A prefabricated reagent bag for detecting ammonia nitrogen in surface water and a preparation method thereof

Abstract

The application relates to the technical field of water quality environment monitoring, and discloses a prefabricated reagent bag for surface water ammonia nitrogen detection and a preparation method thereof. The prefabricated reagent bag for surface water ammonia nitrogen detection comprises independently packaged pre-adjusted reagent C, high-alkali color developing reagent A and oxidation color developing reagent B. The pre-adjusted reagent C is used for constructing a weak-alkali buffer system; the high-alkali color developing reagent A comprises micro-bead-shaped sodium hydroxide and sodium salicylate matrix particles, realizes physical isolation of strong alkali and easily-degradable components; and the oxidation color developing reagent B comprises coated sodium dichloroisocyanurate microcapsules, and the water-soluble pore-forming agent is used for controlling the effective chlorine release rate. Through reagent sub-packaging, step-by-step addition, powder granulation and microcapsule coating processes, powder moisture absorption and caking and component cross-reaction are avoided, color developing side reactions are controlled, and the stability and reproducibility of detection are improved.

Description

Technical Field

[0001] This invention relates to the field of water quality environmental monitoring technology, specifically to a pre-made reagent package for detecting ammonia nitrogen in surface water and its preparation method. Background Technology

[0002] Salicylic acid spectrophotometry is a commonly used standard method for detecting ammonia nitrogen in surface water. In practice, conventionally prepared liquid reagents suffer from chemical instability, susceptibility to oxidation and degradation, and short shelf life. To extend reagent shelf life and facilitate field use, the industry often prepares the test reagents as a solid mixed powder.

[0003] However, existing solid powder reagents are highly susceptible to hygroscopic agglomeration during preparation and storage. Because the strong base, the chromogenic substrate salicylate, and the oxidant are components with different chemical properties, direct mixing and contact can easily lead to cross-compatibility reactions during storage, causing premature reagent failure. In the actual water sample detection dissolution stage, the instantaneous dissolution of the powdered strong base in the mixed reagent causes a dramatic local pH jump and exothermic reaction. This uncontrollable change in the system environment can easily lead to the precipitation of calcium and magnesium ions as hydroxides, causing optical interference. Simultaneously, the uncontrolled and rapid release of the oxidant after entering the water results in excessively strong instantaneous oxidizing power within the system, triggering non-chromogenic side reactions such as over-oxidation of the salicylic acid substrate. The combination of these factors leads to problems such as high background blanks and poor reproducibility of low-concentration ammonia nitrogen signals when using existing solid reagents, affecting the accuracy of the analytical results.

[0004] Therefore, this invention proposes a pre-made reagent package for the detection of ammonia nitrogen in surface water and its preparation method to overcome the shortcomings of the prior art. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a pre-made reagent package for ammonia nitrogen detection in surface water and its preparation method. This solves the problems of existing solid reagents for ammonia nitrogen detection being prone to moisture absorption and clumping during storage, cross-inactivation, and increased colorimetric side reactions, high background blank, and poor detection reproducibility due to drastic changes in system pH and uncontrolled release of oxidants during dissolution.

[0006] To address the above problems, the present invention provides the following technical solution:

[0007] In a first aspect, the present invention provides a pre-made reagent package for detecting ammonia nitrogen in surface water, employing the following technical solution:

[0008] A pre-prepared reagent kit for detecting ammonia nitrogen in surface water includes individually packaged pre-conditioning reagent C, high-alkali colorimetric reagent A, and oxidation colorimetric reagent B.

[0009] The pre-conditioning reagent C comprises the following components by weight: 25.0–35.0 parts of anhydrous sodium pyrophosphate, 8.0–15.0 parts of sodium hexametaphosphate, 4.0–8.0 parts of D-mannitol, 10.0–20.0 parts of anhydrous sodium sulfate, 3.0–8.0 parts of boric acid, and 5.0–12.0 parts of anhydrous sodium tetraborate.

[0010] The high-alkali colorimetric reagent A comprises matrix particles and microbeaded sodium hydroxide, wherein the mass ratio of the microbeaded sodium hydroxide to the matrix particles is 15.0–25.0:45.2–82.0. The matrix particles, by weight, comprise the following components: 10.0–15.0 parts sodium salicylate, 15.0–25.0 parts anhydrous sodium carbonate, 10.0–20.0 parts anhydrous sodium pyrophosphate, 2.0–6.0 parts D-mannitol, 8.0–15.0 parts anhydrous sodium sulfate, and 0.2–1.0 parts poloxamer 188.

[0011] The oxidation colorimetric reagent B comprises, by weight, the following components: 0.5–1.5 parts of sodium nitrosoferricyanide dihydrate, 15.0–25.0 parts of anhydrous sodium carbonate, and 1.8–3.5 parts of coated sodium dichloroisocyanurate microcapsules. The coated sodium dichloroisocyanurate microcapsules comprise sodium dichloroisocyanurate and a coating layer covering the surface of the sodium dichloroisocyanurate.

[0012] By adopting the above technical solution, the present invention packages the pre-conditioning component, the high-alkali colorimetric component, and the oxidation colorimetric component separately, and allows sodium dichloroisocyanurate to exist in a coating form, which helps to reduce the mutual influence of different components during storage and use, and allows the water sample to go through the pre-conditioning, high-alkali colorimetric base solution construction, and oxidation colorimetric stages in sequence during the detection process.

[0013] When preconditioning reagent C is added to the aqueous phase, anhydrous sodium pyrophosphate and sodium hexametaphosphate dissolve and complex with calcium and magnesium ions in the water sample. Boric acid and anhydrous sodium tetraborate together provide a buffer environment, adjusting the pH of the system to a low alkaline range of 9.6 to 10.6, which helps reduce turbidity changes in high-hardness water samples during subsequent alkali addition. Anhydrous sodium sulfate and D-mannitol in this stage improve the dispersion and dissolution of powders in water.

[0014] After adding the high-alkali colorimetric reagent A, the microbeaded sodium hydroxide dissolves, and the pH of the system is adjusted to 12.15 to 12.45. Since the water sample has already undergone pre-conditioning, the impact of the localized high-alkali environment on turbidity and the optical baseline is reduced. In this stage, the matrix particles obtained by dry compression granulation reduce direct contact between components such as sodium salicylate and the microbeaded sodium hydroxide during storage; poloxamer 188, as a non-ionic wetting conditioner, reduces interfacial tension during the dissolution process of solid particles and minimizes the impact of air bubbles on photometric measurements.

[0015] Finally, oxidation colorimetric reagent B was added to carry out the oxidation colorimetric reaction. In this highly alkaline environment, the ammonium ions in the water sample were mainly converted into free ammonia.

[0016] Reaction formula: NH4 + +OH - →NH3+H2O;

[0017] At this point, the coated sodium dichloroisocyanurate microcapsules gradually release available chlorine species in the aqueous phase and react with free ammonia to generate monochloramine.

[0018] Reaction formula: NH3 + ClO - →NH2Cl+OH - ;

[0019] This release method helps reduce the impact of excessively high initial effective chlorine concentration on the salicylate colorimetric system. Subsequently, in the presence of sodium nitrosoferricyanide dihydrate, monochloramine reacts with sodium salicylate to generate a blue-green colorimetric product detectable at 697 nm, which can then be used for ammonia nitrogen concentration determination.

[0020] Preferably, the coated sodium dichloroisocyanurate microcapsules are made from raw materials comprising the following parts by weight: 500 parts sodium dichloroisocyanurate, 100 parts polyethylene glycol 6000, and 50-200 parts micron-sized anhydrous sodium sulfate.

[0021] By employing the above technical solution, polyethylene glycol 6000 forms a coating layer on the surface of sodium dichloroisocyanurate, and micron-sized anhydrous sodium sulfate is dispersed in this coating system as a water-soluble release regulator. When the microcapsules come into contact with the aqueous phase, the water-soluble anhydrous sodium sulfate gradually dissolves, altering the rate at which the aqueous phase enters the particle interior and the rate at which available chlorine species are released. By adjusting the proportion of micron-sized anhydrous sodium sulfate, the initial release rate and the degree of sustained release of the oxidant in the colorimetric system can be controlled.

[0022] Preferably, the median diameter D50 of the micron-sized anhydrous sodium sulfate is 5 μm to 15 μm, and the D90 is ≤ 40 μm; at least 90% of the particles in the microbeaded sodium hydroxide have a particle size of 0.5 mm to 1.0 mm; the average molecular weight of the poloxamer 188 is 7680 to 9510; and the average molecular weight of the polyethylene glycol 6000 is 5400 to 7000.

[0023] By adopting the above technical solutions, the median diameter of micron-sized anhydrous sodium sulfate is limited to 5μm to 15μm and D90≤40μm, which can reduce the release rate fluctuations caused by excessive differences in particle size of the release regulating components. Microbead-like sodium hydroxide is limited to coarse particles of 0.5mm to 1.0mm, which can reduce localized rapid dissolution and dust problems when fine powder strong alkali is introduced into water. Polyethylene glycol 6000 and poloxamer 188 are used to form the coating layer and improve the wettability and dispersibility of solid particles, respectively.

[0024] Preferably, the pre-conditioning reagent C comprises, by weight, 30.0 parts of anhydrous sodium pyrophosphate, 12.0 parts of sodium hexametaphosphate, 6.0 parts of D-mannitol, 15.0 parts of anhydrous sodium sulfate, 5.0 parts of boric acid, and 8.0 parts of anhydrous sodium tetraborate; in the high-alkali colorimetric reagent A, the mass ratio of the microbeaded sodium hydroxide to the matrix particles is 20.0:63.5; the matrix particles comprise, by weight, 12.0 parts of sodium salicylate, 20.0 parts of anhydrous sodium carbonate, 15.0 parts of anhydrous sodium pyrophosphate, 4.0 parts of D-mannitol, 12.0 parts of anhydrous sodium sulfate, and 0.5 parts of poloxamer 188; the oxidation colorimetric reagent B comprises, by weight, 1.0 part of sodium nitrosoferricyanide dihydrate, 20.0 parts of anhydrous sodium carbonate, and 2.5 parts of the coated sodium dichloroisocyanurate microcapsules.

[0025] By adopting the above technical solution, the ratio of each reagent component is matched with the amount of 10 mL water sample used in a single test, which can make the system have appropriate complexing ability, buffering ability, amount of colorimetric reagent and amount of oxidizing colorimetric component, thereby helping to reduce blank absorbance and improve the repeatability of low concentration ammonia nitrogen determination.

[0026] Preferably, the pre-conditioning reagent C and the high-alkali colorimetric reagent A are respectively sealed in separate aluminum-plastic composite bags, and the oxidation colorimetric reagent B is sealed in separate light-proof aluminum-plastic composite bags.

[0027] By adopting the above technical solution, the aluminum-plastic composite bag can reduce the influence of external moisture on the reagent components. The oxidation colorimetric reagent B is packaged in a light-proof aluminum-plastic composite bag, which reduces the impact of light on sodium nitrosoferricyanide dihydrate and the oxidant components, thus helping to maintain blank background and effective chlorine release performance during storage.

[0028] Secondly, the present invention provides a method for preparing a pre-made reagent package for detecting ammonia nitrogen in surface water, using the following technical solution:

[0029] A method for preparing a pre-made reagent kit for detecting ammonia nitrogen in surface water includes the following steps:

[0030] S1: Under the conditions of relative humidity of 12% to 18% and ambient temperature of 20℃ to 25℃, the components of preconditioning reagent C are mixed in a mixer, and the mixed powder is quantitatively dispensed into aluminum-plastic composite bags and sealed to obtain preconditioning reagent C.

[0031] S2: Under conditions of relative humidity of 12% to 18% and ambient temperature of 20℃ to 25℃, the components of the matrix particles are mixed and then pressed into tablets using a dry roller press granulator under a system pressure of 5MPa to 15MPa. The matrix particles with a particle size between 0.5mm and 1.0mm are crushed and sieved. Subsequently, the matrix particles are mixed with microbeaded sodium hydroxide, quantitatively dispensed into aluminum-plastic composite bags and sealed to obtain high-alkali colorimetric reagent A.

[0032] S3: Under the conditions of relative humidity of 12% to 18% and ambient temperature of 20℃ to 25℃, sodium nitrosoferricyanide dihydrate and anhydrous sodium carbonate were mixed to prepare catalytic dry powder. Then, sodium dichloroisocyanurate microcapsules coated with catalytic dry powder were added and mixed. The mixture was quantitatively dispensed into light-proof aluminum-plastic composite bags and sealed to obtain oxidation colorimetric reagent B.

[0033] By adopting the above technical solutions, the preparation process is carried out under low humidity and relatively constant temperature conditions, which helps to reduce the influence of environmental moisture on components such as sodium dichloroisocyanurate, sodium hydroxide, and sodium salicylate. Pre-conditioning reagent C can be mixed using a dry method to obtain a uniform powder. In high-alkali colorimetric reagent A, sodium salicylate, anhydrous sodium carbonate, anhydrous sodium pyrophosphate, D-mannitol, anhydrous sodium sulfate, and poloxamer 188 are first prepared into matrix particles, and then mixed with microbeaded sodium hydroxide. This helps to reduce stratification caused by differences in powder specific gravity and reduces direct contact between the colorimetric components and the strong alkali components during storage. In oxidation colorimetric reagent B, sodium nitrosoferricyanide dihydrate is first mixed with anhydrous sodium carbonate to form a catalytic dry powder, and then coated sodium dichloroisocyanurate microcapsules are added. This helps to improve the dispersion uniformity of trace catalytic components and reduce the mechanical impact of subsequent mixing processes on the coated particles.

[0034] Preferably, the preparation step of the coated sodium dichloroisocyanurate microcapsules in step S3 includes:

[0035] Polyethylene glycol 6000 was added to anhydrous ethanol and stirred to dissolve. Then, micron-sized anhydrous sodium sulfate powder was added and ultrasonically dispersed at a frequency of 20 kHz to 40 kHz for 15 min to 30 min to obtain a coated suspension.

[0036] Sodium dichloroisocyanurate powder was added to a bottom-spray fluidized bed, with the inlet air temperature set at 45℃~50℃ and the atomization pressure at 0.10MPa~0.20MPa; the coating suspension was then sprayed onto the surface of the sodium dichloroisocyanurate powder.

[0037] After the coating is completed, the coated particles are vacuum dried and cooled to room temperature to obtain coated sodium dichloroisocyanurate microcapsules.

[0038] By employing the above technical solution and using anhydrous ethanol as the solvent for polyethylene glycol 6000, the possibility of premature hydrolysis of sodium dichloroisocyanurate during water-based coating can be reduced. Ultrasonic dispersion treatment helps reduce the agglomeration of micron-sized anhydrous sodium sulfate in the coating suspension. During bottom-spray fluidized bed coating, the sodium dichloroisocyanurate powder is in a fluidized state, allowing the coating suspension to disperse and adhere to the particle surface. As ethanol evaporates, polyethylene glycol 6000 forms a coating layer, dispersing the micron-sized anhydrous sodium sulfate within this coating system. Subsequent vacuum drying removes residual ethanol at lower temperatures, reducing the impact of high-temperature treatment on the oxidant components.

[0039] Preferably, when spraying in a bottom-spray fluidized bed, the spraying rate is 8.0 mL / min to 12.0 mL / min, and the coating suspension is mechanically stirred during the spraying process. The vacuum drying conditions are: vacuum drying at 35℃ to 40℃ and an absolute pressure of 0.07 MPa to 0.09 MPa for 2h to 4h.

[0040] By adopting the above technical solution, maintaining mechanical agitation of the coating suspension during spraying helps reduce the sedimentation of micron-sized anhydrous sodium sulfate. Controlling the spraying rate at 8.0 mL / min to 12.0 mL / min balances the adhesion of the coating suspension and ethanol evaporation, reducing particle adhesion or uneven coating. Vacuum drying at 35℃ to 40℃ and absolute pressure at 0.07 MPa to 0.09 MPa removes residual ethanol under relatively mild conditions and reduces the impact of the drying process on the available chlorine content of sodium dichloroisocyanurate.

[0041] Preferably, in step S1, the components of the pre-conditioning reagent C are mixed in a three-dimensional mixer at a speed of 30 r / min for 15 min to 20 min; in step S2, the components of the matrix particles are mixed in a V-type mixer for 15 min, and the matrix particles and microbeaded sodium hydroxide are mixed in a V-type mixer at a speed of 10 r / min to 20 r / min for 5 min to 10 min; in step S3, sodium nitrosoferricyanide dihydrate and anhydrous sodium carbonate are mixed in a three-dimensional mixer for 15 min, and after adding coated sodium dichloroisocyanurate microcapsules, mixing continues for 5 min to 8 min.

[0042] By adopting the above technical solutions, the three-dimensional mixer is suitable for mixing pre-conditioned reagent C and catalytic dry powder; the V-type mixer is suitable for mixing matrix particles and microbeaded sodium hydroxide. After adding the coated sodium dichloroisocyanurate microcapsules, continue mixing for 5 to 8 minutes to achieve the desired dispersion effect while reducing the mechanical impact of excessively long mixing time on the coated particles.

[0043] This invention provides a pre-made reagent kit for detecting ammonia nitrogen in surface water and its preparation method. It has the following beneficial effects:

[0044] 1. This invention divides the ammonia nitrogen detection formula into three independently packaged components: pre-conditioning reagent C, high-alkalinity colorimetric reagent A, and oxidation colorimetric reagent B. These are added to the water sample in stages to sequentially construct a weakly alkaline buffer and transition to a highly alkaline detection environment. This design mitigates the drastic local pH changes caused by the instantaneous addition of strong alkali, inhibits metal ion precipitation and colorimetric side reactions, and avoids cross-reactions of the mixed powders during storage, thus maintaining the long-term effectiveness of the reagents.

[0045] 2. This invention employs a granulation and isolation process for high-alkali colorimetric reagent A. Sodium salicylate and anhydrous sodium carbonate are compressed into matrix particles, which are then mixed with microbeaded sodium hydroxide in a specific ratio. This method physically isolates the easily degradable sodium salicylate from the strong alkali, reducing their contact area. Simultaneously, by controlling the particle size of the matrix particles to between 0.5 mm and 1.0 mm, making them similar in size to the microbeaded sodium hydroxide, powder segregation during packaging and transportation is reduced, ensuring the uniformity of the dosage used in a single test.

[0046] 3. This invention introduces coated sodium dichloroisocyanurate microcapsules into the oxidative colorimetric reagent B, utilizing polyethylene glycol for film formation and incorporating micron-sized anhydrous sodium sulfate as a water-soluble porogen. During detection, the porogen preferentially dissolves to form microporous channels, thereby controlling the rate at which internal sodium dichloroisocyanurate releases hypochlorite ions into the aqueous phase. This release mechanism avoids non-targeted oxidative damage to the substrate caused by excessively high instantaneous concentrations of the oxidant, ensuring a stable formation of monochloramine and the coupled colorimetric reaction, thus improving the signal reproducibility of low-concentration ammonia nitrogen detection.

[0047] 4. The preparation method of this invention combines the physicochemical properties of different materials. In the coating stage, anhydrous ethanol is used in conjunction with a bottom-spray fluidized bed process to eliminate the risk of premature hydrolysis of active ingredients caused by water-based coating. In the mixing stage, appropriate mixing equipment is selected according to the powder morphology, and the mixing time of materials with coating or granulation structures is controlled. This process achieves effective dispersion under controllable shear force, maintains the structural integrity of the polymer coating film and granules, and reduces batch-to-batch variations in the preparation process. Detailed Implementation

[0048] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0049] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0050] The conventional chemical reagents used in this invention include anhydrous sodium pyrophosphate (CAS No.: 7722-88-5), sodium hexametaphosphate or water-soluble sodium polymetaphosphate (CAS No.: 10124-56-8), D-mannitol (CAS No.: 69-65-8), boric acid (CAS No.: 10043-35-3), anhydrous sodium tetraborate (CAS No.: 1330-43-4) or sodium tetraborate pentahydrate (CAS No.: 12045-88-4), sodium salicylate (CAS No.: 54-21-7), anhydrous sodium carbonate (CAS No.: 497-19-8), sodium nitrosoferricyanide dihydrate (also known as sodium nitroprusside, CAS No.: 13755-38-9), and anhydrous sodium sulfate (CAS No.: 7757-82-6). All of the above conventional reagents are commercially available analytical grade products.

[0051] Micron-sized anhydrous sodium sulfate was obtained by air-jet milling of commercially available anhydrous sodium sulfate. Its particle size distribution had a median diameter (d50) of 5 μm to 15 μm and a D90 ≤ 40 μm. It was used as a water-soluble release regulator and pore-forming agent in the coating of sodium dichloroisocyanurate microcapsules in oxidation colorimetric reagent B. Unmilled commercially available anhydrous sodium sulfate crystals were directly used as an inert diluent and cooling matrix. Microbeaded sodium hydroxide (CAS No.: 1310-73-2) used commercially available products with a purity ≥ 98.0%, and its particle size distribution required at least 90% of the particles to be between 0.5 mm and 1.0 mm. Sodium dichloroisocyanurate (CAS No.: 2893-78-9) used commercially available anhydrous products with an available chlorine content ≥ 60.0%. Poloxamer 188 (CAS No.: 9003-11-6) is a commercially available pharmaceutical-grade product. It is a nonionic triblock copolymer of polyethylene oxide, polypropylene oxide, and polyethylene oxide, with an average molecular weight ranging from 7680 to 9510. Polyethylene glycol 6000 (CAS No.: 25322-68-3) is a commercially available chemically pure product. It is a linear polyether obtained by ring-opening polymerization of ethylene oxide, with an average molecular weight ranging from 5400 to 7000.

[0052] To control the ammonia nitrogen background blank, blank screening was performed on each batch of raw materials and reagent kits. Raw material screening was used to exclude batches with obvious color, turbidity, or high background. The finished reagent kit used ammonia-free water instead of water samples, and the complete colorimetric test procedure was completed by adding the pre-conditioning reagent C, high-alkali colorimetric reagent A, and oxidation colorimetric reagent B in the actual order. The resulting apparent ammonia nitrogen concentration was not higher than the detection limit set by the method, or the blank absorbance ΔA at 697 nm was ≤0.005.

[0053] Preparation Example 1:

[0054] This preparation example provides a method for preparing coated sodium dichloroisocyanurate microcapsules, including the following steps:

[0055] (1) Add 100g of polyethylene glycol 6000 to 1250mL of anhydrous ethanol and stir to dissolve at 45℃; then add 120g of micron-sized anhydrous sodium sulfate powder with a median diameter of 8μm and ultrasonically disperse at 30kHz for 20 minutes to obtain a coated suspension.

[0056] (2) Add 500g of sodium dichloroisocyanurate powder to an explosion-proof bottom spray fluidized bed, set the inlet air temperature to 48℃ and the atomization pressure to 0.15MPa. Under the condition of continuous mechanical stirring of the coating suspension, spray it evenly on the surface of sodium dichloroisocyanurate raw material particles at a spraying rate of 10.0mL / min.

[0057] (3) After the spraying is completed, the obtained particles are transferred to a vacuum drying oven and vacuum dried for 3 hours at 38°C and 0.08MPa absolute pressure. After natural cooling to room temperature, the coated sodium dichloroisocyanurate microcapsules are obtained.

[0058] Preparation Example 2:

[0059] This preparation example provides a method for preparing coated sodium dichloroisocyanurate microcapsules, including the following steps:

[0060] (1) Add 100g of polyethylene glycol 6000 to 1250mL of anhydrous ethanol and stir to dissolve at 40℃; then add 50g of micron-sized anhydrous sodium sulfate powder with a median diameter of 5μm and ultrasonically disperse at 20kHz for 30 minutes to obtain a coated suspension.

[0061] (2) Add 500g of sodium dichloroisocyanurate powder to an explosion-proof bottom spray fluidized bed, set the inlet air temperature to 45℃ and the atomization pressure to 0.10MPa. Under the condition of continuous mechanical stirring of the coating suspension, spray it evenly on the surface of sodium dichloroisocyanurate raw material particles at a spraying rate of 8.0mL / min.

[0062] (3) After the spraying is completed, the obtained particles are transferred to a vacuum drying oven and vacuum dried for 4 hours at 35°C and 0.09MPa absolute pressure. After natural cooling to room temperature, the coated sodium dichloroisocyanurate microcapsules are obtained.

[0063] Preparation Example 3:

[0064] This preparation example provides a method for preparing coated sodium dichloroisocyanurate microcapsules, including the following steps:

[0065] (1) Add 100g of polyethylene glycol 6000 to 1250mL of anhydrous ethanol and stir to dissolve at 45℃; then add 200g of micron-sized anhydrous sodium sulfate powder with a median diameter of 12μm and ultrasonically disperse at 40kHz for 15 minutes to obtain a coated suspension.

[0066] (2) Add 500g of sodium dichloroisocyanurate powder to an explosion-proof bottom spray fluidized bed, set the inlet air temperature to 50℃ and the atomization pressure to 0.20MPa. Under the condition of continuous mechanical stirring of the coating suspension, spray it evenly on the surface of sodium dichloroisocyanurate raw material particles at a spraying rate of 12.0mL / min.

[0067] (3) After the spraying is completed, the obtained particles are transferred to a vacuum drying oven and vacuum dried for 2 hours at 40°C and 0.07MPa absolute pressure. After natural cooling to room temperature, the coated sodium dichloroisocyanurate microcapsules are obtained.

[0068] In the following embodiments, each pre-prepared reagent kit consists of one pre-conditioning reagent C, one high-alkali colorimetric reagent A, and one oxidation colorimetric reagent B, and is suitable for a single ammonia nitrogen detection of 10 mL surface water samples.

[0069] Example 1:

[0070] This embodiment provides a pre-made reagent kit for detecting ammonia nitrogen in surface water and its preparation method, including the following steps:

[0071] (1) Preparation of preconditioning reagent C: Under the conditions of 15% relative humidity and 22℃, weigh 30.0g of anhydrous sodium pyrophosphate, 12.0g of sodium hexametaphosphate, 6.0g of D-mannitol, 15.0g of anhydrous sodium sulfate, 5.0g of boric acid, and 8.0g of anhydrous sodium tetraborate. Place the above raw materials in a three-dimensional mixer and mix at 30 rpm for 20 minutes. After mixing, use a powder dispensing machine to quantitatively dispense the mixed powder into individual aluminum-plastic composite bags according to the specification of 76.0mg / bag, and seal to obtain preconditioning reagent C.

[0072] (2) Preparation of high-alkali colorimetric reagent A: Under the conditions of relative humidity 15% and ambient temperature 22℃, weigh 12.0g of sodium salicylate, 20.0g of anhydrous sodium carbonate, 15.0g of anhydrous sodium pyrophosphate, 4.0g of D-mannitol, 12.0g of anhydrous sodium sulfate, and 0.5g of poloxamer 188. After mixing the above raw materials in a V-type mixer for 15 minutes, use a dry roller press granulator to compress the tablets under a system pressure of 10MPa. Then, pulverize the tablets using a granulator and sieve them using a vibrating screen to retain and collect matrix particles with a particle size between 0.5mm and 1.0mm. According to the mass ratio of matrix particles to microbeaded sodium hydroxide of 63.5:20.0, weigh an appropriate amount of the collected matrix particles and the corresponding weight of microbeaded sodium hydroxide, and place them together in a V-type mixer and mix them at a speed of 15 rpm for 10 minutes. After mixing, the solution was quantitatively dispensed into individual aluminum-plastic composite bags at a specification of 83.5 mg / packet and sealed to obtain high-alkali colorimetric reagent A.

[0073] (3) Preparation of Oxidation Colorimetric Reagent B: Under conditions of 15% relative humidity and 22℃, 1.0g of sodium nitrosoferricyanide dihydrate and 20.0g of anhydrous sodium carbonate were weighed and mixed in a three-dimensional mixer for 15 minutes to obtain a catalytic dry powder. Then, 2.5g of coated sodium dichloroisocyanurate microcapsules prepared in Preparation Example 1 were added to the catalytic dry powder and the mixture was stirred for another 5 minutes. After mixing, the mixture was quantitatively dispensed into individual light-proof aluminum-plastic composite bags at a specification of 23.5mg / bag and sealed to obtain oxidation colorimetric reagent B.

[0074] Example 2:

[0075] This embodiment provides a pre-made reagent kit for detecting ammonia nitrogen in surface water and its preparation method, including the following steps:

[0076] (1) Preparation of preconditioning reagent C: Under the conditions of relative humidity 12% and ambient temperature 20℃, weigh 25.0g of anhydrous sodium pyrophosphate, 8.0g of sodium hexametaphosphate, 4.0g of D-mannitol, 10.0g of anhydrous sodium sulfate, 3.0g of boric acid, and 5.0g of anhydrous sodium tetraborate. Place the above raw materials in a three-dimensional mixer and mix at a speed of 30 rpm for 15 minutes. After mixing, use a powder dispensing machine to quantitatively dispense into individual aluminum-plastic composite bags according to the specification of 55.0mg / bag, and seal to obtain preconditioning reagent C.

[0077] (2) Preparation of high-alkali colorimetric reagent A: Under the conditions of relative humidity 12% and ambient temperature 20℃, weigh 10.0g of sodium salicylate, 15.0g of anhydrous sodium carbonate, 10.0g of anhydrous sodium pyrophosphate, 2.0g of D-mannitol, 8.0g of anhydrous sodium sulfate, and 0.2g of poloxamer 188. After mixing the above raw materials in a V-type mixer for 15 minutes, use a dry roller press granulator to press the tablets under a system pressure of 5MPa. After crushing and sieving, retain and collect the matrix particles with a particle size between 0.5mm and 1.0mm. According to the mass ratio of matrix particles to microbeaded sodium hydroxide of 45.2:15.0, weigh an appropriate amount of the collected matrix particles and the corresponding weight of microbeaded sodium hydroxide, and place them together in a V-type mixer, and mix at a speed of 10 rpm for 5 minutes. After mixing, the solution was quantitatively dispensed into individual aluminum-plastic composite bags at a rate of 60.2 mg / packet and sealed to obtain high-alkali colorimetric reagent A.

[0078] (3) Preparation of Oxidation Colorimetric Reagent B: Under conditions of 12% relative humidity and 20℃, 0.5g of sodium nitrosoferricyanide dihydrate and 15.0g of anhydrous sodium carbonate were weighed and mixed in a three-dimensional mixer for 15 minutes to obtain a catalytic dry powder. 1.8g of coated sodium dichloroisocyanurate microcapsules prepared in Preparation Example 2 were added to the powder, and mixing was continued for 5 minutes. After mixing, the powder was quantitatively dispensed into individual light-proof aluminum-plastic composite bags according to the specification of 17.3mg / bag, and sealed to obtain oxidation colorimetric reagent B.

[0079] Example 3:

[0080] This embodiment provides a pre-made reagent kit for detecting ammonia nitrogen in surface water and its preparation method, including the following steps:

[0081] (1) Preparation of preconditioning reagent C: Under conditions of 18% relative humidity and 25℃, weigh 35.0g of anhydrous sodium pyrophosphate, 15.0g of sodium hexametaphosphate, 8.0g of D-mannitol, 20.0g of anhydrous sodium sulfate, 8.0g of boric acid, and 12.0g of anhydrous sodium tetraborate. Place the above raw materials in a three-dimensional mixer and mix at 30 rpm for 20 minutes. After mixing, use a powder dispensing machine to quantitatively dispense into individual aluminum-plastic composite bags according to the specification of 98.0mg / bag, and seal to obtain preconditioning reagent C.

[0082] (2) Preparation of high-alkali colorimetric reagent A: Under the conditions of relative humidity 18% and ambient temperature 25℃, weigh 15.0g of sodium salicylate, 25.0g of anhydrous sodium carbonate, 20.0g of anhydrous sodium pyrophosphate, 6.0g of D-mannitol, 15.0g of anhydrous sodium sulfate, and 1.0g of poloxamer 188. After mixing the above raw materials in a V-type mixer for 15 minutes, press them into tablets using a dry roller press granulator under a system pressure of 15MPa. After crushing and sieving, retain and collect matrix particles with a particle size between 0.5mm and 1.0mm. According to the mass ratio of matrix particles to microbeaded sodium hydroxide of 82.0:25.0, weigh an appropriate amount of the collected matrix particles and the corresponding weight of microbeaded sodium hydroxide, and place them together in a V-type mixer, mixing at a speed of 20 rpm for 10 minutes. After mixing, the solution was quantitatively dispensed into individual aluminum-plastic composite bags at a specification of 107.0 mg / packet and sealed to obtain high-alkali colorimetric reagent A.

[0083] (3) Preparation of Oxidation Colorimetric Reagent B: Under conditions of 18% relative humidity and 25℃, 1.5g of sodium nitrosoferricyanide dihydrate and 25.0g of anhydrous sodium carbonate were weighed and mixed in a three-dimensional mixer for 15 minutes to obtain a catalytic dry powder. 3.5g of coated sodium dichloroisocyanurate microcapsules prepared in Preparation Example 3 were added to the powder, and mixing was continued for 8 minutes. After mixing, the powder was quantitatively dispensed into individual light-proof aluminum-plastic composite bags at a specification of 30.0mg / bag, and sealed to obtain Oxidation Colorimetric Reagent B.

[0084] In the following test examples, unless otherwise stated, the pre-prepared reagent kits of each embodiment are used for the determination of ammonia nitrogen in surface water in the following manner.

[0085] (1) Sampling and preconditioning: Accurately transfer 10 mL of the surface water sample to be tested or the diluted water sample into a clean colorimetric tube. Open the individual packaging of preconditioning reagent C, add all the powder into the colorimetric tube, tighten the cap and shake well to dissolve or disperse it. Let it stand for 10 to 30 seconds to allow the system to enter a low-alkaline preconditioning state, with a system pH of 9.6 to 10.6.

[0086] (2) Construction of high-alkaline colorimetric substrate: Open the individual packaging of high-alkaline colorimetric reagent A, add all the powder to the colorimetric tube, tighten the cap, and shake well by inverting the tube. Let stand for 30 to 60 seconds to allow the system to enter the high-alkaline colorimetric substrate state, with a system pH of 12.15 to 12.45.

[0087] (3) Oxidation color development: Open the individual packaging of oxidation color development reagent B, add all the powder into the colorimetric tube, tighten the cap and shake well. Let it stand at room temperature for 15 to 20 minutes to allow the ammonia nitrogen and salicylate color development system to complete the reaction.

[0088] (4) Absorbance measurement: After the color development is completed, wipe the outer wall of the colorimetric tube clean, place it in a spectrophotometer or portable colorimeter, measure the absorbance at a wavelength of 697 nm, and calculate the ammonia nitrogen concentration in the water sample according to the pre-established standard curve, expressed as nitrogen.

[0089] Comparative Example 1:

[0090] Compared to Example 1, the difference lies in that boric acid and anhydrous sodium tetraborate are not added in the preparation of preconditioning reagent C; instead, they are replaced with an equal mass of anhydrous sodium carbonate. All other aspects are the same.

[0091] Comparative Example 2:

[0092] Compared with Example 1, the differences are as follows: Anhydrous sodium sulfate and poloxamer 188 are not added to the raw materials for preparing the high-alkali colorimetric reagent A; the mixing mass ratio of matrix particles to microbeaded sodium hydroxide is adjusted to 51.0:20.0; and the single-packet packaging specification is adjusted to 71.0 mg / packet. All other aspects remain the same.

[0093] Comparative Example 3:

[0094] Compared to Example 1, the difference lies in the following: in the preparation of the oxidation colorimetric reagent B, the amount of coated sodium dichloroisocyanurate microcapsules added is reduced from 2.5g to 0.6g, and the single-packet packaging specification of the oxidation colorimetric reagent B is correspondingly adjusted to 21.6mg / packet. All other aspects remain the same.

[0095] Comparative Example 4:

[0096] Compared to Example 1, the difference lies in that, in the preparation of the oxidation colorimetric reagent B, the coated sodium dichloroisocyanurate microcapsules obtained from Preparation Example 1 are not added; instead, 1.7g of uncoated sodium dichloroisocyanurate powder is added directly. The single-packet packaging specification of the oxidation colorimetric reagent B is adjusted accordingly to 22.7mg / packet. All other aspects remain the same.

[0097] Comparative Example 5:

[0098] Compared to Example 1, the difference lies in that the system is not divided into three reagents. Instead, all the solid materials corresponding to the pre-conditioning reagent C, high-alkali colorimetric reagent A, and oxidation colorimetric reagent B in Example 1 are directly mixed together in the same single-test dosage to prepare a single solid premixed reagent package. The single-test dosage of the single solid premixed reagent package is equal to the sum of the dosages of the pre-conditioning reagent C, high-alkali colorimetric reagent A, and oxidation colorimetric reagent B in Example 1. The preparation of reagent B and the rest are the same.

[0099] Test Example 1:

[0100] Test objective: To investigate the pH adjustment effect of pre-conditioning reagent C on different simulated surface water samples and its influence on the turbidity of the water samples, and to examine the pH changes, local temperature rise, and optical baseline fluctuations at 697 nm after the addition of high-alkali colorimetric reagent A.

[0101] The experimental steps are as follows:

[0102] (1) Prepare three simulated surface water samples with different initial characteristics, and take 10 mL of each sample and place them in a colorimetric tube. The three water samples are: a conventional simulated water sample with an initial pH of 7.32 and a total hardness of 115.4 mg / L; a high hardness simulated water sample with an initial pH of 7.86 and a total hardness of 462.8 mg / L; and a high alkalinity simulated water sample with an initial pH of 8.63 and a total alkalinity of 318.5 mg / L.

[0103] (2) For each type of simulated water sample, the pre-conditioning reagent C corresponding to each example and comparative example was added. After sealing, the sample was placed on a vortex mixer and mixed. The pH value of the system was recorded at 30s, 60s and 90s using a glass electrode pH meter. The pH value at 90s was taken as the steady-state pH after adding C. At the same time, the turbidity of the corresponding water sample was measured using a portable turbidimeter.

[0104] (3) After completing the pre-conditioning, add the corresponding high-alkali colorimetric reagent A to the colorimetric tube, mix well, and record the pH value when the system reaches a stable state. At the same time, place the fast-response temperature probe 1 cm below the liquid surface and record the local maximum temperature rise during the dissolution process of reagent A.

[0105] (4) Place the colorimetric tube in the colorimetric cell of the spectrophotometer, set the detection wavelength to 697 nm, record the absorbance change from 0 to 60 s using continuous scanning, and use the difference between the maximum absorbance and the minimum absorbance during this time period as the baseline fluctuation value.

[0106] The experimental results are shown in Table 1:

[0107] Table 1: pH adjustment and physical stability data of each pre-prepared reagent system in simulated water samples

[0108]

[0109] As shown in Table 1, under the test conditions, after adding pre-conditioning reagent C in Examples 1 to 3, the steady-state pH of the three types of simulated water samples ranged from 9.62 to 10.42, generally falling within the low-alkalinity pre-conditioning range. Comparative Example 1, using anhydrous sodium carbonate instead of the borate buffer component, achieved a turbidity reading of 16.38 NTU in the high-hardness simulated water sample, higher than the 0.28 to 0.39 NTU corresponding to the Example group. This result indicates that in high-hardness water samples, pre-conditioning systems containing carbonate are more likely to cause an increase in turbidity; the examples using a carbonate-free borate buffer system are beneficial in reducing turbidity interference during the pre-conditioning stage.

[0110] After adding the high-alkali colorimetric reagent A, the pH of the systems in Examples 1 to 3 was in the range of 12.18 to 12.44, which could form high-alkali colorimetric conditions. Comparative Example 2, without the addition of anhydrous sodium sulfate and poloxamer 188, showed a local temperature rise of 5.8 to 6.4 °C and a baseline fluctuation of 0.038 to 0.046 at 697 nm. The local temperature rise in the Example group was 1.3 to 2.4 °C, and the baseline fluctuation was 0.002 to 0.005. These results indicate that under the test conditions, the matrix composition of the high-alkali colorimetric reagent A in the examples is beneficial in reducing the local temperature rise during the dissolution of the strong alkali component and reducing the impact of the dissolution process on the optical baseline.

[0111] Based on the above results, the preconditioning reagent C and the high-alkali colorimetric reagent A in the examples can enable the simulated surface water sample to sequentially enter the low-alkali preconditioning state and the high-alkali colorimetric state, and maintain low turbidity changes and baseline fluctuations in the high-hardness water sample, strong alkali addition and optical reading stages.

[0112] Test Example 2:

[0113] Test objective: To investigate the apparent available chlorine release of oxidative colorimetric reagent B under different temperature conditions, and to evaluate the effect of coating treatment on the initial release rate and the blank absorbance of the finished product throughout the process.

[0114] The experimental steps are as follows:

[0115] (1) Prepare ammonia-free pure water and add an appropriate amount of buffer solution to adjust its pH to 12.15 to 12.45 as a simulated colorimetric substrate. Establish three temperature conditions of 5℃, 25℃ and 35℃ respectively using a constant temperature water bath device, and use them after the simulated colorimetric substrate temperature stabilizes.

[0116] (2) Weigh out equivalent amounts of the oxidation colorimetric reagent B prepared in Examples 1 to 3, as well as the materials corresponding to Comparative Examples 3 and 4, for each single test. Add the above materials to the simulated colorimetric substrate at the corresponding temperature at once, and conduct the test under the same stirring conditions.

[0117] (3) Starting from the time the material enters the water, samples are taken at 15s, 60s and 180s respectively. The apparent effective chlorine concentration in the system is determined by N,N-diethyl-p-phenylenediamine spectrophotometry and converted into the percentage of the theoretical total effective chlorine released.

[0118] (4) Take ammonia-free pure water as a blank test matrix, and add the pre-conditioning reagent C, high-alkali colorimetric reagent A, and oxidation colorimetric reagent B corresponding to each example and comparative example in the actual usage order. After the reaction is completed, read the blank absorbance value of the whole process at a wavelength of 697 nm.

[0119] The experimental results are shown in Table 2:

[0120] Table 2: Available chlorine release kinetics and blank data of each reagent system at different temperatures

[0121]

[0122] As shown in Table 2, under 25°C conditions, the apparent available chlorine release rates of Examples 1 to 3 were 24.1% to 28.6% at 15 s, 64.8% to 71.5% at 60 s, and 91.3% to 95.9% at 180 s. At the same temperature, Comparative Example 4 showed a release rate of 91.8% at 15 s and 99.5% at 180 s. These results indicate that under the test conditions, the coated oxidative colorimetric reagent B had a lower initial release rate, while the uncoated sodium dichloroisocyanurate powder released more quickly upon contact with water.

[0123] Regarding the effect of temperature, the release rates of Example 1 at 5℃, 25℃, and 35℃ were 18.4%, 26.8%, and 33.7% in 15 seconds, respectively, and the release rates at 180 seconds were 86.1%, 93.5%, and 97.8%, respectively. These results indicate that Example 1 can release available chlorine at different test temperatures, and the initial release rate increases with increasing temperature. Comparative Example 4 showed release rates of 87.2%, 91.8%, and 96.4% in 15 seconds at 5℃, 25℃, and 35℃, respectively, indicating that the uncoated oxidant exhibited relatively rapid initial release under all temperature conditions.

[0124] In the full-process blank test, the blank absorbance of Examples 1 to 3 ranged from 0.002 to 0.005; the blank absorbance of Comparative Example 4 ranged from 0.035 to 0.058. These results indicate that under the test conditions, the coating treatment of the oxidizing chromogenic reagent B is beneficial in reducing the impact of excessively rapid initial release of available chlorine on the system's blank background. The blank absorbance of Comparative Example 3 was 0.001, but its total available chlorine dosage was lower than that of Example 1, suggesting a potential risk of insufficient oxidant residue in complex surface water samples containing reducing background substances. This point can be further evaluated in conjunction with subsequent spiked tests on complex matrices.

[0125] Based on the results in Table 2, the oxidizing chromogenic reagent B in the examples exhibited a relatively mild initial release characteristic at different temperatures, and released a high proportion of available chlorine at 180s; at the same time, its blank absorbance throughout the process was lower than that of the uncoated oxidant control.

[0126] Test Example 3:

[0127] Test objective: To investigate the applicability of pre-prepared reagent packages in simulated surface water with high hardness, iron content, and humus, and to evaluate the differences between the three-component segmented dosing method and the single-package mixed dosing method in terms of blank value, spiked recovery rate, intra-batch repeatability, and turbidity interference.

[0128] The experimental steps are as follows:

[0129] (1) Three types of simulated surface water matrix were prepared using laboratory pure water. The three types of water samples were: a high-hardness simulated water sample with calcium and magnesium salts added to achieve a total hardness of 427.6 mg / L; an iron-containing simulated water sample with ferric chloride hexahydrate added to achieve a total iron ion concentration of 1.63 mg / L; and a humic simulated water sample with sodium humate added to form a background absorption.

[0130] (2) For the above three types of simulated water samples, an unspecified blank group and an ammonia nitrogen spiking group were set up respectively, and the ammonia nitrogen spiking amount of the spiking group was 1.15 mg / L.

[0131] (3) Take the pre-prepared reagent packages prepared in Examples 1 to 3, and the solid reagents corresponding to Comparative Examples 1, 3, 4 and 5. For Examples 1 to 3 and Comparative Examples 1, 3 and 4, add them in the order of pre-conditioning reagent C, high-alkali colorimetric reagent A and oxidation colorimetric reagent B and mix them well; for Comparative Example 5, add a single package of solid premixed reagent to the water sample at once and shake to dissolve.

[0132] (4) After the colorimetric reaction is completed, a spectrophotometer is used for determination. The absorbance increment is measured at a reference wavelength of 800 nm to characterize changes in turbidity or scattering background; at the same time, the absorbance is read at a measurement wavelength of 697 nm, and the apparent ammonia nitrogen blank concentration and medium concentration spiked recovery rate of each system are calculated. Each group of conditions is measured in parallel 5 times, and the intra-batch relative standard deviation is calculated.

[0133] The experimental results are shown in Table 3:

[0134] Table 3: Anti-interference test data of each reagent system in three types of complex matrix simulated water samples

[0135]

[0136] As shown in Table 3, in the simulated high-hardness water samples, the absorbance at the 800 nm reference wavelength for Comparative Example 1 and Comparative Example 5 were 0.137 and 0.092, respectively, with corresponding apparent blank values ​​of 0.163 mg / L and 0.118 mg / L. The absorbance at the reference wavelength for Examples 1 to 3 in similar water samples ranged from 0.002 to 0.004, with apparent blank values ​​ranging from 0.011 mg / L to 0.018 mg / L. These results indicate that under the test conditions, pre-conditioning systems containing carbonate or single-packet mixed addition methods are more likely to cause an increase in the scattering background of high-hardness water samples; using carbonate-free pre-conditioning reagent C and adding it in stages helps to reduce the influence of the high-hardness matrix on photometric measurements.

[0137] In iron-containing simulated water samples, the apparent blank value of Comparative Example 5 was 0.067 mg / L, the recovery rate at medium concentration spikes was 87.2%, and the intra-batch RSD was 5.8%. In Examples 1 to 3, the apparent blank values ​​in iron-containing simulated water samples ranged from 0.015 mg / L to 0.019 mg / L, the recoveries at medium concentration spikes ranged from 98.1% to 103.5%, and the intra-batch RSD was 1.8% to 2.4%. These results indicate that, under the test conditions, the pre-treatment of reagent C helps reduce the influence of the iron matrix on subsequent colorimetric determinations.

[0138] In the humic-simulated water sample, the recovery rate of medium-concentration spiked reagent in Comparative Example 3 was 68.3%, the apparent blank value of Comparative Example 4 was 0.092 mg / L, and the intra-batch RSD was 11.2%. The spiked recoveries of Examples 1 to 3 in this type of water sample ranged from 96.4% to 98.8%, with intra-batch RSDs ranging from 2.5% to 3.7%. These results indicate that insufficient available chlorine dosage and humic background may affect the completeness of the ammonia nitrogen colorimetric reaction; uncoated oxidants may cause increased fluctuations in system blank values ​​and repeatability. The oxidizing colorimetric reagent B in the examples, after coating treatment, exhibited better spiked recoveries and intra-batch repeatability in the humic-simulated water sample.

[0139] Based on the results in Table 3, Examples 1 to 3 all exhibited low apparent blank values, spiked recoveries closer to theoretical values, and small intra-batch RSDs in three types of simulated surface water matrices: high hardness, iron-containing, and humic. Compared with the comparative examples, the three-component staged dosing method and the coating treatment of oxidation chromogenic reagent B improved the stability of the determination under complex matrix conditions.

[0140] Test Example 4:

[0141] Test objective: To examine the consistency between the results obtained by the pre-prepared reagent kit in real surface water samples and the results obtained by the standard method, and to evaluate its spiked recovery rate and repeatability in different types of surface water samples.

[0142] The experimental steps are as follows:

[0143] (1) Three types of typical surface water samples were collected: inland river water in the suburbs, high-hardness surface water in karst landform areas, and humus-rich surface water in forest areas. After collection, the water samples were filtered through a 0.45μm microporous membrane and stored temporarily under low temperature and light-proof conditions for later use.

[0144] (2) The pre-prepared reagent kits from Examples 1 to 3 and the standard salicylic acid spectrophotometric method were used to perform parallel determinations on the three types of water samples. For the reagent kit test group, the pre-conditioning reagent C, high-alkali colorimetric reagent A, and oxidation colorimetric reagent B were added sequentially and mixed thoroughly. For the standard method group, reagents were prepared according to the corresponding standard methods, and the colorimetric reaction was completed. After the colorimetric reaction was completed, the absorbance was measured at a wavelength of 697 nm and converted to ammonia nitrogen concentration.

[0145] (3) Ammonia nitrogen standard solution was added to three types of real surface water samples, and representative spiked concentrations were set according to the background ammonia nitrogen concentration of each water sample. Specifically, 0.53 mg / L was spiked for inland river water, 1.18 mg / L for karst high-hardness water, and 2.64 mg / L for humus-rich forest water. Two operators independently conducted parallel measurements on each spiked sample, with each operator performing three measurements. The spiked recovery rate and intra-batch relative standard deviation were calculated after the data were summarized.

[0146] (4) Using the mean value of the original sample determination of the standard method as a benchmark, calculate the relative error of the determination results of the pre-prepared reagent kits in each embodiment, which is used to evaluate the consistency between the pre-prepared reagent kits and the standard method.

[0147] The experimental results are shown in Table 4:

[0148] Table 4: Comparison of test results and spiked recovery rates of each pre-prepared reagent pack in real surface water samples

[0149]

[0150] As shown in Table 4, the relative errors between the measurement results of the three types of real surface water samples in Examples 1 to 3 and the measurement results of the standard method ranged from -3.80% to 5.91%. Under the test conditions, each example achieved measurement results that were close to those of the standard method in different real surface water samples.

[0151] For karst high-hardness water samples, the mean values ​​measured by the reagent kits in Examples 1 to 3 were 0.245 mg / L, 0.251 mg / L, and 0.228 mg / L, respectively. Compared with the value measured by the standard method (0.237 mg / L), the relative errors were -3.80% to 5.91%; the corresponding spiked recoveries were 98.6% to 101.3%, and the intra-batch RSD was 2.4% to 3.5%. These results indicate that the reagent kits in the examples can maintain low measurement bias and good repeatability in the tested high-hardness real water samples.

[0152] For humus-rich water samples from forest areas, the relative errors of Examples 1 to 3 ranged from -2.27% to 2.48%, the spiked recoveries ranged from 96.8% to 101.4%, and the intra-batch RSDs ranged from 2.6% to 3.9%. These results indicate that in real water samples with a natural organic background, the reagent kits from the examples can still obtain determination results that are close to those of the standard method and maintain relatively stable spiked recovery performance.

[0153] For inland river samples, the relative errors of Examples 1 to 3 ranged from -1.35% to 1.60%, the spiked recoveries ranged from 98.4% to 103.7%, and the intra-batch RSDs ranged from 1.5% to 2.1%. These results indicate that under common surface water sample conditions, the original sample determination results, spiked recoveries, and repeatability of the reagent kits from the examples are all within a relatively stable range.

[0154] Based on the results in Table 4, Examples 1 to 3 all exhibited small relative errors, spiked recoveries close to theoretical values, and low intra-batch RSDs in the three types of real surface water samples. These results indicate that the pre-prepared reagent kit has good consistency with the standard salicylic acid spectrophotometric method and is suitable for the determination of ammonia nitrogen in different types of surface water samples.

[0155] Test Example 5:

[0156] Test objective: To examine the pH adjustment performance, available chlorine release performance, and changes in the blank absorbance of the pre-prepared reagent kits after storage under different temperature and humidity conditions, and to evaluate the consistency of indicators among different batches of reagent kits.

[0157] The experimental steps are as follows:

[0158] (1) Following the preparation method of Example 1, three batches of pre-prepared reagent kits were prepared independently and consecutively, and were designated as batch 1, batch 2, and batch 3, respectively. Each reagent kit was packaged in aluminum foil composite film and stored in a light-proof, sealed container. Meanwhile, solid reagent kits corresponding to Comparative Example 4 and Comparative Example 5 were prepared as controls.

[0159] (2) Two storage conditions were established: one group was placed in a normal temperature storage environment of 25℃ and 60% relative humidity; the other group was placed in a constant temperature and humidity environment of 40℃ and 75% relative humidity for accelerated storage investigation.

[0160] (3) Samples were taken at month 0, month 3 and month 6 for testing. The reagents were dissolved in ammonia-free pure water in the order of actual use. The first steady-state pH after adding pre-adjustment reagent C and the second steady-state pH after adding high-alkali colorimetric reagent A were recorded using a pH meter.

[0161] (4) The apparent available chlorine release rate when the oxidizing colorimetric reagent B was dissolved for 180 s was determined by N,N-diethyl-p-phenylenediamine spectrophotometry. After the complete colorimetric process was completed, the absorbance of the finished product blank was measured at a wavelength of 697 nm using a spectrophotometer.

[0162] The experimental results are shown in Table 5:

[0163] Table 5: Evolution of physicochemical properties of each reagent system under different storage conditions

[0164]

[0165] As shown in Table 5, after 6 months of storage at room temperature (25°C), the steady-state pH of batch 1 in Example 1 changed from 10.12 to 10.04 in the first stage, from 12.31 to 12.25 in the second stage, the effective chlorine release rate at 180s changed from 93.5% to 91.2%, and the blank absorbance of the finished product changed from 0.003 to 0.004. These results indicate that under sealed storage conditions at room temperature, the pH adjustment performance, effective chlorine release performance, and blank background of the reagent kit in Example 1 showed minimal changes.

[0166] Under accelerated storage conditions of 40℃ and 75% relative humidity, the steady-state pH of batch 1 of Example 1 after 6 months of storage was 9.82 in the first stage and 12.16 in the second stage, with an effective chlorine release rate of 85.9% over 180 seconds and a blank absorbance of 0.005. For batches 2 and 3, under the same accelerated storage conditions, the steady-state pH of the first stage was 9.87 and 9.84, respectively, and the steady-state pH of the second stage was 12.17 and 12.16, respectively. The effective chlorine release rates over 180 seconds were 86.4% and 86.1%, respectively, and the blank absorbance of both batches was 0.005. These results indicate that the differences in the main physicochemical properties among different batches of the Example 1 reagent kit after accelerated storage are relatively small.

[0167] Comparative Example 4 used uncoated sodium dichloroisocyanurate powder as the oxidant component. After storage at 40°C and 75% relative humidity for 3 months and 6 months, the available chlorine release rates at 180 s were 67.8% and 38.6%, respectively, and the blank absorbances of the finished products were 0.112 and 0.183, respectively. Compared with Example 1, Comparative Example 4 showed a more significant decrease in available chlorine release capacity and an increase in blank absorbance after accelerated storage.

[0168] Comparative Example 5 was a single solid premixed reagent package. After being stored at 40°C and 75% relative humidity for 6 months, its second-stage steady-state pH was 10.82, the effective chlorine release rate at 180 s was 27.4%, and the blank absorbance was 0.264. These results indicate that under the test conditions, storing the strong base component, chromogenic component, and oxidant component together makes it more likely to experience a decrease in alkalinity after reconstitution, a reduction in effective chlorine release capacity, and an increase in blank background.

[0169] Based on the results in Table 5, Example 1, after using individual packaging of reagents and coating with oxidation colorimetric reagent B, was able to maintain relatively stable pH stage control, effective chlorine release rate, and finished product blank absorbance under both room temperature and accelerated storage conditions; the test results between different batches also showed small differences in the indicators.

[0170] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A pre-made reagent kit for detecting ammonia nitrogen in surface water, characterized in that, This includes individually packaged pre-conditioning reagent C, high-alkali colorimetric reagent A, and oxidation colorimetric reagent B; The pre-conditioning reagent C comprises the following components by weight: Anhydrous sodium pyrophosphate 25.0–35.0 parts, sodium hexametaphosphate 8.0–15.0 parts, D-mannitol 4.0–8.0 parts, anhydrous sodium sulfate 10.0–20.0 parts, boric acid 3.0–8.0 parts, and anhydrous sodium tetraborate 5.0–12.0 parts; The high-alkali colorimetric reagent A comprises matrix particles and microbeaded sodium hydroxide, wherein the mass ratio of the microbeaded sodium hydroxide to the matrix particles is 15.0–25.0:45.2–82.0; the matrix particles comprise the following components by weight: 10.0–15.0 parts sodium salicylate, 15.0–25.0 parts anhydrous sodium carbonate, 10.0–20.0 parts anhydrous sodium pyrophosphate, 2.0–6.0 parts D-mannitol, 8.0–15.0 parts anhydrous sodium sulfate, and 0.2–1.0 parts poloxamer 188; The oxidation colorimetric reagent B comprises the following components by weight: 0.5-1.5 parts of sodium nitroferricyanide dihydrate, 15.0-25.0 parts of anhydrous sodium carbonate, and 1.8-3.5 parts of coated sodium dichloroisocyanurate microcapsules; the coated sodium dichloroisocyanurate microcapsules comprise sodium dichloroisocyanurate and a coating layer covering the surface of the sodium dichloroisocyanurate.

2. The pre-made reagent kit for detecting ammonia nitrogen in surface water according to claim 1, characterized in that, The coated sodium dichloroisocyanurate microcapsules are made from the following raw materials in parts by weight: 500 parts sodium dichloroisocyanurate; 100 parts polyethylene glycol 6000; and 50-200 parts micron-sized anhydrous sodium sulfate.

3. The pre-made reagent kit for detecting ammonia nitrogen in surface water according to claim 2, characterized in that, The median diameter (D50) of the micron-sized anhydrous sodium sulfate is 5 μm to 15 μm, and the diameter (D90) is ≤ 40 μm; at least 90% of the particles in the microbeaded sodium hydroxide have a particle size of 0.5 mm to 1.0 mm; the average molecular weight of the poloxamer 188 is 7680 to 9510; and the average molecular weight of the polyethylene glycol 6000 is 5400 to 7000.

4. The pre-made reagent kit for detecting ammonia nitrogen in surface water according to claim 1, characterized in that, The pre-conditioning reagent C comprises, by weight, 30.0 parts of anhydrous sodium pyrophosphate, 12.0 parts of sodium hexametaphosphate, 6.0 parts of D-mannitol, 15.0 parts of anhydrous sodium sulfate, 5.0 parts of boric acid, and 8.0 parts of anhydrous sodium tetraborate; In the high-alkali colorimetric reagent A, the mass ratio of the microbeaded sodium hydroxide to the matrix particles is 20.0:63.5; the matrix particles, by weight, comprise: 12.0 parts sodium salicylate, 20.0 parts anhydrous sodium carbonate, 15.0 parts anhydrous sodium pyrophosphate, 4.0 parts D-mannitol, 12.0 parts anhydrous sodium sulfate, and 0.5 parts poloxamer 188. The oxidation colorimetric reagent B comprises, by weight, 1.0 part of sodium nitrosoferricyanide dihydrate, 20.0 parts of anhydrous sodium carbonate, and 2.5 parts of the coated sodium dichloroisocyanurate microcapsules.

5. The pre-made reagent kit for detecting ammonia nitrogen in surface water according to claim 1, characterized in that, The pre-conditioning reagent C and the high-alkali colorimetric reagent A are respectively sealed in separate aluminum-plastic composite bags, and the oxidation colorimetric reagent B is sealed in separate light-proof aluminum-plastic composite bags.

6. A method for preparing a pre-made reagent package for detecting ammonia nitrogen in surface water as described in any one of claims 1-5, characterized in that, Includes the following steps: S1: Under the conditions of relative humidity of 12% to 18% and ambient temperature of 20℃ to 25℃, the components of the pre-conditioning reagent C are mixed in a mixer, and the mixed powder is quantitatively dispensed into aluminum-plastic composite bags and sealed to obtain the pre-conditioning reagent C. S2: Under conditions of relative humidity of 12% to 18% and ambient temperature of 20℃ to 25℃, the components of the matrix particles are mixed and then compressed into tablets using a dry roller press granulator under a system pressure of 5MPa to 15MPa. The matrix particles are then pulverized and sieved to retain particles with a diameter between 0.5mm and 1.0mm. Subsequently, the matrix particles are mixed with microbeaded sodium hydroxide, quantitatively dispensed into aluminum-plastic composite bags, and sealed to obtain high-alkali colorimetric reagent A. S3: Under the conditions of relative humidity of 12% to 18% and ambient temperature of 20℃ to 25℃, sodium nitrosoferricyanide dihydrate and anhydrous sodium carbonate are mixed to prepare catalytic dry powder. Then, sodium dichloroisocyanurate microcapsules coated with the catalytic dry powder are added and mixed. The mixture is quantitatively dispensed into light-proof aluminum-plastic composite bags and sealed to obtain oxidation colorimetric reagent B.

7. The method for preparing the pre-made reagent package for ammonia nitrogen detection in surface water according to claim 6, characterized in that, The preparation steps of the coated sodium dichloroisocyanurate microcapsules in S3 include: Polyethylene glycol 6000 was added to anhydrous ethanol and stirred to dissolve. Then, micron-sized anhydrous sodium sulfate powder was added and ultrasonically dispersed at a frequency of 20kHz to 40kHz for 15 to 30 minutes to obtain a coated suspension. Sodium dichloroisocyanurate powder is added to a bottom-spray fluidized bed, with the inlet air temperature set at 45℃~50℃ and the atomization pressure at 0.10MPa~0.20MPa; the coating suspension is then sprayed onto the surface of the sodium dichloroisocyanurate powder. After the coating is completed, the coated particles are vacuum dried and cooled to room temperature to obtain the coated sodium dichloroisocyanurate microcapsules.

8. The method for preparing the pre-made reagent package for ammonia nitrogen detection in surface water according to claim 7, characterized in that, When spraying the bottom-spray fluidized bed, the spraying rate is 8.0 mL / min to 12.0 mL / min, and the coating suspension is mechanically stirred during the spraying process.

9. The method for preparing the pre-made reagent package for ammonia nitrogen detection in surface water according to claim 7, characterized in that, The vacuum drying conditions are: vacuum drying for 2 to 4 hours at 35℃~40℃ and absolute pressure of 0.07MPa~0.09MPa.

10. The method for preparing the pre-made reagent package for ammonia nitrogen detection in surface water according to claim 6, characterized in that, In step S1, the components of the pre-conditioning reagent C are mixed in a three-dimensional mixer at a speed of 30 r / min for 15 min to 20 min. In step S2, the components of the matrix particles are mixed in a V-type mixer for 15 minutes, and the matrix particles and the microbeaded sodium hydroxide are mixed in a V-type mixer at a speed of 10 r / min to 20 r / min for 5 minutes to 10 minutes. In step S3, the sodium nitrosoferricyanide dihydrate and the anhydrous sodium carbonate are mixed in a three-dimensional mixer for 15 minutes, and then the coated sodium dichloroisocyanurate microcapsules are added and the mixing continues for 5 to 8 minutes.

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