Water hardness detection reagent, preparation method and application thereof

Abstract

The application relates to the technical field of water hardness detection, in particular to a water quality hardness detection reagent, a preparation method and application thereof, the water quality hardness detection reagent comprises the following raw materials in parts by weight: ethanolamine 0.8-1.5 parts, diethanolamine 5-7 parts, triethanolamine 35-40 parts, ammonia-ammonium chloride buffer solution 52-57 parts, chrome black T indicator 1.5-2 parts, ethylenediaminetetraacetic acid disodium magnesium salt 1-1.5 parts, sodium chloride 0.1-0.3 parts and formaldehyde aqueous solution 0.1-0.3 parts. The water quality hardness detection reagent prepared by the application has the characteristics of good stability and high sensitivity.

Description

Technical Field

[0001] This invention relates to the field of water hardness testing technology, specifically to a water hardness testing reagent, its preparation method, and its application. Background Technology

[0002] Water hardness is typically determined by the total concentration of dissolved calcium and magnesium ions in the water; the content of these ions determines the degree of softness or hardness of the water. Water with a high concentration of calcium and magnesium salts is called hard water; conversely, water with a low concentration is called soft water. Hard water has many impacts on daily life and industrial production. For example, in the textile industry, washing with hard water can cause stains on textiles, affecting not only their appearance but also potentially reducing their strength. In food processing, hard water can cause protein precipitation, making food difficult to cook thoroughly. Furthermore, hard water can adversely affect the effectiveness of pesticides, boiler operation, and the efficiency of heat exchangers. However, traditional water hardness indicators suffer from poor stability, easy oxidation, and indistinct endpoint color changes.

[0003] Patent CN1584560A discloses a solid reagent for testing water hardness, composed of the following components: disodium ethylenediaminetetraacetate (EDTA), sodium tetraborate, chrome black T, sodium carbonate, and sodium chloride. This reagent is portable, easy to operate, and can detect water hardness without the need for professional personnel, greatly facilitating water hardness testing in many industries. It can be applied to the testing of softened water in boilers, brewing, beverage, and wool textile processes, as well as for testing by relevant inspection departments. Patent CN102749324A discloses a rapid water hardness testing reagent and its applicable reagent bottle, test tube, and method. This rapid water hardness testing reagent includes an alkaline solution, an indicator, and an EDTA aqueous solution, each separately packaged in different containers. The indicator comprises a mixture of calcium red and alkali metal salts and a mixture of chrome black T and alkali metal salts. When using this invention to test water hardness, the reagent components are packaged in separate containers for easy portability. Through the precise design of the reagent bottles and test tubes, even non-professionals can quickly test water hardness on-site. Furthermore, by applying different alkaline solutions and indicators, the total hardness and calcium hardness of the water can be obtained. However, neither of the aforementioned patents considered the problem of chrome black T, which is prone to oxidation and failure in alkaline solutions, resulting in a less sensitive endpoint color change in the water hardness testing reagent.

[0004] Therefore, there is an urgent need in the market for a water hardness testing reagent with good stability and high sensitivity. Summary of the Invention

[0005] In view of the problems existing in the prior art, the purpose of this invention is to obtain a water hardness testing reagent with good stability and high sensitivity.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] The first aspect of this invention provides a water hardness testing reagent, comprising, by weight, the following raw materials: 0.8-1.5 parts of ethanolamine, 5-7 parts of diethanolamine, 35-40 parts of triethanolamine, 52-57 parts of ammonia-ammonium chloride buffer solution, 1.5-2 parts of chrome black T indicator, 1-1.5 parts of disodium magnesium ethylenediaminetetraacetate, 0.1-0.3 parts of sodium chloride, and 0.1-0.3 parts of formaldehyde aqueous solution.

[0008] This application presents a water hardness testing reagent prepared by blending ethanolamine, diethanolamine, triethanolamine, ammonia-ammonium chloride buffer solution, Eriochrome Black T indicator, disodium magnesium ethylenediaminetetraacetate, sodium chloride, and formaldehyde aqueous solution. This reagent exhibits advantages such as good stability and high sensitivity. Ethanolamine, diethanolamine, and triethanolamine can mask Fe... 3 +, Al3+, Cu 2 +、Mn 2 + metal ions, reducing the influence of these ions on the detection results. Among them, triethanolamine, as the core complexing agent, preferentially binds with Ca. 2 +, Mg 2 + binding, while ethanolamine and diethanolamine preferentially complex Fe. 3 Al+, Al3+, and sodium chloride work synergistically to eliminate interference from other ions in endpoint determination. Disodium magnesium ethylenediaminetetraacetate (EDTA) improves the colorimetric sensitivity of Eriochrome Black T indicator; sodium chloride maintains ionic strength and reduces electrochemical interference. Formaldehyde inhibits the photolytic oxidation of Eriochrome Black T, extending the reagent's shelf life.

[0009] In some embodiments, the preparation method of the ammonia-ammonium chloride buffer solution includes the following steps: dissolving ammonium chloride in deionized water, adding concentrated ammonia, stirring at room temperature for 3-5 minutes, adding deionized water to make up to volume, stirring at room temperature for 3-5 minutes, adjusting the pH to 10, and obtaining the ammonia-ammonium chloride buffer solution.

[0010] In some embodiments, the preparation method of the Chrome Black T indicator includes the following steps:

[0011] A1. Iron salts are mixed with organic ligands, acetic acid, and solvent, and ultrasonically mixed to obtain a metal-organic mixture; the metal-organic mixture undergoes a solvothermal reaction to obtain an Fe-MOF suspension.

[0012] A2. Centrifuge, wash and dry the Fe-MOF suspension obtained in step A1 to obtain Fe-MOF material;

[0013] A3. Dissolve Chrome Black T in a 45-55 wt% aqueous ethanol solution, add the Fe-MOF material obtained in step A2, stir in the dark for 12-24 h at pH 7, filter, wash, centrifuge, and vacuum dry at 55-65℃ to obtain Chrome Black T indicator.

[0014] Preferably, the iron salt is a trivalent iron salt.

[0015] In some embodiments, the organic ligand is a composition of 2-aminoterephthalic acid and biphenyl phthalic acid in a mass ratio of 1:(0.2-0.5).

[0016] The structure of Chrome Black T contains an oxidizing group (nitro) and two different reducing groups (azo and phenolic hydroxyl), making it prone to intramolecular redox reactions that can destroy the indicator. To address this issue, this application loads Chrome Black T onto a metal-organic framework (MOF) material, reducing its direct contact with air / solvent and improving its stability to enhance the accuracy of water hardness testing results. Fe-MOF possesses a high specific surface area and tunable pore structure, allowing selective adsorption of calcium and magnesium ions in water, which are then expressed through color changes such as alterations in ligand structure or Fe... 3 The redox reaction amplifies the signal, improving detection sensitivity. This application further enhances the dispersibility of the MOF material loaded with Eriochrome Black T in water by grafting amino groups onto the MOF material, and also improves the Fe... 3 Al3+ and Al3+ are further masked, reducing interference and further improving the accuracy of the detection results. In addition, the rigid ligand biphenyl dicarboxylic acid selected in this application can expand the metal nodes and form macropores. By limiting the pore size of the MOF material, the MOF material has a better loading capacity, while making it easier for calcium and magnesium ions to complex with chrome black T.

[0017] In some embodiments, the mass ratio of the iron salt to the organic ligand is 1:(0.8-1.2).

[0018] This application can further improve the stability and sensitivity of water hardness testing reagents by limiting the mass ratio of iron salts and organic ligands. This may be because the MOF material has a suitable porosity at this ratio, which is beneficial to increasing the loading of chrome black T.

[0019] In some embodiments, the solvent is a composition of N,N-dimethylformamide and deionized water in a volume ratio of (2-6):1.

[0020] In some embodiments, the mass ratio of the chrome black T to the Fe-MOF material is 1:(7-11).

[0021] This application can further improve the stability and sensitivity of water hardness testing reagents by limiting the mass ratio of iron metal salt and organic ligand. This may be because Fe-MOF nanoparticles can be uniformly dispersed in the system at this ratio, reducing the influence of contrast color.

[0022] In some embodiments, the water hardness testing reagent further contains 3-7 parts by weight of hydroxylamine hydrochloride.

[0023] The addition of hydroxylamine hydrochloride can prevent the effects of external oxidizing substances on Chrome Black T.

[0024] The second aspect of this application provides a method for preparing a water hardness testing reagent, comprising the following steps: adding ethanolamine, diethanolamine, and triethanolamine to an ammonia-ammonium chloride buffer solution, stirring at 25℃±2℃ for 20-30 min, then sequentially adding formaldehyde aqueous solution, chrome black T indicator, disodium magnesium ethylenediaminetetraacetate, and sodium chloride, ultrasonically dispersing under light-protected conditions for 20-30 min, filtering, and sealing in a brown reagent bottle to obtain the water hardness testing reagent.

[0025] The third aspect of this application provides an application of a water hardness testing reagent, comprising the following steps: placing a water sample in a colorimetric chamber, adding a water hardness testing reagent, continuously adding a standard titration solution of 0.01 mol / L or 0.005 mol / L ethylenediaminetetraacetic acid disodium salt to the water sample using a pump, and calculating the hardness of the water sample by measuring the volume of reagent consumed until the titration endpoint is reached.

[0026] Preferably, the water sample is one of tap water, boiler water, or synthetic water.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) The water hardness testing reagent prepared by blending ethanolamine, diethanolamine, triethanolamine, ammonia-ammonium chloride buffer, chrome black T indicator, disodium magnesium ethylenediaminetetraacetate, sodium chloride, formaldehyde aqueous solution, and water has the advantages of good stability and high sensitivity. Among them, ethanolamine, diethanolamine, and triethanolamine can mask Fe... 3 +, Al3+, Cu 2 +、Mn 2 + Metal ions, reduce the influence of these ions on the detection results; disodium magnesium ethylenediaminetetraacetate can improve the colorimetric sensitivity of Chrome Black T indicator.

[0029] (2) This invention reduces the direct contact between chrome black T and air / solvent by loading chrome black T onto a metal-organic framework material, thereby improving stability and thus enhancing the accuracy of the detection results.

[0030] (3) This invention improves the dispersibility of MOF materials loaded with Eriochrome Black T in water by grafting amino groups onto the MOF material, and also enhances the dispersibility of Fe... 3 Al3+ and Al3+ are further masked, reducing interference and further improving the accuracy of the detection results. In addition, the rigid ligand biphenyl dicarboxylic acid in the system can expand the metal nodes and form macropores. By limiting the pore size of the MOF material, the MOF material can have a better loading capacity, while making it easier for calcium and magnesium ions to combine with chrome black T. Attached Figure Description

[0031] Figure 1 Schematic diagram of a colorimetric chamber for measuring water hardness;

[0032] Figure labels: 1. Water sample inlet; 2. Reagent dosing port; 3. 515nm detection light source; 4. Water sample outlet; 5. Light intensity sensor. Detailed Implementation

[0033] The present invention will be described below with reference to specific embodiments. It should be noted that the following embodiments are examples of the present invention and are used only to illustrate the invention, not to limit it. Other combinations and various modifications within the scope of the present invention can be made without departing from its spirit or scope.

[0034] In the following examples and comparative examples, all compounds and related reagents used, except for Chrome Black T indicator, were commercially available.

[0035] Preparation Example 1

[0036] The preparation method of Chrome Black T indicator-1 includes the following steps:

[0037] A1. Mix 1g of ferric chloride with 1g of organic ligand, 1.67ml of acetic acid, 44ml of N,N-dimethylformamide and 11ml of deionized water, and sonicate to obtain a metal-organic mixture; subject the metal-organic mixture to a solvothermal reaction at a temperature of 140℃ for 24h to obtain an Fe-MOF suspension.

[0038] A2. The Fe-MOF suspension obtained in step A1 is centrifuged, washed, and dried to obtain Fe-MOF material;

[0039] A3. Dissolve 1g of Chrome Black T in 50g of 50wt% ethanol aqueous solution, add 9g of Fe-MOF material obtained in step A2, stir in the dark for 18h under pH 7, filter, wash, centrifuge, and vacuum dry at 60℃ to obtain Chrome Black T indicator-1.

[0040] The organic ligands are a combination of 2-aminoterephthalic acid and biphenyl phthalic acid in a mass ratio of 1:0.35.

[0041] Preparation Example 2

[0042] The preparation method of Chrome Black T indicator-2 is the same as that in preparation example 1, except that the organic ligand is 2-aminoterephthalic acid.

[0043] Preparation Example 3

[0044] The preparation method of Chrome Black T indicator-3 is the same as that of preparation example 1, except that the organic ligand is a combination of 2-aminoterephthalic acid and biphenyl dicarboxylic acid, with a mass ratio of 1:0.1.

[0045] Preparation Example 4

[0046] The preparation method of Chrome Black T indicator-4 is the same as that in preparation example 1, except that the amount of organic ligand added is 1.4g.

[0047] Preparation Example 5

[0048] The preparation method of Chrome Black T indicator-5 is the same as that of preparation example 1, except that the amount of Fe-MOF material added is 13g.

[0049] Preparation Example 6

[0050] The preparation method of ammonia-ammonium chloride buffer solution includes the following steps: dissolving 5.35g of ammonium chloride in 200ml of deionized water, adding 7ml of 26wt% concentrated ammonia solution, stirring at room temperature for 4min, adding deionized water to make up to 1L, stirring at room temperature for 4min, adjusting the pH to 10, and obtaining the ammonia-ammonium chloride buffer solution.

[0051] Example 1

[0052] A water hardness testing reagent, by weight, comprises the following raw materials: 1.2 parts ethanolamine, 6 parts diethanolamine, 37 parts triethanolamine, 54 parts ammonia-ammonium chloride buffer solution, 1.7 parts chrome black T indicator-1, 1.2 parts disodium magnesium ethylenediaminetetraacetate, 0.2 parts sodium chloride, and 0.2 parts 40 wt% formaldehyde aqueous solution.

[0053] The preparation method of the water hardness testing reagent in this embodiment includes the following steps: adding ethanolamine, diethanolamine, and triethanolamine to an ammonia-ammonium chloride buffer solution, stirring at 25°C for 25 min, then sequentially adding 40 wt% formaldehyde aqueous solution, Eriochrome Black T indicator-1, disodium magnesium ethylenediaminetetraacetate, and sodium chloride, ultrasonically dispersing under light-protected conditions for 25 min, filtering, and sealing in a brown reagent bottle to obtain the water hardness testing reagent.

[0054] Example 2

[0055] A water hardness testing reagent, by weight, comprises the following raw materials: 0.8 parts ethanolamine, 5 parts diethanolamine, 35 parts triethanolamine, 52 parts ammonia-ammonium chloride buffer solution, 1.5 parts chrome black T indicator-1, 1 part disodium magnesium ethylenediaminetetraacetate, 0.1 parts sodium chloride, and 0.1 parts 40 wt% formaldehyde aqueous solution.

[0056] The preparation method of the water hardness testing reagent in this embodiment includes the following steps: adding ethanolamine, diethanolamine, and triethanolamine to an ammonia-ammonium chloride buffer solution, stirring at 23°C for 30 min, then sequentially adding 40 wt% formaldehyde aqueous solution, Eriochrome Black T indicator-1, disodium magnesium ethylenediaminetetraacetate, and sodium chloride, ultrasonically dispersing under light-protected conditions for 20 min, filtering, and sealing in a brown reagent bottle to obtain the water hardness testing reagent.

[0057] Example 3

[0058] A water hardness testing reagent, by weight, comprises the following raw materials: 1.5 parts ethanolamine, 7 parts diethanolamine, 40 parts triethanolamine, 57 parts ammonia-ammonium chloride buffer solution, 2 parts chrome black T indicator-1, 1.5 parts disodium magnesium ethylenediaminetetraacetate, 0.3 parts sodium chloride, and 0.3 parts 40 wt% formaldehyde aqueous solution.

[0059] The preparation method of the water hardness testing reagent in this embodiment includes the following steps: adding ethanolamine, diethanolamine, and triethanolamine to an ammonia-ammonium chloride buffer solution, stirring at 28°C for 20 minutes, then sequentially adding 40wt% formaldehyde aqueous solution, Eriochrome Black T indicator-1, disodium magnesium ethylenediaminetetraacetate, and sodium chloride, ultrasonically dispersing under light-protected conditions for 30 minutes, filtering, and sealing in a brown reagent bottle to obtain the water hardness testing reagent.

[0060] Example 4

[0061] A water hardness testing reagent, by weight, comprises the following raw materials: 1.2 parts ethanolamine, 6 parts diethanolamine, 37 parts triethanolamine, 54 parts ammonia-ammonium chloride buffer solution, 1.7 parts chrome black T indicator-1, 1.2 parts disodium magnesium ethylenediaminetetraacetate, 0.2 parts sodium chloride, 0.2 parts 40 wt% formaldehyde aqueous solution, and 5 parts hydroxylamine hydrochloride.

[0062] The preparation method of the water hardness testing reagent in this embodiment includes the following steps: adding ethanolamine, diethanolamine, triethanolamine, and hydroxylamine hydrochloride into an ammonia-ammonium chloride buffer solution, stirring at 25°C for 25 min, then sequentially adding 40 wt% formaldehyde aqueous solution, Eriochrome Black T indicator-1, disodium magnesium ethylenediaminetetraacetate, and sodium chloride, ultrasonically dispersing under light-protected conditions for 25 min, filtering, and sealing in a brown reagent bottle to obtain the water hardness testing reagent.

[0063] Example 5

[0064] A water hardness testing reagent and its preparation method are disclosed. The specific implementation method is the same as that in Example 1, except that Chrome Black T indicator-1 is replaced with Chrome Black T indicator-2 in equal amounts.

[0065] Example 6

[0066] A water hardness testing reagent and its preparation method are disclosed. The specific implementation method is the same as that in Example 1, except that Chrome Black T indicator-1 is replaced with Chrome Black T indicator-3 in equal amounts.

[0067] Example 7

[0068] A water hardness testing reagent and its preparation method are disclosed. The specific implementation method is the same as in Example 1, except that Chrome Black T indicator-1 is replaced with Chrome Black T indicator-4 in equal amounts.

[0069] Example 8

[0070] A water hardness testing reagent and its preparation method are described. The specific implementation method is the same as in Example 6, except that Chrome Black T indicator-1 is replaced with Chrome Black T indicator-5 in equal amounts.

[0071] Example 9

[0072] A water hardness testing reagent and its preparation method are disclosed. The specific implementation method is the same as in Example 1, except that Chrome Black T indicator-1 is replaced with Chrome Black T in equal amounts.

[0073] Performance testing

[0074] The water hardness testing reagents obtained in the above embodiments were tested for the following properties:

[0075] (1) Preparation of simulated water sample: Dissolve CaCl, FeCl3, and MgCl in deionized water to prepare a simulated water sample with a hardness of 200 mg / L, wherein Fe... 3 The concentration of + is 5 ppm.

[0076] (2) Simulated water sample hardness measurement: A schematic diagram of the colorimetric chamber for water hardness measurement is shown below. Figure 1As shown, the water sample to be tested in the colorimetric chamber is updated by the automatic detection system's sample injection control device. The water sample is added through the water sample inlet 1. The water hardness testing reagents obtained in Examples 1-9 are added to the simulated water sample through the reagent dosing port 2 after being stored at 25°C for 0 days and 180 days, respectively. A 0.01 mol / L disodium ethylenediaminetetraacetate standard titration solution is continuously added to the simulated water sample through the reagent dosing port 2 by a plunger pump. Illumination is emitted from the 515 nm detection light source 3 on the left side of the colorimetric chamber and emitted from the right side. Light intensity sensor 5 measures absorbance. As reagent is continuously added, the water sample color deepens, and the light intensity sensor reading decreases until the calcium and magnesium ions in the water sample have completely reacted. The water sample color then abruptly changes from red to blue, and the light intensity sensor reading suddenly rises. The hardness of the water sample (expressed as molar concentration c1, in mmol / L) can be calculated by measuring the amount of reagent added. After testing, distilled water is continuously introduced into the colorimetric chamber through water sample inlet 1 to rinse the chamber, and the water sample flows out through water sample outlet 4. The calculation formula is as follows:

[0077] c1=(V1×c×10 3 ) / V

[0078] In the formula:

[0079] V1 is the volume of EDTA solution consumed in the titration of the water sample, in ml;

[0080] c represents the concentration of the EDTA solution, in mol / L.

[0081] V represents the volume of the water sample in the colorimetric chamber, expressed in ml.

[0082] The water hardness was converted to CaCO3, and the conversion method was: 1 mmol / L = 100 mg / L (CaCO3).

[0083] (3) Light intensity signal attenuation rate: The light intensity signal attenuation rate of the water hardness test reagent stored at 25℃ for 6 months was tested using a spectrophotometer.

[0084] The test results are shown in Table 1:

[0085] Table 1

[0086]

[0087] As shown in Table 1, the water hardness testing reagents in Examples 1-3 of this invention exhibit high colorimetric sensitivity and good stability. A comparison between Example 4 and Example 1 shows that the addition of hydroxylamine hydrochloride further improves the colorimetric sensitivity and stability of the water hardness testing reagent. A comparison between Examples 5 and 6 and Example 1 shows that using only 2-aminoterephthalic acid as the organic ligand or changing the ratio of 2-aminoterephthalic acid to biphenyl phthalic acid affects the loading of the MOF material or the complexation efficiency of calcium and magnesium ions with chrome black T, thus affecting the water hardness testing reagent. The colorimetric sensitivity decreased; a comparison between Example 7 and Example 1 shows that changing the ratio of iron salt and organic ligand affects the porosity and loading of MOF material, thus worsening the colorimetric sensitivity of the water hardness test reagent; a comparison between Example 8 and Example 1 shows that changing the ratio of Chrome Black T to Fe-MOF material affects the dispersibility of Chrome Black T indicator, leading to a decrease in the colorimetric sensitivity of Chrome Black T indicator; a comparison between Example 9 and Example 1 shows that when Chrome Black T is used directly, the colorimetric sensitivity of the water hardness test reagent is low and the reagent stability decreases.

[0088] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it. They should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A water hardness test reagent, characterized by comprising: The water hardness detection reagent comprises the following raw materials in parts by weight: ethanolamine 0.8-1.5 parts, diethanolamine 5-7 parts, triethanolamine 35-40 parts, ammonia-ammonium chloride buffer solution 52-57 parts, chrome black T indicator 1.5-2 parts, ethylenediaminetetraacetic acid disodium magnesium salt 1-1.5 parts, sodium chloride 0.1-0.3 parts, and aqueous formaldehyde solution 0.1-0.3 parts; The preparation method of the chrome black T indicator comprises the following steps: A1, mixing iron salt with organic ligand, acetic acid, solvent, ultrasonic mixing, obtaining metal organic mixed solution; metal solvent thermal reaction of organic mixed solution, obtaining Fe MOF suspension A2. Fe was obtained by adding A1 MOF suspension was centrifuged, washed, and dried to obtain Fe MOF material; A3, dissolve chromium black T in 45-55wt% ethanol aqueous solution, add Fe obtained in step A2 MOF material, under the condition of pH 7, avoid light stirring for 12-24h, filter, wash, centrifuge, vacuum drying at 55-65℃, get chromium black T indicator The organic ligand is a combination of 2-amino terephthalic acid and biphenyl dicarboxylic acid, and the mass ratio of the two is 1: (0.2-0.5) ; The solvent is a combination of N,N dimethylformamide and deionized water in a volume ratio of (2-6):

1.

2. The water hardness test reagent according to claim 1, characterized by The preparation method of the ammonia-ammonium chloride buffer solution comprises the following steps: dissolving ammonium chloride in deionized water, adding concentrated ammonia water, stirring at room temperature for 3-5 min, adding deionized water to constant volume, stirring at room temperature for 3-5 min, adjusting the pH to 10, and obtaining the ammonia-ammonium chloride buffer solution.

3. The water hardness test reagent according to claim 1, characterized by The mass ratio of the iron salt and the organic ligand is 1: (0.8-1.2).

4. The water hardness test reagent according to claim 1, characterized by The chromium black T and Fe The mass ratio of the MOF material is 1: (7-11).

5. The water hardness test reagent according to claim 1, characterized by The water hardness detection reagent further comprises 3-7 parts by weight of hydroxylamine hydrochloride.

6. A method for preparing the water hardness test reagent according to any one of claims 1 to 5, characterized by, The preparation method of the water hardness detection reagent comprises the following steps: adding ethanolamine, diethanolamine and triethanolamine into the ammonia-ammonium chloride buffer solution, stirring at 25℃±2℃ for 20-30 min, sequentially adding aqueous formaldehyde solution, chrome black T indicator, ethylenediaminetetraacetic acid disodium magnesium salt and sodium chloride, ultrasonic dispersing for 20-30 min under light shielding condition, filtering, and then packaging in a brown reagent bottle to obtain the water hardness detection reagent.

7. Use of a water hardness test reagent according to any one of claims 1 to 5 or a water hardness test reagent obtainable by the method of claim 6, characterized in that, The preparation method of the water hardness detection reagent comprises the following steps: placing the water sample in a colorimetric chamber, adding the water hardness detection reagent, continuously adding ethylenediaminetetraacetic acid disodium standard titration solution with a concentration of 0.01 mol / L or 0.005 mol / L to the water sample through a pump, calculating the hardness of the water sample by the volume of the reagent consumed until the titration end point is reached.

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