Detection method for total hardness and calcium and magnesium ion content

Abstract

The invention discloses a water quality total hardness and calcium and magnesium ion content detection method, which comprises: extracting a water quality sample to be detected, and injecting into a cuvette; taking a color developing reagent, injecting the color developing reagent into the cuvette, blowing, stirring and uniformly mixing to obtain a reaction solution; measuring the initial current i0 of the reaction liquid in the cuvette at the wavelength of 475nm and the initial current I0 of the reaction liquid in the cuvette at the wavelength of 640nm; then titrating, and recording a measured current value and a titration volume while titrating; according to the obtained relation curve of the current and the titration volume under the two wavelengths, obtaining the titration volume corresponding to a titration judgment end point, and substituting the titration volume into the calibration curve to obtain the concentration of total hardness or the content of calcium and magnesium ions in the water sample. The measuring method disclosed by the invention not only has extremely high accuracy and precision, but also can be applied to measurement of total hardness or calcium ions under different indicators at the same time, and the turbidity of a water sample or magnesium hydroxide precipitate generated during calcium ion measurement hardly affects a test result.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical detection, and specifically to a method for detecting the total hardness, calcium ion content, and magnesium ion content of water quality. Background Art

[0002] Currently, for water quality detection in the market, methods such as ion-selective electrode method, spectrophotometry, photometric / potentiometric titration method, etc. are generally used. Generally, one instrument can only test one parameter, either total hardness or calcium ions. In addition, products using the ion-selective electrode method and spectrophotometry have problems such as large errors in test data and being greatly affected by interference, and the photometric / potentiometric titration method also has problems such as inaccurate determination of the titration end point.

[0003] The principle of total hardness measurement is that under the condition of pH = 10, the indicator forms a purple-red solution with calcium and magnesium. EDTA solution is used for complexometric titration of calcium and magnesium ions. During the titration process, the free calcium and magnesium ions react with EDTA first, and then the calcium and magnesium ions complexed with the indicator react with EDTA. When reaching the end point, the color of the solution changes from purple-red to blue, and the concentration of total hardness in the water sample is calculated according to the titration volume.

[0004] The principle of calcium and magnesium ion measurement is that under the condition of pH 12 - 13, the indicator forms a red complex with calcium, while magnesium ions form magnesium hydroxide precipitate, which does not interfere with the determination. EDTA solution is used for complexometric titration of calcium ions. During the titration, the free calcium ions react with EDTA first, and then the calcium ions complexed with the indicator react with EDTA. When reaching the end point, the solution changes from red to bright blue, and the concentration of calcium ions in the water sample is calculated according to the titration volume, and then the concentration of magnesium ions is obtained by conversion based on the total hardness and the concentration of calcium ions.

[0005] Therefore, providing a detection method for the total hardness, calcium ion content, and magnesium ion content of water quality with more accurate detection accuracy and not being affected by interference is a technical problem that needs to be urgently solved by those skilled in the art. Summary of the Invention

[0006] In view of this, the present invention provides a method for detecting the total hardness, calcium ion content, and magnesium ion content of water quality with high precision.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for detecting the total hardness, calcium ion content, and magnesium ion content of water quality, characterized by comprising the following steps:

[0009] (1) Extract 4 - 5 mL of the water quality sample to be measured and inject it into a cuvette.

[0010] (2) Take reagent A and reagent B or take reagent C and reagent D, inject them into the cuvette, and then blow air to drain the excess liquid in the pipeline; use a stirring motor to stir and mix the solution in the cuvette to obtain a reaction solution.

[0011] (3) Measure the initial current i0 of the reaction solution in the cuvette at a wavelength of 475 nm and the initial current I0 at a wavelength of 640 nm.

[0012] (4) Take reagent E and slowly inject it into the reaction solution at pH = 10 - 13 to start titration. Record the measured current value and the titration volume simultaneously during titration.

[0013] (5) After titration is completed, empty the cuvette, inject clear water, and repeat twice.

[0014] (6) According to the relationship curves of the current and the titration volume obtained at the two wavelengths, obtain the titration volume corresponding to the titration judgment end point, and substitute it into the calibration curve to obtain the concentration of the total hardness or the content of calcium and magnesium ions in the water sample.

[0015] Further, reagent A and reagent B described in step (2) are used to detect the total hardness of water quality.

[0016] Reagent C and reagent D are used to detect the content of calcium and magnesium ions in water.

[0017] Further still, when detecting the total hardness of water quality, the pH value of the reaction solution is adjusted to 10.

[0018] When detecting the content of calcium and magnesium ions in water, the pH value of the reaction solution is adjusted to 12 - 13.

[0019] Further, reagent A is a sodium hydroxide solution.

[0020] Reagent B is a mixed solution of magnesium disodium EDTA, ammonium chloride, 57.2% ammonia water, and calcium chloride.

[0021] Reagent C is a mixed solution of disodium hydroxynaphthol blue and calcium chloride.

[0022] Reagent D is a chromazurol S solution.

[0023] Further still, the concentration of sodium hydroxide in reagent A is 40 g / L.

[0024] The concentration of magnesium disodium EDTA in reagent B is 5.0 g / L, the concentration of ammonium chloride is 67.6 g / L, the ammonia water is 57.2%, and the concentration of calcium chloride is 0.83 g / L.

[0025] The concentration of disodium hydroxynaphthol blue in reagent C is 0.20 g / L, and the concentration of calcium chloride is 0.83 g / L.

[0026] The concentration of chromazurol S in reagent D is 0.30 g / L.

[0027] Further, the rotation speed of the stirring motor described in step (2) is 100 - 150 revolutions per minute, and the stirring time is 2 - 5 minutes.

[0028] Further, the reagent E is disodium EDTA with a concentration of 7.45 g / L.

[0029] Further, after the titration is completed, the relationship curves of the current and the titration volume of the reaction solution at 475 nm and 640 nm are i = f(v) and I = F(v) respectively;

[0030] Query the curves. When i = k1 * k2 * I, that is, f(v) = k1 * k2 * F(v), the obtained v value is the titration end point;

[0031] Where k1 is a compensation coefficient, and the value of k1 is 0.8 - 1.2; k2 = i0 / I0.

[0032] Generally, the laboratory standard analysis methods for total hardness and calcium and magnesium ions are "Determination of total calcium and magnesium in water - EDTA titration method (GB 7477 - 87)" and "Determination of calcium in water - EDTA titration method (GB 7476 - 87)". This invention partially refers to these two standard methods. During the actual detection and analysis process, there will be a color change from red - purple - blue. The real titration end point is at the moment of purple - blue, rather than the moment of red - purple. The judgment result of this end point directly affects the accuracy of the test result. And it is difficult for the analytical instrument to accurately determine this color change through the detected signal, resulting in a large error.

[0033] In this invention, after adding the water sample and the indicator, before adding the titrant, stirring is started. At this time, the initial current of a solution is measured first. The initial current at a wavelength of 475 nm is i0, and the initial current at a wavelength of 640 nm is I0. Subsequently, the titrant is extracted and titration is started. During the titration process, the current values (the current measured at a wavelength of 480 nm is recorded as i, and the current measured at a wavelength of 640 nm is recorded as I) and the titration volume are recorded simultaneously. After the titration is completed, the relationship curves of the current and the titration volume at two wavelengths, i = f(v) and I = F(v), can be obtained. Subsequently, query the curves. When i = k1 * k2 * I, that is, f(v) = k1 * k2 * F(v), the obtained v value is the titration end point. Where k1 is a compensation coefficient, which is adjusted according to different test parameters and reagents, generally 0.8 - 1.2; k2 = i0 / I0, which is used to compensate for the difference in the intensity of the light source itself and the influence of turbidity on the test data.

[0034] In addition, during the detection titration process, the normal color change end point color has a maximum absorption peak at 620 nm to 640 nm. As the titration volume increases, the absorbance suddenly increases when the reaction solution changes from red to purple. Subsequently, the absorbance also continues to increase during continuous titration, but it is impossible to determine the true end point when the color changes from purple to blue. During the research process, the inventor unexpectedly discovered that the absorbance at 475 nm gradually decreases during titration, and the detected current also gradually increases. After converting the two currents through a formula, there will be an intersection point. Using the titration volume corresponding to this intersection point as the end point, the true titration end point can be accurately obtained.

[0035] The measurement method of the present invention not only has extremely high accuracy and precision, but can also be simultaneously applied to the measurement of total hardness or calcium ions under different indicators. Moreover, whether it is the turbidity of the water sample itself or the magnesium hydroxide precipitate generated during the calcium ion determination, it has almost no influence on the test results. Specific embodiments

[0036] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0037] In the embodiment of the present invention, reagent A is an aqueous sodium hydroxide solution with a concentration of 40 g / L;

[0038] Reagent B is a mixed aqueous solution with a concentration of 5.0 g / L of disodium magnesium EDTA, a concentration of 67.6 g / L of ammonium chloride, a mass ratio of ammonia of 57.2%, and a concentration of 0.83 g / L of calcium chloride;

[0039] Reagent C is a mixed aqueous solution with a concentration of 0.20 g / L of disodium hydroxynaphthol blue and a concentration of 0.83 g / L of calcium chloride;

[0040] Reagent D is an aqueous solution of chromazurol S with a concentration of 0.30 g / L.

[0041] Reagent E is an aqueous solution of disodium EDTA with a concentration of 7.45 g / L.

[0042] Example 1

[0043] (1) Extract 4.5 mL of the water quality sample to be measured and inject it into a cuvette;

[0044] (2) Take reagent A and reagent B to detect the total hardness of the water quality. After injecting them into the cuvette, blow air to drain the excess liquid in the pipeline; use a stirring motor to stir and mix the solution in the cuvette at 12 revolutions per minute for 3 minutes to obtain a reaction solution;

[0045] (3) Measure the initial current i0 of the reaction solution in the cuvette at a wavelength of 475 nm and the initial current I0 at a wavelength of 640 nm;

[0046] (4) Take reagent E and slowly inject it into the reaction solution at pH = 10 to start titration. Record the measured current value and the titration volume simultaneously during titration;

[0047] (5) After titration is completed, empty the cuvette, inject clear water, and repeat twice;

[0048] (6) According to the relationship curves of the current and the titration volume at the two obtained wavelengths, obtain the titration volume corresponding to the titration judgment end point, and substitute it into the calibration curve to obtain the concentration of the total hardness in the water sample; The relationship curves of the current and the titration volume of the reaction solution at 475 nm and 640 nm are i = f(v) and I = F(v) respectively; Query the curve. When i = k1 * k2 * I, that is, f(v) = k1 * k2 * F(v), the obtained v value is the titration end point; where k1 is the compensation coefficient, and the value of k1 is 0.8 - 1.2; k2 = i0 / I0.

[0049] Example 2

[0050] (1) Extract the water quality sample to be measured and inject it into the cuvette;

[0051] (2) Take reagent C and reagent D to detect the calcium and magnesium ion content. After injecting into the cuvette, blow air to empty the excess liquid in the pipeline; Use the stirring motor to stir and mix the solution in the cuvette at 12 revolutions per minute for 3 minutes to obtain the reaction solution;

[0052] (3) Measure the initial current i0 of the reaction solution in the cuvette at a wavelength of 475 nm and the initial current I0 at a wavelength of 640 nm;

[0053] (4) Take reagent E and slowly inject it into the reaction solution at pH = 12.5 to start titration. Record the measured current value and the titration volume simultaneously during titration;

[0054] (5) After titration is completed, empty the cuvette, inject clear water, and repeat twice;

[0055] (6) According to the relationship curves of the current and the titration volume at the two obtained wavelengths, obtain the titration volume corresponding to the titration judgment end point. The relationship curves of the current and the titration volume of the reaction solution at 475 nm and 640 nm are i = f(v) and I = F(v) respectively; Query the curve. When i = k1 * k2 * I, that is, f(v) = k1 * k2 * F(v), the obtained v value is the titration end point;

[0056] Where k1 is the compensation coefficient, and the value of k1 is 0.8 - 1.2; k2 = i0 / I0.

[0057] Test Example

[0058] According to the method provided in Example 1, hardness detection data was collected from June to August 2024, and the manual titration data was used as a comparative example. Among them, k1 was 1.03, and k2 was determined according to the measured current value during each measurement. The results are shown in Tables 1 - 3.

[0059] Table 1 Comparison Table of Hardness Detection Data in June 2024

[0060]

[0061] Table 2 Comparison Table of Hardness Detection Data in July 2024

[0062]

[0063] Table 3 Comparison Table of Hardness Detection Data in August 2024

[0064]

[0065]

[0066] The results in Tables 1 - 3 show that the method of the present invention has a more accurate titration effect, can avoid the influence of the components in the liquid on the titration end point, and has good application prospects.

[0067] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for detecting total water hardness and calcium and magnesium ion content, characterized in that: The following steps are involved: (1) Take the water sample to be tested and inject it into the cuvette; (2) taking reagent A and reagent B or taking reagent C and reagent D, injecting them into a cuvette, and then blowing air to drain the excess liquid in the pipeline; stirring and mixing the solution in the cuvette with a stirring motor to obtain a reaction solution; (3) measuring the initial current i0 of the reaction solution in the cuvette at a wavelength of 475 nm and the initial current I0 at a wavelength of 640 nm; (4) Take reagent E and slowly inject it into the reaction solution at pH = 10-13 to start titration. During the titration, record the measured current value and titration volume; (5) After the titration is completed, empty the cuvette and fill it with clean water. Repeat twice. (6) Based on the relationship curve between the current and the titration volume at the two wavelengths, the titration volume corresponding to the titration judgment endpoint is obtained, and the concentration of the total hardness or the content of calcium and magnesium ions in the water sample is obtained by substituting it into the calibration curve.

2. The method for detecting total water hardness and calcium and magnesium ion content according to claim 1, characterized in that: The reagent A and reagent B described in step (2) are used to detect the total hardness of water; The reagent C and reagent D are used to detect the calcium and magnesium ion contents in water.

3. A method for detecting total water hardness and calcium and magnesium ion content according to claim 1 or 2, characterized in that: When testing the total hardness of water, the pH value of the reaction solution is adjusted to 10; When testing the calcium and magnesium ion content in water, the pH value of the reaction solution is adjusted to 12-13.

4. A method for detecting total water hardness and calcium and magnesium ion content according to claim 1 or 2, characterized in that: The reagent A is a sodium hydroxide solution; The reagent B is a mixed solution of disodium magnesium EDTA, ammonium chloride, 57.2% ammonia water and calcium chloride; The reagent C is a mixed solution of hydroxynaphthol blue disodium salt and calcium chloride; The reagent D is chrome black T solution.

5. The method for detecting total water hardness and calcium and magnesium ion content according to claim 4, characterized in that: The sodium hydroxide concentration in the reagent A is 40 g / L; The reagent B contains 5.0 g / L magnesium disodium EDTA, 67.6 g / L ammonium chloride, 57.2% ammonia water, and 0.83 g / L calcium chloride. The concentration of hydroxynaphthol blue disodium salt in the reagent C is 0.20 g / L, and the concentration of calcium chloride is 0.83 g / L; The concentration of chrome black T in the reagent D is 0.30 g / L.

6. The method for detecting total water hardness and calcium and magnesium ion content according to claim 1, characterized in that: The stirring motor speed in step (2) is 100-150 rpm, and the stirring time is 2-5 minutes.

7. The method for detecting total water hardness and calcium and magnesium ion content according to claim 1, characterized in that: The reagent E is disodium EDTA with a concentration of 7.45 g / L.

8. The method for detecting total water hardness and calcium and magnesium ion content according to claim 1, characterized in that: After the titration, the relationship curves between the current and the titration volume of the reaction solution at 475nm and 640nm are i=f(v) and I=F(v), respectively; Query the curve. When i=k1*k2*I, that is, f(v)=k1*k2*F(v), the obtained v value is the titration endpoint; Wherein k1 is the compensation coefficient, and the value of k1 is 0.8~1.2; k2=i0 / I0.

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