Microfluidic detection system and method for content of nitrate and nitrite in water

Abstract

The invention provides a microfluidic detection system and method for the content of nitrate and nitrite in water. The microfluidic detection system comprises a detection unit, a liquid inlet unit and a circulation unit. The micro-fluidic technology is combined with a Griess reagent detection method and a vanadium chloride reduction method, nitrate and nitrite in water are detected, samples are subjected to pretreatment, mixing, heating reaction and detection through flow injection of a pump and an electromagnetic valve, and the whole detection system is small in size, low in reagent consumption, high in automation degree, easy to operate and high in detection accuracy. The method is suitable for small-scale detection analysis of water samples. The water quality sample to be detected and the detection reagent are circularly mixed for multiple times in the liquid mixing flow channel through the circulating unit, the mixing efficiency and the reaction efficiency are improved, a stirring device is not needed, and therefore the size of the detection system is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of water quality detection, and in particular to a microfluidic detection system and method for nitrate and nitrite content in water. Background Art

[0002] Nitrite is nitrogen in the form of NO 2 ﹣ Compounds that exist in the form of NO are generally the intermediate stage of ammonia nitrogen oxidation to nitrates, which are unstable and toxic; nitrates are nitrogen elements in the form of NO 3 ﹣ Compounds that exist in the form of nitrogen are one of the final products of the ecological nitrogen cycle. The content of nitrite and nitrate in water bodies is increasing due to agricultural activities, landfills, industrial emissions and other reasons around the world. In aquaculture, high concentrations of nitrogen-containing compounds are toxic to aquatic organisms such as fish, causing them to suffocate and die. In addition, when the content of nitrogen-containing compounds in water bodies is excessive, it will promote the rapid growth and reproduction of algae and plankton in the water, leading to eutrophication and hypoxia of the water body, greatly affecting the cultivation of various aquatic products. Therefore, the detection of nitrite and nitrate in water quality has important environmental monitoring and ecological protection significance.

[0003] The most widely used method for detecting nitrite is the detection method using Griess reagent. The Griess detection method is based on diazotization reaction and realizes quantitative determination through color development reaction. Its basic principle is to use nitrite to react with aromatic amine compounds under acidic conditions to generate diazo compounds, and then react with coupling reagents (N-1-naphthylethylenediamine) to form stable red azo compounds, whose absorbance can be measured at a wavelength of about 540nm, thereby calculating the concentration of nitrite.

[0004] One of the methods for detecting nitrate is to reduce nitrate to nitrite first and then detect it, thereby indirectly detecting the nitrate concentration. Nitrate reduction methods include bio-enzyme reduction method, ultraviolet reduction method, copper-coated cadmium column reduction method, vanadium chloride reduction method, etc. Among them, the vanadium chloride reduction method has the advantages of low toxicity, high reduction rate, low cost, simple operation, etc., which is convenient for on-site detection.

[0005] The use of Griess reagent and vanadium chloride reducing reagent to detect the nitrate and nitrite content in water quality has the advantages of simple operation, fast detection speed, low cost, and relatively stable reaction color products. However, there are problems such as large reagent consumption, large detection system size, and insufficient system integration.

[0006] For example, the utility model with the authorization announcement number CN214011044U discloses an intelligent water quality detection device, which includes a frame, on which a sampling mechanism, a colorimetric detection mechanism, a parameter detection mechanism, a reagent bin and a control system are installed, the sampling mechanism is used to collect water samples, the colorimetric detection mechanism is connected to the sampling mechanism through a pipeline, the colorimetric detection mechanism is used to detect the nutrient salt content in the water sample, the parameter detection mechanism is connected to the sampling mechanism through a pipeline, the parameter detection mechanism is used to detect the pH value, dissolved oxygen content, conductivity and sodium ion content of the water sample, the reagent bin is used to provide the reagents required in the detection process of the colorimetric detection mechanism, and the control system is used to control the automatic operation of the sampling mechanism, the parameter detection mechanism, the colorimetric detection mechanism and the reagent bin to detect the water sample. The detection system is large in size and is not suitable for small-scale detection and analysis.

[0007] The utility model with authorization announcement number CN211205982U discloses an online total nitrogen monitor, including an outer shell and a reaction chamber, the reaction chamber is installed on one side of the outer shell, a sample liquid inlet pipe is installed on one side of the upper end of the reaction chamber, and a reaction reagent liquid inlet pipe is installed on the other side, a stirring mechanism is installed inside the reaction chamber, a detection chamber is installed in the inner cavity of the outer shell, a total nitrogen analyzer is installed directly above the detection chamber, and a controller is fixedly installed on the outer wall of the outer shell. The detection system has the problem of large reagent consumption. Summary of the invention

[0008] Based on the above technical problems existing in the prior art, the present invention provides a microfluidic detection system and method for the nitrate and nitrite content in water quality. The detection system and method have low reagent consumption, high degree of automation, and small equipment size. They can quickly and accurately detect on-site water quality conditions and assess the pollution pressure on water bodies, providing a reliable basis for water quality assessment, pollution prevention and control, ecological protection, aquaculture, etc.

[0009] The present invention provides a microfluidic detection system for nitrate and nitrite content in water, comprising:

[0010] The detection unit comprises a detection cavity, the detection cavity has a liquid inlet and a liquid outlet, the liquid inlet and the liquid outlet are respectively connected to a liquid mixing channel; the detection unit also comprises a detection mechanism for detecting the absorbance of the liquid in the detection cavity;

[0011] The liquid inlet unit comprises a first solenoid valve, a second solenoid valve, a third solenoid valve, a fourth solenoid valve, a fifth solenoid valve, a sixth solenoid valve and an infusion pump, wherein the first solenoid valve, the second solenoid valve, the fifth solenoid valve and the sixth solenoid valve are three-way valves with two inlets and one outlet, and the third solenoid valve and the fourth solenoid valve are three-way valves with one inlet and two outlets; one of the inlets of the first solenoid valve is connected to the sample injection tube, and the other inlet is connected to the cleaning liquid tube; one of the inlets of the second solenoid valve is connected to the outlet of the first solenoid valve through a pipeline, and the other inlet is used as a circulation inlet; the inlet of the third solenoid valve is connected to the outlet of the second solenoid valve through a pipeline, and one of the inlets of the third solenoid valve is connected to the outlet of the second solenoid valve through a pipeline. The outlet is connected to one of the inlets of the sixth solenoid valve through a pipeline, and the other outlet is connected to the inlet of the fourth solenoid valve through a pipeline; the two outlets of the fourth solenoid valve are respectively connected to the first metering tube and the second metering tube, and the first metering tube and the second metering tube are both used for waste liquid discharge and liquid discharge calculation; the two inlets of the fifth solenoid valve are respectively connected to the Griess reagent tube and the vanadium chloride reduction reagent tube for switching into the reagent; the other inlet of the sixth solenoid valve is connected to the outlet of the fifth solenoid valve, and the outlet of the sixth solenoid valve is connected to the liquid mixing channel located at the liquid inlet end of the detection cavity through a driving pipeline, and the infusion pump is provided on the driving pipeline;

[0012] The circulation unit includes a seventh solenoid valve, which is a three-way valve with one inlet and two outlets. The inlet is connected to the liquid mixing channel at the liquid outlet end of the detection chamber, one of the outlets is connected to the inlet of the second solenoid valve as the circulation inlet, and the other outlet is used for waste liquid discharge.

[0013] Furthermore, the sample inlet tube is provided with a pre-treatment filter for filtering and removing impurities from the water sample to be tested. The pre-treatment filter is provided with a filter membrane, a filter screen or a filter column, which can be selected according to the actual impurity situation of the water sample.

[0014] Furthermore, the first metering tube and the second metering tube are respectively arranged between the two outlets of the fourth solenoid valve and the waste liquid discharge port, and are respectively preset with liquid volume markings for determining the volume of the injected reagent to facilitate control of the reagent injection amount.

[0015] Furthermore, the detection mechanism comprises a light source and an optical sensor module respectively arranged on both sides of the detection cavity. The light source can be an LED lamp.

[0016] Furthermore, the central wavelength of the light source is 540nm; and the optical sensing module is a light sensor or a camera whose corresponding wavelength band includes 540nm.

[0017] Furthermore, a light shield is provided at the interface between the light source and the optical sensor module, and a filter with a central wavelength of 540 nm is installed to eliminate stray light during detection.

[0018] Furthermore, circuit board modules are provided on opposite sides of the detection cavity, the circuit board modules include epoxy resin boards, and the light source and optical sensor module are located between the circuit board modules on both sides. The circuit board modules are used to provide power supply, control the operation of the microfluidic detection system, and receive and transmit data.

[0019] Furthermore, the liquid inlet and liquid outlet of the detection cavity are respectively located on two opposite sides and are staggered with the light source and the optical sensing module, wherein the liquid inlet is located at the lowest point on one side and the liquid outlet is located at the highest point on the opposite side, so that the liquid can fill the detection cavity as much as possible after flowing in, thereby reducing the interference that bubbles may cause to the detection.

[0020] Furthermore, heating modules are respectively provided at positions corresponding to the detection cavity and the two liquid mixing channels on the circuit board module. Simultaneous heating on both sides is conducive to uniform heating of the mixed liquid, thereby improving the efficiency of the mixing reaction between the detection reagent and the water quality sample to be tested. An insulating layer is provided on the periphery of the heating module to isolate the heating module from other modules except the liquid mixing channel and the detection cavity to avoid affecting the detection.

[0021] Furthermore, both the infusion pump and the solenoid valve are small, which reduces the overall volume of the microfluidic detection system and the demand for detection reagents and water quality samples to be tested. The solenoid valve is preferably made of plastic, and PTFE (polytetrafluoroethylene) or PEEK (polyetheretherketone) can be selected, which is corrosion-resistant and has excellent sealing performance. The infusion pump is preferably a peristaltic pump.

[0022] The present invention also provides a microfluidic detection method for the content of nitrate and nitrite in water, which is detected using the above-mentioned microfluidic detection system. The microfluidic detection method comprises the following steps:

[0023] (1) Distilled water is input into the detection unit through the cleaning liquid inlet pipe, and the detection mechanism performs absorbance detection on the detection area to obtain a background signal;

[0024] (2) The water sample to be tested is input into the detection unit through the sample injection tube, and the Griess reagent is input into the detection unit through the Griess reagent inlet tube until the liquid in the first metering tube reaches the mark. Then the second solenoid valve, the third solenoid valve, the sixth solenoid valve, the detection unit and the circulation unit are connected to form a loop, and the water sample to be tested and the Griess reagent are mixed and circulated multiple times in the loop;

[0025] (3) The detection device detects the absorbance of the detection area to obtain a detection signal A, calculates the absorbance by comparing it with the background signal, and compares it with the nitrite standard curve to obtain the nitrite concentration C1 in the water sample to be tested;

[0026] (4) The vanadium chloride reducing reagent is input into the detection unit through the vanadium chloride reducing reagent inlet tube until the liquid in the second metering tube reaches the mark. Then the second solenoid valve, the third solenoid valve, the sixth solenoid valve, the detection unit and the circulation unit are connected to form a loop, so that the water sample to be tested and the vanadium chloride reducing reagent are mixed and circulated multiple times in the loop;

[0027] (5) heating the liquid mixing channel and the detection chamber by a heating module so that the water sample to be tested and the vanadium chloride reducing reagent fully react;

[0028] (6) The detection device detects the absorbance of the detection area to obtain a detection signal B, compares the absorbance with the background signal, and compares the total nitrogen standard curve to obtain the sum of the nitrite and nitrate concentrations C2 in the water sample to be tested;

[0029] (7) Calculate the nitrate concentration C3 in the water sample to be tested, and the calculation formula is C3 = C2-C1.

[0030] The nitrite standard curve and the total nitrogen standard curve are obtained by replacing the water quality sample to be tested input in step (2) with nitrite standard solutions of different concentrations and performing preliminary experimental calibration in steps (1) to (6);

[0031] The nitrite standard curve is a curve of the corresponding relationship between absorbance and concentration obtained after the absorbance is detected in step (3);

[0032] The total nitrogen standard curve is a curve of the corresponding relationship between absorbance and concentration obtained after the absorbance is detected in step (6).

[0033] Furthermore, in step (2) or step (4), before the detection reagent is input into the detection unit, the second solenoid valve, the third solenoid valve and the seventh solenoid valve are switched to discharge the air in the circuit through which the subsequent water quality sample to be tested and the detection reagent are mixed in advance, thereby reducing the influence of bubbles in the liquid on the detection reaction during subsequent colorimetric detection. The detection reagent is a Griess reagent or a vanadium chloride reduction reagent.

[0034] Preferably, the heating temperature in step (4) is set to 50°C.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] The present invention combines microfluidics technology with Griess reagent detection method and vanadium chloride reduction method to detect nitrate and nitrite in water quality. Through flow injection of a pump and an electromagnetic valve, the sample is pretreated, mixed, heated, reacted, and detected. The entire detection system has a small volume, low reagent consumption, a high degree of automation, and simple operation, and is suitable for small-scale detection and analysis of water quality samples.

[0037] The present invention allows the water quality sample to be tested and the detection reagent to be circulated and mixed multiple times in a liquid mixing channel through a circulation unit, thereby improving the mixing efficiency and the reaction efficiency, and does not require a stirring device, thereby reducing the volume of the detection system. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a schematic diagram of the overall structure of the microfluidic detection system for nitrate and nitrite content in water.

[0039] Figure 2 It is a structural schematic diagram of the detection unit.

[0040] Figure 3 It is a schematic diagram of the circuit board module structure.

[0041] Figure 4 It is a schematic diagram of the pipeline when the microfluidic detection system for nitrate and nitrite content in water quality inputs the water quality sample to be tested.

[0042] Figure 5 This is a schematic diagram of the pipeline when the Griess reagent is input into the microfluidic detection system for nitrate and nitrite content in water.

[0043] Figure 6 This is a schematic diagram of the pipeline when the vanadium chloride reducing reagent is input into the microfluidic detection system for the nitrate and nitrite content in water.

[0044] Figure 7 It is a schematic diagram of the pipeline when the microfluidic detection system of nitrate and nitrite content in water quality performs a mixed reaction between the detection reagent and the water quality sample to be tested.

[0045] Figure numerals: pretreatment filter chamber 1, pretreatment filter 2, first solenoid valve 3, liquid circulation pipe 4, second solenoid valve 5, third solenoid valve 6, fourth solenoid valve 7, fifth solenoid valve 8, sixth solenoid valve 9, first metering tube 10, second metering tube 11, infusion pump 12, detection mechanism 13, detection chamber 14, liquid mixing flow channel 15, circuit board module 16, seventh solenoid valve 17, light source 18, optical sensor module 19, heating module 20, thermal insulation layer 21, main control module 22, light source driving module 23, heating control module 24, signal processing module 25, power supply module 26, detection unit 27, liquid inlet unit 28, circulation unit 29,

[0046] The inlet S of the sample injection tube, the inlet C of the cleaning liquid tube, the inlet D1 of the Griess reagent tube, the inlet D2 of the vanadium chloride reduction reagent tube, the waste liquid discharge outlet W1 of the seventh solenoid valve, the waste liquid discharge outlet W2 of the first metering tube, and the waste liquid discharge outlet W3 of the second metering tube. DETAILED DESCRIPTION

[0047] like Figure 1-Figure 7 As shown, this embodiment provides a microfluidic detection system for nitrate and nitrite content in water, including a detection unit 27, a liquid inlet unit 28 and a circulation unit 29.

[0048] The detection unit 27 includes a detection chamber 14, which has a liquid inlet and a liquid outlet, and the liquid inlet and the liquid outlet are respectively connected to a liquid mixing channel 15. The liquid inlet and the liquid outlet of the detection chamber 14 are respectively located on two opposite sides, wherein the liquid inlet is located at the lowest point on one side, and the liquid outlet is located at the highest point on the opposite side, so that the liquid fills the detection chamber 14 as much as possible after flowing in, reducing the interference of bubbles on the detection.

[0049] Circuit board modules 16 are respectively disposed on two opposite sides of the detection cavity 14 , and the light source 18 and the optical sensor module 19 are located between the circuit board modules 16 on the two sides.

[0050] Heating modules 20 are respectively provided at positions corresponding to the detection chamber 14 and the two liquid mixing channels 15 on the circuit board module 16. Heating on both sides at the same time is conducive to uniform heating of the mixed liquid and improves the efficiency of the mixed reaction of the detection reagent and the water quality sample to be tested. By controlling the heating module 20, the liquid mixing channel 15 and the detection chamber 14 can be controlled at a specified temperature. In a preferred embodiment, the heating module 20 uses PID software control to control the temperature of the liquid mixing channel 15 and the detection chamber 14 at about 50°C.

[0051] A heat insulating layer 21 is provided on the periphery of the heating module 20 to isolate the heating module 20 from other modules except the liquid mixing channel 15 and the detection chamber 14 to avoid affecting the detection.

[0052] The circuit board module 16 can be an epoxy resin board, on which a main control module 22, a light source driving module 23, a heating control module 24, a signal processing module 25, and a power module 26 are arranged. The main control module 22 is used for the overall operation control of the detection system, the light source driving module 23 is used for light source control, the heating control module 24 is used for heating module control drive, the signal processing module 25 is used to receive sensor data and transmit it to the user end or the host computer through the interface, and the power module 26 is used to provide the power required for the operation of the detection system.

[0053] The detection unit 27 also includes a detection mechanism 13 for detecting the absorbance of the liquid in the detection cavity 14. The detection mechanism 13 includes a light source 18 and an optical sensor module 19 respectively arranged on both sides of the detection cavity 14. The light source 18 and the optical sensor module 19 are staggered with the liquid inlet and the liquid outlet of the detection cavity 14. The light source 18 can use an LED lamp, and the central wavelength of the light source 18 is 540nm. The optical sensor module 19 is a light sensor (such as OPT101) or a camera whose corresponding band includes 540nm (such as a camera with a response band of 400-700nm). A light shield is set at the interface between the light source 18 and the optical sensor module 19, and a filter with a central wavelength of 540nm is installed to eliminate stray light during detection (not shown in the accompanying drawings).

[0054] The liquid inlet unit 28 includes a first solenoid valve 3, a second solenoid valve 5, a third solenoid valve 6, a fourth solenoid valve 7, a fifth solenoid valve 8, a sixth solenoid valve 9 and an infusion pump 12. The first solenoid valve 3, the second solenoid valve 5, the fifth solenoid valve 8 and the sixth solenoid valve 9 are all three-way valves with two inlets and one outlet, and the third solenoid valve 6 and the fourth solenoid valve 7 are three-way valves with one inlet and two outlets. The infusion pump 12 is used to drive and control the flow of liquid, and a peristaltic pump is preferably used. One of the inlets of the first solenoid valve 3 is connected to the sample injection tube, and the other inlet is connected to the cleaning liquid tube. The inlet of the sample injection tube is marked as S in the figure, and the inlet of the cleaning liquid tube is marked as C in the figure. The sample injection tube is provided with a pretreatment filter 2 for filtering and removing impurities from the water sample to be tested. The pretreatment filter 2 includes a pretreatment filter chamber 1. A filter membrane, a filter screen or a filter column is provided in the pretreatment filter chamber 1, which can be selected according to the actual impurity situation of the water quality sample. The cleaning liquid can use distilled water for cleaning the pipeline, the chamber, and for background signal determination for subsequent detection.

[0055] One of the inlets of the second solenoid valve 5 is connected to the outlet of the first solenoid valve 3 through a pipeline, and the other inlet is used as a circulation inlet. The inlet of the third solenoid valve 6 is connected to the outlet of the second solenoid valve 5 through a pipeline, and one of the outlets of the third solenoid valve is connected to one of the inlets of the fourth solenoid valve 7 through a pipeline, and the other outlet is connected to the inlet of the fourth solenoid valve 7. The two outlets of the fourth solenoid valve 7 are respectively connected to the first metering tube 10 and the second metering tube 11, which are used for liquid discharge calculation and waste liquid discharge. The waste liquid discharge outlet of the first metering tube 10 is marked as W2 in the figure, and the waste liquid discharge outlet of the second metering tube 11 is marked as W3 in the figure. The two inlets of the fifth solenoid valve 8 are respectively connected to the Griess reagent tube and the vanadium chloride reduction reagent tube for switching into the reagent. The inlet of the Griess reagent tube is marked as D1 in the figure, and the inlet of the vanadium chloride reduction reagent tube is marked as D2 in the figure. Another inlet of the sixth solenoid valve 9 is connected to the outlet of the fifth solenoid valve 8, and the outlet of the sixth solenoid valve 9 is connected to the liquid mixing channel 15 located at the liquid inlet end of the detection chamber 10 through a driving pipeline, and an infusion pump 12 is provided on the driving pipeline.

[0056] The circulation unit 29 includes a seventh solenoid valve 17, which is a three-way valve with one inlet and two outlets. The inlet is connected to the liquid mixing channel 15 located at the liquid outlet end of the detection chamber 14, and one of the outlets of the seventh solenoid valve 17 is connected to the inlet of the second solenoid valve 5 serving as the circulation inlet; the other outlet is used for waste liquid discharge, which is marked as W1 in the figure.

[0057] The infusion pump 12 and the electromagnetic valve in this embodiment are both small, which reduces the overall volume of the microfluidic detection system and the demand for detection reagents and water quality samples to be tested. The electromagnetic valve is preferably made of plastic material, and PTFE or PEEK material can be selected, which is corrosion-resistant and has excellent sealing performance. The liquid circulation tube 4 carrying the liquid in the pipeline can use a silicone tube or a polytetrafluoroethylene tube, which is corrosion-resistant and ensures smooth flow of the liquid.

[0058] This embodiment also provides a microfluidic detection method for the content of nitrate and nitrite in water quality, using the above-mentioned microfluidic detection system to detect the content of nitrate and nitrite in water quality. Before detection, nitrate and nitrite detection reagents are prepared, including Griess reagent and vanadium chloride reducing reagent. The preferred preparation method of Griess reagent and vanadium chloride reducing reagent is as follows:

[0059] Accurately weigh 0.2g of N-(1-naphthyl)ethylenediamine hydrochloride and dissolve it in 50ml of pure water, stir until completely dissolved, transfer to a 100ml volumetric flask, dilute to the mark with pure water, shake well, and set aside; accurately weigh 2g of p-aminobenzenesulfonamide and dissolve it in 50ml of pure water, add 10ml of hydrochloric acid, stir until completely dissolved, transfer to a 100ml volumetric flask, dilute to the mark with pure water, shake well, and set aside; mix the above two solutions in a ratio of 1:1 to obtain Griess reagent, one of the nitrate and nitrite detection reagents.

[0060] Accurately weigh 0.8g of vanadium chloride and dissolve it in 20ml of pure water. Add 8.4ml of hydrochloric acid and stir until completely dissolved. Transfer it into a 100ml volumetric flask, dilute it to the mark with pure water, and shake well to obtain a vanadium chloride reducing reagent, which is one of the nitrate and nitrite detection reagents.

[0061] The microfluidic detection method for nitrate and nitrite content in water quality includes the following steps:

[0062] (1) Keep the waste liquid discharge outlet W1 of the cleaning liquid inlet pipe, the first solenoid valve 3, the second solenoid valve 5, the third solenoid valve 6, the sixth solenoid valve 9, the detection unit 27 and the seventh solenoid valve connected, input distilled water into the detection unit 27 through the cleaning liquid inlet pipe, and use the detection mechanism 13 to perform absorbance detection on the detection area. After the signal is stable, the background signal is obtained.

[0063] (2) Switch the first solenoid valve 3, and input the water quality sample to be tested into the detection unit 27 through the sample inlet tube. The pipeline diagram at this time is shown in Figure 4 Then switch the second solenoid valve 5, the third solenoid valve 6, the sixth solenoid valve 9 and the seventh solenoid valve 17, connect the fourth solenoid valve 7 and the first metering tube 10, input the Griess reagent into the detection unit 27 through the Griess reagent inlet tube, and exhaust the air in the pipeline until the liquid in the first metering tube 10 reaches the mark. The pipeline diagram at this time is shown in Figure 5 The third solenoid valve 6 and the sixth solenoid valve 9 are switched again, so that the second solenoid valve 5, the third solenoid valve 6, the sixth solenoid valve 9, the detection unit 27 and the circulation unit 29 are connected to form a loop, and the water quality sample to be tested and the Griess reagent are mixed and circulated multiple times in the loop. The volume ratio of the added Griess reagent to the water quality sample to be tested is 1:2 to 2:3.

[0064] (3) The detection mechanism 13 performs absorbance detection on the detection area to obtain a detection signal A, and calculates the absorbance by comparing it with the background signal. The nitrite concentration C1 in the water quality sample to be tested is obtained by comparing it with the nitrite standard curve.

[0065] (4) Then, the third solenoid valve 6, the fourth solenoid valve 7, the fifth solenoid valve 8 and the fifth and sixth solenoid valves 9 are switched, and the vanadium chloride reducing reagent is input into the detection unit 27 through the vanadium chloride reducing reagent inlet pipe until the liquid in the second metering pipe 11 reaches the mark. The pipeline schematic diagram at this time is shown in FIG. Figure 6 The third solenoid valve 6 and the sixth solenoid valve 9 are switched again, so that the second solenoid valve 5, the third solenoid valve 6, the sixth solenoid valve 9, the detection unit 27 and the circulation unit 29 are connected to form a loop, and the water sample to be tested and the vanadium chloride reducing agent are circulated and mixed in the loop for multiple times. The volume ratio of the added vanadium chloride reducing agent to the water sample to be tested is 1:3 to 1:2.

[0066] (5) The liquid mixing channel 15 and the detection chamber 14 are heated to 50° C. by the heating module 20 to allow the water sample to be tested and the vanadium chloride reducing reagent to fully react;

[0067] (6) The detection mechanism 13 performs absorbance detection on the detection area to obtain a detection signal B, and calculates the absorbance by comparing it with the background signal. The total nitrogen standard curve is compared to obtain the sum C2 of the nitrite and nitrate concentrations in the water quality sample to be tested.

[0068] (7) Calculate the nitrate concentration C3 in the water sample to be tested, and the calculation formula is C3 = C2-C1.

[0069] The nitrite standard curve and the total nitrogen standard curve are obtained by replacing the water quality sample to be tested input in step (2) with nitrite standard solutions of different concentrations and performing preliminary experimental calibration in steps (1) to (6);

[0070] The nitrite standard curve is a curve of the corresponding relationship between absorbance and concentration obtained after the absorbance is detected in step (3);

[0071] The total nitrogen standard curve is a curve of the corresponding relationship between absorbance and concentration obtained after the absorbance is detected in step (6).

Claims

1. A microfluidic detection system for nitrate and nitrite content in water, characterized in that: include: The detection unit comprises a detection cavity, the detection cavity has a liquid inlet and a liquid outlet, the liquid inlet and the liquid outlet are respectively connected to a liquid mixing channel; the detection unit also comprises a detection mechanism for detecting the absorbance of the liquid in the detection cavity; The liquid inlet unit comprises a first solenoid valve, a second solenoid valve, a third solenoid valve, a fourth solenoid valve, a fifth solenoid valve, a sixth solenoid valve and an infusion pump, wherein the first solenoid valve, the second solenoid valve, the fifth solenoid valve and the sixth solenoid valve are three-way valves with two inlets and one outlet, and the third solenoid valve and the fourth solenoid valve are three-way valves with one inlet and two outlets; one of the inlets of the first solenoid valve is connected to the sample injection tube, and the other inlet is connected to the cleaning liquid inlet tube; one of the inlets of the second solenoid valve is connected to the outlet of the first solenoid valve through a pipeline, and the other inlet is used as a circulation inlet; the inlet of the third solenoid valve is connected to the outlet of the second solenoid valve through a pipeline, and one of the outlets of the third solenoid valve is connected to the sample injection tube through a pipeline. A pipeline is connected to one of the inlets of the sixth solenoid valve, and the other outlet is connected to the inlet of the fourth solenoid valve through a pipeline; the two outlets of the fourth solenoid valve are respectively connected to the first metering tube and the second metering tube, and the first metering tube and the second metering tube are both provided with liquid volume markings for waste liquid discharge and liquid discharge calculation; the two inlets of the fifth solenoid valve are respectively connected to the Griess reagent tube and the vanadium chloride reduction reagent tube for switching into the reagent; the other inlet of the sixth solenoid valve is connected to the outlet of the fifth solenoid valve, and the outlet of the sixth solenoid valve is connected to the liquid mixing channel located at the liquid inlet end of the detection cavity through a driving pipeline, and the driving pipeline is provided with the infusion pump; The circulation unit includes a seventh solenoid valve, which is a three-way valve with one inlet and two outlets. The inlet is connected to the liquid mixing channel at the liquid outlet end of the detection chamber, one of the outlets is connected to the inlet of the second solenoid valve as the circulation inlet, and the other outlet is used for waste liquid discharge.

2. The microfluidic detection system for nitrate and nitrite content in water according to claim 1, characterized in that: The sample inlet tube is provided with a pre-treatment filter for filtering and removing impurities from the water sample to be tested.

3. The microfluidic detection system for nitrate and nitrite content in water according to claim 1, characterized in that: The detection mechanism comprises a light source and an optical sensing module respectively arranged on two sides of the detection cavity.

4. The microfluidic detection system for nitrate and nitrite content in water according to claim 3, characterized in that: The central wavelength of the light source is 540nm; the optical sensing module is a light sensor or a camera whose corresponding wavelength band includes 540nm.

5. The microfluidic detection system for nitrate and nitrite content in water according to claim 3, characterized in that: A circuit board module is respectively arranged on two opposite sides of the detection cavity, and the circuit board module comprises an epoxy resin board. The light source and the optical sensor module are located between the circuit board modules on the two sides.

6. The microfluidic detection system for nitrate and nitrite content in water according to claim 5, characterized in that: The liquid inlet and the liquid outlet of the detection cavity are respectively located on two opposite sides and staggered with the light source and the optical sensor module, wherein the liquid inlet is located at the lowest point on one side and the liquid outlet is located at the highest point on the opposite side.

7. The microfluidic detection system for nitrate and nitrite content in water according to claim 5, characterized in that: Heating modules are respectively arranged at positions on the circuit board module corresponding to the detection cavity and the two liquid mixing channels, and a heat insulation layer is arranged at the periphery of the heating modules.

8. A microfluidic detection method for nitrate and nitrite content in water, characterized in that: Using the microfluidic detection system for nitrate and nitrite content in water according to any one of claims 1 to 7, the microfluidic detection method comprises the following steps: (1) Distilled water is input into the detection unit through the cleaning liquid inlet pipe, and the detection mechanism performs absorbance detection on the detection area to obtain a background signal; (2) The water sample to be tested is input into the detection unit through the sample injection tube, and the Griess reagent is input into the detection unit through the Griess reagent inlet tube until the liquid in the first metering tube reaches the mark. Then the second solenoid valve, the third solenoid valve, the sixth solenoid valve, the detection unit and the circulation unit are connected to form a loop, and the water sample to be tested and the Griess reagent are mixed and circulated multiple times in the loop; (3) The detection device detects the absorbance of the detection area to obtain a detection signal A, calculates the absorbance by comparing it with the background signal, and compares it with the nitrite standard curve to obtain the nitrite concentration C1 in the water sample to be tested; (4) The vanadium chloride reducing reagent is input into the detection unit through the vanadium chloride reducing reagent inlet tube until the liquid in the second metering tube reaches the mark. Then the second solenoid valve, the third solenoid valve, the sixth solenoid valve, the detection unit and the circulation unit are connected to form a loop, so that the water sample to be tested and the vanadium chloride reducing reagent are mixed and circulated multiple times in the loop; (5) heating the liquid mixing channel and the detection chamber by a heating module so that the water sample to be tested and the vanadium chloride reducing reagent fully react; (6) The detection device detects the absorbance of the detection area to obtain a detection signal B, compares the absorbance with the background signal, and compares the total nitrogen standard curve to obtain the sum of the nitrite and nitrate concentrations C2 in the water sample to be tested; (7) Calculate the nitrate concentration C3 in the water sample to be tested, and the calculation formula is C3=C2-C1; The nitrite standard curve and the total nitrogen standard curve are obtained by replacing the water quality sample to be tested input in step (2) with nitrite standard solutions of different concentrations and performing preliminary experimental calibration in steps (1) to (6); The nitrite standard curve is a curve of the corresponding relationship between absorbance and concentration obtained after the absorbance is detected in step (3); The total nitrogen standard curve is a curve of the corresponding relationship between absorbance and concentration obtained after the absorbance is detected in step (6).

9. The microfluidic detection method for nitrate and nitrite content in water according to claim 8, characterized in that: In step (2) or step (4), before inputting the detection reagent into the detection unit, the second solenoid valve, the third solenoid valve and the seventh solenoid valve are switched to discharge in advance the air in the circuit through which the subsequent water quality sample to be tested and the detection reagent are mixed, and the detection reagent is a Griess reagent or a vanadium chloride reduction reagent.

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