A method for detecting ammonia nitrogen

Abstract

This invention discloses a method for ammonia nitrogen detection. The apparatus used in the detection method includes a flow mechanism and a detection mechanism. One end of the flow mechanism receives an external water sample to be tested, and the other end is connected to the detection mechanism. The two ends of the detection mechanism serve as an inlet and an outlet, respectively, both connected to a liquid flow tube provided in the flow mechanism. The flow mechanism guides the water sample to be tested through the liquid flow tube for cyclic mixing before flowing into the detection mechanism for ammonia nitrogen concentration detection. The ammonia nitrogen detection method proposed in this invention is a flow analysis turbidity correction method for the detection of ammonia nitrogen by the orthophthalaldehyde fluorescence method, and establishes a relationship model between turbidity and ammonia nitrogen concentration. This method can significantly reduce the interference of turbidity on the fluorescence method for ammonia nitrogen detection. The method has a wide applicable turbidity correction range and is suitable for ammonia nitrogen detection correction in complex water samples.

Description

Technical Field

[0001] This invention relates to the field of water quality testing technology, specifically to a method for detecting ammonia nitrogen. Background Technology

[0002] Fluorescence spectrophotometry is a method for detecting the emission of light of a specific wavelength by certain substances when exposed to excitation light of a specific wavelength. In the absence of excitation light, most electrons of a fluorescent substance are in the ground state. When exposed to light of a specific wavelength, they transition to an excited state. These excited electrons consume energy through collisions with each other and with solvent molecules, and most quickly return to the ground state, releasing energy in the form of fluorescence. The energy required for electrons to transition from the ground state to the excited state varies among different fluorescent substances, resulting in different wavelengths of fluorescence when the electrons return to the ground state. The greatest advantage of fluorescence spectrophotometry is its high sensitivity; without considering other technological improvements, its sensitivity is approximately 10 to 100 times higher than that of colorimetric methods.

[0003] The principle of fluorescence spectrophotometry for measuring ammonia nitrogen is based on the fluorescence reaction between o-phthalaldehyde (OPA) and ammonia nitrogen. The fluorescence intensity of the generated product exhibits a linear relationship with its concentration within a certain range, allowing the ammonia nitrogen concentration to be calculated from the measured fluorescence intensity. Compared to other current methods for analyzing ammonia nitrogen in water, the o-phthalaldehyde-based fluorescence spectrophotometry offers advantages such as high sensitivity, ease of operation, stable and low-toxicity reagents, minimal interference from natural fluorescent substances, and minimal influence from sample salinity. However, for water samples with high turbidity, the detection results will be affected, leading to significant deviations without a suitable correction method. Summary of the Invention

[0004] To address the aforementioned technical problems in existing technologies, this invention provides a turbidity correction system and method for detecting ammonia nitrogen concentration in water using the phthalaldehyde fluorescence method. The correction method, based on an established model relating turbidity to ammonia nitrogen concentration, calibrates the measured ammonia nitrogen concentration. The correction system is used for both ammonia nitrogen fluorescence detection and turbidity detection.

[0005] The technical solution provided by this invention is as follows: I. An ammonia nitrogen detection device The ammonia nitrogen detection device is a flow analysis turbidity correction system for detecting ammonia nitrogen concentration in water based on the o-phthalaldehyde fluorescence method. The detection device includes a flow mechanism and a detection mechanism. One end of the flow mechanism receives the water sample to be tested from the outside, and the other end is connected to the detection mechanism. The two ends of the detection mechanism serve as the inlet and outlet, respectively, and both the inlet and outlet are connected to a liquid flow tube provided in the flow mechanism. The flow mechanism guides the water sample to be tested to undergo circulation and mixing in the liquid flow tube before flowing into the detection mechanism for ammonia nitrogen concentration detection.

[0006] The detection mechanism includes a fluorescence detection module, an absorbance detection module, a light source, and a heating module. The heating module has a roughly elongated strip-shaped structure with a hollow heating channel along its elongated direction. Three through holes, perpendicular to the heating channel and located on different surfaces of the heating module, are formed in the vertical direction. All three through holes are perpendicular to the surface of the heating module and pass through its center point. Two of the three through holes are opposite and parallel, serving as the absorbance detection module mounting hole and the light source mounting hole, respectively housing the absorbance detection module and the light source. The third through hole, perpendicular to the absorbance detection module mounting hole, serves as the fluorescence detection module mounting hole for mounting the fluorescence detection module.

[0007] The heating module includes two heating aluminum blocks, two thermistors, a heating element, and a detection cavity. Each heating aluminum block is a cubic structure and is installed together. Each heating aluminum block is equipped with a thermistor. The heating element is installed in a heating element groove that runs through the two heating aluminum blocks. The two opposite planes of the two heating aluminum blocks are respectively provided with grooves in the strip direction. The two grooves match to form the heating channel. The detection cavity is installed in the heating channel.

[0008] The two ends of the heating channel serve as the liquid inlet and the liquid outlet, respectively. The liquid inlet and the liquid outlet are each connected to a liquid pipe for connection with the flow mechanism. The detection chamber is connected to the liquid inlet and the liquid outlet of the flow mechanism via the two ends of the heating channel.

[0009] The flow mechanism includes an inlet pipe, a cleaning liquid pipe, a pretreatment filtration module, a first solenoid valve, multiple liquid flow pipes, a second solenoid valve, a third solenoid valve, a fourth solenoid valve, and a peristaltic pump.

[0010] The first, second, and third solenoid valves are all three-way valves with two inlets and one outlet, while the fourth solenoid valve is a three-way valve with one inlet and two outlets. One inlet of the first solenoid valve serves as the sample inlet, connected to the sample tube via the pretreatment module, and the other inlet connects to the cleaning fluid tube as the cleaning fluid inlet. The outlet of the first solenoid valve connects to one inlet of the second solenoid valve, and the other inlet of the second solenoid valve connects to one outlet of the fourth solenoid valve via a liquid flow pipe. The outlet of the second solenoid valve connects to one inlet of the third solenoid valve. The other inlet of the third solenoid valve serves as the detection reagent inlet, connected to an external detection reagent tube, and the outlet of the third solenoid valve connects to the inlet of the detection mechanism via a peristaltic pump. The other outlet of the fourth solenoid valve serves as the waste liquid discharge outlet for the outflow of the water sample to be tested, and the inlet of the fourth solenoid valve connects to the outlet of the detection mechanism. The inlets and outlets of the solenoid valves between the flow mechanisms are all connected via liquid flow pipes.

[0011] II. A method for detecting ammonia nitrogen in an ammonia nitrogen detection device. The ammonia nitrogen detection method specifically employs a flow analysis turbidity correction method based on the o-phthalaldehyde fluorescence method for detecting ammonia nitrogen concentration in water. The method includes the following steps: S1. Prepare ammonia nitrogen solutions with known concentrations, and measure the ammonia nitrogen reaction fluorescence value and turbidity detection absorbance of the ammonia nitrogen solutions as a detection training set. Construct a relationship model and input it into the training set to train and obtain a model of the relationship between turbidity and ammonia nitrogen concentration. S2. Base liquid is input into the detection unit through the cleaning liquid pipe. The base liquid flows into the detection unit through the flow mechanism to detect the background signal. After obtaining the background signal, the pipeline is cleaned. S3. Input the water sample to be tested into the testing institution through the sample inlet tube, and input the testing reagent through the reagent inlet; S4. Switch the conduction state of the second solenoid valve, the third solenoid valve and the fourth solenoid valve so that the second solenoid valve, the third solenoid valve and the fourth solenoid valve and the detection mechanism form a circuit, so that the water quality sample to be tested and the detection reagent are circulated and mixed in the detection mechanism and the flow mechanism. S5. The detection mechanism is heated by the heating module, and the water quality sample to be tested and the detection reagent react fully in the heating module to obtain the test solution; the absorbance and fluorescence value of the test solution are measured by the detection mechanism, and then the ammonia nitrogen concentration of the test solution is calculated according to the background signal obtained in step S2 and the relationship model between turbidity and ammonia nitrogen concentration, which is used as the ammonia nitrogen concentration of the water quality sample to be tested.

[0012] Step S1 involves preparing turbidity standard solutions of different known concentrations, and using these turbidity standard solutions to prepare corresponding ammonia nitrogen solutions of different known concentrations. The fluorescence detection module and absorbance detection module constitute a flow analysis turbidity correction system for detecting ammonia nitrogen concentration based on the phthalaldehyde fluorescence method. The ammonia nitrogen solution is detected by the flow analysis turbidity correction system, and the measured ammonia nitrogen reaction fluorescence value and turbidity detection absorbance of the ammonia nitrogen solution are used as a detection training set. A relational model is constructed and input into the training set to train and obtain a model relating turbidity and ammonia nitrogen concentration.

[0013] The relational model is as follows: Y = [c(aX1+b)+d]X2+e; Where a, b, c, d, and e are constants, X1 is the measured absorbance value of turbidity detection, X2 is the measured ammonia nitrogen concentration, and Y is the measured ammonia nitrogen fluorescence value.

[0014] The final calculated relationship between turbidity and ammonia nitrogen concentration is as follows: Y=[-3.49×10 -6 ×(21318.56X1-656.75)+1.51×10 -3 ]X2+0.2105.

[0015] The turbidity and fluorescence values ​​of the samples were measured using a flow analysis turbidity correction system.

[0016] In step S1, the fluorescence value of the ammonia nitrogen reaction in the ammonia nitrogen solution is measured using the phthalaldehyde fluorescence method; the ammonia nitrogen concentration of the ammonia nitrogen solution prepared in step S1 and the water sample to be tested in step S3 are both 0-200 ug / L, and the turbidity value is both 0-400 NTU.

[0017] In step S2, the base solution is one or a combination of two of pure water and a detection reagent, wherein the detection reagent is an orthophthalaldehyde detection reagent. The base solution, i.e., the base water sample, refers to the corresponding test water sample that does not contain ammonia nitrogen. The detection reagent in S4 is the reagent used for detecting ammonia nitrogen concentration using the orthophthalaldehyde method.

[0018] Specifically, step S3 involves inputting the water sample to be tested into the flow mechanism through the inlet (S) of the sample inlet tube. The water sample to be tested flows into the detection mechanism after passing through the pretreatment module, the first solenoid valve, the second solenoid valve, the third solenoid valve, and the peristaltic pump.

[0019] Then, the conduction state of the third solenoid valve is switched, and the test reagent is input into the flow mechanism through the test reagent inlet (D). The test reagent flows into the test mechanism after passing through the third solenoid valve and the peristaltic pump.

[0020] Then, the conduction states of the second, third, and fourth solenoid valves are switched, and the water sample to be tested and the test reagent are circulated and mixed in the detection mechanism and the flow mechanism.

[0021] The beneficial effects of this invention are: This invention proposes a turbidity correction method for the detection of ammonia nitrogen by the fluorescence method of phthalaldehyde and establishes a relationship model between turbidity and ammonia nitrogen concentration. This method can significantly reduce the interference of turbidity on the detection of ammonia nitrogen by fluorescence method. In addition, the method has a wide applicable turbidity correction range and is suitable for the detection and correction of ammonia nitrogen in complex water samples.

[0022] This invention proposes a flow analysis turbidity correction system for the detection of ammonia nitrogen using the phthalaldehyde fluorescence method. It can simultaneously measure the ammonia nitrogen concentration and turbidity of a water sample in a complete detection process, eliminating the need for additional instruments for turbidity measurement. This simplifies and speeds up the correction process. Furthermore, the same light source is used for both turbidity and ammonia nitrogen concentration detection, avoiding the influence of different light sources. This invention combines a flow analysis system for sample pretreatment, mixing, heating reaction, and detection. The entire detection system is small in size, consumes few reagents, is highly automated, and is easy to operate, making it suitable for small-scale water sample analysis.

[0023] This invention uses a circulating loop to repeatedly mix the water sample and the detection reagent during the reaction process, improving mixing and reaction efficiency, and eliminating the need for a mixing device, thereby reducing the size of the detection system. Attached Figure Description

[0024] Figure 1 This is a curve showing the slope of the linear fitting working curve for ammonia nitrogen and the turbidity value of the corresponding solution in an embodiment of the present invention.

[0025] Figure 2 This is a fitting curve of the absorbance value detected in the embodiments of the present invention and the turbidity value of the corresponding solution.

[0026] Figure 3 This is a graph showing the relationship between the intercept of the linear fitting working curve for ammonia nitrogen and the turbidity value of the corresponding solution in an embodiment of the present invention.

[0027] Figure 4 This is a schematic diagram of the overall structure of a flow analysis turbidity correction system for detecting ammonia nitrogen concentration based on the phthalaldehyde fluorescence method.

[0028] Figure 5 This is a schematic diagram of the detection unit of the flow analysis turbidity correction system for detecting ammonia nitrogen concentration based on the orthophthalaldehyde fluorescence method in an embodiment of the present invention.

[0029] Figure 6This is an exploded view of the detection unit of the flow analysis turbidity correction system for detecting ammonia nitrogen concentration based on the orthophthalaldehyde fluorescence method in an embodiment of the present invention.

[0030] Figure 7 This is a schematic diagram of the pipeline when inputting the water sample to be tested into a flow analysis turbidity correction system for detecting ammonia nitrogen concentration based on the ortho-phthalaldehyde fluorescence method.

[0031] Figure 8 This is a schematic diagram of the piping for inputting test reagents in a flow analysis turbidity correction system for detecting ammonia nitrogen concentration based on the phthalaldehyde fluorescence method.

[0032] Figure 9 This is a schematic diagram of the pipeline for mixing and reacting the test reagent with the water sample in a flow analysis turbidity correction system based on the phthalaldehyde fluorescence method for detecting ammonia nitrogen concentration.

[0033] In the diagram: 1. Pretreatment filtration module; 2. First solenoid valve; 3. Liquid flow pipe; 4. Second solenoid valve; 5. Third solenoid valve; 6. Peristaltic pump; 7. Detection unit; 71. Fluorescence detection mechanism mounting hole; 72. Absorbance detection mechanism mounting hole; 73. Light source mounting hole; 74. Heating aluminum block; 75. NTC thermistor mounting hole (one of each half of the aluminum block); 76. Heating element mounting hole; 77. Detection chamber; 8. Fourth solenoid valve; S. Inlet of sample inlet tube; C. Inlet of cleaning solution inlet tube; D. Inlet of test reagent inlet tube; W. Waste liquid discharge outlet. Detailed Implementation

[0034] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0035] A detection device, an ammonia nitrogen detection device, is a flow analysis turbidity correction system based on the o-phthalaldehyde fluorescence method for detecting ammonia nitrogen concentration in water, such as... Figure 4 As shown, it includes a flow mechanism and a detection mechanism 7. One end of the flow mechanism serves as the input end to receive the water quality sample to be tested from the outside, and the other end serves as the output end to connect to the detection mechanism 7. The detection mechanism 7 is installed in the pipeline provided by the flow mechanism. The two ends of the detection mechanism 7 serve as the inlet and outlet of the liquid, respectively, and both the inlet and outlet are connected to the liquid flow pipe 3 provided by the flow mechanism. The flow mechanism guides the water quality sample to be tested to undergo circulation and mixing treatment in the liquid flow pipe 3, and then flows in the pipeline provided by the flow mechanism and flows into the detection mechanism 7 for ammonia nitrogen concentration detection.

[0036] like Figure 5 and Figure 6As shown, the detection mechanism 7 includes a fluorescence detection module, an absorbance detection module, a light source, and a heating module. The heating module has a roughly elongated structure with a hollow heating channel along its elongated direction. Three through holes, perpendicular to the heating channel and located on different surfaces of the heating module, are formed in the vertical direction. All three through holes are perpendicular to the surface of the heating module and pass through its center point. Two of the three through holes are opposite and parallel, serving as an absorbance detection module mounting hole 72 and a light source mounting hole 73, respectively housing the absorbance detection module and the light source. The other through hole, perpendicular to the absorbance detection module mounting hole 72, serves as a fluorescence detection module mounting hole 71 for mounting the fluorescence detection module.

[0037] The heating module includes two heating aluminum blocks 74, two NTC thermistors, a heating element, and a detection chamber 77. Each heating aluminum block 74 is a cubic structure and is tightly installed together to form the main body of the heating module. Each heating aluminum block 74 has an NTC thermistor mounting hole 75 for mounting an NTC thermistor and a heating element mounting hole 76 for mounting a heating element. The two opposite planes of the two heating aluminum blocks 74 have grooves in the strip direction. The two grooves match to form a hollow heating channel. The detection chamber 77 is installed in the heating channel for liquid mixing and detection reaction. The main body of the heating module composed of the two heating aluminum blocks 74 has through holes as mounting holes 72 for absorbance detection module, 73 for light source, and 71 for fluorescence detection module.

[0038] The heating channel serves as the detection chamber of the detection mechanism 7. The two ends of the detection chamber serve as the liquid inlet and liquid outlet of the detection mechanism 7, respectively. The liquid inlet and liquid outlet are each connected to a liquid pipe for connection with the flow mechanism. The detection chamber 77 is connected to the liquid inlet and liquid outlet of the flow mechanism through the two ends of the heating channel, respectively.

[0039] Specifically, the detection mechanism 7 includes two sets of detection modules for optical detection of the liquid inside the detection chamber 77 and a light source. The two sets of modules are at a 90-degree angle, with the light source opposite the module for detecting turbidity and at a 90-degree angle to the module for detecting fluorescence. The heating module includes a temperature control module, a heating element, and a heating aluminum block 74. The temperature control module includes two NTC thermistors as sensors and a temperature control circuit board. The two thermistors serve as temperature references; an alarm is triggered if the temperature difference between them is too large. The heating element heats the heating aluminum block 74. There are two heating aluminum blocks 74, which have undergone surface treatment. One function is to heat the detection chamber 77, and the other is to serve as a support structure for the circuit board, enclosing the detection chamber 77 and providing a light-shielding environment for it.

[0040] The flow mechanism includes an inlet pipe, a cleaning liquid pipe, a pretreatment filter module 1, a first solenoid valve 2, multiple liquid flow pipes 3, a second solenoid valve 4, a third solenoid valve 5, a fourth solenoid valve 8, and a peristaltic pump 6.

[0041] The first solenoid valve 2, the second solenoid valve 4, and the third solenoid valve 5 are all three-way valves with two inlets and one outlet, while the fourth solenoid valve 8 is a three-way valve with one inlet and two outlets. One inlet of the first solenoid valve 2 serves as the sample inlet S, connected to the sample inlet tube via the pretreatment module 1 to receive the sample to be tested. The other inlet is connected to the cleaning fluid tube as the cleaning fluid inlet C, used to receive pure water or base liquid. The outlet of the first solenoid valve 2 is connected to one inlet of the second solenoid valve 4 via the liquid flow tube 3. The other inlet of the second solenoid valve 4 serves as the circulation inlet, connected to one outlet of the fourth solenoid valve 8 via the liquid flow tube 3. The outlet of the second solenoid valve 4 is connected to one inlet of the third solenoid valve 5. The other inlet of the third solenoid valve 5 serves as the detection reagent inlet D, connected to the external detection reagent tube. The outlet of the third solenoid valve 5 is connected to the inlet of the detection mechanism 7 via the peristaltic pump 6. The other outlet of the fourth solenoid valve 8 serves as the waste liquid discharge outlet W, used to discharge the water quality sample to be tested. The inlet of the fourth solenoid valve 8 is connected to the outlet of the detection mechanism 7. The inlets and outlets of the solenoid valves between the flow mechanisms are all connected through the liquid flow tube 3.

[0042] An ammonia nitrogen detection method for an ammonia nitrogen detection device, specifically employing a flow analysis turbidity correction method based on the o-phthalaldehyde fluorescence method for detecting ammonia nitrogen concentration in water, the method comprising the following steps: S1. Prepare ammonia nitrogen solutions of known concentrations and measure the ammonia nitrogen reaction fluorescence value and turbidity detection absorbance of the ammonia nitrogen solutions as a detection training set. Construct a relational model and input it into the training set to train and obtain the turbidity-ammonia nitrogen concentration relationship model. The turbidity-ammonia nitrogen concentration relationship model can output the ammonia nitrogen concentration corresponding to the measured ammonia nitrogen reaction fluorescence value and turbidity detection absorbance, and obtain the turbidity detection curve and ammonia nitrogen working curve. S2. Base liquid is introduced into the detection unit through the cleaning liquid pipe. The base liquid flows into the detection mechanism 7 through the flow mechanism to detect the background signal. The background signal is used to perform zero-point correction on the working curve, and then the pipeline is cleaned. S3, such as Figure 7 , Figure 8 and Figure 9 As shown, the flow mechanism includes a sample introduction mode, a detection mode, and a circulation mode. When the flow mechanism is switched to the sample introduction mode, the water quality sample to be tested is input into the detection mechanism 7 through the sample introduction tube. Then, the flow mechanism is switched to the detection mode, and the detection reagent is input through the detection reagent inlet D. S4. After a set time, switch the flow mechanism to the circulation mode, that is, switch the conduction state of the second solenoid valve 4, the third solenoid valve 5 and the fourth solenoid valve 8, so that the second solenoid valve 4, the third solenoid valve 5, the fourth solenoid valve 8 and the detection mechanism 7 form a loop, so that the water quality sample to be tested and the phthalic acid test reagent are circulated and mixed in the detection mechanism 7 and the flow mechanism. S5. The detection unit 7 is heated by the heating module, and the water quality sample to be tested and the detection reagent react fully in the heating module to obtain the test solution. After reacting fully for 10-30 minutes, the absorbance and fluorescence value of the test solution are measured by the detection unit 7. Then, the ammonia nitrogen concentration of the test solution is calculated according to the background signal obtained in step S2 and the relationship model between turbidity and ammonia nitrogen concentration, which is used as the ammonia nitrogen concentration of the water quality sample to be tested.

[0043] Step S1 specifically involves preparing turbidity standard solutions of different known concentrations, using the turbidity standard solutions to prepare corresponding ammonia nitrogen solutions of different known concentrations, and constructing a flow analysis turbidity correction system for detecting ammonia nitrogen concentration in water based on the phthalic acid fluorescence method using a fluorescence detection module and an absorbance detection module. The ammonia nitrogen solution is detected by the flow analysis turbidity correction system, and the measured ammonia nitrogen reaction fluorescence value and turbidity detection absorbance of the ammonia nitrogen solution are used as the detection training set. A relational model is constructed and input into the training set to train and obtain the turbidity-ammonia nitrogen concentration relationship model. The turbidity-ammonia nitrogen concentration relationship model is used to calibrate the ammonia nitrogen concentration.

[0044] The relational model is as follows: Y = [c(aX1+b)+d]X2+e; Where a, b, c, d, and e are constants, X1 is the measured absorbance value of turbidity detection, X2 is the measured ammonia nitrogen concentration, and Y is the measured ammonia nitrogen fluorescence value.

[0045] The final calculated relationship between turbidity and ammonia nitrogen concentration is as follows: Y=[-3.49×10 -6 ×(21318.56X1-656.75)+1.51×10 -3 ]X2+0.2105.

[0046] The turbidity and fluorescence values ​​of the samples were measured using a flow analysis turbidity correction system.

[0047] In step S1, the fluorescence value of the ammonia nitrogen reaction in the ammonia nitrogen solution is measured by the phthalaldehyde fluorescence method. The ammonia nitrogen concentration of the ammonia nitrogen solution prepared in step S1 and the water sample to be tested in step S3 are both 0-200 ug / L, and the turbidity value is both 0-400 NTU.

[0048] In step S2, the base solution is a combination of pure water and phthalaldehyde detection reagent. The detection base solution is used to calibrate the zero degree of the working curve.

[0049] Step S3 specifically involves the flow mechanism including a sample introduction mode, a detection mode, and a circulation mode. When the flow mechanism is switched to the sample introduction mode, the water quality sample to be tested is input into the flow mechanism through the inlet S of the sample introduction tube. The water quality sample to be tested flows into the detection mechanism 7 after passing through the pretreatment module 1, the first solenoid valve 2, the second solenoid valve 4, the third solenoid valve 5, and the peristaltic pump 6.

[0050] Then, the conduction state of the third solenoid valve 5 is switched, so that the flow mechanism is switched to the detection module. The detection reagent is input into the flow mechanism through the detection reagent inlet D. The detection reagent flows into the detection mechanism 7 after passing through the third solenoid valve 5 and the peristaltic pump 6.

[0051] Then, the conduction states of the second solenoid valve 4, the third solenoid valve 5, and the fourth solenoid valve 8 are switched, so that the second solenoid valve 4, the third solenoid valve 5, the fourth solenoid valve 8, and the detection mechanism 7 form a loop, and the flow mechanism becomes a circulation mode. The water quality sample to be tested and the test reagent are circulated and mixed in the detection mechanism 7 and the flow mechanism. Specifically, the water quality sample to be tested and the test reagent pass through the second solenoid valve 4, the third solenoid valve 5, the peristaltic pump 6, the detection mechanism 7, and the fourth solenoid valve 8 in sequence. The water quality sample to be tested and the test reagent are circulated and mixed multiple times in the loop through the detection mechanism 7.

[0052] Step S5 specifically involves: After a full reaction of 20 min, the absorbance of the test solution in the detection chamber 77 is detected by the turbidity detection module to obtain absorbance A, and the turbidity value X1 is obtained through the turbidity detection curve; the fluorescence value is detected by the fluorescence detection module in the detection chamber 77 to obtain fluorescence value B, and the ammonia nitrogen concentration X2 in the water sample to be tested is obtained through the ammonia nitrogen working curve corresponding to the turbidity value.

[0053] First, turbidity standard solutions of different concentrations were prepared. Since hydrazine sulfate, the main component of the commonly used turbidity standard solution, formalin, reacts with phthalaldehyde to form a colored product, nano-titanium dioxide was chosen as the turbidity standard solution standard, and potassium hydrogen phthalate was added as a dispersant. 0.416 g of nano-titanium dioxide was accurately weighed and dissolved in 100 mL of pure water, stirred until homogeneous, and set aside. 3 g of potassium hydrogen phthalate was accurately weighed and dissolved in 100 mL of pure water, stirred until completely dissolved. Both solutions were then transferred to a 1000 mL volumetric flask, diluted to the mark with pure water, shaken well, allowed to stand for a moment, and then transferred to a polyethylene reagent bottle. The turbidity of the solution used is 2000 NTU. Turbidity standard solutions of other concentrations are prepared by gradient dilution of this solution. In this embodiment, turbidity standard solutions with turbidity values ​​of 0, 50, 75, 100, 200, 250, 300, 350, 400, 450, 500, and 1000 NTU are prepared.

[0054] Next, prepare the ammonia nitrogen standard solution stock solution. Accurately weigh 10 mL of ammonia nitrogen standard stock solution (100 mg / L) into a 100 mL volumetric flask, dilute to the mark with pure water, shake well, let stand for a while, and then transfer to a polyethylene reagent bottle. The ammonia nitrogen concentration of this stock solution is 10 mg / L.

[0055] Next, different amounts of ammonia nitrogen standard solution stock solution were added dropwise to turbidity standard solutions of different concentrations. Ammonia nitrogen solutions with concentrations of 0, 5, 10, 50, 100, and 200 ug / L were prepared for use by adding the turbidity standard solution for each turbidity value.

[0056] Next, a flow analysis turbidity correction system based on the o-phthalaldehyde fluorescence method for detecting ammonia nitrogen concentration was used for detection. The detection procedure is as follows: (1) The base liquid is introduced into the detection unit 7 through the cleaning liquid inlet pipe. The detection mechanism detects the background signal of the detection chamber 77, obtains the background signal, and performs zero-point correction on the working curve. Then the pipeline is cleaned. (2) Switch the pipeline to the sample inlet state and input the water quality sample to be tested into the detection unit 7 through the sample inlet tube. Switch the pipeline to the reagent inlet state and input the reagent into the detection unit 7 through the reagent inlet tube. After the set time, switch the states of the second solenoid valve 4, the third solenoid valve 5, and the fourth solenoid valve 8 to switch the pipeline to the circulation state. Then, connect the second solenoid valve 4, the third solenoid valve 5, the fourth solenoid valve 8, and the detection unit 7 to form a loop. The water quality sample to be tested and the reagent are circulated and mixed multiple times through the detection unit 7 in the loop. (3) The detection unit 7 is heated by the heating module to ensure that the water sample to be tested and the detection reagent react fully; (4) After the reaction for 20 min, the absorbance of the detection chamber 77 is detected by the turbidity detection module to obtain the absorbance A, and the turbidity value X1 is obtained by the turbidity detection curve; the fluorescence value of the detection chamber 77 is detected by the fluorescence detection module to obtain the fluorescence value B.

[0057] Fitting curves were established by comparing the detected absorbance values ​​with the corresponding turbidity values ​​of the solutions, and the detected fluorescence values ​​with the corresponding ammonia nitrogen concentrations of the solutions. Figure 1 This is a curve showing the linear fitting of ammonia nitrogen and the fitting of the corresponding turbidity values ​​of the solution. Figure 2 This is a fitted curve of the detected absorbance value and the corresponding turbidity value of the solution.

[0058] pass Figure 1 , Figure 2 The linear relationship between turbidity and ammonia nitrogen concentration can be used to derive a model for the relationship between turbidity and ammonia nitrogen concentration, and the formula is as follows: Y=[-3.49×10 -6 ×(21318.56X1-656.75)+1.51×10-3 X2 + 0.2105; Wherein, X1 is the measured absorbance value of turbidity detection, X2 is the measured ammonia nitrogen concentration, and Y is the measured ammonia nitrogen fluorescence value. The turbidity range is between 100 and 400 NTU, and the ammonia nitrogen concentration range is between 0 and 200 ug / L.

[0059] It should be noted that when the turbidity ranges from 0 to 100 NTU, the effect of turbidity on the fluorescence reaction is negligible. At this time, the relationship between ammonia nitrogen concentration and ammonia nitrogen fluorescence value is Y = 0.0012X2 + 0.2105. When the turbidity is greater than 400 NTU, the fluorescence will be mostly masked and a linear relationship cannot be formed, thus exceeding the application range of the calibration model.

[0060] Furthermore, turbidity significantly affects the slope of the linear relationship between ammonia nitrogen concentration and ammonia nitrogen fluorescence value, but its effect on the curve intercept is as follows: Figure 3 As shown, this impact is relatively small (<5 ug / L) and can be removed through zero-point calibration in the detection process.

[0061] It should be noted that the above embodiments can be freely combined as needed. The above description is only a detailed explanation of the preferred embodiments and principles of the present invention. For those skilled in the art, there will be changes in the specific implementation methods based on the ideas provided by the present invention, and these changes should also be considered within the scope of protection of the present invention.

Claims

1. An ammonia nitrogen detection device, characterized in that, It includes a flow mechanism and a detection mechanism (7). One end of the flow mechanism receives the water quality sample to be tested from the outside, and the other end is connected to the detection mechanism (7). The two ends of the detection mechanism (7) serve as the inlet and outlet, respectively. The inlet and outlet are both connected to the liquid flow pipe (3) provided in the flow mechanism. The flow mechanism guides the water quality sample to be tested to flow into the detection mechanism (7) after being circulated and mixed in the liquid flow pipe (3) for ammonia nitrogen concentration detection.

2. The ammonia nitrogen detection device according to claim 1, characterized in that, The detection mechanism (7) includes a fluorescence detection module, an absorbance detection module, a light source, and a heating module. The heating module is a strip-shaped structure with a hollow heating channel in the strip direction. Three through holes are opened in the vertical direction of the heating channel, perpendicular to the heating channel and on different heating module surfaces. The three through holes are perpendicular to the surface of the heating module and pass through the center point of the heating module. Two of the three through holes are opposite and parallel to each other, namely the absorbance detection module mounting hole (72) and the light source mounting hole (73). The absorbance detection module mounting hole (72) and the light source mounting hole (73) are respectively provided with the absorbance detection module and the light source. The other through hole is perpendicular to the absorbance detection module mounting hole (72) and serves as the fluorescence detection module mounting hole (71) for installing the fluorescence detection module.

3. The ammonia nitrogen detection device according to claim 2, characterized in that, The heating module includes two heating aluminum blocks (74), two thermistors, a heating element, and a detection cavity (77). Each heating aluminum block (74) is a cubic structure and is installed together. Each heating aluminum block (74) is equipped with a thermistor. The heating element is installed in a heating element groove provided through the two heating aluminum blocks (74). The two opposite planes of the two heating aluminum blocks (74) are respectively provided with grooves in the strip direction. The two grooves match to form the heating channel. The detection cavity (77) is installed in the heating channel. The two ends of the heating channel serve as the liquid inlet and the liquid outlet, respectively. The liquid inlet and the liquid outlet are each connected to a liquid pipe for connection with the flow mechanism. The detection chamber (77) is connected to the liquid inlet and the liquid outlet of the flow mechanism through the two ends of the heating channel, respectively.

4. The ammonia nitrogen detection device according to claim 1, characterized in that, The flow mechanism includes an inlet pipe, a cleaning liquid pipe, a pretreatment filtration module (1), a first solenoid valve (2), multiple liquid flow pipes (3), a second solenoid valve (4), a third solenoid valve (5), a fourth solenoid valve (8), and a peristaltic pump (6). The first solenoid valve (2), the second solenoid valve (4), and the third solenoid valve (5) are all three-way valves with two inlets and one outlet, while the fourth solenoid valve (8) is a three-way valve with one inlet and two outlets. One inlet of the first solenoid valve (2) is connected to the sample inlet (S) via the pretreatment module (1) and the other inlet is connected to the cleaning fluid inlet (C). The outlet of the first solenoid valve (2) is connected to one inlet of the second solenoid valve (4), and the other inlet of the second solenoid valve (4) is connected to one outlet of the fourth solenoid valve (8) via the liquid flow pipe (3). The outlet of the second solenoid valve (4) is connected to one of the inlets of the third solenoid valve (5); the other inlet of the third solenoid valve (5) is connected to the external test reagent tube as the test reagent inlet (D); the outlet of the third solenoid valve (5) is connected to the liquid inlet of the test mechanism (7) via the peristaltic pump (6); the other outlet of the fourth solenoid valve (8) is used as the waste liquid discharge outlet (W) for the outflow of the water quality sample to be tested; the inlet of the fourth solenoid valve (8) is connected to the liquid outlet of the test mechanism (7); the inlets and outlets of the solenoid valves between the flow mechanisms are all connected through the liquid flow pipe (3).

5. The ammonia nitrogen detection method of the ammonia nitrogen detection device according to any one of claims 1-4, characterized in that, S1. Prepare ammonia nitrogen solutions with known concentrations, and measure the ammonia nitrogen reaction fluorescence value and turbidity detection absorbance of the ammonia nitrogen solutions as a detection training set. Construct a relationship model and input it into the training set to train and obtain a model of the relationship between turbidity and ammonia nitrogen concentration. S2. The base liquid is input into the detection unit through the cleaning liquid pipe. The base liquid flows into the detection mechanism (7) through the flow mechanism to detect the background signal. After obtaining the background signal, the pipeline is cleaned. S3. Input the water sample to be tested into the testing unit (7) through the sample inlet tube, and input the testing reagent through the testing reagent inlet (D); S4. Switch the conduction state of the second solenoid valve (4), the third solenoid valve (5) and the fourth solenoid valve (8) so that the second solenoid valve (4), the third solenoid valve (5) and the fourth solenoid valve (8) and the detection mechanism (7) form a loop, so that the water quality sample to be tested and the detection reagent are circulated and mixed in the detection mechanism (7) and the flow mechanism. S5. The detection mechanism (7) is heated by the heating module, and the water quality sample to be tested and the detection reagent react fully in the heating module to obtain the test solution; the absorbance and fluorescence value of the test solution are measured by the detection mechanism (7), and then the ammonia nitrogen concentration of the test solution is calculated according to the background signal obtained in step S2 and the turbidity-ammonia nitrogen concentration relationship model, which is used as the ammonia nitrogen concentration of the water quality sample to be tested.

6. The ammonia nitrogen detection method of the ammonia nitrogen detection device according to claim 5, characterized in that, Step S1 involves preparing turbidity standard solutions of different known concentrations, and using these turbidity standard solutions to prepare corresponding ammonia nitrogen solutions of different known concentrations. The fluorescence detection module and absorbance detection module constitute a flow analysis turbidity correction system for detecting ammonia nitrogen concentration based on the phthalaldehyde fluorescence method. The ammonia nitrogen solution is detected by the flow analysis turbidity correction system, and the measured ammonia nitrogen reaction fluorescence value and turbidity detection absorbance of the ammonia nitrogen solution are used as a detection training set. A relational model is constructed and input into the training set to train and obtain a model relating turbidity and ammonia nitrogen concentration.

7. The ammonia nitrogen detection method of the ammonia nitrogen detection device according to claim 5, characterized in that, In step S1, the fluorescence value of the ammonia nitrogen reaction in the ammonia nitrogen solution is measured using the phthalaldehyde fluorescence method; the ammonia nitrogen concentration of the ammonia nitrogen solution prepared in step S1 and the water sample to be tested in step S3 are both 0-200 ug / L, and the turbidity value is both 0-400 NTU.

8. The ammonia nitrogen detection method of the ammonia nitrogen detection device according to claim 5, characterized in that, In step S2, the base solution is one or a combination of two of pure water and a detection reagent, and the detection reagent is an orthophthalaldehyde detection reagent.

9. The ammonia nitrogen detection method of the ammonia nitrogen detection device according to claim 5, characterized in that, Specifically, step S3 involves inputting the water quality sample to be tested into the flow mechanism through the inlet (S) of the sample inlet tube. The water quality sample to be tested flows into the detection mechanism (7) after passing through the pretreatment module (1), the first solenoid valve (2), the second solenoid valve (4), the third solenoid valve (5), and the peristaltic pump (6). Then switch the conduction state of the third solenoid valve (5) and input the test reagent into the flow mechanism through the test reagent inlet (D). The test reagent flows into the test mechanism (7) after passing through the third solenoid valve (5) and the peristaltic pump (6). Then switch the conduction state of the second solenoid valve (4), the third solenoid valve (5) and the fourth solenoid valve (8), and the water quality sample to be tested and the test reagent are circulated and mixed in the detection mechanism (7) and the flow mechanism.

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