4.1.14 Weighing cups (bugs) according to GOST 25336-82:

SV-19/9 - 2 pcs.

SV-24/10 - 1 pc.

SV-34/12 - 1 pc.

4.1.15 Mortar No. 3 or 4 according to GOST 9147-80 - 1 pc.

4.1.16 Chromatographic column with a diameter of 1.5 - 2.0 cm and

length 25 - 30 cm - 1 pc.

4.1.17 Watch glass - 1 pc.

4.1.18 Glass rods - 2 pcs.

4.1.19 Bottles for storing samples and solutions made of light and dark glass with screw-on or ground-in caps with a capacity of 100 cm3, 250 cm3, 500 cm3, 1000 cm3.

4.1.20 Polyethylene (polypropylene) containers for storing samples and solutions with a capacity of 100 cm3, 250 cm3, 500 cm3, 1000 cm3.

4.1.21 Household refrigerator.

4.1.22 Drying cabinet for general laboratory purposes.

4.1.23 Electric stove with a closed spiral according to GOST 14919-83.

4.1.24 Device for filtering samples using membrane or paper filters.

It is allowed to use other types of measuring instruments, utensils and auxiliary equipment, including imported ones, with characteristics no worse than those given in.

When performing measurements, the following reagents and materials are used:

4.2.1 Calcium carbonate (calcium carbonate) according to GOST 4530-76, chemically pure.

4.2.2 Disodium salt ethylenediamine -N,N ,N,N-tetraacetic acid 2-water (trilon B) according to GOST 10652-73, analytical grade.

4.2.3 Granulated zinc according to TU 6-09-5294-86, analytical grade.

4.2.4 Ammonium chloride (ammonium chloride) according to GOST 3773-72, analytical grade.

4.2.5 Aqueous ammonia according to GOST 3760-79, analytical grade.

4.2.6 Sodium chloride (sodium chloride) according to GOST 4233-77, analytical grade.

4.2.7 Sodium hydroxide (sodium hydroxide) according to GOST 4328-77, analytical grade.

4.2.8 Sodium sulphide 9-water (sodium sulfide) according to GOST 2053-77, analytical grade, or sodium N,N -diethyldithiocarbamate 3-water (sodium diethyldithiocarbamate) according to GOST 8864-71, analytical grade.

4.2.9 Hydrochloric acid according to GOST 3118-77, analytical grade.

4.2.10 Ammonium purpurate (murexide) according to TU 6-09-1657-72, analytical grade.

4.2.11 Naphthol green B.

4.2.12 Eriochrome black T (chromogen black ET).

4.2.13 Hydroxylamine hydrochloride according to GOST 5456-79, analytical grade.

4.2.14 Active carbon.

4.2.15 Potassium alum according to GOST 4329-77, analytical grade.

4.2.16 Barium chloride 2-water (barium chloride) according to GOST 4108-72, analytical grade.

4.2.17 Distilled water according to GOST 6709-72.

4.2.17 Universal indicator paper (pH 1-10) according to TU 6-09-1181-76.

4.2.18 Membrane filters “Vladipor MFAS-OS-2”, 0.45 microns, according to TU 6-55-221-1-29-89 or another type, equivalent in characteristics or ash-free paper filters “blue tape” according to TU 6-09-1678-86.

4.2.19 Ash-free paper filters “white tape” according to TU 6-09-1678-86.

It is allowed to use reagents manufactured according to other regulatory and technical documentation, including imported ones, with qualifications not lower than those specified in.

5 Measurement method

The measurements are based on the ability of calcium ions to form a slightly dissociated compound that is stable in an alkaline environment with Trilon B. The end point of the titration is determined by the color change of the indicator (murexide) from pink to red-violet. To increase the clarity of the color transition, it is preferable to use a mixed indicator (murexide + naphthol green B). At the same time, at the end point of titration, the color changes from dirty green to blue.

Under analytical conditions, magnesium precipitates in the form of hydroxide and does not interfere with the determination.

6 Safety and environmental requirements

6.1 When performing measurements of the mass concentration of calcium in samples of natural and treated wastewater, comply with the safety requirements established in national standards and relevant regulatory documents.

6.2 According to the degree of impact on the body, harmful substances used when performing measurements belong to hazard classes 2 and 3 according to GOST 12.1.007.

6.4 There are no additional requirements for environmental safety.

7 Operator qualification requirements

Persons with secondary vocational education or without vocational education, but who have worked in the laboratory for at least a year and have mastered the technique, are allowed to perform measurements and process their results.

8 Measurement conditions

When performing measurements in the laboratory, the following conditions must be met:

Ambient air temperature (22 ± 5) °C;

Atmospheric pressure from 84.0 to 106.7 kPa (from 630 to 800 mm Hg);

Air humidity no more than 80% at 25 °C;

Mains voltage (220 ± 10) V;

AC power frequency (50 ± 1) Hz.

9 Sampling and storage

Sampling for measurements of calcium mass concentration is carried out in accordance with GOST 17.1.5.05 and GOST R 51592. Sampling equipment must comply with GOST 17.1.5.04 and GOST R 51592. Turbid samples are filtered through a 0.45 µm membrane filter or blue ribbon paper filter. The first portion of the filtrate should be discarded. Samples are stored in glass or polyethylene containers for no more than 6 months.

10 Preparing to take measurements

10.1 Preparation of solutions and reagents

10.1.1 Trilon B solution with a molar concentration of 0.02 mol/dm 3 amount of substance equivalent (hereinafter referred to as EQE).

Dissolve 3.72 g of Trilon B in 1 dm 3 of distilled water. The exact concentration of the solution is determined using a solution of zinc chloride in accordance with at least 1 time per month.

The solution is stored in a tightly closed container.

Weigh out about 0.35 g of metallic zinc, moisten it with a small amount of concentrated hydrochloric acid and immediately wash it with distilled water. Zinc is dried in an oven at a temperature of 105 ° C for 1 hour, then cooled and weighed on a laboratory balance accurate to the fourth decimal place.

A sample of zinc is transferred quantitatively into a volumetric flask with a capacity of 500 cm 3, into which 10 - 15 cm 3 of bidistilled water and 1.5 cm 3 of concentrated hydrochloric acid are first added. Zinc is dissolved. After dissolution, the volume of the solution is brought to the mark on the flask with distilled water and mixed.

Calculate the molar concentration of zinc chloride C Zn , mol/dm 3 KVE, in the resulting solution according to the formula

(1)

where q - weighed amount of metallic zinc, g;

32.69 - molar mass of zinc equivalent (1/2 Zn 2+ ), g/mol;

V is the capacity of the volumetric flask, dm 3.

When calculating the value of C Zn rounded so that it contains 4 significant figures.

10.1.3 Ammonium-ammonia buffer solution

In a volumetric flask with a capacity of 500 cm 3, 7.0 g of ammonium chloride is dissolved in 100 cm 3 of distilled water and 75 cm 3 of concentrated ammonia solution is added. The volume of the solution is adjusted to the mark on the flask with distilled water and mixed thoroughly. The buffer solution is stored in a plastic container for no more than 2 months.

10.1.4 Eriochrome black T indicator

In a mortar with 50 g of sodium chloride, carefully grind 0.5 g of eriochrome black T. Store in a dark glass bottle for no more than 6 months.

In a mortar with 100 g of sodium chloride, thoroughly grind 0.2 g of murexide. Store in a dark glass bottle for no more than 6 months.

In a mortar with 100 g of sodium chloride, carefully grind 0.2 g of murexide and 0.4 g of naphthol green B. Store in a dark glass bottle for no more than 6 months.

10.1.7 Naphthol green solution B, 0.8%

0.4 g of naphthol green B is dissolved in 50 cm 3 of distilled water. The solution is stored in a dark bottle for 3 months.

To 5 cm 3 of a 0.8% solution of naphthol green B, add 45 cm 3 of distilled water and mix. The solution is stored for no more than 3 days.

10.1.9 Sodium hydroxide solution, 20%

Dissolve 20 g of sodium hydroxide in 80 cm 3 of distilled water.

10.1.10 Sodium hydroxide solution, 8%

Dissolve 40 g of sodium hydroxide in 460 cm 3 of distilled water.

10.1.11 Sodium hydroxide solution, 0.4%

Dissolve 2 g of sodium hydroxide in 500 cm 3 of distilled water.

Sodium hydroxide solutions are stable when stored in tightly closed plastic containers.

10.1.12 Sodium sulfide solution

2 g of sodium sulfide are dissolved in 50 cm 3 of distilled water. Store in a tightly closed plastic container in the refrigerator for no more than a week.

10.1.13 Sodium diethyldithiocarbamate solution

5 g of sodium diethyldithiocarbamate are dissolved in 50 cm 3 of distilled water. Store for no more than 2 weeks in the refrigerator.

10.1.14 Hydroxylamine hydrochloride solution

5 g of hydroxylamine hydrochloride are dissolved in 100 cm 3 of distilled water. Store in a tightly closed dark bottle in the refrigerator for a month.

10.1.15 Hydrochloric acid solution, 1:3

Mix 200 cm 3 of concentrated hydrochloric acid with 600 cm 3 of distilled water.

10.1.16 Activated carbon

The preparation of activated carbon is given in the Appendix.

10.1.17 Aluminum hydroxide suspension

The preparation of a suspension of aluminum hydroxide is given in the Appendix.

In a conical flask with a capacity of 250 cm 3, using a pipette with one mark, add 10.0 cm 3 of zinc chloride solution (), add 90 cm 3 of distilled water, 5 cm 3 of ammonium-ammonia buffer solution and 70 - 100 mg of eriochrome black T indicator. The contents of the flask are thoroughly mixed and titrated from a 25 cm 3 burette with a solution of Trilon B until the color changes from violet-red to blue (blue).

The molar concentration of a solution of Trilon B C Tr, mol/dm 3 KVE, is calculated using the formula

(2)

where C Zn - molar concentration of zinc chloride solution, mol/dm 3 KVE;

V Zn is the volume of zinc chloride solution, cm 3.

V Zn is the volume of Trilon B solution used for titration, cm 3.

11 Taking measurements

11.1 Selection of titration conditions

The volume of an aliquot of a water sample for measuring the mass concentration of calcium is selected based on the known value of water hardness or based on the results of an evaluative titration.

For evaluation titration, take 10 cm 3 of water, add 0.2 cm 3 of 8% sodium hydroxide solution, 20 - 30 mg of murexide indicator and titrate with Trilon B solution until the color changes from pink to red-violet. Based on the volume of Trilon B solution consumed for titration, select from the table the appropriate volume of an aliquot of the water sample to measure the mass concentration of calcium.

Table 2 - Volume of water sample recommended for measuring the mass concentration of calcium

Depending on the calcium concentration, the titration should be carried out using a burette of suitable capacity. If, according to the results of the evaluation titration, the volume of Trilon B is less than 0.4 cm 3 or the hardness value is less than 1 mmol/dm 3 KVE, use a burette with a capacity of 5 cm 3; when the volume of Trilon is less than 0.8 cm 3 or the hardness value is from 1 to 2 mmol/dm 3 KVE - a burette with a capacity of 10 cm 3; at a higher calcium concentration or hardness value - a burette with a capacity of 25 cm 3. If you do not have a burette with a capacity of 10 cm 3, you can use a burette with a capacity of 25 cm 3; It is permissible to replace a burette with a capacity of 5 cm3 with a burette with a capacity of 10 cm3, but replacing a microburette with a capacity of 5 cm3 with a burette with a capacity of 25 cm3 is unacceptable.

Up to 3 incl.

St. 3 to 8 inclusive.

St. 8 to 12 incl.

Permissible discrepancy in Trilon B volumes, cm 3

11.2.3 To obtain a sufficiently clear color transition during titration with a mixed indicator, the ratio of murexide and naphthol green in the mixture is important. For different batches of indicators, this ratio may be different. If, when using a dry mixed indicator, it is not possible to obtain a clear color transition at the end point of the titration, naphthol green should be used in the form of a 0.08% solution (see). Titration is carried out as follows. Take an aliquot of water into a conical flask, add 2 cm 3 of 8% sodium hydroxide solution, 0.2 - 0.3 g of murexide indicator (see), mix and add a solution of naphthol green B until the solution becomes dirty. green color (in total there is approximately 0.9 - 1.2 cm 3 of solution). After this, the sample is titrated in accordance with.

11.3 Elimination of interfering influences

11.3.1 Measurements of the mass concentration of calcium are interfered with by iron ions (more than 10 mg/dm 3), cobalt, nickel (more than 0.1 mg/dm 3), aluminum (more than 10 mg/dm 3), copper (> 0.05 mg/dm 3), causing an unclear color change at the equivalence point, or completely eliminating the possibility of indicating the end point of the titration.

Other cations, such as lead, cadmium, manganese ( II ), zinc, strontium, barium at high concentrations (usually not found in natural waters) can be partially titrated together with calcium and magnesium and increase the consumption of Trilon B. To eliminate or reduce the interfering effect of metal cations, add 0.5 cm to the sample before titration 3 solutions of sodium sulfide or diethyldithiocarbamate and 0.5 cm 3 solution of hydroxylamine hydrochloride.

11.3.2 Titration results may be distorted in the presence of significant amounts of anions (HCO 3 -, CO 3 -, PO 4 -, SiO 3 2-). To reduce their influence, the sample should be titrated immediately after adding sodium hydroxide and indicator.

11.3.3 The interfering influence of suspended substances is eliminated by filtering the sample.

11.3.4 If the water sample is noticeably colored due to the presence of substances of natural or anthropogenic origin, it becomes difficult to fix the titration end point. In this case, before performing measurements, the sample should be passed at a speed of 3 - 5 cm 3 /min through a chromatographic column filled with active carbon (layer height 15 - 20 cm). The first 25 - 30 cm 3 of the sample passing through the column is discarded.

As a rule, colored compounds of anthropogenic origin are sorbed by active carbon almost completely, while natural ones (humic substances) are only partially sorbed. If the color of the sample, caused by humic substances, cannot be eliminated by activated carbon, determining the end point of titration is greatly facilitated by using a slightly overtitrated sample of the same water (witness sample) for comparison.

The precipitate in the beaker and the filter are washed 2-3 times with small portions of distilled water, collecting the washing water in the same flask. After this, bring the solution in the flask to the mark, mix, take the required aliquot from the flask and titrate it in accordance with.

11.3.6 If the calcium concentration is sufficiently high, interfering influences can be eliminated by diluting the sample with distilled water.

12 Calculation and presentation of measurement results

12.1 Mass X, mg/dm 3, and molar X m, mmol/dm 3 KVE, calcium concentration in the analyzed water sample is determined by the formulas

(3)

where 20.04 is the mass of a mole of calcium CE (1/2 Ca 2+), g/mol;

WITH m r- molar concentration of Trilon B solution, mol/dm 3 KVE;

V m R- volume of Trilon B solution used for sample titration, cm 3;

V is the volume of water sample taken for titration, cm3.

If the color of the sample was removed using a suspension of aluminum hydroxide (see), the result obtained is multiplied by 1.25.

12.2 The measurement result in documents providing for its use is presented in the form:

(4)

Where - the arithmetic mean of two results, the difference between which does not exceed the repeatability limit r(2.77 s r ). Values ​​of s r are given in the table;

±D - limits of the error characteristics of the measurement results for a given mass concentration of calcium (table).

The numerical values ​​of the measurement result must end with a digit of the same digit as the values ​​of the error characteristic; the latter should not contain more than two significant figures.

12.3 It is acceptable to present the result in the form

(4)

where ± D l - the limits of the error characteristics of the measurement results, established during the implementation of the methodology in the laboratory and ensured by monitoring the stability of the measurement results.

Note - It is permissible to establish the characteristic of the error of measurement results when introducing a technique in a laboratory on the basis of the expression D l = 0.84 × D with subsequent clarification as information is accumulated in the process of monitoring the stability of measurement results.

12.4 The measurement results are documented in a protocol or journal entry according to the forms given in the Laboratory Quality Manual.

13 Quality control of measurement results when implementing the technique in the laboratory

13.1 General provisions

13.1.1 Quality control of measurement results when implementing the methodology in the laboratory includes:

Operational control by the performer of the measurement procedure (based on an assessment of repeatability, error in the implementation of a separate control procedure);

13.1.2 The frequency of operational control and procedures for monitoring the stability of measurement results are regulated in the Laboratory Quality Manual.

13.2 Algorithm for operational control of repeatability

13.2.1 Repeatability control is carried out for each of the measurement results obtained in accordance with the procedure. To do this, the selected water sample is divided into two parts, and measurements are performed in accordance with section.

13.2.2 Result of the control procedure r To , mg/dm 3, calculated by the formula

r k = |X 1 - X 2 |, (6)

where X 1, X 2 are the results of measurements of the mass concentration of calcium in the sample, mg/dm 3.

13.2.3 Repeatability limit rn, mg/dm 3, calculated by the formula

r n = 2.77 × s r , (7)

where s r - repeatability indicator, mg/dm 3 (table).

13.2.4 The result of the control procedure must satisfy the condition

13.3 Algorithm for operational control of the measurement procedure using the additive method together with the sample dilution method

13.3.1 Operational control of the measurement procedure using the additive method together with the sample dilution method is carried out if the mass concentration of calcium in the working sample is 10 mg/dm3 or more. Otherwise, operational control is carried out using the additive method according to. To introduce additives, use GSO or a certified calcium solution (Appendix).

13.3.2 Operational control by the performer of the measurement procedure is carried out by comparing the results of a separate control procedure K to with the control standard K.

13.3.3 The result of the control procedure K k, mg/dm 3, is calculated using the formula

(9)

where is the result of a control measurement of the mass concentration of calcium in a sample diluted in h times, with a known additive, mg/dm 3 ;

The result of a control measurement of the mass concentration of calcium in a sample diluted in h times, mg/dm 3 ;

13.3.4 Control standard K, mg/dm3, is calculated using the formula

(10)

where D lx ² ( D lx ¢ and D lx ) - values ​​of the error characteristics of the measurement results, established during the implementation of the method in the laboratory, corresponding to the mass concentration of calcium in a diluted sample with an additive (diluted sample, working sample), mg/dm 3 .

Note - To calculate the control standard, it is permissible to use the values ​​of the error characteristics obtained by calculation using the formulas D lx ¢

13.3.5 If the result of the control procedure satisfies the condition:

13.4.1 The performer’s control of the measurement procedure is carried out by comparing the results of a separate control procedure K to with the control standard K.

13.4.2 The result of the control procedure K k, mg/dm 3, is calculated using the formula

(12)

where is the result of a control measurement of the mass concentration of calcium in a sample with a known additive, mg/dm 3 ;

The result of measuring the mass concentration of calcium in the working sample, mg/dm 3 ;

C is the concentration of the additive, mg/dm3.

13.4.3 Error control standard K, mg/dm3, is calculated using the formula

(13)

where D lx ¢ (D lx ) - values ​​of the error characteristic of the measurement results, established during the implementation of the method in the laboratory, corresponding to the mass concentration of calcium in the sample with the additive (working sample), mg/dm 3.

Note - To calculate the control standard, it is permissible to use the values ​​of the error characteristics obtained by calculation using the formulas D lx ¢ = 0.84× D x ¢ and D ls = 0.84× D x.

3.4.4 If the result of the control procedure satisfies the condition

B.5 Procedure for preparing certified solutions

B.5.1 Preparation of a certified calcium solution AP1-Ca

Using high-precision scales, 31.216 g of calcium carbonate is weighed in a polypropylene glass with a capacity of 250 cm 3 to the fourth decimal place. The sample is moistened with distilled water and 120 cm 3 of hydrochloric acid (1:1) is gradually added with stirring. Cover the glass with a clean watch glass and leave until dissolved.

After dissolution, carefully, using a stick, transfer the solution through a funnel into a volumetric flask with a capacity of 250 cm 3 . Rinse the glass and funnel three or four times with distilled water and transfer the washes into the same flask. Bring the solution in the flask to the mark with distilled water and mix.

The resulting solution is assigned a calcium mass concentration of 50.0 mg/cm 3 .

B.5.2 Preparation of a certified AP2-Ca solution

25.0 cm 3 of AP1-Ca calcium solution is added to a volumetric flask with a capacity of 250 cm 3 using a pipette with one mark with a capacity of 5 cm 3. The volume of the solution is adjusted to the mark on the flask with distilled water and mixed.

The resulting solution is assigned a calcium mass concentration of 5.00 mg/cm 3 .

B.6 Calculation of metrological characteristics of certified solutions

B.6.1 Calculation of metrological characteristics of the certified AP1-Ca solution

The certified value of the mass concentration of calcium C1, mg/cm3, is calculated using the formula

(IN 1)

where m - mass of calcium carbonate sample, g;

V is the capacity of the volumetric flask, cm 3;

40.08 and 100.09 are the mass of a mole of calcium and calcium carbonate, respectively, g/mol.

Calculation of the limit of possible error values ​​for establishing the mass concentration of calcium in the AP1-Ca solution D 1

, (AT 2)

where C 1 is the value of the mass concentration of calcium assigned to the solution, mg/cm 3 ;

D m - the limiting value of the possible deviation of the mass fraction of the main substance in the reagent from the assigned value m, %;

m - mass fraction of the main substance in the reagent assigned to the chemically pure reagent, %;

D m - maximum possible weighing error, g;

m is the mass of a sample of calcium carbonate, g;

D V - the limit value of the possible deviation of the volume of the volumetric flask from the nominal value, cm 3;

V is the nominal volume of the volumetric flask used, cm 3.

The error in establishing the mass concentration of calcium in the AP1-Ca solution is equal to

B.6.2 Calculation of metrological characteristics of the certified AP2-Ca solution

The certified value of the mass concentration of calcium C 2, mg/cm 3, is calculated using the formula

(AT 3)

where C 1 is the value of the mass concentration of calcium assigned to the AP1-Ca solution, mg/cm 3 ;

V 1

V 2 - volumetric flask capacity, cm3.

Calculation of the error in establishing the mass concentration of calcium in the AP2-Ca solution D 2 , mg/cm 3, is carried out according to the formula:

(AT 4)

where C 2 is the value of the mass concentration of calcium assigned to the AP2-Ca solution, mg/cm 3 ;

D 1 - error in preparing the certified AP1-Ca solution, mg/cm 3 ;

C 1 - the value of the mass concentration of calcium assigned to the AP1-Ca solution, mg/dm 3 ;

D V 1 - limit value of possible volume deviation V 1 from the nominal value, cm 3;

V 1 - volume of AP1-Ca solution taken with a pipette, cm 3;

D V 2 - the limit value of the possible deviation of the capacity of the volumetric flask from the nominal value, cm 3;

V 2 - volumetric flask capacity, cm 3.

The error in establishing the mass concentration of calcium in the AP2-Ca solution is equal to

AT 7 Safety requirements

General safety requirements when working in chemical laboratories must be observed.

B.8 Requirements for the qualifications of performers

Certified solutions can be prepared by an engineer or laboratory technician with secondary vocational education, who has undergone special training and has worked in a chemical laboratory for at least 6 months.

B.9 Labeling requirements

Flasks with certified solutions must be labeled with the symbol indicating the certified solution, the mass concentration of calcium in the solution, the error in its determination and the date of preparation.

B.10 Storage conditions

The certified AP1-Ca solution is stored in a tightly closed bottle for a year.

The certified AP2-Ca solution is stored in a tightly closed bottle for no more than 3 months.

Federal Service for Hydrometeorology and Monitoring
environment

GOVERNMENT INSTITUTION
"HYDROCHEMICAL INSTITUTE"

CERTIFICATE No. 55.24-2006
about MVI certification

Measurement procedure mass concentration of calcium in water using the titrimetric method with Trilon B.

developed GU "Hydrochemical Institute" (GU GHI)

and regulated RD 52.24.403-2007

certified in accordance with GOST R 8.563-96 as amended in 2002.

Certification was carried out based on the results experimental research

As a result of the MVI certification, it was established:

1. The MVI meets the metrological requirements imposed on it and has the following basic metrological characteristics:

Measurement range, values ​​of error characteristics and its components (P = 0.95)

Measuring range of calcium mass concentration X, mg/dm 3	Repeatability index (standard deviation of repeatability) s r, mg/dm 3	Reproducibility index (standard deviation of reproducibility) s R, mg/dm3	Correctness index (limit of systematic error at probability P = 0.95) ± D s, mg/dm 3	Accuracy indicator (error limits at probability P = 0.95) ±D, mg/dm 3
From 1.0 to 200.0 incl.	0.1 + 0.004× X	0.1 + 0.031× X	0.1 + 0.018× X	0.2 + 0.063× X

2. Measurement range, values ​​of repeatability and reproducibility limits at confidence level P = 0.95

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

Operational control by the performer of the measurement procedure (based on the assessment of repeatability and error when implementing a separate control procedure);

Monitoring the stability of measurement results (based on monitoring the stability of standard deviation of repeatability, standard deviation of intra-laboratory precision, error).

The frequency of operational monitoring and procedures for monitoring the stability of measurement results are regulated in the Laboratory Quality Manual.

Chief metrologist of the State Chemical Institute A. A. Nazarova

INTERSTATE COUNCIL FOR STANDARDIZATION, METROLOGY AND CERTIFICATION
(MGS)

INTERSTATE COUNCIL FOR STANDARDIZATION, METROLOGY AND CERTIFICATION
(ISC)

Preface

The goals, basic principles and basic procedure for carrying out work on interstate standardization are established by GOST 1.0-2015 “Interstate standardization system. Basic provisions" and GOST 1.2-2015 "Interstate standardization system. Interstate standards, rules and recommendations for interstate standardization. Rules for development, adoption, application, updating and cancellation"

Standard information

1 PREPARED by the Limited Liability Company "Protector" together with the Closed Joint Stock Company "Center for Research and Control of Water"

2 INTRODUCED by the Federal Agency for Technical Regulation and Metrology

Short name of the country according to MK (ISO 3166) 004-97	Country code by MK (ISO 3166) 004-97	Abbreviated name of the national authority on standardization
Armenia		Ministry of Economy of the Republic of Armenia
Belarus		State Standard of the Republic of Belarus
Kazakhstan		Gosstandart of the Republic of Kazakhstan
Kyrgyzstan		Kyrgyzstandard
Moldova		Moldova-Standard
Russia		Rosstandart
Tajikistan		Tajikstandard
Uzbekistan		Uzstandard

4 By Order of the Federal Agency for Technical Regulation and Metrology dated December 12, 2012 No. 1899-st, the interstate standard GOST 31954-2012 was put into effect as a national standard of the Russian Federation on January 1, 2014.

5 This standard takes into account the main regulatory provisions of international standards:

ISO 6059:1984 “Water quality. Determination of the total content of calcium and magnesium. Titrimetric method using EDTA" (“Water quality - Determination of the sum of calcium and magnesium - EDTA titrimetric method", NEQ);

ISO 7980:1986 “Water quality. Determination of calcium and magnesium. Atomic absorption spectrometric method (Water quality - Determination of calcium and magnesium - Atomic absorption spectrometric method, NEQ).

The standard was prepared based on the application of GOST R 52407-2005

6 INTRODUCED FOR THE FIRST TIME

7th Edition (July 2018) with Amendment (ICS 1-2017)

Information about changes to this standard is published in the annual information index “National Standards”, and the text of changes and amendments is published in monthly information index “National Standards”. In case of revision (replacement) or cancellation of this standard, the corresponding notice will be published in the monthly information index “National Standards”. Relevant information, notices and texts are also posted in the public information system- on the official website of the Federal Agency for Technical Regulation and Metrology on the Internet (www.gost.ru)

Introduction

Water hardness is one of the main indicators characterizing the use of water in various industries.

Water hardness is a set of properties determined by the content of alkaline earth elements in it, mainly calcium and magnesium ions.

Depending on the pH and alkalinity of the water, hardness above 10 °F can cause the formation of sludge in the water distribution system and scale when heated. Water with a hardness of less than 5 °F can have a corrosive effect on water pipes. The hardness of water can also affect its suitability for human consumption in terms of its taste properties.

In the complexometric (titrimetric) determination of hardness, ions of aluminum, cadmium, lead, iron, cobalt, copper, manganese, tin and zinc affect the establishment of the equivalent point and interfere with the determination. Orthophosphate and carbonate ions can precipitate calcium under titration conditions. Certain organic substances may also interfere with determination. If the interfering influence cannot be eliminated, it is recommended to determine hardness using atomic spectrometry methods.

This standard provides for the use of various methods for determining water hardness, taking into account the reduction of the quantitative characteristics of water hardness (unit of hardness) through degrees of hardness (°ZH) according to GOST 31865.

GOST 31954-2012

INTERSTATE STANDARD

DRINKING WATER

Methods for determining hardness

Drinking water. Methods of hardness determination

Date of introduction -2014-01 -01

1 area of ​​use

This standard applies to natural (surface and underground) waters, including water from drinking water supply sources, as well as drinking water, including packaged in containers, and establishes the following methods for determining water hardness:

Complexometric method (method A);

Atomic spectrometry methods (methods B and C).

Method B is used to determine the mass concentration of calcium and magnesium ions.

Method B is arbitrary in relation to other methods for determining rigidity.

2 Normative references

This standard uses normative references to the following interstate standards:

A sample with a volume of at least 400 cm 3 for analysis using method A and at least 200 cm 3 for analysis using methods B and C is taken into a container made of polymer materials or glass.

The shelf life of the water sample is no more than 24 hours.

To increase the shelf life of the sample and to prevent the precipitation of calcium carbonates from the water (which is typical for groundwater or bottled water), the sample is acidified with acid to pH< 2. При определении жесткости по методу А подкисление проводят соляной кислотой, по методу Б - соляной или азотной кислотой, при использовании метода В - азотной кислотой. Контроль рН проводят по универсальной индикаторной бумаге или с использованием рН-метра. Срок хранения подкисленной пробы воды - не более 1 мес.

For water packaged in containers, storage periods and temperature conditions must comply with the requirements specified in the regulatory documentation* for the finished product.

* In the Russian Federation - the requirements of GOST R 52109-2003 “Drinking water, packaged in containers. General technical conditions" - is being reissued into an interstate standard.

4 Complexometric method (method A)

The method is based on the formation of complex compounds of Trilon B with ions of alkaline earth elements. The determination is carried out by titrating the sample with a solution of Trilon B at pH = 10 in the presence of an indicator. The lowest detectable water hardness is 0.1 °F.

If the test sample has been acidified for preservation or the sample has an acidic environment, then a sodium hydroxide solution (see) is added to an aliquot of the sample to pH = 6 - 7. If the water sample has a highly alkaline environment, then a solution of hydrochloric acid is added to the sample aliquot (see. ) to pH = 6 - 7. pH control is carried out using universal indicator paper or using a pH meter. To remove carbonate and bicarbonate ions from water (which is typical for underground or bottled waters), after adding a hydrochloric acid solution to an aliquot of the sample to pH = 6 - 7, boil it or blow it with air or any inert gas for at least five minutes to remove carbon dioxide gas The criterion for the presence of a significant amount of carbonates in water can be the alkaline reaction of water.

The presence of more than 10 mg/dm 3 of iron ions in water; more than 0.05 mg/dm 3 of each of the ions of copper, cadmium, cobalt, lead; more than 0.1 mg/dm 3 of each of the ions of manganese (II), aluminum, zinc, cobalt, nickel, tin, as well as color more than 200 °G and increased turbidity cause an unclear color change at the equivalence point during titration and lead to an overestimation of the results determination of hardness. Orthophosphate and carbonate ions can precipitate calcium under titration conditions at pH = 10.

To reduce the influence of zinc contained in water up to 200 mg/dm 3, aluminum, cadmium, lead up to 20 mg/dm 3, iron up to 5 mg/dm 3, manganese, cobalt, copper, nickel up to 1 mg/dm 3 caliquot of sample up to introducing the indicator, add 2 cm 3 of sodium sulfide solution (see); to reduce the influence of manganese to 1 mg/dm 3, iron, aluminum to 20 mg/dm 3, copper to 0.3 mg/dm 3, add 5 to 10 drops of hydroxylamine hydrochloride solution (see). Turbidity (suspended solids) of the sample is removed by filtration through membrane filters with a pore diameter of 0.45 microns or ash-free paper “blue tape” filters. The influence of color and other factors is eliminated by diluting the sample during analysis, if the determined value of water hardness allows this.

Note - Filtering the sample may lead to an underestimation of the results of determining the hardness of water, especially water with an alkaline reaction.

If interfering influences cannot be eliminated, then hardness is determined using atomic spectrometry methods.

State (interstate) standard sample (GSO) of the composition of water hardness (total hardness) with the relative error of the certified value with a confidence probability R= 0.95 no more than ± 1.5%.

Laboratory scales* with a maximum weighing limit of 220 g, ensuring weighing accuracy with a maximum permissible absolute error of no more than ± 0.75 mg.

* In the Russian Federation, GOST R 53228-2008 “Non-automatic scales” is in force. Part 1. Metrological and technical requirements. Tests."

pH meter of any type.

Flasks are flat-bottomed or conical according to GOST 25336.

Heat-resistant chemical glasses according to GOST 25336.

A device for filtering samples using membrane filters.

Membrane filters with a pore diameter of 0.45 microns or ash-free “blue tape” paper filters.

Laboratory drying cabinet that maintains a temperature of (80 ± 5) °C.

Universal indicator paper for pH control.

Indicator eriochrome black T (chromogen black ET) or chrome dark blue acid (acid chrome blue T).

Hydroxylamine hydrochloride according to GOST 5456, analytical grade. or x. h.

Note - It is permitted to use other measuring instruments, equipment and reagents, including imported ones, with technical and metrological characteristics no worse than those specified.

(Amendment).

Trilon B is dried at 80 °C for two hours, weighed out 9.31 g, placed in a volumetric flask with a capacity of 1000 cm 3, dissolved in bidistilled water warm from 40 °C to 60 °C and, after cooling the solution to room temperature, adjusted to the mark bidistilled water. Setting the correction factor to the concentration of the Trilon B solution (see), prepared from a sample, is carried out using a solution of magnesium sulfate (see). A solution from the GSO composition of Trilon B or standard titer (fixanal) of Trilon B is prepared in accordance with the instructions for use, diluting it to the required concentration.

Trilon B solution is suitable for use for 6 months. It is recommended to check the value of the correction factor at least once a month.

The solution is prepared from the GSO composition of an aqueous solution of magnesium ions or standard-titer (fixanal) magnesium sulfate (sulfate) in accordance with the instructions for its use, if necessary, diluting to the required concentration.

Note - If in the standard titres (fixanals) or GSO of the composition of aqueous solutions used, the concentration of the substance is expressed in normality (n), mg/dm 3, g/m 3, etc., it is necessary to recalculate the concentration of the substance in mol/dm 3 .

To prepare 500 cm 3 of a buffer solution, 10 g of ammonium chloride is placed in a volumetric flask with a capacity of 500 cm 3, 100 cm 3 of double-distilled water is added to dissolve it and 50 cm 3 of 25% aqueous ammonia, mixed thoroughly and adjusted to the mark with double-distilled water.

The buffer solution is suitable for use for 2 months when stored in a tightly closed container made of polymer material. It is recommended to periodically check the pH of the buffer solution using a pH meter before using it. If the pH value has changed by more than 0.2 pH units, then prepare a new buffer solution.

To prepare 100 cm 3 of an indicator solution, 0.5 g of the indicator eriochrome black T is placed in a glass with a capacity of at least 100 cm 3, 20 cm 3 of a buffer solution is added, thoroughly mixed and 80 cm 3 of ethyl alcohol is added. The solution is suitable for use for 10 days when stored in a dark glass container.

Instead of the eriochrome black T indicator, it is allowed to use the chrome dark blue acid indicator, the solution of which is prepared in a similar way. The shelf life of this solution is no more than 3 months.

The dry indicator mixture is prepared in the following sequence: 0.25 g of eriochrome black T is mixed with 50 g of sodium chloride in a porcelain mortar and thoroughly ground. The mixture is suitable for use for one year when stored in a dark glass container.

To prepare a 100 cm 3 solution, 1 g of hydroxylamine hydrochloride (NH 2 OH HCl) is dissolved in 100 cm 3 of bidistilled water. The solution is suitable for use for 2 months.

To prepare a 100 cm 3 solution, 5 g of sodium sulfide Na 2 S · 9H 2 O or 3.5 g Na 2 S · 5H 2 O are dissolved in 100 cm 3 of bidistilled water. The solution is prepared on the day of the determination.

In a volumetric flask with a capacity of 1000 cm 3, half filled with double-distilled water, pour 8 cm 3 of hydrochloric acid and adjust to the mark with double-distilled water. The shelf life of the solution is no more than 6 months.

The preparation of an acid solution from a standard titer (fixanal) is carried out in accordance with the instructions for its preparation.

To prepare a 1000 cm 3 solution, place 8 g of sodium hydroxide in a glass, dissolve it in double-distilled water, after cooling, the solution is transferred to a 1000 cm 3 volumetric flask and diluted to the mark with double-distilled water. The shelf life of the solution in a container made of polymer material is no more than 6 months.

In a conical flask with a capacity of 250 cm 3 add 10.0 cm 3 of a solution of magnesium ions (see), add 90 cm 3 of bidistilled water, 5 cm 3 of a buffer solution (see), 5 to 7 drops of an indicator solution (see) or from 0.05 to 0.1 g of a dry indicator mixture (see) and immediately titrate with a solution of Trilon B (see) until the color changes at the equivalent point from wine red (red-violet) to blue (with a greenish tint) when used indicator eriochrome black T, and when using the indicator chrome dark blue acidic to blue (blue-violet).

The Trilon B solution is added quite quickly at the beginning of the titration with constant stirring. Then, when the color of the solution begins to change, the Trilon B solution is added slowly. The equivalent point is reached when the color changes, when the color of the solution stops changing when adding drops of Trilon B solution.

Titration is carried out against the background of a titrated control sample. A slightly overtitrated test sample can be used as a control sample. The arithmetic mean of the results of at least two determinations is taken as the result. The correction factor value should be 1.00 ± 0.03.

Correction factor K To concentrations of Trilon B solution are calculated using the formula

Where V- volume of Trilon B solution consumed for titration, cm 3,

10 - volume of solution of magnesium ions (cm), cm 3.

Note - When preparing solutions according to - it is allowed to use distilled water instead of double-distilled water if the determined hardness value is more than 1 °F.

4.5.1 Two determinations are performed, for which the sample of analyzed water is divided into two parts.

Notes

1 An unclear change in color of the indicator at the equivalent point or a change in color to gray indicates the presence of interfering substances. Elimination of interfering influences - by. If interfering influences cannot be eliminated, hardness is determined using atomic spectrometry methods (see section).

2 If the flow rate of the Trilon B solution exceeds 20 cm 3 - when using a burette with a capacity of 25 cm 3 or 9 cm 3 - when using a burette with a capacity of 10 cm 3, then the volume of the analyzed sample is reduced by adding bidistilled water to a volume of 100 cm 3. The sample aliquot is also reduced to eliminate the influence of water color.

3 If the flow rate of the Trilon B solution is less than 1 cm 3 - when using a burette with a capacity of 25 cm 3 or less than 0.5 cm 3 - when using a burette with a capacity of 10 cm 3, then it is recommended to use a Trilon B solution with a molar concentration of 5 mmol / dm 3 or 2, 5 mmol/dm 3 respectively. Trilon B solution is diluted 5 or 10 times.

4.6 Processing of determination results

4.6.1 Water hardness AND, °J, calculated by the formula

Where M- conversion factor equal to 2 WITH TR,

Where WITH TP - concentration of Trilon B solution, mol/m 3 (mmol/dm 3), (usually M= 50);

F F= 1);

TO- correction factor to the concentration of Trilon B solution, calculated using the formula ();

V TP is the volume of Trilon B solution consumed for titration, cm 3 ;

V PR - volume of water sample taken for analysis, cm 3.

4.6.2 The arithmetic mean of the results of two determinations is taken as the measurement result. The acceptability of the determination results is assessed based on the following conditions:

|F 1 - AND 2 | ≤ r,

Where r- repeatability limit (see table);

AND 1 and AND 2 - results of determinations for and , °Zh.

If the discrepancy between the two results exceeds the established value, then the determination of water hardness is repeated. In this case, the acceptance check is carried out according to [, section 5].

4.7 Metrological characteristics

The method ensures obtaining measurement results with metrological characteristics not exceeding the values ​​given in the table, with a confidence level P = 0,95.

Table 1

	where the error lies with confidence probability R= 0,95), ± D , °W	Limit repeatabilityr, °F	Limit reproducibilityR, °F
From 0.1 to 0.4 incl.	0,05	0,05	0,07
St. 0.4	0.15 AND	0.1 AND	0.21 AND
* The established numerical values ​​of the interval limits for the error correspond to the numerical values ​​of the expanded uncertainty U rel (in relative units) at coverage rate k = 2. Uncertainty assessment is carried out as specified in.

Monitoring the quality indicators of measurement results in the laboratory involves monitoring the stability of measurement results taking into account the requirements [, section 6] or using GSO or a GSO solution of water hardness composition that best reflects the hardness value of the waters analyzed in the laboratory.

Note - If the hardness in the used GSO is expressed in mmol/dm 3 (mol/m 3), it is necessary to convert it into degrees of hardness *.

* The water hardness value expressed in mmol/dm 3 is numerically equal to the value expressed in °W.

The measurement results are recorded in a protocol (report) in accordance with GOST ISO/IEC 17025. The protocol indicates the method used in the laboratory according to this standard.

The measurement result can be presented as:

Where AND- water hardness value, °W;

D - boundaries of the interval in which the error in determining water hardness is with confidence probability P = 0.95 (see table).

5 Atomic spectrometry methods

5.1 Determination of water hardness by measuring the concentrations of calcium and magnesium ions by flame atomic absorption spectrometry (method B)

5.1.1 Essence of the method

The method is based on measuring the resonant absorption of light by free atoms of the chemical elements magnesium and calcium when light passes through the atomic vapor of the sample under study, formed in a flame. To eliminate interfering influences, lanthanum chloride or cesium chloride is added to an aliquot of the sample.

5.1.2 Measuring instruments, auxiliary equipment, reagents, materials - with the following additions:

atomic absorption spectrometer, configured and installed in accordance with the operating manual, equipped to use an air-acetylene or nitrous oxide-acetylene flame, a hollow cathode lamp for the determination of calcium and magnesium.

Note - The nitrous oxide-acetylene flame is recommended for use if the composition of the samples is complex or unknown, as well as for samples with a high content of phosphates, sulfates, aluminum or silicon ions;

GSO composition of aqueous solutions of magnesium ion and calcium ion with a relative error of certified mass concentration values ​​of no more than ± 1% with a confidence level P = 0,95;

lanthanum chloride heptahydrate, LaCl 3 7H 2 O or lanthanum oxide La 2 O 3, x. h., if using an air-acetylene flame, or cesium chloride CsCl, x. h., if using a nitrous oxide-acetylene flame;

nitrous oxide;

To prepare a 1000 cm 3 solution, 24 g of lanthanum oxide is slowly and carefully dissolved in 50 cm 3 of concentrated hydrochloric acid, shaking until the lanthanum oxide dissolves, the solution is transferred to a 1000 cm 3 volumetric flask and brought to the mark with bidistilled water or 54 g of lanthanum chloride is dissolved in from 500 to 600 ml of hydrochloric acid solution (see), transfer to a volumetric flask with a capacity of 1000 cm 3 and adjust to the mark with hydrochloric acid solution. The shelf life of the solution is no more than 3 months.

To prepare a 1000 cm 3 solution, 25 g of cesium chloride are placed in a volumetric flask with a capacity of 1000 cm 3 and adjusted to the mark with a solution of hydrochloric acid (see). The shelf life of the solution is no more than 3 months.

5.1.3.3 Calcium-magnesium stock solution

To prepare a basic solution of calcium-magnesium with a mass concentration of calcium 20 mg/dm 3 and magnesium 4 mg/dm 3, 20.0 cm 3 of the GSO composition of an aqueous solution of calcium with a mass concentration of 1 g/dm 3 and 4 are pipetted into a volumetric flask with a capacity of 1000 cm 3 .0 cm 3 GSO composition of an aqueous solution of magnesium with a mass concentration of 1 g/dm 3 and adjusted to the mark with a solution of hydrochloric acid (see). It is allowed to prepare a basic calcium-magnesium solution with other concentrations of calcium and magnesium ions, which best reflect the composition of the analyzed waters. The shelf life of the solution is no more than 2 months.

In seven volumetric flasks with a capacity of 100 cm 3 add 10 cm 3 of a solution of lanthanum chloride (see), if using an air-acetylene flame, or 10 cm 3 of a solution of cesium chloride (see), if using a nitrous oxide-acetylene flame; then the required volume of the main calcium-magnesium solution is added to six volumetric flasks (see table); it is not added to the seventh flask (blank solution). Bring the contents of all seven flasks to the mark with a solution of hydrochloric acid (see). The shelf life of the solution is no more than 1 month.

Examples of the resulting concentrations of calcium and magnesium calibration solutions are given in the table.

Table 2

	Volume of the main calcium-magnesium solution, cm 3
calcium ions
magnesium ions

5.1.4 Spectrometer preparation

5.1.4.1 The atomic absorption spectrometer is prepared for operation in accordance with the operating manual (instructions). The analytical wavelength values ​​for calcium are 422.7 nm, for magnesium - 285.2 nm.

In accordance with the manual (instructions) for operating the spectrometer, calibration solutions are sprayed into the burner flame and the absorption of each element is recorded at the analytical wavelength. In the intervals between calibration solutions, it is recommended to introduce a solution of hydrochloric acid. Calibration dependences of the absorption of calcium and magnesium on their content in calibration solutions are established using the arithmetic mean values ​​of the results of three measurements for each calibration solution minus the arithmetic mean value of the results of three measurements of the blank solution.

5.1.4.3 The stability of calibration dependencies is monitored every ten samples, repeating the measurement of one of the calibration solutions. If the measured concentration of this calibration solution differs from the actual concentration by more than 7%, then the calibration is repeated.

In volumetric flasks with a capacity of 100 cm 3 add 10 cm 3 of lanthanum chloride solution if using an air-acetylene flame, or 10 cm 3 of cesium chloride solution if using a nitrous oxide-acetylene flame, then add an aliquot of a water sample (usually no more than 10 cm 3) and bring to the mark with a solution of hydrochloric acid (see).

If the measured calcium or magnesium content in the test sample is higher than the maximum values ​​​​set during calibration of the spectrometer, then a reduced volume of the analyzed sample is used for determinations.

5.1.6.2 At the same time, conduct a blank experiment using the same reagents and in the same quantities as when preparing samples according to, replacing the test volume of the analyzed sample with double-distilled water.

5.1.7 Processing determination results

Using the calibration dependence (see), including using the spectrometer software, determine the mass concentrations of calcium and magnesium in the solutions under study and in the blank solution and calculate the calcium and magnesium content in the sample, taking into account the dilution of the sample and the value obtained in the experiment with the blank solution.

Hardness of water AND, °J, calculated by the formula

Where With i- mass concentration of the element in the water sample, determined from the calibration dependence, minus the result of the analysis of the blank solution, mg/dm 3 ;

With i e is the mass concentration of the element, mg/dm 3, numerically equal to its 1/2 mole;

F- dilution factor of the initial water sample during canning (usually F= 1);

V K is the capacity of the flask in which the sample was prepared, in cm 3;

V P is the volume of water sample taken for analysis, cm3.

5.1.8 Metrological characteristics

The method provides results of measurements of elements (calcium and magnesium) with metrological characteristics not exceeding the values ​​​​given in the table, with a confidence level R= 0,95.

Table 3

	Accuracy indicator (boundaries * interval, in which the measurement error is located with confidence probability P = 0.95) ± D e, mg/dm 3	Repeatability limit r, mg/dm 3	Reproducibility limit R, mg/dm 3
From 1.0 to 50 incl.	0.1 WITH	0.1 WITH	0.14 WITH
Over 50	0.07 WITH	0.07 WITH	0.1 WITH
* The established numerical values ​​of the interval limits for the error correspond to the numerical values ​​of the expanded uncertaintyU rel (in relative units) at coverage ratek =2. Uncertainty assessment is carried out as specified in [ ].

5.1.9 Control of quality indicators of determination results - according to. In this case, instead of the GSO composition of water hardness, you can use the GSO composition of aqueous solutions of magnesium and calcium ions. The values ​​of repeatability and reproducibility limits are in accordance with the table.

5.1.10 Registration of results - according to. The Δ value is calculated using the formula

where D e - the boundaries of the interval in which the error in measuring an element in a water sample lies with a confidence probability P =

5.2.1 Determination of the content of alkaline earth element ions (magnesium, calcium, strontium, barium) in a water sample is carried out according to GOST 31870.

Hardness of water AND, °J, calculated by the formula

AND = ∑(C i/C i e),

Where With i- mass concentration of the element in the water sample, determined according to GOST 31870, mg/dm 3;

With i e is the mass concentration of the element, mg/dm 3, numerically equal to 1/2 of its mole.

International standard
ISO 5725-6:1994*

Accuracy (trueness and precision) of measurement methods and results. Part 6. Use in practice of accuracy values ​​(Accuracy (correctness and precision) of measurement methods and results. Part 6. Use of accuracy values ​​in practice)

EUROCHEM/SITAK manual “Quantitative description of uncertainty in analytical measurements.” 2nd edition, 2000, trans. from English - St. Petersburg, VNIIM im. DI. Mendeleev, 2002

State system for ensuring the uniformity of measurements. Methods of quantitative chemical analysis. Procedures for checking the acceptability of analytical results

* In the Russian Federation, GOST R ISO 5725-6-2002 “Accuracy (correctness and precision) of measurement methods and results is in force. Part 6. Using accuracy values ​​in practice." Before the adoption of an interstate standard, similar national standards are used if they are identical to the international standard ISO 5725-6:1994.

Key words: drinking water, natural water, hardness, determination methods, complexometry, atomic spectrometry