RU2233439C1 - Reagent for automatic photometric determination of total hardness of water (versions) - Google Patents

Abstract

FIELD: analytical chemistry.

SUBSTANCE: proposed reagent contains trilon, solution of dark blue chromic indicator and solution of agent for forming alkaline medium in three versions for different ranges of hardness. Used as agent for forming alkaline medium is agent containing aliphatic amine of the following formula RNH₂, R₂NH or R₃N, where R=C_nH_2n+1 or R=C_nH_2nOH which are normal or branched at n=2-4. All components of reagent are combined in single aqueous solution at the following relationship in g per 100 cu cm of bidistilled water: trilon, depending on total hardness, indicator, 0.04 to 0.15 depending on total hardness and aliphatic amine, 10.00-10.80.

EFFECT: enhanced accuracy and reproducibility of results.

6 cl, 12 tbl

Description

The invention relates to analytical chemistry, in particular to reagents for photometric or colorimetric determination of calcium and magnesium ions in water, and can be used in power engineering and other sectors of the economy where constant monitoring of the total hardness of water is required.

Automatic photometric determination of the total water hardness (total content of calcium and magnesium ions) is a variant of the widely used complexometric titration method based on the ability of calcium and magnesium ions to form stable complex compounds with trilon B (disodium salt of ethylenediaminetetraacetic acid) (Holzbeher Z., Divish L. and other Organic reagents in inorganic analysis. M: Mir, 1979, p. 421). Trilon B titration is carried out in the presence of an indicator and a substance with basic properties to create an alkaline medium, the solutions of which are successively added to the analyzed sample. Thus, the known reagent for determining the concentration of calcium and magnesium ions by this method consists of three separate solutions, which are prepared in advance and stored in separate containers. Some indicators can be used in dry form in a mixture with sodium chloride, which is previously thoroughly ground in a mortar.

Using a known reagent to determine the total hardness of water makes the process multi-stage and significantly increases the duration of the analysis. The known reagent is practically not suitable for automatic determination, since the use of such a reagent in automatic analysis would require the sequential addition of three solutions, which would significantly complicate the design of the device and significantly reduce the metrological parameters of the analysis (reproducibility, accuracy, etc.).

Closest to the proposed invention (prototype) is a reagent for complexometric determination of the total hardness of drinking water, described in GOST 4151-72. This reagent is three separate solutions:

1) 0.05 N solution of Trilon B in distilled water;

2) a buffer solution prepared by dissolving 10 g of ammonium chloride in a small amount of distilled water, adding 50 ml of 25% ammonia solution and diluting with distilled water to 500 ml;

3) an aqueous-alcoholic solution of the indicator of chrome dark blue, prepared by dissolving 0.5 g of the indicator in 20 ml of the buffer solution described above and diluting with ethyl alcohol to 100 ml.

The determination of the total hardness of water by this known reagent is prevented by ions of iron, copper, zinc and manganese. They are freed from the effects of iron salts by filtering the analyzed water sample. To eliminate the effect of copper and zinc, 1-2 ml of sodium sulfide solution is added to 100 ml of analyzed water, the interfering effect of manganese is eliminated by adding a few drops of a 1% solution of hydroxylamine hydrochloride.

The essence of colorimetric titration with the prototype reagent is as follows: first, a buffer solution is added to the analyzed water sample, which provides the pH value of 10 necessary for determination, then an indicator solution, which instantly forms a weak complex with calcium and magnesium ions (compared with a stable complex of these ions with Trilon B), while the analyzed solution acquires, depending on the stiffness, a color from weak to bright pink. Immediately begin titration with Trilon B solution with vigorous agitation until the color changes at an equivalent point. At the equivalence point, all calcium and magnesium ions are bound by Trilon B into a strong complex, and the analyzed solution changes color - it turns blue, since the indicator is released from the weak complex.

The accuracy of determination according to GOST 4151-72 when titrating 100 ml of a sample containing not more than 0.5 mEq of the total content of calcium and magnesium ions is 0.05 mEq / l (10%). If the hardness of the analyzed water exceeds 5 mEq / l, it is diluted with distilled water.

Using the prototype reagent to determine the total hardness of water makes the process multi-stage and significantly increases the duration of the analysis. The prototype reagent is practically not suitable for automatic determination, since the use of such a reagent in automatic analysis would require the sequential addition of several solutions, which would significantly complicate the design of the device and significantly reduce the metrological parameters of the analysis (reproducibility, accuracy, etc.).

The objective of the invention is to provide such a reagent for determining the total hardness of water, which would be suitable not only for manual titration, but also for automatic photometric analysis, and would ensure high accuracy and reproducibility of the results.

The solution to this problem is achieved:

- the proposed reagent for photometric determination of the total hardness of water, including an aqueous solution of Trilon B, a solution of an indicator of chrome dark blue and a solution of a substance to create an alkaline medium, which for determining the total hardness of water in the range of the total content of calcium and magnesium ions is 5-300 μg-eq / dm ³ contains, as a substance for creating an alkaline medium, an aliphatic amine of the formula RNH ₂ , R ₂ NH or R ₃ N, where R = C _n H _{2n + 1} or R = C _n H _2n OH, normal or branched, at n = 2-4, and all components of the reagent are combined into a single aqueous the solution in the following ratio, g per 100 cm ³ bidistilled water:

Trilon B 0.1861-0.2791

Indicator 0.08-0.15

Aliphatic amine 10.00-10.80

- the proposed reagent for photometric determination of the total hardness of water, including an aqueous solution of Trilon B, a solution of an indicator of chrome dark blue and a solution of a substance to create an alkaline environment, which is used to determine the total hardness of water in the range of the total content of calcium and magnesium ions of 10-500 μg-eq / dm ³ contains, as a substance for creating an alkaline medium, an aliphatic amine of the formula RNH ₂ , R ₂ NH or R ₃ N, where R = C _n H _{2n + 1} or R = C _n H _2n OH, normal or branched, with n = 2-4, and all components of the reagent are combined into a single aqueous p the solution in the following ratio, g per 100 cm ³ bidistilled water:

Trilon B 0.3722-0.4652

Indicator 0.06-0.08

Aliphatic amine 10.00-10.80

- the proposed reagent for photometric determination of the total hardness of water, including an aqueous solution of Trilon B, a solution of an indicator of chrome dark blue and a solution of a substance to create an alkaline environment, which for determining the total hardness of water in the range of the total content of calcium and magnesium ions is 100-5000 μg-eq / dm ³ contains, as a substance for creating an alkaline medium, an aliphatic amine of the formula RNH ₂ , R ₂ NH or R ₃ N, where R = C _n H _{2n + 1} or R = C _n H _2n OH, normal or branched, with n = 2-4, and all components of the reagent are combined into a single aqueous the solution in the following ratio, g per 100 cm ³ bidistilled water:

Trilon B 3.7220-4.6525

Indicator 0.04-0.06

Aliphatic amine 10.00-10.80

The proposed reagent in all three variants may additionally contain a methanol yellow indicator in the amount ^of _{1/4 of the} mass part of the indicator content of chrome dark blue.

It should be noted that the content of calcium and magnesium salts, which determines the total hardness of water, varies depending on the type of water in a very wide range - by several orders of magnitude. So. the hardness of natural water sources can be from 5 to 20 mEq / dm ³ , the hardness of drinking water lies in the range of 3-7 mEq / dm ³ , and the hardness of softened water prepared for the power industry is measured in the range of 5-400 mcg- equiv / dm ³ (Kostrikin Yu.M. et al. Instructions for the analysis of water, steam and deposits in a heat-power economy. M: Soyuztekhenergo, 1979, p. 7)

To ensure high accuracy of determination in a wide range of total water hardness - from softened to drinking water, the proposed reagent has three options: with different concentrations of Trilon B and an indicator depending on the analyzed hardness range, which is especially important for automatic photometric analysis.

When developing the proposed reagent, various indicators and organic and inorganic substances with the main properties were tested in combination with Trilon B in various concentrations - the ability of the reagent to provide fast and accurate determination of calcium and magnesium ions was studied, provided that all components of the reagent can be combined into a single aqueous solution.

An alkaline medium is necessary for complexometric titration of calcium and magnesium ions, and the optimum pH value for analysis changes depending on the indicator used and the ion being determined. So, in the determination of magnesium ions, the pH should not exceed 10-11, since when the alkalinity is higher than pH 11, the complex of magnesium ions with the indicator is destroyed, and titration becomes impossible, therefore, the use of alkalis in the proposed reagent had to be abandoned. In addition, aqueous solutions of alkalis strongly absorb CO ₂ from the air, which leads to a significant change in their initial concentration. We studied the ammonia buffer solution used in the prototype reagent, and aliphatic alkyl and hydroxyalkylamines (primary, secondary and tertiary, normal or branched), since their addition to the reagent in certain quantities provides the required pH value of 10.

Tables 1-3 show the results of analyzes of water with a given hardness of 100 μg-eq / L, carried out with the same reagent for 6 months.

The reagent contained either triethylamine or triethanolamine or ammonia as a base. Determination of water hardness was carried out on a Tekhnofam 002 device, as in Example 1. From the obtained data it is seen that the reproducibility and accuracy of the analysis using organic amines is much higher than when using ammonia. Perhaps this is due to the high volatility of ammonia.

Tables 1-3.

Metrological indicators of automatic photometric determination of the total hardness of water, a given concentration equal to 100 μg-eq / l, carried out with reagents containing various bases for creating an alkaline environment. The concentration of trilon B in the reagents is 0.01 N, the content of the indicator of chrome dark blue is 0.04 g per 100 cm ^{3 of} water. The standard error (S) and the probable relative error (ε) were calculated from the range of variation (R) using coefficients depending on the number of experiments accepted in analytical practice (A.I. Lazarev, I.P. Kharlamov, P.Ya. Yakovlev , EF Yakovleva. Handbook of the chemist-analyst. M: Metallurgy, 1976, p. 172).

Elimination of the effect of interfering ions with the help of additional solutions provided for in GOST 4151-72 is unacceptable for automatic photometric analysis. It is known that aliphatic amines can eliminate the interfering effect of manganese ions and, to some extent, other ions: iron, aluminum, zinc and copper (Methods of researching the quality of water in water bodies. M: Medicine, 1990, p. 70; Kostrikin Yu.M. and other Instructions for the analysis of water, steam and sediments in the heat power economy. M: Soyuztekhenergo, 1979, p.7).

We have carried out special studies to establish limits for the content of interfering ions: ferric iron, copper and zinc, which do not affect the results of automatic photometric analysis using the proposed reagent. The found concentration limits are: for iron ions - 1.0 mg / l for softened water and 1.5 mg / l for drinking water, for copper - 0.1 and 0.3 mg / l and for zinc - 0.0005 and 0.01 mg / l, respectively. Softened water always contains the indicated ions in much lower concentrations, drinking water may contain iron in a limiting amount, copper and zinc it contains in smaller quantities.

The selected indicator chrome dark blue, contained in the proposed reagent in the declared concentration, provides high metrological indicators of the analysis. An increase in the indicator content in the reagent leads to increased color, and during photometric measurements, the optical density of the analyzed solution will exceed the average values of the scale that are optimal for determination.

The accuracy of the analysis can be improved by changing the color at the equivalence point from blue (as when using chrome dark blue) to green. For this purpose was made a mixed indicator: _^1/4 part by mass chrome dark blue in the reagent has been replaced by metanilovy yellow. Methanyl yellow does not fulfill the role of an indicator in determining water hardness, since it does not chemically interact with calcium and magnesium ions (its color changes from red to yellow in an acidic environment at pH 1.2-2.3), but it changes the color of the solution - it It is an internal filter that allows you to more clearly record the color change at the equivalence point: the lilac color changes in its presence, not blue, but pure green. The addition of methanyl yellow to the reagent will be especially beneficial in manual titration, since it is known that the human eye has maximum sensitivity to green color (RU 2023261 C1, G 01 N 31/16). With an increase in the content of methanyl yellow in the reagent, dirty colors appear in the color of the solution at the equivalence point, which leads to overestimated results.

The proposed reagent is prepared as follows.

Weighed portions of the indicator and aliphatic amine are placed in a volumetric flask of 100 cm ³ (or more), add the right amount of ml of 0.1 N Trilon B solution prepared in advance from a standard titer or a weight taken accurate to the 4th digit, adjusted to tags with redistillate and mix until the components are completely dissolved. The reagent is poured into a plastic container, where it can be stored for 6-9 months.

The proposed reagent can be used both for manual titration and for automatic photometric determination of the total hardness of water.

Manual titration of the proposed reagent can be carried out according to the method described in GOST 4151-72. The accuracy of the determination is at least 10%.

Automatic photometric analysis of the total water hardness of the proposed reagent can be carried out on any devices intended for this.

Example 1

Determination of water hardness was carried out on a Tekhnofam 002 instrument, a light filter with a wavelength of 450-480 nm. The volume of the analyzed sample depends on the value of the set stiffness: for the stiffness concentration of 5 μg-eq / l, the sample volume is 200 cm ³ , for the concentrations of 100 and 300 μg-eq / l - the sample volume is 40 cm ³ . Dosing of the reagent into the volume of the analyzed water sample was carried out with a medical syringe for injection (V-40 INSULIN) with a volume of 1 cm ³ with a division price of 0.025 cm ³ and a thinness of the needle providing a droplet size of 0.01 cm ³ . The duration of the analysis did not exceed 3-5 minutes. The reagent contained 100 cm ³ bidistilled water: 0.1861 g Trilon B, 0.08 g chrome dark blue indicator and 10.00 g triethylamine. Water with a given hardness was prepared from fixanal (0.1 N magnesium sulfate solution). The results are presented in table 4.

Example 2

The determination was carried out as in example 1. The reagent contained 100 cm ³ bidistilled water: 0.2791 g Trilon B, 0.15 g indicator of chrome dark blue and 10.80 g of triethanolamine. Water with a given hardness: 5 μg-eq / L, 100 μg-eq / L and 300 μg-eq / L was prepared from fixanal (0.1 N magnesium sulfate solution). The results are presented in table 5.

Example 3

The determination was carried out as in example 1. The reagent contained 100 cm ³ bidistilled water: 0.2326 g of Trilon B, 0.12 g of chrome dark blue indicator, 0.03 g of methanyl yellow and 10.40 g of monoethanolamine. Water with a given hardness: 5 μg-eq / L, 100 μg-eq / L and 300 μg-eq / L was prepared from fixanal (0.1 N magnesium sulfate solution). The results are presented in table 6.

Example 4

The determination was carried out, as in example 1, only the sample volume equal to 200 cm ³ was used for water hardness 10 μg-eq / l, for hardness 100 and 500 μg-eq / l sample volume 40 cm ³ . The reagent contained 100 cm ³ bidistilled water: 0.3722 g Trilon B, 0.04 g chrome dark blue indicator and 10.40 g tert-butylamine. Water with a given hardness: 10 μg-eq / L, 100 μg-eq / L and 500 μg-eq / L was prepared from fixanal (0.1 N magnesium sulfate solution). The results are presented in table 7.

Example 5

The determination was carried out as in example 4. The reagent contained 100 cm ³ bidistilled water: 0.4652 g Trilon B, 0.06 g indicator of chromic dark blue, 0.015 g of methanyl yellow and 10.80 g of diisopropanolamine. Water with a given hardness: 20 μg-eq / L, 100 μg-eq / L and 500 μg-eq / L was prepared from fixanal (0.1 N magnesium sulfate solution). The results are presented in table 8.

Example 6

The determination was carried out as in example 4. The reagent contained 100 cm ³ bidistilled water: 0.4187 g Trilon B, 0.08 g indicator of chromic dark blue and 10.20 g of diisopropylamine. Water with a given hardness: 20 μg-eq / L, 100 μg-eq / L and 500 μg-eq / L was prepared from fixanal (0.1 N magnesium sulfate solution). The results are presented in table 9.

Example 7

The determination was carried out, as in example 1, only a sample volume of 200 cm ³ was used for water hardness of 100 μg-eq / l, for hardness of 2500 and 5000 μg-eq / l sample volume of 40 cm ³ . The reagent contained 100 cm ³ bidistilled water: 4.6525 g Trilon B, 0.04 g chrome dark blue indicator and 10.00 g n-butylamine. Water with a given hardness: 100 μg-eq / L, 2500 μg-eq / L and 5000 μg-eq / L was prepared from fixanal (0.1 N magnesium sulfate solution). The results are presented in table 10.

Example 8

The determination was carried out as in example 7. The reagent contained 100 cm ³ bidistilled water: 3.7222 g Trilon B, 0.04 g chrome dark blue indicator, 0.01 g methanol yellow and 10.40 g diethanolamine. Water with a given hardness: 100 μg-eq / L, 2500 μg-eq / L and 5000 μg-eq / L was prepared from fixanal (0.1 N magnesium sulfate solution). The results are presented in table 11.

Example 9

The determination was carried out as in example 7. The reagent contained 100 cm ³ bidistilled water: 4.1872 g Trilon B, 0.06 g indicator of chrome dark blue and 10.80 g of triethanolamine. Water with a given hardness: 100 μg-eq / L, 2500 μg-eq / L and 5000 μg-eq / L was prepared from fixanal (0.1 N magnesium sulfate solution). The results obtained are presented in table 12.

Thus, the present invention provides a reagent suitable not only for manual titration, but also for automatic photometric analysis, which provides high accuracy and reproducibility of the results when determining the content of calcium and magnesium in water in a wide range of their total concentrations: from 5 to 5000 μg -eq / dm ³ . The combination of reagent components in one aqueous solution simplifies the determination procedure and reduces analysis time. In addition, the claimed reagent is characterized by increased shelf life.

Claims (6)

1. A reagent for photometric determination of the total hardness of water, including an aqueous solution of Trilon B, a solution of an indicator of chrome dark blue and a solution of a substance to create an alkaline medium, characterized in that for determining the total hardness of water in the range of the total content of calcium and magnesium ions 5-300 μg-equiv / dm ³ it contains an aliphatic amine of the formula RNH ₂ , R ₂ NH or R ₃ N as a substance for creating an alkaline medium, where R = С _n Н _{2n + 1} or R = С _n Н _2n ОН, normal or branched , at n = 2-4 and all reagent components are combined into a single solution was the following ratio g to 100 cm ³ bidistilled water: Trilon B 0.1861-0.2791 Indicator 0.08-0.15 Aliphatic amine 10.00-10.80 2. The reagent according to claim 1, characterized in that it further comprises a methanyl yellow indicator in an amount of 1/4 of the mass content of the indicator of chrome dark blue. 3. A reagent for photometric determination of the total hardness of water, including an aqueous solution of Trilon B, a solution of an indicator of chrome dark blue and a solution of a substance to create an alkaline medium, characterized in that for determining the total hardness of water in the range of the total content of calcium and magnesium ions 10-500 μg-equiv / dm ³ it contains an aliphatic amine of the formula RNH ₂ , R ₂ NH or R ₃ N as a substance for creating an alkaline medium, where R = C _n H _{2n + 1} or R = C _n H _2n OH, normal or branched , at n = 2-4 and all reagent components are combined into a single water the first solution in the following ratio of 100 g per cm ³ bidistilled water: Trilon B 0.3722-0.4652 Indicator 0.06-0.08 Aliphatic amine 10.00-10.80 4. The reagent according to claim 3, characterized in that it further comprises a methanyl yellow indicator in an amount of 1/4 of the mass content of the indicator of chrome dark blue. 5. A reagent for photometric determination of the total hardness of water, including an aqueous solution of Trilon B, a solution of an indicator of chrome dark blue and a solution of a substance to create an alkaline medium, characterized in that for determining the total hardness of water in the range of the total content of calcium and magnesium ions 100-5000 μg-equiv / dm ³ it contains an aliphatic amine of the formula RNH ₂ , R ₂ NH or R ₃ N as a substance for creating an alkaline medium, where R = C _n H _{2n + 1} or R = C _n H _2n OH, normal or branched , at n = 2-4 and all reagent components are combined into a single solution was the following ratio g to 100 cm ³ bidistilled water: Trilon B 3.7220-4.6525 Indicator 0.04-0.06 Aliphatic amine 10.00-10.80 6. The reagent according to claim 5, characterized in that it further comprises a methanilic yellow indicator in an amount of 1/4 of the mass content of the chrome dark blue indicator.