A qualitative and quantitative detection method for micro / nanoplastics in water based on solid phase microextraction combined with GC-MS

Abstract

The present invention provides a method for qualitative and quantitative detection of micro- and nanoplastics in water based on solid-phase microextraction (SPME) combined with GC-MS, relating to the technical field of micro- and nanoplastic detection. The method involves immersing an SPME fiber in a water sample to directly extract PMMA and PVDC micro- and nanoplastics. After extraction, the samples are directly fed into a GC-MS for thermal desorption and analysis. By combining SPME with GC-MS techniques, the present invention enables the detection of PMMA and PVDC micro- and nanoplastics in water samples. The detection method is simple, highly sensitive, and accurate, while also being environmentally friendly.

Description

Technical Field

[0001] The present invention relates to the technical field of micro / nanoplastic detection, and in particular to a method for qualitative and quantitative detection of micro / nanoplastics in water based on solid phase microextraction combined with GC-MS. Background Art

[0002] Microplastics are generally defined as plastic fibers, particles or films with a particle size of less than 5mm, and nanoplastics are defined as those with a size of less than 0.001mm. They have become a hot new pollutant and have quickly become a key area of ​​scientific research. These micro / nanoplastic particles are difficult to remove from wastewater treatment systems due to their small particle size and hydrophobicity. They are widely present in water, air, soil and food around the world, raising concerns about their impact on human health. In order to fully address these issues, it is necessary to monitor reliable concentration information of microplastics in the environment. However, micro / nanoplastic particles are extremely complex and diverse in terms of size, shape, polymer type, density, surface properties, etc. The particle concentrations in different environmental media can vary by multiple orders of magnitude, which highlights the importance of appropriate detection methods for the chemical identification, quantification and characterization of microplastics and nanoplastics.

[0003] Currently, the main qualitative and quantitative methods for micro- and nanoplastics include infrared spectroscopy, Raman spectroscopy, thermal decomposition-gas chromatography-mass spectrometry, and thermogravimetry-differential scanning calorimetry. Among the numerous micro- and nanoplastic analysis methods, thermal decomposition-gas chromatography-mass spectrometry utilizes high temperatures to induce the pyrolysis of micro- and nanoplastics, releasing small-molecule monomers and surface attachments, which can then be used for qualitative and quantitative analysis using gas chromatography-mass spectrometry. However, this method requires high experimental conditions, and the pyrolysis products are complex and variable. Especially for the pyrolysis analysis of complex matrix samples, the diversity of pyrolysis products and other organic matter in the sample can easily interfere with the target analytes, limiting its application in the analysis of low-level micro- and nanoplastics. Furthermore, the detection of micro- and nanoplastics in environmental water samples using this method requires filtering the micro- and nanoplastic particles, transferring them to a filter membrane, and even further extraction and concentration using organic solvents to improve analytical sensitivity. These cumbersome sample pretreatment steps inevitably lead to contamination of the micro- and nanoplastics, resulting in uncertain analytical results. Therefore, it is necessary to develop a new sample processing technology combined with GC-MS to analyze micro / nanoplastics in water samples.

[0004] Solid-phase microextraction (SPME), a sample pretreatment technology proposed by Professor Janusz Pawliszyn, integrates four functions: sampling, extraction, concentration, and injection. Simply put, SPME is simple to operate, requires no extraction solvent, and can be used for online or in vivo sampling, automated, and direct desorption within instrumental analysis systems. The technology has been widely applied in environmental analysis, the food industry, pharmaceutical quality control, clinical research, and other fields, demonstrating its excellent performance. Summary of the Invention

[0005] In light of this, the present invention provides a method for qualitative and quantitative detection of micro- and nanoplastics in water based on solid-phase microextraction (SPME) combined with GC-MS. An SPME fiber is immersed in a water sample to directly extract micro- and nanoplastics. After extraction, the sample is directly fed into the GC-MS for thermal desorption and analysis. By combining SPME with GC-MS techniques, the present invention enables the detection of micro- and nanoplastics in water samples. This detection method is simple, highly sensitive, and accurate, while also being environmentally friendly.

[0006] The present invention is a method for qualitative and quantitative detection of micro / nanoplastics in water based on solid phase microextraction combined with GC-MS, comprising the following steps:

[0007] Step (1), preparing a water sample to be tested, wherein the water sample contains micro / nanoplastics;

[0008] Step (2), extracting the water sample to be tested with the SPME fiber;

[0009] Step (3): After the extraction is completed, the SPME fiber is removed from the water body and immediately inserted into the GC-MS injection port for thermal decomposition and analysis; the thermal cracking products of the micro / nanoplastics are analyzed using the Scan mode to calculate the content of the micro / nanoplastics in the water body.

[0010] Preferably, the micro / nano plastics in step (1) include but are not limited to any one or two of PMMA and PVDC.

[0011] Preferably, the water sample to be tested in step (1) is any one of mineral water and tea bag water.

[0012] Preferably, the SPME fiber in step (2) is any one of PDMS / DVB SPME coated fiber, PDMS SPME coated fiber, PDMS / DVB / CAR SPME coated fiber, carbon nitride SPME coated fiber, hydroxylated multi-walled carbon nanotube SPME coated fiber, and nitrogen-doped porous carbon SPME coated fiber.

[0013] Among them, PDMS / DVB SPME coated fiber, PDMS SPME coated fiber, and PDMS / DVB / CAR SPME coated fiber were all purchased from the market; carbon nitride SPME coated fiber, hydroxylated multi-walled carbon nanotube SPME coated fiber, and nitrogen-doped porous carbon SPME coated fiber were homemade.

[0014] The PDMS / DVB was purchased from Shanghai Xintuo Analytical Instrument Technology Co., Ltd., model SPME-C-02, specification 55 μm; the PDMS was purchased from Shanghai Xintuo Analytical Instrument Technology Co., Ltd., model SPME-C-01, specification 75 μm; the PDMS / DVB / CAR was purchased from Shanghai Xintuo Analytical Instrument Technology Co., Ltd., model SPME-C-04, specification 75 μm.

[0015] The carbon nitride SPME coated fiber process is as follows: (1) First, carbon nitride material is synthesized by pyrolysis treatment of urea. The specific steps are as follows: weigh 15g of urea into a 100mL crucible and seal it with tin foil. Then the sample is placed in a muffle furnace, heated from 30°C to 550°C at a rate of 5°C / min, and maintained for 4h. After the reaction system is cooled to room temperature, a yellow solid is obtained, which is the carbon nitride material, and carbon nitride powder is obtained by grinding in an agate mortar. (2) Then, the stainless steel wire is cleaned and pretreated. The specific steps are as follows: the stainless steel wire with a diameter of about 130μm is cut into a metal wire segment with a length of about 10cm, and ultrasonically cleaned for 10min using hydrochloric acid solution (3mol / L), sodium hydroxide solution (3mol / L) and anhydrous ethanol solution in sequence. (3) Using stainless steel wire as the substrate and Sylgard 184 as the main body and curing agent (10:1) as the adhesive, a carbon nitride SPME coating was prepared and assembled into a solid phase microextraction empty needle, which was then placed in the GC-MS injection port and aged for 10 minutes to finally obtain a carbon nitride SPME coated fiber.

[0016] The process for preparing the hydroxylated multi-walled carbon nanotube SPME-coated fiber is as follows: hydroxylated multi-walled carbon nanotubes purchased from Aladdin are first finely ground in an agate mortar to obtain a powder. Next, stainless steel wire is cleaned and pretreated. Finally, the stainless steel wire is used as the substrate and combined with an adhesive to prepare the hydroxylated multi-walled carbon nanotube SPME-coated fiber.

[0017] The process of nitrogen-doped porous carbon SPME coated fiber is as follows: (1) First, nitrogen-doped porous carbon material is prepared by pyrolyzing and modifying grapefruit peel under nitrogen atmosphere. The specific steps are as follows: after removing the outer yellow layer of grapefruit peel, it is cut into small pieces, placed in a freeze dryer for drying, and then ground into powder. Then, 10g of grapefruit peel powder is weighed and thoroughly mixed with 50mL of urea (1M) and 10g of sodium hydroxide (5M) aqueous solution, and dried in an oven. Next, it is placed in a quartz tube furnace, heated to 800℃ at a heating rate of 5℃ / min and maintained for heat treatment for 2h. Finally, the obtained powder is washed with hydrochloric acid solution (0.1M) and deionized water until neutral, dried to obtain nitrogen-doped porous carbon material, and ground to obtain nitrogen-doped porous carbon powder. (2) Then, the stainless steel wire is cleaned and pretreated; (3) Then, the stainless steel wire is used as the substrate and combined with an adhesive to prepare nitrogen-doped porous carbon SPME coated fiber.

[0018] Preferably, the extraction temperature in step (2) is 30-70° C., the extraction time is 10-60 min, and the rotation speed during the extraction process is 300 rpm.

[0019] More preferably, the extraction temperature in step (2) is 60° C., the extraction time is 50 min, and the rotation speed during the extraction process is 300 rpm.

[0020] Preferably, the temperature of the injection port in step (3) is 240-360° C.; and the thermal decomposition time is 3-12 minutes.

[0021] More preferably, the temperature of the injection port in step (3) is 320° C.; and the thermal desorption time is 6 minutes.

[0022] In a specific embodiment of the present invention, PMMA and PVDC micro / nanoplastics in actual water samples are measured. Before the determination using the method of the present invention, a standard curve needs to be drawn and then the standard curve equation is calculated. The specific method is:

[0023] S1. Preparation of standard stock solutions: Weigh PMMA and PVDC micro / nanoplastics separately and disperse them in ultrapure water to obtain PMMA and PVDC standard stock solutions, as well as PMMA / PVDC mixed micro / nanoplastics standard stock solutions; the size of the PMMA micro / nanoplastics is 50 nm, and the size of the PVDC micro / nanoplastics is 5 μm; the concentration of the PMMA standard stock solution is 1000 mg / L, the concentration of the PVDC standard stock solution is 1000 mg / L, and the concentration of the PMMA / PVDC mixed micro / nanoplastics standard stock solution is 500 mg / L.

[0024] S2. Accurately pipette the 500 mg / L PMMA / PVDC mixed micro / nanoplastic standard stock solution in step S1 into a headspace bottle containing 10 mL of deionized water to obtain a concentration of 50 μg L -1 The spike solution was prepared and the SPME fiber was immersed in the spike solution for extraction.

[0025] S3. After the extraction is completed, the SPME fiber is immediately inserted into the GC-MS injection port for thermal decomposition and analysis. The thermal decomposition products of PMMA micro / nanoplastics, methyl methacrylate, and the thermal decomposition products of PVDC micro / nanoplastics, m-dichlorobenzene and trichlorobenzene, are qualitatively analyzed using the Scan mode. Appropriate markers are selected based on the total ion current chromatogram and mass spectrum displayed by the GC-MS to establish the SIM method.

[0026] S4. Dilute the standard stock solution in step S1 with ultrapure water to obtain a series of standard dispersion solutions; the concentrations of the series of standard dispersion solutions are 100 mg / L, 50 mg / L, 10 mg / L, 5 mg / L, 1 mg / L, and 0.5 mg / L.

[0027] S5. According to the SIM method established in step S3, the micro / nanoplastics in the series of standard dispersions are quantitatively analyzed and detected; a standard curve is drawn with the concentration of the micro / nanoplastics standard dispersion as the horizontal axis and the peak area of ​​the marker of the PMMA / PVDC mixed micro / nanoplastics as the vertical axis, and the standard curve equation is calculated.

[0028] S6. Use the above-established method to perform qualitative and quantitative extraction analysis of micro / nanoplastics in actual water samples.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] (1) Simple operation, low cost, and simple equipment requirements;

[0031] (2) No organic solvents are required, green and environmentally friendly;

[0032] (3) This paper proposes for the first time the application of SPME technology to the detection and analysis of micro / nanoplastics, achieving the separation and quantitative determination of micro / nanoplastics at the μg / L level and successfully applying it to actual water samples;

[0033] (4) High enrichment multiple, complete analysis in one step. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Schematic diagram of the process of the present invention for qualitative and quantitative analysis of PMMA and PVDC micro / nanoplastics in water samples based on solid phase microextraction combined with gas chromatography-mass spectrometry in one step;

[0035] Figure 2 This is a scanning electron microscope image of the homemade nitrogen-doped porous carbon SPME coated fiber used in the present invention to extract micro / nanoplastic PMMA (3μm) in water;

[0036] Figure 3 This is a gas chromatography-mass spectrometry total ion current diagram of the method for qualitative and quantitative analysis of PMMA and PVDC micro / nanoplastics in water samples based on solid phase microextraction combined with gas chromatography-mass spectrometry in one step of the present invention. DETAILED DESCRIPTION

[0037] The present invention will be further described below with reference to the embodiments.

[0038] Example 1

[0039] A qualitative and quantitative detection method for PMMA and PVDC micro / nanoplastics in mineral water based on solid phase microextraction combined with GC-MS, the steps are as follows:

[0040] (1) Draw the standard curve and calculate the standard curve equation:

[0041] S1. Preparation of standard stock solutions: Weigh 0.01 g of PMMA and PVDC micro / nanoplastics respectively and disperse them in 10 mL of ultrapure water to obtain 1000 mg / L concentrations of PMMA and PVDC standard stock solutions. The concentration of the PMMA / PVDC mixed micro / nanoplastics standard stock solution is 500 mg / L. The size of the PMMA micro / nanoplastics is 50 nm, and the size of the PVDC micro / nanoplastics is 5 μm.

[0042] S2. Accurately pipette the 500 mg / L PMMA / PVDC mixed micro / nanoplastic standard stock solution in step (1) into a 20 mL headspace bottle containing 10 mL of deionized water to obtain a spiked solution with a concentration of 50 μg L -1 The solution was placed in a water bath at 60°C for extraction, with a rotation speed of 300 rpm to speed up the extraction process. The homemade nitrogen-doped porous carbon SPME coated fiber was then immersed in the solution for extraction for 50 minutes.

[0043] S3. After the extraction is completed, the SPME fiber is immediately inserted into the GC-MS injection port for thermal decomposition and analysis. The temperature of the injection port is 320°C; the thermal decomposition time is 6 minutes; the thermal decomposition products of PMMA and PVDC micro / nanoplastics are qualitatively analyzed using the Scan mode, and appropriate markers are selected based on the total ion current chromatogram and mass spectrum displayed by GC-MS, and a SIM method is established for standby use; the content of PMMA / PVDC mixed micro / nanoplastics can be qualitatively analyzed based on the retention time, qualitative ion, and structural formula of the PMMA and PVDC micro / nanoplastic markers.

[0044] The marker of PMMA micro / nanoplastics is methyl methacrylate, whose main characteristic ions are 41, 69, 85, and 100. 69 is selected as the quantitative ion. The retention time of methyl methacrylate is 2.79 min, and its structural formula is C5H8O2.

[0045] There are two markers for micro / nanoplastic PVDC. The first is m-dichlorobenzene with the structural formula C5H4Cl2. Its characteristic ions are mainly 75, 111, 146, and 207, and the final quantitative ion selected is 146. The second is trichlorobenzene with the structural formula C5H3Cl3. Its main characteristic ions are 85, 109, 145, and 180, and the quantitative ion selected is 180. The retention times of the two markers are 7.49 and 8.79 min, respectively.

[0046] S4. Dilute the standard stock solution in step S1 with ultrapure water to obtain a series of standard dispersion solutions; the concentrations of the series of standard dispersion solutions are 100 mg / L, 50 mg / L, 10 mg / L, 5 mg / L, 1 mg / L, and 0.5 mg / L.

[0047] S5. Quantitatively analyze and detect the micro / nanoplastics in the series of standard dispersions using the SIM method established in step S3. Plot a standard curve using the concentration of the standard dispersion as the horizontal axis and the peak area of ​​the PMMA / PVDC mixed micro / nanoplastics marker as the vertical axis, and then calculate the standard curve equation. Immersion extraction was used throughout the experiment, using the same extraction conditions as in step S2. The analytical performance results for the PMMA / PVDC mixed micro / nanoplastics are shown in Table 1.

[0048] Table 1 Analytical properties of PMMA / PVDC mixed micro / nano plastics

[0049]

[0050] As can be seen from Table 1, the established method has a good –1 The concentration range showed a good linear relationship (R 2 ≥0.9960), and the lower detection limit was 0.0004–0.0183 μg L –1 , good reproducibility RSD≤11.9.

[0051] (2) Determination of PMMA and PVDC microplastics in mineral water:

[0052] Step (1), preparing a water sample to be tested, which is mineral water commonly purchased from the market, wherein the water sample contains micro / nanoplastics;

[0053] Step (2), extracting the water sample to be tested with the SPME fiber, and analyzing the content of PMMA / PVDC mixed micro / nanoplastics in the water sample; accurately pipetting 10 mL of mineral water into the extraction bottle, and then placing the bottle in a water bath at a speed of 300 rpm and 60° C. for extraction for 50 min;

[0054] Step (3): After the extraction is completed, the SPME fiber is immediately inserted into the GC-MS injection port at a temperature of 320° C. for thermal desorption for 6 minutes; the SIM mode is used for measurement, and the measured peak area is substituted into the standard curve to calculate the content of PMMA / PVDC mixed micro / nanoplastics in the mineral water;

[0055] Add PMMA / PVDC mixed micro / nano plastic (5 μg L -1 The experiment was repeated three times in parallel and the precision was calculated. The results are shown in Table 2.

[0056] The schematic flow chart of the method for qualitative and quantitative analysis of PMMA and PVDC micro / nanoplastics in water samples based on solid phase microextraction combined with gas chromatography-mass spectrometry in one step is shown in the figure. Figure 1 .

[0057] Example 2

[0058] A method for qualitative and quantitative detection of PMMA and PVDC micro / nanoplastics in tea bag water based on solid phase microextraction combined with GC-MS, comprising the same steps as in Example 1, except that in Example 2, tea bag water is used instead of mineral water. The tea bag water is prepared as follows: first, a commercially available green tea bag is placed in a clean glass beaker, hot water is added, and the beaker is covered with a glass slide, and the beaker is allowed to cool to room temperature.

[0059] The analysis results and recovery rates of PMMA / PVDC mixed micro / nanoplastics in actual water samples are shown in Table 2.

[0060] Table 2 Analysis results and recovery rates of PMMA / PVDC mixed micro / nanoplastics in actual water samples

[0061]

[0062] As shown in Table 2, the established method was successfully applied to actual water samples, with spiked recoveries ranging from 87.15% to 109.48%. This method is simple to operate and low-cost, enabling the analysis and detection of various micro- and nanoplastics in complex environmental samples. Furthermore, the present invention provides a new approach to detecting micro- and nanoplastic environmental pollution, broadens the application of solid-phase microextraction technology in micro- and nanoplastic detection, and overall improves the accuracy of micro- and nanoplastic detection.

[0063] The scanning electron micrograph of PMMA (3 μm) micro / nano plastics extracted from water using a self-made nitrogen-doped porous carbon SPME coating is shown in the figure. Figure 2 ,from Figure 2 It can be seen that PMMA microplastic particles have been successfully extracted on the surface of the nitrogen-doped porous carbon SPME coating, which effectively proves the feasibility of this method.

[0064] Figure 3 This is a gas chromatography-mass spectrometry total ion chromatogram (GC-MS) of the present invention's method for the qualitative and quantitative analysis of PMMA and PVDC micro / nanoplastics in water samples using solid-phase microextraction (SPME) combined with GC-MS in one step. The extraction time was 50 minutes, the extraction temperature was 60°C, the inlet desorption temperature was 320°C, and the desorption time was 6 minutes. The concentration of PMMA / PVDC mixed micro / nanoplastics in the solution was 5 mg / L. The three thermal decomposition products, methyl methacrylate, m-dichlorobenzene, and trichlorobenzene, are shown in the figure, with retention times of 2.79, 7.49, and 8.79 minutes, respectively.

[0065] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for qualitative and quantitative detection of micro / nanoplastics in water based on solid phase microextraction combined with GC-MS, characterized in that: The following steps are involved: Step (1), preparing a water sample to be tested, wherein the water sample contains micro / nanoplastics; Step (2), extracting the water sample to be tested with the SPME fiber; After step (3) extraction is completed, the SPME fiber is removed from the water body and immediately inserted into the GC-MS injection port for thermal decomposition and analysis; the thermal decomposition products of the micro / nanoplastics are analyzed using the Scan mode to calculate the content of the micro / nanoplastics in the water body; The extraction temperature of step (2) is 30-70°C, the extraction time is 10-60 min, and the rotation speed of the extraction process is 300 rpm; The temperature of the injection port in step (3) is 240-360°C; the thermal desorption time is 3-12 min; The SPME fiber in step (2) is a nitrogen-doped porous carbon SPME coated fiber, and the nitrogen-doped porous carbon SPME coated fiber process is as follows: (1) After removing the outer yellow layer of grapefruit peel, cut it into small pieces, place it in a freeze dryer for drying, and then grind it into powder; then weigh 10g of grapefruit peel powder and fully mix it with 50mL of urea and 10g of sodium hydroxide aqueous solution, and dry it in an oven; then place it in a quartz tube furnace, heat it to 800℃ at a heating rate of 5℃ / min and keep it for 2h; finally, the obtained powder is washed with hydrochloric acid solution and deionized water until it is neutral, and then dried to obtain nitrogen-doped porous carbon material, which is then ground to obtain nitrogen-doped porous carbon powder; (2) Cleaning and pretreatment of stainless steel wire; (3) Using stainless steel wire as substrate and adhesive to prepare nitrogen-doped porous carbon SPME coated fiber; In the step (3), the micro / nano plastics are PMMA and PVDC; in the thermal cracking products, methyl methacrylate is used as a marker of PMMA micro / nano plastics; and m-dichlorobenzene and trichlorobenzene are used as markers of PVDC micro / nano plastics.

2. The method for qualitative and quantitative detection of micro / nanoplastics in water based on solid phase microextraction combined with GC-MS according to claim 1, characterized in that: The water sample to be tested in step (1) is any one of mineral water and tea bag water.

3. The method for qualitative and quantitative detection of micro / nanoplastics in water based on solid phase microextraction combined with GC-MS according to claim 1, characterized in that: The extraction temperature in step (2) is 60° C., the extraction time is 50 min, and the rotation speed during the extraction process is 300 rpm.

4. The method for qualitative and quantitative detection of micro / nanoplastics in water based on solid phase microextraction combined with GC-MS according to claim 1, characterized in that: The temperature of the injection port in step (3) is 320°C; the thermal desorption time is 6 minutes.

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