Analytical methods for microplastics in air

Abstract

The present invention discloses a method for analyzing microplastics in the air, comprising the following steps: collecting microplastics in the air by using a filter membrane method; dissolving the filter membrane with the collected microplastics by using an organic solvent, so that the microplastics are dispersed in an organic solution; obtaining a hyperspectral image of the organic solution with the dispersed microplastics; comparing the spectrum of the microplastics in the hyperspectral image with a standard spectrum, and performing a qualitative analysis on the microplastics to determine the type of the microplastics. The method of the present invention can image and characterize microplastics without dyeing and marking, and has the advantages of simple pre-treatment, good treatment effect, and fast and convenient method.

Description

Technical Field

[0001] The present invention relates to the technical field of workplace air sampling and analysis, and in particular to a sampling and qualitative method for microplastics. Background Art

[0002] Microplastics are plastic particles or plastic fragments with a diameter of less than 5mm. As a new type of pollutant, microplastics have gradually been recognized and studied. Plastic and fiber products are one of the sources of microplastics. At present, the annual production of plastics in the world has reached 430 million tons. There are about 9 million people engaged in the production and post-processing of plastic raw materials. They are very likely to be exposed to microplastics in their occupational activities. Epidemiological studies have shown that long-term exposure to plastic dust can lead to lung damage and the occurrence of COPD. Long-term exposure to polyvinyl chloride dust can also increase the risk of lung cancer. Therefore, it is extremely important to assess the exposure risk of microplastics in the air of the workplace.

[0003] At present, the qualitative analysis methods of microplastics mainly include infrared spectroscopy, micro-Raman method, mass spectrometry, etc. However, due to the complex composition of air samples, sample pre-treatment is often complicated, requiring transfer, elution, flotation, staining and other steps. If the concentration of microplastics is low, it is not easy to complete qualitative analysis. Therefore, in order to more conveniently understand the exposure of microplastics in the air of the workplace, it is urgent to establish a reliable and convenient microplastic sampling and qualitative method. Summary of the invention

[0004] In view of the deficiencies of existing technologies, the present invention provides a method for analyzing microplastics in the air which has simple sample pre-treatment and can quickly obtain analysis results.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0006] A method for analyzing microplastics in the air, comprising the following steps:

[0007] Using membrane filtration to collect microplastics in the air;

[0008] Using an organic solvent to dissolve the filter membrane that collects the microplastics, so that the microplastics are dispersed in the organic solution;

[0009] Acquire hyperspectral images of organic solutions with dispersed microplastics;

[0010] The spectrum of microplastics in the hyperspectral image is compared with the standard spectrum, and qualitative analysis is performed on the microplastics to determine their types.

[0011] The step of using an organic solvent to dissolve the filter membrane containing the collected microplastics to disperse the microplastics in the organic solution comprises:

[0012] Place the filter membrane with collected microplastics on a microscope slide and cover it with a coverslip to flatten the filter membrane to prevent curling;

[0013] Use a syringe to take the acetone reagent, insert the needle between the slide and the cover glass, and continue to slowly inject the acetone reagent onto the filter membrane, and observe the filter membrane until it is completely infiltrated and dissolved;

[0014] Press the coverslip to eliminate bubbles generated during the infiltration and dissolution process;

[0015] Hot melt adhesive was applied at the junction of the slide and the cover glass to form a sealed sample with the acetone inside being in liquid state.

[0016] Acetone can react with polymerized cellulose ester to dissolve the filter membrane, but it cannot dissolve microplastics, thus separating microplastics from the filter membrane.

[0017] A nano-hyperspectral microscope was used to obtain images of suspected microplastics and the optical spectrum of each pixel in the image. The image magnification was 60 times and the exposure time was 0.1~0.15ms.

[0018] Nano-hyperspectral microscopy can identify particles larger than 10nm without fluorescent labeling and can present images with high signal-to-noise ratio and high resolution.

[0019] The standard spectral wavelength range is 400-1000nm, and the spectral resolution is 1.5nm.

[0020] Using the SAM (Spectral Angle Mapper) algorithm, the matching angle is set to 0.1 radians, and the spectrum of each pixel in the hyperspectral image is similarly matched with the standard spectrum. The pixels that match the same characteristics as the standard spectrum are marked in color, and the type of the color-marked part is the type corresponding to the standard.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The present invention can disperse microplastics into the solution by injecting an organic solvent to dissolve the filter membrane, and can achieve the effect of separating microplastics without the need for pre-treatment steps such as filtration, flotation, and dyeing, thereby avoiding a relatively complicated pre-treatment process.

[0023] The present invention adopts an organic solution to dissolve the filter membrane and obtain an organic solution with dispersed microplastics, which is sealed into a sealed sample with high light transmittance. The treated microplastics are dispersed in the sealed sample with high light transmittance, with fewer interference factors, thus improving the visualization effect, allowing the morphology of the microplastics to be clearly observed and the spectral characteristics of the microplastics to be obtained.

[0024] 3. During sample pretreatment, the injection speed of the organic solvent is controlled at 4 μL / s~6 μL / s, and the cover glass is kept fixed at all times, ensuring that the microplastics are positioned on the glass slide and not dispersed, and also avoiding the curling of the filter membrane affecting the dissolution efficiency.

[0025] 4. The present invention has a total of five steps: sampling, pretreatment, spectrum acquisition, scanning observation and qualitative analysis. It takes 30 min to 60 min to collect an air sample, 5 min to 10 min for pretreatment, 5 min to 10 min for spectrum acquisition, 10 min to 15 min for scanning observation and 10 min to 15 min for qualitative analysis. The whole process from sampling to final qualitative analysis can be completed within 2 hours, achieving the goal of quickly confirming the type of microplastics.

[0026] In summary, the present invention has the characteristics of simple pre-treatment, good treatment effect, and fast and convenient method. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Hyperspectral images showing suspected microplastic particles;

[0028] Figure 2 is the standard spectrum of polystyrene (PS) microplastics;

[0029] Figure 3 For Figure 1 Image rendered in color after SAM algorithm is performed on the basis of

[0030] Figure 4 Spectral images of two color-rendered pixels. DETAILED DESCRIPTION

[0031] The technical solution of the invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only used to help understand the invention and should not be regarded as specific limitations of the invention.

[0032] A method for analyzing microplastics in the air, comprising the following steps:

[0033] Using membrane filtration to collect microplastics in the air;

[0034] Using an organic solvent to dissolve the filter membrane that collects the microplastics, so that the microplastics are dispersed in the organic solution;

[0035] Acquire hyperspectral images of organic solutions with dispersed microplastics;

[0036] The spectrum of microplastics in the hyperspectral image is compared with the standard spectrum, and qualitative analysis of the microplastics is performed to determine their types.

[0037] The step of using an organic solvent to dissolve the filter membrane containing the collected microplastics to disperse the microplastics in the organic solution comprises:

[0038] Place the filter membrane with collected microplastics on a microscope slide and cover it with a coverslip to flatten the filter membrane to prevent curling;

[0039] Use an injection needle to take acetone reagent, or ethyl acetate, methanol and other reagents. Insert the needle between the glass slide and the coverslip, and continue to slowly inject acetone reagent onto the filter membrane. Observe the filter membrane until it is completely soaked and dissolved. Acetone can react with polymerized cellulose ester to dissolve the filter membrane, but it cannot dissolve microplastics, thus separating microplastics from the filter membrane.

[0040] Press the coverslip to eliminate bubbles generated during the infiltration and dissolution process;

[0041] Hot melt adhesive was applied at the junction of the slide and the cover glass to form a sealed sample with the acetone inside being in liquid state.

[0042] A nano-hyperspectral microscope was used to obtain images of suspected microplastics and the optical spectrum of each pixel in the image. The image magnification was 60 times and the exposure time was 0.1~0.15ms.

[0043] Nano-hyperspectral microscopy can identify particles larger than 10nm without fluorescent labeling, and can present images with high signal-to-noise ratio and high resolution. The processed microplastics are fixed in a sealed sample with high light transmittance, with few interference factors, which can achieve better imaging effects and facilitate the observation of the morphology of microplastics.

[0044] The standard spectral wavelength range is 400-1000nm, and the spectral resolution is 1.5nm.

[0045] Using the SAM (Spectral Angle Mapper) algorithm, the matching angle is set to 0.1 radians, and the spectrum of each pixel in the hyperspectral image is similarly matched with the standard spectrum. The pixels that match the same characteristics as the standard spectrum are marked in color, and the type of the color-marked part is the type corresponding to the standard. Example 1

[0046] A method for analyzing microplastics in the air, the steps are as follows:

[0047] S1. Air sampling was carried out in a crushing workshop using polystyrene (PS) as raw material, and microplastics in the air were collected using the filter membrane method; the sampling used the fixed-point sampling method, and the flow rate was 10L / min for 30min or 60min; the filter membrane was a microporous filter membrane made of polymerized cellulose ester with a pore size of 0.8μm;

[0048] S2. Cut the filter membrane and add organic solvent to pre-treat the sample; Sample pre-treatment process:

[0049] (1) Use a scalpel to cut the microporous filter membrane into 8 equally divided sectors;

[0050] (2) Use metal tweezers to pick up one of the membranes and place it on a microscope slide. Gently cover it with a coverslip to flatten the membrane and prevent it from curling.

[0051] (3) Use a microinjection needle to take 100 μL of acetone reagent, insert the needle between the slide and the cover glass, and slowly inject the organic solvent into the microporous filter membrane at a speed of 5 μL / s. Observe the filter membrane until it is completely infiltrated and dissolved;

[0052] (4) Use metal tweezers to gently press the coverslip to eliminate any bubbles.

[0053] (5) Within 2 minutes after the previous step is completed, apply hot melt adhesive to the junction of the slide and the cover glass to quickly seal the sample, keeping the acetone inside in liquid state to complete the sample pretreatment;

[0054] S3, obtain the sample hyperspectral image after pre-processing, and obtain the optical spectrum of each pixel in the image. The image magnification is 60 times, and the exposure time is 0.1~0.15ms, such as Figure 1 The hyperspectral images shown here show a large number of suspected microplastic particles;

[0055] S4. Obtain known standard spectra from the standard library, such as Figure 2 Shown is the standard spectrum of polystyrene (PS);

[0056] S5. Qualitative analysis of microplastics is performed by comparing with standard spectra to determine the type of microplastics. The wavelength range of the standard spectrum is 400-1000nm, and the spectral resolution is 1.5nm. Using the SAM (Spectral Angle Mapper) algorithm, the matching angle is set to 0.1 radians, and the spectrum of each pixel in the hyperspectral image is similarly matched with the standard spectrum, and the pixel points that match the same standard spectrum characteristics are color-marked. The type of the color-marked part is the type corresponding to the standard product.

[0057] like Figure 3 As shown in the figure, the color-marked pixels are all suspected microplastic particles. Select two of the marked pixels and display the spectrum, as shown in the figure below. Figure 4 As shown, its spectral characteristics are Figure 2 Therefore, the type of microplastic particles collected in step S1 is polystyrene (PS), which is consistent with the type of raw and auxiliary materials used in the workplace.

Claims

1. A method for analyzing microplastics in the air, characterized in that: The following steps are involved: Using membrane filtration to collect microplastics in the air; An organic solvent is used to dissolve the filter membrane that collects the microplastics. The organic solvent dissolves the filter membrane but cannot dissolve the microplastics, thereby separating the microplastics from the filter membrane and dispersing the microplastics in the organic solution. Acquire hyperspectral images of organic solutions with dispersed microplastics; Compare the spectrum of microplastics in the hyperspectral image with the standard spectrum, and conduct qualitative analysis on the microplastics to determine the type of microplastics; In the step of obtaining a hyperspectral image of an organic solution dispersed with microplastics, a nano-hyperspectral microscope is used to obtain a hyperspectral image, and an optical spectrum of each pixel in the image is obtained. The image magnification is 60 times, and the exposure time is 0.1-0.15 ms; The spectrum of microplastics in the hyperspectral image is compared with the standard spectrum. In the qualitative analysis step of microplastics, the wavelength range of the standard spectrum is 400-1000nm and the spectral resolution is 1.5nm; The spectrum of microplastics in the hyperspectral image is compared with the standard spectrum. In the step of qualitative analysis of microplastics, the SAM algorithm is used, and the matching angle is set to 0.1 radians. The spectrum of each pixel in the hyperspectral image is similarly matched with the standard spectrum, and the pixels that match the same characteristics as the standard spectrum are color-marked. The type of the color-marked part is the type corresponding to the standard.

2. The analysis method according to claim 1, characterized in that The steps of obtaining a hyperspectral image of an organic solution in which microplastics are dispersed include: The organic solution in which the microplastics are dispersed is sealed to form a sealed sample; Acquire a hyperspectral image of the sealed sample.

3. The analysis method according to claim 2, characterized in that The step of using an organic solvent to dissolve the filter membrane containing the collected microplastics to disperse the microplastics in the organic solution comprises: Place the filter membrane with collected microplastics on a microscope slide and cover it with a coverslip to flatten the filter membrane to prevent curling; Use an injection needle to take the acetone reagent, insert the needle between the slide and the cover glass, and continue to slowly inject the acetone reagent onto the filter membrane, observing the filter membrane until it is completely infiltrated and dissolved.

4. The analysis method according to claim 3, characterized in that The injection speed of the acetone reagent is 4 μL / s~6 μL / s.

5. The analysis method according to claim 3, characterized in that The organic solution containing dispersed microplastics is sealed to form a sealed sample, including: Press the coverslip to eliminate bubbles generated during the infiltration and dissolution process; Hot melt adhesive was applied at the junction of the slide and the cover glass to form a sealed sample with the acetone inside being in liquid state.

6. The analysis method according to any one of claims 1 to 5, characterized in that: The steps of collecting microplastics in the air using the membrane filter method are to use a fixed-point sampling method and collect data at a flow rate of 10L / min for 30min or 60min.

7. The analysis method according to any one of claims 1 to 5, characterized in that: In the step of collecting microplastics in the air using the membrane filter method, the membrane filter is a microporous membrane made of polymer cellulose ester with a pore size of 0.8 μm and a membrane diameter of 40 mm.

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