Water quality detection method based on microfluidic technology

Abstract

The invention relates to the technical field of water quality detection, in particular to a water quality detection method based on a microfluidic technology. According to the method disclosed by the invention, the water quality index in the water body is detected on the micro-fluidic chip, a corresponding micro-aperture channel is processed on a special material by utilizing a flying carving process, and a peristaltic pump is used for sampling, so that the consumption of a water sample and a reagent is greatly reduced, and the water sample and the reagent can be quickly and uniformly mixed on the micro-fluidic chip, and the detection accuracy is improved. According to the method, air is supplemented into the primary mixed liquid, so that tiny bubbles further promote mixing of the water sample and the reagent on one hand in the process, and on the other hand, when the supplemented air is subjected to ultrasonic cavitation in the next step, bubble breakage intensifies the mixing strength and the reaction strength of the reagent and the water sample; the detection of the water sample is not influenced after the gas is discharged from the sample outlet in the rear of the detection pool, so that the water sample and the reagent can be detected after being mixed, the color development time required by the detection of the water sample is greatly shortened, and the detection efficiency is favorably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of water quality detection, and in particular to a water quality detection method based on microfluidics technology. Background Art

[0002] Water quality monitoring refers to the monitoring of water quality indicators, such as ammonia nitrogen, COD, total nitrogen and five water quality parameters. Water quality monitoring plays an important role in maintaining the health of the water environment. Among them, ammonia nitrogen refers to nitrogen in the form of free ammonia and ionized ammonium. Ammonia nitrogen is a basic item for surface water environment monitoring and one of the important items for river water quality monitoring and evaluation. Ammonia nitrogen in water comes from domestic sewage, industrial wastewater and farmland drainage. Excessive ammonia nitrogen in water is an important indicator of eutrophication of water bodies, which seriously affects the ecological environment and endangers the survival of humans and other organisms, especially fish. Therefore, monitoring of ammonia nitrogen indicators in water is particularly important.

[0003] Traditional methods for detecting ammonia nitrogen include Nessler colorimetry and salicylic acid-hypochlorite colorimetry, which can detect the ammonia nitrogen content in water and play a positive role in preventing ammonia nitrogen from exceeding the standard in water. However, with the development of technology, the disadvantages of these traditional methods have also begun to emerge. The problem of low detection efficiency is common. For example, the current standard method of salicylic acid-hypochlorite colorimetry requires a color development time of 60 minutes during the detection process. The long color development time obviously has a serious impact on the efficiency of water quality detection. In addition, the serious hysteresis also affects the timeliness of water quality monitoring and process control in sewage treatment. Although some improvements have been made to the standard method in the existing technology, such as Zhang Wei, Sun Yi, Wang Liangliang, et al. Improvement of salicylic acid spectrophotometric determination of ammonia nitrogen [J]. Chemistry and Bioengineering, 2017, 34 (8): 68-70. The improved method has greatly improved the detection efficiency, from the original 60 minutes to 5 minutes, and the detection efficiency has increased by 12 times, but there is still a big gap from timely response.

[0004] Microfluidics is a technology that precisely controls and manipulates microscale fluids. It has been widely used in biochemical analysis, disease diagnosis, minimally invasive surgery, environmental testing, and other fields. In the field of environmental testing, microfluidics can not only effectively reduce the amount of samples and drugs to be tested, but also play a positive and effective role in improving detection efficiency, and it has attracted more and more attention.

[0005] Therefore, we proposed a more efficient detection method for ammonia nitrogen in water based on microfluidics, in order to enable a more timely response in the process of water quality testing and sewage treatment, improve efficiency while also improving the timeliness of water quality monitoring and process control in sewage treatment. Summary of the invention

[0006] The purpose of the present invention is to provide a water quality detection method based on microfluidics technology to solve the problem.

[0007] To achieve the above object, the present invention adopts the following technical solution: a water quality detection method based on microfluidics technology, comprising the following steps:

[0008] S1. Use a peristaltic pump to pump the water sample to be tested, salicylic acid-sodium potassium tartrate solution, sodium nitrosoferrocyanide solution and sodium hypochlorite solution into the microfluidic chip;

[0009] S2, preliminarily mixing the water sample to be tested, salicylic acid-sodium potassium tartrate solution, sodium nitrosoferrocyanide solution and sodium hypochlorite solution in a microfluidic chip to obtain a preliminarily mixed solution;

[0010] S3, using a venturi tube in the microfluidic chip to introduce air into the primary mixed liquid obtained in S2, and the primary mixed liquid is intermediately mixed under the impact of the air to obtain an intermediate mixed liquid;

[0011] S4, cavitating the intermediate mixed solution obtained in S3 by ultrasonication in a microfluidic chip to obtain a final mixed reaction solution;

[0012] The reaction liquid obtained in S5 and S4 is passed into the detection pool in the microfluidic chip, and the reaction liquid is detected by spectrophotometry to obtain the ammonia nitrogen content in the water sample to be tested.

[0013] Furthermore, in the above S1, the water sample to be tested needs to be pretreated according to actual conditions before use, and the pretreatment methods include filtration, pre-distillation and dilution; the pretreated water sample is used as the water sample to be tested.

[0014] Furthermore, in the S1, the flow ratio of the water sample to be tested, the salicylic acid-potassium sodium tartrate solution, the sodium nitrosoferricyanide solution and the sodium hypochlorite solution is 80-100:20-50:1:1.

[0015] Furthermore, the flow rate of the water sample to be tested is 0.4-0.5 mL / min; the flow rate of salicylic acid-sodium potassium tartrate solution is 0.1-0.25 mL / min; the flow rate of sodium nitrosoferricyanide solution is 5 μL / min; and the flow rate of sodium hypochlorite solution is 5 μL / min.

[0016] Furthermore, in S2, the primary mixing is performed in a primary mixing channel in the microfluidic chip, and the primary mixing channel is formed by connecting a plurality of elliptical channels in sequence.

[0017] Furthermore, in the above S3, the rear of the primary mixing pipe is connected to the connecting pipe, the venturi tube is arranged on the connecting pipe, and an air intake port is provided at the throat of the venturi tube, and air is sucked into the venturi tube from the air intake port and impacts the primary mixing liquid in the venturi tube.

[0018] Furthermore, in the above S4, the rear of the communicating pipe is connected to the pipe in the cavitation zone, cavitation is carried out in the cavitation zone, and the pipe in the cavitation zone is wavy.

[0019] Furthermore, the frequency of the ultrasonic wave in the cavitation zone is 20 to 50 kHz.

[0020] Furthermore, in the above S5, the detection pool is located behind the cavitation zone and is connected to the cavitation zone, and is connected to the sample outlet at the rear of the detection pool.

[0021] Furthermore, the central wavelength of the spectrophotometry is 697 nm. By comparing the absorbance detected by the spectrophotometry with the standard curve, the ammonia nitrogen content in the water sample to be tested can be calculated.

[0022] Beneficial effects of the present invention:

[0023] 1. The mixing and reaction of water samples and reagents are carried out on the microfluidic chip, which greatly reduces the amount of water samples and reagents used in the process, and is of great significance to the saving of detection costs;

[0024] 2. The water sample and the reagent are mixed multiple times on the microfluidic chip, including initial mixing, intermediate mixing and final mixing. The intermediate mixing adopts the method of inhaling tiny bubbles through a venturi tube, which helps the mixing of the water sample and the reagent under the impact of the bubbles; the final mixing adopts the method of ultrasonic cavitation to achieve the final mixing of the water sample and the reagent;

[0025] 3. The combination of Venturi and ultrasound is realized. The bubbles sucked in by the Venturi are cavitated in the subsequent ultrasonic stage. When the bubbles burst, the mixing and reaction degree of the water sample and the reagent is intensified, which greatly reduces the time for the water sample to react and develop color. The water sample and the reagent can be mixed and measured immediately, which greatly improves the detection efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the structure of the microfluidic chip involved in the method of the present invention;

[0027] Figure 2 The present invention Figure 1 A partial enlarged schematic diagram of part A;

[0028] Figure 3 It is a standard curve diagram in Example 1 of the present invention.

[0029] The names corresponding to the marks in the figure are:

[0030] 1. Microfluidic chip; 11. Sample inlet; 12. Sample inlet pipe; 13. Primary mixing pipe; 14. Connecting pipe; 141. Venturi tube; 15. Air inlet; 16. Cavitation zone; 17. Detection cell; 18. Sample outlet. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0032] like Figure 1-2 As shown, the method of the present invention relates to a microfluidic chip. The production of the microfluidic chip is an existing mature technical means and will not be described in detail here. An injection port is arranged in the microfluidic chip, wherein there are four injection ports, which are respectively used for adding a water sample to be tested, a salicylic acid-potassium sodium tartrate solution, a sodium nitrosoferricyanide solution and a sodium hypochlorite solution. The injection port is in the shape of a slot protruding upward, which is common in the prior art and can be well adapted to the peristaltic pump hose, and will not be described in detail.

[0033] Each of the above-mentioned injection ports is respectively connected to an injection pipe, and the rear of the injection pipe is connected to a primary mixing pipe, which is formed by connecting a plurality of elliptical pipes in sequence, and is connected to a connecting pipe at the rear of the primary mixing pipe, and a venturi tube is arranged on the connecting pipe, and an air intake port is arranged at the throat of the venturi tube, and the air intake port is connected to the outside atmosphere; the connecting pipe is connected to the cavitation zone at the rear, and the cavitation zone pipe is wavy, and is connected to the detection pool at the rear of the cavitation zone, and is connected to the window at the rear of the detection pool.

[0034] The principle of the present invention is:

[0035] When the method of the present invention is used to detect water samples, the water samples must first be pretreated. The pretreatment method can refer to the existing treatment method. When the water sample is turbid, filtration is used; when the water sample is colored and the ion concentration is high, pre-distillation is used.

[0036] However, it should be noted that the method of the present invention has certain requirements on the sample concentration due to the small optical path during the detection process. Traditionally, the sample needs to be diluted during detection, but in the detection process of the present invention, dilution is generally not required, and the sample pretreatment method is simpler. However, it is inevitable that when the ammonia nitrogen concentration in the sample is low, the method of the present invention needs to concentrate the water sample to be tested to meet the detection limit of the present invention; in actual detection, reasonable treatment can be carried out as needed.

[0037] The method of the present invention adopts a peristaltic pump continuous sampling mode, and the peristaltic pump can realize the sampling of samples at the microliter level during the process; the salicylic acid-sodium potassium tartrate solution, the sodium nitrosoferricyanide solution and the sodium hypochlorite solution used in the method of the present invention are solutions prepared according to the current standard HJ 536-2009, wherein the flow rate ratio of the water sample to be tested to the sampling of the above reagents is 80-100:20-50:1:1, specifically in actual operation, the flow rate of the water sample to be tested is 0.4-0.5mL / min, the flow rate of the salicylic acid-sodium potassium tartrate solution is 0.1-0.25mL / min, the flow rate of the sodium nitrosoferricyanide solution is 5μL / min, and the flow rate of the sodium hypochlorite solution is 5μL / min.

[0038] The above-mentioned sampling is preliminarily mixed in the primary mixing pipe through the sampling pipe, and then introduced into the cavitation zone through the connecting pipe. Air is inhaled through the venturi tube on the connecting pipe. The inhaled air forms tiny bubbles in the primary mixed liquid, which plays a positive role in the mixing of the sample. In the cavitation zone, the mixed sample in the venturi tube is cavitated by ultrasound. On the one hand, cavitation can remove tiny bubbles. In the technical solution of the present invention, since air is added to the front-end venturi tube, the severity of cavitation is aggravated in the cavitation stage, which makes the material further mixed. At the same time, the local heat generated by cavitation promotes the color development reaction, so that the reaction is completed almost instantly, thereby greatly improving the detection efficiency.

[0039] The cavitated reaction liquid is passed into the detection cell. During the process of the reaction liquid entering the detection cell, cavitation is always ongoing. Due to the radiation of energy, cavitation will also occur in the detection cell, which can discharge the gas in the reaction liquid without affecting subsequent detection. When the reaction liquid in the detection cell is overflowing, the injection can be stopped. At this time, the microfluidic chip can be removed and the absorbance of the sample can be detected by a spectrophotometer, and compared with the standard curve to calculate the concentration of ammonia nitrogen in the sample.

[0040] For the above-mentioned cavitation process, the microfluidic chip can be fixed and an ultrasonic generator can be installed above or below it, wherein the frequency of the ultrasonic generator is 20 to 50 kHz; when detecting, under dark conditions, the light source of the spectrophotometer can be aimed at the detection cell to detect the absorbance of the sample.

[0041] For the above-mentioned spectrophotometer detection, a standard curve needs to be drawn during the process. Standard samples of different concentrations are used in the process, and then their absorbance is measured to draw a standard curve. During the detection process, the absorbance of the sample detection is compared with the standard curve to calculate the concentration of ammonia nitrogen in the sample. However, it should be noted that when testing the sample, pure water needs to be used as the background to ensure the accuracy of the measurement.

[0042] It should be noted that the method of the present invention is not only applicable to the detection of ammonia nitrogen, a water quality indicator, but can also be used for the detection of other water quality indicators, such as COD, total nitrogen, and five water quality parameters through the core idea of ​​the method of the present invention, which will not be repeated here.

[0043] Example 1

[0044] The salicylic acid-potassium sodium tartrate solution, sodium nitrosoferrocyanide solution and sodium hypochlorite solution in this embodiment are solutions prepared according to the current standard HJ 536-2009; the flow rate of the water sample to be tested is 0.4 mL / min, the flow rate of the salicylic acid-potassium sodium tartrate solution is 0.2 mL / min, and the flow rates of the sodium nitrosoferrocyanide solution and the sodium hypochlorite solution are 5 μL / min; the thickness of the detection cell is 1 mm.

[0045] Drawing of standard curve:

[0046] S1. Prepare 0.5 mg / L, 1 mg / L, 2 mg / L, 4 mg / L, 6 mg / L, 8 mg / L and 10 mg / L ammonia nitrogen standard solutions (ammonium chloride solutions) respectively;

[0047] S2. The absorbance of the above standard solution was detected by the method of the present invention, with a central wavelength of 697 nm and pure water as a reference. The measured absorbance was recorded as follows (each sample was measured 5 times, and the average value was calculated after removing the maximum and minimum values):

[0048] Table 1 Absorbance values ​​of standard samples

[0049]

[0050] S3, draw a standard curve based on the data in S2, the standard curve is as follows Figure 3 As shown, the fitting curve is y = 0.0654x + 0.0017, R 2 ≥0.99.

[0051] Sample 1

[0052] Water from a river was filtered and tested. During the test, it was found that the absorbance was small. It was concentrated 5 times by reverse osmosis and tested with pure water as a reference. The absorbance was 0.082. After calculation, the concentration of ammonia nitrogen in the water was 0.246 mg / L.

[0053] Sample 2

[0054] After filtering a municipal sewage, the absorbance was tested with pure water as reference, and the result was 0.837. After calculation, the concentration of ammonia nitrogen in the water was 12.77 mg / L.

[0055] Sample 3

[0056] The treated sewage from a sewage treatment plant was tested with pure water as a reference and the absorbance was 0.106. After calculation, the concentration of ammonia nitrogen in the water was 1.59 mg / L.

[0057] After the above samples were tested, they were left to stand for 60 minutes and tested again. The results were 0.245 mg / L, 12.77 mg / L, and 1.60 mg / L, respectively. The results were almost unchanged.

[0058] Comparative Example 1

[0059] The samples in Example 1 of the present invention were tested using the method described in the current standard HJ 536-2009.

[0060] After testing, the concentrations of ammonia nitrogen in samples 1 to 3 were 0.245 mg / L, 12.77 mg / L and 1.58 mg / L; it can be seen that the accuracy of the method of the present invention can fully meet the requirements. At the same time, the method of the present invention greatly shortens the detection time and significantly improves the detection efficiency.

[0061] The present invention is not limited to the above-mentioned optimal implementation mode. Anyone can derive other various forms of products under the inspiration of the present invention. However, no matter what changes are made in the shape or structure, all technical solutions that are the same or similar to those of the present application fall within the protection scope of the present invention.

Claims

1. A water quality detection method based on microfluidics technology, characterized in that: The following steps are involved: S1, using a peristaltic pump to pump the water sample to be tested, salicylic acid-sodium potassium tartrate solution, sodium nitrosoferrocyanide solution and sodium hypochlorite solution into the microfluidic chip (1); S2, preliminarily mixing the water sample to be tested, salicylic acid-sodium potassium tartrate solution, sodium nitrosoferrocyanide solution and sodium hypochlorite solution in the microfluidic chip (1) to obtain a preliminarily mixed solution; S3, using a venturi tube (141) in the microfluidic chip (1) to introduce air into the primary mixed liquid obtained in S2, and the primary mixed liquid is intermediately mixed under the impact of the air to obtain an intermediate mixed liquid; S4, cavitating the intermediate mixed solution obtained in S3 by ultrasonication in the microfluidic chip (1) to obtain a final mixed reaction solution; The reaction liquid obtained in S5 and S4 is introduced into the detection pool (17) in the microfluidic chip (1), and the reaction liquid is detected by spectrophotometry to obtain the ammonia nitrogen content in the water sample to be tested.

2. The water quality detection method based on microfluidics technology according to claim 1, characterized in that: In the above-mentioned S1, the water sample to be tested needs to be pretreated according to actual conditions before use, and the pretreatment methods include filtration, pre-distillation and concentration; the pretreated water sample is used as the water sample to be tested.

3. The water quality detection method based on microfluidics technology according to claim 1, characterized in that: In the S1, the flow ratio of the water sample to be tested, salicylic acid-sodium potassium tartrate solution, sodium nitrosoferricyanide solution and sodium hypochlorite solution is 80-100:20-50:1:

1.

4. The water quality detection method based on microfluidics technology according to claim 3 is characterized in that: The flow rate of the water sample to be tested is 0.4-0.5 mL / min; the flow rate of salicylic acid-sodium potassium tartrate solution is 0.1-0.25 mL / min; the flow rate of sodium nitrosoferricyanide solution is 5 μL / min; and the flow rate of sodium hypochlorite solution is 5 μL / min.

5. The water quality detection method based on microfluidics technology according to claim 1, characterized in that: In the above-mentioned S2, the primary mixing is performed in a primary mixing channel (13) in the microfluidic chip (1), and the primary mixing channel (13) is formed by connecting a plurality of elliptical channels in sequence.

6. The water quality detection method based on microfluidics technology according to claim 5, characterized in that: In the above-mentioned S3, the rear of the primary mixing pipe (13) is connected to the connecting pipe (14), the venturi tube (141) is arranged on the connecting pipe (14), and an air intake port (15) is arranged at the throat of the venturi tube (141), and air is sucked into the venturi tube (141) from the air intake port (15) and impacts the primary mixing liquid in the venturi tube (141).

7. A water quality detection method based on microfluidics technology according to claim 6, characterized in that: In the above-mentioned S4, the rear of the communicating pipe (14) is connected to the pipe of the cavitation zone (16), cavitation is carried out in the cavitation zone (16), and the pipe of the cavitation zone (16) is wavy.

8. The water quality detection method based on microfluidics technology according to claim 7, characterized in that: The frequency of the ultrasonic wave in the cavitation zone (16) is 20 to 50 kHz.

9. The water quality detection method based on microfluidics technology according to claim 7, characterized in that: In the above-mentioned S5, the detection pool (17) is located behind the cavitation zone (16) and is connected to the cavitation zone (16), and is connected to the sample outlet (18) at the rear of the detection pool (17).

10. A water quality detection method based on microfluidics technology according to claim 9, characterized in that: The central wavelength of the spectrophotometry is 697 nm. By comparing the absorbance detected by the spectrophotometry with the standard curve, the content of ammonia nitrogen in the water sample to be tested can be calculated.

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