A method for quantitative analysis of micro-nano plastic particle mixture by Raman / SERS spectrum and slope matching strategy

Abstract

The present application provides a method for quantitative analysis of micro-nano plastic particle mixture by Raman / SERS spectrum and slope matching strategy. The method of the present application separates and enriches microplastics and nanoplastics larger than 500 nanometers through glass fiber membrane and quantitatively determines them by Raman, establishes a series of quantitative curves between Raman spectrum intensity of microplastics and nanoplastics of different sizes and standard concentration, and records the slope thereof; nanoplastics from 50 nanometers to 500 nanometers are enriched through nylon membrane and quantitatively determined by SERS using Ag NPs as a substrate, KI as a cleaning agent and a condensing agent, a series of quantitative curves between SERS spectrum intensity of nanoplastics of different sizes and standard concentration are established, and the slope thereof is recorded; the sample to be tested is tested, a quantitative curve between spectrum intensity of micro-nano plastic particles to be tested and concentration is established, the slope of the quantitative curve is obtained, the quantitative curve slope of the particles to be tested is matched with the quantitative curve of the standard plastic particles, and quantitative detection of micro-nano plastic particle pollutants is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for quantitative analysis of micro-nano plastic particle mixture by Raman / SERS spectrum and slope matching strategy, belonging to the field of analytical chemistry and environmental analysis. BACKGROUND

[0002] Microplastics and nanoplastics have become a new type of anthropogenic particulate pollutants, which have rapidly attracted the attention of the scientific community and the public. They are widely distributed in the global environment, not only penetrating into drinking water supply systems and food chains, but also raising concerns about their potential environmental effects and human health impacts. Compared with microplastics, nanoplastics often exhibit stronger biological toxicity 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 developing scientific management strategies.

[0003] Currently, the analysis methods for microplastics and nanoplastics include mass-based analysis, 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 analysis, including Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, and single particle inductively coupled plasma mass spectrometry (SP-ICP-MS). Raman spectroscopy utilizes the non-elastic scattering effect of microplastics to generate vibrational fingerprint spectra, and when combined with imaging techniques, it can provide chemical composition, concentration, and size information simultaneously.

[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, which enhance the spectral signal by shortening the distance between nanoplastic particles and SERS hotspots. On silver nanowire film SERS substrates, nanoplastics can be enriched and detected in situ, or high-sensitivity sensing can be achieved using silver nanoparticles coaggregation. In addition, nanoplastics can also obtain indirect responses through signal molecule labeling.

[0005] In the case of coexistence of microplastics and nanoplastics, accurate measurement of the mass concentration of nanoplastics requires high-quality spectral purity by eliminating the spectral interference of microplastics. SERS substrates with size-selective capability, such as structures in anodic aluminum oxide or piezoelectric nanowire bowls, are used to enrich nanoplastics, thereby preventing microplastic particles from depositing on the SERS substrate. In addition, by taking advantage of the difference in the electromigration behavior of PS nanoplastics of different sizes, PS nanoplastics smaller than a certain size can be selectively enriched and detected by controlling the electric adsorption time. In terms of data processing, the quantitative analysis of particles is different from that of small molecules, because the Raman and SERS response of plastic particles depends 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 use standard particles with the same composition and particle size as the measured particles to construct a calibration curve. In actual samples, the particle size distribution of microplastics is unknown and uneven, which makes accurate quantification of plastic particles a challenge in this field. SUMMARY

[0006] In view of the deficiencies of the prior art, the present application provides a method for quantitative analysis of micro-nano plastic particle mixture by Raman / SERS spectrum and slope matching strategy. SUMMARY:

[0008] The method of the present application enriches and quantitatively determines microplastics and nanoplastics greater than 500 nanometers by glass fiber membrane separation using Raman, establishes a series of quantitative curves between Raman spectral intensity and standard concentration of microplastics and nanoplastics of different sizes, and records their slopes; 50 nanometers to 500 nanometers of nanoplastics are enriched by nylon membrane and quantitatively determined by SERS using Ag NPs as substrate, KI as cleaning agent and coagulant, a series of quantitative curves between SERS spectral intensity and standard concentration of nanoplastics of different sizes are established, and their slopes are recorded; test the sample to be tested, establish the quantitative curve between the spectral intensity and the concentration of the microplastic and nanoplastic to be tested, obtain the slope of the quantitative curve, and match the slope of the quantitative curve of the particle to be tested with the quantitative curve of the standard plastic particle, so as to realize the quantitative detection of microplastic and nanoplastic particle pollutants.

[0009] The present application is realized by the following scheme:

[0010] A method for quantitative analysis of micro-nano plastic particle mixture by Raman / SERS spectrum and slope matching strategy, comprising the following steps:

[0011] (1) Using a glass fiber membrane with a pore size of 0.6-0.8 μm as a filter membrane, a filter device is used to filter a standard water sample containing microplastic and nanoplastic mixture, and a microplastic filter membrane with a particle size greater than 500 nanometers is obtained;

[0012] (2) using a filtering device with a nylon membrane with a pore size of 0.22 μm as a filter membrane to filter the water sample filtered in step (1), after the filtration is completed, Ag NPs and KI are added, under the physical interception and adsorption interception filtration, the nano-plastic, Ag NPs and KI are filtered together on the nylon membrane to obtain a 50-nanometer to 500-nanometer nano-plastic filter membrane;

[0013] (3) using a Raman spectrometer to collect Raman spectra of the micro-nano plastic particle pollutants on the micro-plastic filter membrane with a particle size greater than 500 nanometers, establishing a series of quantitative curves between the Raman spectrum intensity of micro-plastics and nano-plastics of different sizes and the standard concentration, and recording the slope;

[0014] (4) using a Raman spectrometer to collect SERS spectra of the nano-plastic particle pollutants on the 50-nanometer to 500-nanometer nano-plastic filter membrane, establishing a series of quantitative curves between the SERS spectrum intensity of nano-plastics of different sizes and the standard concentration, and recording the slope;

[0015] (5) testing the sample to be tested, establishing a quantitative curve between the spectrum intensity and the concentration of the micro-plastic and nano-plastic to be tested, obtaining the slope of the quantitative curve, and matching the quantitative curve slope of the particle to be tested with the quantitative curve of the standard plastic particle, so as to realize quantitative detection of the micro-plastic and nano-plastic particle pollutants.

[0016] According to the application, preferably, in step (1), the amount of the water sample to be tested is 0.1-50 mL / cm 2 .

[0017] According to the application, preferably, in step (1), the diameter of the glass fiber membrane is 12-15 mm.

[0018] According to the application, preferably, in step (1), the particle size of the micro-plastic obtained on the glass fiber membrane is 500 nm-5 μm.

[0019] According to the application, preferably, in step (2), the pore size of the nylon membrane is 0.22 μm, and the diameter is 12-15 mm.

[0020] According to the application, preferably, in step (2), the amount of Ag NPs is 2-4 mL.

[0021] According to the application, preferably, in step (2), the amount of KI is added to make the concentration reach 0.02-0.1 M.

[0022] Further preferably, in step (2), the amount of KI is added to make the concentration reach 0.06 M.

[0023] According to the application, preferably, in step (2), the particle size of the nano-plastic particles on the nylon membrane is 50-500 nm.

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

[0025] According to the present application, preferably, in step (2), the specific adding method of Ag NPs and KI is as follows: after the obtained nano-plastic particles are filtered and mixed with Ag NPs, KI solution is immediately added and mixed, and then incubated at room temperature for 10 min.

[0026] According to the present application, preferably, in step (1) and step (2), the sol or solution is filtered until no filtrate is produced.

[0027] According to the present application, preferably, in step (3) and step (4), the laser wavelength of the Raman spectrometer is 785 nm, 633 nm or 532 nm, and the laser power is 1-50 mW; the integral time of single-point Raman spectrum collection is 5-30 s.

[0028] According to the present application, preferably, in step (5), the slope matching strategy is as follows:

[0029] Assuming that the size of PS micro-plastic or PS nano-plastic in the unknown sample is unique,

[0030] 1) Obtain the spectral intensity of PS micro / nano-plastic by Raman and SERS;

[0031] 2) Assuming that the size of the unknown particle is "size 1", its concentration is calculated as "C1" using the linear equation derived from the size 1 standard PS plastic particle;

[0032] 3) Dilute the sample to C 1-1 to C 1-5 Five concentration levels, and analyze using Raman / SERS method;

[0033] 4) Draw a working curve of spectral response-concentration from C 1-1 to C 1-5 , and obtain "slope assumed size 1";

[0034] 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 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 application are as follows:

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

[0038] 2. The present application can simultaneously realize the concentration and enrichment of small-sized nanoplastics and SERS detection by filtering 50nm-500nm nanoplastics together with silver sol and KI onto a nylon membrane; the present application refers to the conventional analysis process of particulate matter in the environment, i.e. sampling, separation, enrichment and detection, and the analysis process can be simplified by the device of the present application; the present application can be used for the separation and enrichment of microplastic and nanoplastic mixture solutions by assembling different filter membranes; microplastics and nanoplastics above 500nm are separated and enriched by glass fiber membranes and quantitatively determined by Raman; a series of quantitative curves between the Raman spectral intensity and the concentration of standard microplastics and nanoplastics of different sizes are established, and their slopes are recorded; nanoplastics of 50nm-500nm are enriched by nylon membranes and quantitatively determined by SERS using Ag NPs as a substrate; a series of quantitative curves between the SERS spectral intensity and the concentration of standard nanoplastics of different sizes are established, and their slopes are recorded; for unknown samples, the quantitative curve slope of the particulate matter to be tested is matched with the quantitative curve of the standard plastic particles, thereby realizing accurate quantitative detection of microplastic and nanoplastic particulate pollutants.

[0039] 3. The method of the present application combines Raman / SERS spectral detection technology and slope matching strategies, thereby improving the quantitative accuracy of spectral data acquisition and data processing; Raman spectral analysis is performed on micro / nanoplastics above 500nm, and SERS spectral analysis is performed on nanoplastics below 500nm; this method minimizes the influence of spectral interference between microplastics and nanoplastics, thereby achieving more accurate spectral intensity measurement; regarding data processing, the slope matching strategy is used in external standard quantification to achieve more accurate quantification and provide average particle size information; for microplastics and nanoplastics of different particle sizes, a good linear relationship is established between microplastic / nanoplastic concentration and characteristic peak intensity; this system method is successfully demonstrated by analyzing micro / nanoplastics released from disposable PS cups; the present application retains the advantages of both technologies, including simple operation, low cost, high enrichment efficiency, high sensitivity, fast detection speed, water resistance, non-destructive, suitability for particulate matter of multiple particle sizes, and ability to provide fingerprint information; the present application can realize the detection of particulate matter with a particle size as low as 50nm; for concentrations as low as 10-4 The method can still achieve effective detection when the concentration of the particles is 0.1 g / L, and the accuracy of the measured concentration is 90%-110%; therefore, the method has higher sensitivity, a wider applicable particle size range and higher accuracy.

[0040] 4, The method has simple process, easy operation and repetition; meanwhile, the enrichment effect of the nano-plastics can be adjusted by adjusting the amount of the silver sol and KI, so that smaller nano-particles can be intercepted. It has high continuity and simplifies the operation process. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 The quantitative analysis process schematic diagram for Raman / SERS spectrum and slope matching strategy quantitative analysis of micro-nano plastic particle mixture;

[0042] Figure 2 The Raman spectrum of the same mass concentration and different size micro-nano plastics in experimental example 1;

[0043] Figure 3 The SERS spectrum of the same mass concentration and different size nano-plastics in experimental example 1;

[0044] Figure 4 The quantitative analysis of the mixed size nano-plastics in experimental example 3 using the slope matching strategy and the average size thereof;

[0045] Figure 5 The Raman spectrum of the actual sample PS micro-plastic in experimental example 4;

[0046] Figure 6 The SERS spectrum of the actual sample PS nano-plastic in experimental example 4;

[0047] Figure 7 The SEM image of the actual sample PS micro-plastic in experimental example 4;

[0048] Figure 8 The SEM image of the actual sample PS nano-plastic in experimental example 4; DETAILED DESCRIPTION

[0049] In order to more clearly illustrate the technical problems to be solved by the present application and the advantages of the present application, specific embodiments will be described in detail below, but the scope of the present application is not limited to this.

[0050] Unless otherwise specified, the experimental methods used in the examples are conventional methods; the reagents and equipment used, unless otherwise specified, are prior art and can be commercially available.

[0051] The filtration device and the Raman spectrometer are prior art equipment.

[0052] Example 1

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

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

[0055] (2) Using a filtering device with a nylon membrane with a pore size of 0.22 μm as a filtering membrane to filter the water sample filtered in step (1), and after filtering, adding Ag NPs and KI, under the action of physical interception and adsorption interception, nanoplastics, Ag NPs and KI are filtered together onto the nylon membrane to obtain nanoplastics with a particle size of 50 nanometers to 500 nanometers;

[0056] (3) Using a Raman spectrometer to collect Raman spectra of micro-nano plastic particle pollutants on the glass fiber membrane in step (1), establishing a series of quantitative curves between Raman spectrum intensity and standard concentration of microplastics and nanoplastics of different sizes, and recording the slope;

[0057] (4) Using a Raman spectrometer to collect SERS spectra of nanoplatic particle pollutants on the nylon membrane in step (2), establishing a series of quantitative curves between SERS spectrum intensity and standard concentration of nanoplastics of different sizes, and recording the slope;

[0058] (5) Testing the sample to be tested, establishing a quantitative curve between the spectrum intensity and the concentration of the microplastic and nanoplatic particles 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, so as to realize quantitative detection of microplastic and nanoplatic particle pollutants.

[0059] Experimental Example 1

[0060] (1) Preparation of microplastic and nanoplatic particle water sample to be tested: The microplastic and nanoplatic particle sample is prepared in the laboratory, and the prepared PS micro-nano plastic particle aqueous solution has a concentration of 0.1 g / L and particle sizes of 5 μm, 3 μm, 1 μm, 800 nm, 700 nm, and 600 nm, and a concentration of 0.04 g / L and particle sizes of 500 nm, 400 nm, 300 nm, 200 nm, 100 nm, and 50 nm.

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

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

[0063] (4) The filter material after enrichment is taken out of the filter device and detected by a Raman spectrometer with an excitation wavelength of 785 nm, a laser power of 50 mW, and an integration time of 30 s. Raman spectroscopy is used to analyze micro-nano plastics larger than 500 nm, and SERS spectroscopy is used to analyze nano plastics smaller than 500 nm.

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

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

[0066]

[0067]

[0068] Experimental Example 2

[0069] The accuracy analysis of micro-nano plastic quantification includes the following steps:

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

[0071] (2) Take 1 mL of PS micro-nano plastic particle aqueous solution with a concentration of 0.04 g / L and a particle size of 500 nm, 400 nm, 300 nm, 200 nm, 100 nm, 50 nm in step (1), and filter the water sample to be tested by adding 3 mL of Ag NPs and 1 mL of KI (final concentration 0.06 M) using a nylon membrane with a pore size of 0.22 μm as the filter membrane.-3 -0.1 g / L and particle size of 5 pm, 3 pm, 1 pm, 800 nm, 700 nm, 600 nm PS micro-nano plastic particles 1 mL, and the water sample to be tested was filtered by using a glass fiber membrane (pore size 1 pm).

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

[0073] (4) The filter material after enrichment was taken out of the filter device and detected by a Raman spectrometer with an excitation wavelength of 785 nm, a laser power of 50 mW, and an integration time of 30 s. Raman spectroscopy was used to analyze micro-nano plastics with a particle size of 500 nm or more, and SERS spectroscopy was used to analyze nano plastics with a particle size of less than 500 nm. A series of quantitative curves of spectral intensity and concentration of standard micro-nano plastics with different sizes were established.

[0074] (5) For a PS micro / nano plastic with a known size, different size Raman / SERS quantitative curves were used to analyze it, and the relative error between the 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 the appropriate size of the quantitative curve, the relative error of the measured concentration is the smallest, and the accuracy is the highest. For example, when the particle size to be measured is 5 pm, only the standard size of 5 pm is used, the relative error is 2%, and the relative error is greater than 60% when other size standard curves in the table are used.

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

[0077]

[0078] Experimental Example 3

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

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

[0081] (4) The filter material after enrichment was taken out of the filter device and detected by a Raman spectrometer with an excitation wavelength of 785 nm, a laser power of 50 mW and an integration time of 30 s to perform SERS spectral analysis on the nano-plastic to obtain a series of SERS spectral intensities at different concentrations.

[0082] (5) The slope matching strategy was used for analysis, assuming that the size of PS micro-plastic or PS nano-plastic in the unknown sample was unique, which can be described as follows: Figure 1 ):

[0083] 1) Obtain the spectral intensity of PS micro / nano-plastic by Raman and SERS;

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

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

[0086] 4) Draw 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 particle 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 method of Raman / SERS spectrum combined with slope matching strategy for mixed sample size analysis is shown in Figure 4 , the size of PS nano-plastic measured by this method is 300 nm, with an accuracy of 100%; the concentration is 9.53 x 10 -3 , with an accuracy of 95.3%.

[0090] Experimental Example 4

[0091] (1) Preparation of the test water sample of the actual sample microplastics and nanoplastics mixture particles: After cutting disposable PS plastic cups into fragments and placing them in a 20 mL glass vial, 20 mL of deionized water was added. After oscillation on a shaker for 36 h, the solution was concentrated to 4 mL to obtain a microplastics and nanoplastics mixture particle solution. The mixed particle solution was diluted by different multiples to obtain microplastics and nanoplastics mixture particle solutions with different concentrations.

[0092] (2) 1 mL of the microplastics and nanoplastics mixture particle solution with different concentrations in step (1) was filtered to separate and enrich the microplastics and nanoplastics particle pollutants above 500 nm using a glass fiber membrane as the filter membrane. The filtrate was filtered using a nylon membrane to enrich the fraction of 50 nm-500 nm nanoplastics particle pollutants by adding 3 mL of Ag NPs and 1 mL of KI (final concentration of 0.06 M) to the test water sample.

[0093] (3) After the separation and enrichment were completed, the filter membrane material was taken out of the filter 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. The micro- and nanoplastics on the glass fiber membrane collected Raman spectra, and the nanoplastics on the nylon membrane collected SERS spectra. Finally, the size of the micro- and nanoplastics in the actual sample was analyzed using the slope matching strategy.

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

Claims

1. A method for quantitative analysis of micro / nano plastic particle mixtures using Raman / SERS spectroscopy and slope matching strategy, comprising the following steps: (1) A standard water sample containing a mixture of microplastics and nanoplastics was filtered using a filtration device with a glass fiber membrane with a pore size of 0.6-0.8 μm as the filter membrane to obtain a microplastic filter membrane with a particle size greater than 500 nanometers. (2) The water sample filtered in step (1) was filtered using a filtration device with a 0.22 μm nylon membrane as the filter membrane. After filtration, Ag NPs and KI were added. Under the action of physical interception and adsorption interception filtration, the nanoplastic, Ag NPs and KI were filtered together onto the nylon membrane to obtain a 50 nm to 500 nm nanoplastic filter membrane. (3) Raman spectrometry was used to collect the Raman spectra of micro- and nano-plastic particles on microplastic filter membranes with a particle size greater than 500 nanometers. A series of quantitative curves between the Raman spectral intensity of microplastics and nanoplastics of different sizes and the standard concentration were established and their slopes were recorded. (4) Use Raman spectrometer to collect SERS spectra of nanoplastic particulate pollutants on nanoplastic filter membranes ranging from 50 nm to 500 nm, establish a series of quantitative curves between the SERS spectral intensity of nanoplastics of different sizes and the standard concentration, and record their slopes. (5) Test the sample to be tested, establish a quantitative curve between the spectral intensity and concentration of the microplastics and nanoplastics to be tested, obtain the slope of the quantitative curve, match the slope of the quantitative curve of the particulate matter to be tested with the quantitative curve of the standard plastic particles, so as to realize the quantitative detection of microplastics and nanoplastic particulate pollutants. In steps (3), (4), and (5), the slope matching strategy is as follows: Assuming the size of PS microplastics or PS nanoplastics in the unknown sample is unique, 1) Obtain the spectral intensity of PS micro / nanoplastics using Raman and SERS methods; 2) Assuming the size of the unknown particles is size 1, its concentration is calculated as C1 using a 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 were analyzed using the Raman / SERS method; 4) Using C 1-1 To C 1-5 The spectral response-concentration curve was plotted to obtain the slope with an assumed size of 1. 5) Compare the assumed slope size 1 with the standard slope 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, the size is re-assumed until the best-fit slope is determined. 6) Calculate the mass concentration of the sample using the best-fit size and its linear equation.

2. The method according to claim 1, characterized in that, In step (1), the volume of the water sample to be tested is 0.1-50 mL / cm³. 2 The diameter of the glass fiber membrane is 12-15 mm, and the microplastic particles obtained on the glass fiber membrane have a size of 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 50-500 nm.

6. The method according to claim 1, characterized in that, In step (2), the specific method for adding Ag NPs and KI is as follows: After adding Ag NPs to the filtered nanoplastic particles and mixing them, immediately add KI solution, mix well, and incubate at room temperature for 10 minutes.

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

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

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