Method for testing residual chlorine and other oxidants

Abstract

The invention relates to the technical field of water quality detection, and particularly discloses a method for testing residual chlorine and other oxidants, a detection reagent composed of a color-developing substance and an organic dissolution promoter is used in the method, during detection, the color-developing substance in the reagent is oxidized and becomes pink from colorless, and the organic dissolution promoter is used for detecting the residual chlorine and other oxidants. The stable dissolution promoter can increase the stability of the color development substance in the oxidation color development process, so that the detection reagent can be stable for a long time in a liquid phase state, and the method for testing residual chlorine and other oxidants has the advantages of being easy and convenient to operate, accurate in result, low in price, convenient to store and transport, suitable for on-site rapid detection and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of water quality detection, and specifically to a method for testing residual chlorine and other oxidants. Background Art

[0002] Residual chlorine and other oxidizing biocides are very commonly used in the water treatment industry, and are involved in water treatment applications in various industries such as industrial cooling circulating water, papermaking, iron and steel, municipal, and building air conditioning. Chlorine and other oxidizing biocides are widely used around the world and have great economic and social value. The correct application of chlorine and other oxidizing biocides in the actual production and treatment process is of great significance. If the content of the oxidant is too high, it will cause harm to the equipment system and the human body. If the content of the oxidant is too low, the sterilization is incomplete, which will also cause harm to the equipment system and the human body. Therefore, it is crucial to accurately measure the content of the oxidant in the system.

[0003] Currently, the mainstream method for testing residual chlorine and other oxidants is the DPD (N,N - diethyl - p - phenylenediamine substances and their derivatives) method. During the application test of DPD, the following problems are found. First, although the commercially available DPD solid reagent powder packs or tablet reagent packs have a long service life, they are difficult to operate and cause dust pollution during use. Second, if DPD is formulated into a liquid reagent, due to the special nature of DPD itself, it is extremely easy to be oxidized in the liquid state, resulting in a short service life of the reagent. If the reagent state is not determined sufficiently, it will also cause error interference to the test. In addition, during the use of the DPD method, the colorimetric cuvette is easily stained and polluted by the oxidized DPD. Moreover, due to the presence of other ionic substances and microorganisms in water, such as iron ions, calcium and magnesium ions, and cyanobacteria, these substances are easily attached, polluted, and blocked the colorimetric cuvette due to their special characteristics.

[0004] In view of the above actual application situation, based on the redox color - development characteristics of DPD and oxidants, this patent combines other inorganic or organic solvents to invent a rapid, effective, and convenient method for testing residual chlorine and other oxidants, effectively solving the problems of long - term instability of liquid reagents and easy staining, pollution, and blockage of colorimetric cuvettes, and improving the operability of the actual application of DPD. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for testing residual chlorine and other oxidants. The reagent used in this detection method is a liquid reagent, which is convenient to carry, simple to use based on the liquid characteristics, and the test process is fast. It can quickly and accurately detect the content of residual chlorine and other oxidants in drinking water, industrial circulating water, sewage, and natural water, solve the problems of long - term instability of liquid reagents and easy staining, pollution, and blockage of colorimetric cuvettes, and improve the operability of the actual application of DPD.

[0006] To solve the above technical problems, the present invention provides the following technical solutions:

[0007] A method for testing residual chlorine and other oxidants, specifically:

[0008] Mix the liquid to be tested with the detection reagent to obtain a mixed solution, measure the absorbance of the mixed solution, and based on the linear relationship between the absorbance and the concentration of residual chlorine or other oxidants, obtain the concentration of residual chlorine or other oxidants in the liquid to be tested.

[0009] As a limitation of the present invention, the detection reagent consists of a main chromogenic agent and an organic co-solvent, and the mass ratio of the main chromogenic agent to the organic co-solvent is (1.4 - 38):(26 - 50).

[0010] As a limitation of the present invention, in the mixed solution, the volume ratio of the liquid to be tested to the detection reagent is 10 mL:(0.04 - 0.05) mL.

[0011] As a limitation of the present invention, the main chromogenic agent is one or a mixture of N,N - diethyl - p - phenylenediamine, N,N - diethyl - p - phenylenediamine sulfate, N,N - diethyl - p - phenylenediamine oxalate, N,N - diethyl - p - phenylenediamine hydrochloride, N,N - diethyl - p - phenylenediamine methanesulfonate, N,N - diethyl - p - phenylenediamine complex salt.

[0012] As a limitation of the present invention, the organic co - solvent includes organic acids, organic acid salts, and organic alcohols.

[0013] As a limitation of the present invention, the organic acids include but are not limited to: one or a mixture of tartaric acid, acetic acid, lactic acid, glycolic acid, citric acid.

[0014] As a limitation of the present invention, the organic acid salts include but are not limited to: one or a mixture of sodium citrate, sodium acetate, sodium ethylenediaminetetraacetate, sodium tartrate.

[0015] As a limitation of the present invention, the organic alcohols include but are not limited to: one or a mixture of polyethylene glycol, ethanol, ethylene glycol, glycerol, 1,2 - propanediol, 1,4 - butanediol.

[0016] As a limitation of the present invention, the method for establishing the linear relationship between the absorbance and the concentration of residual chlorine or other oxidants is:

[0017] Dilute the residual chlorine standard solution or other oxidants into five different concentrations of test standard solutions, and use the test standard solution without adding the detection reagent as a blank sample for zero calibration;

[0018] Take the above-mentioned diluted test standard solution of different concentrations and mix it with the detection reagent to obtain mixed solutions of different concentrations. Then, perform absorbance test on the obtained mixed solutions of different concentrations to obtain the absorbance of the mixed solution at different residual chlorine or other oxidant concentrations after adding the detection reagent. Use it to perform linear analysis to obtain the linear relationship between absorbance and residual chlorine or other oxidant concentration.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The present invention discloses a method for testing residual chlorine and other oxidants, wherein a detection reagent used for testing reacts rapidly with residual chlorine and other oxidants, and colorless N,N-diethyl-p-phenylenediamine and its derivatives are rapidly oxidized into quinone structures, showing pink color, and the degree of pink color development is proportional to the content of the oxidant in the reaction system.

[0021] The present invention can significantly inhibit the oxidation of N,N-diethyl-p-phenylenediamine and its derivatives by adding organic acid substances and organic alcohol substances as stable solubilizing agents of N,N-diethyl-p-phenylenediamine and its derivatives in the detection reagent, and at the same time increase the stability of N,N-diethyl-p-phenylenediamine and its derivatives in the oxidation color development process, so that the detection reagent can be stable for a long time in the liquid phase state and have a long service life. The N,N-diethyl-p-phenylenediamine and its derivatives in the reagent are not easy to be oxidized and precipitated in transition to contaminate the cuvette. In addition, due to the unique characteristics of organic acids and organic alcohols, they can play a role in cleaning activity, thereby effectively preventing the cuvette from being contaminated by pollutants in the water body, ensuring the accuracy of the test results, and the reagent is a single stable liquid reagent, which has the advantages of simple operation, accurate results, low price, easy storage and transportation, and suitable for on-site rapid detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The linear relationship diagram of residual chlorine concentration and absorbance after adding the detection reagent in Example 1;

[0023] Figure 2 The linear relationship diagram of residual chlorine concentration and absorbance after adding the detection reagent in Example 2;

[0024] Figure 3 The linear relationship diagram of residual chlorine concentration and absorbance after adding the detection reagent in Example 3;

[0025] Figure 4 The linear relationship diagram of residual chlorine concentration and absorbance after adding the detection reagent in Example 4;

[0026] Figure 5 This is a linear relationship diagram between the concentration of sodium dichloroisocyanurate and the absorbance after adding the detection reagent in Example 4. DETAILED DESCRIPTION

[0027] Residual chlorine standard solution (standard concentration: 10 mg / L), from the National Institute of Metrology.

[0028] Example 1: A detection reagent for testing residual chlorine and other oxidants, and the preparation method is as follows:

[0029] Weigh 2.0 g of glycolic acid, 20 g of sodium citrate, 20 g of ethylene glycol, and 1.4 g of DPD sulfate by weight, dissolve them with pure water, and finally make up the volume to 100 mL with pure water to form a detection reagent for testing residual chlorine and other oxidants;

[0030] The method for establishing the linear relationship between absorbance and residual chlorine concentration is as follows:

[0031] Take the residual chlorine standard solution, and dilute it into test standard solutions with residual chlorine concentrations of 0 ppm, 0.45 ppm, 0.9 ppm, and 1.35 ppm respectively. Take 10 mL of the test standard solution and put it into a colorimetric flask as a blank sample for zero calibration; then take 10 mL of each test standard solution with different residual chlorine concentrations, put them into colorimetric flasks respectively, add 0.05 mL of the detection reagent prepared by the above preparation method to each flask, finally seal the colorimetric flask, turn the colorimetric flask up and down to make the liquid in the colorimetric flask fully mixed, and then perform absorbance measurement. The absorbance of the liquid at different residual chlorine concentrations after adding the detection reagent is obtained. Taking the absorbance as the abscissa and the residual chlorine concentration as the ordinate, the linear relationship between the residual chlorine concentration and the absorbance as shown in Figure 1 is obtained. The linear relationship between the residual chlorine concentration and the absorbance is good, and the determination coefficient R 2 = 0.9949;

[0032] Example 2: A detection reagent for testing residual chlorine and other oxidants, and the preparation method is as follows:

[0033] Weigh 3 g of acetic acid, 8 g of sodium acetate, 15 g of glycerol, and 1.4 g of DPD hydrochloride by weight, dissolve them with pure water, and finally make up the volume to 100 mL with pure water to form a detection reagent for testing residual chlorine and other oxidants;

[0034] The method for establishing the linear relationship between absorbance and residual chlorine concentration is as follows:

[0035] Take the residual chlorine standard solution and dilute it into test standard solutions with residual chlorine concentrations of 0 ppm, 0.66 ppm, 1.26 ppm, and 1.85 ppm respectively. Take 10 mL of the test standard solution and put it into a colorimetric flask as a blank sample for zero calibration; then take 10 mL of the test standard solution with each residual chlorine concentration, put them into colorimetric flasks respectively, add 0.05 mL of the detection reagent prepared by the above preparation method to each flask, finally seal the colorimetric flask, turn the colorimetric flask upside down to fully mix the liquid in the colorimetric flask, and then conduct absorbance tests to obtain the absorbance of the liquid at different residual chlorine concentrations after adding the detection reagent. Using the absorbance as the abscissa and the residual chlorine concentration as the ordinate, the Figure 2 shown linear relationship between the residual chlorine concentration and the absorbance is obtained. The linear relationship between the residual chlorine concentration and the absorbance is good, and the determination coefficient R 2 = 0.9944;

[0036] Example 3: A detection reagent for testing residual chlorine and other oxidants, and the preparation method is as follows:

[0037] Weigh 6 g of citric acid, 24 g of sodium citrate, 20 g of triethylene glycol, and 14 g of DPD sulfate by weight, dissolve them with pure water, and finally make up the volume to 100 mL with pure water to form a detection reagent for testing residual chlorine and other oxidants;

[0038] The method for establishing the linear relationship between the absorbance and the residual chlorine concentration is as follows:

[0039] Take the residual chlorine standard solution and dilute it into test standard solutions with residual chlorine concentrations of 0 ppm, 0.66 ppm, 1.26 ppm, and 1.85 ppm respectively. Take 10 mL of the test standard solution and put it into a colorimetric flask as a blank sample for zero calibration; then take 10 mL of the test standard solution with each residual chlorine concentration, put them into colorimetric flasks respectively, add 0.05 mL of the detection reagent prepared by the above preparation method to each flask, finally seal the colorimetric flask, turn the colorimetric flask upside down to fully mix the liquid in the colorimetric flask, and then conduct absorbance tests to obtain the absorbance of the liquid at different residual chlorine concentrations after adding the detection reagent. Using the absorbance as the abscissa and the residual chlorine concentration as the ordinate, the Figure 3 shown linear relationship between the residual chlorine concentration and the absorbance is obtained. The linear relationship between the residual chlorine concentration and the absorbance is good, and the determination coefficient R 2 = 0.9978;

[0040] Example 4: A detection reagent for testing residual chlorine and other oxidants, and the preparation method is as follows:

[0041] Weigh 8 g of citric acid, 20 g of sodium citrate, 20 g of glycerol, and 1.4 g of DPD sulfate by weight, dissolve them with pure water, and finally make up the volume to 100 mL with pure water to form a detection reagent for testing residual chlorine and other oxidants;

[0042] The method for establishing the linear relationship between absorbance and residual chlorine concentration is as follows:

[0043] Take the residual chlorine standard solution and dilute it into test standard solutions with residual chlorine concentrations of 0 ppm, 0.45 ppm, 0.9 ppm, 1.35 ppm, and 1.8 ppm respectively. Take 10 mL of the test standard solution and put it into a colorimetric flask as a blank sample for zero calibration; then take 10 mL of each test standard solution with different residual chlorine concentrations, put them into colorimetric flasks respectively, and add 0.05 mL of the detection reagent prepared by the above preparation method to each flask. Finally, seal the colorimetric flask well, turn the colorimetric flask upside down to fully mix the liquid in the flask, and then perform absorbance measurement. Obtain the absorbance of the liquid at different residual chlorine concentrations after adding the detection reagent, and use the absorbance as the abscissa and the residual chlorine concentration as the ordinate to obtain as Figure 4 shown in the linear relationship between residual chlorine concentration and absorbance. The linear relationship between residual chlorine concentration and absorbance is good, and the determination coefficient R 2 = 0.9997;

[0044] The method for establishing the linear relationship between absorbance and sodium dichloroisocyanurate concentration is as follows:

[0045] Take sodium dichloroisocyanurate and prepare test standard solutions with sodium dichloroisocyanurate concentrations of 0 ppm, 0.45 ppm, 0.9 ppm, 1.35 ppm, and 1.8 ppm respectively. Take 10 mL of the test standard solution and put it into a colorimetric flask as a blank sample for zero calibration; then take 10 mL of each test standard solution with different sodium dichloroisocyanurate concentrations, put them into colorimetric flasks respectively, and add 0.05 mL of the detection reagent prepared by the above preparation method to each flask. Finally, seal the colorimetric flask well, turn the colorimetric flask upside down to fully mix the liquid in the flask, and then perform absorbance measurement. Obtain the absorbance of the liquid at different sodium dichloroisocyanurate concentrations after adding the detection reagent, and use the absorbance as the abscissa and the sodium dichloroisocyanurate concentration as the ordinate to obtain as Figure 5 shown in the linear relationship between sodium dichloroisocyanurate concentration and absorbance. The linear relationship between sodium dichloroisocyanurate concentration and absorbance is good, and the determination coefficient R 2 = 0.9969.

[0046] Example 5: A detection reagent for testing residual chlorine and other oxidants, and the preparation method is as follows:

[0047] Weigh 8 g of citric acid, 20 g of sodium citrate, 20 g of glycerol, and 1.4 g of DPD sulfate by weight, dissolve them with pure water, and finally make up to 100 mL with pure water to form a detection reagent for testing residual chlorine and other oxidants.

[0048] Example 6: A detection reagent for testing residual chlorine and other oxidants, and the preparation method is as follows:

[0049] After weighing 8 g of citric acid, 20 g of sodium citrate, 20 g of glycerol, and 7 g of DPD sulfate by weight, dissolve them in pure water, and finally make up the volume to 100 mL with pure water to form a detection reagent for testing residual chlorine and other oxidants.

[0050] Example 7: A detection reagent for testing residual chlorine and other oxidants, and the preparation method is as follows:

[0051] After weighing 8 g of citric acid, 20 g of sodium citrate, 20 g of glycerol, and 14 g of DPD sulfate by weight, dissolve them in pure water, and finally make up the volume to 100 mL with pure water to form a detection reagent for testing residual chlorine and other oxidants.

[0052] Example 8: A detection reagent for testing residual chlorine and other oxidants, and the preparation method is as follows:

[0053] After weighing 12 g of citric acid, 25 g of glycerol, and 38 g of DPD sulfate by weight, dissolve them in pure water, and finally make up the volume to 100 mL with pure water to form a detection reagent for testing residual chlorine and other oxidants.

[0054] Detection test: Prepare detection reagents for testing residual chlorine and other oxidants according to the methods in Example 5, Example 6, Example 7, and Example 8 respectively, denoted as Reagent A, Reagent B, Reagent C, and Reagent D, and conduct stability tests.

[0055] Stability test of detection reagents at different DPD contents: Place Reagent A, Reagent B, and Reagent C in a water bath at 60 °C for high-temperature accelerated aging, and periodically test the reagents with a residual chlorine standard solution. During the test, dilute the residual chlorine standard solution respectively to obtain test standard solutions with different residual chlorine concentrations. The residual chlorine concentration of the solution is denoted as the theoretical concentration. Measure the absorbance of the test standard solutions with different residual chlorine concentrations using Reagent A, Reagent B, and Reagent C after high-temperature accelerated aging, and calculate the residual chlorine concentration according to the obtained absorbance and the absorbance-residual chlorine concentration standard curve, denoted as the measured concentration. Compare the theoretical concentration with the measured concentration to judge the stability of the reagent.

[0056] Long-term stability test of the detection reagent: Place Reagent D in a water bath at 60 °C for high-temperature accelerated aging, and periodically test the reagent with a residual chlorine standard solution. During the test, dilute the residual chlorine standard solution respectively to obtain test standard solutions with different residual chlorine concentrations. The residual chlorine concentration of the solution is denoted as the theoretical concentration. Measure the absorbance of the test standard solutions with different residual chlorine concentrations using the reagent after high-temperature accelerated aging, and calculate the residual chlorine concentration according to the obtained absorbance and the absorbance-residual chlorine concentration standard curve, denoted as the measured concentration. Compare the theoretical concentration with the measured concentration to judge the long-term stability of the reagent.

[0057] Test results: The stability test results of reagent A, reagent B, and reagent C are shown in Table 1, Table 2, and Table 3, respectively. The long-term stability test results of reagent D are shown in Table 4.

[0058]

[0059] Table 1: Stability Test Results Table of Reagent A

[0060]

[0061] Table 2: Stability Test Results Table of Reagent B

[0062]

[0063] Table 3: Stability Test Results Table of Reagent C

[0064]

[0065] Table 4: Long-Term Stability Test Results Table of the Detection Reagent

[0066] As can be seen from Table 1, Table 2, and Table 3, reagent A is a low-content DPD detection reagent. After aging at 60°C for 1 day, the difference between its measured concentration and the theoretical concentration is much higher than that of reagent B (medium-content DPD detection reagent) and reagent C (high-content DPD detection reagent). Moreover, after aging at 60°C for 34 days, when using reagent A to measure the residual chlorine standard solution, the measured concentration is almost only half of the theoretical concentration, showing a large difference from the actual value. At this time, reagent A can no longer be used to measure the residual chlorine concentration. However, after aging at 60°C for 39 days, the difference between the measured concentration and the theoretical concentration of reagent B and reagent C can still be maintained at a small level. This shows that the stability of the low-content DPD detection reagent is poor, but as the DPD content in the detection reagent increases, the stability of the reagent also increases. After aging at 60°C for 39 days, the reagent still has relatively accurate detection results.

[0067] As can be seen from Table 4, after aging the detection reagent at 60°C for 72 days, the difference between the residual chlorine concentration measured by the reagent and the theoretical concentration of the standard solution is not significant, indicating that the stability of this detection reagent is good and its service life is long. At 60°C, it can remain stable for more than 72 days.

[0068] Conclusion: The present invention relates to a method for testing residual chlorine and other oxidants. In the detection reagent thereof, organic acid substances and organic alcohol substances are added as stabilizing solubilizers, which can significantly inhibit the oxidation of N,N-diethyl-p-phenylenediamine and its derivatives, and at the same time increase the stability of N,N-diethyl-p-phenylenediamine and its derivatives during the oxidation color development process. After the reagent is aged at a high temperature of 60 °C for 72 days, it can still maintain relatively accurate detection results. The detection reagent provided by the present invention can be stable in the liquid phase for a long time and has a long service life. The method for testing residual chlorine and other oxidants of the present invention has the advantages of simple operation, accurate results, low cost, convenient storage and transportation, and suitability for on-site rapid detection, etc.

Claims

1. A method for testing residual chlorine and other oxidants, characterized in that: Specifically: Mix the liquid to be tested with the detection reagent to obtain a mixed solution. Measure the absorbance of the mixed solution to get the absorbance of the mixed solution. According to the linear relationship between the absorbance and the concentration of residual chlorine or other oxidants, obtain the concentration of residual chlorine or other oxidants in the liquid to be tested.

2. The method for testing residual chlorine and other oxidants according to claim 1, characterized in that: The detection reagent consists of a main chromogenic agent and an organic co-solvent. The mass ratio of the main chromogenic agent to the organic co-solvent is (1.4 - 38):(26 - 50).

3. A method for testing residual chlorine and other oxidants according to claim 1, characterized in that: In the mixed solution, the volume ratio of the liquid to be tested to the detection reagent is 10 mL:(0.04 - 0.05) mL.

4. A method for testing residual chlorine and other oxidants according to claim 3, characterized in that: The main chromogenic agent is one or a mixture of N,N-diethyl-p-phenylenediamine, N,N-diethyl-p-phenylenediamine sulfate, N,N-diethyl-p-phenylenediamine oxalate, N,N-diethyl-p-phenylenediamine hydrochloride, N,N-diethyl-p-phenylenediamine methanesulfonate, and N,N-diethyl-p-phenylenediamine complex salt.

5. A method for testing residual chlorine and other oxidants according to claim 3, characterized in that: The organic co-solvent includes organic acids, organic acid salts, and organic alcohols.

6. A method for testing residual chlorine and other oxidants according to claim 5, characterized in that: The organic acid is one or a mixture of tartaric acid, acetic acid, lactic acid, glycolic acid, and citric acid.

7. A method for testing residual chlorine and other oxidants according to claim 5, characterized in that: The organic acid salt is one or a mixture of sodium citrate, sodium acetate, sodium ethylenediaminetetraacetate, and sodium tartrate.

8. A method for testing residual chlorine and other oxidants according to claim 5, characterized in that: The organic alcohol is one or a mixture of polyethylene glycol, ethanol, ethylene glycol, glycerol, 1,2-propanediol, and 1,4-butanediol.

9. A method for testing residual chlorine and other oxidants according to claim 1, characterized in that: The method for establishing the linear relationship between the absorbance and the concentration of residual chlorine or other oxidants is as follows: Dilute the residual chlorine standard solution or other oxidants into test standard solutions with different concentrations. Use the test standard solution without adding the detection reagent as a blank sample for zero calibration. Take the above-diluted test standard solutions with different concentrations and mix them thoroughly with the detection reagent to obtain mixed solutions with different concentrations. Subsequently, measure the absorbance of the obtained mixed solutions with different concentrations to get the absorbance of the mixed solution at different concentrations of residual chlorine or other oxidants after adding the detection reagent. Use it for linear analysis to obtain the linear relationship between the absorbance and the concentration of residual chlorine or other oxidants.

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