A method for the sequential injection analysis of nitrate / nitrite in water

Abstract

The application discloses a method for analyzing nitrate / nitrite in water quality by sequential injection. The application can accurately sample and ensure complete reaction by setting a bubble detector and using an air column, and water samples and reagents are not in contact with pure water, and there is no diffusion dilution, so that the accuracy and reliability of the detection result are improved. By using the air action package, the accurate sampling of the liquid is further ensured, the complete reaction is ensured, the water sample and the reagent are not in contact with pure water, there is no diffusion dilution, so that the accuracy and reliability of the detection result are improved. The sequential injection module, the detection unit and the control unit are all modularly designed, users can flexibly replace detectors and reaction conditions according to detection requirements, the detection requirements of different water quality parameters are adapted, and the adaptability and expansibility of the system are improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of water quality monitoring, and particularly relates to a sequential injection analysis method for nitrate / nitrite in water quality. BACKGROUND

[0002] Nitrate and nitrite in nutrient salts are important indicators for water quality monitoring and evaluation of water quality eutrophication. Traditional laboratory manual determination is prone to sample contamination and takes a long time, and is not suitable for long-term on-site monitoring. The emergence of flow analysis technology realizes the automation and miniaturization of fluid control, reduces the risk of sample contamination and reagent consumption. The development of flow analysis technology has greatly promoted the development of automatic nutrient salt detection technology. Among them, the sequential injection analysis technology (SIA) is gradually applied in water quality nutrient salt monitoring due to its advantages of simple and reliable hardware, good universality of sample injection pipeline, and small sample and reagent consumption.

[0003] The sequential injection analysis system mainly includes a pump, a multi-channel selection valve, and a liquid storage ring therebetween. Each channel of the multi-channel selection valve is connected to a sample channel, a reagent channel, a waste liquid channel, a detector channel, and the like.

[0004] For example, the application with the publication number CN102980858A discloses a small sequential injection nitrite analysis system. A first electromagnetic valve is connected to a nitrite standard solution, a second electromagnetic valve is connected to a color developing agent and deionized water, the first electromagnetic valve and the second electromagnetic valve are jointly connected to a third electromagnetic valve, the third electromagnetic valve is connected to a fourth electromagnetic valve connected to a water sample, a fifth electromagnetic valve is connected to deionized water and a waste liquid bottle provided with a liquid level detection device, the fourth electromagnetic valve and the fifth electromagnetic valve are connected to a six-way valve through a first peristaltic pump and a second peristaltic pump respectively, and the six-way valve is connected to a waste liquid, a quantitative ring and a colorimetric cell respectively.

[0005] For another example, the application with the publication number CN117517227A discloses an environmental water body nitrite micro gas phase molecular absorption spectrum online detection device and detection method. The device is based on the principle of gas phase molecular absorption spectrum, integrates a carrier gas system, a reaction system and a detection system through a sequential injection analysis system, improves the detection sensitivity of nitrite at a visible wavelength, reduces the interference of water vapor in the gas phase on the detection, reduces the energy consumption requirement and manufacturing cost of the nitrite gas phase molecular absorption determination analysis device, reduces the volume of the detection device, and realizes trace level detection of nitrite in a complex matrix.

[0006] In order to realize accurate detection of nutrient salts in water samples, it is necessary to accurately control the volume of the detection water sample and the reagent, as well as the mixing procedure of the two, which requires accurate control of the flow path of the sample. SUMMARY

[0007] To address the aforementioned shortcomings in existing technologies, this invention provides a sequential injection analysis method for nitrate / nitrite in water, enabling efficient and accurate detection of water nutrients such as nitrate and nitrite.

[0008] A sequential injection analysis method for nitrate / nitrite in water, using a sequential injection analysis system, the sequential injection analysis system comprising:

[0009] The sequential injection module includes a multi-channel selection valve, a plunger pump, and a reservoir ring. The multi-channel selection valve includes a common end interface and multiple inlet and outlet interfaces. The common end interface is connected to the injection line. The reservoir ring and the plunger pump are sequentially arranged on the injection line from near the common end interface to away from the common end interface. The free end of the injection line is used to connect to a pure water bottle. The common end interface of the multi-channel selection valve is equipped with a bubble detector.

[0010] A water sample collection unit includes a water sample collection tube, one end of which is used to draw in the water sample to be tested, and the other end is connected to one of the inlet and outlet ports of the multi-channel selection valve.

[0011] The reagent unit includes a reagent inlet tube, one end of which is connected to a reagent bottle and the other end of which is connected to one of the inlet / outlet ports of the multi-channel selection valve.

[0012] The reaction unit includes a mixing tube, one end of which is connected to one of the inlet / outlet ports of the multi-channel selection valve;

[0013] The detection unit includes a detection tube, one end of which is connected to one of the inlet / outlet ports of the multi-channel selector valve;

[0014] The waste liquid pipe is connected at one end to one of the inlet / outlet ports of the multi-channel selector valve;

[0015] One of the inlet and outlet ports of the multi-channel selector valve is used as the air end for air intake;

[0016] The sequential injection analysis method includes an initialization phase, an injection phase, a reaction phase, a detection phase, and a cleaning phase.

[0017] During the initialization and cleaning phases, each phase is reset, cleaned, and then reset in sequence. During reset, the pure water in the plunger pump is drained to restore the initial position, and the liquid storage ring is filled with pure water, but an air column is left at the end of the injection line connected to the common terminal interface.

[0018] During the sample introduction stage, the common end interface is connected to the water sample collection tube, and the plunger pump draws the water sample to be tested until the bubble detector changes from a state of no liquid to a state of liquid presence. The pump continues to draw the required volume of water sample or a volume greater than the required volume. Then, the common end interface is connected to the mixing tube, and the required volume of liquid is pushed into the mixing tube. The common end interface is connected to the waste liquid tube to discharge any excess water sample to be tested. Then, the common end interface is connected to the air end, and sufficient air is drawn in. The common end interface is then connected to the mixing tube, and the water sample is completely pushed into the mixing tube by injecting air.

[0019] During the reaction phase, the common terminal interface is connected to the reagent inlet tube, and the plunger pump draws the test reagent from the reagent bottle until the bubble detector changes from a liquid-free state to a liquid-containing state. The pump continues to draw the required volume of test reagent or a volume greater than the required volume. Then, the common terminal interface is connected to the mixing tube, and the required volume of test reagent is pushed into the mixing tube. The common terminal interface is connected to the waste liquid tube to discharge any excess water sample to be tested. Then, the common terminal interface is connected to the air terminal, and sufficient air is drawn in. The common terminal interface is then connected to the mixing tube, and the test reagent is completely pushed into the mixing tube by injecting air, allowing the test reagent to mix with the water sample to obtain a mixed reaction solution.

[0020] During the detection phase, the common terminal interface is connected to the mixing tube, and the plunger pump draws the mixed reaction liquid from the mixing tube until the bubble detector changes from a liquid-free state to a liquid-containing state. The pump continues to draw the required volume of mixed reaction liquid or a volume greater than the required volume. Then, the common terminal interface is connected to the detection tube, and the required volume of mixed reaction liquid is pushed into the detection tube. The common terminal interface is connected to the waste liquid tube to discharge any excess mixed reaction liquid. Then, the common terminal interface is connected to the air terminal, sufficient air is drawn in, and the common terminal interface is connected to the detection tube. The detection reagent is then completely pushed into the detection tube by injecting air.

[0021] The sequential injection analysis method of this application can be used to directly test and analyze water samples on-site, such as at the riverbank. In this case, one end of the water sample collection tube is directly inserted into the location where the water sample to be tested needs to be collected; alternatively, the water sample to be tested can be collected and tested in the laboratory.

[0022] During the testing phase, only a portion of the mixed reaction solution can be drawn into the testing tube for testing, and the excess mixed reaction solution can be discharged to ensure that there is a sufficient amount of mixed reaction solution for testing.

[0023] Preferably, the sequential injection analysis system further includes a control unit, which is used to control the operation of each component;

[0024] The control programs for some repetitive actions are integrated and packaged into an action package, which includes a reset action package, a cleaning action package, a liquid inlet action package, and an air inlet action package.

[0025] The reset action package includes a control program that performs the following actions in sequence: emptying the pure water in the plunger pump to restore the initial position, and filling the reservoir ring with pure water, but leaving an air column at the end of the injection line connected to the common terminal interface;

[0026] The cleaning action package includes a control program that performs the following actions in sequence: connecting the common terminal interface to the waste liquid pipe, drawing pure water from the pure water bottle through the plunger pump, and cleaning the liquid storage ring;

[0027] The liquid inlet package includes a control program that performs the following actions sequentially: the plunger pump draws liquid until the bubble detector changes from a state of no liquid to a state of liquid presence, continues to draw the required volume of liquid or a volume greater than the required volume of liquid, then connects the common terminal interface to the pipeline that needs to be inlet, and pushes the required volume of liquid into the corresponding pipeline; connects the common terminal interface to the waste liquid pipe, and discharges the excess liquid.

[0028] The air intake action package includes a control program that performs the following actions in sequence: connecting the common terminal interface to the air terminal, extracting sufficient air, connecting the common terminal interface to the pipeline that needs to be filled with liquid, and injecting air to completely push the liquid into the corresponding pipeline.

[0029] This invention, through the design of action packages (reset action package, cleaning action package, liquid inlet action package, and air inlet action package), achieves a high degree of automation and standardization of operations at each stage of the water quality testing process, reducing the need for manual intervention and lowering the possibility of human error.

[0030] More preferably, during the initialization phase, the reset action package is used during reset, and the cleaning action package is used during cleaning.

[0031] More preferably, during the sample introduction stage, a liquid injection pack is used first, followed by an air injection pack.

[0032] More preferably, during the reaction phase, the liquid injection pack is used first, followed by the air injection pack.

[0033] More preferably, during the detection phase, a liquid inlet action pack is used, followed by an air inlet action pack.

[0034] Preferably, the detection unit has a detector on the detection tube, and the detector includes one or more, each detector being selected from optical detectors, conductivity detectors or electrochemical detectors.

[0035] More preferably, the optical detector is used to measure the absorbance of certain components in the water sample or the fluorescence signal generated therefrom, and the optical detector includes a flow cuvette connected to the detection tube;

[0036] The flow cuvette is provided with a light-shielding structure on its exterior. The light-shielding structure includes two light-shielding sheets that interlock with each other. The interlocking surfaces of the two light-shielding sheets are provided with a first receiving groove for accommodating the flow cuvette and a second receiving groove for installing a detection light source. One side of the second receiving groove has a first detection port that communicates with the first receiving groove and faces the side of the flow cuvette.

[0037] One of the light-shielding plates is provided with a third receiving groove for mounting a detector, and one side of the third receiving groove has a second detection port that communicates with the first receiving groove and faces the side of the flow cuvette;

[0038] The first receiving tank is also provided with clearance holes to avoid the inlet and outlet ends of the flowing cuvette;

[0039] The two light-shielding sheets are fastened together, and on the fastening surfaces, there are mutually cooperating protrusions and grooves on both sides of the first receiving groove. Each light-shielding sheet has a protrusion and a groove on each side of the first receiving groove.

[0040] Compared with the prior art, the beneficial effects of the present invention are:

[0041] 1. This invention, through the setting of a bubble detector and the application of an air column, enables precise sample injection, ensures complete reaction, and prevents water samples and reagents from contacting pure water, thus avoiding diffusion and dilution, thereby improving the accuracy and reliability of the detection results.

[0042] The use of an air intake manifold further ensures accurate liquid injection, complete reaction, and prevents water samples and reagents from coming into contact with pure water, thus avoiding diffusion and dilution and improving the accuracy and reliability of test results.

[0043] 2. The sequential injection module, detection unit and control unit of this invention are all modularly designed, allowing users to flexibly change the detector and reaction conditions according to their detection needs, adapting to the detection requirements of different water quality parameters, and improving the adaptability and scalability of the system. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of the sequential injection analysis system of the present invention.

[0045] Figure 2 This is a partial structural diagram of the reaction unit.

[0046] Figure 3 This is a schematic diagram of the light-shielding structure in the detection unit.

[0047] Figure 4 This is a first-view diagram of the exploded structure of the light-shielding structure in the detection unit.

[0048] Figure 5 This is a schematic diagram of the exploded structure from a second perspective of the light-shielding structure in the detection unit.

[0049] Figure 6 This is a schematic diagram of the structure of a flow cuvette.

[0050] Reference numerals: Multi-channel selector valve 1, common port 11, inlet / outlet port 12, inlet / outlet port 13, inlet / outlet port 14, inlet / outlet port 15, inlet / outlet port 16, inlet / outlet port 17.

[0051] Injection tubing 2, plunger pump 21, reservoir ring 22, pure water bottle 23, bubble detector 24.

[0052] Water sample collection tube 3, automatic water sample collection device 31, water sample bottle 32.

[0053] Reagent tube 4, reagent bottle 41

[0054] Mixing tube 5, heating wire 51, temperature sensor 52,

[0055] Detection tube 6, detector 61, optical detector 62, flowing cuvette 621, light shield 622, first receiving groove 623, second receiving groove 624, first detection port 625, clearance hole 626, protrusion 627, groove 628, third receiving groove 629, second detection port 6210.

[0056] Waste liquid pipe 7, waste liquid bottle 71. Detailed Implementation

[0057] like Figures 1-6 As shown, a sequential injection analysis system is used for sequential injection analysis of nitrate / nitrite in water. The sequential injection analysis system includes a sequential injection module, a water sample collection unit, a reagent unit, a reaction unit, a detection unit, and a waste liquid tube 7.

[0058] The sequential injection module includes a multi-channel selection valve 1, which includes a common end interface 11 and multiple inlet and outlet interfaces. The common end interface 11 is connected to the injection line 2. The injection line 2 is provided with a liquid storage ring 22 and a plunger pump 21 in sequence from the point closer to the common end interface 11 to the point farther away from the common end interface 11. The free end of the injection line 2 is used to connect to a pure water bottle 23. A bubble detector 24 is provided at the common end interface 11 of the multi-channel selection valve 1.

[0059] The plunger pump 21 is used to precisely control the volume and flow rate of samples and reagents. It is driven by a motor and controlled by a solenoid valve. When the solenoid valve is closed (de-energized), the plunger cylinder in the pump is connected to the liquid reservoir ring 22. When the solenoid valve is open (energized), the plunger cylinder in the pump is connected to a pure water bottle. The other end of the liquid reservoir ring 22 is connected to the common end of the multi-channel selector valve to store liquid and prevent samples and reagents from being sucked into the pump, so as to avoid contamination of the pump by reagents or damage to the pump by corrosive reagents.

[0060] The inlet and outlet ports on the multi-channel selector valve 1 include inlet and outlet ports 12, 13, 14, 15, 16, and 17. There are also two unused inlet and outlet ports in the structure shown in the figure.

[0061] The bubble detector 24 can be used to detect bubbles. When a bubble is detected, it indicates a liquid-free state; when no bubble is detected, it indicates a liquid-containing state.

[0062] By discharging liquid to the pure water bottle 23 via the plunger pump 21, the corresponding liquid can enter the liquid storage ring 22 from the common end interface 11 for temporary storage. By driving the plunger pump 21 in the reverse direction, the liquid temporarily stored in the liquid storage ring 22 can re-enter the corresponding unit through the common end interface 11.

[0063] The water sampling unit includes a water sampling tube 3, one end of which is used to draw in the water sample to be tested, and the other end is connected to the inlet / outlet port 12 of the multi-channel selection valve 1. An automatic water sampling device 31 is connected to the water sampling tube 3. The automatic water sampling device 31 has sample pretreatment functions such as filtration and temperature control to remove suspended solids.

[0064] The sequential injection analysis method of this application allows for direct on-site testing and analysis of water samples, such as at riverbanks, by simply inserting one end of the water sample collection tube 3 into the location where the water sample to be tested needs to be collected; alternatively, the water sample can be collected and tested in a laboratory. Figure 1 The structure shown illustrates laboratory testing, with one end of the water sample collection tube 3 extending into the water sample bottle 32, which contains the water sample to be tested.

[0065] The reagent unit includes a reagent inlet tube 4, one end of which is connected to a reagent bottle 41, and the other end is connected to the inlet / outlet interface 16 of a multi-channel selector valve 1.

[0066] The reaction unit includes a mixing tube 5, one end of which is connected to the inlet / outlet port 13 of a multi-channel selector valve 1. For example... Figure 2 As shown, the reaction unit also includes a heating device, which comprises a heating wire 51 wound around the surface of the mixing tube 5. The reaction unit also includes a temperature sensor 52 for detecting the temperature of the liquid inside the mixing tube 5.

[0067] The detection unit includes a detection tube 6, one end of which is connected to the inlet / outlet port 14 of the multi-channel selector valve 1. The detection unit has a detector 61 on the detection tube 6, which may include one or more detectors, each of which is selected from optical detectors, conductivity detectors or electrochemical detectors.

[0068] Optical detector 62 is used to measure the absorbance or fluorescence signal of certain components in a water sample. Optical detector 62 includes a flow cuvette 621 connected to the detection tube 6. The structure of the flow cuvette 621 is as follows: Figure 6 As shown, the flow cuvette 621 is an existing structure that can be purchased directly. The two ends of the flow cuvette 621 are the inlet and the outlet, respectively.

[0069] The flow cuvette 621 has a light-shielding structure on its exterior. A schematic diagram of the light-shielding structure in the detection unit is shown below. Figures 3-5 As shown, the light-shielding structure includes two interlocking light-shielding sheets 622. The interlocking surfaces of the two light-shielding sheets 622 are provided with a first receiving groove 623 for accommodating a flowing cuvette 621 and a second receiving groove 624 for mounting a detection light source. One side of the second receiving groove 624 has a first detection port 625 communicating with the first receiving groove 623 and facing the side of the flowing cuvette 621. One of the light-shielding sheets 622 is provided with a third receiving groove 629 for mounting a detector. One side of the third receiving groove 629 has a second detection port 6210 communicating with the first receiving groove 623 and facing the side of the flowing cuvette 621. The first receiving groove 623 is also provided with clearance holes 626 to avoid the inlet and outlet ends of the flowing cuvette 621.

[0070] After the two light-shielding plates 622 are interlocked, their mating surfaces are provided with mutually cooperating protrusions 627 and grooves 628 on both axial sides of the first receiving groove 623. Each light-shielding plate 622 has a protrusion 627 and a groove 628 on each side of the first receiving groove 623. The light-shielding structure, especially the staggered and cooperating protrusions 627 and grooves 628 on the two light-shielding plates 622, effectively prevents ambient light leakage at the interface, making the detection more accurate.

[0071] Conductivity detectors are used to detect the ion concentration in a solution. Electrochemical detectors are used to detect specific target substances such as heavy metals. The detection unit features a modular design, allowing users to flexibly replace detectors according to actual detection needs to address different water quality analysis scenarios.

[0072] One end of the waste liquid pipe 7 is connected to the inlet / outlet port 15 of the multi-channel selector valve 1, and the other end is connected to the waste liquid bottle 71. The waste liquid pipe 7 is used to receive the waste liquid discharged from each unit, and the waste liquid is collected in the waste liquid bottle 71.

[0073] The inlet / outlet port 17 of the multi-channel selector valve 1 is used as the air end for air intake.

[0074] The sequential injection analysis system of this invention also includes a control unit, which is used to control the operation of each component. The control programs for some repetitive actions are integrated and packaged into action packages, which include reset action packages, cleaning action packages, liquid injection action packages, and air injection action packages.

[0075] The reset procedure includes a control program that performs the following actions sequentially: empties the pure water from the plunger pump 21 to restore its initial position, and fills the reservoir ring 22 with pure water, but leaves a section of air at one end of the injection line 2 connected to the common port 11. Leaving an air section prevents the water sample or reagent from contacting the pure water, thus eliminating the possibility of diffusion affecting the test results or contaminating the plunger pump 21 and affecting the equipment's lifespan.

[0076] The cleaning procedure includes a control program that performs the following actions sequentially: connecting the common terminal interface 11 to the waste liquid pipe 7, drawing pure water from the pure water bottle 23 using the plunger pump 21, and cleaning the reservoir ring 22. This prevents reagent or water sample residue from remaining in the reservoir ring 22 and other parts of the injection tubing 2.

[0077] The liquid inlet package includes a control program that performs the following actions in sequence: the plunger pump 21 draws liquid until the bubble detector 24 changes from a state of no liquid to a state of liquid presence, continues to draw the required volume of liquid or a volume greater than the required volume of liquid, then connects the common end interface 11 to the pipeline that needs to be filled with liquid, and pushes the required volume of liquid into the corresponding pipeline; connects the common end interface 11 to the waste liquid pipe 7 to discharge the excess liquid.

[0078] The liquid injection kit can be used for precise single-sample injection. Due to differences in equipment or changing scenarios, the length of the tube connecting the multi-channel selection valve 1 to the water sample bottle 32 or reagent bottle 41 may change. If a conventional quantitative volume is drawn, the liquid volume in the mixing tube 5 of the reaction unit will change, potentially leading to insufficient reagent or water sample, incomplete reaction, and thus lower results, affecting the accuracy of the test results. However, by setting up the bubble detector 24 and using the liquid injection kit, the above problems can be solved, ensuring accurate liquid injection volume and guaranteeing the accuracy of the test results.

[0079] The air intake control package includes the following sequential actions: connecting the common port 11 to the air port (inlet / outlet port 17), drawing sufficient air, connecting the common port 11 to the pipeline requiring liquid intake, and injecting air to completely push the liquid into the corresponding pipeline. Since there is a connecting pipe between the mixing tube 5 and the multi-channel selector valve 1, some liquid will remain in this connecting pipe when the water sample or reagent is pushed into the mixing tube 5. Air is needed to push this liquid into the reaction tube 5 for reaction. Furthermore, the air also acts as a "stirring" agent between the water sample and reagent, ensuring thorough mixing and reaction. Excess gas is discharged from the sample outlet at the top of the mixing tube 5.

[0080] This invention, through the design of action packages (reset action package, cleaning action package, liquid inlet action package, and air inlet action package), achieves a high degree of automation and standardization of operations at each stage of the water quality testing process, reducing the need for manual intervention and lowering the possibility of human error.

[0081] The sequential injection analysis method for nitrate / nitrite in water quality described in this application includes an initialization stage, a sample injection stage, a reaction stage, a detection stage, and a cleaning stage.

[0082] During the initialization phase, a reset, a cleanup, and a reset are performed sequentially. A reset action package is used during reset, and a cleanup action package is used during cleanup.

[0083] During the sample introduction phase, the liquid injection package is used first, followed by the air injection package. Specifically, during the sample introduction phase, the common end interface 11 is connected to the water sample collection tube 3, and the plunger pump 21 draws the water sample to be tested until the state of the bubble detector 24 changes from no liquid to liquid. Continue to draw the required volume of water sample or a volume greater than the required volume of water sample. Then, the common end interface 11 is connected to the mixing tube 5, and the required volume of liquid is pushed into the mixing tube 5. The common end interface 11 is connected to the waste liquid tube 7 to discharge the excess water sample to be tested. Then, the common end interface 11 is connected to the air end to draw in enough air. The common end interface 11 is then connected to the mixing tube 5, and the water sample is completely pushed into the mixing tube 5 by injecting air.

[0084] During the reaction phase, the liquid injection package is used first, followed by the air injection package. Specifically, during the reaction phase, the common port 11 is connected to the reagent inlet tube 4, and the plunger pump 21 draws the test reagent from the reagent bottle 41 until the bubble detector 24 changes from a liquid-free state to a liquid-containing state. The pump continues to draw the required volume of test reagent or a volume greater than the required volume. Then, the common port 11 is connected to the mixing tube 5, and the required volume of test reagent is pushed into the mixing tube 5. The common port 11 is then connected to the waste liquid tube 7 to discharge any excess water sample to be tested. Next, the common port 11 is connected to the air end, and sufficient air is drawn in. The common port 11 is then connected to the mixing tube 5, and the test reagent is completely pushed into the mixing tube 5 by injecting air, allowing the test reagent to mix with the water sample to obtain a mixed reaction solution. If a specific temperature condition is required during the reaction phase, the heating wire 51 at the mixing tube 5 heats the mixing tube 5, and the temperature is detected by the temperature sensor 52.

[0085] During the detection phase, a liquid injection package is used, followed by an air injection package. Specifically, during the detection phase, the common port 11 is connected to the mixing tube 5, and the plunger pump 21 draws the mixed reaction liquid from the mixing tube 5 until the bubble detector 24 changes from a liquid-free state to a liquid-containing state. The pump continues to draw the required volume of mixed reaction liquid or a volume greater than the required volume. Then, the common port 11 is connected to the detection tube 6, and the required volume of mixed reaction liquid is pushed into the detection tube 6. The common port 11 is then connected to the waste liquid tube 7 to discharge any excess mixed reaction liquid. Finally, the common port 11 is connected to the air port, sufficient air is drawn in, and the common port 11 is connected to the detection tube 6. By injecting air, the detection reagent is completely pushed into the detection tube 6.

[0086] During the testing phase, only a portion of the mixed reaction solution can be drawn into the testing tube for testing, and the excess mixed reaction solution can be discharged to ensure that there is a sufficient amount of mixed reaction solution for testing.

[0087] During the cleaning phase, a reset, cleaning, and then reset process is performed sequentially. A reset action package is used during reset, and a cleaning action package is used during cleaning. The system is reset and cleaned, covering all tubing and reaction channels that come into contact with samples and reagents, to ensure the accuracy and validity of the next test.

Claims

1. A method for the sequential injection analysis of nitrate / nitrite in water, characterized in that, A sequential injection analysis system is used, which comprises: a sequential injection module, comprising a multi-channel selection valve, a plunger pump and a liquid storage ring, the multi-channel selection valve comprising one common end interface and a plurality of inlet and outlet interfaces, the common end interface being connected to an injection pipeline, the injection pipeline being provided with the liquid storage ring and the plunger pump in sequence from close to the common end interface to far from the common end interface, and the free end of the injection pipeline being used to connect a pure water bottle; the common end interface of the multi-channel selection valve being provided with a bubble detector; a water sample collection unit, comprising a water sample collection tube, one end of the water sample collection tube being used to suck in a water sample to be detected, and the other end being connected to one of the inlet and outlet interfaces of the multi-channel selection valve; a reagent unit, comprising a reagent inlet tube, one end of the reagent inlet tube being connected to a reagent bottle, and the other end being connected to one of the inlet and outlet interfaces of the multi-channel selection valve; a reaction unit, comprising a mixing tube, one end of the mixing tube being connected to one of the inlet and outlet interfaces of the multi-channel selection valve; a detection unit, comprising a detection tube, one end of the detection tube being connected to one of the inlet and outlet interfaces of the multi-channel selection valve; a waste liquid tube, one end of the waste liquid tube being connected to one of the inlet and outlet interfaces of the multi-channel selection valve; one of the inlet and outlet interfaces of the multi-channel selection valve being used as an air end for air inlet; the sequential injection analysis method comprising an initialization stage, a sample inlet stage, a reaction stage, a detection stage and a cleaning stage, in the initialization stage and the cleaning stage, each of the stages is sequentially reset, cleaned and reset; when reset, the pure water in the plunger pump is emptied to restore the initial position, and the liquid storage ring is filled with pure water, but an air column is left at one end of the injection pipeline connected to the common end interface; the water sample to be detected and the detection reagent in the reagent bottle are not in contact with pure water; in the sample inlet stage, the common end interface is connected to the water sample collection tube, the water sample to be detected is extracted by the plunger pump, until the state of the bubble detector changes from no liquid to liquid, the required volume of water sample or more than the required volume of water sample is continuously extracted, then the common end interface is connected to the mixing tube, the required volume of liquid is pushed into the mixing tube; the common end interface is connected to the waste liquid tube, and the excess water sample to be detected is discharged; then the common end interface is connected to the air end, enough air is extracted, the common end interface is connected to the mixing tube, and the water sample is completely pushed into the mixing tube by injecting air; In the reaction stage, the common interface is connected to the reagent tube, the reagent in the reagent bottle is drawn by the plunger pump until the state of the bubble detector changes from no liquid to liquid, the required volume of reagent for reaction or more than the required volume of reagent for reaction is continuously drawn, then the common interface is connected to the mixing tube, the required volume of reagent for reaction is pushed into the mixing tube; the common interface is connected to the waste liquid tube, the excess water sample to be detected is discharged; then the common interface is connected to the air end, enough air is drawn, the common interface is connected to the mixing tube, the reagent is completely pushed into the mixing tube by injecting air, and the reagent is mixed with the water sample to be detected to obtain a mixed reaction liquid; In the detection stage, the common interface is connected to the mixing tube, the mixed reaction liquid in the mixing tube is drawn by the plunger pump until the state of the bubble detector changes from no liquid to liquid, the required volume of mixed reaction liquid for detection or more than the required volume of mixed reaction liquid for detection is continuously drawn, then the common interface is connected to the detection tube, the required volume of mixed reaction liquid for detection is pushed into the detection tube; the common interface is connected to the waste liquid tube, the excess mixed reaction liquid is discharged; then the common interface is connected to the air end, enough air is drawn, and the common interface is connected to the detection tube, the reagent is completely pushed into the detection tube by injecting air.

2. The method for the sequential injection analysis of nitrate / nitrite in water according to claim 1, characterized in that, The sequential injection analysis system further comprises a control unit for controlling the operation of each component; The control programs of the repeated actions are integrated and packaged into action packages, and the action packages include a reset action package, a cleaning action package, a liquid inlet action package, and an air inlet action package; The reset action package includes control programs of the following actions performed in sequence: the pure water in the plunger pump is discharged to restore the initial position, and the storage ring is filled with pure water, but an air column is left at one end of the injection pipeline connected to the common interface; The cleaning action package includes control programs of the following actions performed in sequence: the common interface is connected to the waste liquid tube, pure water is drawn from the pure water bottle by the plunger pump, and the storage ring is cleaned; The liquid inlet action package includes control programs of the following actions performed in sequence: liquid is drawn by the plunger pump until the state of the bubble detector changes from no liquid to liquid, the required volume of liquid or more than the required volume of liquid is continuously drawn, then the common interface is connected to the pipeline requiring liquid inlet, and the required volume of liquid is pushed into the corresponding pipeline; the common interface is connected to the waste liquid tube, and the excess liquid is discharged; The air inlet action package includes control programs of the following actions performed in sequence: the common interface is connected to the air end, enough air is drawn, the common interface is connected to the pipeline requiring liquid inlet, and the liquid is completely pushed into the corresponding pipeline by injecting air.

3. The method for the sequential injection analysis of nitrate / nitrite in water according to claim 2, characterized in that, In the initialization stage, the reset action package is used for resetting, and the cleaning action package is used for cleaning.

4. The method for the sequential injection analysis of nitrate / nitrite in water according to claim 2, characterized in that, In the sample injection stage, the liquid injection action package is used first, and then the air injection action package is used.

5. The method for the sequential injection analysis of nitrate / nitrite in water according to claim 2, characterized in that, In the reaction stage, the liquid injection action package is used first, and then the air injection action package is used.

6. The method for the sequential injection analysis of nitrate / nitrite in water according to claim 2, characterized in that, In the detection stage, the liquid injection action package is used first, and then the air injection action package is used.

7. The method for the analysis of nitrate / nitrite in water according to claim 1, wherein, The detection unit is provided with detectors on the detection tube, and each detector is selected from an optical detector, an electrical conductivity detector, or an electrochemical detector.

8. The method for the sequential injection analysis of nitrate / nitrite in water according to claim 7, characterized in that, The optical detector is used to measure the absorbance or fluorescence signal of certain components in the water sample, and the optical detector includes a flow cuvette inserted into the detection tube. The flow cuvette is externally provided with a light shielding structure, and the light shielding structure includes two light shielding plates that are buckled to each other. One of the light shielding plates is provided with a third accommodating groove for mounting the detector, and one side of the third accommodating groove is provided with a second detection port that is connected to the first accommodating groove and faces the side of the flow cuvette. The first accommodating groove is also provided with avoiding holes that avoid the entrance and exit of the flow cuvette. The buckling surface of the two light shielding plates after being buckled to each other is provided with a protrusion and a groove on both sides of the first accommodating groove in the axial direction, and each light shielding plate is provided with a protrusion and a groove on each side of the first accommodating groove.

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