Working electrode, electrochemical sensor, electrochemical detection system and method

Abstract

The invention discloses a working electrode which comprises a substrate electrode, and the surface of the substrate electrode is modified with a graphene-gold nanoparticle-cerium dioxide compound or a graphene-gold nanoparticle-molybdic acid compound. The nitrite and nitrate are detected by using the working electrode modified with the graphene-gold nanoparticle-cerium dioxide compound, the phosphate is detected by using the working electrode modified with the graphene-gold nanoparticle-molybdic acid compound, and both the sensitivity and the detection response speed are high. On the basis of the working electrode, the invention further provides an electrochemical sensor which has multiple parameter analysis item selections. Furthermore, the invention further provides an electrochemical detection system which can perform online sampling, online detection and automatic cleaning and provide more comprehensive detection information, and the electrochemical detection system is simple and reliable in corresponding structure, convenient to carry and beneficial to online monitoring or field detection. In addition, the invention also correspondingly provides an electrochemical detection method.

Description

Technical Field

[0001] The present invention relates to the field of electrochemical detection technology, and in particular to a working electrode, an electrochemical sensor, an electrochemical detection system and a method. Background Art

[0002] Water quality monitoring is the process of monitoring and measuring the types of pollutants in water bodies, the concentrations of various pollutants and their changing trends, and evaluating water quality conditions. It is not only a guarantee of water safety, but also provides important support for the control and research of water pollution.

[0003] Taking the monitoring of nitrite, nitrate and phosphate concentrations in water environment as an example, nitrite, nitrate and phosphate are all important inorganic nutrients and play a vital role in aquatic ecosystems. However, if these substances exist in excess, they will have a negative impact on the water environment and human health. Therefore, monitoring the concentrations of nitrite, nitrate and phosphate in the water environment is an important task to ensure water quality safety, maintain ecological balance and achieve sustainable development of water resources. In this regard, the electrochemical detection method is a relatively efficient, sensitive and low-cost analytical method. It is based on redox reactions and can respond quickly and provide real-time data. However, there are still some problems in the actual water sample detection work.

[0004] For example, the sensitivity of working electrodes for nitrite, nitrate, and phosphate detection needs to be further improved. During detection, the reaction speed of the detection target on the surface of the working electrode is slow, and the transmission between electrons is also slow, and the detection response time is long. For example, it is difficult for many working electrodes to maintain good detection characteristics after long-term use. For example, because the pretreatment of each target is different, it is impossible to achieve simultaneous detection of multiple water parameters. Only one target can be detected each time the sample is injected, and the detection efficiency is low. For example, the system with continuous measurement function is complex, which makes the corresponding equipment inconvenient to carry and difficult to detect on site. For example, the reagents used in the test may produce harmful waste or by-products, which pose a potential threat to the environment and human health and need to be avoided as much as possible. Summary of the invention

[0005] The object of the present invention is to provide a working electrode, an electrochemical sensor, an electrochemical detection system and a method to improve the detection sensitivity of one or more target substances among nitrite, nitrate and phosphate.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A working electrode comprises a base electrode, the surface of which is modified with a graphene-gold nano-cerium dioxide composite or a graphene-gold nano-molybdic acid composite.

[0008] Furthermore, the substrate electrode has a test end, and the graphene-gold nano-cerium dioxide composite or the graphene-gold nano-molybdate composite is modified 7 to 10 mm along the length direction of the substrate electrode starting from the test end, and the modification amount of the graphene-gold nano-cerium dioxide composite or the graphene-gold nano-molybdate composite is 0.5 to 10.0 mg.

[0009] Furthermore, the substrate electrode is a tungsten needle electrode.

[0010] An electrochemical sensor comprises a detection cell, a reference electrode and a counter electrode, and also comprises one or more of a nitrite selective electrode, a nitrate selective electrode and a phosphate selective electrode; the nitrite selective electrode and the nitrate selective electrode are the working electrodes according to any one of claims 1 to 3, and are surface-modified with a graphene-gold nano-cerium dioxide composite; the phosphate selective electrode is the working electrode according to any one of claims 1 to 3, and is surface-modified with a graphene-gold nano-molybdic acid composite.

[0011] An electrochemical detection system comprises a sampling module, a control module, a data acquisition module and the electrochemical sensor as claimed in claim 4; the sampling module is connected to the detection pool, the control module is electrically connected to the sampling module, the data acquisition module is electrically connected to the electrochemical sensor, and can send data to the control module.

[0012] Furthermore, the sampling module includes a sample liquid bottle, a buffer bottle, a mixed liquid bottle, a sampling tube, a buffer tube and a mixing tube. The sample liquid bottle is connected to the mixed liquid bottle through the sampling tube, the buffer bottle is connected to the mixed liquid bottle through the buffer tube, and the mixed liquid bottle is connected to the detection pool through the mixing tube. The sampling tube is provided with a sampling pump, the buffer tube is provided with a buffer pump, and the mixing tube is provided with a mixing pump; the control module is electrically connected to the sampling pump, the buffer pump and the mixing pump.

[0013] Furthermore, it also includes a filtering module, a cleaning module and a waste discharge module, the filtering module includes a filtering device and a filtering pump, the filtering device and the filtering pump are arranged on the pipeline between the sampling module and the detection tank, the cleaning module includes a cleaning liquid bottle and a cleaning pump, the cleaning liquid bottle is connected to the detection tank through a pipeline provided with the cleaning pump, the waste discharge module includes a waste liquid bottle and a waste discharge pump, the waste liquid bottle is connected to the detection tank through a pipeline provided with the waste discharge pump; the control module electrically connects the filtering pump, the cleaning pump and the waste discharge pump.

[0014] An electrochemical detection method, using the above electrochemical sensor for detection, or using the above electrochemical detection system for detection, the detection steps are as follows:

[0015] S1. Take a sample and dilute the test solution with a buffer solution, and then send the diluted test solution into the detection pool;

[0016] S2. inserting the reference electrode and the counter electrode into the solution to be tested in the detection cell, and selecting one or more of the nitrite selective electrode, the nitrate selective electrode and the phosphate selective electrode and inserting them into the solution to be tested in the detection cell;

[0017] S3. Use cyclic voltammetry or current-time method to perform detection to obtain one or more data of nitrite concentration, nitrate concentration, and phosphate concentration.

[0018] Furthermore, in step S1: 1-5 mL of sample is taken, the dilution ratio is 1:1 to 1:10000, and the buffer solution is a 0.5 mol / L sulfuric acid-potassium chloride mixed solution.

[0019] Furthermore, in step S3: before using cyclic voltammetry for detection, the solution is left to stand for 3 to 5 minutes to keep the surface of the solution to be tested in the detection cell calm; the detection potential when using cyclic voltammetry for detection is -0.8 to 0.8 V, and the scanning speed is 20 to 200 mv / s.

[0020] Furthermore, in step S1, the diluted test solution is continuously allowed to flow into the detection cell, and in step S3, the current-time method is used for detection. During detection, the test solution in the detection cell is continuously stirred, and during detection, the excitation voltage of the nitrite selective electrode is 0.70 to 0.74 V, the excitation voltage of the nitrate selective electrode is -0.68 to -0.72 V, and the excitation voltage of the phosphate selective electrode is -0.12 to -0.16 V.

[0021] Further, in step S3: the nitrite current value y and the nitrite concentration value x are linearly related in the range of 3.00 to 1550.00 μM, and the linear relationship is: y=0.015x+4.762; the nitrite current value y and the nitrite concentration value x are linearly related in the range of 1550.00 to 2580.00 μM, and the linear relationship is: y=0.0093x+12.3262.

[0022] The present invention has the following beneficial effects:

[0023] 1. The present invention provides a working electrode, which is modified with a graphene-gold nanoparticle-ceria composite. The excellent conductivity and large specific surface area of ​​graphene are used to provide a good supporting platform for gold nanoparticles and ceria, and gold nanoparticles and ceria are used to provide more active sites to promote the adsorption and reaction of target substances (such as nitrite and nitrate) on the surface of the working electrode, thereby improving the sensitivity of detection. The three work together to improve the performance of the working electrode and provide excellent analytical operating conditions for the detection of nitrite and nitrate.

[0024] 2. The present invention provides a working electrode modified with a graphene-gold nanoparticle-molybdic acid composite, which utilizes the high conductivity of graphene and the large specific surface area of ​​gold nanoparticles and molybdic acid particles, combined with the catalytic effect of molybdic acid, to promote the electron transfer process between the gold nanoparticles and the target substance, thereby improving the sensitivity of the working electrode to phosphate and accelerating the detection response speed.

[0025] 3. The present invention adopts tungsten needle electrode to replace the traditional glassy carbon electrode as the base electrode to improve the anti-fouling performance of the working electrode, which is conducive to long-term monitoring and can improve the conductivity and response speed of the working electrode. At the same time, the electrochemical reaction can be set at the tiny tip of the tungsten needle electrode, which significantly reduces the consumption of samples and reagents during detection and is more environmentally friendly.

[0026] 4. The present invention is based on a working electrode modified with a graphene-gold nano-cerium dioxide composite or a graphene-gold nano-molybdate composite, which provides conditions for quickly obtaining the concentration information of nitrite, nitrate and phosphate in the water environment, and also provides a basis for the simultaneous detection of multiple parameters of nitrite, nitrate and phosphate. The corresponding electrochemical sensor, electrochemical detection system and electrochemical detection method have a variety of parameter analysis items to choose from, can provide more comprehensive detection information, and the corresponding structure is simple and reliable, easy to carry and for on-site detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematic diagram of the working electrode structure of the present invention.

[0028] Figure 2 It is a schematic diagram of the structure of the electrochemical detection system of the present invention.

[0029] Figure 3 This is a cyclic voltammetry curve diagram under different phosphate concentrations in Experiment 1 of the present invention.

[0030] Figure 4 It is a timing curve diagram and a nitrite current-nitrite concentration relationship diagram in Experiment 2 of the present invention.

[0031] Explanation of the main component symbols: 1. Working electrode; 2. Base electrode; 3. Test end; 4. Detection cell; 5. Reference electrode; 6. Counter electrode; 7. Control module; 8. Data acquisition module; 9. Sample liquid bottle; 10. Buffer liquid bottle; 11. Mixing liquid bottle; 12. Sampling tube; 13. Buffer tube; 14. Mixing tube; 15. Sampling pump; 16. Buffer pump; 17. Mixing pump; 18. Filter device; 19. Filter pump; 20. Cleaning liquid bottle; 21. Cleaning pump; 22. Waste liquid bottle; 23. Waste pump; L, modified length. DETAILED DESCRIPTION

[0032] The present invention will be further described below in conjunction with the accompanying drawings and specific implementation methods.

[0033] Embodiment 1

[0034] The present invention discloses a working electrode 1, comprising a substrate electrode 2, the surface of which is modified with a graphene-gold nano-cerium dioxide composite (Au-CeO2@rGO) or a graphene-gold nano-molybdate composite (Au-MoO@rGO).

[0035] When the base electrode 2 is modified with a graphene-gold nanoparticle-cerium dioxide composite, the high conductivity of graphene can be used to accelerate the electron transfer speed in the electrochemical reaction, thereby increasing the response time of the working electrode 1. The large specific surface area of ​​gold nanoparticles and ceria can provide sufficient active sites to promote the adsorption and reaction of target substances (such as nitrite and nitrate) on the surface of the base electrode 2, thereby improving the detection sensitivity. Ceria can reduce the activation energy of the reaction in the electrochemical reaction, increase the reaction rate, and promote the electron transfer process. The three work together to make the working electrode 1 have excellent sensitivity, selectivity and stability for nitrite and nitrate, providing excellent analytical operating conditions for the detection of nitrite and nitrate.

[0036] When a graphene-gold nanoparticle-molybdate composite substrate electrode 2 is used, the high conductivity of graphene and the large specific surface area of ​​gold nanoparticles and molybdate particles can be utilized, combined with the catalytic effect of molybdate, to effectively improve the sensitivity of the working electrode 1 to phosphate and accelerate the detection response speed.

[0037] like Figure 1 As shown, the substrate electrode 2 has a test end 3 that can be inserted into the solution to be tested, and the graphene-gold nano-cerium dioxide composite or graphene-gold nano-molybdic acid composite is modified from the test end 3 along the length direction of the substrate electrode 2, and the modified length L is 7 to 10 mm. Accordingly, the modified amount of the graphene-gold nano-cerium dioxide composite or graphene-gold nano-molybdic acid composite is controlled at 0.5 to 10.0 mg to avoid excessive coverage, so as to ensure the sensitivity and response speed of the working electrode 1.

[0038] Preferably, the base electrode 2 is a tungsten needle electrode, and the anti-fouling performance of the tungsten needle electrode is used to increase the service life of the working electrode 1, which is conducive to long-term monitoring of the water environment. At the same time, the electrochemical reaction can be set at the tiny tip of the tungsten needle electrode, that is, the above-mentioned test end 3, to significantly reduce the consumption of samples and reagents during detection, which is more environmentally friendly.

[0039] Embodiment 2

[0040] On the basis of the above-mentioned embodiment 1, the present invention also provides an electrochemical sensor, including a detection cell 4, a reference electrode 5 and a counter electrode 6, wherein the reference electrode 5 is an Ag / AgCl electrode, and the counter electrode 6 is a platinum electrode. In addition, the electrochemical sensor also includes one or more electrodes of a nitrite selective electrode, a nitrate selective electrode and a phosphate selective electrode set according to the detection requirements. Among them, the nitrite selective electrode and the nitrate selective electrode are the above-mentioned working electrode 1 with a surface modified with a graphene-gold nano-cerium dioxide complex, and the phosphate selective electrode is the above-mentioned working electrode 1 with a surface modified with a graphene-gold nano-molybdate complex. Based on the excellent characteristics of the above-mentioned working electrode 1 and the actual selective setting, the electrochemical sensor can be used for the detection and acquisition of one or more information of nitrite, nitrate and phosphate concentrations, has more detection functions, can provide more comprehensive detection information, has high sensitivity during detection, and has a short detection response time.

[0041] Embodiment 3

[0042] like Figure 2 As shown, on the basis of the above-mentioned embodiment 2, the present invention also provides an electrochemical detection system, including a sampling module, a control module 7, a data acquisition module 8 and the above-mentioned electrochemical sensor. The sampling module is connected to the detection pool 4, can perform sampling operations, and send the solution to be tested into the detection pool 4 for detection. The control module 7 is electrically connected to the sampling module to control the operation of the sampling module. The data acquisition module 8 is electrically connected to the electrochemical sensor to identify and record electrochemical signals and perform data acquisition. The data acquisition module 8 and the control module 7 are wirelessly connected via Bluetooth. The data acquisition module 8 can send the collected relevant information to the control module 7 for analysis and processing, thereby obtaining real-time indicator data and system operation status.

[0043] The sampling module specifically includes a sample liquid bottle 9, a buffer bottle 10, a mixed liquid bottle 11, a sampling tube 12, a buffer tube 13 and a mixing tube 14. Among them, the sample liquid bottle 9 is used to store the solution to be tested, the buffer bottle 10 is used to store the buffer solution, and the mixed liquid bottle 11 is used to provide a place for mixing the solution to be tested and the buffer solution. The sample liquid bottle 9 is connected to the mixed liquid bottle 11 through the sampling tube 12, and the sampling tube 12 is provided with a sampling pump 15 to provide sampling power; the buffer bottle 10 is connected to the mixed liquid bottle 11 through the buffer tube 13, and the buffer tube 13 is provided with a buffer pump 16 to provide power for extracting the buffer solution; the mixed liquid bottle 11 is connected to the detection pool 4 through the mixing tube 14, and the mixing tube 14 is provided with a mixing pump 17, which can transport the mixed solution to be tested to the detection pool 4.

[0044] The control module 7 is electrically connected to the sampling pump 15, the buffer pump 16 and the mixing pump 17 to control their opening and closing to perform corresponding extraction operations. Based on the relevant settings of the buffer bottle 10, the buffer tube 13, the buffer pump 16, etc., the sampling module has sampling and dilution functions, and can extract the corresponding proportion of the test solution and the buffer solution during detection, and dilute the test solution for pretreatment.

[0045] In addition, the electrochemical detection system also includes a filtering module, a cleaning module and a waste discharge module. The filtering module includes a filtering device 18 and a filtering pump 19, which are arranged on the pipeline between the sampling module and the detection tank 4, and can filter the solution to be tested sent into the detection tank 4 to prevent impurities from affecting the detection.

[0046] The cleaning module includes a cleaning liquid bottle 20 and a cleaning pump 21. The cleaning liquid bottle 20 is connected to the detection tank 4 through a pipeline provided with the cleaning pump 21. The cleaning liquid can be drawn from the cleaning liquid bottle 20 through the cleaning pump 21 and pumped into the detection tank 4 for cleaning. The waste discharge module includes a waste liquid bottle 22 and a waste discharge pump 23. The waste liquid bottle 22 is connected to the detection tank 4 through a pipeline provided with the waste discharge pump 23. The waste liquid in the detection tank 4 can be drawn out through the waste discharge pump 23 and stored in the waste liquid bottle 22 for waste discharge operation. The control module 7 is electrically connected to the filter pump 19, the cleaning pump 21 and the waste discharge pump 23 to control the filtering, cleaning and waste discharge operations accordingly.

[0047] The electrochemical detection system has a continuous detection function. During operation, the solution to be tested can be extracted through the mixing pump 17 and continuously delivered to the detection tank 4 at a certain flow rate. With the cooperation of the waste discharge module, the solution to be tested in the detection tank 4 is continuously injected, renewed, and discharged, thereby achieving the purpose of continuous detection.

[0048] Embodiment 4

[0049] On the basis of the above-mentioned embodiment 2 or the above-mentioned embodiment 3, the present invention also provides an electrochemical detection method, which adopts the above-mentioned electrochemical sensor for detection, or adopts the above-mentioned electrochemical detection system for detection, and the number of the electrochemical sensors used for detection, the nitrite selective electrodes, the nitrate selective electrodes, and the phosphate selective electrodes in the electrochemical detection system are set according to the detection requirements.

[0050] The specific detection steps are as follows:

[0051] S1. Sampling, extracting 1-5mL of the solution to be tested, and diluting the solution to be tested with a buffer solution, the dilution multiple is 1:1 to 1:10000, and then sending the diluted solution to be tested into the detection pool 4. In this embodiment, the buffer solution used is a 0.5mol / L sulfuric acid-potassium chloride (H2SO4-KCl) mixed solution, which can be used for pretreatment of nitrite, nitrate, and phosphate detection, providing a basis for simultaneous analysis of multiple parameters.

[0052] S2. Insert the reference electrode 5 and the counter electrode 6 into the solution to be tested in the detection cell 4, and select one or more of the nitrite selective electrode, nitrate selective electrode and phosphate selective electrode according to the detection requirements and insert them into the solution to be tested in the detection cell 4.

[0053] S3. Use cyclic voltammetry or current-time method to perform detection to obtain one or more data of nitrite concentration, nitrate concentration, and phosphate concentration.

[0054] More specifically, in step S3, if cyclic voltammetry is used for detection, the detection cell 4 may be left still for 3 to 5 minutes before detection to keep the surface of the solution to be tested in the detection cell 4 calm, so as to reduce current fluctuations caused by solution flow or stirring, thereby ensuring the accuracy and reliability of the measurement results. The detection potential when cyclic voltammetry is used for detection is set to -0.8 to 0.8 V, and the scanning speed is 20 to 200 mv / s, preferably 100 mv / s.

[0055] As another optional method, in step S1, the diluted test solution can be continuously allowed to flow into the detection tank 4, and the current-time method can be used for detection in step S3. The flow rate when inputting the test solution can be controlled between 4 and 4800 μL / min. The test solution in the detection tank 4 is continuously stirred during detection. During detection, the excitation voltage of the nitrite selective electrode is set between 0.70 and 0.74 V, preferably 0.72 V; the excitation voltage of the nitrate selective electrode is -0.68 to -0.72 V, preferably -0.70 V; the excitation voltage of the phosphate selective electrode is -0.12 to -0.16 V, preferably -0.14 V.

[0056] The following experiments were used to verify the effect of the present invention:

[0057] Experiment 1

[0058] The phosphate concentration was detected by the electrochemical detection method in the fourth embodiment. Figure 3 As shown. Before detection, extract 1-5mL of the solution to be tested and dilute it 10-20 times with a 0.5mol / L sulfuric acid-potassium chloride (H2SO4-KCl) mixed solution as a buffer solution. After dilution, the solution to be tested is pumped into the detection tank 4 through the corresponding pump and kept flowing, and the flow rate is controlled at 100uL / min. During detection, the solution to be tested in the detection tank 4 is continuously stirred, and the cyclic voltammetry method is used to detect the phosphate concentration. The detection potential during detection is set to -0.8~0.8V, and the scanning speed is 100mv / s.

[0059] Experiment 2

[0060] The electrochemical detection method in the fourth embodiment is used, and the current-time method is used to detect the nitrite concentration. Figure 4 As shown, when the excitation voltage of the nitrite selective electrode is 0.72 V, the nitrite concentration shows a good linear relationship when it is in the range of 3.00-1550.00 μM and 1550.00-2580.00 μM.

[0061] When the nitrite concentration value x is in the range of 3.00 to 1550.00 μM, there is a linear relationship between the nitrite current value y (μA) and the nitrite concentration value x (μM), and the linear relationship is: y=0.015x+4.762.

[0062] When the nitrite concentration value x is in the range of 1550.00 to 2580.00 μM, there is a linear relationship between the nitrite current value y and the nitrite concentration value x, and the linear relationship is: y = 0.0093x + 12.3262. The detection limit (LOD) is 0.406 μM.

[0063] Although the present invention has been specifically shown and described in conjunction with the preferred embodiments, it should be understood by those skilled in the art that various changes in form and details may be made to the present invention without departing from the spirit and scope of the invention as defined in the appended claims, all of which are within the scope of protection of the present invention.

Claims

1. A working electrode, characterized in that: The invention comprises a base electrode, the surface of which is modified with a graphene-gold nano-cerium dioxide compound or a graphene-gold nano-molybdic acid compound.

2. A working electrode according to claim 1, characterized in that: The substrate electrode has a test end, and the graphene-gold nano-cerium dioxide composite or the graphene-gold nano-molybdic acid composite is modified 7 to 10 mm along the length direction of the substrate electrode starting from the test end, and the modification amount of the graphene-gold nano-cerium dioxide composite or the graphene-gold nano-molybdic acid composite is 0.5 to 10.0 mg.

3. A working electrode according to claim 1, characterized in that: The substrate electrode is a tungsten needle electrode.

4. An electrochemical sensor comprising a detection cell, a reference electrode and a counter electrode, characterized in that: It also includes one or more of a nitrite selective electrode, a nitrate selective electrode and a phosphate selective electrode; the nitrite selective electrode and the nitrate selective electrode are the working electrodes described in any one of claims 1-3, and their surfaces are modified with a graphene-gold nano-cerium dioxide complex; the phosphate selective electrode is the working electrode described in any one of claims 1-3, and its surface is modified with a graphene-gold nano-molybdic acid complex.

5. An electrochemical detection system, characterized in that: It includes a sampling module, a control module, a data acquisition module and the electrochemical sensor as claimed in claim 4; the sampling module is connected to the detection pool, the control module is electrically connected to the sampling module, the data acquisition module is electrically connected to the electrochemical sensor, and can send data to the control module.

6. An electrochemical detection system as claimed in claim 5, characterized in that: The sampling module includes a sample liquid bottle, a buffer bottle, a mixed liquid bottle, a sampling tube, a buffer tube and a mixing tube. The sample liquid bottle is connected to the mixed liquid bottle through the sampling tube, the buffer bottle is connected to the mixed liquid bottle through the buffer tube, and the mixed liquid bottle is connected to the detection pool through the mixing tube. The sampling tube is provided with a sampling pump, the buffer tube is provided with a buffer pump, and the mixing tube is provided with a mixing pump; the control module is electrically connected to the sampling pump, the buffer pump and the mixing pump.

7. An electrochemical detection system as claimed in claim 5, characterized in that: It also includes a filtration module, a cleaning module and a waste discharge module, the filtration module includes a filtration device and a filtration pump, the filtration device and the filtration pump are arranged on the pipeline between the sampling module and the detection pool, the cleaning module includes a cleaning liquid bottle and a cleaning pump, the cleaning liquid bottle is connected to the detection pool through a pipeline provided with the cleaning pump, the waste discharge module includes a waste liquid bottle and a waste discharge pump, the waste liquid bottle is connected to the detection pool through a pipeline provided with the waste discharge pump; the control module is electrically connected to the filtration pump, the cleaning pump and the waste discharge pump.

8. An electrochemical detection method, characterized in that: The electrochemical sensor according to claim 4 is used for detection, or the electrochemical detection system according to any one of claims 5 to 7 is used for detection, and the detection steps are as follows: S1. Take a sample and dilute the test solution with a buffer solution, and then send the diluted test solution into the detection pool; S2. inserting the reference electrode and the counter electrode into the solution to be tested in the detection cell, and selecting one or more of the nitrite selective electrode, the nitrate selective electrode and the phosphate selective electrode and inserting them into the solution to be tested in the detection cell; S3. Use cyclic voltammetry or current-time method to perform detection to obtain one or more data of nitrite concentration, nitrate concentration, and phosphate concentration.

9. An electrochemical detection method as claimed in claim 8, characterized in that: In step S1: 1-5 mL of sample is taken, the dilution ratio is 1:1 to 1:10000, and the buffer solution is a 0.5 mol / L sulfuric acid-potassium chloride mixed solution.

10. An electrochemical detection method according to claim 8, characterized in that: In step S3: before using cyclic voltammetry for detection, the solution is left to stand for 3 to 5 minutes to keep the surface of the solution to be detected in the detection cell calm; the detection potential when using cyclic voltammetry for detection is -0.8 to 0.8 V, and the scanning speed is 20 to 200 mv / s.

11. An electrochemical detection method according to claim 8, characterized in that: In step S1, the diluted test solution is continuously allowed to flow into the detection cell, and in step S3, the current-time method is used for detection. During the detection, the test solution in the detection cell is continuously stirred, and during the detection, the excitation voltage of the nitrite selective electrode is 0.70 to 0.74 V, the excitation voltage of the nitrate selective electrode is -0.68 to -0.72 V, and the excitation voltage of the phosphate selective electrode is -0.12 to -0.16 V.

12. An electrochemical detection method according to claim 8, characterized in that: In step S3: The nitrite current value y and the nitrite concentration value x are linearly related in the range of 3.00 to 1550.00 μM, and the linear relationship is: y = 0.015x + 4.762; The nitrite current value y and the nitrite concentration value x are linearly related in the range of 1550.00 to 2580.00 μM, and the linear relationship is: y=0.0093x+12.3262.

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