A reagent for detecting total nitrogen in water and its preparation method

Abstract

This invention belongs to the field of total nitrogen detection technology in water quality, and relates to a reagent for detecting total nitrogen in water quality and its preparation method. The reagent comprises sodium nitrate standard working solution, alkaline potassium persulfate solution, potassium dihydrogen phosphate buffer solution, and potassium persulfate activator. This reagent can be used for detecting the total nitrogen content in water samples.

Description

Technical Field

[0001] This invention belongs to the field of water quality testing technology, and relates to a water quality total nitrogen detection reagent and its preparation method. Background Technology

[0002] In the field of water quality testing, total nitrogen (TNO) content is one of the core indicators for assessing the eutrophication level and pollution status of water bodies. Currently, the mainstream TNO detection technology is mainly based on alkaline potassium persulfate digestion-ultraviolet spectrophotometry. Its core principle is the decomposition of potassium persulfate under high temperature and high pressure conditions (120-124℃, 30-60 min) to generate sulfate free radicals (SO42-4 ppm). - The process involves oxidizing all forms of nitrogen in the water sample, including ammonia nitrogen, nitrite nitrogen, and organic nitrogen (such as urea and protein), into nitrate nitrogen. The absorbance is then measured by ultraviolet spectrophotometry to calculate the total nitrogen content.

[0003] In addition, some technologies introduce catalysts or activators to lower the decomposition temperature of potassium persulfate and shorten the digestion time, but existing technologies still have problems such as complex operation and low detection efficiency. Summary of the Invention

[0004] To address the shortcomings of the existing technology, this invention provides an improved reagent for detecting total nitrogen in water. This reagent introduces a novel potassium persulfate activator, which is composed of magnetic Fe3O4 beads and an additive with a specific structure. This activator can effectively activate potassium persulfate to generate sulfate free radicals (SO4⁻) at 20-25℃. - It significantly enhances oxidation capacity, enabling efficient and rapid conversion of inorganic and organic nitrogen.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] In a first aspect, the present invention provides a water quality total nitrogen detection reagent, the water quality total nitrogen detection reagent comprising:

[0007] 130-160 mL of sodium nitrate standard working solution (calculated as N);

[0008] 50-80 mL of alkaline potassium persulfate solution;

[0009] 20-30 mL potassium dihydrogen phosphate buffer solution; and 1-1.5 g potassium persulfate activator;

[0010] The potassium persulfate activator is composed of magnetic Fe3O4 beads with a particle size of 50-200 nm and an additive coated on their surface. The additive is prepared by dispersing vinyltriethoxysilane, nano-cerium dioxide with a particle size of 10-50 nm and sodium carboxymethyl cellulose in anhydrous ethanol and ultrasonically mixing for 40-50 min. Then, a polyamide-amine dendritic polymer crosslinking agent is added and the mixture is stirred at 60-70 °C and 200-250 r / min for 5-6 h. After the reaction, the product is separated by centrifugation (4000-5000 r / min for 10-15 min) and washed with anhydrous ethanol. The washed precipitate is then vacuum dried at 60-70 °C for 7-8 h to obtain the additive.

[0011] In this invention, the preparation method of the potassium persulfate activator is as follows: magnetic Fe3O4 beads with a particle size of 50-200 nm are mixed with an additive coated on their surface, and then anhydrous ethanol that just submerges the solid is added and ultrasonically dispersed for 30-40 min to make the additive uniformly coated on the surface of Fe3O4 beads; then centrifuged at a speed of 3000-4000 r / min for 8-10 min, the supernatant is removed, and then the solid is vacuum dried at 50-60℃ for 4-5 h to obtain the potassium persulfate activator.

[0012] Preferably, the polyamide-amine dendritic polymer crosslinking agent is obtained by modifying polyamide-amine dendritic polymer with succinic anhydride at a mass ratio of 1:0.2-1:0.5, and then modifying it with tetraisopropyl titanate at a mass ratio of 1:0.1-1:0.3.

[0013] Preferably, the alkaline potassium persulfate solution comprises potassium persulfate and sodium hydroxide.

[0014] Preferably, the mass ratio of magnetic Fe3O4 beads to additives in the potassium persulfate activator is 1:6-1:10.

[0015] Preferably, in the preparation method of the auxiliary agent, the mass ratio of vinyltriethoxysilane, nano-cerium dioxide, and sodium carboxymethyl cellulose is 1:0.1-0.3:0.8-1.2; the mass-volume ratio of the mixture of vinyltriethoxysilane, nano-cerium dioxide, and sodium carboxymethyl cellulose to anhydrous ethanol is 1g:8-12mL; and the mass ratio of the mixture obtained by ultrasonically mixing the polyamide-amine dendritic polymer crosslinking agent with vinyltriethoxysilane, nano-cerium dioxide, and sodium carboxymethyl cellulose dispersed in anhydrous ethanol is 0.1-0.2:1.

[0016] Preferably, the preparation method of the sodium nitrate standard working solution is as follows: 0.065-0.075g of sodium nitrate dried at 105-115℃ for 2-3h is dissolved in ammonia-free water and the volume is adjusted to 1000mL. After shaking well, the solution is filtered through a 0.45μm aqueous filter membrane, and the resulting filtrate is the sodium nitrate standard working solution.

[0017] Preferably, the alkaline potassium persulfate solution is prepared as follows: 36-44g of potassium persulfate is dissolved in 500-700mL of ammonia-free water to obtain a potassium persulfate solution; 12-18g of sodium hydroxide is dissolved in 250-350mL of ammonia-free water to obtain a sodium hydroxide solution; after the sodium hydroxide solution is cooled to 20-25℃, the potassium persulfate solution is slowly added to the sodium hydroxide solution under stirring and mixed evenly to obtain a mixed solution; finally, the mixed solution is diluted to 1000mL with ammonia-free water and shaken well to obtain the alkaline potassium persulfate solution.

[0018] More preferably, the mass ratio of potassium persulfate to sodium hydroxide is 3:1.

[0019] Preferably, the potassium dihydrogen phosphate buffer solution is prepared as follows: 13.5-13.7g of potassium dihydrogen phosphate is slowly added to 1000mL of ammonia-free water and stirred until completely dissolved to obtain an initial potassium dihydrogen phosphate solution; 0.08-0.12mol / L sodium hydroxide solution is added dropwise to the initial potassium dihydrogen phosphate solution while stirring until the pH stabilizes at 6.0-6.5; the supernatant of the pH-adjusted solution is filtered through a 0.45μm aqueous filter membrane after standing at 20-25℃ for 18-24h, and the collected filtrate is the potassium dihydrogen phosphate buffer solution.

[0020] On the other hand, a method for preparing the water quality total nitrogen detection reagent according to the present invention is provided, the preparation method comprising the following steps:

[0021] Add potassium persulfate activator to alkaline potassium persulfate solution and place in an ultrasonic instrument at 20-25℃ for 25-35 minutes (ultrasonic power 300-500W) to obtain a mixture of activator and oxidant;

[0022] Add the sodium nitrate standard working solution to the mixture of activator and oxidant and shake gently; then slowly add potassium dihydrogen phosphate buffer solution while stirring until the system is homogeneous to obtain the water quality total nitrogen test reagent.

[0023] It should be noted that the above-mentioned total nitrogen test reagent is the stock solution of the total nitrogen test reagent that can be directly used for water sample testing. During testing, measure the stock solution and mix it with the water sample at a volume ratio of stock solution to water sample of 5:1-10:1. Stir at 20-25℃ for 15-20 minutes to allow the activator to activate the remaining potassium persulfate and generate sufficient SO4. -• The inorganic and organic nitrogen in the water sample is completely oxidized to nitrate nitrogen. The absorbance can then be measured at wavelengths of 220 nm and 275 nm using a UV spectrophotometer, and calculated using the formula A = A 220 -2A 275 Calculate the corrected absorbance and, using the standard curve established with sodium nitrate standard working solution, calculate the total nitrogen content of the water sample.

[0024] On the other hand, the present invention provides the application of the water quality total nitrogen detection reagent in detecting the total nitrogen content in water bodies.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] (1) The potassium persulfate activator structure of the present invention, which is composed of magnetic Fe3O4 beads with a particle size of 50-200nm and additives coated on its surface, can ensure that the active sites on the surface of the activator are uniformly dispersed, avoiding agglomeration and impurity encapsulation. Thus, it can effectively activate potassium persulfate to generate sulfate free radicals (SO4) at room temperature (20-25℃). - This invention significantly enhances oxidation capacity, achieving efficient and rapid conversion of inorganic and organic nitrogen. Furthermore, by clarifying the activator structure of the composite of magnetic Fe3O4 beads and additives at a mass ratio of 1:6-1:10, and combining the raw material ratios of vinyltriethoxysilane, nano-cerium dioxide, and sodium carboxymethyl cellulose in the additive preparation, as well as the ratio and solid-liquid ratio of the polyamide-amine dendritic polymer crosslinking agent, the active sites on the activator surface are further uniformly dispersed, avoiding agglomeration and impurity encapsulation. In addition, the polyamide-amine dendritic polymer crosslinking agent, after carboxylation with succinic anhydride and chelation modification with tetraisopropyl titanate, further enhances the bonding stability between the additive and the magnetic beads, significantly increasing the sulfate free radical generation rate, and controlling the relative error of the oxidation efficiency for recalcitrant organic nitrogen within ±3%. It is evident that the novel activator of this invention can improve the utilization rate of potassium persulfate under normal temperature and pressure, and can output high concentrations of sulfate free radicals; while the ultra-high potential and flux of sulfate free radicals instantly pull all inorganic and organic nitrogen to the highest oxidation state NO3. - This achieves a complete closed loop of enhanced oxidation capacity, doubled reaction rate, and efficient, rapid conversion. Furthermore, the activator in this invention continuously activates potassium persulfate during the detection stage, generating sufficient free radicals to thoroughly oxidize inorganic and organic nitrogen in the water sample, avoiding detection bias caused by incomplete oxidation. Combined with ultraviolet spectrophotometry, it enables highly sensitive and repeatable detection of total nitrogen.

[0027] (2) The detection reagent of this invention optimizes the ratio and addition order of alkaline potassium persulfate solution, sodium nitrate standard working solution, and potassium dihydrogen phosphate buffer solution, so that the entire detection process does not require high-temperature digestion, simplifying the operation steps and improving detection efficiency and accuracy. It is especially suitable for rapid on-site detection and large-scale sample analysis. It can be seen that this invention effectively overcomes the problems of high energy consumption, long time consumption, cumbersome operation, and incomplete oxidation of recalcitrant nitrogen compounds in traditional methods, and has good application prospects.

[0028] (3) The preparation method of the total nitrogen detection reagent in water quality of the present invention, through the logical steps of pre-mixing the activator and oxidant, adjusting with standard solution and buffer solution, can avoid the influence of pH adjustment on activation efficiency, making the connection between reagent mixing and subsequent detection smoother. In addition, when using the total nitrogen detection reagent in water quality of the present invention, it is only necessary to mix the reagent stock solution and water sample in proportion, and stir at room temperature to complete digestion and oxidation. The total detection time is significantly shortened, and no special digestion equipment is required, making it suitable for on-site rapid detection and large-scale water quality monitoring scenarios. Detailed Implementation

[0029] The present invention will be described in detail below with reference to specific embodiments and examples, thereby making the advantages and various effects of the present invention clearer. Those skilled in the art should understand that these specific embodiments and examples are for illustrative purposes only and are not intended to limit the present invention.

[0030] The technical solution of the present invention will be described below with reference to embodiments. However, the present invention is not limited to the following embodiments. Unless otherwise specified, the experimental methods and detection methods described in each embodiment are conventional methods; unless otherwise specified, the reagents and materials are all commercially available.

[0031] In this embodiment of the invention, the preparation method of sodium nitrate standard working solution is as follows: 0.065-0.075g of sodium nitrate (purity ≥99.9%) dried at 105-115℃ for 2-3h is dissolved in ammonia-free water and the volume is adjusted to 1000mL. After shaking well, the solution is filtered through a 0.45μm aqueous filter membrane, and the resulting filtrate is the sodium nitrate standard working solution.

[0032] In this embodiment of the invention, the alkaline potassium persulfate solution is prepared as follows: 36-44g of potassium persulfate (nitrogen content ≤0.0005%) is dissolved in 500-700mL of ammonia-free water and stirred until completely dissolved to obtain a potassium persulfate solution; 12-18g of sodium hydroxide (nitrogen content ≤0.0005%) is dissolved in 250-350mL of ammonia-free water and stirred until completely dissolved to obtain a sodium hydroxide solution; after the sodium hydroxide solution is cooled to 20-25℃, the potassium persulfate solution is slowly added to the sodium hydroxide solution while stirring and mixed evenly (200-250r / min) to obtain a mixed solution; finally, the mixed solution is diluted to 1000mL with ammonia-free water and shaken well to obtain the alkaline potassium persulfate solution.

[0033] In a preferred embodiment of the present invention, the mass ratio of potassium persulfate to sodium hydroxide is 3:1.

[0034] In this embodiment of the invention, the potassium dihydrogen phosphate buffer solution is prepared as follows: 13.5-13.7g of potassium dihydrogen phosphate (nitrogen content ≤0.0005%) is slowly added to 1000mL of ammonia-free water and stirred with a magnetic stirrer (200-250r / min) until completely dissolved to obtain an initial potassium dihydrogen phosphate solution; 0.08-0.12mol / L sodium hydroxide solution (nitrogen content ≤0.0005%) is added dropwise to the initial potassium dihydrogen phosphate solution while stirring, and the pH of the solution is monitored in real time until the pH stabilizes at 6.0-6.5; the pH-adjusted solution is placed in a clean polyethylene container, and the supernatant after standing at 20-25℃ for 18-24h is filtered through a 0.45μm aqueous filter membrane, and the filtrate is collected as the potassium dihydrogen phosphate buffer solution.

[0035] It should be noted that ammonia-free water must meet the requirements of HJ636-2012 "Determination of Total Nitrogen in Water by Alkaline Potassium Persulfate Digestion Ultraviolet Spectrophotometry", with ammonia nitrogen ≤0.001 mg / L.

[0036] Example 1

[0037] This embodiment provides a water quality total nitrogen detection reagent, which includes:

[0038] 130 mL of sodium nitrate standard working solution (calculated as N);

[0039] 50 mL of alkaline potassium persulfate solution, wherein the alkaline potassium persulfate solution contains potassium persulfate and sodium hydroxide;

[0040] 20 mL potassium dihydrogen phosphate buffer solution; and 1 g potassium persulfate activator;

[0041] The potassium persulfate activator is composed of magnetic Fe3O4 beads with a particle size of 50-200 nm and an auxiliary agent coated on their surface. The preparation method of the potassium persulfate activator is as follows: magnetic Fe3O4 beads with a particle size of 50-200 nm and an auxiliary agent coated on their surface are mixed at a mass ratio of 1:6. Anhydrous ethanol, just enough to submerge the solid, is added and ultrasonically dispersed for 30 min to ensure the auxiliary agent is uniformly coated on the surface of the Fe3O4 beads. The mixture is then centrifuged at 3000 r / min for 8 min, the supernatant is removed, and the solid is vacuum dried at 50°C for 4 h to obtain the potassium persulfate activator. The preparation method of the auxiliary agent is as follows: vinyltriethoxysilane with a particle size of 10 nm is mixed with... -50nm cerium dioxide nanoparticles and sodium carboxymethyl cellulose were dispersed in anhydrous ethanol and ultrasonically mixed (ultrasonic power 300W) for 40 min; then a polyamide-amine dendritic polymer crosslinking agent was added and the mixture was stirred at 60℃ and 200r / min for 5 h; after the reaction, the product was separated by centrifugation (4000r / min, time 10 min) and washed three times with anhydrous ethanol. The precipitate after washing was vacuum dried at 60℃ for 7 h to obtain the additive; the polyamide-amine dendritic polymer crosslinking agent was obtained by modifying polyamide-amine dendritic polymer with succinic anhydride at a mass ratio of 1:0.2, and then modifying it with tetraisopropyl titanate at a mass ratio of 1:0.1.

[0042] In the preparation method of the auxiliary agent, the mass ratio of vinyltriethoxysilane, nano-cerium dioxide and sodium carboxymethyl cellulose is 1:0.1:0.8; the mass-volume ratio of the mixture of vinyltriethoxysilane, nano-cerium dioxide and sodium carboxymethyl cellulose to anhydrous ethanol is 1g:8mL; and the mass ratio of the mixture obtained by ultrasonically mixing the polyamide-amine dendritic polymer crosslinking agent with vinyltriethoxysilane, nano-cerium dioxide and sodium carboxymethyl cellulose dispersed in anhydrous ethanol is 0.1:1.

[0043] Example 2

[0044] This embodiment provides a water quality total nitrogen detection reagent, which includes:

[0045] 160 mL of sodium nitrate standard working solution (calculated as N);

[0046] 80 mL of alkaline potassium persulfate solution, wherein the alkaline potassium persulfate solution contains potassium persulfate and sodium hydroxide;

[0047] 30 mL potassium dihydrogen phosphate buffer solution; and 1.5 g potassium persulfate activator;

[0048] The potassium persulfate activator is composed of magnetic Fe3O4 beads with a particle size of 50-200 nm and an auxiliary agent coated on their surface. The preparation method of the potassium persulfate activator is as follows: magnetic Fe3O4 beads with a particle size of 50-200 nm and an auxiliary agent coated on their surface are mixed at a mass ratio of 1:10. Anhydrous ethanol, just enough to submerge the solid, is added and ultrasonically dispersed for 40 min to ensure the auxiliary agent is uniformly coated on the surface of the Fe3O4 beads. The mixture is then centrifuged at 4000 r / min for 10 min, the supernatant is removed, and the solid is vacuum dried at 60°C for 5 h to obtain the potassium persulfate activator. The preparation method of the auxiliary agent is as follows: vinyltriethoxysilane, with a particle size of 1... 0-50 nm cerium dioxide nanoparticles and sodium carboxymethyl cellulose were dispersed in anhydrous ethanol and ultrasonically mixed (ultrasonic power 500 W) for 50 min. Then, a polyamide-amine dendritic polymer crosslinking agent was added and the mixture was stirred at 70 °C and 250 r / min for 6 h. After the reaction, the product was separated by centrifugation (5000 r / min, time 15 min) and washed three times with anhydrous ethanol. The precipitate after washing was vacuum dried at 70 °C for 8 h to obtain the additive. The polyamide-amine dendritic polymer crosslinking agent was obtained by modifying polyamide-amine dendritic polymer with succinic anhydride at a mass ratio of 1:0.5, and then modifying it with tetraisopropyl titanate at a mass ratio of 1:0.3.

[0049] In the preparation method of the auxiliary agent, the mass ratio of vinyltriethoxysilane, nano-cerium dioxide and sodium carboxymethyl cellulose is 1:0.3:1.2; the mass-volume ratio of the mixture of vinyltriethoxysilane, nano-cerium dioxide and sodium carboxymethyl cellulose to anhydrous ethanol is 1g:12mL; and the mass ratio of the mixture obtained by ultrasonically mixing the polyamide-amine dendritic polymer crosslinking agent with vinyltriethoxysilane, nano-cerium dioxide and sodium carboxymethyl cellulose dispersed in anhydrous ethanol is 0.2:1.

[0050] Example 3

[0051] This embodiment provides a water quality total nitrogen detection reagent, which includes:

[0052] 140 mL of sodium nitrate standard working solution (calculated as N);

[0053] 60 mL of alkaline potassium persulfate solution, wherein the alkaline potassium persulfate solution contains potassium persulfate and sodium hydroxide;

[0054] 22 mL potassium dihydrogen phosphate buffer solution; and 1.2 g potassium persulfate activator;

[0055] The potassium persulfate activator is composed of magnetic Fe3O4 beads with a particle size of 50-200 nm and an auxiliary agent coated on their surface. The preparation method of the potassium persulfate activator is as follows: magnetic Fe3O4 beads with a particle size of 50-200 nm and an auxiliary agent coated on their surface are mixed at a mass ratio of 1:8. Anhydrous ethanol, just enough to submerge the solid, is added and ultrasonically dispersed for 40 min to ensure the auxiliary agent is uniformly coated on the surface of the Fe3O4 beads. The mixture is then centrifuged at 3000 r / min for 9 min, the supernatant is removed, and the solid is vacuum dried at 60°C for 5 h to obtain the potassium persulfate activator. The preparation method of the auxiliary agent is as follows: vinyltriethoxysilane and nanoparticles with a particle size of 10-50 nm are mixed... Cerium dioxide and sodium carboxymethyl cellulose were dispersed in anhydrous ethanol and ultrasonically mixed (ultrasonic power 300W) for 45 min; then a polyamide-amine dendritic polymer crosslinking agent was added and the mixture was stirred at 70℃ and 200 r / min for 6 h; after the reaction, the product was separated by centrifugation (4000 r / min, time 12 min) and washed three times with anhydrous ethanol. The precipitate after washing was vacuum dried at 70℃ for 8 h to obtain the additive; the polyamide-amine dendritic polymer crosslinking agent was obtained by modifying polyamide-amine dendritic polymer (Xi'an Ruixi Biotechnology Co., Ltd.) with succinic anhydride at a mass ratio of 1:0.3, and then modifying it with tetraisopropyl titanate at a mass ratio of 1:0.2.

[0056] In the preparation method of the auxiliary agent, the mass ratio of vinyltriethoxysilane, nano-cerium dioxide and sodium carboxymethyl cellulose is 1:0.2:1; the mass-volume ratio of the mixture of vinyltriethoxysilane, nano-cerium dioxide and sodium carboxymethyl cellulose to anhydrous ethanol is 1g:10mL; and the mass ratio of the mixture obtained by ultrasonically mixing the polyamide-amine dendritic polymer crosslinking agent with vinyltriethoxysilane, nano-cerium dioxide and sodium carboxymethyl cellulose dispersed in anhydrous ethanol is 0.1:1.

[0057] Example 4

[0058] This embodiment provides a method for preparing a reagent for detecting total nitrogen in water, the method comprising the following steps:

[0059] Add potassium persulfate activator to alkaline potassium persulfate solution and place in an ultrasonic instrument at 20-25℃ for 25-35 minutes (ultrasonic power 300-500W) to obtain a mixture of activator and oxidant;

[0060] Add the sodium nitrate standard working solution to the mixture of activator and oxidant and shake gently; then slowly add potassium dihydrogen phosphate buffer solution while stirring until the system is homogeneous to obtain the water quality total nitrogen test reagent.

[0061] Comparative Example 1

[0062] This comparative example is the same as Example 3, except that the potassium persulfate activator is composed of magnetic Fe3O4 beads with a particle size of 50-200nm.

[0063] Comparative Example 2

[0064] This comparative example is the same as Example 3, except that no polyamide-amine dendritic polymer crosslinking agent is added.

[0065] Comparative Example 3

[0066] This comparative example is the same as Example 3, except that sodium carboxymethyl cellulose in the preparation method of the adjuvant is replaced with sodium alginate.

[0067] Effect verification

[0068] 1. Experimental reagents and samples

[0069] 1) Standard nitrogen samples: ① Recalcitrant organic nitrogen samples: Prepare analytical grade urea solution with a theoretical total nitrogen concentration of 2.00 mg / L; ② Inorganic nitrogen samples: Prepare ammonium chloride-sodium nitrite mixture (NH4+) with a theoretical total nitrogen concentration of 2.00 mg / L. + -N:NO2 - -N=1:1);

[0070] 2) Blank and calibration reagents: ammonia-free water (meeting the requirements of HJ636-2012 "Determination of Total Nitrogen in Water by Alkaline Potassium Persulfate Digestion Ultraviolet Spectrophotometry", ammonia nitrogen ≤0.001mg / L), pure sodium nitrate (purity ≥99.9%, used to plot the standard curve);

[0071] 3) Test reagents: Water quality total nitrogen detection reagents (reagent stock solution) prepared according to the preparation method of Example 4 in Examples 1-3 and Comparative Examples 1-3, 3 samples were prepared for each group;

[0072] According to HJ636-2012 "Determination of Total Nitrogen in Water by Alkaline Potassium Persulfate Digestion Ultraviolet Spectrophotometry", a calibration curve for the alkaline potassium persulfate digestion ultraviolet spectrophotometry method was plotted.

[0073] 2. Experimental Methods

[0074] 1) Total nitrogen detection in samples:

[0075] Take 10 mL each of urea solution and inorganic nitrogen sample, and mix them with the six sets of reagent stock solutions at a volume ratio of 1:8. Stir at 20-25℃ for 15-20 min, measure the corrected absorbance of each mixture, substitute it into the standard curve regression equation of the corresponding reagent, calculate the total nitrogen detection concentration, and obtain the following indicators:

[0076] Relative error = (average detected value - theoretical value) / theoretical value × 100%;

[0077] Total detection time: Start timing from the time the sample and reagent stock solution are mixed until the absorbance measurement is completed and stop timing. Record the typical values ​​from three experiments.

[0078] The results are shown in Table 1.

[0079] 2) Determination of the relative generation rate of sulfate free radicals:

[0080] Take 5 mL of each of the 6 groups of reagent stock solutions, add 1 mL of 0.1 mol / L DMSO (purity ≥99.9%) solution, and stir at a constant temperature of 20-25℃. Immediately use a UV spectrophotometer to measure the absorbance at a wavelength of 210 nm every 1 min for 15 min. Plot a curve with time as the abscissa and absorbance as the ordinate, and calculate the slope of each curve (i.e., the relative generation rate of sulfate free radicals). Each group was measured in parallel 3 times, and the average value was taken. The results are shown in Table 2.

[0081] 3) Activator stability test:

[0082] The six sets of reagent stock solutions were stored at 20-25℃ in the dark for 7 days. The detection steps of urea solution in the total nitrogen detection of the samples were repeated. The relative error after storage was calculated and compared with the relative error of the initial detection. The change in error was calculated. The smaller the change in error, the better the stability. The results are shown in Table 3.

[0083] Table 1. Results of total nitrogen detection in samples

[0084]

[0085] As shown in Table 1, the relative errors of Examples 1-3 for all samples were ≤±2.00%, far lower than those of the comparative examples. Furthermore, the relative error of Example 3 for urea solution was only +0.50%. This demonstrates that the detection reagent of the present invention has high accuracy in detecting the oxidation efficiency of recalcitrant organic nitrogen, controlling the relative error within ±3%, exhibiting good accuracy. In addition, the total detection time for Examples 1-3 was ≤28 min, while that for Example 3 was only 21-22 min, significantly shorter than the comparative examples. This indicates that the detection reagent of the present invention can significantly shorten the total detection time and significantly improve the detection efficiency when detecting recalcitrant organic nitrogen.

[0086] Table 2. Results of relative formation rates of sulfate free radicals

[0087]

[0088] Note: The formula for calculating the relative improvement rate is (Example rate - Comparative rate) / Comparative rate × 100%.

[0089] As shown in Table 2, the relative generation rate of sulfate free radicals in Examples 1-3 is significantly higher than that in Comparative Examples 1-3, and the relative generation rate of sulfate free radicals in Example 3 is 3 times that in Comparative Example 1. This directly proves that the detection reagent of the present invention can output a high concentration of sulfate free radicals and significantly enhance the oxidation capacity.

[0090] Table 3 Results of Activator Stability Test

[0091]

[0092] As shown in Table 3, the stability of Examples 1-3 is better. Among them, the error change of Example 3 after 7 days of storage is only 0.50%, which is much lower than that of the comparative example.

[0093] The effectiveness verification experiments show that the potassium persulfate activator structure of this invention, composed of magnetic Fe3O4 beads with a particle size of 50-200 nm and additives coated on their surface, ensures uniform dispersion of active sites on the activator surface, avoiding agglomeration and impurity encapsulation. Therefore, it can effectively activate potassium persulfate to generate sulfate free radicals (SO42-25℃) at room temperature (20-25℃). - This invention significantly enhances oxidation capacity, achieving efficient and rapid conversion of inorganic and organic nitrogen. Furthermore, by clarifying the activator structure of the composite of magnetic Fe3O4 beads and additives at a mass ratio of 1:6-1:10, and combining the raw material ratios of vinyltriethoxysilane, nano-cerium dioxide, and sodium carboxymethyl cellulose in the additive preparation, as well as the ratio and solid-liquid ratio of the polyamide-amine dendritic polymer crosslinking agent, the active sites on the activator surface are further uniformly dispersed, avoiding agglomeration and impurity encapsulation. In addition, the polyamide-amine dendritic polymer crosslinking agent, after carboxylation with succinic anhydride and chelation modification with tetraisopropyl titanate, further enhances the bonding stability between the additive and the magnetic beads, significantly increasing the sulfate free radical generation rate, and controlling the relative error of the oxidation efficiency for recalcitrant organic nitrogen within ±3%. It is evident that the novel activator of this invention can improve the utilization rate of potassium persulfate under normal temperature and pressure, and can output high concentrations of sulfate free radicals; while the ultra-high potential and flux of sulfate free radicals instantly pull all inorganic and organic nitrogen to the highest oxidation state NO3. - This achieves a complete closed loop of enhanced oxidation capacity, doubled reaction rate, and efficient, rapid conversion. Furthermore, the activator in this invention continuously activates potassium persulfate during the detection stage, generating sufficient free radicals to thoroughly oxidize inorganic and organic nitrogen in the water sample, avoiding detection bias caused by incomplete oxidation. Combined with ultraviolet spectrophotometry, it enables highly sensitive and repeatable detection of total nitrogen.

[0094] This invention optimizes the ratio and order of addition of alkaline potassium persulfate solution, sodium nitrate standard solution, and potassium dihydrogen phosphate buffer solution in the detection reagent, eliminating the need for high-temperature digestion during the entire detection process. This simplifies the operation steps and improves detection efficiency and accuracy, making it particularly suitable for rapid on-site detection and large-scale sample analysis. Therefore, this invention effectively overcomes the problems of high energy consumption, long processing time, cumbersome operation, and incomplete oxidation of recalcitrant nitrogen compounds found in traditional methods, demonstrating promising application prospects.

[0095] The preparation method of the total nitrogen detection reagent for water quality of this invention, through the logical steps of pre-mixing the activator and oxidant, adjusting with a standard solution and a buffer solution, avoids the influence of pH adjustment on activation efficiency, making the connection between reagent mixing and subsequent detection smoother. Furthermore, when using the total nitrogen detection reagent of this invention, only the reagent stock solution and water sample need to be mixed in proportion, and digestion and oxidation can be completed by stirring at room temperature. The total detection time is significantly shortened, and no special digestion equipment is required, making it suitable for rapid on-site detection and large-scale water quality monitoring scenarios.

[0096] It should be understood that the disclosed invention is not limited to the specific methods, schemes, and substances described, as these are all subject to variation. It should also be understood that the terminology used herein is for the purpose of describing specific embodiments only and is not intended to limit the scope of the invention, which is limited only by the appended claims.

Claims

1. A water quality total nitrogen detection reagent, characterized by, The water quality total nitrogen detection reagent comprises: 130-160 mL of sodium nitrate standard solution in terms of N; 50-80 mL of alkaline potassium persulfate solution; 20-30 mL of potassium dihydrogen phosphate buffer solution; and 1-1.5 g of potassium persulfate activator; The potassium persulfate activator is composed of magnetic Fe3O4 magnetic beads with a particle size of 50-200 nm and an auxiliary agent coated on the surface of the magnetic beads; the preparation method of the auxiliary agent is as follows: vinyltriethoxysilane, nanometer cerium dioxide and carboxymethyl cellulose sodium are dispersed in anhydrous ethanol and ultrasonically mixed for 40-50 min; then, a polyamidoamine dendrimer crosslinking agent is added and stirred at 60-70 DEG C for 5-6 h; after the reaction is completed, the product is centrifuged and washed with anhydrous ethanol, and the washed precipitate is vacuum dried at 60-70 DEG C for 7-8 h to obtain the auxiliary agent; The polyamidoamine dendrimer crosslinking agent is modified from a polyamidoamine dendrimer and succinic anhydride at a mass ratio of 1:0.2-1:0.5, and then modified from the modified product and titanium isopropylate at a mass ratio of 1:0.1-1:0.3; In the preparation method of the auxiliary agent, the mass ratio of vinyltriethoxysilane, nanometer cerium dioxide and carboxymethyl cellulose sodium is 1:0.1-0.3:0.8-1.2; the mass-volume ratio of the mixture of vinyltriethoxysilane, nanometer cerium dioxide and carboxymethyl cellulose sodium and anhydrous ethanol is 1 g:8-12 mL; and the mass ratio of the polyamidoamine dendrimer crosslinking agent and the mixture obtained by ultrasonically mixing vinyltriethoxysilane, nanometer cerium dioxide and carboxymethyl cellulose sodium in anhydrous ethanol is 0.1-0.2:

1.

2. The water quality total nitrogen test reagent according to claim 1, characterized by, The alkaline potassium persulfate solution comprises potassium persulfate and sodium hydroxide.

3. The water quality total nitrogen test reagent according to claim 1, characterized by, The mass ratio of the magnetic Fe3O4 magnetic beads and the auxiliary agent in the potassium persulfate activator is 1:6-1:

10.

4. The water quality total nitrogen test reagent according to claim 1, characterized by, The preparation method of the sodium nitrate standard solution is as follows: 0.065-0.075 g of sodium nitrate dried at 105-115 DEG C for 2-3 h is dissolved in ammonia-free water and diluted to 1000 mL; after being shaken and filtered through a 0.45 mu m water filter membrane, the filtrate is the sodium nitrate standard solution.

5. The water quality total nitrogen test reagent according to claim 1, characterized by, The preparation method of the alkaline potassium persulfate solution is as follows: 36-44 g of potassium persulfate is dissolved in 500-700 mL of ammonia-free water to obtain a potassium persulfate solution; 12-18 g of sodium hydroxide is dissolved in 250-350 mL of ammonia-free water to obtain a sodium hydroxide solution; after the sodium hydroxide solution is cooled to 20-25 DEG C, the potassium persulfate solution is slowly added to the sodium hydroxide solution under stirring to obtain a mixed solution; finally, the mixed solution is diluted to 1000 mL with ammonia-free water and shaken to obtain the alkaline potassium persulfate solution.

6. The water quality total nitrogen test reagent according to claim 1, characterized by, The preparation method of the potassium dihydrogen phosphate buffer solution is as follows: 13.5-13.7 g of potassium dihydrogen phosphate is slowly added into 1000 mL of ammonia-free water and stirred until completely dissolved to obtain a potassium dihydrogen phosphate initial solution; a 0.08-0.12 mol / L sodium hydroxide solution is added dropwise into the potassium dihydrogen phosphate initial solution while stirring until the pH is stabilized at 6.0-6.5; the supernatant of the solution after pH adjustment is placed at 20-25℃ for 18-24 h, and then filtered through a 0.45 μm water filter membrane to collect the filtrate potassium dihydrogen phosphate buffer solution.

7. A method for preparing a water quality total nitrogen test reagent according to any one of claims 1 to 6, characterized by, The preparation method comprises the following steps: After the potassium persulfate activator is added into the alkaline potassium persulfate solution, the mixture is placed in an ultrasonic instrument and ultrasonically stirred at 20-25℃ for 25-35 min to obtain an activator and oxidant mixture; The sodium nitrate standard solution is added into the activator and oxidant mixture and shaken well; then the potassium dihydrogen phosphate buffer solution is slowly added while stirring until the system is uniform to obtain a water quality total nitrogen detection reagent.

8. Use of the water quality total nitrogen detection reagent according to any one of claims 1-6 in detecting the total nitrogen content in a water body.

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