Industrial sewage orthophosphate detection kit and detection method

Abstract

The invention discloses an industrial sewage orthophosphate detection kit and a detection method. The orthophosphate detection kit comprises a color developing agent A and a color developing agent B. The color developing agent A comprises molybdate, acid and water, and the color developing agent B comprises stannous chloride and glycerin. The kit can realize on-site qualitative or semi-quantitative detection of orthophosphate in a water sample, has the advantages of simplicity in operation, less time consumption and reduction of chromatic aberration, and is suitable for on-site rapid detection.

Description

Technical Field

[0001] This invention belongs to the field of industrial wastewater detection technology, specifically relating to an industrial wastewater orthophosphate detection kit and detection method. Background Technology

[0002] Excessive phosphate in wastewater increases the difficulty of wastewater treatment and poses a risk of exceeding orthophosphate limits in effluent. Phosphate is widely used in wastewater treatment, and high concentrations can impact the activated sludge in treatment units, leading to substandard orthophosphate concentrations in the effluent. Furthermore, the time from influent to effluent in most wastewater treatment plants exceeds two hours. Conventional analytical methods involve lengthy processes, often missing the optimal intervention window when orthophosphate levels are found to be excessive, increasing operating costs and risks for wastewater treatment plants. Convenient and efficient detection of orthophosphate concentration in wastewater can facilitate timely adjustment of orthophosphate treatment technologies within the window of opportunity, reducing operating costs and risks for wastewater treatment plants.

[0003] Based on the above objectives, convenient and efficient detection of orthophosphate concentration in wastewater is crucial for timely adjustment of orthophosphate treatment technology within the designated window, thereby reducing the operating costs and risks of wastewater treatment plants. The ammonium molybdate spectrophotometric method is a commonly used method for determining orthophosphate in water. Its basic principle is to digest the sample under neutral conditions with potassium persulfate (or nitric acid-perchloric acid), oxidizing all phosphorus to orthophosphate. In an acidic medium, orthophosphate reacts with ammonium molybdate, forming phosphomolybdic heteropolyacid in the presence of antimony salts. This phosphomolybdic acid is then immediately reduced by ascorbic acid or stannous chloride to form a blue complex. The absorbance is measured spectrophotometrically at 700 nm to obtain the orthophosphate content. CN109406426A discloses a rapid reagent for determining orthophosphate in wastewater, its preparation method, and its application. After digestion, the water sample is removed, cooled, and then mixed with molybdate and ascorbic acid solutions. The sample concentration is measured at 700 nm, using a zero-concentration solution as a reference. CN109632662A discloses a reagent, its preparation method, and its application for rapid determination of orthophosphate in wastewater. The method involves adding molybdate solution to the water sample, mixing thoroughly, and measuring the orthophosphate concentration at 700 nm wavelength, using a zero-concentration solution as a reference. CN102998266A discloses a method for analyzing orthophosphate in industrial wastewater samples, utilizing the ammonium molybdate spectrophotometric principle for orthophosphate determination. The orthophosphate content is determined under normal pressure using a UV-Vis spectrophotometer. Currently, the detection of orthophosphate concentration in wastewater mainly relies on UV spectrophotometry. This method is relatively complex to operate and cannot achieve on-site monitoring. Furthermore, conventional detection methods have long detection cycles, making it difficult to provide guidance for timely adjustment of wastewater orthophosphate treatment technologies within the specified time window. Summary of the Invention

[0004] The purpose of this invention is to provide an industrial wastewater orthophosphate detection kit and detection method, which can realize on-site qualitative or semi-quantitative detection of orthophosphate in water samples. It has the advantages of simple operation, short time, and reduced color difference, and is suitable for rapid on-site detection.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides an orthophosphate detection kit, comprising a chromogenic agent A and a chromogenic agent B, wherein the chromogenic agent A comprises molybdate, acid and water, and the chromogenic agent B comprises stannous chloride and glycerol.

[0006] In the above-mentioned orthophosphate detection kit, the concentration of molybdate in the colorimetric reagent A is 22.5 g / L to 27.5 g / L; And / or, based on sulfur, the concentration of the acid in the colorimetric reagent A is 0.5 mol / L to 0.8 mol / L, and the acid is selected from sulfuric acid or a mixture of sulfuric acid and hydrochloric acid.

[0007] In the above-mentioned orthophosphate detection kit, the concentration of stannous chloride in the colorimetric reagent B is 225 g / L to 275 g / L.

[0008] The above-mentioned orthophosphate detection kit also includes a standard colorimetric card, which includes colors corresponding to P element concentrations of 0–2 mg / L.

[0009] In the above-mentioned orthophosphate detection kit, the standard colorimetric card is a coarse test card, which includes colors corresponding to P element concentrations of 0 mg / L, 0.1 mg / L, 0.2 mg / L, 0.3 mg / L, 0.5 mg / L, 1 mg / L, 1.5 mg / L, and 2 mg / L.

[0010] In the above-mentioned orthophosphate detection kit, the standard colorimetric card is a precision test card, which includes colors corresponding to P element concentrations of 0 mg / L, 0.04 mg / L, 0.12 mg / L, 0.20 mg / L, 0.28 mg / L, and 0.34 mg / L.

[0011] The above-mentioned orthophosphate detection kit further includes a reaction bottle, which includes a bottle body and a bottle cap; further, the bottle body is provided with quantitative graduation lines; further, the bottle cap is provided with a sealed dropper opening; And / or, the kit further includes a reagent bottle, the reagent bottle including a cap, a nozzle and a body; further, the inner diameter of the nozzle of the color developer A and the color developer B are 1.5 mm to 2 mm, respectively; And / or, the kit further includes a detection box, which includes a lid and a body; further, the lid has an opening for sample addition and detection observation; further, the body includes an upper colorimetric reaction layer and a lower absorption layer, the colorimetric reaction layer carries a colorimetric material, the colorimetric material is preferably a PVDF membrane with a pore size of 0.45 μm, the absorption layer is used to adsorb excess liquid, and the material of the absorption layer is preferably wood pulp fiber; the body of the box is provided with a limiting structure for fixing the colorimetric reaction layer and the absorption layer.

[0012] Secondly, the present invention provides a method for detecting orthophosphate, using the kit described in any one of the above claims, comprising the following steps: The colorimetric reagent A and the colorimetric reagent B are added dropwise to the water sample in sequence to carry out the reaction, and the concentration of orthophosphate in the water sample is determined based on the color after the reaction.

[0013] In the above-mentioned method for detecting orthophosphate, the volume of the water sample is 2.5–3.5 ml; And / or, the amount of color developer A is 2 drops; And / or, the colorimetric reagent B is added dropwise 25–40 s after the colorimetric reagent A; And / or, the amount of color developer B used is 1 drop; And / or, the reaction time is 3 to 10 minutes.

[0014] In the above-mentioned method for detecting orthophosphate, the water sample includes industrial wastewater, surface water, or any water sample containing orthophosphate.

[0015] The present invention has the following beneficial effects: (1) The detection method provided by this invention enables direct detection of industrial wastewater, and the detection results are more intuitive and efficient. It has high detection sensitivity, with a linear range of 0.02 to 2.0 mg / L and a total phosphorus detection limit as low as 0.02 mg / L; it has a wide detection range, applicable to samples of 0.02 to 2 mg / L, and can meet the determination of low and high concentration samples without multiple dilutions; it has good selectivity, and can still stably develop color under high salt, chloride ion or sulfate interference, with low background absorbance and interference rate of less than 5%, which is significantly better than the 10% to 15% of the literature methods.

[0016] (2) The detection method provided by this invention has a simple operation process, short detection time, and low sample requirement. The color development is stable and has good repeatability; glycerol stabilizes Sn². + The color development is completed within 10 minutes; the operation is quick and simple, the color development system reacts completely, the measurement time does not exceed 20 minutes, it can be completed without the need for a conventional colorimeter, and no complicated instruments or pretreatment are required.

[0017] (3) The colorimetric process of the detection method provided by the invention is to compare the color of the fiber adsorption and PVDF filter membrane enrichment with the color on the colorimetric card to avoid the difference in reading caused by the color difference between the liquid color and the color of the colorimetric card; Optionally, by a series of combined treatments (filtration and / or dilution) of industrial wastewater, the interference of chloride ions in the water sample is avoided, and the accuracy of the detection results is further improved; The reagent kit used in this method is highly economical.

[0018] In summary, the method of the present invention is superior to the prior art in terms of sensitivity, detection range, selectivity, colorimetric stability and ease of operation, and is suitable for rapid and reliable detection of total phosphorus in industrial wastewater, surface water and high salinity samples. Attached Figure Description

[0019] Appendix Figure 1 This is a schematic diagram of the reaction flask in the industrial wastewater orthophosphate detection kit of the present invention.

[0020] Figure 1 The markings are as follows: 100 - bottle body; 101 - bottle cap; 102 - sealed drip inlet; L - bottle length; D - bottle bottom diameter.

[0021] Appendix Figure 2 This is a schematic diagram of the detection box in the industrial wastewater orthophosphate detection kit of the present invention.

[0022] Figure 2 The markings in the middle are as follows: 200-box body; 201-box lid; 202-opening; 203-color development reaction layer; 204-absorption layer; 205-limiting groove; L1-length; W1-width; D1-height; Appendix Figure 3 The present invention provides a process flow diagram for determining the concentration of orthophosphate in industrial wastewater.

[0023] Appendix Figure 4 The image shows a rough measurement of samples with high concentration gradients in Example 1 of this invention (concentrations: top row from right to left: 0 mg / L, 0.1 mg / L, 0.2 mg / L, 0.3 mg / L; bottom row from right to left: 0.5 mg / L, 1.0 mg / L, 1.5 mg / L, 2 mg / L).

[0024] Appendix Figure 5 A standard colorimetric card (crude card) for determining the concentration of orthophosphate in industrial wastewater is provided as an embodiment of the present invention.

[0025] Appendix Figure 6The images show detailed measurements of samples with low concentration gradients in Example 2 of this invention (concentrations: top row from right to left: 0 mg / L, 0.04 mg / L, 0.12 mg / L; bottom row from right to left: 0.20 mg / L, 0.28 mg / L, 0.34 mg / L).

[0026] Appendix Figure 7 A standard colorimetric card (fine card) for determining the concentration of orthophosphate in industrial wastewater is provided as an embodiment of the present invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0028] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects.

[0029] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "assembly," "setup," and "connection" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0030] As described in the background section, existing methods for detecting orthophosphate concentration in wastewater suffer from problems such as complex operation and long detection cycles. In view of this, in the first part, the present invention provides an orthophosphate detection kit, comprising a chromogenic agent A and a chromogenic agent B, wherein the chromogenic agent A comprises molybdate, acid and water, and the chromogenic agent B comprises stannous chloride and glycerol.

[0031] Based on the above technical solutions, this invention employs colorimetric reagent A and colorimetric reagent B, mainly involving molybdate (MoO4²).- ) with phosphate (PO4³) - The reaction of α and β forms a phosphomolybdic acid complex under acidic conditions. This complex can be further reduced to molybdenum blue in the presence of a reducing agent. The color intensity of molybdenum blue is proportional to the concentration of the analyte and can be used for colorimetric analysis.

[0032] Total phosphorus usually exists in the form of phosphate, and the relevant reaction equations are as follows: (1) Formation of phosphomolybdic heteropolyacids:

[0033] (2) Reduction of phosphomolybdic acid heteropolyacids:

[0034] In the second reaction, stannous chloride reduces phosphomolybdic heteropolyacid to blue molybdenum blue. In this invention, the resulting molybdenum blue is used to reflect the concentration of phosphorus by the depth of the blue color.

[0035] The inventors discovered that the addition of glycerol to the reagent kit B can prevent the hydrolysis, oxidation, and inactivation of stannous chloride, thereby ensuring that the colorimetric reaction is controllable and repeatable, and improving the accuracy of detection.

[0036] According to an embodiment of the present invention, the concentration of molybdate in the colorimetric reagent A is 22.5 g / L to 27.5 g / L, including but not limited to 25 g / L. This concentration range ensures sufficient formation of phosphomolybdic heteropolyacid, resulting in sufficient color development and stable blue color, while avoiding precipitation or unstable color development caused by excessive heteropolyacid. The concentration and amount of molybdate solution in colorimetric reagent A are both set within the effective range suitable for the color development of the detection reaction. If the molybdate concentration is too low, it will react with PO4³⁺. - The amount of phosphomolybdate heteropolyacids formed is insufficient, and the color is light, the absorbance is low, and the detection limit is high; the molybdate is too high: heteropolyacids are supersaturated or excessive, the background absorbance is increased, the blank is too high, the reaction is unstable, and the risk of precipitation is increased.

[0037] The concentration of the acid in the colorimetric reagent A, calculated as sulfur, is 0.5 mol / L to 0.8 mol / L, including but not limited to 0.6 mol / L. Experimental results show that the colorimetric process cannot proceed normally when the acid concentration is below 0.5 mol / L, and the reaction also fails when the concentration is above 0.8 mol / L. Therefore, the acid concentration is determined to be 0.5 mol / L to 0.8 mol / L. The acid is selected from sulfuric acid or a mixture of sulfuric acid and hydrochloric acid. Specifically, the colorimetric reagent A is prepared by mixing a certain proportion of acidic solution with molybdate, followed by appropriate dilution. The specific ratio and preparation method are adjusted according to actual detection requirements. The proportions of each component in the colorimetric reagent A are within a preset range to ensure colorimetric effect and reaction stability.

[0038] According to an embodiment of the present invention, the concentration of stannous chloride in the colorimetric reagent B is 225 g / L to 275 g / L, including but not limited to 250 g / L. This concentration range is determined under the premise of ensuring sufficient color development, color stability, and good repeatability of phosphomolybdic blue. Too low a concentration will lead to incomplete reduction of Mo(VI), resulting in pale color development and an increased detection limit; too high a concentration may lead to excessively rapid color development, increased background absorbance, or yellowing of the solution, thereby affecting the stability of the color development. The concentration and amount of reducing agent solution in colorimetric reagent B are both set within the effective range suitable for the color development of the detection reaction, while the glycerol solution can stabilize Sn. 2+ This prevents oxidation and hydrolysis, thereby ensuring the effectiveness of the reducing agent and the reproducibility of the colorimetric reaction.

[0039] Specifically, colorimetric reagent B is prepared by adding a reducing agent to a glycerol solution within a certain mass range, allowing it to dissolve completely, and the solution concentration can be adjusted according to application requirements. The distribution ratio of each component in colorimetric reagent B is set within the effective range suitable for orthophosphate colorimetric reactions, and the specific values ​​are optimized based on actual applications.

[0040] According to embodiments of the present invention, the kit further includes a standard colorimetric card, which includes colors corresponding to phosphorus (P) concentrations of 0–2 mg / L. Optionally, the standard colorimetric card is a coarse colorimetric card, which includes colors corresponding to P concentrations of 0 mg / L, 0.1 mg / L, 0.2 mg / L, 0.3 mg / L, 0.5 mg / L, 1 mg / L, 1.5 mg / L, and 2 mg / L. Optionally, the standard colorimetric card is a fine colorimetric card, which includes colors corresponding to P concentrations of 0 mg / L, 0.04 mg / L, 0.12 mg / L, 0.20 mg / L, 0.28 mg / L, and 0.34 mg / L. The standard colorimetric card is designed as follows: a standard solution of P concentration is prepared according to the method in GB / T 11893-1989. The kit is then used to detect and determine the colors corresponding to different orthophosphate concentrations, ultimately resulting in a colorimetric card with a gradient of color depths. The colorimetric card is designed with both "coarse" and "fine" modes. It also includes accompanying text to help users quickly determine whether the tested water meets the requirements of a specific treatment process or discharge standards. The colorimetric card's development time is designed to be 3–10 minutes; for example, 5 minutes, the colorimetric time can be extended to 10 minutes, depending on whether the reagent kit's filter membrane is completely dry. Colorimetric analysis can be performed before it is completely dry.

[0041] According to an embodiment of the present invention, the kit further includes reaction flasks, such as... Figure 1As shown, the reaction flask includes a body 100 and a cap 101; further, the body is provided with quantitative graduation lines (not shown in the figure); further, the cap is provided with a sealed dropper 103. In this invention, the reaction flask adopts a combined body and cap structure. The body is provided with quantitative graduation lines, and the cap has a sealed dropper design to ensure no spillage during shaking. The vessel material is selected from materials with good chemical corrosion resistance, suitable for colorimetric reactions in phosphomolybdic heteropolyacid systems. In a specific embodiment of this invention, the body length L = 60 mm; the bottom diameter D = 10 mm.

[0042] According to an embodiment of the present invention, the reagent kit further includes a reagent bottle, which includes a cap, a nozzle, and a body. Further, the inner diameter of the nozzle is matched to the dropping volume, and the inner diameters of the nozzles for colorimetric reagent A and colorimetric reagent B are 1.5 mm to 2 mm, ensuring that the dropping volume of colorimetric reagent A is approximately 100 μL and the dropping volume of colorimetric reagent B is approximately 50 μL. The dropping bottle in this invention adopts a multi-body structure design, with the nozzle inner diameter matched to the dropping volume, ensuring that the volume of solution added in a single drop is stably controlled within a preset range.

[0043] According to an embodiment of the present invention, the kit further includes a detection cartridge, such as... Figure 2As shown, the detection box includes a box body 200 and a box lid 201; further, the box lid 201 has an opening 202 for sample addition and detection observation; further, the box body includes an upper colorimetric reaction layer 203 and a lower absorption layer 204. The colorimetric reaction layer 203 carries a colorimetric material, preferably a PVDF membrane with a pore size of 0.45 μm. The absorption layer 204 is used to absorb excess liquid, and the material of the absorption layer is preferably wood pulp fiber. Further, the box body 200 has a positioning structure, such as a limiting groove 205, for fixing the colorimetric reaction layer 202 and the absorption layer 204. The detection box adopts a portable structural design, with a small overall size and light weight, making it convenient for on-site detection, carrying, and operation. The detection box lid has an opening for sample addition and detection observation, and uses a rounded corner structure to optimize liquid flow and ensure uniform and stable colorimetric effect. The detection box body has a positioning structure for fixing internal components, preventing liquid leakage during the detection process, and facilitating the disassembly and replacement of internal components. The test kit has upper and lower partitions to ensure a clean and standardized testing process. In a specific embodiment of the invention, the colorimetric material is a PVDF filter membrane, which can enrich the colorimetric substances already in the reaction unit and filter the low-concentration, indistinct colored substances after the reaction onto the surface of the PVDF membrane, thereby deepening the color at low concentrations. The absorbent layer is made of solution adsorption material, which provides the driving force for the solution to pass through the PVDF membrane. The adsorption material is specifically one or more water-absorbing materials such as wood pulp fiber and sponge. The arrangement of the adsorption material inside the kit is PVDF membrane and adsorption material. To ensure the stability and accuracy of the arrangement inside the kit, the PVDF membrane is cut into a rectangle with a length × width of 4.0 cm × 2.5 cm, and the adsorption material is shaped with a length × width × height of 4.0 cm × 2.5 cm × 0.4 cm. The external length of the kit is L1 = 43 mm, the external width is W1 = 25 mm, and the external height is H1 = 7 mm. In addition, a limiting groove with dimensions of 4.0 cm × 2.5 cm × 0.4 cm (length × width × height) is designed inside the kit to fix the PVDF membrane and adsorbent material.

[0044] For PVDF membranes, the inventors conducted screening experiments on membrane materials during the experimental exploration process. Polyvinylidene fluoride (PVDF), as a linear semi-crystalline polymer, is known to possess excellent chemical stability, mainly due to its short C-F bond length and high bond energy. This material exhibits outstanding performance in corrosion resistance, high-temperature resistance, and oxidation resistance, and is often considered an ideal choice for preparing water treatment separation membranes. Under normal temperature conditions, PVDF shows significant resistance to acid, alkali, and strong oxidizing agent solutions, making it suitable for use. When applying the phosphomolybdate colorimetric method, the colorimetric product dissolves in water, and excessive residual water may cause uneven color distribution, thus increasing detection errors. In the experiment, filter paper with a pore size of 0.45 μm, PVDF membranes with a pore size of 0.45 μm, PVDF membranes with a pore size of 0.2 μm, and PVDF membranes with a pore size of 1.0 μm were compared. Under constant temperature and pressure conditions, filtration through the 0.45 μm PVDF membrane showed better filtration performance. PVDF membranes are highly hydrophobic, which allows solutions to pass through quickly while filtering colored substances. They also ensure that the colorimetric reaction of the phosphomolybdic acid complex on the filter paper is more uniform and stable, which is beneficial to the accuracy of colorimetric analysis.

[0045] Regarding absorbent materials, the inventors conducted screening experiments during the experimental exploration process. The main function of the absorbent medium is to quickly remove the solution not retained by the filter membrane after mixing samples and reagents, while ensuring the fixation of the indicator on the filter paper. This liquid absorption process helps to avoid colorimetric distortion caused by excessive liquid, thereby improving the accuracy of the detection results. The inventors evaluated the performance of different absorbent materials, selecting materials with strong water absorption and fast absorption rate for experiments, and compared and analyzed the water absorption capacity of wood pulp fiber, sponge, and sodium polyacrylate or its cross-linked polymers. The experimental method was to drop equal volumes (0.5 mL) of treated liquid with different concentrations onto the same filter membrane and record the liquid penetration time. The experimental data showed that wood pulp fiber had a better water absorption effect and higher water absorption efficiency compared to the other two materials. It was also economical, practical, and inexpensive. Therefore, wood pulp fiber was selected as the absorbent material.

[0046] Understandably, the kit also includes a dropper for sampling and transfer.

[0047] The reagent kit of this invention mainly includes a colorimetric reagent, auxiliary reaction equipment, and a matching colorimetric device, through a specific reagent combination and a simple operation procedure. The volume of the reaction bottle and the colorimetric reaction layer, the diameter of the dropper, and the arrangement of the standard colorimetric card are all designed to meet the needs of convenient on-site testing.

[0048] In the second part, the present invention provides a method for detecting orthophosphate, using the kit described in any of the above-mentioned methods, comprising the following steps: sequentially adding the colorimetric reagent A and the colorimetric reagent B to a water sample for reaction, and determining the orthophosphate concentration in the water sample based on the color after the reaction.

[0049] According to embodiments of the present invention, the water sample is industrial wastewater, surface water, or any water sample containing high phosphate levels; optionally, the volume of the water sample is 2.5–3.5 ml, such as 3 ml; optionally, the amount of colorimetric reagent A is 2 drops; optionally, the colorimetric reagent B is added 25–40 s after the colorimetric reagent A, such as 30 s; optionally, the amount of colorimetric reagent B is 1 drop; optionally, the reaction time is 3–10 min, such as 5 min. The single-drop volume and reaction time of each reagent bottle can be designed to meet the needs of convenient on-site detection.

[0050] According to embodiments of the present invention, such as Figure 3 As shown, the specific operation of the detection method is as follows: S1, take 3 ml of water sample into the reaction bottle; S2, add 2 drops of color reagent A to the reaction bottle, and after 30 s, add 1 drop of color reagent B, shake well, and react for 5 min; S3, drop the sample from the reaction bottle into the color reaction layer in the detection box, and then wait for all the sample in the color reaction layer to be absorbed; S4, then compare the color of the color window in the detection box with the color of the standard colorimetric card to determine the concentration of orthophosphate in the sample.

[0051] Optionally, when the water sample is turbid, the sample pretreatment method is to filter the water sample through a 0.45 μm filter membrane.

[0052] Optionally, when the phosphorus concentration in the water sample is too high, the sample pretreatment method is as follows: dilute the water sample (e.g., dilute 5 to 10 times) and record the dilution ratio for final calculation of the actual orthophosphate concentration. The detection range of the method of this invention, calculated as phosphorus, is 0–2 mg / L.

[0053] The method of this invention includes steps such as sampling, sequential addition of colorimetric reagents, colorimetric reaction, and comparison with a color standard card. The operation is simple, the detection results are intuitive, and it can quickly determine the concentration of orthophosphate in wastewater on-site. This invention has the advantages of convenient operation, high detection efficiency, and suitability for rapid on-site detection, providing a practical and efficient technical solution for industrial wastewater monitoring.

[0054] The present invention will now be described in further detail with reference to specific embodiments. The given embodiments are merely illustrative of the invention and not intended to limit its scope. The embodiments provided below can serve as a guide for further improvements by those skilled in the art and do not constitute a limitation on the invention in any way.

[0055] Unless otherwise specified, the methods used in the following embodiments are conventional methods, performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Unless otherwise specified, the materials and reagents used in the following embodiments are commercially available.

[0056] Preparation Example 1: Preparation of Crude Calorie Due to the refraction and absorption of light by glass containers, it is difficult to accurately distinguish color differences in colorimetric tubes with the naked eye. Therefore, this product is designed with reference to pH test paper and features a colorimetric card for enriching phosphorus content. Prepare standard solutions of phosphorus (P) with concentrations of 0 mg / L, 0.1 mg / L, 0.2 mg / L, 0.3 mg / L, 0.5 mg / L, 1 mg / L, 1.5 mg / L, and 2 mg / L according to the method in GB / T11893-1989. Pipette 2.5 mL of the test liquid into the reaction unit, add 2 drops (1 drop ≈ 50 μL) of colorimetric reagent A (composed of molybdate, sulfuric acid, and water; the concentration of molybdate in colorimetric reagent A is 25 g / L, and the concentration of sulfur in colorimetric reagent A is 0.6 mol / L), and after 30 seconds add 1 drop of colorimetric reagent B (composed of stannous chloride and glycerol; the concentration of stannous chloride in colorimetric reagent B is 250 g / L). Mix well and let stand for 5 minutes. Add the liquid to the circular opening in the center of the test box lid. After water filtration, observe the color. Detect using this kit, and fix it as a coarse colorimetric card with color gradients. See details. Figure 4 The concentration of the standard solution should be selected based on the national emission standards or the requirements for phosphorus in typical processes of wastewater treatment plants. Figure 4 The corresponding standard colorimetric card (coarse card) can be found here. Figure 5 .

[0057] Preparation Example 2: Preparation of Fine Card Due to the refraction and absorption of light by glass containers, it is difficult to accurately distinguish color differences in colorimetric tubes with the naked eye. Therefore, this product is designed with reference to pH test paper and features a colorimetric card for enriching phosphorus content. Prepare standard solutions of phosphorus (P) with concentrations of 0 mg / L, 0.04 mg / L, 0.12 mg / L, 0.2 mg / L, 0.28 mg / L, and 0.34 mg / L, respectively, according to the method in GB / T11893-1989. Pipette 2.5 mL of the test liquid into the reaction unit. Add 2 drops (1 drop ≈ 50 μL) of colorimetric reagent A (composed of molybdate, sulfuric acid, and water; the concentration of molybdate in colorimetric reagent A is 25 g / L, and the concentration of sulfur in colorimetric reagent A is 0.6 mol / L). After 30 seconds, add 1 drop of colorimetric reagent B (composed of stannous chloride and glycerol; the concentration of stannous chloride in colorimetric reagent B is 250 g / L). Mix well and let stand for 5 minutes. Add the liquid to the circular opening in the center of the test box lid. After water filtration, observe the color. Detect using this kit, and fix it as a coarse colorimetric card with color gradients. See details. Figure 6 The concentration of the standard solution should be selected based on the national emission standards or the requirements for phosphorus in typical processes of wastewater treatment plants. Figure 6 The corresponding standard colorimetric card (fine card) can be found here. Figure 7 .

[0058] Example 1: Detection of orthophosphate in wastewater using the crude card from Example 1. The orthophosphate concentration in the influent of a wastewater treatment plant was -1.8 mg / L (calculated as phosphorus).

[0059] First, 3 ml of water sample was placed in the reaction unit. Since the water sample showed no obvious discoloration, no pretreatment was required. Then, 2 drops of colorimetric reagent A were added to the reaction unit, followed by 1 drop of colorimetric reagent B after 30 seconds. After reacting for 5 minutes, the reagents from the reaction unit were added to the colorimetric unit. Once the liquid in the groove of the colorimetric unit disappeared, the color of the colorimetric pane on the colorimetric unit was compared with the standard colorimetric card. The color of the colorimetric pane on the colorimetric unit was determined to be between 1.5 mg / L and 2.0 mg / L on the standard colorimetric card. Therefore, the final determined orthophosphate concentration in the water sample was between 1.5 mg / L and 2.0 mg / L, consistent with the actual orthophosphate concentration in the water sample.

[0060] Example 2: Detection of orthophosphate in wastewater using the fine-scale method described in Example 1. The orthophosphate concentration in the effluent of a wastewater treatment plant was -0.05 mg / L (calculated as phosphorus).

[0061] First, 3 ml of water sample was placed in the reaction unit. Since the water sample showed no obvious discoloration, no pretreatment was required. Then, 2 drops of colorimetric reagent A were added to the reaction unit, followed by 1 drop of colorimetric reagent B after 30 seconds. After reacting for 5 minutes, the reagents from the reaction unit were added to the colorimetric unit. Once the liquid in the groove of the colorimetric unit disappeared, the color of the colorimetric window on the colorimetric unit was compared with the standard colorimetric card. The color of the colorimetric window on the colorimetric unit was determined to be between 0 mg / L and 0.1 mg / L on the standard colorimetric card. Therefore, the final determined orthophosphate concentration in the water sample was between 0.04 mg / L and 0.12 mg / L, consistent with the actual orthophosphate concentration in the water sample.

[0062] Example 3: Detection of orthophosphate in wastewater using the crude card from Example 1. The concentration of orthophosphate in the laboratory wastewater was -1.2 mg / L (as phosphorus).

[0063] First, 3 ml of water sample was placed in the reaction unit. Since the water sample showed no obvious discoloration, no pretreatment was required. Then, 2 drops of colorimetric reagent A were added to the reaction unit, followed by 1 drop of colorimetric reagent B after 30 seconds. After reacting for 5 minutes, the reagents from the reaction unit were added to the colorimetric unit. Once the liquid in the groove of the colorimetric unit disappeared, the color of the colorimetric window on the colorimetric unit was compared with the standard colorimetric card. The color of the colorimetric window on the colorimetric unit was determined to be between 1.0 mg / L and 1.5 mg / L on the standard colorimetric card. Therefore, the final determined orthophosphate concentration in the water sample was between 1.0 mg / L and 1.5 mg / L, consistent with the actual orthophosphate concentration in the water sample.

[0064] As can be seen from Examples 1-3, the ammonium molybdate-stannous chloride colorimetric system of this invention for total phosphorus detection has significant advantages: high detection sensitivity, with a linear range of 0.02–2.0 mg / L and a total phosphorus detection limit as low as 0.02 mg / L; wide detection range, applicable to samples of 0.02–2 mg / L, meeting the requirements for determination of both low and high concentration samples without multiple dilutions; good selectivity, maintaining stable color development even under high salt, chloride ion, or sulfate interference conditions, with low background absorbance and an interference rate of less than 5%, significantly better than the 10%–15% of literature methods; stable color development and good repeatability, with glycerol stabilizing Sn. 2+ The colorimetric reaction is completed within 10 minutes; the operation is rapid and simple, the colorimetric system reacts completely, the determination time does not exceed 20 minutes, and it can be completed without the need for a conventional colorimeter, complex instruments, or pretreatment. In summary, the method of this invention is superior to existing methods in terms of sensitivity, detection range, selectivity, colorimetric stability, and ease of operation, and is suitable for rapid and reliable detection of total phosphorus in industrial wastewater, surface water, and high-salinity samples.

[0065] The present invention has been described in detail above. Those skilled in the art will recognize that the invention can be practiced in a wide range of ways with equivalent parameters, concentrations, and conditions without departing from its spirit and scope. While specific embodiments have been provided, it should be understood that further modifications can be made to the invention. In summary, according to the principles of the invention, this application is intended to include any changes, uses, or improvements to the invention, including modifications made using conventional techniques known in the art that depart from the scope disclosed herein.

Claims

1. A kit for detecting orthophosphate, characterized in that, It includes color developer A and color developer B, wherein color developer A comprises molybdate, acid and water, and color developer B comprises stannous chloride and glycerol.

2. The orthophosphate detection kit according to claim 1, characterized in that: The concentration of the molybdate in the colorimetric reagent A is 22.5 g / L to 27.5 g / L; And / or, based on sulfur, the concentration of the acid in the colorimetric reagent A is 0.5 mol / L to 0.8 mol / L, and the acid is selected from sulfuric acid or a mixture of sulfuric acid and hydrochloric acid.

3. The orthophosphate detection kit according to claim 1 or 2, characterized in that: The concentration of stannous chloride in the colorimetric reagent B is 225 g / L to 275 g / L.

4. The orthophosphate detection kit according to any one of claims 1-3, characterized in that: The kit also includes a standard colorimetric card, which includes colors corresponding to P element concentrations of 0–2 mg / L.

5. The orthophosphate detection kit according to claim 4, characterized in that: The standard colorimetric card is a coarse test card, which includes colors corresponding to P element concentrations of 0 mg / L, 0.1 mg / L, 0.2 mg / L, 0.3 mg / L, 0.5 mg / L, 1 mg / L, 1.5 mg / L, and 2 mg / L.

6. The orthophosphate detection kit according to claim 4, characterized in that: The standard colorimetric card is a precision colorimetric card, which includes colors corresponding to P element concentrations of 0 mg / L, 0.04 mg / L, 0.12 mg / L, 0.20 mg / L, 0.28 mg / L, and 0.34 mg / L.

7. The orthophosphate detection kit according to any one of claims 1-6, characterized in that: The kit also includes a reaction bottle, which comprises a bottle body and a cap; further, the bottle body is provided with quantitative graduation lines; further, the cap is provided with a sealed dropper opening; And / or, the kit further includes a reagent bottle, the reagent bottle including a cap, a nozzle and a body; further, the inner diameter of the nozzle of the color developer A and the color developer B are 1.5 mm to 2 mm, respectively; And / or, the kit further includes a detection box, the detection box including a lid and a box body; further, the lid has an opening for sample addition and detection observation; further, the box body includes an upper colorimetric reaction layer and a lower absorption layer, the colorimetric reaction layer carries a colorimetric material, the colorimetric material is preferably a PVDF membrane with a pore size of 0.45 μm, the absorption layer is used to adsorb excess liquid, the material of the absorption layer is preferably wood pulp fiber; further, the box body has a positioning structure for fixing the colorimetric reaction layer and the absorption layer.

8. A method for detecting orthophosphate, using the kit according to any one of claims 1-7, comprising the following steps: The colorimetric reagent A and the colorimetric reagent B are added dropwise to the water sample in sequence to carry out the reaction, and the concentration of orthophosphate in the water sample is determined based on the color after the reaction.

9. The method for detecting orthophosphate according to claim 8, characterized in that: The volume of the water sample is 2.5–3.5 ml; And / or, the amount of color developer A is 2 drops; And / or, the colorimetric reagent B is added dropwise 25–40 s after the colorimetric reagent A; And / or, the amount of color developer B used is 1 drop; And / or, the reaction time is 3 to 10 minutes.

10. The method for detecting orthophosphate according to claim 8 or 9, characterized in that: The water samples include industrial wastewater, surface water, or any water sample containing orthophosphate.

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