Water quality total nitrogen detection reagent and preparation method thereof

Abstract

The invention belongs to the technical field of water quality total nitrogen detection, and relates to a water quality total nitrogen detection reagent and a preparation method thereof. The water quality total nitrogen detection reagent comprises a sodium nitrate standard working solution, an alkaline potassium persulfate solution, a monopotassium phosphate buffer solution and a potassium persulfate activator. The water quality total nitrogen detection reagent can be used for detecting the total nitrogen content of a water sample.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of water quality detection, and relates to a water quality total nitrogen detection reagent and a preparation method thereof. BACKGROUND

[0002] In the field of water quality detection, the total nitrogen content is one of the core indexes for evaluating the eutrophication degree and pollution condition of water bodies. At present, the mainstream total nitrogen detection technology is mainly based on the alkaline potassium persulfate digestion-ultraviolet spectrophotometry method. The core principle is to generate sulfate free radicals (SO4 - ) by decomposing potassium persulfate under high temperature and high pressure conditions (120-124℃, 30-60min), and then oxidize all forms of nitrogen (such as ammonia nitrogen, nitrite nitrogen and organic nitrogen (such as urea and protein)) in the water sample into nitrate nitrogen. Finally, the absorbance is measured by ultraviolet spectrophotometry, and the total nitrogen content is calculated.

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

[0004] In view of the above problems of the prior art, the application provides an improved water quality total nitrogen detection reagent. The reagent introduces a new type of potassium persulfate activator, which is composed of magnetic Fe3O4 magnetic beads and an auxiliary agent with a specific structure. The activator can effectively activate potassium persulfate to generate sulfate free radicals (SO4 - ) at 20-25℃, significantly enhance the oxidation ability, and realize efficient and rapid conversion of inorganic nitrogen and organic nitrogen.

[0005] To achieve the above purpose, the technical scheme of the application is as follows: In a first aspect, the application provides a water quality total nitrogen detection reagent, which comprises: 130-160mL of sodium nitrate standard solution (calculated in terms of N); 50-80mL of alkaline potassium persulfate solution; 20-30mL of potassium dihydrogen phosphate buffer solution; and 1-1.5g 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 Fe3O4 magnetic beads; the preparation method of the auxiliary agent is as follows: vinyltriethoxysilane, nanometer cerium dioxide with a particle size of 10-50 nm and sodium carboxymethyl cellulose are dispersed in anhydrous ethanol and ultrasonically mixed for 40-50 min; then a polyamidoamine dendrimer crosslinking agent is added and stirred at a temperature of 60-70 DEG C and a stirring speed of 200-250 r / min for 5-6 h; after the reaction is completed, the product is centrifugally separated (at a rotating speed of 4000-5000 r / min for 10-15 min), 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.

[0006] In the present application, the preparation method of the potassium persulfate activator is as follows: the magnetic Fe3O4 magnetic beads with a particle size of 50-200 nm are mixed with the auxiliary agent coated on the surface of the magnetic Fe3O4 magnetic beads, anhydrous ethanol is added to just immerse the solid, and ultrasonic dispersion is performed for 30-40 min to make the auxiliary agent uniformly coated on the surface of the Fe3O4 magnetic beads; then centrifugal separation is performed at a rotating speed of 3000-4000 r / min for 8-10 min, the supernatant is removed, and then the solid is vacuum dried at 50-60 DEG C for 4-5 h to obtain the potassium persulfate activator.

[0007] Preferably, the polyamidoamine dendrimer crosslinking agent is obtained by modifying a polyamidoamine dendrimer with succinic anhydride at a mass ratio of 1:0.2-1:0.5, and then modifying with titanium isopropylate at a mass ratio of 1:0.1-1:0.3.

[0008] Preferably, the basic potassium persulfate solution comprises potassium persulfate and sodium hydroxide.

[0009] Preferably, the mass ratio of the magnetic Fe3O4 magnetic beads to the auxiliary agent in the potassium persulfate activator is 1:6-1:10.

[0010] Preferably, in the preparation method of the auxiliary agent, the mass ratio of the vinyltriethoxysilane, nanometer cerium dioxide and sodium carboxymethyl cellulose is 1:0.1-0.3:0.8-1.2; the mass-volume ratio of the mixture of the vinyltriethoxysilane, nanometer cerium dioxide and sodium carboxymethyl cellulose to anhydrous ethanol is 1 g:8-12 mL; and the mass ratio of the polyamidoamine dendrimer crosslinking agent to the mixture obtained by ultrasonically mixing the vinyltriethoxysilane, nanometer cerium dioxide and sodium carboxymethyl cellulose in anhydrous ethanol is 0.1-0.2:1.

[0011] Preferably, the preparation method of the sodium nitrate standard solution is as follows: 0.065-0.075 g of sodium nitrate dried at 105-115 ℃ for 2-3 h is dissolved in water and diluted to 1000 mL, and the obtained filtrate after being filtered through a 0.45 μm water filter membrane is the sodium nitrate standard solution.

[0012] Preferably, 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 water to obtain a potassium persulfate solution; 12-18 g of sodium hydroxide is dissolved in 250-350 mL of 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 to obtain a mixed solution, and finally the mixed solution is diluted to 1000 mL with water, and the obtained solution is the alkaline potassium persulfate solution after being stirred.

[0013] More preferably, the mass ratio of the potassium persulfate to the sodium hydroxide is 3:1.

[0014] Preferably, 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 to 1000 mL of water under stirring until completely dissolved to obtain a potassium dihydrogen phosphate initial solution; 0.08-0.12 mol / L of a sodium hydroxide solution is added dropwise to the potassium dihydrogen phosphate initial solution under stirring until the pH is stabilized at 6.0-6.5; the supernatant of the solution after being placed at 20-25 ℃ for 18-24 h is filtered through a 0.45 μm water filter membrane, and the obtained filtrate is the potassium dihydrogen phosphate buffer solution.

[0015] In another aspect, the application provides a preparation method of the water quality total nitrogen detection reagent, and the preparation method comprises the following steps: After the potassium persulfate activator is added to the alkaline potassium persulfate solution, the mixture is placed in an ultrasonic instrument and stirred at 20-25 ℃ for 25-35 min (ultrasonic power: 300-500 W) to obtain an activator and oxidant mixture. The sodium nitrate standard solution is added to the activator and oxidant mixture and stirred gently, and then the potassium dihydrogen phosphate buffer solution is slowly added and stirred until the system is uniform to obtain the water quality total nitrogen detection reagent.

[0016] It should be noted that the above water quality total nitrogen detection reagent is a total nitrogen detection reagent mother liquor which can be directly used for water sample detection. During detection, the reagent mother liquor and the water sample are mixed in a volume ratio of 5:1-10:1, and stirred at 20-25 ℃ for 15-20 min to activate the activator to generate sufficient SO4 -The inorganic nitrogen and the organic nitrogen in the water sample are completely oxidized into nitrate nitrogen, and then the absorbance can be measured at 220 nm and 275 nm wavelengths by a UV spectrophotometer, and the total nitrogen content of the water sample is calculated according to the formula A=A 220 -2A 275 The corrected absorbance is calculated, and the total nitrogen content of the water sample is calculated by combining the standard curve established by the sodium nitrate standard solution.

[0017] In another aspect, the application provides the use of the water quality total nitrogen detection reagent in detecting the total nitrogen content in the water body.

[0018] Compared with the prior art, the application has the following beneficial effects: (1) The potassium persulfate activator structure of the application, which 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, can ensure uniform dispersion of the active site on the surface of the activator, avoid agglomeration and impurity wrapping, and thus effectively activate potassium persulfate to generate sulfate radicals (SO4 - ·) at room temperature (20-25℃), significantly enhance the oxidation ability, and realize efficient and rapid conversion of inorganic nitrogen and organic nitrogen. Furthermore, by using the activator structure in which the magnetic Fe3O4 magnetic beads and the auxiliary agent are compounded at a mass ratio of 1:6-1:10, and by using the raw material ratio of vinyltriethoxysilane, nanometer cerium dioxide, and sodium carboxymethyl cellulose in the preparation of the auxiliary agent, and by using the ratio of polyamide-amine dendrimer crosslinking agent, the surface active site of the activator is uniformly dispersed, agglomeration and impurity wrapping are avoided, and the stability of the auxiliary agent and the magnetic beads is further enhanced by modifying the polyamide-amine dendrimer crosslinking agent with succinic anhydride carboxylation and titanium tetraisopropyl titanate chelation, so that the generation rate of sulfate radicals is significantly improved, and the relative error of the oxidation efficiency of difficult-to-oxidize organic nitrogen is controlled within ±3%. It can be seen that the new activator of the application can improve the utilization rate of potassium persulfate at room temperature and normal pressure, and can output high-concentration sulfate radicals; the ultra-high potential and flux of sulfate radicals can instantaneously pull all inorganic nitrogen and organic nitrogen to the highest valence NO3 - , thereby realizing a complete closed loop of enhanced oxidation ability, doubled reaction rate, and efficient and rapid conversion. In addition, the activator of the application can continuously activate potassium persulfate during the detection stage to generate sufficient free radicals, completely oxidize the inorganic nitrogen and the organic nitrogen in the water sample, avoid detection deviation caused by incomplete oxidation, and realize high-sensitivity and high-repeatability total nitrogen detection by combining with the ultraviolet spectrophotometry method.

[0019] (2) The application optimizes the ratio and adding order of the alkaline potassium persulfate solution, the sodium nitrate standard solution and the potassium dihydrogen phosphate buffer solution in the detection reagent, so that the whole detection process does not need high-temperature digestion, the operation steps are simplified, the detection efficiency and accuracy are improved, and it is especially suitable for on-site rapid detection and large-scale sample analysis. It can be seen that the application effectively overcomes the problems of high energy consumption, long time consumption, complicated operation and incomplete oxidation of refractory nitrogen compounds in the traditional method, and has good application prospect.

[0020] (3) In the preparation method of the water quality total nitrogen detection reagent, the logical steps of pre-mixing the activator and the oxidant, adjusting the standard solution and the buffer solution can avoid the influence of pH adjustment on the activation efficiency, make the connection between the reagent mixing and the subsequent detection more smooth. In addition, when using the water quality total nitrogen detection reagent of the application, only the reagent mother liquor and water sample need to be mixed in proportion, and the digestion and oxidation can be completed by stirring at room temperature, the total detection time is significantly shortened, and no special digestion equipment is needed, which is suitable for on-site rapid detection and large-scale water quality monitoring scene. DETAILED DESCRIPTION

[0021] The advantages and various effects of the application will be more clearly presented by the following specific embodiments and examples. Those skilled in the art should understand that the specific embodiments and examples are used to illustrate the application, not to limit the application.

[0022] In the following, the technical solutions of the application will be described in conjunction with examples, but the application is not limited to the following examples. The experimental methods and detection methods described in each example are conventional methods unless otherwise specified. The reagents and materials described are commercially available unless otherwise specified.

[0023] In the embodiments of the application, the preparation method of the sodium nitrate standard solution is as follows: 0.065-0.075 g of sodium nitrate (purity ≥ 99.9%) dried at 105-115°C for 2-3 h is dissolved with ammonia-free water and constant volume to 1000 mL, and the obtained filtrate after shaking and filtering through a 0.45 μm water filter membrane is the sodium nitrate standard solution.

[0024] In the embodiment of the present application, the preparation method of the alkaline potassium persulfate solution is as follows: 36-44 g of potassium persulfate (nitrogen content ≤0.0005%) is dissolved in 500-700 mL of ammonia-free water, and stirred until completely dissolved to obtain a potassium persulfate solution; 12-18 g of sodium hydroxide (nitrogen content ≤0.0005%) is dissolved in 250-350 mL 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 °C, the potassium persulfate solution is slowly added to the sodium hydroxide solution under stirring (200-250 r / min) to obtain a mixed solution, and finally the mixed solution is diluted to 1000 mL with ammonia-free water and shaken to obtain the alkaline potassium persulfate solution.

[0025] In the preferred embodiment of the present application, the mass ratio of potassium persulfate to sodium hydroxide is 3:1.

[0026] In the embodiment of the present application, the preparation method of the potassium dihydrogen phosphate buffer solution is as follows: 13.5-13.7 g of potassium dihydrogen phosphate (nitrogen content ≤0.0005%) is slowly added to 1000 mL of ammonia-free water, and stirred with a magnetic stirrer (speed 200-250 r / min) until completely dissolved to obtain a potassium dihydrogen phosphate initial solution; 0.08-0.12 mol / L of a sodium hydroxide solution (nitrogen content ≤0.0005%) is added dropwise to the potassium dihydrogen phosphate initial solution while stirring, and the pH of the solution is monitored in real time until the pH is stabilized at 6.0-6.5; the solution after adjusting the pH is placed in a clean polyethylene container, and the supernatant after standing at 20-25 °C for 18-24 h is filtered through a 0.45 μm water filter membrane, and the filtrate is collected to obtain the potassium dihydrogen phosphate buffer solution.

[0027] It should be noted that the ammonia-free water should meet the requirements of HJ636-2012 "Determination of Total Nitrogen in Water - Alkaline Potassium Persulfate Digestion Ultraviolet Spectrophotometry", and the ammonia nitrogen should be ≤0.001 mg / L.

[0028] Example 1 The present embodiment provides a water quality total nitrogen detection reagent, which comprises: 130 mL of sodium nitrate standard solution, calculated as N; 50 mL of alkaline potassium persulfate solution, the alkaline potassium persulfate solution comprising potassium persulfate and sodium hydroxide; 20 mL of potassium dihydrogen phosphate buffer solution; and 1 g of potassium persulfate activator; 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. 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.

[0029] Example 2 This embodiment provides a water quality total nitrogen detection reagent, which includes: 160 mL of sodium nitrate standard working solution (calculated as N); 80 mL of alkaline potassium persulfate solution, wherein the alkaline potassium persulfate solution contains potassium persulfate and sodium hydroxide; 30 mL potassium dihydrogen phosphate buffer solution; and 1.5 g potassium persulfate activator; 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. 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.

[0030] Example 3 This embodiment provides a water quality total nitrogen detection reagent, which includes: 140 mL of sodium nitrate standard working solution (calculated as N); 60 mL of alkaline potassium persulfate solution, wherein the alkaline potassium persulfate solution contains potassium persulfate and sodium hydroxide; 22 mL potassium dihydrogen phosphate buffer solution; and 1.2 g potassium persulfate activator; 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. 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.

[0031] Example 4 This embodiment provides a method for preparing a reagent for detecting total nitrogen in water, the method comprising the following steps: 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; 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.

[0032] Comparative Example 1 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.

[0033] Comparative Example 2 This comparative example is the same as Example 3, except that no polyamide-amine dendritic polymer crosslinking agent is added.

[0034] Comparative Example 3 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.

[0035] Effect verification 1. Experimental reagents and samples 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); 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); 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; 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.

[0036] 2. Experimental Methods 1) Total nitrogen detection in samples: 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: Relative error = (average detected value - theoretical value) / theoretical value × 100%; 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. The results are shown in Table 1.

[0037] 2) Determination of the relative generation rate of sulfate free radicals: 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.

[0038] 3) Activator stability test: 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.

[0039] Table 1. Results of total nitrogen detection in samples

[0040] 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.

[0041] Table 2. Results of relative formation rates of sulfate free radicals

[0042] Note: The formula for calculating the relative improvement rate is (Example rate - Comparative rate) / Comparative rate × 100%.

[0043] 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.

[0044] Table 3 Results of Activator Stability Test

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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 reagent for detecting total nitrogen in water, characterized in that, The water quality total nitrogen detection reagent includes: 130-160 mL of sodium nitrate standard working solution (calculated as N); 50-80 mL of alkaline potassium persulfate solution; 20-30 mL potassium dihydrogen phosphate buffer solution; and 1-1.5 g potassium persulfate activator; 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 and sodium carboxymethyl cellulose in anhydrous ethanol and ultrasonically mixing for 40-50 min; then adding a polyamide-amine dendritic polymer crosslinking agent and stirring at 60-70 °C for 5-6 h; after the reaction, centrifuging to separate the product and washing with anhydrous ethanol, and vacuum drying the washed precipitate at 60-70 °C for 7-8 h to obtain the additive.

2. The water quality total nitrogen detection reagent according to claim 1, characterized in that, 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.

3. The water quality total nitrogen detection reagent according to claim 1, characterized in that, The alkaline potassium persulfate solution comprises potassium persulfate and sodium hydroxide.

4. The water quality total nitrogen detection reagent according to claim 1, characterized in that, The mass ratio of magnetic Fe3O4 beads to additives in the potassium persulfate activator is 1:6-1:

10.

5. The water quality total nitrogen detection reagent according to claim 1, characterized in that, 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.

6. The water quality total nitrogen detection reagent according to claim 1, characterized in that, 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. The resulting filtrate is the sodium nitrate standard working solution.

7. The water quality total nitrogen detection reagent according to claim 1, characterized in that, 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.

8. The water quality total nitrogen detection reagent according to claim 1, characterized in that, The method for preparing the potassium dihydrogen phosphate buffer solution is 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 after standing at 20-25℃ for 18-24h is filtered through a 0.45μm aqueous filter membrane, and the filtrate is collected as potassium dihydrogen phosphate buffer solution.

9. The method for preparing the water quality total nitrogen detection reagent according to any one of claims 1-8, characterized in that, The preparation method includes the following steps: Add potassium persulfate activator to alkaline potassium persulfate solution and place in an ultrasonic instrument at 20-25℃ for 25-35 minutes to ultrasonically stir, thereby obtaining a mixture of activator and oxidant; Add the sodium nitrate standard working solution to the mixture of activator and oxidant and shake well; then slowly add potassium dihydrogen phosphate buffer solution while stirring until the system is homogeneous to obtain the water quality total nitrogen detection reagent.

10. The application of the water quality total nitrogen detection reagent according to any one of claims 1-8 in detecting the total nitrogen content in water bodies.

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