A device and method for detecting ammonia nitrogen in an environmental water body

Abstract

The application discloses a kind of ammonia nitrogen micro quick on-line detection device and detection method in environment water body, belong to ammonia nitrogen concentration detection technical field, the device with salicylate spectrophotometry as detection principle, integrated sequential injection system, ammonia nitrogen conversion reaction system, chromogenic reaction system and detection system, realize ammonia nitrogen on-line conversion, effectively improve the anti-matrix interference ability of salicylate spectrophotometry analysis ammonia nitrogen.Salicylate spectrophotometry is used as detection principle in the device, integrated sequential injection system, ammonia nitrogen conversion reaction system, chromogenic reaction system and detection system, realize ammonia nitrogen on-line conversion, effectively improve the anti-matrix interference ability of salicylate spectrophotometry analysis ammonia nitrogen.Ammonia gas absorption chromogenic process does not use gas-permeable membrane, avoid the pollution and replacement problem of gas-permeable membrane.The device quantitative analysis uses absorbance instantaneous change rate as quantitative basis, does not need to wait for chromogenic reaction to end, saves analysis time.The device has the advantages of simple operation, fast, miniaturization, reagent consumption is less, anti-matrix interference ability is strong, etc., is suitable for the on-line detection of ammonia nitrogen in surface water, domestic sewage and other water quality.

Description

Technical Field

[0001] This invention belongs to the field of ammonia nitrogen concentration detection technology, specifically relating to a miniature rapid online detection device and method for ammonia nitrogen in environmental water bodies. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Ammonia nitrogen is an important indicator for evaluating the quality of natural water environments. Appropriate concentrations of ammonia nitrogen are necessary for the growth of aquatic organisms in environmental water bodies, while high concentrations promote the unhealthy growth of plankton and algae, thus damaging the aquatic ecosystem. Therefore, timely monitoring of ammonia nitrogen levels in water is crucial for protecting the aquatic ecosystem. Existing methods for direct detection of ammonia nitrogen mainly include spectrophotometry, fluorescence methods, and electrochemical methods. Spectrophotometry is the most commonly used method for ammonia nitrogen detection in water quality. It is stable, easy to operate, and has low analytical costs, making it a standard method. However, when directly analyzing environmental water samples with complex matrices using spectrophotometry, it is easily affected by coexisting ions and the color and turbidity of the water sample itself. Therefore, spectrophotometry is generally suitable for detecting ammonia nitrogen in relatively pure water samples. Fluorescence methods have good sensitivity and selectivity, but fluorescence efficiency is easily affected by the sample matrix. Therefore, fluorescence methods are also suitable for detecting ammonia nitrogen in relatively pure water samples. Electrochemical methods for detecting ammonia nitrogen consume fewer reagents and have low operating costs, but the electrodes are easily contaminated and interfered with by the sample matrix, affecting their lifespan and stability.

[0004] Online ammonia nitrogen detection facilitates the automation of analysis, effectively simplifying operational procedures for analysts, reducing human error, and lowering labor costs. Currently, online ammonia nitrogen detection and analysis methods in water samples are mainly based on online ammonia nitrogen conversion and ammonia diffusion absorption detection methods developed using flow injection and sequential injection systems. However, these methods typically require gas diffusion membranes, necessitating consideration of membrane lifespan and replacement, and thus cannot achieve rapid detection and analysis of ammonia nitrogen in complex matrix water bodies. Therefore, developing devices and analytical methods suitable for online ammonia nitrogen analysis in complex matrix water bodies remains crucial. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a miniature rapid online detection device and method for ammonia nitrogen in environmental water bodies. The miniature rapid online detection device for ammonia nitrogen in environmental water bodies provided by the present invention is suitable for online, sensitive, and rapid detection of ammonia nitrogen in various environmental water bodies.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A first aspect of the present invention provides a miniature rapid online detection device for ammonia nitrogen in environmental water, comprising:

[0008] A sequential injection system for online addition and transfer of reagents, comprising a syringe pump, a reservoir ring, and a multi-position valve connected in sequence;

[0009] A colorimetric reaction system for providing a reaction site for ammonia and a colorimetric reagent includes a colorimetric reaction tank connected to a valve on the multi-position valve.

[0010] The ammonia nitrogen conversion system is used to convert ammonia nitrogen into ammonia gas and transport the ammonia gas to the colorimetric reaction tank through pipelines and carrier gas;

[0011] The detection system is used to detect the absorbance of the solution in the colorimetric reaction cell after color development, and to quantitatively analyze the ammonia nitrogen content in the environmental water body based on the slope of the absorbance change. It includes a light-emitting diode (LED), a flow cell, a photodiode, a data acquisition card, and a computer. The flow cell is vertically arranged and its sidewalls are shielded from light. The LED is fixed to one end of the flow cell, and the photodiode is fixed to the other end to ensure optical path collimation. The photodiode, data acquisition card, and computer are connected in sequence. The inlet of the flow cell is connected to a valve on the multi-position valve.

[0012] In some embodiments of the present invention, the sequential injection system further includes a pure water storage bottle connected to the injection pump; the injection pump is connected to the central channel of the multi-position valve via a storage ring;

[0013] One valve on the multi-position valve is connected to the color developer tank, another valve is connected to the waste liquid tank, and another valve is connected to the sodium hypochlorite tank.

[0014] In some embodiments of the present invention, the colorimetric reagent container contains a mixture of sodium salicylate and sodium nitrosoferricyanide dihydrate.

[0015] In some embodiments of the present invention, the colorimetric reaction chamber is a sealed device, and preferably, the colorimetric reaction chamber is a centrifuge tube.

[0016] In some embodiments of the present invention, the ammonia nitrogen conversion system includes:

[0017] The conversion reaction tank is a sealed device that provides a reaction site for the conversion of ammonium ions into ammonia gas.

[0018] A carrier gas supply device provides carrier gas for transporting ammonia from the conversion reaction tank to the colorimetric reaction tank;

[0019] Waste liquid discharge device, used for discharging waste liquid from the conversion reaction tank;

[0020] A sample input device is used to transport the water sample to be treated to the conversion reaction tank;

[0021] An alkali input device is used to deliver alkali solution to the conversion reaction tank;

[0022] An ammonia output pipeline is used to transport the generated ammonia gas to the colorimetric reaction tank.

[0023] In some embodiments of the present invention, the conversion reaction device is a centrifuge tube.

[0024] In some embodiments of the present invention, the carrier gas supply device includes an air pump and a flow restrictor needle, the flow restrictor needle being disposed on the pipeline between the air pump and the conversion reaction device for controlling the flow rate therebetween; preferably, the flow restrictor needle is a stainless steel capillary tube with different aperture.

[0025] In some embodiments of the present invention, both the sample input device and the alkali input device are syringes.

[0026] In some embodiments of the present invention, the end of the ammonia gas delivery pipe in the colorimetric reaction tank is provided with a blocking device, so that the ammonia gas is bulging out at the bottom of the colorimetric reaction tank in the form of small bubbles.

[0027] A second aspect of the present invention provides a method for rapid online detection of ammonia nitrogen in environmental water bodies, employing the miniature rapid online detection device for ammonia nitrogen in environmental water bodies described in the first aspect, comprising the following steps:

[0028] Step 1: Before ammonia nitrogen detection, turn off the light-emitting diode and record the intensity I of the dark current signal generated by the photodiode. d ,

[0029] Step 2: Turn on the air pump to provide carrier gas, and turn on the LED and photodiode;

[0030] Step 3: Using a sequential injection system, the colorimetric reagent solution and sodium hypochlorite solution are successively added to the colorimetric reaction cell; after being mixed evenly by carrier gas, the solution in the colorimetric reaction cell is filled into the flow cell using the sequential injection system, and excess solution is discharged to the waste liquid.

[0031] Step 4: Add the water sample to be tested into the conversion reaction cell; use a sequential injection system to draw an equal amount of colorimetric reagent solution as in Step 3 and add it into the colorimetric reaction cell;

[0032] Step 5: Add the alkaline solution to the conversion reaction tank; ammonia nitrogen reacts with hydroxide ions to produce ammonia gas, which is then carried into the colorimetric reaction tank by the carrier gas;

[0033] Step Six: After waiting for the carrier gas to carry the ammonia into the colorimetric reaction cell for a period of time, add an equal amount of sodium hypochlorite solution to the colorimetric reaction cell using a sequential injection system; at the same time, turn on the data acquisition card to record data; at this time, the signal intensity of the flow cell is recorded as I0;

[0034] Step 7: Use a sequential injection system to draw solution from the colorimetric reaction cell and fill it into the flow cell; discharge excess solution into the waste liquid; record the signal intensity I of the flow cell in real time; after the sample detection is completed, turn off the light-emitting diode and the data acquisition card;

[0035] Step 8: Connect the computer to the data acquisition card to record and process data; convert the real-time acquired electrical signals into absorbance A, and use the absorbance change rate to quantitatively analyze the ammonia nitrogen concentration in the environmental water.

[0036] In some embodiments of the present invention, the carrier gas flow rate is 35–130 mL / min. -1 Preferably 130 mL min -1 .

[0037] In some embodiments of the present invention, in step six, the ammonia sample loading time is 3 to 5 minutes, preferably 3 minutes.

[0038] In some embodiments of the present invention, the alkaline solution is a sodium hydroxide solution with a concentration of 2–5 mol / L. -1 Preferably 2 mol L -1 .

[0039] In some embodiments of the present invention, the concentration of the sodium hypochlorite solution is 0.4–0.6 mmol / L. -1 Preferably 0.5 mmol L -1 .

[0040] In some embodiments of the present invention, the concentration of sodium salicylate in the colorimetric reagent solution is ≥45 mmol / L. -1 Preferably 45 mmol L -1 The concentration of sodium nitrosoferricyanide dihydrate is ≥0.15 mmol / L. -1 Preferably 0.15 mmol L -1 .

[0041] In some embodiments of the present invention, in step three, the volume ratio of the colorimetric reagent solution to the sodium hypochlorite solution is 3:1.

[0042] In some embodiments of the present invention, the formula A = log(I0 - I) is used. d ) / (II d It converts the real-time collected electrical signals into absorbance.

[0043] The beneficial effects of this invention are as follows:

[0044] This invention discloses a miniature rapid online detection device for ammonia nitrogen in environmental water bodies, comprising: a sequential injection system, including an injection pump, a storage ring, and a multi-position valve connected in sequence, for online addition and transfer of reagents; a colorimetric reaction system connected to one valve on the multi-position valve, including a colorimetric reaction cell, for providing a reaction site for ammonia gas and colorimetric reagents; an ammonia nitrogen conversion system connected to the colorimetric reaction cell, for converting ammonia nitrogen into ammonia gas and transporting the ammonia gas to the colorimetric reaction cell through pipelines and a carrier gas; and a detection system connected to one valve on the multi-position valve, for detecting the absorbance of the solution in the colorimetric reaction cell, and quantitatively analyzing the ammonia nitrogen content in the environmental water body based on the slope of the absorbance change. This invention overcomes the problems of poor anti-interference ability and poor universality in current spectrophotometric, fluorescence, and electrochemical methods for detecting ammonia nitrogen content in water quality. Furthermore, this invention also solves the limitations of gas diffusion membranes on online ammonia nitrogen detection methods. This invention utilizes a sequential injection system to transfer water samples and required reagents. Based on the detection principle of "Determination of Ammonia Nitrogen in Water Quality: Salicylic Acid Spectrophotometry" (HJ536-2009), it constructs an ammonia nitrogen conversion system, a colorimetric reaction system, and a visible light absorption detection system suitable for use with the sequential injection system, thus developing an online, sensitive, and rapid detection device suitable for ammonia nitrogen analysis in various environmental water bodies. The miniature rapid online detection device for ammonia nitrogen in environmental water bodies provided by this invention uses the salicylate spectrophotometry method as the detection principle, integrating a sequential injection system, an ammonia nitrogen conversion reaction system, a colorimetric reaction system, and a detection system. This achieves online conversion and detection of ammonia nitrogen, effectively improving the matrix interference resistance of the salicylate spectrophotometric method for ammonia nitrogen analysis. Ammonia is an alkaline gas; a carrier gas is used to separate ammonia from the alkaline environmental water body. The ammonia is directly absorbed by the colorimetric reagent for a colorimetric reaction. During this process, the environmental water does not mix with the colorimetric reagent, avoiding interference from other ions in the environmental water and greatly improving the sensitivity of the device. By using a carrier gas to transport ammonia, the use of a permeable membrane is avoided, effectively preventing membrane contamination and replacement issues, and facilitating online, sensitive, and rapid detection of ammonia in environmental water bodies. Secondly, the device of this invention uses the instantaneous change rate of absorbance as a quantitative basis to calculate the ammonia nitrogen content in environmental water bodies, eliminating the need to wait for the complete colorimetric reaction between ammonia and the colorimetric reagent, thus saving analysis time. Statistics show that the analysis time for a single sample using the detection device provided by this invention is approximately 12 minutes, far less than the time consumed by a single sample analysis using standard methods (approximately 60 minutes). This device has advantages such as simple and rapid operation, miniaturization, low reagent consumption, and strong resistance to matrix interference, making it suitable for online detection of ammonia nitrogen in surface water, domestic sewage, and other water qualities. Attached Figure Description

[0045] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0046] Figure 1 This is a structural diagram of the miniature rapid online detection device for ammonia nitrogen in environmental water provided in an embodiment of the present invention;

[0047] Figure 2 The absorbance variation graph of ammonium chloride standard solutions of different concentrations was measured by the micro rapid online detection device for ammonia nitrogen in environmental water provided in this embodiment of the invention.

[0048] Figure 3 The graph shows the effect of carrier gas flow rate (a) and ammonia loading time (b) on the absorbance slope of ammonia nitrogen detection using the miniature rapid online detection device for ammonia nitrogen in environmental water provided in this embodiment of the invention.

[0049] Figure 4 The graph shows the effect of sodium hydroxide concentration (c) and sodium hypochlorite concentration (d) on the absorbance slope of ammonia nitrogen detection using the miniature rapid online ammonia nitrogen detection device provided in this embodiment of the invention.

[0050] Figure 5 The graph shows the effect of sodium salicylate concentration (e) and sodium nitrosoferricyanide dihydrate concentration (f) on the absorbance slope of ammonia nitrogen detection using the miniature rapid online ammonia nitrogen detection device provided in this embodiment of the invention.

[0051] Figure 6 A standard curve of ammonia nitrogen in environmental water bodies detected using the micro rapid online detection device for ammonia nitrogen provided in this embodiment of the invention.

[0052] Among them, 1 is a pure water storage bottle, 2 is a syringe pump, 3 is a storage ring, 4 is a multi-position valve, 5 is a sodium hypochlorite tank, 6 is a colorimetric reagent tank, 7 is a colorimetric reaction cell, 8 is a conversion reaction cell, 9 is an air pump, 10 is a flow-limiting needle, 11 is a peristaltic pump, 12 is a first syringe, 13 is a second syringe, 14 is a photodiode, 15 is a flow cell, and 16 is a light-emitting diode. Detailed Implementation

[0053] 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 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.

[0054] This invention provides a miniature rapid online detection device for ammonia nitrogen in environmental water bodies, comprising:

[0055] A sequential injection system for online addition and transfer of reagents, comprising a syringe pump, a reservoir ring, and a multi-position valve connected in sequence;

[0056] A colorimetric reaction system for providing a reaction site for ammonia and a colorimetric reagent includes a colorimetric reaction tank connected to a valve on the multi-position valve.

[0057] The ammonia nitrogen conversion system is used to convert ammonia nitrogen into ammonia gas and transport the ammonia gas to the colorimetric reaction tank through pipelines and carrier gas;

[0058] The detection system is used to detect the absorbance of the solution in the colorimetric reaction cell after color development, and to quantitatively analyze the ammonia nitrogen content in the environmental water body based on the slope of the absorbance change. It includes a light-emitting diode (LED), a flow cell, a photodiode, a data acquisition card, and a computer. The flow cell is vertically arranged and its sidewalls are shielded from light. The LED is fixed to one end of the flow cell, and the photodiode is fixed to the other end to ensure optical path collimation. The photodiode, data acquisition card, and computer are connected in sequence. The inlet of the flow cell is connected to a valve on the multi-position valve.

[0059] See Figure 1 , Figure 1 This is a structural diagram of the miniature rapid online detection device for ammonia nitrogen in environmental water provided in an embodiment of the present invention. Figure 1 In the diagram, 1 is a pure water storage bottle, 2 is a syringe pump, 3 is a storage ring, 4 is a multi-position valve, 5 is a sodium hypochlorite tank, 6 is a colorimetric reagent tank, 7 is a colorimetric reaction cell, 8 is a conversion reaction cell, 9 is an air pump, 10 is a flow-limiting needle, 11 is a peristaltic pump, 12 is a first syringe, 13 is a second syringe, 14 is a photodiode, 15 is a flow cell, and 16 is a light-emitting diode.

[0060] The present invention provides a miniature rapid online detection device for ammonia nitrogen in environmental water, comprising: a sequential injection system, an ammonia nitrogen conversion system, a colorimetric reaction system, and a detection system; the gas outlet of the ammonia nitrogen conversion system is connected to the colorimetric reaction cell 7 of the colorimetric reaction system; the colorimetric reaction cell 7 of the colorimetric reaction system is connected to valve position 8 of the multi-position valve 4 in the sequential injection system; valve position 5 of the multi-position valve 4 in the sequential injection system is connected to the In port of the flow cell 15 of the detection system; and the Out port of the flow cell 15 of the detection system is connected to a waste liquid bottle.

[0061] The micro rapid online detection device for ammonia nitrogen in environmental water provided by this invention includes a sequential injection system comprising an injection pump 2 and a multi-position valve 4. The In end of the injection pump 2 is connected to a pure water storage bottle 1. The Out end of the injection pump 2 is connected to the central channel of the multi-position valve 4 via a storage ring 3. The storage ring 3 is a polytetrafluoroethylene tube with dimensions of 1.0 mm inner diameter, 1.6 mm outer diameter, and 3.20 m length. Valve position 3 of the multi-position valve 4 is connected to a sodium hypochlorite tank 5. Valve position 4 of the multi-position valve 4 is connected to a colorimetric reagent tank 6. Valve position 5 of the multi-position valve 4 is connected to the solution inlet of the flow cell 15 in the detection system. Valve position 6 of the multi-position valve 4 is connected to waste liquid. Valve position 8 of the multi-position valve 4 is connected to a colorimetric reaction cell 7. Valve positions 1, 2, and 7 of the multi-position valve 4 are left unused and open to air. The operation of the injection pump 2 and the switching of the multi-position valve 4 are both controlled by a computer. The In terminal of the syringe pump 2 is connected to the pure water storage bottle via a polytetrafluoroethylene (PTFE) tube. The multi-position valve 4 is also connected to the sodium hypochlorite tank, the colorimetric reagent tank, the solution inlet of the flow cell 15 of the detection system, the waste liquid, and the colorimetric reaction cell 7 via PTFE tubes. For portability, the volume of the syringe pump 2 can be 2.5 mL.

[0062] The ammonia nitrogen micro-rapid online detection device for ammonia nitrogen in environmental water provided by this invention includes an ammonia nitrogen conversion system comprising a conversion reaction tank 8, an air pump 9, a flow-limiting needle 10, a peristaltic pump 11, and two syringes (12 and 13). The conversion reaction tank 8 is a centrifuge tube with a volume of 50 mL, serving as the conversion reaction tank for the ammonia nitrogen conversion system. The air pump 9 is connected in series with the flow-limiting needle 10 and is connected to the conversion reaction tank 8 to provide a constant flow rate of carrier gas for ammonia nitrogen conversion. The flow-limiting needle 10 is a stainless steel capillary tube with different pore sizes. The peristaltic pump is connected to the centrifuge tube for waste liquid discharge. The two syringes (12 and 13) are respectively connected to the conversion reaction tank 8 for adding sodium hydroxide solution and samples. In the ammonia nitrogen conversion system, all components are connected by polytetrafluoroethylene (PTFE) tubing. The ammonia gas generated by the ammonia nitrogen conversion system is transferred to the colorimetric reaction system via PTFE tubing. The PTFE tubing has an inner diameter of 1.8 mm and an outer diameter of 2.6 mm.

[0063] In the micro-rapid online detection device for ammonia nitrogen in environmental water provided by this invention, the colorimetric reaction system can utilize a 5mL centrifuge tube as the colorimetric reaction tank 7; the reagent required for the colorimetric reaction 7 is injected by a sequential injection system through valve position 8 of a multi-position valve 4. Ammonia gas generated by the ammonia nitrogen conversion system is transported through a polytetrafluoroethylene (PTFE) tube into the bottom of the colorimetric reaction tank 7 and reacts with the colorimetric reagent. The end of the PTFE tube transporting ammonia gas in the colorimetric reaction tank 7 is equipped with a blocking device, causing the ammonia gas to bubble out at the bottom of the colorimetric reaction tank in the form of small bubbles. Optionally, four smaller inner diameter PTFE tubes are inserted into the end of the PTFE tube, and the gaps are filled with hot melt adhesive, allowing the ammonia gas to bubble out at the bottom of the colorimetric reaction tank in the form of small bubbles from the smaller inner diameter PTFE tubes, ensuring sufficient reaction between the ammonia gas and the colorimetric reagent solution; the smaller inner diameter PTFE tubes have an inner diameter of 0.2mm and an outer diameter of 0.6mm. The reagent solution after the colorimetric reaction is drawn out through valve position 8 of multi-position valve 4 and transferred to the detection system for detection; the colorimetric reagent is stored in the colorimetric reagent tank and is a mixed solution of sodium salicylate and sodium nitrosoferricyanide dihydrate.

[0064] The present invention provides a miniature rapid online detection device for ammonia nitrogen in environmental water. The detection system includes a light-emitting diode (LED) 16, a flow cell 15, a photodiode 14, a data acquisition card, and a computer. The flow cell 15 can be a straight PVC tube. The LED 16 and photodiode 14 are fixed to both ends of the straight PVC tube using hot melt adhesive, ensuring optical path collimation. The straight PVC tube has the following dimensions: inner diameter 2.7 mm, outer diameter 7.0 mm, and length 30 cm. Holes are drilled near both ends of the straight PVC tube to serve as the In / Out ports of the flow cell 15. The In port of the flow cell 15 is connected to valve position 5 of the multi-position valve 4; the Out port of the flow cell 15 is connected to a waste liquid bottle.

[0065] Furthermore, the flow cell 15 should be placed vertically and wrapped with black tape to avoid the influence of air bubbles introduced during solution replacement and interference from natural light.

[0066] In the above detection system, the light-emitting diode 16 can be a deep red light-emitting diode with an emission wavelength range of 660-665nm; the photodiode 14 is a TSL 257; and the data acquisition card is a USB-1208LS.

[0067] at the same time, Figure 1In the schematic diagram shown, the connection between the light-emitting diode 16, the flow cell 15, and the photodiode 14 is fixed and sealed with transparent hot melt adhesive; the gap between the 5mL centrifuge tube cap, which serves as the color development reaction cell 7, and the 3 polytetrafluoroethylene tubes is also fixed and sealed with transparent hot melt adhesive; the gap between the 50mL centrifuge tube cap, which serves as the conversion reaction cell 8, and the 5 polytetrafluoroethylene tubes is also fixed and sealed with transparent hot melt adhesive.

[0068] This invention also provides a method for rapid online detection of ammonia nitrogen in environmental water bodies, which is carried out in the micro rapid online detection device for ammonia nitrogen in environmental water bodies described in the above technical solution, and includes the following steps:

[0069] Step 1: Before ammonia nitrogen detection, turn off LED 16 and record the dark current signal intensity I generated by photodiode 14. d ;

[0070] Step 2: Turn on air pump 9 to provide carrier gas and turn on LED 16;

[0071] Step 3: Using a sequential injection system, the colorimetric reagent solution and sodium hypochlorite solution are successively added to the colorimetric reaction cell 7; after being mixed evenly by carrier gas, the solution in the colorimetric reaction cell 7 is filled into the flow cell 15 using the sequential injection system, and the excess solution is discharged to the waste liquid.

[0072] Step 4: Add the water sample to be tested to the conversion reaction cell 8; use a sequential injection system to draw an equal amount of colorimetric reagent solution as in Step 3 and add it to the colorimetric reaction cell 7;

[0073] Step 5: Add the alkaline solution to the conversion reaction tank 8; ammonia nitrogen reacts with hydroxide ions to produce ammonia gas, which is then carried by the carrier gas into the colorimetric reaction tank 7;

[0074] Step Six: After waiting for the carrier gas to carry the ammonia into the colorimetric reaction cell 7 for a period of time, add an equal amount of sodium hypochlorite solution to the colorimetric reaction cell 7 using a sequential injection system; at the same time, turn on the data acquisition card to record data; at this time, the signal intensity of the flow cell is recorded as I0;

[0075] Step 7: Use a sequential injection system to draw the solution from the colorimetric reaction cell 7 and fill it into the flow cell 15. Discharge the excess solution into the waste liquid; record the signal intensity I of the flow cell in real time; after the sample detection is completed, turn off the light-emitting diode 16 and the data acquisition card.

[0076] Step 8: Connect the computer to the data acquisition card to record and process data; convert the real-time acquired electrical signals into absorbance A, and use the absorbance change rate to quantitatively analyze the ammonia nitrogen concentration in the environmental water.

[0077] In the rapid detection method for ammonia nitrogen in environmental water provided by this invention, the carrier gas flow rate is 35–130 mL / min. -1 Preferably 35 mL min -1 50mL min -1 80mL min -1 and 130mL min -1 More preferably 130 mL min -1 .

[0078] In the rapid detection method for ammonia nitrogen in environmental water provided by this invention, in step six, the ammonia loading time (i.e., the time for the carrier gas to load ammonia into the colorimetric reaction cell 7) is 3-5 minutes, specifically 3 minutes, 4 minutes, or 5 minutes. In one embodiment provided by this invention, to ensure the sensitivity of ammonia nitrogen detection and shorten the analysis time, the ammonia loading time is selected as 3 minutes.

[0079] In the rapid detection method for ammonia nitrogen in environmental water provided by this invention, the alkaline solution is a sodium hydroxide solution with a concentration of 2-5 mol / L. -1 Specifically, it can be 2 mol L. -1 3 mol L -1 4 mol L -1 5 mol L -1 In one embodiment of the present invention, to avoid the use of excessive strong alkali, the concentration of the sodium hydroxide solution is 2 mol / L. -1 .

[0080] In the rapid detection method for ammonia nitrogen in environmental water provided by this invention, the concentration of the sodium hypochlorite solution is 0.4–0.6 mmol / L. -1 Specifically, it can be 0.4 mmol / L. -1 0.5 mmol L -1 0.6 mmol / L -1 In one embodiment of the present invention, to avoid a decrease in absorbance due to excessive sodium hypochlorite, the concentration of the sodium hypochlorite solution is 0.5 mmol / L. -1 .

[0081] In the rapid detection method for ammonia nitrogen in environmental water provided by this invention, the concentration of sodium salicylate in the colorimetric reagent solution is ≥45 mmol / L. -1 Specifically, it can be 45 mmol / L. -1 50 mmol L -1 60 mmol / L -1 80 mmol L -1 100 mmol L -1 200 mmol L -1In one embodiment of the present invention, to ensure detection sensitivity, the concentration of sodium salicylate is 45 mmol / L. -1 .

[0082] In the rapid detection method for ammonia nitrogen in environmental water provided by this invention, the concentration of sodium nitrosoferricyanide dihydrate in the colorimetric reagent solution is ≥0.15 mmol / L. -1 Specifically, it can be 0.15 mmol / L. -1 0.20 mmol / L -1 0.30 mmol / L -1 0.40 mmol / L -1 0.50 mmol / L -1 0.60 mmol / L -1 In one embodiment of the present invention, to ensure detection sensitivity, the concentration of sodium nitrosoferricyanide dihydrate is 0.15 mmol / L. -1 .

[0083] In the rapid detection method for ammonia nitrogen in environmental water provided by the present invention, in step three, the volume ratio of the colorimetric reagent solution and the sodium hypochlorite solution is 3:1.

[0084] In the rapid detection method for ammonia nitrogen in environmental water provided by this invention, the formula A = log(I0 - I) is used. d ) / (II d It converts the real-time collected electrical signals into absorbance.

[0085] Currently, the analysis and detection of ammonia nitrogen in environmental water samples still faces problems such as severe matrix interference and the inability to perform rapid on-site analysis. This invention, based on the fundamental principles of the "Determination of Ammonia Nitrogen in Water Quality: Salicylic Acid Spectrophotometric Method" (HJ 536-2009), develops an online ammonia nitrogen detection device based on a sequential injection system. By separately developing an ammonia nitrogen conversion reaction system, a colorimetric reaction system, and a detection system suitable for use with a sequential injection system, online detection and analysis of ammonia nitrogen in water samples with complex matrices is achieved. The detection system is assembled using a light-emitting diode as the light source, a photoelectric converter as the detector, and a polyvinyl chloride tube as the detection flow cell, thus significantly reducing the device's size, energy consumption, and manufacturing cost.

[0086] Testing showed that the developed device could analyze ammonia nitrogen in water samples for 12 minutes, with a detection limit (LOD) of 1.1 μmol / L. -1 The precision (relative standard deviation, RSD) was 4.3% (c = 10 μmol L). -1 (n=7), linear range is 5-1000 μmol L. -1Interference tests confirmed that common coexisting ions and components in environmental water bodies have no significant impact on ammonia nitrogen analysis, allowing the device to be directly used to analyze ammonia nitrogen concentrations in reservoir water, domestic sewage, seawater, and landfill leachate. The results of ammonia nitrogen analysis in actual water bodies using this device showed no significant difference from those obtained using standard methods, with spiked recoveries ranging from 92.3% to 98.1%, further demonstrating the accuracy and practicality of the developed device.

[0087] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0088] Reagent instructions:

[0089] Unless otherwise specified, all reagents used in this invention are analytical grade reagents, and the water used for preparing solutions and diluting samples is ultrapure water (18.2 MΩcm). Sodium salicylate (C7H5O3Na), sodium nitrosoferricyanide dihydrate (Na2[Fe(CN)5NO]·2H2O), sodium hypochlorite (NaClO, available chlorine 5.2%, free alkali 7.8-8.0%, chemically pure), ammonium chloride (NH4Cl), and sodium hydroxide (NaOH) were all purchased from Sinopharm Chemical Reagents Shanghai Co., Ltd.

[0090] Prepare 100mmol L -1 NH4Cl solution was used as an ammonia nitrogen stock solution, and after quantitative dilution, it was used for plotting ammonia nitrogen standard curves and optimizing experimental parameters.

[0091] Prepare 5mol L -1 NaOH solution is used as an alkaline reagent for converting ammonia nitrogen into ammonia gas.

[0092] Prepare 1.4 mol L -1 C7H5O3Na stock solution, 50 mmol L -1 The Na2[Fe(CN)5NO] stock solution (can be stored away from light for ≤30 days) was appropriately diluted and mixed as a colorimetric reagent for ammonia nitrogen detection.

[0093] Configure an effective chlorine concentration of 400 mmol / L -1 A NaClO stock solution, after appropriate dilution, is used as an oxidant for the ammonia nitrogen colorimetric reaction.

[0094] Example 1:

[0095] like Figure 1As shown, a miniature rapid online detection device for ammonia nitrogen in environmental water includes: a pure water storage bottle 1, an injection pump 2, a storage ring 3, a multi-position valve 4, a sodium hypochlorite tank 5, a colorimetric reagent tank 6, a colorimetric reaction cell 7, a conversion reaction cell 8, an air pump 9, a flow-limiting needle 10, a peristaltic pump 11, a first syringe 12, a second syringe 13, a photodiode 14, a flow cell 15, a light-emitting diode 16, a data acquisition card, and a computer.

[0096] The sequential injection system consists of one injection pump 2 (2.5 mL volume) and one multi-position valve 4 (FIAlab Instruments, Bellevue, WA, USA). The inlet of injection pump 2 is connected to a pure water storage bottle 1 as a flow carrier, and the outlet of injection pump 2 is connected to the central channel of multi-position valve 4 via a storage ring 3 (PTFE tubing with ID = 1.0 mm, OD = 1.6 mm, L = 3.20 m). Valve position 3 of multi-position valve 4 is connected to the sodium hypochlorite tank 5; valve position 4 is connected to the colorimetric reagent tank 6; valve position 5 is connected to the solution inlet of the flow cell 15 of the detection system; valve position 6 is connected to the waste liquid; valve position 8 is connected to the colorimetric reaction cell 7; valve positions 1, 2, and 7 are left unused and open to air. The operation of injection pump 2 and the switching of multi-position valve 4 are both computer-controlled.

[0097] The ammonia-nitrogen conversion system consists of a 50 mL centrifuge tube (conversion reaction cell 8), an air pump 9 (type 030-3, Foshan Weilizi Electronic Technology Co., Ltd.), a peristaltic pump 11 (type LFP102BLW, Zhejiang Lifu Automation Technology Co., Ltd.), and two syringes (12 and 13). The air pump 9, connected in series with a flow-limiting needle 10 (stainless steel capillary tubes of different orifice sizes), provides a constant flow rate of carrier gas for ammonia-nitrogen conversion; the peristaltic pump 11 is used for waste liquid discharge; and the two syringes (12 and 13) are used for adding NaOH solution and samples, respectively. All components of the ammonia-nitrogen conversion system are connected by PTFE tubing (ID = 1.8 mm, OD = 2.6 mm), and the generated ammonia gas is transferred to the colorimetric reaction system via PTFE tubing.

[0098] The colorimetric reaction system uses 5mL centrifuge tubes as the colorimetric reaction chamber 7. The reagents required for the colorimetric reaction are injected via a sequential injection system through valve position 8 of multi-position valve 4. Ammonia gas generated by the ammonia-nitrogen conversion system is transmitted through PTFE tubing to the bottom of colorimetric reaction chamber 7 and reacts with the colorimetric reagent. To ensure sufficient reaction between the ammonia gas and the colorimetric reagent solution, four smaller-diameter PTFE tubes (ID = 0.2mm, OD = 0.6mm) are inserted into the end of the PTFE tubing, and the gaps are filled with hot melt adhesive, allowing ammonia gas to bubble out from the smaller-diameter PTFE tubes as small air bubbles at the bottom of colorimetric reaction chamber 7. The reagent solution after the colorimetric reaction is drawn out through valve position 8 of multi-position valve 4 and transmitted to the detection system for detection.

[0099] The detection system consists of a light-emitting diode (LED) 16 (660-665nm), a flow cell 15 (PVC pipe, L=30cm, ID=2.7mm, OD=7.0mm), a photodiode 14 (PD, TSL 257), a data acquisition card (DAQ, USB-1208LS), and a computer. The LED and PD are fixed to both ends of the straight PVC pipe using hot melt adhesive, ensuring optical path collimation. Holes are drilled near both ends of the PVC pipe to serve as the In / Out ports of the flow cell 15. The In port of the flow cell 15 connects to valve position 5 of the multi-position valve 4, and the Out port connects to the waste liquid bottle. The flow cell 15 must be placed vertically and wrapped with black tape to prevent air bubbles introduced during solution changes and interference from natural light.

[0100] Example 2

[0101] A rapid online detection method for ammonia nitrogen in environmental water bodies, employing the miniature rapid online detection device for ammonia nitrogen in environmental water bodies described in Example 1, includes the following steps:

[0102] Before ammonia nitrogen detection, turn off LED 16 and record the dark current signal intensity I generated by PD 14. d .

[0103] The specific operating steps for ammonia nitrogen sample testing include:

[0104] (1) Turn on air pump 9 to provide a continuous and stable flow rate of carrier gas for ammonia nitrogen conversion and color development reaction, and turn on LED 16.

[0105] (2) Using a sequential injection system, 1.8 mL of colorimetric reagent solution and 0.6 mL of NaClO solution were successively added to the colorimetric reaction cell 7. After being mixed evenly by carrier gas, the solution in the colorimetric reaction cell 7 was drawn into the flow cell 15 of the detection system using the sequential injection system, and the excess solution was discharged to the waste liquid.

[0106] (3) Use the second syringe 13 to draw 38 mL of sample and add it to the conversion reaction cell 8, and keep the syringe connected to the sample pipeline. After the detection is completed, clean the reaction cell.

[0107] (4) Control the sequential injection system to draw 1.8 mL of colorimetric reagent solution and add it to the colorimetric reaction cell 7.

[0108] (5) Use the first syringe 12 to draw 2 mL of NaOH solution into the conversion reaction cell 8. Ammonia nitrogen reacts with NaOH to produce ammonia gas, which is then carried into the colorimetric reaction cell 7 by the carrier gas.

[0109] (6) After waiting for the carrier gas to load ammonia into the colorimetric reaction cell for a period of time (ammonia loading time), add 0.6 mL of NaClO solution to the colorimetric reaction cell 7 using a sequential injection system, and simultaneously control the data acquisition card to start recording data. At this moment, the flow cell 14 contains a mixed solution of colorimetric reagent and NaClO, which does not contain ammonia nitrogen, so the signal intensity is recorded as I0.

[0110] (7) Using a sequential injection system, draw the solution from the colorimetric reaction cell 7 and fill it into the flow cell 15 of the detection system. Discharge any excess solution into the waste liquid. Record the signal intensity I of the flow cell in real time.

[0111] (8) Use a sequential injection system to aspirate and empty all the remaining solution in the colorimetric reaction cell 7, and then use the sequential injection system to aspirate 2.5 mL of pure water to rinse the colorimetric reaction cell 2-3 times. Clean the sample syringe with pure water or the sample to be tested, and clean the conversion reaction cell with pure water or the sample to be tested 2-3 times to prepare for the next sample test.

[0112] (9) After all samples have been tested, turn off the LED and data acquisition card. Rinse the multi-position valve 4, flow cell 15, and colorimetric reaction cell 7 using the sequential injection system, and manually clean the conversion reaction cell 8, etc.

[0113] During the above experiment, the carrier gas flow rate was 130 mL / min. -1 Ammonia loading time was 3 min; sodium hydroxide concentration was 2 mol / L. -1 The sodium hypochlorite solution concentration is 0.5 mmol / L. -1 The concentration of sodium salicylate in the colorimetric reagent solution is 45 mmol / L. -1 The concentration of sodium nitrosoferricyanide dihydrate is 0.15 mmol / L. -1 .

[0114] Data processing:

[0115] Use the formula A = log(I0 - I) d ) / (II d The system converts the real-time acquired electrical signal into absorbance. Here, I0 represents the intensity of the electrical signal under illumination when the detection cell is filled with blank chromogenic reagent. d I represents the dark current signal strength of the PD, and I represents the electrical signal strength during real-time detection.

[0116] Blank sample, 10 and 200 μmol L -1 Ammonia nitrogen analysis DAQ records real-time signals such as Figure 2 As shown in the illustration, the real-time absorbance signal is as follows: Figure 2As shown. The data acquisition card records the I0 signal for the first 70 seconds. During this time, the flow cell contains pure chromogenic reagent solution and NaClO solution, and the slow signal change can be attributed to baseline drift. When the sequential injection system fills the flow cell with the chromogenic solution that has absorbed ammonia, the pressure change in the flow cell causes a slight deformation, resulting in a violent fluctuation in the detection signal (approximately 70-100 seconds). After the solution in the flow cell settles (approximately 100-180 seconds), the absorbance signal gradually and steadily increases. This gradual increase in absorbance is due to the colorimetric reaction of ammonia nitrogen with C7H5O3Na, Na2[Fe(CN)5NO], and NaClO. To save detection time, this embodiment does not collect data until the colorimetric reaction is completely finished, but only collects data for approximately 180 seconds for analysis. Furthermore, to avoid errors caused by fluctuations in instantaneous absorbance and deviations in data acquisition time, this embodiment uses the rate of change of absorbance over a period of time for quantitative analysis, specifically using the slope of absorbance change between 120-160 seconds for quantitative analysis (S = (A 160 -A 120 ) / (160-120)).

[0117] Example 3

[0118] The carrier gas flow rate, the concentration of NaOH solution required for ammonia conversion from ammonia nitrogen to ammonia gas, the ammonia absorption time of the colorimetric reagent (ammonia loading time), and the concentrations of C7H5O3Na, Na2[Fe(CN)5NO], and available chlorine in the NaClO solution in the colorimetric reaction reagent all have a significant impact on ammonia nitrogen detection. This example uses 10 μmol / L... -1 Using ammonium chloride standard solution as the test object, the influence of relevant experimental conditions on ammonia nitrogen detection performance was investigated using a single-factor variable method. The specific process includes the following steps:

[0119] (1) Effect of carrier gas flow rate on absorbance slope of ammonia nitrogen detection

[0120] The carrier gas flow rate and the absorption time of ammonia by the chromogenic reagent (ammonia loading time) jointly determine the absorption efficiency of ammonia by the chromogenic reagent solution, directly affecting the sensitivity of ammonia detection. To improve analytical efficiency, this embodiment first fixes the ammonia loading time at 3 minutes and examines the effect of the carrier gas flow rate. The carrier gas flow rate is determined by changing the flow-limiting needle model and using a soap film flow meter to measure the flow rate at the exhaust port of the chromogenic reaction cell. Figure 3 As shown in curve a, the values ​​of 35, 50, 80, and 130 mL min were examined. -1 The effect of carrier gas flow rate on the ammonia nitrogen detection signal was investigated while keeping other experimental conditions constant. The results showed that the carrier gas flow rate increased from 35 mL / min... -1 Increase to 130 mL min -1As the absorbance changes, the rate of change gradually increases. This is mainly due to the limited carrier gas loading time; at low flow rates, the generated ammonia cannot be completely carried into the colorimetric reaction cell and absorbed by the colorimetric reagent solution in time, resulting in a low absorbance signal. However, when the carrier gas flow rate is increased to greater than 130 mL / min... -1 The solution in the colorimetric reaction cell will overflow with the carrier gas. Therefore, this invention selects a carrier gas flow rate of 130 mL / min. -1 The effect of ammonia loading time will be further investigated.

[0121] (2) Effect of ammonia loading time on the absorbance slope of ammonia nitrogen detection

[0122] like Figure 3 The b-curve was used to examine the effect of ammonia loading times of 0.5, 1, 2, 3, and 5 min on ammonia nitrogen detection, while keeping other experimental conditions constant. The results showed that within a 5-min loading time, the absorbance slope of ammonia nitrogen detection gradually increased and then leveled off with increasing loading time. Increasing the loading time from 0.5 to 3 min resulted in a more significant increase in the absorbance slope; however, when the loading time exceeded 3 min, the increase in the ammonia nitrogen signal value detected by the device slowed down. This may be because within 3 min, the flow rate was 130 mL / min. -1 The carrier gas can transfer most of the generated ammonia to the colorimetric reagent solution, and further increasing the ammonia loading time has little effect on improving the sensitivity of ammonia nitrogen detection. To shorten the analysis time, this invention ultimately selected a 3-minute ammonia loading time as the experimental condition.

[0123] (3) Effect of sodium hydroxide concentration on absorbance slope of ammonia nitrogen detection

[0124] The concentration of NaOH solution directly affects the efficiency of ammonia nitrogen conversion to ammonia gas. For example... Figure 4 The c-curve was used to investigate 0.5, 1, 2, and 5 mol L. -1 The effect of sodium hydroxide concentration on ammonia nitrogen detection was investigated, while keeping other experimental conditions constant. The results showed that under low-concentration sodium hydroxide solution conditions (0.5 mol / L), the concentration of sodium hydroxide significantly increased the detection rate of ammonia nitrogen. -1 The ammonia nitrogen in the sample could not be quickly and efficiently converted into ammonia gas; the concentration of sodium hydroxide solution was gradually increased to 2 mol / L. -1 Detection of 10 μmol L -1 The absorbance slope of the ammonium chloride standard solution increased significantly, indicating that the efficiency of ammonia nitrogen conversion to ammonia gas in the water sample gradually increased. The concentration of sodium hydroxide was further increased to 5 mol / L. -1The absorbance slope continued to increase, but the slower increase in signal intensity indicated a slower increase in the efficiency of ammonia nitrogen conversion to ammonia gas. Furthermore, the use of a high concentration of sodium hydroxide for ammonia nitrogen conversion resulted in a large amount of residual sodium hydroxide in the waste liquid. To avoid excessive use of strong alkali, this invention selected 2 mol / L... -1 Sodium hydroxide was used as an experimental condition for the conversion of ammonia nitrogen into ammonia gas.

[0125] (4) Effect of sodium hypochlorite concentration on absorbance slope of ammonia nitrogen detection

[0126] The function of NaClO is to oxidize ammonia nitrogen into monochloramine, which can react with salicylate ions. For example... Figure 4 The d-curve was used to examine values ​​of 0.1, 0.5, 1, 2, and 4 mmol / L. -1 The effect of sodium hypochlorite solution concentration (available chlorine) on the ammonia nitrogen detection signal was investigated, while keeping other experimental conditions constant. The results showed that a low concentration of sodium hypochlorite solution (0.1 mmol / L) significantly increased the effective chlorine content. -1 The generated ammonia gas cannot be completely oxidized, resulting in a very low absorbance slope for the ammonium chloride. When the concentration of the sodium hypochlorite solution is increased to 0.5 mmol / L... -1 At 10 μmol L -1 The absorbance slope of the ammonium chloride standard solution reached its maximum value. However, further increasing the sodium hypochlorite solution concentration from 0.5 to 4 mmol / L... -1 The absorbance slope of the same concentration of ammonium chloride standard solution gradually decreased. This phenomenon occurs because excess sodium hypochlorite solution further reacts with the products of the ammonia nitrogen colorimetric reaction, causing oxidation and fading, thus reducing the absorbance of the solution. Therefore, this invention selected 0.5 mmol / L... -1 A sodium hypochlorite solution of a certain concentration was used as the experimental condition.

[0127] (5) Effect of sodium salicylate concentration on absorbance slope of ammonia nitrogen detection

[0128] Sodium salicylate is a colorimetric reagent for ammonia nitrogen detection, such as... Figure 5 The e-curve was used to examine values ​​of 15, 45, 90, 150, and 210 mmol / L. -1 The effect of sodium salicylate concentration on the ammonia nitrogen detection signal was investigated while keeping other experimental conditions constant. The results showed that sodium salicylate concentrations between 15-45 mmol / L... -1 The instantaneous rate of change of ammonium chloride absorbance increased significantly with increasing concentration, exceeding 45 mmol / L. -1 Sodium salicylate did not significantly improve the signal for detecting ammonium chloride. Therefore, this invention selected 45 mmol / L... -1 The concentration of sodium salicylate was used as the final experimental condition.

[0129] (6) Effect of sodium dinitrosoferricyanide concentration on absorbance slope of ammonia nitrogen detection

[0130] Na₂[Fe(CN)₅NO] is a catalyst for the colorimetric reaction of ammonia nitrogen with salicylic acid, and the amount of Na₂[Fe(CN)₅NO] affects the speed of the colorimetric reaction. Since the quantification of ammonia nitrogen in this example is based on the rate of change in absorbance during the colorimetric reaction, the concentration of Na₂[Fe(CN)₅NO] also affects the sensitivity of ammonia nitrogen analysis. Figure 5 The f-curve was used to examine values ​​of 0.015, 0.15, 0.3, 0.45, and 0.6 mmol / L. -1 The effect of the concentration of sodium nitrosoferricyanide dihydrate on the ammonia nitrogen analysis signal was investigated, while keeping other experimental conditions constant. The results showed that the catalyst concentration increased from 0.015 mmol / L... -1 Increase to 0.15 mmol / L -1 The absorbance slope of ammonium chloride detection increased significantly, but the catalyst concentration was greater than 0.15 mmol / L. -1 The concentration had no significant effect on the increase in the absorbance slope of ammonium chloride detection. Therefore, this invention selected 0.15 mmol / L. -1 Sodium nitrosoferricyanide dihydrate was used for ammonia nitrogen analysis.

[0131] In summary, the selected experimental conditions are: carrier gas flow rate of 130 mL / min. -1 Ammonia loading time was 3 min; sodium hydroxide concentration was 2 mol / L. -1 The sodium hypochlorite solution concentration is 0.5 mmol / L. -1 The concentration of sodium salicylate in the colorimetric reagent solution is 45 mmol / L. -1 The concentration of sodium nitrosoferricyanide dihydrate is 0.15 mmol / L. -1 .

[0132] Under the selected experimental conditions, the sample blank, 5, 10, 200, 500, 700, and 1000 μmol L were tested respectively. -1 The analytical performance of the R&D device was evaluated using ammonium chloride standard solutions of varying concentrations, and the results are shown in Table 1. Figure 6 The figure shown is a standard curve for detecting ammonia nitrogen using the device of the present invention.

[0133] The performance test results of the device show that the detection limit of the device developed in this invention is lower than the national standard limit of 0.15 mg / L for ammonia nitrogen in Class I surface water. -1 (10.7 μmol L) -1 The standard limit for ammonia nitrogen in Class I groundwater is 0.02 mg / L. -1 (1.4 μmol L) -1 It is suitable for sensitive analysis of ammonia nitrogen in surface water and groundwater.

[0134] Table 1 Analytical performance of the ammonia nitrogen micro rapid detection device

[0135] Correlation coefficient 0.9953 Linear range <![CDATA[5-1000μmol L -1 ]]> Detection limit <![CDATA[1.1μmol L -1 ]]> Relative standard deviation <![CDATA[4.3%(10μmol L -1 ,n=7)]]> Analysis time ≤12min / sample

[0136] Example 4

[0137] Anti-interference test:

[0138] This embodiment examines some major ions and components present in environmental water samples, such as: Na+ + Ca 2+ K + Cl - F - NO2 - NO3 - SO4 2- CO3 2- SO3 2- HCO3 - The effects of urea and other substances on ammonia nitrogen detection. Following the steps described in Example 2, in 10 μmol L... -1 A comparison of the detection signals of ammonia nitrogen standard solutions with those of pure ammonium chloride standard solutions after adding certain concentrations of interfering ions revealed that 1000 mmol / L... -1 Na + and Cl - 10 mmol L -1 F - NO2 - NO3 - SO4 2- K + CO3 2- SO3 2- HCO3 - Ca 2+ 5 mmol L -1 Urea has no significant effect on ammonia nitrogen detection. When Mg in the water sample... 2+ The concentration is 10 mmol / L -1 At this time, it has a weak impact on the detection of ammonium chloride, resulting in a decrease in the recovery rate of ammonia nitrogen detection to 88.8%. Therefore, in the detection of Mg... 2+ When ammonia nitrogen levels are high in water bodies, the water sample needs to be appropriately diluted to avoid interference from magnesium ions. Since the concentrations of coexisting ions and components in actual water samples are usually not higher than the concentrations that interfere with experimental determinations, the device developed in this invention is suitable for direct use in the analysis of ammonia nitrogen in environmental water samples. The specific results summarizing the effects of coexisting ions and components on ammonia nitrogen detection are shown in Table 2.

[0139] Table 2. Effects of common interfering ions and components on the detection of ammonia nitrogen in the research and development device (ammonium chloride concentration: 10 μmol / L)-1 )

[0140]

[0141] Example 4

[0142] Practical Applications

[0143] Using the apparatus of Example 1, and following the steps described in Example 2, the ammonia nitrogen concentrations in water samples from Dingjiahe Reservoir, the oxidation pond (sewage I) and primary sedimentation pond (sewage II) of an urban wastewater treatment plant, seawater, and landfill leachate were detected and analyzed. The results are summarized in Table 3. Specifically, the ammonia nitrogen content detected in the Dingjiahe Reservoir water sample was 34.65 ± 0.13 μmol / L. -1 Ammonia nitrogen content of 1028.38 ± 6.19 μmol / L was detected in a wastewater sample from the oxidation pond (wastewater I) of a wastewater treatment plant in Qingdao. -1 The ammonia nitrogen content detected in the landfill leachate was 2.90 ± 0.31 μmol L. -1 Spiked with 20, 1000, and 10 μmol L, respectively. -1 The recovery rate of ammonia nitrogen spiked tests ranged from 92.3% to 98.1%. Using the apparatus described in Example 1 and the standard method (HJ 536-2009), a primary sedimentation tank sample (wastewater II) from a wastewater treatment plant was analyzed, and a concentration of 511.23 ± 15.43 μmol / L was detected. -1 and 531.92±30.09 μmol L -1 Ammonia nitrogen; analysis of seawater samples revealed levels of 21.71 ± 0.83 μmol / L. -1 and 20.21±1.50 μmol L -1 Ammonia nitrogen. Analysis of the results using both methods (F-test and t-test) showed no significant difference between the two methods for analyzing wastewater II and seawater. Analysis of multiple environmental water samples indicates that the developed device is accurate and reliable, and has promising practical application prospects.

[0144] Table 3. Analytical results of environmental water samples detected using applied research and development equipment and standard methods.

[0145]

[0146] a Mean ± standard deviation, n = 3

[0147] This invention utilizes the salicylate spectrophotometry method as its detection principle and designs and constructs a novel online ammonia nitrogen detection device. This device integrates a sequential injection system, an ammonia nitrogen conversion reaction system, a colorimetric reaction system, and a detection system, achieving online ammonia nitrogen conversion and effectively improving the resistance to matrix interference in ammonia nitrogen analysis using the salicylate spectrophotometric method. No permeable membrane is used during the ammonia absorption and colorimetric process, avoiding the problems of membrane contamination and replacement. The device uses the instantaneous change rate of absorbance as the quantitative basis, eliminating the need to wait for the colorimetric reaction to complete, thus saving analysis time. Furthermore, this device has advantages such as simple and rapid operation, miniaturization, low reagent consumption, and strong resistance to matrix interference, making it suitable for online detection of ammonia nitrogen in surface water, domestic sewage, and other water qualities.

[0148] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A miniature rapid online detection device for ammonia nitrogen in environmental water bodies, characterized in that, include: A sequential injection system for online addition and transfer of reagents includes an injection pump, a reservoir ring, and a multi-position valve connected in sequence; one valve on the multi-position valve is connected to a colorimetric reagent tank, another valve is connected to a waste liquid tank, and another valve is connected to a sodium hypochlorite tank; the colorimetric reagent tank contains a mixture of sodium salicylate and sodium nitrosoferricyanide dihydrate. A colorimetric reaction system for providing a reaction site for ammonia and a colorimetric reagent includes a colorimetric reaction tank connected to a valve on the multi-position valve. The ammonia nitrogen conversion system is used to convert ammonia nitrogen into ammonia gas and transport the ammonia gas to the colorimetric reaction tank through pipelines and carrier gas; the end of the ammonia gas transport pipeline in the colorimetric reaction tank is equipped with a blocking device, so that the ammonia gas is bubbled out at the bottom of the colorimetric reaction tank in the form of small bubbles; The detection system is used to detect the absorbance of the solution in the colorimetric reaction cell after color development, and to quantitatively analyze the ammonia nitrogen content in the environmental water body based on the slope of the absorbance change. It includes a light-emitting diode (LED), a flow cell, a photodiode, a data acquisition card, and a computer. The flow cell is vertically arranged and its sidewalls are shielded from light. The LED is fixed to one end of the flow cell, and the photodiode is fixed to the other end to ensure optical path collimation. The photodiode, data acquisition card, and computer are connected in sequence. The inlet of the flow cell is connected to a valve on the multi-position valve.

2. The miniature rapid online detection device for ammonia nitrogen in environmental water bodies as described in claim 1, characterized in that, The sequential injection system also includes a pure water storage bottle connected to the injection pump; the injection pump is connected to the central channel of the multi-position valve via a storage ring.

3. The miniature rapid online detection device for ammonia nitrogen in environmental water bodies as described in claim 1, characterized in that, The colorimetric reaction chamber is a sealed device.

4. The miniature rapid online detection device for ammonia nitrogen in environmental water bodies as described in claim 3, characterized in that, The colorimetric reaction chamber is a centrifuge tube.

5. The miniature rapid online detection device for ammonia nitrogen in environmental water bodies as described in claim 1, characterized in that, The ammonia nitrogen conversion system includes: The conversion reaction tank is a sealed device that provides a reaction site for the conversion of ammonium ions into ammonia gas. A carrier gas supply device provides carrier gas for transporting ammonia from the conversion reaction tank to the colorimetric reaction tank; Waste liquid discharge device, used for discharging waste liquid from the conversion reaction tank; A sample input device is used to transport the water sample to be treated to the conversion reaction tank; An alkali input device is used to deliver alkali solution to the conversion reaction tank; An ammonia output pipeline is used to transport the generated ammonia gas to the colorimetric reaction tank.

6. The miniature rapid online detection device for ammonia nitrogen in environmental water bodies as described in claim 5, characterized in that, The conversion reaction tank is a centrifuge tube; Alternatively, the carrier gas supply device includes an air pump and a flow restrictor, with the flow restrictor installed on the pipeline between the air pump and the conversion reaction device to control the flow rate of the carrier gas; Alternatively, both the sample input device and the alkali input device may be syringes.

7. The miniature rapid online detection device for ammonia nitrogen in environmental water bodies as described in claim 6, characterized in that, The flow-limiting needles are stainless steel capillaries with different apertures.

8. A rapid online detection method for ammonia nitrogen in environmental water bodies, characterized in that, The micro rapid online detection device for ammonia nitrogen in environmental water bodies according to any one of claims 1-7 includes the following steps: Step 1: Before ammonia nitrogen detection, turn off the light-emitting diode and record the intensity I of the dark current signal generated by the photodiode. d , Step 2: Turn on the air pump to provide carrier gas, and turn on the LED and photodiode; Step 3: Using a sequential injection system, the colorimetric reagent solution and sodium hypochlorite solution are successively added to the colorimetric reaction cell; after being mixed evenly by carrier gas, the solution in the colorimetric reaction cell is filled into the flow cell using the sequential injection system, and excess solution is discharged to the waste liquid. Step 4: Add the water sample to be tested into the conversion reaction cell; use a sequential injection system to draw an equal amount of colorimetric reagent solution as in Step 3 and add it into the colorimetric reaction cell; Step 5: Add the alkaline solution to the conversion reaction tank; ammonia nitrogen reacts with hydroxide ions to produce ammonia gas, which is then carried into the colorimetric reaction tank by the carrier gas; Step Six: After waiting for the carrier gas to carry the ammonia into the colorimetric reaction cell for a period of time, add an equal amount of sodium hypochlorite solution to the colorimetric reaction cell using a sequential injection system; at the same time, turn on the data acquisition card to record data; at this time, the signal intensity of the flow cell is recorded as I0; Step 7: Use a sequential injection system to draw the solution from the colorimetric reaction cell and fill it into the flow cell; discharge excess solution into the waste liquid; record the signal intensity I of the flow cell in real time; after the sample detection is completed, turn off the light-emitting diode and the data acquisition card; Step 8: Connect the computer to the data acquisition card to record and process data; convert the real-time acquired electrical signals into absorbance A, and use the absorbance change rate to quantitatively analyze the ammonia nitrogen concentration in the environmental water.

9. The rapid online detection method for ammonia nitrogen in environmental water bodies as described in claim 8, characterized in that, The carrier gas flow rate is 35~130 mL / min. -1 ; Alternatively, in step six, the ammonia sample loading time is 3-5 minutes; Alternatively, the alkaline solution is a sodium hydroxide solution with a concentration of 2-5 mol / L. -1 ; Alternatively, the concentration of the sodium hypochlorite solution is 0.4~0.6 mmol / L. -1 ; Alternatively, the sodium salicylate concentration in the colorimetric reagent solution is ≥45 mmol / L. -1 The concentration of sodium nitrosoferricyanide dihydrate is ≥0.15 mmol / L. -1 ; Alternatively, in step three, the volume ratio of the colorimetric reagent solution to the sodium hypochlorite solution is 3:

1.

10. The rapid online detection method for ammonia nitrogen in environmental water bodies as described in claim 9, characterized in that, The carrier gas flow rate is 130 mL / min. -1 ; Alternatively, in step six, the ammonia loading time is 3 minutes; Alternatively, the alkaline solution is a sodium hydroxide solution with a concentration of 2 mol / L. -1 ; Alternatively, the sodium hypochlorite solution has a concentration of 0.5 mmol / L. -1 ; Alternatively, the concentration of sodium salicylate in the colorimetric reagent solution is 45 mmol / L. -1 The concentration of sodium nitrosoferricyanide dihydrate was 0.15 mmol / L. -1 .

11. The rapid online detection method for ammonia nitrogen in environmental water bodies as described in claim 8, characterized in that, Use the formula A = log(I0 - I) d ) / (I - I d It converts the real-time collected electrical signals into absorbance.

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