RU2631618C1 - Method of experimental data receipt for determination of hydrocarbonate ions in mineral waters by potentiometric and acid-base titration methods - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention can be used to determine hydrocarbonate ions at mineral water analysis by potentiometric titration, which includes titration of the mineral water sample with the acid titrant and pH measurement in the potentiometric cell solution by adding each titrant portion. The solution of hydrochloric acid (HC1) is used as the titrant, the exact concentration of which is set according to the borax (sodium tetraborate- Na₂B₄O₇⋅10H₂O). For that 10 cm³ of mineral water is introduced into the electrochemical cell with two electrodes - the glass (measuring) and chlorine silver (auxiliary), connected to pH meter-millivoltmeter (pH-150), then one drop of methyl orange indicator 0.1% solution is added. The HCl solution is added from the burette, while stirring the reaction mixture on the magnetic stir bar. When titrating, the experimental data are obtained simultaneously by two methods - the acid-base titration (neutralisation) and potentiometric titration, after addition of each titrant, the solution is stirred until the constant pH value is set on the device instrument panel. Then pH value of the analysed solution is fixed according to the device (the potentiometric titration), and after the solution colour change in the presence of the indicator, the total volume of the titrant (T_VT) according to the burette (acid-base titration method) is measured. Each analysis is repeated 3 times. The results are entered into the computer program, which performs the calculation with the statistical processing.

EFFECT: decrease in cost, complexity and carrying out the express analysis of mineral waters.

1 dwg, 12 tbl

Description

The invention relates to the field of analytical chemistry, in particular to the analysis of mineral waters for determination of hydrocarbon alkalinity in objects of research.

In analytical chemistry, a flow-injection conductometric method is known for determining bicarbonate ions in bottled drinking water of various salt composition [1].

The disadvantage of this method is the use of a rather expensive installation that requires experienced operators. The method also requires for the analysis of sufficiently large volumes of the studied samples, which affects the consumption of reagents, and the duration of the experiment.

A known method of obtaining experimental data for the determination of bicarbonate ions by methods of conductometric and acid-base titration [2].

However, the known method has the following disadvantages. The use of acid-base and conductometric titration at the same time to obtain experimental data and determine the content of bicarbonate ions in drinking mineral waters does not eliminate the need to use the third (arbitration) method in case of disagreements, and this affects the duration of the experiment and requires additional consumption of both reagents and and test samples.

A known method of obtaining experimental data for determining bicarbonate ions by the titrimetric method [3] using indicators. The titrimetric method (pH-metry) is based on the neutralization of bicarbonate ions with hydrochloric acid in the presence of a methyl orange indicator.

The disadvantage of this method is the consumption of large volumes of test samples for analysis.

). Последующее, точное титрование проводят вблизи эквивалентной точки, но, начиная с объема V₂, титрант прибавляют по каплям и снова по максимальному скачку рН определяют объем титранта. Результаты оформляют в виде табл. 1The closest technical solution to the method for determining bicarbonate ions, selected as a prototype, is a method for potentiometric determination of bicarbonates in the waters of mineral drinking medicinal, medicinal-canteen and natural canteens (GOST 23268.3.0-78) [3]. In the selected prototype for the determination of bicarbonate ions in mineral waters, a potentiometric method for the largest change in the pH value recorded by a glass electrode is proposed. The method is implemented using an apparatus including a pH meter such as a pH meter-millivoltmeter (pH-340, pH-121) or an EV-74 ionomer, an electrochemical cell (beaker with a capacity of 150 cm ³ ), glass and silver chloride electrodes, magnetic stirrer, 25 cm ³ burette. To conduct an analysis in an electrochemical cell (beaker, with a capacity of 150 cm ³ ), 1 to 100 ml of mineral water is measured so that it contains 5 to 120 mg of bicarbonate ions, topped up with distilled water to 100 cm (if measured the sample was less than 100 cm ³ ). Glass and silver chloride electrodes are immersed in the solution. Titration is carried out with 0.1 N or 0.02 N (when the sample contains less than 10 mg of bicarbonate ions) with a HCl solution from an ordinary burette with a division value of not more than 0.1 cm ³ , mixing the titrated solution with a magnetic stirrer. First, an approximate titration is carried out in order to determine the approximate position of the equivalent point. For this, the titrant solution is added in portions of 0.5-1.0 cm ³ and after the addition of each portion, the readings of the device (pH value) are taken. Initially, the pH varies slightly, but near the equivalent point there is a sharp jump in pH. After the pH jump, another 2-3 portions of titrant are added and the tentative titration is completed. Notice the volumes of titrant (V ₂ ) and (V ₃ ) at which a maximum change in pH was observed

) Subsequent, accurate titration is carried out near the equivalent point, but, starting from volume V ₂ , the titrant is added dropwise and again the titrant volume is determined by the maximum jump in pH. The results are made out in the form of a table. one

The mass concentration of bicarbonate ions (X), mg / DM ³ , calculated by the formula

where V is the volume of the hydrochloric acid solution spent on titration;

H - the normality of a solution of hydrochloric acid;

61 is the gram equivalent of bicarbonate ions;

V ₁ - the volume of water taken for analysis, cm ³ .

However, the known method has the following disadvantages.

The disadvantage of this method is the consumption of large volumes of test samples for analysis (up to 100 cm ³ for the analysis of one water sample), which affects the consumption of reagents. To confirm the correct determination of bicarbonate ions, the pH-potentiometric method (GOST) used as a chemical method should also be compared with data obtained by another method, which also needs its own setup, its own reagents and solutions prepared from them, samples of mineral water, which additionally leads to a rise in the cost of the overall analysis and an increase in the time it takes. In the selected prototype there are no indications that the quality control of measurements and the establishment of their metrological characteristics is carried out in an automated way.

The invention is aimed at increasing the expressness, cost reduction, acceleration and simplification of the analysis.

This is achieved by the fact that in the method of obtaining experimental data for determining the content of bicarbonate ions by potentiometric and acid-base titration methods, including titration of a mineral water sample with an acid titrant and measuring the pH in a potentiometric cell solution with the addition of each portion of the titrant (up to 20 measurements), moreover a solution of hydrochloric acid (HCl) is used as a titrant in the determination of bicarbonate ions in mineral water; for this, 10 cm ^{3 of} mineral water is introduced into an electrochemical cell with two electrodes (glass and silver chloride), then one drop of a 0.1% solution of methyl orange indicator and a magnet are added to mix the solution in the cell on a magnetic stirrer; an electrochemical cell is connected to a pH meter-millivoltmeter (pH-150); the titration burette is filled with a HCl solution, and when determining the content of bicarbonate ions in drinking mineral waters, the exact concentration of the HCl titrant is pre-determined by the drill (sodium tetraborate - Na ₂ B ₄ O ₇ ⋅ 10H ₂ O); experimental data during titration are obtained simultaneously by two methods - the acid-base titration method, based on the neutralization of HCl hydrocarbon ions in the presence of an orange methyl indicator, and potentiometric titration; for this, after adding each portion of the titrant, the pH of the analyzed solution is recorded, which corresponds to potentiometric titration, and after changing the color of the solution in the presence of an indicator, namely, the transition of the pink color of the solution to yellow, the total titrant volume (V _TE ) is measured (acid-base titration method ); mass concentration of bicarbonate ions, X mg / l, calculated by the formula:

X = V _TE × H _t × 61 × 1000 / V _B,

where 61 is the gram equivalent of bicarbonate ions, V _TE is the titrant volume corresponding to the titration end point in the potentiometric method or TE in the acid-base titration of a mineral water sample, cm ³ ; V _B is the volume of water taken for analysis, cm ³ ; 3 more water samples are analyzed in the same way as described above with statistical processing of the results.

Thus, the purpose of the proposed method is realized: experimental data (pH; V _TE ) for determining the content of bicarbonate ions in mineral waters are obtained.

In the development of the proposed method, an additional increase in expressity, a decrease in the complexity and an increase in the economy of the subsequent determination of the content of bicarbonate ions is achieved by the fact that according to experimental data obtained simultaneously by both of these methods and designed in the form of a table. 2

(the results of determinations and calculations in potentiometric titration were carried out similarly [4, p. 456], taking into account the presence in the solution of bicarbonate ions with an alkaline reaction), the content of bicarbonate ions in the analyzed mineral water was calculated with subsequent statistical processing simultaneously using the known mathematical relationships of the method acid-base titration (GOST), which relates the content of bicarbonate ions to the total volume of titrant measured after the color of the solution is changed, and according to known materials the mathematical relationships of the potentiometric titration method (GOST), which relates the content of bicarbonate ions to the totality of the measured pH values of the analyzed solution and the corresponding volumes of titrant.

The specified calculation of the content of bicarbonate ions in the analyzed mineral water according to the experimental data of the titrant volume at the equivalence point (TE), obtained simultaneously by both methods, is preferably carried out using technical means of calculation, for example, using a computer and computer program [5]. A computer program as such is not the subject of the alleged invention. However, the use of an automated computer program can facilitate the work of the analyst by replacing many manual, labor-intensive operations with automatic ones, reduce the errors of individual operations, increase the speed of analysis, and reduce its cost. The specified calculation is characterized by the fact that it uses, in particular, the following known relations 2-4 [6, Ch. 1, § 10] to calculate the titrant volume at the equivalence point from the measured pH values.

As mentioned above, in potentiometric titration, the end point of titration (CTT) is found by a sharp jump in the pH of the measuring electrode corresponding to the moment of completion of the reaction [3]. To more clearly identify the features of the titration process and for applied purposes, differential titration curves are most often constructed, plotting the volume of added titrant V _T along the abscissa axis and the first derivative of the logarithm of the concentration of added titrant dlgc (x) / dV (x) along the abscissa axis. Such titration curves are usually widely used in physicochemical methods of analysis, for example, in potentiometric titration. On the differential titration curves, the position of the equivalence point (TE) corresponds to the maximum of the curve and therefore is determined quite reliably [4, p. 69-70]; [7, p. 62-63].

In the proposed application, the end point of titration (CTT) is determined graphically, associated with the construction of the obtained experimental data of a differential titration curve for the first derivative (see table. 2)

where the position of the FC corresponds to the intersection point of the extrapolated branches of the curves [4, p. 70, Fig. 3.1-in; p. 456, fig. 10, 1-6]; [7, p. 63, fig. 3/2]. The titration curve constructed determines the titrant volume V (TE) in the TE [4, p. 455-456].

The use of a differential curve to determine the TE allows you to more accurately determine the titrant volume corresponding to this moment, in addition, it should be noted that this method of determining the TE and the titrant volume corresponding to it is also very obvious.

From the found value of the titrant volume, the exact normality of the HCl titrant for each method is obtained using the formula:

where H _T is the exact normality of the titrant (Hcl); V _TE - the volume of the titrant solution corresponding to the end point of the titration in the potentiometric method or TE in the acid-base titration, cm ³ ; H ₂ - the norm of the borax solution; V ₂ - the volume of an aliquot of borax in the cell, cm ³ .

From the found value of H _{t the} exact normality of the titrant, the mass concentration X of bicarbonate ions, mg / l, is obtained by the ratio:

where 61 is the gram equivalent of bicarbonate ions;

V _TE - titrant volume corresponding to the titration end point in the potentiometric method or TE in the acid-base titration of a mineral water sample, cm ³ ;

V _B is the volume of water taken for analysis, cm ³ (see the indicated relation 4 in [3, p. 3]; [6, Ch. 1, § 10]; [8, Ch. 6.3.1.]).

This is due to the fact that during potentiometric and acid-base titration, the same acid-base reaction of the interaction of bicarbonate ions with a HCl titrant proceeds in solution, while the titration of bicarbonate ions HCO ₃ ^- (alkaline medium, pH 8.34) proceeds to H ₂ CO ₃ (acidic medium, the pH of the solution is 4.25). The introduction of an acid-base indicator of methyl orange into such a solution changes its color upon transition from an alkaline medium to an acidic medium (pink → yellow) and thereby allows one to fix the equivalence point (TE) and measure its corresponding (V _TE ) - titrant volume ( acid-base titration), creates the conditions for the simultaneous obtaining of experimental data in one analyzed sample both by the potentiometric analysis method and by the acid-base titration. Changing the color of the analyzed solution does not affect the obtaining of experimental data by potentiometric titration, since this method can be used to carry out the analysis in turbid and colored solutions. Obtaining experimental data simultaneously by two methods in the presence of an indicator in a sample of mineral water ensures the achievement of the main part of the technical result — acceleration and simplification of the analysis, increase of expressness, reduction of the complexity and cost of analysis.

In the development of the proposed method, the simultaneous calculation of the content of bicarbonate ions with their statistical processing according to the experimental data obtained by both methods using

an automated computer program [5] provides an additional increase in expressivity, a decrease in the complexity, simplification and cheapening of the analysis.

Studies conducted on the sources of patent and scientific and technical information showed that the inventive method for simultaneously obtaining experimental data and determining bicarbonate ions by potentiometric and acid-base titration methods is unknown in the claimed combination of features.

In FIG. 1 shows the installation that implements the proposed method.

It includes a pH meter-millivoltmeter (pH-150) (measuring unit) (1) with control knobs (2) measuring unit (1); an electrochemical (potentiometric) cell (3) with two electrodes (4) - glass and silver chloride; magnet (5); a burette with a capacity of 25 cm (6); burette stand (7); magnetic stirrer (8) and computer (9).

As a computer program can be used not only [5], but also any known program for mathematical processing of chemical experiment data, configured to work in accordance with the processing of these experimental data according to Table. 2 and the prior art relationships (2-4).

The method is as follows.

To determine the content of bicarbonate ions in mineral waters, the burette (6) is filled with HCl titrant with a precisely determined pre-concentration over the storm. In a cell (3) with two electrodes (glass and silver chloride), 10 cm ³ of mineral water selected for analysis and 1 drop of a 0.1% solution of methyl orange indicator are added. At the bottom of the cell, lower the magnet (5), turn on the stirrer (8) and the pH meter-millivoltmeter (pH-150) device (1), then on the front panel of the device turn on the button for taking pH readings (2), the scale in this case turns out to be calibrated in pH units, and the measured value of pH for the initial analyzed solution (mineral water) appears on the light panel of the device (1). The solution is stirred until a constant pH value is displayed on the instrument panel. The resulting pH value is recorded in a table and proceed to titration. For this, a titrant (from 0.05 to 1.0 cm ³ ) is added in portions from the burette (6) to the analyzed sample, depending on the concentration of bicarbonate ions indicated in the quality certificate of the commercial product and determined after each added portion of the solution pH in the cell ( 3). After adding each portion of the HCl titrant, the solution in the cell is stirred, the pH is measured, and all the obtained experimental data are recorded in the table. Titration is continued until (in the presence of an indicator) the solution in the cell changes its color from pink to yellow. At this moment, the total volume V of _TEs is measured by the burette (6), corresponding to TEs when the indicator changes color (acid-base titration), and it is also recorded in the table. After changing the color of the solution in the cell (3), another 5-7 pH measurements are made during titration, recording them each time in the table. Thus, the results of all measurements — the pH and the corresponding volumes (V) of the titrant and the volume of the burette when changing the color of the solution in cell V _TE — are recorded in the table. After measuring, turn off the device pH-meter-millivoltmeter (1) and magnetic stirrer (8). The contents of the cell (3) are poured, and then rinsed with distilled water (without losing the magnet (5) from the cell (3)). Then, the experimental data obtained simultaneously using two methods are processed in accordance with Table 2 and relations (2-4) using a PC (9) using a computer program [5], and thus the content of bicarbonate ions in the mineral water simultaneously by two methods - acid-base (GOST) and potentiometric (GOST) titration. Next, statistical processing is carried out using the same program [5], after analyzing previously 3-4 samples of the taken mineral water.

The method is illustrated by the following examples:

- Establishing the exact concentration of HCl titrant with sodium tetraborate (borax);

- Establishing the exact concentration of HCl titrant with sodium tetraborate (borax);

- analysis of the medicinal-table natural mineral water "Essentuki 4" of average salinity (7.0-10.0 g / dm ³ ); (3400-4800 HCO ₃ ^- );

- analysis of the medicinal-dining room natural mineral water “Rychal-Su” with low mineralization (4.0-5.0 g / dm ³ ); (2500-3000 HCO ₃ ^- );

- analysis of the medicinal-table natural mineral water "Narzan" low mineralized (up to 3.0-4 g / dm ³ ); (1000-1500 HCO ₃ ^- );

- analysis of the medicinal-table natural mineral water “Evian” slightly mineralized (0.3-0.75 g / dm ³ ); (300-360 HCO ₃ ^- );

- analysis of drinking artesian natural water "Aqua-balance" with low salinity (0.3-0.5 g / dm ³ ). (200-300 HCO ₃ ^- ).

Example 1

Establishing the exact concentration of HCl titrant with sodium tetraborate (borax).

For this, 10 cm ^{3 of} 0.1 M (molar equivalent concentration) of the borax solution is introduced into the electrochemical cell (3). Then, one drop of a 0.1% solution of methyl orange indicator is added to the electrochemical cell (3), two electrodes are placed in the same place - glass (measuring) and silver-silver (auxiliary). The titration burette (6) is filled with a solution with an approximate 0.1 M hydrochloric acid solution. A magnet (5) is lowered into the electrochemical (potentiometric) cell (3) and a magnetic stirrer (8) is turned on to mix the solution in the electrochemical cell (3). Turn on the device (1), then the switch (2) - light panel on the front panel of the device (1). During titration, experimental data are obtained simultaneously by two methods - the acid-base titration method (neutralization) and potentiometric titration. After adding each portion of the titrant, the pH value of the analyzed solution (potentiometric titration) is fixed using the instrument (1), and after changing the color of the solution in the cell in the presence of an indicator (the pink color of the solution turns yellow), the titrant volume (V _TE ) is measured by the burette (6 ) (acid-base titration method). After changing the color of the solution in the cell (3), another 5-7 pH measurements are made during titration, recording them each time in the table. According to experimental data obtained simultaneously by both methods, the exact concentration of HCl titrant at the same time for each method is calculated using a PC and an automated computer program [5] using the formula (2):

N _T = N ₂ × V ₂ / V _TE

where H _T is the exact normality of the titrant (HCl); V _TE - titrant volume corresponding to the end point of the titration in the potentiometric method or TE in the acid-base titration, cm ³ ; H ₂ - the norm of the borax; V ₂ - the volume of an aliquot of borax in the cell, see

The concentration of the initial ~ 0.1 mol / L HCl solution is updated weekly. Further, this HCl solution with an established exact concentration by the storm is used in the analysis of mineral waters of various degrees of mineralization as a titrant.

Example 2

As an object of study, the medicinal-table natural mineral water “Essentuki 4” of medium mineralization (7-10 g / dm ³ ) with the following composition was selected:

The work is performed on the installation (Fig. 1). As a titrant in the determination of bicarbonate ions in Essentuki 4 mineral water, a solution of hydrochloric acid (HCl) is used, the exact concentration of which is established by the storm (Example 1). To do this, 10 cm ^{3 of} Essentuki 4 mineral water is introduced into the electrochemical cell (3). Then, one drop of a 0.1% solution of methyl orange indicator is added to the electrochemical cell (3), two electrodes are placed in the same place - glass (measuring) and silver-silver (auxiliary). The titration burette (6) is filled with hydrochloric acid solution. A magnet (5) is lowered into the electrochemical cell (3) and a magnetic stirrer (8) is turned on to mix the solution in the electrochemical cell (3), the device (1) is turned on, then the toggle switch (2) displays a light board on the front panel of the device (1). During titration, experimental data are obtained simultaneously by two methods - the acid-base titration method (neutralization) and potentiometric titration. After adding each portion of the titrant, the pH of the analyzed solution (potentiometric titration) is fixed using the instrument (1), and after changing the color of the solution in the presence of an indicator (the pink color of the solution turns yellow), the total titrant volume (V _TE ) is measured by the burette (6) (acid-base titration method). After changing the color of the solution in the cell (3), another 5-7 pH measurements are made during titration, recording them each time in the table. According to experimental data obtained simultaneously by both methods, the content of bicarbonate ions in the analyzed water "Essentuki 4" is calculated simultaneously with the acid-base method (GOST) and potentiometric titration (GOST) using PC for this purpose and then, similarly to those described above, another 3 are analyzed water samples “Essentuki 4” each with a volume of 10 cm ³ (total 4 samples each with a volume of 10 cm ³ ). After obtaining the experimental data, they are entered into a PC in a computer program [5], processed, and then using the same program their statistical processing is carried out.

In the table. 4 presents the data for determining the content of bicarbonate ions in mineral water "Essentuki 4", obtained by the proposed method and processed on a PC using a special program [5], operating in accordance with table. 2 and with ratios (2-4) known from the prior art.

The calculation shows that the content of bicarbonate ions in Essentuki 4 mineral water in both methods does not exceed the values stated in the certificate, and the determination error is in the range of 3.2-4.6%. Statistical processing of the data of both methods shows the same reproducibility of the methods, the insignificance of the systematic error and the possibility of combining both samples of the two methods into one common set, and the relative measurement error in this case is 5.5%.

Example 3

As the object of study, the medicinal-table natural mineral water “Rychal-Su” of medium mineralization (up to 4.0-5.0 g / mg / dm ³ ) with the following composition was selected:

Preparation, measurement and calculation were carried out as in example 2, for analysis, 4 samples of Rychal-Su water were taken, each with a volume of 10 cm ³ .

The calculation shows that the content of bicarbonate ions in Rychal-Su mineral water in both methods does not exceed the values stated in the certificate, and the determination error is in the range of 4.3-6.5%. Statistical processing of the data of both methods showed the same reproducibility of the methods, the insignificance of the systematic error and the possibility of combining both samples of the two methods into one common set, and the relative measurement error in this case is 7.4%.

Example 4

As the object of study, the treatment and dining room natural low-mineralized (up to 3.0-4.0 g / mg / dm ³ ) mineral water “Narzan” with the following composition was selected:

Preparation, measurement and calculation were carried out as in example 2, only for analysis were taken 4 water samples of "Narzan" - one water sample with a volume of 10 cm ³ and 3 water samples with volumes of 12 cm ³ .

The calculation shows that the content of bicarbonate ions in the mineral water “Narzan” in both methods does not exceed the values stated in the certificate, and the error of determination is in the range of 3.3-3.7%. Statistical processing of the data of both methods showed the same reproducibility of the methods, the insignificance of the systematic error and the possibility of combining both samples of the two methods into one common set, and the relative measurement error in this case is 4.9%.

Example 5

As the object of study, the treatment and dining room natural low-mineralized (up to 2.0-2.6 g / mg / dm) mineral water “Evian” with the following composition was selected:

Preparation, measurement and calculation were carried out as in example 2, only for analysis were taken 4 samples of Evian water — two samples with a volume of 10 cm ³ and two samples with a volume of 12 and 14 cm ^3, respectively.

The calculation shows that the content of bicarbonate ions in the Evian mineral water in both methods does not exceed the values stated in the certificate, and the error of determination is in the range 3.4-7.2%). Statistical processing of the data of both methods showed the same reproducibility of the methods, the insignificance of the systematic error and the possibility of combining both samples of the two methods into one common set, and the relative measurement error in this case is 7.6%.

Example 6

As the object of study, we selected drinking artesian natural water “Aqua-balance” with low salinity (0.3-0.5 g / l) with the following composition:

Preparation, measurement and calculation were carried out as in example 2, only for analysis were taken 4 samples of Aqua-balance water, two samples with volumes of 15 cm ³ and two samples with volumes of 10 and 12 cm ^3, respectively.

In the table. 12 presents the data for determining the content of bicarbonate ions in mineral water "Aqua-balance", obtained by the proposed method and processed on a PC using a special program [4].

The calculation shows that the content of bicarbonate ions in the Aqua-balance artesian drinking water in both methods does not exceed the values stated in the certificate, and the determination error is in the range of 3.1-7.1%. Validation of the claimed method was carried out by comparing the data obtained by the method of neutralization (acid-base titration) and potentiometric titration. A comparison of the results shows the same reproducibility of the methods, the insignificance of the systematic error and the possibility of combining both samples of the two methods into one common set, i.e. the data obtained from both methods belong to the same general population, and the relative measurement error is 7.0%.

As a computer program can be used not only [5], but also any known program for mathematical processing of chemical experiment data, configured to work in accordance with the processing of these data according to Table. 2 and the known relations (2-4). The inventors used a program of their own development [5], acting in accordance with table. 2 and the prior art relationships (2-4).

Using the proposed method for obtaining experimental data simultaneously by two methods for determining the content of bicarbonate ions in mineral waters, followed by simultaneous calculation of their content using a special computer program [5] on a PC, can significantly save time spent on general analysis, increase expressivity, and reduce labor intensity , simplifies and reduces the cost of analysis in contrast to the prototype, where for the potentiometric analysis used (which in this case is used as a chemical cue method) another independent method is necessary for checking and comparing the obtained data, moreover, both methods are usually carried out separately; facilitate the work of the operator, replacing many manual, labor-intensive operations with automatic ones, reduce the errors of individual operations, increase the speed of analysis, reduce its cost; reduce the amount of water sample per analysis from 100 ml (prototype) to 10-15 ml, use in the work on the proposed simple installation, for example, less qualified employees (laboratory assistants, students). In the development of the proposed method, the process of constructing graphs in potentiometric titration, followed by determination of the titration end point (CTT) from them and determination of the titrant volume corresponding to it, as well as determination of the content of bicarbonate ions in mineral waters simultaneously by both methods, unlike the prototype, is fully automated. Unlike the prototype, in the proposed method, further processing of the analysis results using mathematical statistics is carried out using the same special program [5] on a PC, which allows not only simultaneous automated processing of the experimental results of each method taking into account the error of the result, but also to evaluate the reliability of the result in two samples using the combined totality, which is absent in the prototype. Carrying out all the calculations with the help of a special program on a PC allows to increase the user's work efficiency, increase the speed of calculation and information processing, reduce manual labor time, and minimize the errors in the calculations, which are often caused by insufficient qualifications of employees. Thus, the proposed method for obtaining experimental data for determining the content of bicarbonate ions in comparison with the prototype allows to obtain experimental data simultaneously by two methods (potentiometric (GOST) and acid-base titration (GOST).

Information sources

1. Elipasheva E.V., Kulikov P.N., Sergeeva V.P., Sergeev G.M. Flow-injection analysis of drinking water. Conductometric determination of mineralization and bicarbonates. J. "Analytics and control." T. 15, No. 2, 2011, pp. 187-193.

2. Chernysheva A.V., Stozhko N.Yu., Podshivalova E.M., Tataurov V.P. Patent for invention №2562546 C2, IPC G01N 31/16, G01N 27/26 Russian Federation. Registered on August 12, 2015. A method of obtaining experimental data for the determination of bicarbonate ions by conductometric and acid-base titration methods. Applicant and patent holder FGBOU VPO Ural State Economic University. - No. 2013136626/15; declared 08/05/2013; publ.: Bull. Number 25. 09/10/2015.

3. GOST 23268.3-78 Mineral drinking water, medicinal, medicinal-table and natural table. Methods for the determination of bicarbonate ions (with Change No. 1) // State quality control of mineral water and drinks: Sat. M .: Publishing house of standards, 2003.S. 369-372 (prototype).

4. Kharitonov Yu.Ya. Analytical chemistry. Analytics 2. Quantitative analysis. Physicochemical (instrumental) analysis methods. M .: "Higher School", 2001, p. 69-70, p. 454-456.

5. Podshivalova EM, Chernysheva AV, Stozhko N.Yu., Bortnik B.I. A program for the simultaneous automated determination of the content of a substance or mixture of substances in objects of analysis by acid-base and potentiometric titration methods (Para-Method). Certificate of state registration of computer programs No. 2015617710. It is registered in the Register of computer programs on July 21, 2015. Byul. No. 8, 2015

6. Kreshkov A.P. Fundamentals of analytical chemistry. Theoretical basis. Quantitative analysis, book 2. M .: "Chemistry", 1971, Ch. 1, § 10.

7. Kreshkov A.P. Fundamentals of analytical chemistry. Physico-chemical and instrumental methods of analysis, book 3. M .: "Chemistry", 1970, p. 62-63.

8. Muravyov A.G. Guidelines for determining water quality indicators using field methods, chap. 6.3.1. Carbonates, bicarbonates, carbonate hardness and alkalinity. 3rd ed., St. Petersburg: Krismas +, 2004.

Claims (3)

A method of obtaining experimental data for determining the content of bicarbonate ions in mineral waters by potentiometric and acid-base titration methods, including titration of a mineral water sample with an acid titrant and measuring the pH in a solution of a potentiometric cell with the addition of each portion of the titrant, up to 20 measurements, characterized in that a solution of hydrochloric acid (HCl) is used as a titrant in the determination of bicarbonate ions in mineral water; for this, 10 cm ^{3 of} mineral water is introduced into an electrochemical cell with two electrodes (glass and silver chloride), then one drop of a 0.1% solution of methyl orange indicator and a magnet are added to mix the solution in the cell on a magnetic stirrer; an electrochemical cell is connected to a pH meter-millivoltmeter (pH-150); the titration burette is filled with a HCl solution, and when determining the content of bicarbonate ions in drinking mineral waters, the exact concentration of the HCl titrant is pre-determined by the drill (sodium tetraborate - Na ₂ B ₄ O ₇ ⋅ 10H ₂ O); experimental data during titration are obtained simultaneously by two methods - the acid-base titration method, based on the neutralization of HCl hydrocarbon ions in the presence of an orange methyl indicator, and potentiometric titration; for this, after adding each portion of the titrant, the pH of the analyzed solution is fixed, which corresponds to potentiometric titration, and after changing the color of the solution in the presence of an indicator, namely the transition of the pink color of the solution to yellow, the total titrant volume (V _TE ) is measured (acid-base titration method ); mass concentration of bicarbonate ions, X mg / l, calculated by the formula: X = V _TE × N _t × 61x1000 / V _B , where 61 is the gram equivalent of bicarbonate ions; V _TE - titrant volume corresponding to the titration end point in the potentiometric method or TE in the acid-base titration of a mineral water sample, cm ³ ; V _B is the volume of water taken for analysis, cm ³ ; 3 more water samples are analyzed in the same way as described above with statistical processing of the results.

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