A standard substance of residual chlorine solution, its preparation method and application

Abstract

An embodiment of the present invention discloses a residual chlorine solution reference material, its preparation method and application, belonging to the technical field of reference materials. The method includes: dissolving a hydrogen peroxide solution in an appropriate amount of ultrapure water, transferring it to a 5000 mL volumetric flask, adding a phosphate buffer solution and disodium ethylenediaminetetraacetate, diluting to the mark with ultrapure water for volume fixation, filling and sealing into clean ampoules, storing in refrigeration and avoiding light. Calculated as Cl2, the concentration of the residual chlorine solution reference material is 10 μg / mL to 1000 μg / mL. The residual chlorine solution reference material provided by the present invention has excellent storage stability, with a validity period of up to 2 years. At the same time, during the detection process of the residual chlorine content, the accuracy of the detected value is ensured, providing a more stable and reliable quality control sample for water quality detection.

Description

Technical Field

[0001] The embodiments of the present invention relate to the technical field of reference materials, and particularly to a residual chlorine solution reference material and its preparation method and application. Background Art

[0002] Residual chlorine refers to the total of free chlorine and combined chlorine remaining in water after adding a certain amount of chlorine (usually in the form of chlorine gas, sodium hypochlorite, chloramine, etc.) for disinfection during the water treatment process.

[0003] The main function of residual chlorine is to maintain the disinfection effect of tap water and prevent the large reproduction of microorganisms such as bacteria and Escherichia coli in the water supply pipe network, thereby ensuring water quality safety. GB 5749 "Hygienic Standard for Drinking Water" stipulates that the free chlorine should not be less than 0.3 mg / L and not higher than 2 mg / L after contacting with water for 30 minutes. In addition to the factory water of centralized water supply meeting the above requirements, the network end water should not be less than 0.05 mg / L. The total chlorine should not be less than 0.5 mg / L and not higher than 3 mg / L after contacting with water for 120 minutes. This standard aims to ensure water quality safety while avoiding harm to human health caused by excessive residual chlorine content.

[0004] Currently, the main reference materials for detecting residual chlorine on the market are as follows: 1. Total residual chlorine solution reference material prepared from chloramine; 2. Simulated residual chlorine solution reference material prepared from potassium permanganate; 3. Simulated residual chlorine solution reference material prepared from potassium iodate and potassium iodide. The validity periods of the above reference materials are 6 months to 18 months, and there is a problem of poor stability. Therefore, it is very necessary to develop a residual chlorine solution reference material with a simple preparation process and a longer validity period. Summary of the Invention

[0005] For this reason, the embodiments of the present invention provide a residual chlorine solution reference material using hydrogen peroxide as a raw material and its preparation method and application to solve the problem of insufficient stability of existing residual chlorine reference materials.

[0006] To achieve the above object, the embodiments of the present invention provide the following technical solutions:

[0007] According to the first aspect of the embodiments of the present invention, the present invention provides a preparation method of a residual chlorine solution reference material, and the method includes:

[0008] Dissolve the hydrogen peroxide solution in an appropriate amount of ultrapure water, transfer it to a 5000 mL volumetric flask, add phosphate buffer solution and disodium ethylenediaminetetraacetate, dilute it to the scale with ultrapure water for constant volume, seal it in a clean ampoule bottle, and store it refrigerated and protected from light. Calculated as Cl2, the concentration of the residual chlorine solution reference material is 10 μg / mL to 1000 μg / mL.

[0009] Further, the content of hydrogen peroxide in the hydrogen peroxide solution is 23.94 mg to 2394.36 mg. In some preferred embodiments, the concentration of the hydrogen peroxide solution is 4%, and the dosage is 0.59859 g to 59.85875 g.

[0010] Further, the pH value of the phosphate buffer solution is 3.5 to 4.5, and the dosage of the phosphate buffer solution is 200 mL to 300 mL.

[0011] Further, the preparation method of the phosphate buffer solution is as follows: Weigh 5.3 g to 5.6 g of disodium hydrogen phosphate anhydrous and 5.8 g to 6.0 g of citric acid, dissolve them in ultrapure water in sequence, transfer to a 500 mL volumetric flask, add ultrapure water to the scale line, and mix well.

[0012] Further, the dosage of disodium ethylenediaminetetraacetate is 2 g to 4 g.

[0013] According to the second aspect of the embodiments of the present invention, the present invention provides a residual chlorine solution reference material, which is prepared by the preparation method described in any one of the above.

[0014] According to the third aspect of the embodiments of the present invention, the present invention provides the application of the residual chlorine solution reference material described above, which is used for detecting the residual chlorine content in water.

[0015] Further, the detection is carried out by using the N,N - diethyl - p - phenylenediamine spectrophotometry method of GB / T 5750.11 - 2023 4.1.

[0016] The embodiments of the present invention have the following advantages:

[0017] The present invention prepares a residual chlorine - type reference material with hydrogen peroxide as the raw material. By adding a phosphate buffer solution and disodium ethylenediaminetetraacetate, a more stable system environment is provided for hydrogen peroxide, which can effectively improve the storage stability of the reference material. The validity period is up to 2 years. At the same time, during the detection process of the residual chlorine content, the accuracy of the detected value is ensured. This reference material provides a more stable and reliable detection basis for water quality detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only exemplary, and for those of ordinary skill in the art, other implementation drawings can be obtained by extension based on the provided drawings without creative efforts.

[0019] Figure 1 It is the preparation flow chart of the residual chlorine solution reference material provided by the present invention;

[0020] Figure 2 A standard curve provided by the present invention;

[0021] Figure 3 The long-term stability diagram of the residual chlorine solution standard substances of Example 1, Example 2, Example 3, Comparative Example 1 and Comparative Example 3 provided by the present invention. DETAILED DESCRIPTION

[0022] The following is a description of the implementation of the present invention by specific embodiments. People familiar with the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] Reagents:

[0024] Hydrogen peroxide solution: 4%, Aladdin;

[0025] Anhydrous disodium hydrogen phosphate: analytical grade, Aladdin;

[0026] Citric acid: analytical grade, Aladdin;

[0027] Disodium EDTA: ≥99%, Aladdin;

[0028] Glacial acetic acid: analytical grade, MacLean.

[0029] According to the reaction equations of chlorine and N,N-diethyl-p-phenylenediamine (DPD) and hydrogen peroxide and N,N-diethyl-p-phenylenediamine (DPD), 1 mol of chlorine (Cl2) is equivalent to 1 mol of hydrogen peroxide (H2O2).

[0030] C 10 H 16 N2 + Cl2 → C 10 H 14 N2 + 2HCl

[0031] C 10 H 16 N2 + H2O2 → C 10 H 14 N2 + 2H2O

[0032] Therefore, the mass of hydrogen peroxide required to prepare 5000mL of residual chlorine solution standard substance with a concentration of 10μg / mL is m=(5000×10×34) / 71=23.9436mg.

[0033] Example 1

[0034] This example provides a standard substance of residual chlorine solution with a concentration of 10 μg / mL, and its preparation method includes the following steps.

[0035] (1) Prepare a phosphate buffer solution with pH 4.0: Weigh 5.47 g of anhydrous disodium hydrogen phosphate and 5.89 g of citric acid, dissolve them in a small amount of ultrapure water in sequence, transfer to a 500 mL volumetric flask, add ultrapure water to the scale line, and mix well.

[0036] (2) Accurately weigh 0.59859 g of a hydrogen peroxide solution with a concentration of 4%, dissolve it with a small amount of ultrapure water, transfer to a 5000 mL volumetric flask, then add 250 mL of the phosphate buffer solution with pH 4.0 prepared in step (1) and 3.01 g of disodium ethylenediaminetetraacetate, dissolve with ultrapure water and make up to the scale.

[0037] (3) Seal the solution into clean 20 mL ampoules and store in a refrigerator in the dark.

[0038] Example 2

[0039] This example provides a standard substance of residual chlorine solution with a concentration of 100 μg / mL, and its preparation method includes the following steps:

[0040] (1) Prepare a phosphate buffer solution with pH 4.0: Weigh 5.47 g of anhydrous disodium hydrogen phosphate and 5.89 g of citric acid, dissolve them in a small amount of ultrapure water in sequence, transfer to a 500 mL volumetric flask, add ultrapure water to the scale line, and mix well.

[0041] (2) Accurately weigh 5.98591 g of a hydrogen peroxide solution with a concentration of 4%, dissolve it with a small amount of ultrapure water, transfer to a 5000 mL volumetric flask, then add 250 mL of the phosphate buffer solution with pH 4.0 prepared in step (1) and 3.01 g of disodium ethylenediaminetetraacetate, dissolve with ultrapure water and make up to the scale.

[0042] (3) Seal the solution into clean 20 mL ampoules and store in a refrigerator in the dark.

[0043] Example 3

[0044] This example provides a standard substance of residual chlorine solution with a concentration of 1000 μg / mL, and its preparation method includes the following steps:

[0045] (1) Prepare a phosphate buffer solution with pH 4.0: Weigh 5.47 g of anhydrous disodium hydrogen phosphate and 5.89 g of citric acid, dissolve them in a small amount of ultrapure water in sequence, transfer to a 500 mL volumetric flask, add ultrapure water to the scale line, and mix well.

[0046] (2)Accurately weigh 59.85875 g of a 4% hydrogen peroxide solution, dissolve it with a small amount of ultrapure water, transfer it to a 5000 mL volumetric flask, then add 250 mL of the pH 4.0 phosphate buffer solution prepared in step (1) and 3.01 g of disodium ethylenediaminetetraacetate, dissolve with ultrapure water and make up to the mark.

[0047] (3)Seal the solution into clean 20 mL ampoules and store in a refrigerator in the dark.

[0048] Comparative Example 1

[0049] This comparative example provides a standard substance of a residual chlorine solution with a concentration of 100 μg / mL, and its preparation method includes the following steps:

[0050] (1)Accurately weigh 5.98593 g of a 4% hydrogen peroxide solution, dissolve it with a small amount of ultrapure water, transfer it to a 5000 mL volumetric flask, dissolve with ultrapure water and make up to the mark.

[0051] (2)Seal the solution into clean 20 mL ampoules and store in a refrigerator in the dark.

[0052] Comparative Example 2

[0053] This comparative example provides a standard substance of a residual chlorine solution with a concentration of 100 μg / mL, and its preparation method includes the following steps:

[0054] (1)Prepare an ammonium acetate buffer solution with pH 4.0: Weigh 3.85 g of ammonium acetate and dissolve it in 100 mL of ultrapure water, transfer it to a 500 mL volumetric flask, add ultrapure water to about 400 mL, adjust the pH to 4 with glacial acetic acid, add ultrapure water to the mark, and mix well.

[0055] (2)Accurately weigh 5.98597 g of a 4% hydrogen peroxide solution, dissolve it with a small amount of ultrapure water, transfer it to a 5000 mL volumetric flask, then add 250 mL of the pH 4.0 ammonium acetate buffer solution prepared in step (1) and 3.01 g of disodium ethylenediaminetetraacetate, dissolve with ultrapure water and make up to the mark.

[0056] (3)Seal the solution into clean 20 mL ampoules and store in a refrigerator in the dark.

[0057] Comparative Example 3

[0058] This comparative example provides a standard substance of a residual chlorine solution with a concentration of 100 μg / mL, and its preparation method includes the following steps:

[0059] (1) Prepare a phosphate buffer solution with a pH of 6.6: Weigh 10.33 g of anhydrous disodium hydrogen phosphate and 2.62 g of citric acid, dissolve them successively in a small amount of ultrapure water, transfer to a 500 mL volumetric flask, add ultrapure water to the calibration mark, and mix well.

[0060] (2) Accurately weigh 5.98588 g of a 4% hydrogen peroxide solution, dissolve it with a small amount of ultrapure water, transfer to a 5000 mL volumetric flask, then add 250 mL of the phosphate buffer solution with a pH of 6.6 and 3.01 g of disodium ethylenediaminetetraacetate, dissolve with ultrapure water and make up to the calibration mark.

[0061] (3) Fill the solution into clean 20 mL ampoules and store in the refrigerator in the dark.

[0062] Test Example 1

[0063] I. Establishment of the standard curve

[0064] Use ultrapure water to dilute the residual chlorine solution reference material with a concentration of 1000 μg / mL prepared in Example 3 to prepare standard series working solutions with concentration values of 0, 0.01 μg / mL, 0.05 μg / mL, 0.2 μg / mL, 0.4 μg / mL, 0.8 μg / mL, 1.6 μg / mL, and 2.0 μg / mL in sequence.

[0065] Detect according to the N,N - diethyl - p - phenylenediamine (DPD) spectrophotometry method in GB / T 5750.11 "Standard Test Methods for Drinking Water - Part 11: Disinfectant Indexes", and record the absorbance of the standard series working solutions at 515 nm.

[0066] Perform linear regression with the concentration of the standard working solution as the abscissa and the absorbance as the ordinate, and obtain the regression equation y = 0.2236x + 0.0021, r 2 = 0.9996. The standard curve is shown in Figure 2 .

[0067] II. Quantity value comparison

[0068] Use the secondary reference material as the comparison standard, adopt the same detection method, and conduct a quantity value comparison with the residual chlorine solution reference materials prepared in Examples 1 - 3 and Comparative Examples 1 - 3 to investigate the quantity value accuracy of each residual chlorine solution reference material.

[0069] (1) The comparison standard is the secondary reference material GBW(E)085501 total residual chlorine solution reference material of the National Institute of Metrology, with a concentration of 499 μg / mL.

[0070] (2) Gradually dilute the GBW(E)085501 total residual chlorine solution reference material with ultrapure water to prepare a standard solution with a concentration of 1.996 μg / mL.

[0071] (3) Use ultrapure water to dilute the residual chlorine solution reference materials provided in Examples 1-3 and Comparative Examples 1-3 to standard solutions with a concentration of 2 μg / mL respectively.

[0072] (4) According to the N,N-diethyl-p-phenylenediamine (DPD) spectrophotometry method in GB / T 5750.11 "Standard Test Methods for Drinking Water - Part 11: Disinfectant Indexes", measure the absorbance of the solutions diluted in step (1) and step (3) at 515 nm. The results are shown in Table 1. The results show that the quantity values of the residual chlorine solution reference materials in Examples 1-3 and Comparative Example 1 and Comparative Example 3 are accurate, while the quantity value in Comparative Example 2 using the ammonium acetate buffer system is on the low side. Due to the low quantity value in Comparative Example 2, its stability will not be investigated in subsequent tests.

[0073]

[0074] Test Example 2 Stability Test

[0075] According to the N,N-diethyl-p-phenylenediamine (DPD) spectrophotometry method in GB / T 5750.11 "Standard Test Methods for Drinking Water - Part 11: Disinfectant Indexes", conduct a stability test on the solution reference material.

[0076] Stability Test: The stability study of reference materials usually includes short-term stability study and long-term stability study. Short-term stability refers to the stability of the characteristic quantity values of reference materials during transportation under specified transportation conditions, which is related to the additional effects caused by the transportation of reference materials and the packaging. Long-term stability refers to the stability of the characteristic quantity values of reference materials under the specific storage conditions required in the reference material certificate, which is related to their production, research and development, use and storage conditions.

[0077] Place the reference material prepared in Example 1 under the condition of 60 °C for storage. Take 1 sample at each time point of 0 day, 1 day, 2 days, 3 days, 5 days, 9 days, and 14 days, and conduct parallel measurements 3 times (using the GBW(E)085501 total residual chlorine solution reference material as the comparison standard solution) to investigate the short-term stability. The results are shown in Table 2. The results show that the short-term stability of this reference material is good.

[0078] The reference material prepared in Example 1 was stored under refrigeration (0 - 4°C) in the dark. At 0 month, 1 month, 2 months, 3 months, 6 months, 9 months, 12 months, 18 months, and 24 months, one sample was taken at each time point and measured in parallel three times (using the total residual chlorine solution reference material GBW(E)085501 as the comparison standard solution) to investigate its long-term stability. The results are shown in Table 3. The results indicate that this reference material can be stably stored for 2 years.

[0079]

[0080]

[0081] The short-term and long-term stability tests were carried out on the residual chlorine solution reference materials prepared in Examples 2 - 3 according to the above method, and the results are shown in Table 4. The results indicate that the short-term and long-term stability of this reference material meet the requirements, and it can be stored for 2 years under refrigeration in the dark.

[0082]

[0083] The long-term stability test was carried out on the residual chlorine solution reference materials prepared in Comparative Example 1 and Comparative Example 3 according to the above method, and the results are shown in Table 5. At the same time, the long-term stabilities of the residual chlorine solution reference materials of Example 1, Example 2, Example 3, Comparative Example 1, and Comparative Example 3 were compared, and the results are shown in Figure 3 。

[0084]

[0085] The results indicate that the stability of the residual chlorine solution reference material prepared with ultrapure water (Comparative Example 1) is poor, and it begins to degrade after 3 months. The pH value of the phosphate buffer solution has an impact on the stability of the reference material. When the pH of the phosphate buffer solution is 6.6 (Comparative Example 3), the reference material begins to degrade after being stored for 9 months.

[0086] Test Example 3 Homogeneity Test

[0087] According to the "Technical Specifications for Primary Reference Materials" JJG 1006 - 1994 and the "Certification and Evaluation of the Homogeneity and Stability of Reference Materials" JJF 1343 - 2022, the statistical processing of the homogeneity test results of reference materials usually adopts the analysis of variance method. This method compares the between-group variance and the within-group variance. If the ratio of the two is less than the critical value of the statistical test, the sample is considered to be homogeneous. In this test example, Example 2 was taken as an example to test its homogeneity. The detection was carried out according to the N,N - diethyl - p - phenylenediamine (DPD) spectrophotometry method in GB / T 5750.11 "Standard Test Methods for Drinking Water - Part 11: Disinfectant Indicators". The results are shown in Table 6. The results indicate that the homogeneity of this solution reference material is good.

[0088]

[0089] Uncertainty Evaluation of Test Example 4

[0090] The main sources of uncertainty in the concentration of the solution reference material are as follows: the uncertainty caused by the purity of the raw material; the uncertainty caused by the solution preparation process; the uncertainty caused by the inhomogeneity and instability of the sample.

[0091] Taking Example 2 as an example, the uncertainty of the solution reference material is explained as follows:

[0092] 1. Uncertainty introduced by the purity of the raw material

[0093] The uncertainty introduced by the purity of the raw material is 0.0040%.

[0094] 2. Uncertainty caused by the solution preparation process

[0095] The uncertainty in the solution preparation process is introduced by the balance and volume fixation during the solution preparation process.

[0096] 2.1 Uncertainty u introduced by the balance 天平rel

[0097] (1) Repeatability error of balance weighing: According to the balance verification certificate, for a sample weighing 5.98591 g, the maximum allowable repeatability error is 0.15 mg. The net weight of the sample is obtained from 2 weighing operations, and each time is an independent observation result. Its relative standard uncertainty is:

[0098] .

[0099] (2) Indication error of the balance: According to the balance verification certificate, for a sample weighing 5.98591 g, the maximum allowable indication error is 0.05 mg. The net weight of the sample is obtained from 2 weighing operations, and each time is an independent observation result. Then the relative standard uncertainty is:

[0100] .

[0101] (3) Buoyancy effect: Weighing under normal pressure, the weighing volume is small, and this item can be ignored.

[0102] Therefore, the relative standard uncertainty u introduced by the balance 天平rel is 0.0021%.

[0103] 2.2 Uncertainty u introduced by the fixed volume 体积rel

[0104] There are mainly three factors affecting the fixed volume: the maximum allowable difference in the capacity of the volumetric flask, the repeatability of volume fixation, and temperature.

[0105] The volumetric flask used in the solution preparation process is 5000 mL.

[0106] (1) Maximum allowable tolerance of the volumetric flask volume: As can be seen from the verification certificate of the volumetric flask, the maximum allowable tolerance of the 5000 mL volumetric flask is 1.2 mL. Assuming a uniform distribution, its relative standard uncertainty is:

[0107] .

[0108] (2) Repeatability of volume fixing: For the weighing experiment of filling the 5000 mL volumetric flask 10 times, the standard deviation is obtained as 1.8 mL, then its relative uncertainty is: 1.8 / 5000 × 100% = 0.036%.

[0109] (3) Temperature influence: The temperature during the preparation of the solution reference material in this experiment varies between ±3 °C, and the volume expansion coefficient of water is 2.5×10 -4 mL•°C -1 . Assuming a uniform distribution, the relative standard uncertainty is:

[0110] .

[0111] Combining the components of the above three factors, the relative standard uncertainty u 体积rel introduced by the fixed volume is 0.060%.

[0112] 3. Uncertainty caused by the inhomogeneity and instability of the sample

[0113] The uncertainty caused by the inhomogeneity and instability of the sample is 0.36%.

[0114] Combining the relative uncertainty components of each item, the relative combined standard uncertainty u rel of the reference material is obtained as 0.4%. Taking the coverage factor k = 2, U rel = 0.4% × 2 = 0.8%.

[0115] Although the present invention has been described in detail with general descriptions and specific embodiments above, based on the present invention, some modifications or improvements can be made, which are obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection required by the present invention.

Claims

1. Application of a residual chlorine solution reference material, characterized in that, For detecting the residual chlorine content in water; the preparation method of the residual chlorine solution reference material includes: Dissolve the hydrogen peroxide solution in an appropriate amount of ultrapure water, transfer it to a 5000 mL volumetric flask, add phosphate buffer solution and disodium ethylenediaminetetraacetate, dilute to the scale with ultrapure water for volume fixation, seal it in a clean ampoule bottle, store it refrigerated and protected from light. Calculated as Cl2, the concentration of the residual chlorine solution reference material is 10 μg / mL to 1000 μg / mL; The content of hydrogen peroxide in the hydrogen peroxide solution is 23.94 mg to 2394.36 mg; The pH value of the phosphate buffer solution is 3.5 to 4.5, and the dosage of the phosphate buffer solution is 200 mL to 300 mL; The dosage of disodium ethylenediaminetetraacetate is 2 g to 4 g.

2. The application according to claim 1, characterized in that, The concentration of the hydrogen peroxide solution is 4%, and the dosage is 0.59859 g to 59.85875 g.

3. The application according to claim 1, wherein The preparation method of the phosphate buffer solution is: Weigh 5.3 g to 5.6 g of anhydrous disodium hydrogen phosphate and 5.8 g to 6.0 g of citric acid, dissolve them in ultrapure water in sequence, transfer to a 500 mL volumetric flask, add ultrapure water to the scale line, and mix well.

4. The application according to claim 1, characterized in that Detect by the N,N-diethyl-p-phenylenediamine spectrophotometry method in GB / T 5750.11 "Standard Test Methods for Drinking Water - Part 11: Disinfectant Indexes".

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