Water quality nitrate detection reagent, preparation method thereof and water quality nitrate detection method

Abstract

This invention provides a water nitrate detection reagent, its preparation method, and a method for detecting nitrates in water. The raw materials for preparing the water nitrate detection reagent include chromogenic particles, a reducing agent, a diazotizing reagent, and an acid reagent. The chromogenic particles comprise dihydroxynaphthalenesulfonic acid compounds coated with an outer membrane, and the reducing agent comprises Cu / MnO with a three-dimensional porous nanostructure. X Mixture, where x≤2, Cu / MnO X The purity of the mixture is ≥98%, Cu and MnO X The mass ratio is 1:2 to 6. The acid reagent is a weak organic acid. Using this water nitrate detection reagent for water sample testing offers wide applicability, a broad measurement range, strong anti-interference ability, simple operation, high accuracy, and stable storage. It is suitable for rapid on-site determination of nitrate content in most water samples, including surface water, drinking water, kitchen waste (domestic sewage), and food industry wastewater.

Description

Technical Field

[0001] This invention relates to the field of chemical analysis technology, particularly to water sample testing reagents, and even more particularly to water nitrate testing reagents and their preparation methods, as well as water nitrate testing methods. Background Technology

[0002] Nitrates are widely present in nature as environmental pollutants, especially in gaseous water, surface water, groundwater, and in animal, plant, and food products. Sources of nitrate pollution in the environment are numerous, including residues from artificial fertilizers, domestic sewage and garbage, ammonia-containing waste from industrial production, and byproducts of atmospheric pollutant transformation. Furthermore, nitrates easily accumulate in food (vegetables), and when ingested in large quantities, they can be reduced to nitrites. Nitrites react with human blood to form methemoglobin, impairing the blood's oxygen-carrying capacity and causing hypoxia and poisoning. Mild symptoms include dizziness, palpitations, vomiting, and cyanosis of the lips; severe symptoms include loss of consciousness, convulsions, and rapid breathing, which can be life-threatening if not treated promptly. Moreover, nitrites react with secondary amines inside and outside the body to form nitrosamines. At certain doses in the body, nitrites become carcinogenic, teratogenic, and mutagenic substances, seriously endangering human health. In order to reduce the harmful risks of nitrates, in addition to taking various targeted environmental protection measures in a scientific and reasonable manner, water samples containing nitrates should be tested quickly to ensure that the nitrate content does not exceed the standard, so as to protect surface water and groundwater from nitrate pollution and protect human health from the source.

[0003] There are several methods for detecting nitrate content in water, including electrode methods, ultraviolet spectrophotometry, cadmium reduction methods, and phenol disulfonic acid spectrophotometry. The appropriate method is generally selected based on the type of water sample and the nitrate concentration range. Electrode methods offer a wide measurement range and good anti-interference capabilities, making them suitable for various water samples. However, the equipment itself is limited by portability, and compared to other methods, it lacks the advantage of rapid on-site detection. Ultraviolet spectrophotometry has a measurement range of 0.08 mg / L to 4.0 mg / L, but it is only suitable for surface water or drinking water with low levels of pollution. The measurement results are significantly affected by suspended solids, dissolved organic matter, and surfactants, requiring pretreatment. Cadmium reduction and phenol disulfonic acid spectrophotometry both offer advantages such as stable color development and ease of operation, and can be developed into rapid detection reagents. The former is suitable for measuring seawater and sewage samples, while the latter is suitable for clean surface water and uncontaminated groundwater. However, they are greatly affected by substances such as nitrite and chloride; without cumbersome pretreatment or calibration experiments, the results can be quite inaccurate. Currently, the country is paying increasing attention to water quality and food safety issues caused by nitrate pollution. It is urgent to develop a rapid water nitrate detection reagent and method that is widely applicable, has strong anti-interference ability, is easy to operate, and is suitable for rapid on-site detection. Summary of the Invention

[0004] To address the aforementioned problems, the present invention aims to provide a water nitrate detection reagent, its preparation method, and a water nitrate detection method. Using this water nitrate detection reagent for water sample testing offers wide applicability, a broad measurement range, strong anti-interference capability, simple operation, high accuracy, and stable storage. It is suitable for rapid on-site determination of nitrate content in most water samples, including surface water, drinking water, kitchen waste (domestic sewage), and food industry wastewater.

[0005] To achieve the above objectives, the first aspect of the present invention provides a water nitrate detection reagent, the raw materials of which include chromogenic particles, a reducing agent, a diazotizing reagent, and an acid reagent. The chromogenic particles comprise a dihydroxynaphthalenesulfonic acid compound coated with an outer membrane, and the reducing agent comprises Cu / MnO4 with a three-dimensional porous nanostructure. X A mixture, wherein x≤2, of the Cu / MnO X The purity of the mixture is ≥98%, Cu and MnO X The mass ratio is 1:2 to 6, and the acid reagent is a weak organic acid.

[0006] In the water nitrate detection reagent of this invention, the diazotizing reagent reacts with nitrate in the water sample to generate diazonium salt, which is then detected by color development using a dihydroxynaphthalenesulfonic acid compound. The use of a dihydroxynaphthalenesulfonic acid compound as the colorimetric agent, compared to the traditional naphthylethylenediamine salt used in national standards, offers a wider color change range and more flexible color change intervals. Therefore, the water nitrate detection reagent has broader applicability and a wider measurement range, suitable for rapid detection of nitrate content in most water bodies, including surface water, drinking water, seawater, kitchen waste (domestic) sewage, and food industry wastewater. However, to further adapt to the measurement needs of various water samples and expand the colorimetric effect across different concentration ranges, the content of the colorimetric agent needs to be significantly increased. But when high levels of dihydroxynaphthalenesulfonic acid compounds coexist with the diazotizing agent, the two hydroxyl groups on each dihydroxynaphthalenesulfonic acid compound are prone to ortho / meta dislocation with the sulfonic acid group, leading to a decrease in the overall stability of the detection reagent. By coating the chromogenic agent with an outer membrane, the dislocation effect of the diazotizing agent on the chromogenic agent groups can be effectively isolated during storage, thereby improving the stability between the components of the detection reagent and ensuring its long-term stable storage at room temperature. In addition, the reducing agent includes Cu / MnO with a three-dimensional porous nanostructure. X The mixture utilizes the strong interaction between metals and metal oxides to promote the exchange of MnO in the aqueous medium. X Directional conversion to MnO X+1 This method achieves targeted reduction of nitrate to nitrite and nitrite to nitrous oxide under weakly acidic conditions, avoiding NOCl formation and effectively removing measurement interference from pre-existing nitrite and chloride in water samples. Furthermore, Cu / MnO... XThe unique three-dimensional porous nanostructure of the mixture provides abundant active reduction sites, significantly reducing the time required for nitrate reduction reactions, thus shortening the testing time to just 20 seconds. Controlling the Cu / MnO ratio... X The purity and mass ratio of the mixture ensure the targeted reduction of nitrate to nitrite and nitrite to nitrous oxide, thus guaranteeing the colorimetric ability of the water nitrate detection reagent.

[0007] As a technical solution of the present invention, the colorimetric particles are 55-73% by weight, the reducing agent is 15-25%, the diazotizing agent is 10-15%, and the acid reagent is 2-5%.

[0008] As one technical solution of the present invention, the outer film is formed by coating the color developer with a solution containing a film-forming agent and an adhesive and then drying it.

[0009] As one technical solution of the present invention, the film-forming agent includes polyvinyl alcohol, and the adhesive includes sodium carboxyethyl cellulose or sodium polyacrylate.

[0010] As one technical solution of the present invention, the mass ratio of the color developer to the solution is 1:5 to 10, the content of the film-forming agent in the solution is 80 to 125 g / L, and the content of the adhesive in the solution is 22 to 40 g / L.

[0011] As a technical solution of the present invention, the Cu / MnO X The purity of the mixture is ≥98%, Cu and MnO X The mass ratio is 1:2 to 6.

[0012] As one technical solution of the present invention, the diazotizing agent includes p-aminobenzenesulfonate compounds.

[0013] As one technical solution of the present invention, the acid reagent is at least one of maleic acid, trans-butenedioic acid and tartaric acid.

[0014] The second aspect of the present invention provides a method for preparing a water nitrate detection reagent, wherein the colorimetric particles, the reducing agent, the diazotizing reagent and the acid reagent are mixed and quantitatively packaged into bags, and the packaging amount is 0.2-0.5g / bag.

[0015] A third aspect of this invention provides a method for detecting nitrates in water, comprising the following steps:

[0016] 1) Add the nitrate test reagent to the colorimetric bottle containing the water sample to be tested;

[0017] 2) Shake the colorimetric bottle until the water nitrate test reagent dissolves, then wait 20–60 seconds;

[0018] 3) Use a standard colorimetric card for color comparison to semi-quantitatively determine the nitrate content in the water sample to be tested, or, after plotting a standard curve, use a colorimeter to measure and quantitatively determine the nitrate content in the water sample to be tested.

[0019] In the water nitrate detection method of the present invention, a standard colorimetric card can be used to perform semi-quantitative testing of nitrate content in various water qualities, or a spectrophotometer or portable water quality analyzer can be used to perform quantitative testing of water nitrate. This detection method uses only a fraction of the reagent volume required for a single test compared to conventional laboratory methods, and the testing process is simple and the color development is rapid, which can greatly reduce the testing costs for on-site monitoring.

[0020] As a technical solution of the present invention, the method for preparing a standard colorimetric card includes the following steps:

[0021] ① Prepare nitrate standard solutions with concentrations of 0.02 mg / L, 0.05 mg / L, 0.10 mg / L, 0.20 mg / L, 0.30 mg / L, 0.50 mg / L, 0.80 mg / L, 1.00 mg / L, 3.00 mg / L, 5.00 mg / L, 10.00 mg / L, 15.00 mg / L, 20.00 mg / L, and 30.00 mg / L respectively using water;

[0022] ② Add a 0.02 mg / L nitrate standard solution to a clean colorimetric bottle and dilute to the mark. Add the water quality nitrate detection reagent, shake the water sample in the colorimetric bottle until the nitrate is dissolved, wait 20 seconds, and find the corresponding standard color on the Pantone color chart.

[0023] ③ Repeat step ② to test nitrate standard solutions with concentrations of 0.05 mg / L, 0.10 mg / L, 0.20 mg / L, 0.30 mg / L, 0.50 mg / L, 0.80 mg / L, 1.00 mg / L, 3.00 mg / L, 5.00 mg / L, 10.00 mg / L, 15.00 mg / L, 20.00 mg / L, and 30.00 mg / L, and identify the corresponding standard colors;

[0024] ④ Prepare a standard colorimetric card based on the color values ​​of the standard colors at each concentration. Detailed Implementation

[0025] The water nitrate detection reagent of the present invention is prepared from raw materials including colorimetric particles, a reducing agent, a diazotizing reagent, and an acid reagent. By weight percentage, the colorimetric particles comprise 55-73%, the reducing agent 15-25%, the diazotizing reagent 10-15%, and the acid reagent 2-5%. The colorimetric particles may be, but are not limited to, 55%, 56%, 57%, 60%, 62%, 63%, 64%, 66%, 68%, 70%, or 73%. The reducing agent may be, but is not limited to, 15%, 17%, 19%, 20%, 21%, 22%, 23%, 24%, or 25%. The diazotizing reagent may be, but is not limited to, 10%, 11%, 12%, 13%, 14%, or 15%. The acid reagent may be, but is not limited to, 2%, 2.5%, 3%, 3.5%, 4%, or 5%.

[0026] The content of chromogenic particles in the water nitrate detection reagent should not be too low to avoid a narrow detection range. The chromogenic particles include dihydroxynaphthalene sulfonic acid compounds coated on an outer membrane. These compounds can be 1,8-dihydroxynaphthalene-3,6-disulfonic acid or sodium 1,8-dihydroxynaphthalene-3,6-disulfonic acid, preferably 1,8-dihydroxynaphthalene-3,6-disulfonic acid. The outer membrane is formed by coating the chromogenic agent with a solution containing a film-forming agent and an adhesive, followed by drying. The outer membrane is mainly formed by the film-forming agent, while the adhesive acts as a bridge between the outer membrane and the chromogenic agent, forming the outer membrane solution together with the film-forming agent and serving as an important component of the outer membrane. The coating method can be immersion, spraying, or brushing. The film-forming agent includes polyvinyl alcohol. Further, the film-forming agent can be polyvinyl alcohol 1778, which has good film-forming properties and low alcoholysis degree, is soluble in both water and weakly acidic ethanol-water mixtures, and can rapidly dissolve in most water bodies to release the chromogenic agent for color development. The binder is sodium carboxyethyl cellulose or sodium polyacrylate, preferably sodium carboxyethyl cellulose, which has good adhesion and is readily soluble in water and also in weakly acidic ethanol-water mixtures, allowing the colorimetric reagent to be released for color development. Once the redox reaction of nitrates in the water sample is complete, the Cu / MnO... X Under the slow polymerization action of the film-forming agent, the mixture can quickly aggregate into clusters and settle to the bottom of the water sample, thus avoiding interference with the colorimetric process of the standard colorimetric card or colorimeter reading. The mass ratio of the colorimetric agent to the solution is 1:5 to 10. As examples, the mass ratio of the colorimetric agent to the solution can be, but is not limited to, 1:5, 1:6, 1:7, 1:8, 1:9, or 1:10. The content of the film-forming agent in the solution is 80 to 125 g / L, and the content of the binder is 22 to 40 g / L. The content of the film-forming agent in the solution should not be too high, so as not to prolong the dissolution time of the outer film on the surface of the colorimetric agent, which is not conducive to the effective dissolution and color development of the colorimetric agent in the water sample.

[0027] The reducing agent includes Cu / MnO with a three-dimensional porous nanostructure. X A mixture, where x ≤ 2. Cu / MnOX The purity of the mixture is ≥98%, Cu and MnO X The mass ratio is 1:2 to 6. Furthermore, the reducing agent is Cu / MnO with a three-dimensional porous nanostructure. X A mixture, x≤2, and purity≥98%, of Cu and MnO. X The mass ratio is 1:4.8. (Cu / MnO) X The mixture should ideally have a high purity to avoid a decrease in colorimetric ability due to excessively low purity. Cu and MnO X MnO in the mixture X The content should be relatively high to avoid affecting the directional reduction capacity of nitrates and nitrites, which would prevent normal testing.

[0028] Diazotizing agents include p-aminobenzenesulfonates. Sulfonamides or 4-anilinesulfonic acid are preferred.

[0029] The acid reagent is a solid acid compound that is both alcohol-soluble and water-soluble. This acid reagent can provide weakly acidic conditions in water samples with an alcohol content ≤60% without affecting the color development of the colorimetric reagent. It can adjust the pH of the water sample to 2.5–5. As an example, the acid reagent can be at least one of maleic acid, fumaric acid, and tartaric acid.

[0030] In the preparation of the water nitrate detection reagent of the present invention, the colorimetric particles, reducing agent, diazotizing agent and acid reagent are mixed and quantitatively packaged into bags, and the packaging amount is 0.2-0.5g / bag, preferably 0.3g / bag.

[0031] The water nitrate detection method of the present invention may include the following steps.

[0032] 1) Add the nitrate test reagent to the colorimetric bottle containing the water sample to be tested.

[0033] 2) Shake the colorimetric bottle until the nitrate test reagent dissolves, then wait 20-60 seconds.

[0034] 3) Use a standard colorimetric card for color comparison to semi-quantitatively determine the nitrate content in the water sample to be tested, or, after plotting a standard curve, use a colorimeter to measure and quantitatively determine the nitrate content in the water sample to be tested.

[0035] One packet of rapid nitrate test reagent is added to a 10mL colorimetric bottle containing the water sample to be tested. The water sample is shaken until the reagent dissolves, and then the nitrate content in the water sample is measured using a standard colorimetric card or colorimeter.

[0036] The preparation method of a standard colorimetric card may include the following steps.

[0037] ① Prepare nitrate standard solutions with concentrations of 0.02 mg / L, 0.05 mg / L, 0.10 mg / L, 0.20 mg / L, 0.30 mg / L, 0.50 mg / L, 0.80 mg / L, 1.00 mg / L, 3.00 mg / L, 5.00 mg / L, 10.00 mg / L, 15.00 mg / L, 20.00 mg / L, and 30.00 mg / L using water.

[0038] ② Add the 0.02 mg / L nitrate standard solution to a clean 10 mL colorimetric bottle and dilute to the mark. Add one packet of the aforementioned water nitrate test reagent. Shake the water sample in the colorimetric bottle until the nitrate test solution dissolves. Wait 20 seconds and find the corresponding standard color on the Pantone color chart.

[0039] ③ Repeat step ② to test nitrate standard solutions with concentrations of 0.05 mg / L, 0.10 mg / L, 0.20 mg / L, 0.30 mg / L, 0.50 mg / L, 0.80 mg / L, 1.00 mg / L, 3.00 mg / L, 5.00 mg / L, 10.00 mg / L, 15.00 mg / L, 20.00 mg / L, and 30.00 mg / L and identify the corresponding standard colors.

[0040] ④ Prepare a standard colorimetric card based on the color values ​​of the standard colors at each concentration.

[0041] To better illustrate the purpose, technical solution, and beneficial effects of this invention, the invention will be further described below with reference to specific embodiments. It should be noted that the methods described below are further explanations of this invention and should not be construed as limiting it.

[0042] Example 1

[0043] This embodiment describes a reagent for detecting nitrates in water. By weight percentage, the raw materials include 63% chromogenic particles, 22% a Cu / MnO2 mixture with a three-dimensional porous nanostructure, a purity ≥98%, and a Cu / MnO2 mass ratio of 1:4.8, 12% 4-anilinesulfonic acid, and 3% maleic acid. The raw materials for preparing the chromogenic particles include 1,8-dihydroxynaphthalene-3,6-disulfonic acid, polyvinyl alcohol 1778, and sodium carboxyethyl cellulose. Polyvinyl alcohol 1778 and sodium carboxyethyl cellulose are dissolved in ethanol to prepare an outer membrane solution, which is then uniformly coated onto the surface of 1,8-dihydroxynaphthalene-3,6-disulfonic acid and dried to form an outer membrane. The outer membrane solution contains 85 g / L of polyvinyl alcohol 1778, 34 g / L of sodium carboxyethyl cellulose, and the mass ratio of 1,8-dihydroxynaphthalene-3,6-disulfonic acid to the outer membrane solution is 1:6.

[0044] Mix all components evenly according to the above proportions, and package them in 0.3g / bag quantities to obtain the water nitrate test reagent.

[0045] Example 2

[0046] This embodiment describes a reagent for detecting nitrates in water. By weight percentage, the raw materials include 57% chromogenic particles, 24.8% a Cu / Mn2O3 mixture with a three-dimensional porous nanostructure, a purity ≥98%, and a Cu / Mn2O3 mass ratio of 1:4.8, 14.6% 4-anilinesulfonic acid, and 3.6% tartaric acid. The raw materials for preparing the chromogenic particles include 1,8-dihydroxynaphthalene-3,6-disulfonic acid, polyvinyl alcohol 1778, and sodium polyacrylate. Polyvinyl alcohol 1778 and sodium carboxyethyl cellulose are dissolved in ethanol to prepare an outer membrane solution, which is then uniformly coated onto the surface of 1,8-dihydroxynaphthalene-3,6-disulfonic acid and dried to form an outer membrane. The outer membrane solution contains 85 g / L of polyvinyl alcohol 1778, 22 g / L of sodium polyacrylate, and the mass ratio of 1,8-dihydroxynaphthalene-3,6-disulfonic acid to the outer membrane solution is 1:6.

[0047] Mix all components evenly according to the above proportions, and package them in 0.3g / bag quantities to obtain the water nitrate test reagent.

[0048] Example 3

[0049] This embodiment describes a reagent for detecting nitrates in water. By weight percentage, the raw materials include 30% chromogenic particles, 22% a Cu / MnO2 mixture with a three-dimensional porous nanostructure, a purity ≥98%, and a Cu / MnO2 mass ratio of 1:4.8, 12% 4-aniline sulfonic acid, 3% maleic acid, and 33% anhydrous sodium sulfate filler. The raw materials for preparing the chromogenic particles include 1,8-dihydroxynaphthalene-3,6-disulfonic acid, polyvinyl alcohol 1778, and sodium carboxyethyl cellulose. Polyvinyl alcohol 1778 and sodium carboxyethyl cellulose are dissolved in ethanol to prepare an outer membrane solution, which is then uniformly coated onto the surface of 1,8-dihydroxynaphthalene-3,6-disulfonic acid and dried to form an outer membrane. The outer membrane solution contains 85 g / L of polyvinyl alcohol 1778, 34 g / L of sodium carboxyethyl cellulose, and the mass ratio of 1,8-dihydroxynaphthalene-3,6-disulfonic acid to the outer membrane solution is 1:6.

[0050] Mix all components evenly according to the above proportions, and package them in 0.3g / bag quantities to obtain the water nitrate test reagent.

[0051] Example 4

[0052] This embodiment describes a reagent for detecting nitrates in water. By weight percentage, the raw materials include 63% chromogenic particles, 22% a Cu / MnO2 mixture with a three-dimensional porous nanostructure, a purity ≥98%, and a Cu / MnO2 mass ratio of 1:4.8, 12% 4-anilinesulfonic acid, and 3% maleic acid. The raw materials for preparing the chromogenic particles include 1,8-dihydroxynaphthalene-3,6-disulfonic acid, polyvinyl alcohol 1778, and sodium carboxyethyl cellulose. Polyvinyl alcohol 1778 and sodium carboxyethyl cellulose are dissolved in ethanol to prepare an outer membrane solution, which is then uniformly coated onto the surface of 1,8-dihydroxynaphthalene-3,6-disulfonic acid and dried to form an outer membrane. The outer membrane solution contains 150 g / L of polyvinyl alcohol 1778, 34 g / L of sodium carboxyethyl cellulose, and the mass ratio of 1,8-dihydroxynaphthalene-3,6-disulfonic acid to the outer membrane solution is 1:6.

[0053] Mix all components evenly according to the above proportions, and package them in 0.3g / bag quantities to obtain the water nitrate test reagent.

[0054] Comparative Example 1

[0055] This embodiment describes a reagent for detecting nitrates in water. By weight percentage, the raw materials include 63% chromogenic particles, 22% a Cu / MnO2 mixture with a three-dimensional porous nanostructure, purity <90%, and a Cu / MnO2 mass ratio of 1:4.8, 12% 4-anilinesulfonic acid, and 3% maleic acid. The raw materials for preparing the chromogenic particles include 1,8-dihydroxynaphthalene-3,6-disulfonic acid, polyvinyl alcohol 1778, and sodium carboxyethyl cellulose. Polyvinyl alcohol 1778 and sodium carboxyethyl cellulose are dissolved in ethanol to prepare an outer membrane solution, which is then uniformly coated onto the surface of 1,8-dihydroxynaphthalene-3,6-disulfonic acid and dried to form an outer membrane. The outer membrane solution contains 85 g / L of polyvinyl alcohol 1778, 34 g / L of sodium carboxyethyl cellulose, and the mass ratio of 1,8-dihydroxynaphthalene-3,6-disulfonic acid to the outer membrane solution is 1:6.

[0056] Mix all components evenly according to the above proportions, and package them in 0.3g / bag quantities to obtain the water nitrate test reagent.

[0057] Comparative Example 2

[0058] This embodiment describes a reagent for detecting nitrates in water. By weight percentage, the raw materials include 63% chromogenic particles, 22% a Cu / MnO2 mixture with a three-dimensional porous nanostructure, a purity ≥98%, and a Cu / MnO2 mass ratio of 1:1, 12% 4-anilinesulfonic acid, and 3% maleic acid. The raw materials for preparing the chromogenic particles include 1,8-dihydroxynaphthalene-3,6-disulfonic acid, polyvinyl alcohol 1778, and sodium carboxyethyl cellulose. Polyvinyl alcohol 1778 and sodium carboxyethyl cellulose are dissolved in ethanol to prepare an outer membrane solution, which is then uniformly coated onto the surface of 1,8-dihydroxynaphthalene-3,6-disulfonic acid and dried to form an outer membrane. The outer membrane solution contains 85 g / L of polyvinyl alcohol 1778, 34 g / L of sodium carboxyethyl cellulose, and the mass ratio of 1,8-dihydroxynaphthalene-3,6-disulfonic acid to the outer membrane solution is 1:6.

[0059] Mix all components evenly according to the above proportions, and package them in 0.3g / bag quantities to obtain the water nitrate test reagent.

[0060] Comparative Example 3

[0061] This embodiment describes a reagent for detecting nitrates in water. By weight percentage, the raw materials include 63% chromogenic particles, 22% a Cu / MnO2 mixture with a purity ≥98% and a Cu / MnO2 mass ratio of 1:4.8 without a three-dimensional porous nanostructure, 12% 4-anilinesulfonic acid, and 3% maleic acid. The raw materials for preparing the chromogenic particles include 1,8-dihydroxynaphthalene-3,6-disulfonic acid, polyvinyl alcohol 1778, and sodium carboxyethyl cellulose. Polyvinyl alcohol 1778 and sodium carboxyethyl cellulose are dissolved in ethanol to prepare an outer membrane solution, which is then uniformly coated onto the surface of 1,8-dihydroxynaphthalene-3,6-disulfonic acid and dried to form an outer membrane. The outer membrane solution contains 85 g / L of polyvinyl alcohol 1778, 34 g / L of sodium carboxyethyl cellulose, and the mass ratio of 1,8-dihydroxynaphthalene-3,6-disulfonic acid to the outer membrane solution is 1:6.

[0062] Mix all components evenly according to the above proportions, and package them in 0.3g / bag quantities to obtain the water nitrate test reagent.

[0063] Comparative Example 4

[0064] This embodiment describes a reagent for detecting nitrates in water. By weight percentage, the raw materials include 63% chromogenic particles, 22% a Cu / MnO2 mixture with a three-dimensional porous nanostructure, a purity ≥98%, and a Cu / MnO2 mass ratio of 1:4.8, 12% 4-aniline sulfonic acid, and 3% sodium bisulfate. The raw materials for preparing the chromogenic particles include 1,8-dihydroxynaphthalene-3,6-disulfonic acid, polyvinyl alcohol 1778, and sodium carboxyethyl cellulose. Polyvinyl alcohol 1778 and sodium carboxyethyl cellulose are dissolved in ethanol to prepare an outer membrane solution, which is then uniformly coated onto the surface of 1,8-dihydroxynaphthalene-3,6-disulfonic acid and dried to form an outer membrane. The outer membrane solution contains 85 g / L of polyvinyl alcohol 1778, 34 g / L of sodium carboxyethyl cellulose, and the mass ratio of 1,8-dihydroxynaphthalene-3,6-disulfonic acid to the outer membrane solution is 1:6.

[0065] Mix all components evenly according to the above proportions, and package them in 0.3g / bag quantities to obtain the water nitrate test reagent.

[0066] Comparative Example 5

[0067] This embodiment is a reagent for detecting nitrates in water. By weight percentage, the raw materials for its preparation include 63% 1,8-dihydroxynaphthalene-3,6-disulfonic acid, 22% a Cu / MnO2 mixture with a three-dimensional porous nanostructure, a purity ≥98%, and a Cu / MnO2 mass ratio of 1:4.8, 12% 4-anilinesulfonic acid, and 3% maleic acid.

[0068] Mix all components evenly according to the above proportions, and package them in 0.3g / bag quantities to obtain the water nitrate test reagent.

[0069] Nitrate standard solutions with concentrations of 0.02 mg / L, 0.50 mg / L, 3.00 mg / L, 10.0 mg / L, and 30.0 mg / L were prepared in advance and added to clean 10 mL colorimetric bottles, then diluted to the mark. One packet of the water nitrate detection reagent from Examples 1-4 and Comparative Examples 1-5 was added to each bottle. The bottles were shaken until the reagent dissolved, and after 20 seconds, the absorbance of the standard solutions was measured at 520 nm using a 1 mm cuvette (average 5 tests). Simultaneously, the water nitrate detection reagents from Examples 1-4 and Comparative Examples 1-5 were stored in a 37°C oven for 365 days, and the changes in the reagents were observed. The results are shown in Table 1 below.

[0070] Table 1. Absorbance test and shelf-life effect of each embodiment.

[0071]

[0072]

[0073] As shown in Table 1, the water nitrate detection reagents of Examples 1-2 and Example 4 can normally test nitrate samples with concentrations ranging from 0.02 to 30 mg / L. In Example 3, the content of the chromogenic particles was only 30%, limiting the detection range to nitrate samples with concentrations ranging from 0.02 to 10 mg / L. Therefore, to expand the detection range, the content of the chromogenic agent in the chromogenic particles needs to be increased. Meanwhile, the water nitrate detection reagents of Examples 1-4 showed no change in appearance after being stored at 37°C for 365 days, indicating good storage stability.

[0074] In Comparative Example 1, the purity of the reducing agent Cu / MnO2 mixture was <90%, resulting in a decrease in the colorimetric ability of the water nitrate detection reagent, rendering it ineffective for detection. In Comparative Example 2, the Cu to MnO2 mass ratio of the reducing agent Cu / MnO2 mixture was 1:1, which significantly affected the targeted reduction ability of the water nitrate detection reagent for nitrates and nitrites in the water sample, thus preventing normal testing. In Comparative Example 3, the reducing agent Cu / MnO2 mixture lacked the unique nanoporous structure and had no reducing ability at all, therefore the water nitrate detection reagent failed to develop a color. In Comparative Example 4, the acid reagent was the strong solid acid sodium bisulfate, which caused the pH of the system to be <2. During the dissolution process of the water nitrate detection reagent, the redox reaction was vigorous, resulting in excessive reduction of nitrates in the water sample, accompanied by significant gas generation, and the overall colorimetric test results were significantly lower than expected. Although the water nitrate test reagent of Comparative Example 5 can normally test nitrate samples with concentrations ranging from 0.02 to 30 mg / L, it turns yellow after being stored at a constant temperature of 37°C for 365 days due to the lack of a protective drying outer membrane.

[0075] The four samples were further tested using the water nitrate detection reagents from Examples 1-4 and Comparative Examples 1-5.

[0076] (1) Sample

[0077] Sample A: Weigh 15.00g of white sugar and prepare 100mL of white sugar ethanol-water solution using 30% ethanol:

[0078] Samples B and C: 500 mL of water from a sedimentation tank in a canteen was collected in a sampling bottle, allowed to stand, and 400 mL of the supernatant was collected. 200 mL of this supernatant was placed in bottle A, designated as Sample B; the remaining 200 mL was placed in bottle B, with 100 mg of sodium chloride added, designated as Sample C.

[0079] Sample D: Take 500 mL of surface water from a certain river using a sampling bottle.

[0080] (2) Preparation of standard colorimetric cards, including the following steps.

[0081] 1) Prepare nitrate standard solutions with concentrations of 0.02 mg / L, 0.05 mg / L, 0.10 mg / L, 0.20 mg / L, 0.30 mg / L, 0.50 mg / L, 0.80 mg / L, 1.00 mg / L, 3.00 mg / L, 5.00 mg / L, 10.00 mg / L, 15.00 mg / L, 20.00 mg / L, and 30.00 mg / L using pure water.

[0082] 2) Add 0.02 mg / L nitrate standard solution to a clean 10 mL colorimetric bottle and dilute to the mark. Add one packet of water quality nitrate test reagent from Example 1. Shake the water sample in the colorimetric bottle until the water quality nitrate test reagent dissolves and wait 20 seconds. Then place the colorimetric bottle on a white PVC plate and observe the solution color from top to bottom. Find the corresponding standard color on the Pantone color chart.

[0083] 3) Repeat step 2) to test nitrate standard solutions with concentrations of 0.05 mg / L, 0.10 mg / L, 0.20 mg / L, 0.30 mg / L, 0.50 mg / L, 0.80 mg / L, 1.00 mg / L, 3.00 mg / L, 5.00 mg / L, 10.00 mg / L, 15.00 mg / L, 20.00 mg / L, and 30.00 mg / L, and identify the corresponding standard colors;

[0084] 4) Prepare standard colorimetric cards based on the color values ​​of each concentration of standard color, as shown in Table 2.

[0085] Table 2 Color Comparison Chart

[0086]

[0087] (3) Plotting the standard curve

[0088] Nitrate standard solutions with concentrations of 0.02 mg / L, 0.05 mg / L, 0.10 mg / L, 0.20 mg / L, 0.30 mg / L, 0.50 mg / L, 0.80 mg / L, 1.00 mg / L, 3.00 mg / L, 5.00 mg / L, 10.00 mg / L, 15.00 mg / L, 20.00 mg / L, and 30.00 mg / L were prepared using pure water.

[0089] Take a clean 10mL colorimetric bottle, add nitrate standard solutions of various concentrations and dilute to the mark, add one packet of water quality nitrate detection reagent from Example 1, shake the water sample in the colorimetric bottle until the water quality nitrate detection reagent dissolves, wait 20s, and test the absorbance value of the standard colorimetric solution at a wavelength of 520nm on a colorimeter, using pure water as a reference and a 1cm cuvette, and plot a standard curve.

[0090] The standard curve equation is: C = 11.638A - 0.0246, R 2 =0.999, the test range is 0.02~30mg / L, where C is the nitrate concentration and A is the colorimetric absorbance.

[0091] (4) Sample testing

[0092] Take a clean colorimetric bottle and add four different water samples to the 10mL mark. Develop the color according to the standard solution test method. Place the colorimetric bottle on a white PVC plate to remove background interference. Compare the color with the standard colorimetric card from the bottle opening downwards. The concentration indicated by the color scale on the colorimetric card that is the same as or similar to the hue of the solution in the bottle is the nitrate content in the sample solution. Simultaneously, use a DR3900 spectrophotometer to measure the absorbance of the colorimetric bottle. Substitute the absorbance into the above standard curve equation to calculate the nitrate content. If the water sample test result exceeds the range, it can be appropriately diluted before testing. A spiked recovery test was also conducted based on the photometric test results. The water sample test results are shown in Table 3 below.

[0093] Table 3. Water sample test results

[0094]

[0095] Note: When testing with actual sample A, the measurement range was exceeded. The sample was diluted 10 times and tested again. The test results for water sample A above are obtained by multiplying the measured data by the dilution factor. Spiking tests involve adding a standard substance to the original water sample.

[0096] The results in Table 3 show that the colorimetric and photometric methods yielded consistent results when using the water nitrate detection reagent of this invention. This reagent is highly suitable for rapid on-site detection of nitrates in water, and is applicable to the detection of water containing chloride ions, food-related organic matter interference, and nutrient-rich beverages. The spiked recoveries ranged from 98.00% to 104.00%, indicating that water samples containing salt, sugar, or other food additives, as well as conventional river water, can be directly measured after simple preparation or dilution, and the test results are reliable.

[0097] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, it is not limited to those listed in the embodiments. Those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A reagent for detecting nitrates in water, characterized in that, The raw materials for preparation include chromogenic particles, a reducing agent, a diazotizing reagent, and an acid reagent. The chromogenic particles comprise dihydroxynaphthalene sulfonic acid compounds coated with an outer membrane, and the reducing agent comprises Cu / MnO with a three-dimensional porous nanostructure. X A mixture, wherein x≤2, of the Cu / MnO X The purity of the mixture is ≥98%, Cu and MnO X The mass ratio is 1:2~6, the acid reagent is a weak organic acid, and the outer film is formed by coating the color developer with a solution containing a film-forming agent and an adhesive and then drying it. The film-forming agent includes polyvinyl alcohol, and the adhesive includes sodium carboxyethyl cellulose or sodium polyacrylate.

2. The water nitrate detection reagent according to claim 1, characterized in that, By weight percentage, the colorimetric particles comprise 55-73%, the reducing agent comprises 15-25%, the diazotizing agent comprises 10-15%, and the acid reagent comprises 2-5%.

3. The water nitrate detection reagent according to claim 1, characterized in that, The mass ratio of the color developer to the solution is 1:5~10, the content of the film-forming agent in the solution is 80~125g / L, and the content of the binder in the solution is 22~40g / L.

4. The water nitrate detection reagent according to claim 1, characterized in that, The diazotizing agent includes p-aminobenzenesulfonate compounds.

5. The water nitrate detection reagent according to claim 1, characterized in that, The acid reagent is at least one of maleic acid, fumaric acid, and tartaric acid.

6. The method for preparing the water nitrate detection reagent according to any one of claims 1 to 5, characterized in that, The colorimetric particles, the reducing agent, the diazotizing agent, and the acid reagent are mixed and quantitatively packaged into bags, with a packaging amount of 0.2~0.5g / bag.

7. A method for detecting nitrates in water, characterized in that, Including the following steps: 1) Add the water nitrate detection reagent according to any one of claims 1 to 5 to the colorimetric bottle containing the water sample to be tested; 2) Shake the colorimetric bottle until the water nitrate test reagent dissolves, then wait 20-60 seconds; 3) Use a standard colorimetric card for color comparison to semi-quantitatively determine the nitrate content in the water sample to be tested, or, after plotting a standard curve, use a colorimeter to measure and quantitatively determine the nitrate content in the water sample to be tested.

8. The method for detecting nitrate in water according to claim 7, characterized in that, The method for preparing the standard colorimetric card includes the following steps: ① Prepare nitrate standard solutions with concentrations of 0.02 mg / L, 0.05 mg / L, 0.10 mg / L, 0.20 mg / L, 0.30 mg / L, 0.50 mg / L, 0.80 mg / L, 1.00 mg / L, 3.00 mg / L, 5.00 mg / L, 10.00 mg / L, 15.00 mg / L, 20.00 mg / L, and 30.00 mg / L respectively using water; ② Add a 0.02 mg / L nitrate standard solution to a clean colorimetric bottle and dilute to the mark. Add the water quality nitrate detection reagent, shake the water sample in the colorimetric bottle until the nitrate is dissolved, wait 20 seconds, and find the corresponding standard color on the Pantone color chart. ③ Repeat step ② to test nitrate standard solutions with concentrations of 0.05 mg / L, 0.10 mg / L, 0.20 mg / L, 0.30 mg / L, 0.50 mg / L, 0.80 mg / L, 1.00 mg / L, 3.00 mg / L, 5.00 mg / L, 10.00 mg / L, 15.00 mg / L, 20.00 mg / L, and 30.00 mg / L, and identify the corresponding standard colors; ④ Prepare a standard colorimetric card based on the color values ​​of the standard colors at each concentration.

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