Method for quantitatively analyzing micro-nano plastic particle mixture by Raman / SERS (Surface Enhanced Raman Scattering) spectrum and slope matching strategy

Abstract

The invention provides a method for quantitatively analyzing a micro-nano plastic particle mixture through a Raman / SERS spectrum and a slope matching strategy. According to the method, micro-plastics and nano-plastics larger than 500 nanometers are separated and enriched through a glass fiber membrane and quantitatively measured through Raman, a series of quantitative curves between Raman spectral intensity and standard concentration of the micro-plastics and the nano-plastics with different sizes are established, and the slope of the quantitative curves is recorded; the method comprises the following steps: enriching 50-500nm nano-plastics through a nylon membrane, taking Ag NPs as a substrate, taking KI as a cleaning agent and a coagulant, carrying out quantitative determination by utilizing SERS, establishing a series of quantitative curves between SERS spectral intensities and standard concentrations of the nano-plastics with different sizes, and recording the slope of the quantitative curves; the method comprises the following steps: testing a to-be-detected sample, establishing a quantitative curve between spectral intensity and concentration of to-be-detected micro-plastic and nano-plastic to obtain a quantitative curve slope, and matching the quantitative curve slope of to-be-detected particles with a quantitative curve of standard plastic particles so as to realize quantitative detection of micro-plastic and nano-plastic particle pollutants.

Description

Technical Field

[0001] The present invention relates to a method for quantitatively analyzing a mixture of micro- and nano-plastic particles by Raman / SERS spectroscopy and slope matching strategy, belonging to the fields of analytical chemistry and environmental analysis. Background Art

[0002] Microplastics and nanoplastics have become new anthropogenic particulate pollutants, rapidly attracting the attention of the scientific community and the public. They are widely distributed in the global environment, not only penetrating into the drinking water supply system and food chain, but also raising concerns about their potential environmental effects and impacts on human health. Compared with microplastics, nanoplastics often exhibit stronger biotoxicity due to their larger specific surface area. To effectively address these issues, it is crucial to accurately obtain reliable data on the chemical composition, particle size distribution, and mass concentration of microplastics and nanoplastics, which will provide support for formulating scientific management strategies.

[0003] Currently, the analytical methods for microplastics and nanoplastics include mass-based analyses such as pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS), inductively coupled plasma mass spectrometry (ICP-MS), and total organic carbon (TOC) analysis; and particle-based analyses, including Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, single-particle inductively coupled plasma mass spectrometry (SP-ICP-MS), etc. Raman spectroscopy uses the inelastic scattering effect of microplastics to generate vibrational fingerprint spectra, and when combined with imaging technology, it can simultaneously provide information on chemical composition, concentration, and size.

[0004] In recent years, surface-enhanced Raman spectroscopy (SERS) has become a powerful tool for detecting nanoplastics. Researchers have developed various SERS substrates with cavity structures, such as multi-scale cavity structures, triangular cavity arrays, and covalent organic framework template SERS substrates, to enhance the spectral signal by shortening the distance between nanoplastics particles and SERS hotspots. On silver nanowire film SERS substrates, nanoplastics can be enriched and in-situ detected, or high-sensitivity sensing can be achieved by their co-aggregation with silver nanoparticles. In addition, nanoplastics can also obtain indirect responses through signal molecule labeling.

[0005] In the co - existence of microplastics and nanoplastics, accurately measuring the mass concentration of nanoplastics requires obtaining high - quality spectral purity by eliminating the spectral interference of microplastics. SERS substrates with size - selective capabilities, such as using anodic aluminum oxide or piezoelectric nanowire bowl structures for enriching nanoplastics, can prevent microplastic particles from depositing on the SERS substrate. In addition, by utilizing the differences in the electro - migration behavior of PS nanoplastics of different sizes, and controlling the electro - adsorption time, PS nanoplastics smaller than a certain size can be selectively enriched and detected. In terms of data processing, the quantitative analysis of particles is different from that of small molecules because the Raman and SERS responses of plastic particles depend on the mass concentration and size. Plastic particles of different sizes exhibit spectral intensity - concentration curves with different slopes. The prerequisite for accurate quantification is to construct a calibration curve using standard particles with the same composition and particle size as the particles to be measured. In actual samples, the particle size distribution of microplastics is unknown and uneven, which makes the accurate quantification of plastic particles a challenge in this field. Summary of the Invention

[0006] Aiming at the deficiencies of the prior art, the present invention provides a method for quantitatively analyzing a mixture of micro - and nano - plastic particles by using a Raman / SERS spectroscopy and slope - matching strategy. Overview of the Invention:

[0008] In the method of the present invention, for microplastics and nanoplastics larger than 500 nm, they are separated and enriched by a glass fiber membrane and quantitatively determined by Raman. A series of quantitative curves between the Raman spectral intensity and the standard concentration of microplastics and nanoplastics of different sizes are established, and their slopes are recorded; for nanoplastics with sizes from 50 nm to 500 nm, they are enriched by a nylon membrane, using Ag NPs as the substrate, KI as the cleaner and coagulant, and quantitatively determined by SERS. A series of quantitative curves between the SERS spectral intensity and the standard concentration of nanoplastics of different sizes are established, and their slopes are recorded; the test sample is measured, a quantitative curve between the spectral intensity and the concentration of the microplastics and nanoplastics to be measured is established, the slope of the quantitative curve is obtained, and the slope of the quantitative curve of the particulate matter to be measured is matched with the quantitative curve of the standard plastic particles, so as to achieve the quantitative detection of micro - and nano - plastic particle pollutants.

[0009] The present invention is realized through the following scheme:

[0010] A method for quantitatively analyzing a mixture of micro - and nano - plastic particles by using a Raman / SERS spectroscopy and slope - matching strategy, comprising the following steps:

[0011] (1) Filtering a water sample containing a mixture of microplastics and nanoplastics using a filtering device with a glass fiber membrane having a pore size of 0.6 - 0.8 μm as the filtering membrane to obtain a microplastic filter membrane with a particle size greater than 500 nm;

[0012] (2) Use a filtration device with a nylon membrane with a pore size of 0.22 μm as the filter membrane to filter the water sample filtered in step (1). After filtration is completed, add Ag NPs and KI. Under the action of physical interception and adsorption interception filtration, filter the nanoplastics, Ag NPs, and KI together onto the nylon membrane to obtain a nanoplastics filter membrane with a particle size of 50 nanometers to 500 nanometers;

[0013] (3) Use a Raman spectrometer to collect Raman spectra of micro-nanoplastic particle pollutants on the microplastic filter membrane with a particle size greater than 500 nanometers, establish a series of quantitative curves between the Raman spectral intensities of microplastics and nanoplastics with different sizes and the standard concentration, and record their slopes;

[0014] (4) Use a Raman spectrometer to collect SERS spectra of nanoplastic particle pollutants on the nanoplastics filter membrane with a particle size of 50 nanometers to 500 nanometers, establish a series of quantitative curves between the SERS spectral intensities of nanoplastics with different sizes and the standard concentration, and record their slopes;

[0015] (5) Test the sample to be measured, establish a quantitative curve between the spectral intensities and concentrations of the microplastics and nanoplastics to be measured, obtain the slope of the quantitative curve, and match the slope of the quantitative curve of the particulate matter to be measured with the quantitative curve of the standard plastic particles, so as to realize the quantitative detection of microplastic and nanoplastic particle pollutants.

[0016] Preferably according to the present invention, in step (1), the dosage of the water sample to be measured is 0.1 - 50 mL / cm 2 .

[0017] Preferably according to the present invention, in step (1), the diameter of the glass fiber membrane is 12 - 15 mm.

[0018] Preferably according to the present invention, in step (1), the particle size of the microplastics obtained on the glass fiber membrane is 500 nm - 5 μm.

[0019] Preferably according to the present invention, in step (2), the pore size of the nylon membrane is 0.22 μm and the diameter is 12 - 15 mm.

[0020] Preferably according to the present invention, in step (2), the dosage of Ag NPs is 2 - 4 mL.

[0021] Preferably according to the present invention, in step (2), the addition amount of KI makes its concentration reach 0.02 - 0.1 M.

[0022] More preferably, in step (2), the addition amount of KI makes its concentration reach 0.06 M.

[0023] Preferably according to the present invention, in step (2), the particle size of the nanoplastics on the nylon membrane is 50 - 500 nm.

[0024] KI of the present invention is used as a cleaning agent and a coagulant.

[0025] Preferably according to the present invention, in step (2), the specific addition methods of Ag NPs and KI are as follows: After adding the filtered nano-plastic particles and mixing with Ag NPs, a KI solution is immediately added, and the mixture is mixed well and incubated at room temperature for 10 min.

[0026] Preferably according to the present invention, in step (1) and step (2), the sol or solution is filtered until no more filtrate is produced to obtain the product.

[0027] Preferably according to the present invention, in step (3) and step (4), the laser wavelengths for testing by the Raman spectrometer are 785 nm, 633 nm or 532 nm, and the laser power is 1 - 50 mW; the integration time for single-point Raman spectrum acquisition is 5 - 30 s.

[0028] Preferably according to the present invention, in step (5), the slope matching strategy is specifically as follows:

[0029] Assume that the size of PS microplastics or PS nanoplastics in the unknown sample is unique.

[0030] 1) Obtain the spectral intensities of PS micro / nanoplastics through Raman and SERS.

[0031] 2) Assume that the size of the unknown particle is "size 1", and its concentration is calculated as "C1" using the linear equation obtained from size 1 standard PS plastic particles.

[0032] 3) Dilute the sample to five concentration levels from C 1-1 to C 1-5 and analyze it using the Raman / SERS method.

[0033] 4) Plot a working curve with the spectral response-concentration from C 1-1 to C 1-5 to obtain "assumed slope for size 1".

[0034] 5) Compare "assumed slope for size 1" with "standard slope for size 1". If their relative error is less than 5%, it is considered that the size of the unknown particle matches the assumed size. If not, re-assume the size until the best-fitting slope is determined.

[0035] 6) Calculate the mass concentration of the sample using the best-fitting size and its linear equation.

[0036] The technical features and beneficial effects of the present invention are as follows:

[0037] 1. The method of the present invention combines Raman / SERS (R / S) and the slope matching strategy, thereby improving the quantitative accuracy of spectral data acquisition and data processing, minimizing the influence of spectral interference between microplastics and nanoplastics, and thus achieving more accurate spectral intensity measurement. The slope matching strategy is adopted in external standard quantification to achieve more accurate quantification and provide average particle size information. The success of the method of the present invention is verified by analyzing micro / nanoplastics released from disposable polystyrene (PS) cups, and the quantification accuracy is improved.

[0038] 2. By filtering nanoplastics with sizes of 50 nm - 500 nm together with silver sol and KI onto a nylon membrane, the present invention can simultaneously achieve the concentration enrichment and SERS detection of small-sized nanoplastics. The present invention refers to the conventional analysis process of particulate matter in the environment, namely sampling, separation, enrichment, and detection. The analysis process can be simplified by the device of the present invention. Through the assembly of different filter membranes, the present invention can be used for the separation and enrichment of microplastic and nanoplastic mixture solutions. Microplastics and nanoplastics with sizes above 500 nm are separated, enriched by a glass fiber membrane, and quantitatively determined using Raman. A series of quantitative curves between the Raman spectral intensity and concentration of standard microplastics and nanoplastics with different sizes are established, and their slopes are recorded; Nanoplastics with sizes of 50 nm - 500 nm are enriched by a nylon membrane and quantitatively determined using SERS with Ag NPs as the substrate. A series of quantitative curves between the SERS spectral intensity and concentration of standard nanoplastics with different sizes are established, and their slopes are recorded. For unknown samples, by matching the slope of the quantitative curve of the particulate matter to be measured with the quantitative curve of the standard plastic particles, accurate quantitative detection of microplastic and nanoplastic particle pollutants can be achieved.

[0039] 3. The method of the present invention combines Raman / SERS spectral detection technology with the slope matching strategy, thereby improving the quantitative accuracy of spectral data acquisition and data processing. Raman spectral analysis is performed on micro / nanoplastics with sizes above 500 nm, and SERS spectral analysis is performed on nanoplastics with sizes below 500 nm. This method minimizes the influence of spectral interference between microplastics and nanoplastics, and thus achieves more accurate spectral intensity measurement. Regarding data processing, the slope matching strategy is adopted in external standard quantification to achieve more accurate quantification and provide average particle size information. For microplastics and nanoplastics with different particle sizes, a good linear relationship is established between the microplastic / nanoplastic concentration and the characteristic peak intensity. The success of this systematic method is successfully demonstrated by analyzing micro / nanoplastics released from disposable PS cups. The present invention retains the advantages of the two technologies, including simple operation, low cost, high enrichment efficiency, high sensitivity, fast detection speed, anti-water interference, non-destructive, applicable to particulate matter with multiple particle sizes, and capable of providing fingerprint information, etc. The present invention can detect particulate matter with a particle size as low as 50 nm; for concentrations as low as 10-4 Particulates of g / L can still achieve effective detection; the measured concentration accuracy is within 90%-110%; therefore, the method of the present invention has higher sensitivity, a wider applicable particle size range, and higher accuracy.

[0040] 4. The method of the present invention has a simple process, is easy to operate and repeat; at the same time, it can also adjust the enrichment effect of nanoplastics by adjusting the dosage of silver sol and KI to achieve the interception of smaller particle size nanoparticles. It has high continuity and simplifies the operation process. Description of the Drawings

[0041] Figure 1 Schematic diagram of the quantitative analysis process for quantitatively analyzing a mixture of micro-nanoplastic particles by the Raman / SERS spectral and slope matching strategy;

[0042] Figure 2 Raman spectra of micro-nanoplastics of the same mass concentration but different sizes in Experimental Example 1;

[0043] Figure 3 SERS spectra of nanoplastics of the same mass concentration but different sizes in Experimental Example 1;

[0044] Figure 4 Quantitatively analyzing nanoplastics of mixed sizes using the slope matching strategy and inferring their average size in Experimental Example 3;

[0045] Figure 5 Raman spectrogram of the actual sample PS microplastic in Experimental Example 4;

[0046] Figure 6 SERS spectrogram of the actual sample PS nanoplastics in Experimental Example 4;

[0047] Figure 7 SEM image of the actual sample PS microplastic in Experimental Example 4;

[0048] Figure 8 SEM image of the actual sample PS nanoplastics in Experimental Example 4; Detailed Embodiments

[0049] To more clearly elaborate on the technical problems to be solved by the present invention and the advantages of the present invention, the following will be described in detail with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0050] The experimental methods used in the embodiments are all conventional methods unless otherwise specified; the reagents and equipment used are all prior art and can be obtained commercially unless otherwise specified.

[0051] The filtration device and Raman spectrometer are existing equipment.

[0052] Experimental Example 1

[0053] A method for quantitatively analyzing a mixture of micro-nano plastic particles by Raman / SERS spectroscopy and slope matching strategy, comprising the following steps:

[0054] (1) Filter a water sample containing a mixture of microplastics and nanoplastics standards using a filtering device with a glass fiber membrane with a pore size of 0.6 - 0.8 μm to obtain microplastics with a particle size greater than 500 nanometers;

[0055] (2) Filter the water sample filtered in step (1) using a filtering device with a nylon membrane with a pore size of 0.22 μm. After filtration, add Ag NPs and KI. Under the action of physical interception and adsorption interception filtration, co-filter the nanoplastics, Ag NPs, and KI onto the nylon membrane to obtain nanoplastics with a size of 50 nanometers to 500 nanometers;

[0056] (3) Use a Raman spectrometer to collect Raman spectra of micro-nano plastic particle pollutants on the glass fiber membrane in step (1), establish a series of quantitative curves between the Raman spectral intensities and standard concentrations of microplastics and nanoplastics with different sizes, and record their slopes;

[0057] (4) Use a Raman spectrometer to collect SERS spectra of nanoplastics particle pollutants on the nylon membrane in step (2), establish a series of quantitative curves between the SERS spectral intensities and standard concentrations of nanoplastics with different sizes, and record their slopes;

[0058] (5) Test the sample to be measured, establish a quantitative curve between the spectral intensities and concentrations of the microplastics and nanoplastics to be measured, obtain the slope of the quantitative curve, and match the slope of the quantitative curve of the particulate matter to be measured with the quantitative curve of the standard plastic particles, so as to realize the quantitative detection of microplastic and nanoplastics particle pollutants.

[0059] Experimental Example 1

[0060] (1) Preparation of water samples to be measured for microplastics and nanoplastics particles: The microplastics and nanoplastics particle samples are prepared in the laboratory. An aqueous solution of PS micro-nano plastic particles with a concentration of 0.1 g / L and particle size dimensions of 5 μm, 3 μm, 1 μm, 800 nm, 700 nm, and 600 nm, and an aqueous solution of PS micro-nano plastic particles with a concentration of 0.04 g / L and particle size dimensions of 500 nm, 400 nm, 300 nm, 200 nm, 100 nm, and 50 nm are prepared.

[0061] (2) Take 1 mL of the aqueous solution of PS micro-nano plastic particles with a concentration of 0.1 g / L and particle size dimensions of 5 μm, 3 μm, 1 μm, 800 nm, 700 nm, and 600 nm in step (1), and filter the water sample to be measured using a glass fiber membrane (pore size 1 μm).

[0062] (3) Take 1 mL of the aqueous solution of PS micro-nano plastic particles with a concentration of 0.04 g / L and particle size dimensions of 500 nm, 400 nm, 300 nm, 200 nm, 100 nm, and 50 nm in step (1). By adding 3 mL of Ag NPs and 1 mL of KI (final concentration of 0.06 M), use a nylon membrane with a pore size of 0.22 μm as the filter membrane to filter the water sample to be tested.

[0063] (4) Take out the filter membrane material after enrichment from the filtration device, and detect it with a Raman spectrometer with an excitation wavelength of 785 nm. The laser power is 50 mW, and the integration time is 30 s. Perform Raman spectral analysis on micro-nano plastics above 500 nm and SERS spectral analysis on nano-plastics below 500 nm.

[0064] The relationship between the spectral intensity and size of PS micro-nano plastics is as Figure 2 and Figure 3 shown. At the same mass concentration, the larger the size of the micro-nano plastics, the greater the Raman spectral intensity; at the same mass concentration, the smaller the size of the nano-plastics, the greater the SERS spectral intensity. The relationship between the size of PS micro-nano plastics and the slope is shown in Table 1. At the same mass concentration, the Raman spectral intensity increases with the increase in the size of the micro-nano plastics. Therefore, the larger the size, the greater the slope of the quantitative curve; at the same mass concentration, the SERS spectral intensity increases with the decrease in the size of the nano-plastics. Therefore, the smaller the size, the greater the slope of the quantitative curve.

[0065] Table 1 Relationship between the size of PS micro-nano plastics and the slope

[0066]

[0067]

[0068] Experimental Example 2

[0069] Analysis of the accuracy of micro-nano plastic quantification, including the steps:

[0070] (1) Preparation of water samples to be tested for microplastics and nano-plastics particles: The microplastics and nano-plastics particle samples are prepared in the laboratory, with a concentration of 10 -3 -0.1 g / L and particle size dimensions of 5 μm, 3 μm, 1 μm, 800 nm, 700 nm, and 600 nm of PS micro-nano plastic particle aqueous solution, and a concentration of 10 -4 -0.1 and particle size dimensions of 500 nm, 400 nm, 300 nm, 200 nm, 100 nm, and 50 nm of PS micro-nano plastic particle aqueous solution.

[0071] (2) Take the concentration of 10 in step (1)-3 1 mL of an aqueous solution of PS micro / nano plastic particles with a concentration of -0.1 g / L and particle size dimensions of 5 μm, 3 μm, 1 μm, 800 nm, 700 nm, and 600 nm was filtered using a glass fiber membrane (pore size 1 μm) for the water sample to be tested.

[0072] (3) Take the concentration of 10 in step (1) -4 1 mL of an aqueous solution of PS micro / nano plastic particles with a concentration of -0.1 and particle size dimensions of 500 nm, 400 nm, 300 nm, 200 nm, 100 nm, and 50 nm was filtered for the water sample to be tested using a nylon membrane with a pore size of 0.22 μm as the filter membrane by adding 3 mL of Ag NPs and 1 mL of KI (final concentration 0.06 M).

[0073] (4) After the enrichment was completed, the filter membrane material was taken out of the filtration device and detected using a Raman spectrometer with an excitation wavelength of 785 nm, a laser power of 50 mW, and an integration time of 30 s. By performing Raman spectral analysis on micro / nano plastics above 500 nm and SERS spectral analysis on nano plastics below 500 nm, a series of quantitative curves of the spectral intensity and concentration of standard micro / nano plastics with different sizes were established.

[0074] (5) For a PS micro / nano plastic of a certain known size, different-sized Raman / SERS quantitative curves were used to analyze it respectively, and the relative error between its actual concentration and the measured concentration was calculated to analyze the accuracy.

[0075] The accuracy analysis of micro / nano plastic quantification is shown in Table 2. Only by selecting a quantitative curve with a suitable size can the relative error of the measured concentration be minimized and the accuracy be the highest. For example, when the size of the measured particle is 5 μm, only when using the quantitative curve with a standard size of 5 μm, the measured relative error is 2%, while when using the standard curves of other sizes in the table, the measured relative errors are all greater than 60%.

[0076] Table 2 Accuracy of PS micro / nano plastic quantification

[0077]

[0078] Experimental Example 3

[0079] (1) Preparation of the water sample to be tested for nano plastic particles: The nano plastic particle sample was prepared in the laboratory with a concentration of 10 -4 An aqueous solution of PS nano plastic particles with a concentration of -0.1 and particle size dimensions of 500 nm and 50 nm.

[0080] (2) Take the concentration of 10 in step (1) -4Mix an aqueous solution of PS nanoplastics particles with a size of 500 nm and 50 nm and a concentration of -0.1 to obtain a nanoplastics mixed solution with an average particle size of 300 nm at different concentrations. Take 1 mL each and add 3 mL of Ag NPs and 1 mL of KI (final concentration 0.06 M), and filter the water sample to be tested using a nylon membrane with a pore size of 0.22 μm as the filter membrane.

[0081] (4) Take out the filter membrane material after the enrichment from the filtration device, and use a Raman spectrometer with an excitation wavelength of 785 nm for detection. The laser power is 50 mW, and the integration time is 30 s. Conduct SERS spectral analysis on the nanoplastics to obtain a series of SERS spectral intensities at different concentrations.

[0082] (5) Use the slope matching strategy for analysis. Assume that the size of PS microplastics or PS nanoplastics in the unknown sample is unique. This process can be described as follows ( Figure 1 ):

[0083] 1) Obtain the spectral intensities of PS micro / nanoplastics through Raman and SERS;

[0084] 2) Assume that the size of the unknown particles is "size 1", and its concentration is calculated as "C1" using the linear equation obtained from standard PS plastic particles of size 1;

[0085] 3) Dilute the sample to five concentration levels from C 1-1 to C 1-5 and analyze using the Raman / SERS method;

[0086] 4) Plot a working curve of spectral response-concentration from C 1-1 to C 1-5 to obtain "slope assumed size 1";

[0087] 5) Compare "slope assumed size 1" with "slope standard size 1". If their relative error is less than 5%, it is considered that the size of the unknown particles matches the assumed size. If not, re-assume the size until the best-fitting slope is determined;

[0088] 6) Calculate the mass concentration of the sample using the best-fitting size and its linear equation;

[0089] The combined method of Raman / SERS spectra and slope matching strategy is used for the size analysis of the mixed sample as Figure 4 shown. The size of the PS nanoplastics measured by this method is 300 nm, with an accuracy of 100%; the concentration is 9.53x10 -3 , with an accuracy of 95.3%.

[0090] Experimental Example 4

[0091] (1) Preparation of the water sample to be tested for the actual sample of microplastic and nanoplastic mixture particles: Cut a disposable PS plastic cup into pieces and place them in a 20 mL glass vial. Add 20 mL of deionized water and shake on a shaker for 36 h, then concentrate to 4 mL to obtain a solution of microplastic and nanoplastic mixture particles. Dilute the mixed particle solution by different multiples to obtain solutions of microplastic and nanoplastic mixture particles with different concentrations.

[0092] (2) Take 1 mL of the solutions of microplastic and nanoplastic mixture particles with different concentrations in step (1), and use a glass fiber membrane as the filter membrane to filter the water sample to be tested, so as to separate and enrich microplastic and nanoplastic particle pollutants with a size above 500 nm; Add 3 mL of Ag NPs and 1 mL of KI (final concentration 0.06 M) to the filtrate, and use a nylon membrane as the filter membrane to filter the water sample to be tested, so as to enrich nanoplastic particle pollutants with a size of 50 nm - 500 nm in the fraction.

[0093] (3) Take out the filter membrane material after the separation and enrichment from the filtering device, and detect it with a Raman spectrometer with an excitation wavelength of 785 nm, a laser power of 50 mW, and an integration time of 30 s. Collect the Raman spectrum of micro / nanoplastics on the glass fiber membrane and the SERS spectrum of nanoplastics on the nylon membrane. Finally, use the slope matching strategy to analyze the size of micro / nanoplastics in the actual sample.

[0094] Using the combined method of Raman / SERS and slope matching strategy, as Figures 5 - 8 shown, microplastics and nanoplastics released from the simulated disposable PS plastic cup were successfully detected. The size of the microplastics was 1 μm and the concentration was 0.042 g / L, and the size of the nanoplastics was 100 nm and the concentration was 0.004 g / L. The measured size information was consistent with that characterized by the SEM graph ( Figure 7 and Figure 8 ).

Claims

1. A method for quantitatively analyzing a mixture of micro-nano plastic particles using Raman / SERS spectroscopy and slope matching strategy, comprising the following steps: (1) Using a filtration device with a glass fiber membrane with a pore size of 0.6-0.8 μm as a filter membrane, a standard water sample containing a mixture of microplastics and nanoplastics was filtered to obtain a microplastic filter with a particle size greater than 500 nanometers; (2) filtering the water sample filtered in step (1) using a filtration device with a nylon membrane having a pore size of 0.22 μm as a filter membrane, adding Ag NPs and KI after the filtration is completed, and filtering the nanoplastics, Ag NPs and KI together onto the nylon membrane under the action of physical interception and adsorption and retention filtration to obtain a 50 nm to 500 nm nanoplastic filter membrane; (3) Use a Raman spectrometer to collect Raman spectra of micro- and nano-plastic particle pollutants on microplastic filter membranes with a particle size greater than 500 nanometers, establish a series of quantitative curves between the Raman spectral intensity of microplastics and nanoplastics of different sizes and the standard concentration, and record their slopes; (4) Using a Raman spectrometer to collect SERS spectra of nanoplastic particle pollutants on a nanoplastic filter membrane with a size of 50 to 500 nanometers, a series of quantitative curves between the SERS spectral intensity of nanoplastics of different sizes and the standard concentration were established, and their slopes were recorded; (5) Testing the samples to be tested, establishing a quantitative curve between the spectral intensity and concentration of the microplastics and nanoplastics to be tested, obtaining the slope of the quantitative curve, and matching the slope of the quantitative curve of the particles to be tested with the quantitative curve of the standard plastic particles, thereby achieving quantitative detection of microplastic and nanoplastic particle pollutants.

2. The method according to claim 1, characterized in that In step (1), the amount of water sample to be tested is 0.1-50mL / cm 2 The diameter of the glass fiber membrane is 12-15 mm, and the particle size of microplastics obtained on the glass fiber membrane is 500 nm-5 μm.

3. The method according to claim 1, characterized in that In step (2), the pore size of the nylon membrane is 0.22 μm and the diameter is 12-15 mm.

4. The method according to claim 1, characterized in that: In step (2), the amount of Ag NPs used is 2-4 mL, and the amount of KI added is such that its concentration reaches 0.02-0.1 M.

5. The method according to claim 1, characterized in that In step (2), the particle size of the nanoplastic particles on the nylon membrane is 50-500nm.

6. The method according to claim 1, characterized in that In step (2), the specific method of adding Ag NPs and KI is as follows: after the nanoplastic particles obtained by filtration are added to Ag NPs and mixed evenly, the KI solution is immediately added, mixed evenly, and incubated at room temperature for 10 minutes.

7. The method according to claim 1, characterized in that In step (1) and step (2), the sol or solution is filtered until no filtrate is produced.

8. The method according to claim 1, characterized in that In step (3) and step (4), the laser wavelength tested by the Raman spectrometer is 785nm, 633nm or 532nm, and the laser power is 1-50mW; the integration time of single-point Raman spectrum acquisition is 5-30s.

9. The method according to claim 1, characterized in that: In step (3), step (4) and step (5), the slope matching strategy is specifically as follows: Assuming that the size of PS microplastics or PS nanoplastics in unknown samples is unique, 1) Obtain the spectral intensity of PS micro / nano plastics through Raman and SERS; 2) Assuming the size of the unknown particle is "Size 1", its concentration is calculated as "C1" using the linear equation derived from Size 1 standard PS plastic particles; 3) Dilute the sample to C 1-1 To C 1-5 five concentration levels and analyzed using the Raman / SERS method; 4) Use from C 1-1 to C 1-5 The spectral response-concentration is plotted as a working curve to obtain the "slope assumes size 1"; 5) Compare the "slope assumed size 1" with the "slope standard size 1". If their relative error is less than 5%, the size of the unknown particle is considered to match the assumed size. If not, re-assume the size until the best fitting slope is determined. 6) Calculate the mass concentration of the sample using the best fit size and its linear equation.

Images