A method for rapid detection of microplastic pollution in water based on fluorescence spectroscopy

Abstract

The present invention belongs to the technical field of wastewater quality detection, and provides a method for rapidly detecting microplastic pollution in water based on fluorescence spectroscopy, including steps such as sample preparation, filtration, spectral testing, background correction, and data processing. This method utilizes the principle that microplastics will generate dissolved organic matter with fluorescence characteristics when in contact with water, and uses a fluorescence spectrometer to detect whether there is microplastic pollution in water. It has wide applicability, does not require other pretreatment of the water sample, and the water sample can be recycled into the mother liquor after measurement. Compared with the prior art, this method does not require cumbersome treatment processes such as digestion. The pretreatment only takes a few minutes of filtration, and only needs to measure a judgment ratio once, and the result can be obtained within a few minutes of testing, greatly shortening the time. Therefore, this method has the advantages of simple operation, rapid testing, high sensitivity, and no need for chemical reagents, making up for the defect of the slow detection speed of existing detection technologies.

Description

Technical Field

[0001] The present invention belongs to the technical field of wastewater quality detection, and particularly relates to a method for rapidly detecting microplastic pollution in water based on fluorescence spectroscopy. Background Art

[0002] Microplastics generally refer to plastic fibers or particles with a diameter less than 5 mm. They have a small volume and a large specific surface area, so they can adsorb toxic and harmful substances in the environment and then enter organisms, causing the enrichment of harmful substances in organisms. Therefore, they have become one of the new pollutants. Generally, there is a significant relationship between the particle size of microplastics and their harm degree. Larger microplastics will be intercepted by sewage treatment processes, while smaller micro-nano plastics are easily retained in drinking water, atmospheric aerosols, and food, and enter the human circulation through the digestive or respiratory systems, affecting human health. Currently, the widely used methods for detecting microplastics in water are mainly fluorescence counting method and spectroscopy method. The fluorescence counting method refers to using a filtration device to intercept microplastics in water, then staining with a fluorescent dye and counting under a microscope to judge the degree of microplastic pollution in the water body; the spectroscopy method refers to after filtering the water sample, drying and digesting the filter membrane with microplastics, and then measuring its infrared spectrum, and comparing the result with the standard spectrum of plastic to judge whether there is microplastic pollution in the water body. In addition, the latest pyrolysis gas chromatography-mass spectrometry (Py-GC-MS) technology can also qualitatively / quantitatively detect microplastics in water, but this method has high requirements for instruments and is difficult to apply to on-site determination.

[0003] The fluorescence counting method requires staining the sample containing microplastics. After uniformly mixing a biological stain such as Nile red with the sample to be tested, filtering and drying, then visually counting under a fluorescence microscope. Since the accuracy of visual counting is relatively low, the detection accuracy can only be improved by repeatedly extracting the counting range, which takes a long time. The spectroscopy method requires pretreatment of the sample. After filtering the water sample to be tested and drying the filter membrane, adding Fenton's reagent to digest the filter membrane before testing. Usually, the digestion time is in the range of 3 - 48 h. Although the Py-GC-MS method can omit the filtration and digestion processes of the water sample, it still needs to dissolve the microplastic particles in a solvent such as dichloromethane through an extraction step before testing.

[0004] Both of the above methods can accurately detect the degree of microplastic pollution in the water body, but both take a long time for detection. Therefore, it is necessary to develop a method for rapidly detecting microplastic pollution in water.

[0005] The information disclosed in this background art section is only intended to enhance the overall understanding of the present invention and should not be regarded as an admission or any form of suggestion that this information constitutes prior art already known to those of ordinary skill in the art. Summary of the Invention

[0006] The present invention is made to solve the above problems, and aims to provide a method for rapidly detecting microplastic pollution in water based on fluorescence spectroscopy. This method utilizes the principle that when microplastics come into contact with water, soluble organic matter with fluorescence characteristics is generated to detect whether there is microplastic pollution in the water. It has wide applicability, does not require pretreatment of water samples, and the water samples can be recycled into the mother liquor after measurement. Furthermore, a portable fluorescence analyzer can be used to achieve on-site measurement effects, making up for the defect of slow detection speed in existing detection technologies.

[0007] The present invention provides a method for rapidly detecting microplastic pollution in water based on fluorescence spectroscopy, which has the following characteristics and includes the following steps: Step S1, preparing experimental water sample samples with various plastics; Step S2, using a fluorescence spectrometer, measuring the emission spectra of each experimental water sample sample within the Em measurement range respectively with the excitation wavelength Ex = 235 nm and the excitation wavelength Ex = 295 nm, and taking the maximum peak value as the emission spectrum peak value of each experimental water sample sample to obtain the emission spectrum peak values of each experimental water sample sample at Ex = 235 nm and Ex = 295 nm; Step S3, performing background correction on the measured emission spectrum peak values to obtain the peak value I of the corrected emission spectrum of the experimental water sample sample at Ex = 235 nm 235 and the peak value I of the corrected emission spectrum at Ex = 295 nm 295 ; Step S4, obtaining the ratio of I 295 to I 235 for each experimental water sample sample, and taking the minimum ratio as the judgment ratio; Step S5, using a fluorescence spectrometer, measuring the emission spectrum peak values of the water sample to be measured at Ex = 235 nm and Ex = 295 nm within the same Em measurement range, and performing background correction on the measured emission spectrum to obtain the peak value I of the corrected emission spectrum of the water sample to be measured at Ex = 235 nm 235 and the peak value I of the corrected emission spectrum at Ex = 295 nm 295 , and obtaining the ratio of I 295 to I 235 of the water sample to be measured; Step S6, comparing the ratio of I 295 to I 235 of the water sample to be measured with the judgment ratio. If the ratio of I 295 to I 235 of the water sample to be measured is greater than the judgment ratio, it is determined that there is microplastic pollution in the water sample to be measured. If the ratio of I 295 to I 235 of the water sample to be measured is less than the judgment ratio, it is determined that there is no microplastic pollution in the water sample to be measured.

[0008] In the method for rapidly detecting microplastic pollution in water based on fluorescence spectroscopy provided by the present invention, it may further have the following characteristics: Among them, the various plastics are respectively polystyrene, polyvinyl chloride, and polyethylene.

[0009] In the method for rapid detection of microplastic pollution in water based on fluorescence spectroscopy provided by the present invention, it may also have the following characteristics: Among them, the judgment ratio is 1.12.

[0010] In the method for rapid detection of microplastic pollution in water based on fluorescence spectroscopy provided by the present invention, it may also have the following characteristics: Among them, the minimum value of the Em test interval is greater than the excitation wavelength by 10 nm - 20 nm.

[0011] In the method for rapid detection of microplastic pollution in water based on fluorescence spectroscopy provided by the present invention, it may also have the following characteristics: Among them, in steps S1 and S5, the experimental water sample and the sample to be tested are filtered using a 0.45 μm glass fiber filter membrane and then tested using a fluorescence spectrometer.

[0012] In the method for rapid detection of microplastic pollution in water based on fluorescence spectroscopy provided by the present invention, it may also have the following characteristics: Among them, in steps S2 and S5, the volume of the experimental water sample and the sample to be tested is greater than 1 mL.

[0013] In the method for rapid detection of microplastic pollution in water based on fluorescence spectroscopy provided by the present invention, it may also have the following characteristics: Among them, the experimental water sample and the sample to be tested are adjusted to pH = 2 - 4 with acid and then refrigerated, and measured after a predetermined time.

[0014] In the method for rapid detection of microplastic pollution in water based on fluorescence spectroscopy provided by the present invention, it may also have the following characteristics: Among them, in steps S3 and the step not specified, background correction is performed using the ultrapure water used when preparing the experimental water sample.

[0015] In the method for rapid detection of microplastic pollution in water based on fluorescence spectroscopy provided by the present invention, it may also have the following characteristics: Among them, if the ultrapure water used for background correction and the ultrapure water used when preparing the experimental water sample belong to different batches, then after background correction, the Raman normalization method or the quinine sulfate method is used to correct the emission spectrum peak.

[0016] Functions and effects of the invention

[0017] According to the method for rapid detection of microplastic pollution in water based on fluorescence spectroscopy provided by the present invention, this method utilizes the principle that when microplastics come into contact with water, soluble organic matter with fluorescence characteristics will be generated. A fluorescence spectrometer is used to detect whether there is microplastic pollution in water. It has wide applicability, does not require other pretreatment of water samples, and the water samples can be recycled into the mother liquor after measurement. Compared with the prior art, this method does not require cumbersome treatment processes such as digestion. The pretreatment only needs to filter for a few minutes and the test only needs a few minutes to obtain the result, greatly shortening the time. At the same time, only the judgment ratio needs to be measured once, and then only simple filtration treatment of the water sample is required for other tests. Therefore, the method provided by the present invention has the advantages of simple operation, rapid testing, high sensitivity, and no need for chemical reagents, making up for the defect of the slow detection speed of the existing detection technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is the test flow chart of the method of the present invention;

[0019] Figure 2 is the three-dimensional fluorescence spectrogram of each sample in Example 1 of the present invention;

[0020] Figure 3 is the emission spectrogram of each sample in Example 1 of the present invention at Ex = 235nm and Ex = 295nm. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] In order to make the technical means, creative features, achieved purposes and effects of the present invention easy to understand, the following specifically describes a method for rapid detection of microplastic pollution in water based on fluorescence spectroscopy of the present invention in combination with embodiments and drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0022] Unless otherwise specified, all raw materials used in the following embodiments are commercially available products, and the model of the fluorescence spectrometer used is: Edinburgh Spectrofluorometer FS5. In actual applications, a portable fluorescence analyzer can also be used.

[0023] The manufacturer model of humic acid is: Aladdin humic acid (molecular formula: C 9 H 9 NO 6 ); The manufacturer model of natural organic matter (NOM) is: International Humic Substances Society (IHSS) Suwannee River natural organic matter.

[0024] Figure 1 is the test flow chart of the method of the present invention.

[0025] As Figure 1 shown, a method for rapidly detecting microplastic pollution in water based on fluorescence spectroscopy provided by the present invention specifically includes the following steps:

[0026] Step S1, configuring experimental water sample specimens with various plastics;

[0027] Step S2, using a fluorescence spectrometer, measuring the emission spectra of each experimental water sample specimen within the Em measurement range respectively with the excitation wavelength Ex = 235 nm and the excitation wavelength Ex = 295 nm, taking the maximum peak value as the emission spectrum peak value of each experimental water sample specimen, and obtaining the emission spectrum peak values of each experimental water sample specimen at Ex = 235 nm and Ex = 295 nm;

[0028] Step S3, performing background correction on the measured emission spectrum peak values to obtain the peak value I of the corrected emission spectrum of the experimental water sample specimen at Ex = 235 nm 235 and the peak value I of the corrected emission spectrum at Ex = 295 nm 295 ;

[0029] Step S4, obtaining the ratio of I 295 to I 235 for each experimental water sample specimen, and taking the minimum ratio as the judgment ratio;

[0030] Step S5, using a fluorescence spectrometer, measuring the emission spectrum peak values of the water sample to be measured at Ex = 235 nm and Ex = 295 nm within the same Em measurement range, and performing background correction on the measured emission spectrum to obtain the peak value I of the corrected emission spectrum of the water sample to be measured at Ex = 235 nm 235 and the peak value I of the corrected emission spectrum at Ex = 295 nm 295 , and obtaining the ratio of I 295 to I 235 for the water sample to be measured;

[0031] Step S6, comparing the ratio of I 295 to I 235 of the water sample to be measured with the judgment ratio. If the ratio of I 295 to I 235 of the water sample to be measured is greater than the judgment ratio, it is determined that there is microplastic pollution in the water sample to be measured. If the ratio of I 295 to I 235 of the water sample to be measured is less than the judgment ratio, it is determined that there is no microplastic pollution in the water sample to be measured.

[0032] In the present invention, polystyrene (PS), polyvinyl chloride (PVC), and polyethylene (PE) are selected as solutes, and ultrapure water of the same batch is used as the solvent to prepare ultrapure aqueous solutions of different concentrations of polystyrene (PS), polyvinyl chloride (PVC), and polyethylene (PE) as experimental water samples containing microplastics. An ultrapure aqueous solution containing humic acid and natural organic matter is selected as the water sample to be measured. The Yuehe River water is selected as the actual water sample.

[0033] In steps S1 and S5, the experimental water samples and the samples to be measured are filtered using a 0.45 μm glass fiber filter membrane and then tested using a fluorescence spectrometer. The volume of the experimental water samples and the samples to be measured is greater than 1 mL. If immediate measurement is not possible, the pH should be adjusted to 2 - 4 with acid and then stored refrigerated for measurement; that is, the experimental water samples and the samples to be measured are adjusted to pH = 2 - 4 with acid and then refrigerated, and measured after a predetermined time. When the experimental water samples and the samples to be measured are tested using a fluorescence spectrometer, the same Em test range should be selected, and the minimum value of the Em test range is greater than the excitation wavelength by 10 nm - 20 nm. In steps S3 and S5, the ultrapure water used in the preparation of the experimental water samples is used for background correction. If the ultrapure water used for background correction and the ultrapure water used in the preparation of the experimental water samples belong to different batches, the emission spectrum peak is corrected using the Raman normalization method or the quinine sulfate method after background correction.

[0034] In the above steps, the experimental sample water and the samples to be measured can be filtered together and then tested separately using a fluorescence spectrometer, and the data is processed together. When selecting the type of plastic, it can be selected according to the possible microplastics contained in the samples to be measured. After obtaining the judgment ratio using this method, the samples to be detected can be detected without any other operations.

[0035] <Example 1>

[0036] In this example, the experimental water samples and the samples to be measured are configured and subjected to fluorescence detection together, so the operations in the steps are slightly different.

[0037] Step 1, sample preparation: Prepare experimental water samples using polystyrene (PS), polyvinyl chloride (PVC), and polyethylene (PE). At the same time, select an ultrapure aqueous solution containing humic acid and natural organic matter (NOM) as the simulated water sample to be measured, and then filter all the water samples using a glass fiber filter membrane to avoid interference caused by other solid impurities. The specific process is as follows:

[0038] Weigh 0.5 g of polystyrene (PS), 0.5 g of polyvinyl chloride (PVC), and 0.5 g of polyethylene (PE) microplastics separately, and add them to 100 ml of ultrapure water respectively to prepare suspension solutions containing three different microplastics. After stirring and mixing for 7 days, they are used as experimental water sample samples, and are named PS, PVC, and PE respectively. Take 0.1 g of humic acid and 0.02 g of natural organic matter (NOM), and add them to 100 ml of ultrapure water respectively to prepare humic acid solution and NOM stock solution. In order to simulate the concentration of natural organic matter in real water bodies, use a total organic carbon tester (TOC2000, Shanghai Yuanxi) to calibrate the concentrations of humic acid and NOM stock solutions, and dilute the two to TOC < 10.00 mg / L as the simulated water samples to be measured, and name them humic acid and NOM. Take the Yuehe River water (sampling point: within the Lingang Campus of Shanghai University of Electric Power, Pudong New Area, Shanghai) as the actual water body sample.

[0039] Use a 0.45 μm needle-type glass fiber filter membrane and a 5 mL syringe to filter the above 6 water samples to obtain the filtrates to be measured. Inject ultrapure water and each filtrate to be measured into a four-way cuvette in turn, waiting for fluorescence emission spectrum testing. Take out a part of each water sample for three-dimensional fluorescence spectrum testing, and the test results are shown in Figure 2 .

[0040] From Figure 2 it can be seen that the experimental water samples containing microplastics have obvious different spectral characteristics from samples such as Yuehe River water, NOM, and humic acid, that is, the fluorescence intensity of the fluorophore shown at Ex = 295 nm is greater than the fluorescence intensity of the fluorophore shown at Ex = 235 nm in the same sample, which provides a basis for the determination of the judgment ratio in step S4.

[0041] Step two, testing: Use the excitation wavelength Ex = 235 nm and the excitation wavelength Ex = 295 nm, and in the test range of Em = 280 nm - 550 nm, use a fluorescence spectrometer to test the emission spectra of each experimental water sample and the simulated water samples to be measured respectively. Take the maximum peak value as the emission spectrum peak value of each sample, and obtain the emission spectrum peak value of each experimental water sample at Ex = 235 nm and the emission spectrum peak value at Ex = 295 nm. The results are shown in Figure 3 .

[0042] Step three, background correction: Use the emission spectrum measured with ultrapure water as the background, subtract the emission spectra of the remaining water samples at Ex = 235 nm and Ex = 295 nm from the background spectrum to correct the measured emission spectra, and obtain the peak value I of the corrected emission spectrum measured at Ex = 235 nm 235 and the peak value I of the corrected emission spectrum measured at Ex = 295 nm 295 , record the corrected data, and the results are shown in Table 1.

[0043] Step 4, determine the judgment criterion: Perform data processing on the calibrated data obtained in Step 3 to obtain I 295 / I 235 . Obtain I of each experimental water sample 295 and I 235 . Take the minimum ratio 1.12 as the judgment ratio.

[0044] Step 5, determine whether the water sample to be tested is polluted: Compare the ratio of I of the water sample to be tested 295 and I 235 with the judgment ratio. When I 295 / I 235 > 1.12, there is microplastic pollution in the water sample to be tested; when I 295 / I 235 ≤ 1.12, there is no microplastic pollution in the water sample to be tested.

[0045] Since the simulated wastewater containing humic acid or NOM does not contain microplastics, the ratio of I 295 / I 235 of the simulated water sample containing humic acid or NOM should be less than 1.12, which is consistent with the comparison results in Table 1. In this embodiment, the natural river water (Yuehe River water) is taken locally, filtered and then tested to obtain I 295 / I 235 less than 1.0, that is, there is no microplastic pollution in the Yuehe River water.

[0046] Table 1. Test results of Example 1

[0047]

[0048] Functions and effects of the embodiment

[0049] According to the method for rapid detection of microplastic pollution in water based on fluorescence spectroscopy provided in this embodiment, this method uses the principle that microplastics will produce dissolved organic matter with fluorescence characteristics when contacting water, and uses a fluorescence spectrometer to detect whether there is microplastic pollution in water. It has wide applicability, does not require other pretreatment of the water sample, and the water sample can be recycled into the mother liquor after measurement. Compared with the prior art, this method does not require cumbersome processing procedures such as digestion. The pretreatment only takes a few minutes of filtration, and the result can be obtained in a few minutes of testing, greatly shortening the time. At the same time, only the judgment ratio needs to be measured once, and then only simple filtration treatment of the water sample is required for other tests. Therefore, this method has the advantages of simple operation, rapid testing, high sensitivity, and no need for chemical reagents, making up for the defect of the slow detection speed of the existing detection technology.

[0050] Furthermore, a portable fluorescence analyzer can also be used to achieve the effect of on-site determination, and can quickly and accurately determine whether there is microplastic pollution in the wastewater.

[0051] Since microplastics in water will release dissolved organic matter (MP-DOM) during the natural aging process, and there are significant differences in the fluorescence spectra between this dissolved organic matter and the natural organic matter (NOM) naturally generated in natural water bodies. That is, the fluorescence peak intensity of MP-DOM at Ex = 260 nm - 320 nm is higher than that at Ex = 220 nm - 250 nm, while NOM and commercial humic acid usually show the opposite phenomenon. Therefore, by using the unique spectral characteristics of the dissolved organic matter released by microplastics, it is possible to effectively determine whether there is microplastic pollution in water. Combining with a portable fluorescence analyzer can quickly and accurately judge whether there is microplastic pollution in wastewater, making up for the defect of the slow detection speed of existing detection technologies.

[0052] The above embodiments are preferred cases of the present invention and are not used to limit the protection scope of the present invention.

Claims

1. A method for rapid detection of microplastic pollution in water based on fluorescence spectroscopy, characterized in that, it includes the following steps: Step S1, configuring experimental water sample samples with various plastics; Step S2, using a fluorescence spectrometer, measuring the emission spectra of each of the experimental water sample samples within the Em measurement range at an excitation wavelength Ex = 235 nm and an excitation wavelength Ex = 295 nm respectively, taking the maximum peak value as the emission spectrum peak value of each of the experimental water sample samples, and obtaining the emission spectrum peak values of each of the experimental water sample samples at Ex = 235 nm and Ex = 295 nm; Step S3, perform background correction on the measured peak of the emission spectrum to obtain the peak I of the corrected emission spectrum of the experimental water sample at Ex = 235 nm 235 and the peak I of the corrected emission spectrum at Ex = 295 nm 295 ; Step S4, obtain each of the experimental water sample specimens I 295 and I 235 to obtain the ratio, and use the minimum ratio as the judgment ratio; Step S5: Use a fluorescence spectrometer to measure the peak values of the emission spectra of the water sample to be measured at Ex = 235 nm and Ex = 295 nm within the same Em measurement range, and perform background correction on the measured emission spectra to obtain the peak value I of the corrected emission spectrum of the water sample to be measured at Ex = 235 nm 235 and the peak value I of the corrected emission spectrum at Ex = 295 nm 295 , and obtain the ratio of the water sample I 295 to I 235 ; Step S6, the I of the water sample to be measured 295 and I 235 The ratio of is compared with the judgment ratio. If the I of the water sample to be measured 295 and I 235 If the ratio is greater than the judgment ratio, it is determined that there is microplastic pollution in the water sample to be measured. If the I of the water sample to be measured 295 and I 235 If the ratio is less than or equal to the judgment ratio, it is determined that there is no microplastic pollution in the water sample to be measured.

2. The method for rapid detection of microplastic pollution in water based on fluorescence spectroscopy according to claim 1, characterized in that: wherein, the various plastics are respectively polystyrene, polyvinyl chloride, and polyethylene.

3. The method for rapid detection of microplastic pollution in water based on fluorescence spectroscopy according to claim 1, characterized in that: wherein, the judgment ratio is 1.

12.

4. The method for rapid detection of microplastic pollution in water based on fluorescence spectroscopy according to claim 1, characterized in that: wherein, the minimum value of the Em measurement range is greater than the excitation wavelength by 10 nm - 20 nm.

5. The method for rapid detection of microplastic pollution in water based on fluorescence spectroscopy according to claim 1, characterized in that: wherein, in Step S1 and Step S5, the experimental water sample samples and the water sample to be tested are filtered using a 0.45 μm glass fiber filter membrane and then tested using a fluorescence spectrometer.

6. The method for rapid detection of microplastic pollution in water based on fluorescence spectroscopy according to claim 1, characterized in that: wherein, in Step S2 and Step S5, the volumes of the experimental water sample samples and the water sample to be tested are greater than 1 mL.

7. The method for rapid detection of microplastic pollution in water based on fluorescence spectroscopy according to claim 1, characterized in that: wherein, the experimental water sample samples and the water sample to be tested are adjusted to pH = 2 - 4 with acid and then refrigerated, and measured after a predetermined time.

8. The method for rapid detection of microplastic pollution in water based on fluorescence spectroscopy according to claim 1, characterized in that: wherein, in Step S3 and Step S5, background correction is performed using the ultrapure water used when configuring the experimental water sample samples.

9. The method for rapid detection of microplastic pollution in water based on fluorescence spectroscopy according to claim 8, characterized in that: wherein, if the ultrapure water used for background correction and the ultrapure water used when configuring the experimental water sample samples belong to different batches, then after background correction, the Raman normalization method or the quinine sulfate method is used to correct the emission spectrum peak values.

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