Kit for detecting cod, and preparation method therefor and use thereof

Abstract

A kit for detecting COD, and a preparation method therefor and the use thereof. The kit for detecting COD comprises a reagent tube loaded with a COD detection reagent, and a standard colorimetric card, wherein the COD detection reagent comprises potassium permanganate, a strong alkaline reagent and a weighting agent. The strong alkaline reagent comprises one of or a mixture of sodium carbonate, sodium bicarbonate and sodium phosphate; and the weighting agent comprises one of or a mixture of calcium carbonate, sodium sulfate and potassium sulfate. The kit is based on a potassium permanganate method, wherein reducing substances in water are oxidized under alkaline conditions, and manganese in different valence states is obtained in the case of different amounts of the reducing substances, thereby presenting different colors. The kit has the advantages of no need for instruments and devices, low cost, convenience, rapidness, flexibility, stability, etc., is simple in terms of actual operation, causes little pollution to a laboratory environment, and can be widely used.

Description

A kit for detecting COD, its preparation method and use Technical Field

[0001] The invention belongs to the technical field of detection materials, and particularly relates to a kit for detecting COD and a preparation method thereof. Background Art

[0002] Chemical oxygen demand (COD) refers to the amount of oxidant consumed when a water sample is treated with a strong oxidant under certain conditions. It is an important indicator of the amount of reducing substances in water and the degree of water pollution. It is also one of the control indicators for total emissions in my country.

[0003] The national standard for determining COD includes the potassium dichromate method, the acidic potassium permanganate method, and the alkaline potassium permanganate method. The potassium dichromate method, a COD determination method specified in the national standard, boasts advantages such as good reproducibility, accuracy, and reliability. It is primarily used for wastewater and sewage containing high levels of reducing pollutants. However, its reflux device occupies a large laboratory space, consumes significant amounts of water and electricity, requires large amounts of reagents, is inconvenient to operate, and is difficult to rapidly determine in large quantities. The potassium permanganate method uses potassium permanganate as an oxidant to determine COD in water. The determination principle: COD is determined using potassium permanganate as an oxidant. The measured COD is called the permanganate index (CODMn). After acidifying the water sample by adding sulfuric acid, a certain amount of potassium permanganate solution is added and the sample is heated in a boiling water bath for 30 minutes. The remaining potassium permanganate is reduced by adding an excess of sodium oxalate solution. The excess sodium oxalate is then back-titrated with the potassium permanganate solution, and the permanganate index is calculated. Its main advantage is that the pollution generated by the experiment is smaller than that required by the national standard, so it is relatively more environmentally friendly and is mainly used for river water and surface water with low pollution levels. Accurate test results can be obtained by using the national standard method, but there are the following shortcomings: the cost of specific equipment is high, the operation is cumbersome, the professional requirements are high, and emergency response is difficult, which limits its application in rapid detection. However, the potassium permanganate method requires back titration of excess sodium oxalate, which is time-consuming, and the acidic potassium permanganate method has low oxidizing power and incomplete oxidation, so the measured permanganate index is lower than the dichromate index, which is usually 3-8 times different from the national standard method measurement result. Therefore, CODCr is mainly used for wastewater with a relatively high content of reducing pollutants, while CODMn is mainly used for river water and surface water with relatively low pollutants.

[0004] The principle of the spectrophotometric method is the same as the national standard method. Similarly, in an acidic solution, reducing substances in the test solution react with potassium dichromate to form trivalent chromium ions. Trivalent chromium ions have a strong absorption capacity for light with a wavelength of 600 nm, and the relationship between their absorbance and trivalent chromium ion concentration follows the Lambert-Beer law. The amount of trivalent chromium ions is related to the amount of reducing substances in the test solution, so measuring the absorbance of trivalent chromium can indirectly determine the COD value of the test solution. Compared with the traditional national standard method, it significantly reduces the time spent on preparing chemical reagents, eliminates the need for titration, and is convenient to use. However, the only drawback is that the digestion process still takes two hours. The classic standard method for rapid digestion is the 2-hour reflux method. To increase the speed of analysis, various rapid analysis methods have been proposed. These methods primarily increase the oxidant concentration in the digestion reaction system, increase the sulfuric acid acidity, raise the reaction temperature, and add catalysts to enhance the reaction speed. The sulfuric acid acidity of the digestion system was increased from 9.0 mg / l to 10.2 mg / l, the reaction temperature was raised from 150°C to 165°C, and the digestion time was reduced from 2 hours to 10-15 minutes. The disadvantage is that the power and time of the test vary depending on the type of microwave oven.

[0005] In order to make up for the shortcomings of the above-mentioned tests, COD test kits that are fast, accurate, easy to carry, simple to operate, and quick have been developed in recent years. However, the COD test kits or COD test strips currently available on the market require multiple steps to operate. For example, they require a digester, which is not suitable for field operations. The reagents have a short shelf life and are not easy to preserve for a long time. Existing COD test kits are based on two reaction principles: the potassium dichromate method and the alkaline potassium permanganate method. The potassium dichromate method COD test kit contains a liquid test solution and a powder reagent pack. The liquid test solution contains sulfuric acid and potassium dichromate, etc.; the powder reagent pack contains mercuric sulfate powder, etc. The disadvantages of this test kit are: it requires a digester, it is not suitable for field operations, and the reagent uses toxic mercuric sulfate, which is not environmentally friendly. The alkaline potassium permanganate method COD test kit contains an alkaline test solution and a potassium permanganate test solution. The disadvantages of this test kit are: the potassium permanganate solution has a short shelf life and the liquid reagent is inconvenient to carry. For example, Chinese patent publication number CN114018905A discloses a kit for rapid detection of COD in water quality. The COD detection reagent includes the following components, and the content of each component is: potassium permanganate 1.5-30.0%; strong alkaline agent 80.0-98.0%; anti-caking agent 0.1-2.0%. However, the disadvantage is that the strong alkaline agents potassium hydroxide and sodium hydroxide used have strong water absorption and are not easy to be made into powders. In addition, anti-caking agents including silicon dioxide, diatomaceous earth, and bentonite easily form white microparticles in water, affecting further observation of color. Chinese patent publication number CN103278501B discloses a rapid COD detection solution, test kit, and determination method in water. The patent includes test solution No. I (alkaline solution or alkaline buffer solution) and test solution No. II (potassium permanganate aqueous solution). The present invention is characterized by being independent of instruments, low in cost, convenient, fast, and flexible, and can achieve detection within multiple different COD concentration ranges. However, the disadvantages are that potassium permanganate solution has a short shelf life, the liquid reagent is inconvenient to carry, and the operation is more troublesome. Therefore, it is urgent to improve the determination method of COD test kit.

[0006] Summary of the Invention

[0007] To address the problems existing in the above-mentioned prior art, the present invention provides a kit for detecting COD, its preparation method, and its use. The present invention is based on the potassium permanganate method, which oxidizes reducing substances in water under alkaline conditions, and produces manganese of different valence states, resulting in different colors depending on the amount of reducing substances. The present invention has the advantages of requiring no instrumentation, being low-cost, convenient, fast, flexible, and stable, and is simple to operate and reduces pollution to the laboratory environment, making it widely used.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] A COD detection kit comprises a reagent tube filled with a COD detection reagent and a standard colorimetric card; wherein the COD detection reagent comprises potassium permanganate, a strong alkaline reagent and a weighting agent.

[0010] In the kit for detecting COD, the mass ratio of the potassium permanganate, the strong alkaline reagent and the weighting agent is 0.1-2:50.0-89.9:10.0-50.0.

[0011] In the kit for detecting COD, the strong alkaline reagent comprises a mixture of one or more of sodium carbonate, sodium bicarbonate and sodium phosphate.

[0012] In the kit for detecting COD, the weighting agent comprises a mixture of one or more of calcium carbonate, sodium sulfate and potassium sulfate.

[0013] The method for preparing the kit for detecting COD comprises the following steps:

[0014] (1) Weigh the COD detection reagent, add it to a mortar, grind it thoroughly until it can pass through an 80-mesh standard sieve, and package it into 0.1-0.5 g per tube. Vacuum or seal it with inert gas to obtain a reagent tube containing the COD detection reagent;

[0015] (2) Weigh glucose and dissolve it in ammonia-free water to prepare COD standard solutions of several concentrations. Take the COD standard solutions of various concentrations, add COD detection reagents respectively, seal the packages, shake well, and color the solution for 1 minute until the color is stable to prepare a standard colorimetric card; the glucose is dried at 110°C for 2 hours to remove the moisture therein.

[0016] (3) The reagent tube containing the COD detection reagent obtained in step (1) and the standard colorimetric card obtained in step (2) are placed in a test kit to obtain a test kit for detecting COD.

[0017] In the preparation method, the concentration of the COD standard solution is 0 mg / L, 2.0 mg / L, 5.0 mg / L, 10.0 mg / L, 20 mg / L, 50 mg / L, 100 mg / L, 200 mg / L, 500 mg / L, and 1000 mg / L.

[0018] In the preparation method, the amount of the COD standard solution added in step (2) is 1-5 mL, and the amount of the COD detection reagent added is 0.1-0.5 g.

[0019] The method for using the COD detection kit is as follows: 1-5 mL of a water sample to be tested is added to a reagent tube of the COD detection kit, and the sample is compared with a standard colorimetric card. If COD is present in the water, a blue-purple, gray-purple, gray-green, green, yellow-green or yellow color will be displayed, representing the COD concentration in the water sample to be tested.

[0020] The kit should be stored in a cool and dry place at a temperature below 25°C and has an effective shelf life of more than one year.

[0021] Use of any one of the test kits in detecting COD in water.

[0022] The water body includes chemical wastewater, surface water, urban wastewater recycling, landscape water or urban miscellaneous water.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. The kit of the present invention can be used for water sample testing in just 1 minute.

[0025] 2. The kit of the present invention is easy to operate. You only need to add the water sample to be tested into the colorimetric tube and shake it well to obtain the colorimetric result.

[0026] 3. The kit of the present invention is easy to carry, the size of a noodle, and can be carried around.

[0027] 4. The present invention has strong anti-interference capability.

[0028] 5. The detection kit for determining COD in water quality of the present invention has a simple production process, does not require special environmental requirements, does not cause pollution from special wastes, is low in cost, has simple detection steps and is more accurate in determination, has a short color development time and is highly portable.

[0029] 6. In the present invention, potassium permanganate, a strong alkaline reagent and a weighting agent are all loaded in one container. Compared with traditional methods or other determination forms, the method is more convenient to use and does not require specialized technicians to perform the determination.

[0030] 7. The reagents used in this invention are common chemical reagents that are safe, reliable, and inexpensive. They can be used to determine the COD content of water bodies such as chemical wastewater, surface water, urban wastewater recycling, landscape water, and urban miscellaneous water, especially for environmental COD monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] FIG1 is a colorimetric card for detecting a COD test kit of the present invention. DETAILED DESCRIPTION

[0032] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0033] Example 1:

[0034] 1. Prepare the raw materials in the following proportions: 0.5g potassium permanganate, 80g strong alkaline reagent, and 20g weighting agent. Add the above materials to a mortar and grind them thoroughly until all the raw materials can pass through an 80-mesh standard sieve. Then, package them into 0.1g tubes and seal them with vacuum or inert gas.

[0035] 2. When in use, add 2 ml of water sample into a tube of reagent. If COD exists in the water, it will display blue-purple, gray-purple, gray-green, green, yellow-green, and yellow. The color is related to the concentration of COD in the water.

[0036] 3. Preparation of standard colorimetric card: Accurately weigh glucose (dried at 110℃ for 2h) and dissolve it in ammonia-free water to prepare COD standard solutions with concentrations of 0mg / L, 2.0mg / L, 5.0mg / L, 10.0mg / L, 20mg / L, 50mg / L, 100mg / L, 200mg / L, 500mg / L, and 1000mg / L. Take 2ml of various COD standard solutions, add 0.1g of solid reagent respectively, seal the package, shake well, and color will be basically stable after 1 minute of color development to prepare the standard colorimetric card.

[0037] Example 2:

[0038] 1. Prepare the raw materials in the following proportions: 1g potassium permanganate, 50g strong alkaline reagent, and 10g weighting agent. Add the above materials to a mortar and grind them thoroughly until all the raw materials can pass through an 80-mesh standard sieve. Then, package them into 0.1g tubes and seal them with vacuum or inert gas.

[0039] 2. When in use, add 2 ml of water sample into a tube of reagent. If COD exists in the water, it will display blue-purple, gray-purple, gray-green, green, yellow-green, and yellow. The color is related to the concentration of COD in the water.

[0040] 3. Preparation of standard colorimetric card: Accurately weigh glucose (dried at 110℃ for 2h) and dissolve it in ammonia-free water to prepare COD standard solutions with concentrations of 0mg / L, 2.0mg / L, 5.0mg / L, 10.0mg / L, 20mg / L, 50mg / L, 100mg / L, 200mg / L, 500mg / L, and 1000mg / L. Take 1mL of various COD standard solutions, add 0.3g of solid reagent respectively, seal the package, shake well, and color will develop for 1 minute until the color is basically stable to prepare the standard colorimetric card.

[0041] Example 3:

[0042] 1. Prepare the raw materials in the following proportions: 2g potassium permanganate, 60g strong alkaline reagent, 50g weighting agent. Add the above materials to a mortar and grind them thoroughly until all the raw materials can pass through an 80-mesh standard sieve. Then, package them into 0.1g tubes and seal them with vacuum or inert gas.

[0043] 2. When using, add 2 ml of water sample into a tube of reagent. If COD exists in the water, it will display blue-purple, gray-purple, gray-green, green, yellow-green, and yellow. The color is related to the concentration of COD in the water.

[0044] 3. Preparation of standard colorimetric card: Accurately weigh glucose (dried at 110℃ for 2h) and dissolve it in ammonia-free water to prepare COD standard solutions with concentrations of 0mg / L, 2.0mg / L, 5.0mg / L, 10.0mg / L, 20mg / L, 50mg / L, 100mg / L, 200mg / L, 500mg / L, and 1000mg / L. Take 5mL of various COD standard solutions, add 0.5g of solid reagent respectively, seal the package, shake well, and color will develop for 1 minute until the color is basically stable to prepare the standard colorimetric card.

Claims

1. A kit for detecting COD, characterized in that: It comprises a reagent tube containing a COD detection reagent and a standard colorimetric card; wherein the COD detection reagent comprises potassium permanganate, a strong alkaline reagent and a weighting agent.

2. A kit for detecting COD as claimed in claim 1, characterized in that: The mass ratio of the potassium permanganate, the strong alkaline agent and the weighting agent is 0.1-2:50.0-89.9:10.0-50.

0.

3. A kit for detecting COD as claimed in claim 1, characterized in that: The strong alkaline agent includes a mixture of one or more of sodium carbonate, sodium bicarbonate and sodium phosphate; the weighting agent includes a mixture of one or more of calcium carbonate, sodium sulfate and potassium sulfate.

4. A method for preparing a kit for detecting COD as described in any one of claims 1 to 3, characterized in that: The following steps are involved: (1) Weigh a COD detection reagent, add it to a mortar, grind it thoroughly until it can pass through an 80-mesh standard sieve, and package it into 0.1-0.5 g per tube. Vacuum or seal it with an inert gas to obtain a reagent tube containing a COD detection reagent; (2) Weigh glucose and dissolve it in ammonia-free water to prepare COD standard solutions of several concentrations. Take COD standard solutions of various concentrations, add COD detection reagents respectively, seal the packages, shake well, and color development for 1 minute until the color is stable to prepare a standard colorimetric card; (3) placing the reagent tube containing the COD detection reagent obtained in step (1) and the standard colorimetric card obtained in step (2) into a test kit to obtain a test kit for detecting COD.

5. The preparation method according to claim 4, characterized in that: The concentration of the COD standard solution is 0 mg / L, 2.0 mg / L, 5.0 mg / L, 10.0 mg / L, 20 mg / L, 50 mg / L, 100 mg / L, 200 mg / L, 500 mg / L, and 1000 mg / L.

6. The preparation method according to claim 4, characterized in that: In step (2), the amount of the COD standard solution added is 1-5 mL, and the amount of the COD detection reagent added is 0.1-0.5 g.

7. A method for using a kit for detecting COD according to any one of claims 1 to 3, characterized in that: Take 1-5mL of the water sample to be tested, add it to the reagent tube of the COD detection kit, and compare it with the standard colorimetric card. If COD exists in the water, it will show blue-purple, gray-purple, gray-green, green, yellow-green or yellow, representing the concentration of COD in the water sample to be tested.

8. The method of use according to claim 7, characterized in that: The kit is stored in a cool and dry place at a storage temperature below 25° C. and has an effective shelf life of more than one year.

9. Use of the kit as described in any one of claims 1 to 3 in detecting COD in water bodies.

10. The use according to claim 9, characterized in that The water bodies include: chemical wastewater, surface water, urban wastewater recycling, landscape water or urban miscellaneous water.

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