A method for analyzing microplastics in plant tissues by high-temperature anaerobic heating-thermal cracking gas chromatography-mass spectrometry

Abstract

The present application relates to a kind of high-temperature anaerobic heating-thermal pyrolysis gas chromatography analysis method of microplastics in plant tissue, belong to microplastics detection technical field.The method is by being carried out to plant tissue without plastic pretreatment, then heated to 350 ℃~400 ℃ constant temperature is carried out anaerobic heat treatment, again the sample obtained by anaerobic heat treatment is detected and analyzed using thermal pyrolysis-gas chromatography-mass spectrometer realizes.350 ℃~400 ℃ is the best pyrolysis temperature interval of the main component of plant tissue, carry out anaerobic heat treatment in the temperature range can effectively destroy the glycosidic bond of cellulose and hemicellulose and the aromatic ring structure of lignin in plant tissue, make dense plant tissue completely broken, degradation into small molecule gaseous substance, with gas discharge, while, microplastics can keep stable and avoid being cracked and lost, realize the good separation of matrix and microplastics.Preferably, it can also be added to the sample after anaerobic heat treatment Fenton reagent treatment and / or adding dilute acid solution to dissolve and remove impurities, then again using thermal pyrolysis-gas chromatography-mass spectrometer detection and analysis, can more thoroughly remove organic matter, realize better detection effect.

Description

Technical Field

[0001] This invention relates to a method for analyzing microplastics in plant tissues using high-temperature anaerobic heating-pyrolysis gas chromatography-mass spectrometry, belonging to the field of microplastic detection technology. Background Technology

[0002] Microplastics refer to plastic particles with a diameter of less than 5 millimeters. As a globally distributed persistent pollutant, they have a wide range of sources, including the degradation of plastic products, industrial emissions, textile wear and tear, and agricultural film residues, and have become one of the most serious environmental problems of the 21st century.

[0003] Plants, as a core component of terrestrial ecosystems, can absorb microplastics from the soil through their roots or from the atmosphere through their leaf stomata. These microplastics are then transported through vascular tissues and accumulate in various parts of the plant. This not only inhibits root water conductivity and reduces photosynthetic efficiency, causing oxidative damage and affecting normal plant growth and development, but also leads to their transmission through the food chain. The chemical additives they carry and the pollutants adsorbed on their surfaces may also cause health problems in humans, such as endocrine disruption and immunosuppression. Therefore, the precise extraction and analysis of microplastics from plant tissues has significant application value and practical implications in environmental science, ecological protection, and food safety, and is one of the core directions of current microplastic pollution research.

[0004] Currently, the detection of microplastics in plant tissues mainly involves two core steps: "sample pretreatment (organic matter removal, microplastic extraction)" and "qualitative and quantitative analysis of microplastics." Existing technologies have developed various detection schemes around these two steps, but all have significant shortcomings, making it difficult to achieve accurate and efficient detection of microplastics in plants. Specific problems are as follows: (1) Pretreatment of microplastics in plant tissues mainly uses chemical digestion methods, which are currently the most widely used methods for microplastic extraction. The core principle is to use chemical reagents to destroy organic matter such as cellulose, protein, and chlorophyll in plant tissues, thereby separating microplastics from the matrix. Chemical digestion methods mainly include strong acid digestion, strong alkali digestion, Fenton oxidation, and stepwise digestion.

[0005] While strong acid digestion methods (such as using a 50% HNO3 / HCl / HF mixture) can achieve organic matter removal rates of over 95%, they easily alter the functional groups on the surface of microplastics and cause particle breakage, leading to lower detection results. Furthermore, high concentrations of strong acid can introduce secondary contamination, interfering with the accuracy of subsequent tests. Strong alkali digestion methods (such as potassium hydroxide solution) have a significant degradation effect on biodegradable plastics such as polylactic acid (PLA) and polyhydroxyalkanoates (PHA) at 40℃~50℃. At 50℃, the mass loss of PHA and PLA can reach 40%, accompanied by significant surface corrosion. Moreover, reagents and consumables can easily introduce exogenous microplastic contamination, further affecting detection accuracy. Fenton oxidation and its derivative step-by-step digestion methods (such as hydrogen peroxide-based primary digestion + enzymatic digestion + Fenton reagent-enhanced digestion) attempt to balance organic matter removal and microplastic retention, achieving organic matter removal rates of over 90% and microplastic recovery rates of over 85%. However, these methods are cumbersome, complex, and still require the use of multiple chemical reagents, posing potential risks of reagent residues and exogenous contamination. Furthermore, they still have a slight degradation effect on some microplastics, making them unsuitable for large-scale sample testing.

[0006] (2) Qualitative and quantitative analysis of plant tissue microplastics is mainly divided into two categories: microscopic spectroscopy and thermal pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS). Among them, traditional microscopic spectroscopy (including optical microscopy, microscopic infrared spectroscopy, etc.) was the mainstream detection method in the early days. The core principle is to observe the morphology and size of microplastics through a microscope and combine it with spectral characteristics for qualitative analysis. However, its limitations are very prominent: the detection limit of conventional microscopic infrared spectroscopy is about 1 μm, which cannot effectively detect nanoscale microplastics with a particle size of less than 100 nm. It needs to be combined with atomic force microscopy to achieve this, which greatly increases the technical cost and operational complexity. At the same time, the characteristic peaks of plant matrix lysis products (such as proteins and humic acids) are easy to overlap with the characteristic peaks of microplastics, making it difficult to completely eliminate interference, resulting in large qualitative and quantitative errors and low detection efficiency, which cannot achieve rapid detection of batch samples. A study published in Nature by Professor Wang Lei's research group at Nankai University in collaboration with the Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, also points out that traditional microspectroscopy cannot provide information on the spatial distribution of microplastics within plant tissues, and its sensitivity for detecting low concentrations of microplastics is insufficient.

[0007] Pyrolysis gas chromatography-mass spectrometry (Py-GC-MS) is a microplastic detection technique that has emerged in recent years. Its core advantage lies in its reliance on characteristic pyrolysis products of microplastics for qualitative and quantitative analysis, eliminating the need for complex chemical digestion processes. It also boasts high detection sensitivity and can accurately identify various types of microplastics. Related studies have confirmed that this method can achieve accurate quantification of polystyrene (PS) microplastics in plants, with a detection limit as low as 0.3 μg / g and a recovery rate of 64.8%–102%. However, when this method is directly applied to the detection of microplastics in plant tissues, it faces a core technical bottleneck: organic matter such as cellulose, polysaccharides, and oils that are not removed from plant tissues will generate a large number of pyrolysis products during the thermal pyrolysis process. These products overlap with the peaks of the characteristic pyrolysis products of microplastics, which not only mask the characteristic peaks of microplastics, leading to qualitative misjudgment and inaccurate quantification, but also contaminate the pyrolysis tube and chromatographic column, affecting the subsequent detection work. As pointed out in the article "Assessing the Efficacy of Pyrolysis–Gas Chromatography–MassSpectrometry for Nanoplastic and Microplastic Analysis in Human Blood", organic matter in biological samples is the core interference source for Py-GC-MS detection of microplastics.

[0008] Furthermore, existing patents and research, such as the Chinese patent application with application number 202511743474.X, entitled "A method for the stepwise digestion, extraction and detection of microplastics in plant tissues," although attempting to improve the detection effect by combining stepwise digestion with Py-GC-MS technology, still cannot get rid of the use of chemical reagents, and there are problems such as cumbersome procedures, exogenous contamination, and slight degradation of microplastics; while research that directly uses Py-GC-MS to detect microplastics in plant tissues has not effectively solved the problem of organic matter interference, and cannot achieve accurate detection.

[0009] In summary, existing technologies for detecting microplastics in plant tissues generally suffer from drawbacks such as incomplete removal of organic matter, easy destruction of microplastics, susceptibility to secondary pollution, insufficient detection sensitivity, and cumbersome operation. These limitations fail to meet the demands of environmental monitoring, ecological assessment, and food safety for precise, efficient, and high-volume detection of microplastics in plant tissues. Therefore, there is an urgent need to develop a detection method that can completely remove organic matter from plant tissues, without damaging the microplastic structure, without secondary pollution, and is compatible with pyrolysis-gas chromatography-mass spectrometry (GC-MS) technology. This would overcome the bottlenecks of existing technologies and enable the precise extraction and qualitative and quantitative analysis of microplastics in plant tissues. Summary of the Invention

[0010] To address the problems of incomplete removal of organic and inorganic residues, severe chemical pollution, easy loss of microplastics, and insufficient detection accuracy in existing methods for extracting microplastics from plant tissues, the present invention aims to provide a method for extracting and analyzing microplastics from plant tissues using high-temperature anaerobic heating-pyrolysis gas chromatography-mass spectrometry, so as to achieve efficient enrichment and extraction of microplastics from plant tissues and accurate qualitative and quantitative analysis.

[0011] To achieve the objectives of this invention, the following technical solutions are provided.

[0012] A method for analyzing microplastics in plant tissues using high-temperature anaerobic heating-pyrolysis gas chromatography-mass spectrometry, the method being as follows: Plant tissues were pretreated without plastic, then heated to 350 ℃~400 ℃ for anaerobic heat treatment. The samples obtained from the anaerobic heat treatment were then analyzed by thermal pyrolysis-gas chromatography-mass spectrometry. The high-temperature anaerobic heating was performed using a programmed temperature rise: initial temperature 60 ℃, increased to 350 ℃~400 ℃ at a rate of 10 ℃ / min, and held for 10 min~60 min.

[0013] The root and stem tissues of the preferred plants were subjected to constant temperature anaerobic heat treatment at 400 ℃ for 30 min to 60 min, while the leaf, flower, and fruit tissues were subjected to constant temperature anaerobic heat treatment at 350 ℃ for 10 min to 30 min.

[0014] Furthermore, it is preferable to use Fenton's reagent to digest and remove impurities from the sample obtained after anaerobic heat treatment. The ratio of the sample obtained after plastic-free pretreatment to Fenton's reagent is 10 mg ~ 500 mg : 10 mL ~ 50 mL. Then, the sample is enriched and dried, and then detected and analyzed by thermal pyrolysis-gas chromatography-mass spectrometry.

[0015] Furthermore, it is preferable to dissolve the sample obtained after anaerobic heat treatment in dilute acid, then wash it until neutral, enrich and dry it, and then perform detection and analysis using a thermal pyrolysis-gas chromatography-mass spectrometry system; wherein the dilute acid is one of dilute nitric acid, dilute hydrochloric acid and dilute sulfuric acid with a mass fraction of 5% to 10%; furthermore, the sample to dilute acid ratio is 1 g : 1 mL to 10 mL.

[0016] Furthermore, the preferred method is as follows: (1) Plastic-free pretreatment of plant tissues; (2) The temperature was increased to 350 ℃~ 400 ℃ by programmed heating and constant temperature for oxygen-free heat treatment; (3) Use Fenton's reagent to remove residual non-plastic impurities, then enrich and dry; (4) Dissolve the sample in dilute acid, then wash until neutral, enrich and dry. (5) The detection and analysis were performed using a thermal pyrolysis-gas chromatography-mass spectrometry system.

[0017] Furthermore, the specific steps for the plastic-free pretreatment of plant tissues are as follows: The plant tissue to be tested was cleaned to remove dirt and microplastics adhering to the surface of the tissue, dried to constant weight, crushed, and sieved to obtain a plastic-free pretreated sample. Plastic-free instruments such as glass, quartz, and stainless steel were used throughout the process, and a blank control was set up simultaneously to eliminate contamination. The plant tissue to be tested is one or more of the following: root, stem, leaf, flower, and fruit. The cleaning method is to rinse repeatedly with pure water more than 3 times and wipe away dirt and exogenous microplastics attached to the surface. The preferred drying temperature is 105 ℃; the preferred method is to use a plastic-free oven to dry to constant weight. A high-speed tissue homogenizer or cryogenic grinder can be used to crush the dried sample with quartz or stainless steel grinding components. After sieving, plant tissue particles with a particle size of less than 1 mm are obtained. These are samples that have undergone plastic-free pretreatment and are sealed for later use.

[0018] Furthermore, the specific steps of the method for oxygen-free heat treatment by programmed heating to a constant temperature of 350 ℃~400 ℃ are as follows: Weigh out the plastic-free pretreated sample and place it in an oxygen-free heating furnace. Purge the air in the heating furnace with nitrogen or helium gas with a purity of ≥99.999% to create an oxygen-free environment. Heat treat the sample by using a programmed temperature rise to 350 ℃~400 ℃. The preferred rate of nitrogen or helium purging is 50 mL / min to 100 mL / min, and the time for purging and exhausting air is 15 min to 30 min.

[0019] Furthermore, the specific steps of the method of treating with Fenton's reagent to remove residual non-plastic impurities, followed by enrichment and drying, are as follows: Add Fenton's reagent to the sample after anaerobic heat treatment, and shake at room temperature for 60 min to 300 min until the solution becomes a completely clear and transparent liquid; further, filter and enrich the entire mixture after shaking and dissolving, and then dry it to constant weight to obtain the sample enriched with microplastics. The preferred filtration and enrichment steps are as follows: The mixture after shaking and dissolving was added to a vacuum filtration device and filtered using a plastic-free glass fiber filter membrane with a diameter of 0.22 μm or less. Microplastics and insoluble residues were retained on the filter membrane. The container holding the mixture was rinsed 2 to 3 times with 10 mL to 50 mL of pure water. All the rinsing liquid was poured into the vacuum filtration device for simultaneous filtration to ensure that the sample to be tested was free of residues. The sample enriched with microplastics was obtained by filtration.

[0020] Furthermore, the specific steps of the method of dissolving in dilute acid, then washing until neutral, and enriching and drying are as follows: A dilute acid solution is added to the sample and mixed thoroughly to fully dissolve the inorganic minerals, metal salts, and incompletely decomposed organic residues in the residue. After dissolution, a dilute acid mixture is obtained. The dilute acid solution has no strong oxidizing properties, which can avoid damage to the microplastic structure. The entire dilute acid mixture was filtered under negative pressure to trap microplastics. The filter membrane surface was rinsed with pure water until the pH value of the filter membrane and the trapped material was neutral to remove residual dilute acid on the surface. The trapped material on the filter membrane was collected and transferred to a concentration tube. The trapped material was dried at 105 °C to obtain the enriched microplastic sample. The negative pressure value during negative pressure filtration is 0.05 MPa ~ 0.08 MPa. Negative pressure filtration is performed through a quartz filter membrane with a pore size of less than or equal to 0.22 μm. Furthermore, the surface of the filter membrane is rinsed with pure water 2 to 3 times.

[0021] Furthermore, the specific steps for detection and analysis using a thermal pyrolysis-gas chromatography-mass spectrometry (TCMS) system are as follows: The enriched microplastic sample was placed in the pyrolysis tube of a thermal pyrolysis-gas chromatography-mass spectrometry system. The pyrolysis temperature was set to 500 ℃ ~ 600 ℃ and the pyrolysis time was 10 s ~ 20 s. The microplastic was pyrolyzed into characteristic small molecule products at high temperature. The pyrolysis products were fed into a gas chromatograph via a transfer line and separated using a DB-5MS or equivalent capillary column. The chromatographic temperature program was as follows: initial temperature 40 ℃, held for 3 min, then increased to 320 ℃ at a rate of 10 ℃ / min and held for 15 min to obtain the separated characteristic components. The separated characteristic components are introduced into a mass spectrometer. The mass spectrometer uses an electron impact ion source with an ion source temperature of 230 °C and adopts a full scan mode with a scan range of m / z 50 ~ 500 amu, or it adopts an ion monitoring mode for detection. Qualitative analysis of microplastics such as polyethylene, polypropylene, polyamide, polyethylene terephthalate, and polycarbonate is achieved by comparing the detected characteristic ion peaks with a standard spectral library; quantitative analysis of microplastics is achieved by fitting the characteristic peak area with a standard curve.

[0022] Furthermore, the preferred gas chromatography conditions are as follows: a DB-5MS capillary column with dimensions of 30 m × 0.25 mm × 0.25 μm is used; the carrier gas is helium with a purity of ≥99.999% and a flow rate of 1 mL / min; the temperature program is as follows: initial temperature 40 ℃, hold for 3 min, increase to 320 ℃ at 10 ℃ / min, hold for 15 min, and the split ratio is 50:1 to ensure efficient separation of pyrolysis products.

[0023] Furthermore, the optimal mass spectrometry conditions are as follows: the ion source is an EI source with an electron energy of 70 eV, the ion source temperature is 230℃, and the transfer line temperature is 280℃; the scanning mode is full scan or selected ion scan with a scanning range of m / z 50 ~ 500 amu and a scanning period of 0.5 s, which balances the accuracy of full-spectrum qualitative analysis with the sensitivity of selected ion quantitative analysis.

[0024] Furthermore, the specific steps for qualitative and quantitative analysis of microplastics are as follows: Qualitative analysis: The mass spectrum obtained from the sample is compared with the standard plastic spectral library. The characteristic pyrolysis products are used as the basis for qualitative determination of microplastics. For example, the characteristic pyrolysis product of polyethylene is 1,20-docosadiene, the characteristic pyrolysis product of polypropylene is 2,4-dimethyl-1-heptene, and the characteristic pyrolysis product of polyamide (PA6) is ε-caprolactam. The types of microplastics can be accurately detected. Quantitative analysis: Prepare standard microplastic solutions of a series of concentrations according to the method described in this invention, and plot a standard curve with the peak area of ​​characteristic lysis products as the ordinate and the mass of microplastics as the abscissa; substitute the peak area of ​​the characteristic lysis products of microplastics in the sample into the corresponding standard curve to calculate the specific content of microplastics in the plant tissue.

[0025] Furthermore, the linear correlation coefficient R of the standard curve 2 ≥0.99, the method detection limit is 1 ng / g ~ 8 ng / g dry weight, and the quantitation limit is 4 ng / g ~ 25 ng / g dry weight.

[0026] Furthermore, the entire process of this invention employs plastic-free treatment to avoid introducing new microplastic impurities.

[0027] Beneficial effects (1) This invention provides a method for analyzing microplastics in plant tissues using high-temperature anaerobic heating-thermal pyrolysis gas chromatography-mass spectrometry. In this method, the inventors have creatively discovered that 350 ℃ ~ 400 ℃ is the optimal pyrolysis temperature range for the main components of plant tissues. Anaerobic treatment within this temperature range can effectively destroy the glycosidic bonds of cellulose and hemicellulose and the aromatic ring structure of lignin in plant tissues, so that the dense plant tissues are completely broken down and degraded into small molecule gaseous substances, which are discharged with the gas. The isothermal treatment can ensure that the organic non-plastic components that are not completely pyrolyzed inside the tissues react fully, reducing the residue of unpyrolyzed residues. At the same time, within the temperature range, microplastics can remain stable and avoid being pyrolyzed and lost, achieving good separation of the matrix and microplastics, and solving the problem of incomplete matrix removal by conventional chemical digestion or low-temperature heating.

[0028] (2) This invention provides a method for analyzing microplastics in plant tissues using high-temperature anaerobic heating-pyrolysis gas chromatography-mass spectrometry. The beneficial effects of using programmed temperature rise in this method are as follows: ① Achieve layered and orderly pyrolysis to avoid component damage: The initial temperature of 60℃ is a mild preheating stage, which allows free water and a small amount of volatile small molecules in the plant tissue to slowly precipitate out, avoiding the direct action of high temperature later on that would cause tissue cracking and component carbonization; with a uniform heating rate of 10℃ / min, heat can gradually penetrate into the interior of the plant tissue, allowing different structural components such as cell walls, lignin, and cellulose to pyrolyze in sequence according to their heat resistance, avoiding local overheating that would cause the target components to decompose and be destroyed; ② Adaptable to a variety of plant tissues and highly versatile: This heating program takes into account the compositional differences of different plant tissues (such as wood chips, herbaceous plants, nut shells, etc.). Whether it is dense lignified tissue or herbaceous tissue with high fiber content, efficient lysis can be achieved through this program. At the same time, the isothermal time can be flexibly adjusted according to the thickness, hardness and lysis requirements of the plant tissue, adapting to different experimental scenarios.

[0029] (3) The present invention provides a method for analyzing microplastics in plant tissues by high temperature anaerobic heating-pyrolysis gas chromatography-mass spectrometry. In the method, the high temperature anaerobic heating treatment method is highly compatible with the subsequent pyrolysis gas chromatography-mass spectrometry detection technology, with low detection limit and high sensitivity. It can realize accurate qualitative and quantitative analysis of various microplastics, and the detection results are reliable. It meets the needs of batch detection of microplastics in plant tissues and can be widely used in environmental monitoring, ecological research and other fields.

[0030] (4) This invention provides a method for analyzing microplastics in plant tissues using high-temperature anaerobic heating-pyrolysis gas chromatography-mass spectrometry (GC-MS). In this method, it is preferable to add Fenton's reagent to the sample after anaerobic heat treatment. This effectively removes residual organic matter and clears separation obstacles: after high-temperature anaerobic pyrolysis, plant tissues may still retain a small amount of lignin and other organic matter, which can encapsulate microplastics or have a density similar to that of microplastics, hindering separation; Fenton's reagent, through Fe... 2+ Catalyzing the generation of strongly oxidizing hydroxyl radicals from H2O2 ( Fenton's reagent (Fe(OH)) can efficiently degrade these difficult-to-treat residual organic substances, creating a clean environment for microplastic separation; on the other hand, Fenton's reagent also has a flocculation-aiding effect, which can simplify subsequent separation operations: in the Fenton reaction, Fe(OH .... 2+ It will be oxidized to Fe 3+ Fe 3+ It can subsequently form ferric hydroxide precipitate, which has a good flocculation effect. It can capture tiny microplastic particles and residual impurities in the system, causing the microplastic particles to aggregate and making them easier to separate through filtration, flotation and other methods.

[0031] (5) The present invention provides a method for analyzing microplastics in plant tissues by high temperature anaerobic heating-thermal pyrolysis gas chromatography-mass spectrometry. In the method, it is preferable to add a dilute acid solution to the sample obtained after anaerobic heat treatment and mix thoroughly. This can fully dissolve the inorganic minerals, metal salts and incompletely pyrolyzed organic matter residues in the residue, and reduce the residue's encapsulation of microplastics. The dilute acid solution has no strong oxidizing properties, which can avoid the destruction of the microplastic structure. After plant tissues undergo high-temperature anaerobic heating treatment, incompletely decomposed lignin and other organic matter remain, along with ash precipitated during pyrolysis (mainly alkali / alkaline earth metal salts such as potassium and calcium). These residues can encapsulate microplastics, interfere with microplastic separation, or affect the accuracy of subsequent detection. Adding any one of dilute nitric acid, dilute hydrochloric acid, or dilute sulfuric acid at a mass fraction of 5% to 10% can specifically address these issues, with the following beneficial effects: ① Removing pyrolysis ash and reducing interference factors: During the pyrolysis of plant tissues, minerals such as potassium and calcium contained in the tissues will be converted into ash residues. These ash residues will not only adsorb microplastics, leading to separation losses, but may also affect the subsequent qualitative and quantitative detection of microplastics. Dilute acids can react with metal salts in the ash to generate water-soluble salts, which can be easily removed by filtration and centrifugation, effectively reducing the impurity content in the system. Hydrochloric acid is particularly effective in removing potassium salts and other ash residues. ② The operation is mild and the cost is low, making it suitable for experimental and practical applications: The concentration of dilute acid with a mass fraction of 5% to 10% is moderate. Compared with concentrated acid, it is less corrosive and does not require special high-temperature resistant or corrosion-resistant equipment, making the operation safer. At the same time, the three dilute acids are commonly used reagents in the laboratory, which are easy to obtain and low in cost. There is no need for complicated reagent preparation procedures. They can be directly used for post-pyrolysis system treatment and are suitable for batch sample processing. ③ The ratio of sample to dilute acid is controlled at 1 g : 1 mL ~ 10 mL, which is crucial for improving the treatment effect: This ratio ensures that the dilute acid fully wets the pyrolyzed plant sample, allowing the acid to fully contact the residual organic matter and ash, avoiding problems such as incomplete reaction, excessive organic matter residue, and incomplete ash removal due to insufficient acid. At the same time, it can prevent reagent waste and increased burden on subsequent water washing due to excessive acid, and also avoid unnecessary corrosion of microplastics by excessive acid, further ensuring the integrity of microplastics. Overall, an appropriate concentration of dilute acid combined with a suitable liquid-to-material ratio can balance the treatment effect with the corrosiveness of the reagents and the cost of use. This can achieve the ideal effect of removing impurities and aiding separation, while avoiding damage to microplastics and safety hazards to experimental operations caused by concentrated acid or improper liquid-to-material ratio.

[0032] (6) This invention provides a method for analyzing microplastics in plant tissues using high-temperature anaerobic heating-pyrolysis gas chromatography-mass spectrometry (GC-MS). This method addresses the core shortcomings of existing plant tissue microplastic detection technologies, such as incomplete removal of organic matter, easy destruction of microplastics, susceptibility to secondary contamination, insufficient detection sensitivity, cumbersome operation, and incompatibility with GC-MS technology. The optimal method achieves multi-dimensional technological breakthroughs and precisely overcomes existing technological bottlenecks through a continuous process of "plastic-free pretreatment—high-temperature anaerobic heating treatment—Fenton's reagent removal—dilute acid dissolution and cleaning—GC-MS detection." The specific beneficial effects are as follows: ① Thoroughly remove organic non-plastic impurities, solving the core interference problem in pyrolysis gas chromatography-mass spectrometry detection: In existing technologies, chemical digestion methods struggle to balance organic matter removal with microplastic retention. Furthermore, when using pyrolysis-GC-MS for direct detection, organic matter such as cellulose, polysaccharides, and lipids in plant tissues generates numerous pyrolysis products during the process. These products overlap with the peaks of characteristic microplastic pyrolysis products, leading to qualitative misjudgments, inaccurate quantification, and contamination of the detection device. The method described in this invention achieves complete removal of organic matter without residue through a three-stage purification system: high-temperature anaerobic heating treatment + Fenton's reagent treatment + dilute acid dissolution. First, the high-temperature anaerobic heating process employs programmed temperature rise, allowing organic matter such as cellulose, protein, and chlorophyll in plant tissues to fully decompose and volatilize in an anaerobic environment, avoiding the carbonization and residue of organic matter under aerobic conditions. Simultaneously, the anaerobic environment prevents the microplastics from being oxidized and damaged, reducing interference from organic matter in subsequent detections compared to traditional chemical digestion methods. Next, Fenton's reagent treatment further dissolves residual non-plastic impurities. Finally, treatment with a non-strongly oxidizing dilute acid solution specifically dissolves inorganic minerals, metal salts, and incompletely decomposed organic matter residues in the residue without damaging the microplastic structure. This completely solves the core bottleneck of incomplete organic matter removal and interference with pyrolysis gas chromatography-mass spectrometry (GC-MS) detection in existing technologies, ensuring clear identification of microplastic characteristic peaks and improving qualitative and quantitative accuracy. ② Protect the structural integrity of microplastics and improve the authenticity and reliability of test results: Existing chemical digestion methods often employ strong acids and alkalis, which can easily alter the functional groups on the surface of microplastics, causing particle breakage or degradation, resulting in low detection results. Even with Fenton oxidation and step-by-step digestion methods, some microplastics are slightly degraded. The method described in this invention protects the microplastic structure through a multi-stage synergistic process: The entire process uses plastic-free equipment such as glass, quartz, and stainless steel for plastic-free pretreatment, and blank controls can be set up simultaneously, completely eliminating exogenous microplastic contamination and avoiding the problem of exogenous contamination introduced by reagents and consumables in existing strong alkali digestion methods, thus ensuring the authenticity of the test samples. The high-temperature anaerobic treatment temperature is controlled at 350 ℃ ~ 400 ℃, which is lower than the thermal decomposition temperature of most microplastics (such as polyethylene, polypropylene and polyamide). This avoids the cracking or structural damage of microplastics. Compared with existing technologies, it significantly improves the recovery rate of microplastics and the accuracy of detection results. The detection limit can be as low as 1 ng / g ~ 8 ng / g dry weight, and the quantitation limit is 4 ng / g ~ 25 ng / g dry weight, meeting the requirements for low-concentration microplastic detection. ③ No secondary pollution, suitable for environmental monitoring needs: Existing strong acid digestion methods introduce secondary pollution from high concentrations of strong acid, interfering with subsequent detection; traditional step-by-step digestion methods require the use of multiple chemical reagents, posing risks of reagent residue and exogenous contamination; the method described in this invention significantly optimizes reagent usage and reduces potential contamination risks. High-temperature anaerobic heating treatment eliminates the need for chemical reagents, reducing chemical pollution at the source; Fenton reagent is used only to remove residual non-plastic impurities, the dosage is controllable, and residual reagents can be completely removed by subsequent rinsing with pure water; dilute acid solution is a low-concentration reagent without strong oxidizing properties, leaving no residue after washing to neutral, avoiding secondary pollution and meeting the testing requirements in the fields of environmental monitoring and food safety. The filtration and enrichment process uses plastic-free glass fiber filter membranes and quartz filter membranes with pore sizes of 0.22μm or less, combined with vacuum filtration and negative pressure filtration, to ensure high microplastic collection efficiency while avoiding the introduction of external contamination into the filter membrane, further ensuring the cleanliness of the testing environment; ④ The process has been optimized and simplified, improving testing efficiency and adapting to batch testing needs: Existing stepwise digestion methods are cumbersome and complex, making them unsuitable for large-scale sample detection; traditional microspectroscopy methods are inefficient and cannot achieve batch detection; the method described in this invention precisely optimizes the process, balancing simplicity and efficiency. The plastic-free pretreatment process is simple, with standardized and easy-to-operate cleaning, drying, crushing, and sieving procedures. It uses equipment such as plastic-free drying ovens and high-speed tissue homogenizers, eliminating the need for complex instruments. The high-temperature anaerobic heating treatment uses programmed temperature rise, which is highly automated and requires no manual supervision. The subsequent Fenton reagent treatment, dilute acid dissolution, and washing and enrichment steps are sequential and easy to operate. Compared with the traditional step digestion method, it significantly shortens the detection cycle. Finally, thermal pyrolysis-gas chromatography-mass spectrometry was used for detection. The chromatographic and mass spectrometry conditions were optimized (such as using a DB-5MS capillary column and optimizing the temperature program and scanning mode), which enabled accurate qualitative and quantitative analysis of various microplastics such as polyethylene, polypropylene, and polyamide. The detection is highly sensitive and fast, and can be adapted to the detection needs of batch plant samples (roots, stems, leaves, flowers, and fruits can all be detected), solving the pain point that existing technologies cannot detect in batches. ⑤ It has strong technical adaptability, high detection accuracy, and meets the needs of multiple fields: Existing patents and literature studies have shown that step-by-step digestion combined with pyrolysis-gas chromatography-mass spectrometry (PCMS) still suffers from the drawbacks of using chemical reagents, while directly using PCMS cannot solve the problem of organic interference. The method described in this invention achieves a perfect fit between pretreatment and PCMS. The three-stage impurity removal system thoroughly removes organic matter, preventing contamination of the pyrolysis tube and chromatographic column, extending the lifespan of detection devices, and reducing detection costs. The optimized thermal pyrolysis-gas chromatography-mass spectrometry (TCMS) detection conditions balance full-spectrum qualitative accuracy with selected ion quantitative sensitivity, exhibiting excellent characteristic peak separation. By comparing with a standard spectral library, different types of microplastics can be accurately distinguished, with a linear correlation coefficient R0 on the standard curve. 2 ≥0.99 ensures accurate and reliable quantitative results; The method can detect plant tissue samples with a particle size of less than 1 mm and can effectively detect low concentrations of microplastics. Compared with traditional microspectroscopy (detection limit of about 1 μm), the detection sensitivity is greatly improved. It does not need to be used in conjunction with atomic force microscopy, which reduces technical costs and operational complexity. It can meet the core needs of accurate, efficient and batch detection of microplastics in plant tissues in the fields of environmental monitoring, ecological assessment and food safety. In summary, the optimal technical solution completely solves the shortcomings of existing plant tissue microplastic detection technologies, such as incomplete removal of organic matter, easy damage to microplastics, secondary pollution, cumbersome operation, and insufficient detection accuracy. It achieves accurate extraction and qualitative and quantitative analysis of microplastics, and has the advantages of being environmentally friendly, efficient, and practical, with significant technical advantages and application value. Detailed Implementation

[0033] The present invention will be further described in detail below with reference to specific embodiments, but these embodiments do not constitute a limitation thereof. All embodiments use the same plant samples for testing: fresh wheat roots, stems, leaves, and fruits, which have been confirmed to be free from significant microplastic contamination; the testing methods, instruments, and core judgment criteria are uniform to ensure the comparability of experimental results.

[0034] Unified Test Conditions Description 1. Testing instruments: EGA / PY-3030D Multifunctional Pyrolysis Analyzer, Frontier Corporation, Japan; GCMS-QP2010 Ultra gas chromatograph-mass spectrometer, Shimadzu Corporation, Japan; Analytical balance with a strength of 1 / 100,000, manufactured by Sartorius, Germany; DZF-6050 Vacuum Drying Oven, Shanghai Jinghong Experimental Equipment Co., Ltd. Oxygen-free heating furnace: Model: GSL-1700X, Hefei Kejing Materials Technology Co., Ltd.; Vacuum filtration device: Model: SHB-III, Zhengzhou Great Wall Science, Industry and Trade Co., Ltd.; High-speed tissue homogenizer: Model: FJ200-S, Shanghai Sample Model Factory; Micro-FTIR spectrometer: Model: LUMOS II, Bruker Corporation, Germany.

[0035] 2. Test methods: Qualitative and quantitative analysis is carried out by pyrolysis-gas chromatography-mass spectrometry. The qualitative basis is the comparison between the mass spectrum of the test sample and the NIST standard spectral library, with characteristic pyrolysis products as the judgment basis: Polyethylene: 1,20-heneicosadiene; Polypropylene: 2,4-dimethyl-1-heptene; Polyamide (PA6): ε-caprolactam; The quantitative basis is the fitting calculation of the characteristic peak area and the standard curve, and the linear correlation coefficient R of the standard curve 2 ≥0.99.

[0036] 3. Evaluation indicators: Organic matter removal rate, microplastic recovery rate, limit of detection, limit of quantitation, detection error; Wherein, the detection error is obtained by comparison with the true value of the standard sample; The organic matter removal rate is calculated by the gravimetric method: Organic matter removal rate = (mass of organic matter in the sample before pretreatment - mass of residual organic matter after treatment) / mass of organic matter in the sample before pretreatment × 100%, The microplastic recovery rate is calculated by the standard addition recovery method: Recovery rate = (detected value - blank value) / spiked amount × 100%.

[0037] 4. Blank control: A plastic-free blank control is set throughout the whole process in the examples: Only plastic-free equipment is used for the same operation without adding plant samples to exclude exogenous microplastic contamination. The blank control is qualified if no microplastics are detected in it.

[0038] 5. Prior art control: In the examples, the traditional strong acid digestion method is adopted: a 50% HNO3 / HCl / HF mixed solution is used for treatment, and detection is carried out with a micro-FTIR spectrometer, which serves as a reference for the effect of the prior art.

[0039] Example 1-1 A method for analyzing microplastics in plant tissues by high-temperature oxygen-free heating-pyrolysis-gas chromatography-mass spectrometry, the steps of the method are as follows: (1) Plastic-free pretreatment of plant tissues 10 g each of wheat root and stem tissue were selected and rinsed repeatedly with pure water 5 times. Surface dirt and exogenous microplastics were removed by wiping with a quartz cloth. The samples were then placed in a plastic-free oven and dried at 105 ℃ to constant weight: the root tissue constant weight was 8.2 g, and the stem tissue constant weight was 7.9 g. The samples were then crushed using a high-speed tissue homogenizer (quartz grinding component) and sieved to obtain particles with a diameter of less than 1 mm, which were the plastic-free pretreated samples. The samples were sealed in glass bottles for later use. Glass and quartz instruments were used throughout the process, and a blank control was set up simultaneously. (2) High-temperature oxygen-free heating treatment Weigh 0.5 g each of the root tissue sample and stem tissue sample obtained in step (1) after plastic-free pretreatment, and place them in an anaerobic heating furnace. Purge with 99.999% pure nitrogen gas at a rate of 80 mL / min for 20 min to exhaust the air in the heating furnace and create an anaerobic environment. Use programmed temperature rise: initial temperature 60 ℃, increase to 400 ℃ at 10 ℃ / min, and perform isothermal heat treatment on the root tissue for 60 min and the stem tissue for 30 min. Cool to room temperature to obtain the samples after anaerobic heat treatment. (3) Detection by thermal decomposition gas chromatography-mass spectrometry The samples obtained in step (2) after oxygen-free heat treatment were placed in the pyrolysis tubes of a thermal pyrolysis-gas chromatography-mass spectrometry instrument for pyrolysis; the pyrolysis temperature was set to 550 ℃ and the pyrolysis time was 15 s to obtain the pyrolysis products; The pyrolysis products were fed into a gas chromatograph via a transfer line. The gas chromatographic conditions were as follows: a 30 m × 0.25 mm × 0.25 μm DB-5MS capillary column was used; the carrier gas was 99.999% pure helium at a flow rate of 1 mL / min; the temperature program was as follows: initial temperature 40 ℃, held for 3 min, then increased to 320 ℃ at a rate of 10 ℃ / min and held for 15 min; the split ratio was 50:1, and the separated characteristic components were obtained. The separated characteristic components were introduced into a mass spectrometer. The mass spectrometry conditions were as follows: electron impact ion source, EI source, electron energy 70 eV, ion source temperature 230 ℃, transfer line temperature 280 ℃, full scan mode: scan range m / z 50~500 amu, scan period 0.5 s; Qualitative analysis: The mass spectrum obtained from the sample detection is compared with the standard plastic spectral library. The characteristic pyrolysis products are used as the basis for qualitative determination of microplastics. For example, the characteristic pyrolysis product of polyethylene is 1,20-docosadiene, the characteristic pyrolysis product of polypropylene is 2,4-dimethyl-1-heptene, and the characteristic pyrolysis product of polyamide (PA6) is ε-caprolactam. The types of microplastics can be accurately detected. Quantitative analysis: A series of standard microplastic solutions of varying concentrations were prepared according to the method described in this embodiment. A standard curve was plotted with the peak area of ​​characteristic lysis products as the ordinate and the mass of microplastics as the abscissa. The peak areas of the characteristic lysis products of microplastics in the sample were substituted into the corresponding standard curve to calculate the specific content of microplastics in the plant tissue. The linear correlation coefficient R of the standard curve was calculated. 2 ≥0.99.

[0040] Test results: (1) Organic matter removal rate: 88.3% for root tissue samples and 89.1% for stem tissue samples; (2) Microplastic recovery rate: When 100 ng / g of polyethylene and polypropylene standard microplastics were added to the samples, the recovery rates of root tissue samples were 72.5% and 71.8%, respectively, and the recovery rates of stem tissue samples were 73.2% and 72.4%, respectively. (3) Detection limits: 6.2 ng / g dry weight for polyethylene and 6.5 ng / g dry weight for polypropylene; (4) Limit of quantitation: 19.8 ng / g dry weight for polyethylene and 20.5 ng / g dry weight for polypropylene; (5) Detection error: Compared with the true value of the standard sample, the error range is ±8.3% ~ ±9.1%; (6) Results compared with existing technologies: organic matter removal rate was 75.2%, polyethylene recovery rate was 60.3%, and detection error was ±12.5%; Conclusion: The method described in this embodiment can achieve qualitative and quantitative detection of microplastics in the root and stem tissues of wheat. The results of organic matter removal rate and recovery rate are better than those of the existing technology control. However, a small amount of organic matter remains, which affects the detection accuracy.

[0041] Examples 1-2 A method for analyzing microplastics in plant tissues using high-temperature anaerobic heating-pyrolysis gas chromatography-mass spectrometry, comprising the following steps: (1) Plastic-free pretreatment of plant tissues: 10 g each of wheat leaf tissue and fruit tissue were selected and rinsed repeatedly with pure water four times. Surface dirt and exogenous microplastics were removed by wiping with a quartz cloth. The samples were then placed in a plastic-free oven and dried at 105 ℃ to constant weight: the constant weight of the leaf tissue was 7.5 g, and the constant weight of the fruit tissue was 8.5 g. The samples were then crushed using a high-speed tissue homogenizer (quartz grinding component) and sieved to obtain particles with a diameter of less than 1 mm, which were the plastic-free pretreated samples. The samples were sealed in glass bottles for later use. Glass and quartz instruments were used throughout the process, and a blank control was set up simultaneously. (2) High-temperature oxygen-free heating treatment: Weigh 0.5 g each of the pretreated leaf tissue and fruit tissue samples obtained in step (1) and place them separately in an anaerobic heating furnace; purge with 99.999% pure helium gas at a rate of 60 mL / min for 15 min to exhaust the air in the heating furnace and create an anaerobic environment; use programmed temperature rise: The initial temperature was 60 ℃, and the leaf tissue samples were heated to 350 ℃ at a rate of 10 ℃ / min and kept at that temperature for 10 min. The initial temperature was 60 ℃, and the fruit tissue samples were heated to 350 ℃ at a rate of 10 ℃ / min and kept at that temperature for 30 min. The sample was cooled to room temperature to obtain the sample after oxygen-free heat treatment; (3) Detection by pyrolysis gas chromatography-mass spectrometry: Same as the thermal decomposition gas chromatography-mass spectrometry detection conditions in Example 1-1 (3).

[0042] Test results: (1) Organic matter removal rate: 87.6% for leaf tissue samples and 86.8% for fruit tissue samples; (2) Microplastic recovery rate: When 100 ng / g of polyethylene and polyamide (PA6) standard microplastics were added to the samples, the recovery rates of leaf tissue samples were 71.3% and 70.9%, respectively, and the recovery rates of fruit tissue samples were 70.5% and 70.1%, respectively. (3) Detection limits: 6.8 ng / g dry weight for polyethylene and 7.1 ng / g dry weight for polyamide (PA6); (4) Limit of quantitation: 21.5 ng / g dry weight for polyethylene, 22.3 ng / g dry weight for polyamide (PA6); (5) Detection error: Compared with the true value of the standard sample, the error range is ±8.7% ~ ±9.5%; Conclusion: The method described in this embodiment can achieve qualitative and quantitative detection of microplastics in wheat leaf and fruit tissues. The test results are similar to those in Example 1-1 and are superior to the prior art control results in Example 1. However, organic matter residues still exist, the detection accuracy needs to be improved, and the isothermal parameters for different plant tissues need to be adjusted accordingly.

[0043] Example 2-1 A method for analyzing microplastics in plant tissues using high-temperature anaerobic heating-pyrolysis gas chromatography-mass spectrometry, comprising the following steps: (1) Plastic-free pretreatment of plant tissues: 10 g of wheat stem tissue was selected, and the remaining plastic-free pretreatment steps were the same as step (1) in Example 1-1. (2) High-temperature oxygen-free heating treatment: Weigh 10 mg of the stem tissue sample obtained in step (1) after plastic-free pretreatment and place it in an anaerobic heating furnace; purge with 99.999% pure nitrogen gas at a rate of 50 mL / min for 15 min to exhaust the air in the heating furnace and create an anaerobic environment; use programmed temperature rise: initial temperature 60 ℃, increase to 400 ℃ at 10 ℃ / min and hold at that temperature for 30 min; cool to room temperature to obtain the sample after anaerobic heat treatment; (3) Fenton's reagent treatment for impurity removal: Add 10 mL of Fenton's reagent to the sample obtained after oxygen-free heat treatment in step (2), wherein Fe 2+ The concentration of H2O2 was 0.5 mol / L, and the mixture was dissolved by shaking at room temperature for 60 min until the solution was completely clear and transparent. The entire mixture was then added to a vacuum filtration apparatus and filtered using a plastic-free glass fiber membrane with a pore size of 0.22 μm. The container holding the mixture was rinsed twice with 10 mL of pure water to obtain a rinsing solution, which was then poured into the filtration apparatus for simultaneous filtration to ensure that no residue remained in the sample to be tested. After filtration, the residue on the filter membrane was placed in a plastic-free oven and dried at 105 °C to constant weight to obtain the enriched microplastic sample. (4) Detection by pyrolysis gas chromatography-mass spectrometry: Same as the thermal decomposition gas chromatography-mass spectrometry detection conditions in Example 1-1 (3).

[0044] Test results: (1) Organic matter removal rate: 92.7% in stem tissue, which is 3.6 percentage points higher than 89.1% in stem tissue in Example 1-1; (2) Microplastic recovery rate: After adding 100 ng / g of polyethylene and polypropylene standard microplastics, the recovery rates were 81.2% and 80.7%, respectively, which is about 8 percentage points higher than that in Example 1-1; (3) Detection limits: 4.5 ng / g dry weight for polyethylene and 4.8 ng / g dry weight for polypropylene, which are significantly lower than those in Examples 1-1; (4) Limit of quantitation: 14.2 ng / g dry weight for polyethylene and 15.1 ng / g dry weight for polypropylene, which are significantly lower than those in Examples 1-1; (5) Detection error: Compared with the true value of the standard sample, the error range is ±5.8% ~ ±6.5%, which is about 3 percentage points lower than that in Example 1-1; (6) Standard curve: linear correlation coefficient R of polyethylene 2 = 0.9991, the linear correlation coefficient R of polypropylene 2 =0.9989, all satisfying R 2 The requirement is ≥0.99; Conclusion: The addition of Fenton's reagent can effectively remove residual organic matter, improve the microplastic recovery rate and detection accuracy, and the effect is better than that of Example 1-1; the sample volume to reagent ratio of this example is 10 mg : 10 mL, which can meet the detection requirements of low quality samples and has no exogenous microplastic contamination.

[0045] Example 2-2 A method for analyzing microplastics in plant tissues using high-temperature anaerobic heating-pyrolysis gas chromatography-mass spectrometry, comprising the following steps: (1) Plastic-free pretreatment of plant tissues: 10 g of wheat root tissue was selected, and the remaining plastic-free pretreatment steps were the same as step (1) in Example 1-1. (2) High-temperature oxygen-free heating treatment: Weigh 500 mg of the root tissue sample obtained in step (1) after plastic-free pretreatment and place it in an anaerobic heating furnace; purge with 99.999% pure nitrogen gas at a rate of 100 mL / min for 30 min to exhaust the air in the heating furnace and create an anaerobic environment; use programmed temperature rise: initial temperature 60 ℃, increase to 400 ℃ at 10 ℃ / min and hold for 60 min; cool to room temperature to obtain the sample after anaerobic heat treatment; (3) Fenton's reagent treatment for impurity removal: Add 50 mL of Fenton's reagent to the sample obtained after oxygen-free heat treatment in step (2), wherein Fe 2+ The concentration of H2O2 was 0.5 mol / L, and the mixture was dissolved by shaking at room temperature for 300 min until the solution was completely clear and transparent. The entire mixture was then added to a vacuum filtration apparatus and filtered using a plastic-free glass fiber membrane with a pore size of 0.22 μm. The container holding the mixture was rinsed three times with 50 mL of pure water to obtain the rinsing solution, which was then poured into the filtration apparatus for simultaneous filtration to ensure that no residue remained in the sample to be tested. After filtration, the residue on the filter membrane was placed in a plastic-free oven and dried at 105 °C to constant weight to obtain the enriched microplastic sample. (4) Detection by pyrolysis gas chromatography-mass spectrometry: Same as the thermal decomposition gas chromatography-mass spectrometry detection conditions in Example 1-1 (3).

[0046] Test results: (1) Organic matter removal rate: 93.5% for root tissue, which is 5.2 percentage points higher than 88.3% for root tissue in Example 1-1; (2) Microplastic recovery rate: After adding 100 ng / g of polyethylene and polyamide (PA6) standard microplastics, the recovery rates were 82.5% and 81.9%, respectively, which is about 10 percentage points higher than that in Example 1-1; (3) Detection limits: 4.2 ng / g dry weight for polyethylene and 4.4 ng / g dry weight for polyamide (PA6); (4) Limit of quantitation: 13.5 ng / g dry weight for polyethylene, 14.3 ng / g dry weight for polyamide (PA6); (5) Detection error: ±5.2%~±5.9%, which is about 3.5 percentage points lower than that in Example 1-1; (6) Standard curve: linear correlation coefficient R of polyethylene 2 = 0.9973, the linear correlation coefficient R of polypropylene 2 =0.9982, all satisfying R 2 The requirement is ≥0.99; Conclusion: Matching high sample volume with high Fenton reagent volume can further improve the organic matter removal rate and detection accuracy, with better results than Example 2-1 and significantly better than Example 1-1; under these parameters, the detection requirements of high-quality samples can be met, and reagent residues can be completely removed after rinsing without secondary pollution.

[0047] Example 3-1 A method for analyzing microplastics in plant tissues using high-temperature anaerobic heating-pyrolysis gas chromatography-mass spectrometry, comprising the following steps: (1) Plastic-free pretreatment of plant tissues: 10 g of wheat leaf tissue was selected, and the remaining plastic-free pretreatment steps were the same as steps (1) in Examples 1-2. (2) High-temperature oxygen-free heating treatment: Weigh 1 g of the leaf tissue sample obtained in step (1) after plastic-free pretreatment and place it in an oxygen-free heating furnace; introduce helium gas with a purity of 99.999% and purge at a rate of 70 mL / min for 20 min to exhaust the air in the heating furnace and create an oxygen-free environment; use programmed temperature rise: initial temperature 60 ℃, increase to 400 ℃ at 10 ℃ / min and hold for 10 min; cool to room temperature to obtain the sample after oxygen-free heat treatment; (3) Dilute acid dissolution treatment: Add 1 mL of 5% dilute nitric acid to 1 g of the sample after anaerobic heat treatment obtained in step (2), with a sample-to-dilute acid ratio of 1 g: 1 mL, and mix thoroughly. Place the mixture in a shaker and shake at room temperature for 30 min to fully dissolve the inorganic minerals and incompletely decomposed organic matter residues in the residue. After shaking, a dilute acid mixture is obtained. Filter the entire dilute acid mixture under negative pressure with a negative pressure value of 0.05 MPa. Use a quartz filter membrane with a pore size of 0.22 μm to retain microplastics. Rinse the filter membrane surface twice with 5 mL of pure water until the pH value of the filter membrane and the retained material is 7 (neutral). Transfer the retained material to a concentration tube and dry at 105 °C to obtain a microplastic-enriched sample. (4) Detection by pyrolysis gas chromatography-mass spectrometry: Same as the thermal decomposition gas chromatography-mass spectrometry detection conditions in Example 1-1 (3).

[0048] Test results: (1) Organic matter removal rate: 92.3% in leaf tissue, which is 4.7 percentage points higher than 87.6% in leaf tissue in Examples 1-2; (2) Microplastic recovery rate: When 100 ng / g of polypropylene and polyamide (PA6) standard microplastics were added to the sample, the recovery rates of leaf tissue samples were 80.9% and 80.3%, respectively, which is about 10 percentage points higher than that of Examples 1-2; (3) Detection limits: Polypropylene 4.6 ng / g dry weight, Polyamide (PA6) 4.9 ng / g dry weight; (4) Limit of quantitation: 14.5 ng / g dry weight for polypropylene and 15.2 ng / g dry weight for polyamide (PA6); (5) Detection error: Compared with the true value of the standard sample, the error range is ±5.7% ~ ±6.3%, which is about 3 percentage points lower than that of Examples 1-2; (6) Standard curve: linear correlation coefficient R of polyethylene 2 = 0.9991, the linear correlation coefficient R of polypropylene 2 =0.9993, all satisfying R 2 The requirement is ≥0.99; Conclusion: Dilute acid dissolution can effectively remove inorganic impurities and residual organic matter, and has no strong oxidizing properties, does not damage the microplastic structure, and the detection effect is better than that of Examples 1-2; 5% dilute nitric acid and a material-to-liquid ratio of 1g:1mL can meet the needs of routine sample detection, are easy to operate, and have no secondary pollution.

[0049] Example 3-2 A method for analyzing microplastics in plant tissues using high-temperature anaerobic heating-pyrolysis gas chromatography-mass spectrometry, comprising the following steps: (1) Plastic-free pretreatment of plant tissues: 10 g of wheat fruit tissue was selected, and the remaining plastic-free pretreatment steps were the same as step (1) in Examples 1-2. (2) High-temperature oxygen-free heating treatment: Weigh 1 g of the fruit tissue sample obtained in step (1) after plastic-free pretreatment and place it in an anaerobic heating furnace; purge with 99.999% pure helium gas at a rate of 90 mL / min for 25 min to exhaust the air in the heating furnace and create an anaerobic environment; use programmed temperature rise: initial temperature 60 ℃, increase to 350 ℃ at 10 ℃ / min and hold for 30 min; cool to room temperature to obtain the sample after anaerobic heat treatment; (3) Dilute acid dissolution treatment: Add 10 mL of 10% hydrochloric acid to 1 g of the sample after anaerobic heat treatment obtained in step (2), with a sample-to-acid ratio of 1 g: 10 mL, and mix thoroughly. Place the mixture in a shaker and shake at room temperature for 60 min to fully dissolve the inorganic minerals and incompletely decomposed organic matter residues in the residue. After shaking, a dilute acid mixture is obtained. Filter the entire dilute acid mixture under negative pressure with a negative pressure value of 0.08 MPa. Use a quartz filter membrane with a pore size of 0.22 μm to retain microplastics. Rinse the filter membrane surface three times with 10 mL of pure water until the pH value of the filter membrane and the retained material is 7 (neutral). Transfer the retained material to a concentration tube and dry at 105 °C to obtain a microplastic-enriched sample. (4) Detection by pyrolysis gas chromatography-mass spectrometry: Same as the thermal decomposition gas chromatography-mass spectrometry detection conditions in Example 1-1 (3).

[0050] Test results: (1) Organic matter removal rate: 93.1% in fruit tissue, which is 6.3 percentage points higher than 86.8% in fruit tissue in Examples 1-2; (2) Microplastic recovery rate: When 100 ng / g of polyethylene and polypropylene standard microplastics were added to the sample, the recovery rates of fruit tissue samples were 82.1% and 81.5%, respectively, which is about 11 percentage points higher than that in Examples 1-2; (3) Detection limits: 4.3 ng / g dry weight for polyethylene and 4.5 ng / g dry weight for polypropylene; (4) Limit of quantitation: 13.8 ng / g dry weight for polyethylene and 14.6 ng / g dry weight for polypropylene; (5) Detection error: Compared with the true value of the standard sample, the error range is ±5.1% ~ ±5.8%, which is about 4 percentage points lower than that in Examples 1-2; (6) Standard curve: linear correlation coefficient R of polyethylene 2 = 0.9958, the linear correlation coefficient R of polypropylene 2 =0.9995, all satisfying R 2 The requirement is ≥0.99; Conclusion: The synergistic effect of 10% hydrochloric acid and a 1 g: 10 mL feed-to-liquid ratio can more fully dissolve inorganic impurities and residual organic matter, and the detection accuracy is better than that of Example 3-1, and significantly better than that of Example 1-2. The dilute hydrochloric acid has no strong oxidizing properties and will not damage the microplastic structure. It is suitable for thermal pyrolysis gas chromatography-mass spectrometry detection and can meet the requirements of high purity detection.

[0051] Example 4-1 A method for analyzing microplastics in plant tissues using high-temperature anaerobic heating-pyrolysis gas chromatography-mass spectrometry, comprising the following steps: (1) Plastic-free pretreatment of plant tissues: Same as step (1) in Example 1-1; (2) High-temperature oxygen-free heating treatment: Same as step (1) in Example 1-1; (3) Fenton's reagent treatment for impurity removal: Add 30 mL of Fenton's reagent to the sample obtained after oxygen-free heat treatment in step (2), wherein Fe 2+ The concentration of H2O2 was 0.5 mol / L, and the mixture was dissolved by shaking at room temperature for 180 min until the solution was completely clear and transparent. The entire mixture was then added to a vacuum filtration apparatus and filtered using a plastic-free glass fiber membrane with a pore size of 0.22 μm. The container holding the mixture was rinsed three times with 30 mL of pure water to obtain the rinsing solution, which was then poured into the filtration apparatus for simultaneous filtration to ensure that no residue remained in the sample to be tested. After filtration, the residue on the filter membrane was placed in a plastic-free oven and dried at 105 °C to constant weight to obtain the enriched microplastic sample. (4) Dilute acid dissolution treatment: Add 5 mL of 8% dilute nitric acid to 0.5 g of the sample obtained in step (3) and mix thoroughly. Place the mixture in a shaker and shake at room temperature for 45 min to fully dissolve the inorganic minerals and incompletely decomposed organic residues in the residue. After shaking, a dilute acid mixture is obtained. Filter the entire dilute acid mixture under negative pressure with a negative pressure of 0.06 MPa. Use a quartz filter membrane with a pore size of 0.22 μm to retain microplastics. Rinse the surface of the filter membrane twice with 8 mL of pure water until the pH of the filter membrane and the retained material is 7 (neutral). Transfer the retained material to a concentration tube and dry at 105 °C to obtain the final sample enriched with microplastics. (5) Pyrolysis gas chromatography-mass spectrometry detection - optimized condition settings: The sample enriched with microplastics in step (4) was placed in the pyrolysis tube of the thermal pyrolysis-gas chromatography-mass spectrometry instrument; the pyrolysis temperature was set to 550 ℃ and the pyrolysis time to 15 s to obtain the pyrolysis products; The pyrolysis products were fed into a gas chromatograph via a transfer line. The gas chromatographic conditions were as follows: a 30 m × 0.25 mm × 0.25 μm DB-5MS capillary column was used; the carrier gas was 99.999% pure helium at a flow rate of 1 mL / min; the temperature program was as follows: initial temperature 40 ℃, held for 3 min, then increased to 320 ℃ at a rate of 10 ℃ / min and held for 15 min; the split ratio was 50:1, and the separated characteristic components were obtained. The separated characteristic components were introduced into a mass spectrometer. The mass spectrometry conditions were: electron impact ion source, EI source, electron energy of 70 eV, ion source temperature of 230 ℃, transfer line temperature of 280 ℃, and ion scanning mode: scan range m / z 50 ~ 500 amu, scan period of 0.5 s. Qualitative analysis: The mass spectrum obtained from the sample is compared with the standard plastic spectral library. The characteristic pyrolysis products are used as the basis for qualitative determination of microplastics. For example, the characteristic pyrolysis product of polyethylene is 1,20-docosadiene, the characteristic pyrolysis product of polypropylene is 2,4-dimethyl-1-heptene, and the characteristic pyrolysis product of polyamide (PA6) is ε-caprolactam. The types of microplastics can be accurately detected. Quantitative analysis: A series of standard microplastic solutions of varying concentrations were prepared according to the method described in this embodiment. A standard curve was plotted with the peak area of ​​characteristic lysis products as the ordinate and the mass of microplastics as the abscissa. The peak areas of the characteristic lysis products of microplastics in the sample were substituted into the corresponding standard curve to calculate the specific content of microplastics in the plant tissue. The linear correlation coefficient R of the standard curve was calculated. 2 ≥0.999.

[0052] Test results: (1) Organic matter removal rate: 98.7% for root tissue and 98.9% for stem tissue, which is about 5 percentage points higher than Example 2-1 and 2-1, about 10 percentage points higher than Example 1-1, and about 23 percentage points higher than the prior art; (2) Microplastic recovery rate: 100 ng / g of polyethylene, polypropylene and polyamide (PA6) standard microplastics were added to the sample. The recovery rates of root tissue samples were 95.3%, 94.8% and 94.5% respectively, and the recovery rates of stem tissue samples were 95.8%, 95.2% and 94.9% respectively. This is an improvement of about 13 percentage points compared with Examples 2-1 and 2-2, an improvement of about 23 percentage points compared with Example 1-1, and an improvement of about 35 percentage points compared with the prior art in Example 1-1. (3) Detection limits: 1.2 ng / g dry weight for polyethylene, 1.5 ng / g dry weight for polypropylene, and 1.8 ng / g dry weight for polyamide (PA6), all meeting the requirements of 1 ng / g ~ 8 ng / g dry weight, which is about 3 percentage points lower than that of Examples 2-1 and 2-2, and about 5 percentage points lower than that of Example 1-1; (4) Limit of quantitation: 4.2 ng / g dry weight for polyethylene, 4.8 ng / g dry weight for polypropylene, and 5.5 ng / g dry weight for polyamide (PA6), all meeting the requirement of 4 ng / g ~ 25 ng / g dry weight, which is about 9 percentage points lower than that of Examples 2-1 and 2-2; (5) Detection error: Compared with the true value of the standard sample, the error range is ±1.8% ~ ±2.5%, which is about 3.5 percentage points lower than that of Examples 2-1 and 2-2, about 7 percentage points lower than that of Example 1-1, and about 10 percentage points lower than that of the prior art in Example 1-1; (6) Standard curve: linear correlation coefficient R of polyethylene 2 = 0.9995, the linear correlation coefficient R of polypropylene 2 =0.9993, the linear correlation coefficient R of polyamide 2 = 0.9994, all satisfying R 2 The requirement is ≥0.999; Conclusion: This embodiment, through the synergistic effect of multiple steps, completely removes organic matter and impurities without secondary pollution, and the microplastic structure remains intact. The detection accuracy and recovery rate are significantly better than those of Embodiments 1-1, 2-2, and 2-2. It can achieve accurate qualitative and quantitative detection of microplastics in the root and stem tissues of wheat, meeting the detection needs of multiple fields.

[0053] Example 4-2 A method for analyzing microplastics in plant tissues using high-temperature anaerobic heating-pyrolysis gas chromatography-mass spectrometry, comprising the following steps: (1) Plastic-free pretreatment of plant tissues: Same as step (1) in Examples 1-2; (2) High-temperature oxygen-free heating treatment: Weigh 0.5 g each of the pretreated leaf tissue and fruit tissue samples obtained in step (1) and place them separately in an anaerobic heating furnace; purge with 99.999% pure helium gas at a rate of 70 mL / min for 18 min to exhaust the air in the heating furnace and create an anaerobic environment; use programmed temperature rise: The initial temperature was 60 ℃, and the leaf tissue samples were heated to 350 ℃ at a rate of 10 ℃ / min and kept at that temperature for 20 min. The initial temperature was 60 ℃, and the fruit tissue samples were heated to 350 ℃ at a rate of 10 ℃ / min and kept at that temperature for 25 min. The sample was cooled to room temperature to obtain the sample after oxygen-free heat treatment; (3) Fenton's reagent treatment for impurity removal: Add 25 mL of Fenton's reagent to the sample obtained after oxygen-free heat treatment in step (2), wherein Fe 2+The concentration of H2O2 was 0.5 mol / L, and the mixture was dissolved by shaking at room temperature for 150 min until the solution was completely clear and transparent. The entire mixture was then added to a vacuum filtration apparatus and filtered using a plastic-free glass fiber membrane with a pore size of 0.22 μm. The container holding the mixture was rinsed twice with 25 mL of pure water to obtain a rinsing solution, which was then poured into the filtration apparatus for simultaneous filtration to ensure that no residue remained in the sample to be tested. After filtration, the residue on the filter membrane was placed in a plastic-free oven and dried at 105 °C to constant weight to obtain the enriched microplastic sample. (4) Dilute acid dissolution treatment: Add 6 mL of 7% hydrochloric acid to 0.52 g of the sample obtained in step (3) and mix thoroughly. Place the mixture in a shaker and shake at room temperature for 40 min to fully dissolve the inorganic minerals and incompletely decomposed organic matter residues in the residue. After shaking, a dilute acid mixture is obtained. Filter the entire dilute acid mixture under negative pressure with a negative pressure value of 0.07 MPa. Use a quartz filter membrane with a pore size of 0.22 μm to retain microplastics. Rinse the surface of the filter membrane three times with 9 mL of pure water until the pH value of the filter membrane and the retained product is 7 (neutral). Transfer the retained product to a concentration tube and dry at 105 °C to obtain the final sample enriched with microplastics. (5) Detection by pyrolysis gas chromatography-mass spectrometry: Same as the thermal pyrolysis gas chromatography-mass spectrometry detection conditions in Example 4-1 (5).

[0054] Test results: (1) Organic matter removal rate: 98.5% for leaf tissue and 98.3% for fruit tissue, which is about 5 percentage points higher than that of Examples 3-1 and 3-2, about 11 percentage points higher than that of Examples 1-2, and about 23 percentage points higher than that of the prior art in Example 1-1; (2) Microplastic recovery rate: 100 ng / g of polyethylene, polypropylene and polyethylene terephthalate (PET) standard microplastics were added to the samples. The recovery rates of leaf tissue samples were 94.9%, 94.5% and 94.2% respectively, and the recovery rates of fruit tissue samples were 94.6%, 94.1% and 93.8% respectively. This is an improvement of about 12 percentage points compared with Examples 3-1 and 3-2, an improvement of about 24 percentage points compared with Examples 1-2, and an improvement of about 34 percentage points compared with the prior art in Example 1-1. (3) Detection limits: 1.3 ng / g dry weight for polyethylene, 1.6 ng / g dry weight for polypropylene, and 2.0 ng / g dry weight for PET, all meeting the requirements of 1 ng / g ~ 8 ng / g dry weight; (4) Limit of quantitation: 4.5 ng / g dry weight for polyethylene, 5.0 ng / g dry weight for polypropylene, and 6.2 ng / g dry weight for PET, all meeting the requirements of 4 ng / g ~ 25 ng / g dry weight; (5) Detection error: Compared with the true value of the standard sample, the error range is ±2.0% ~ ±2.7%, which is about 3.3 percentage points lower than that of Examples 3-1 and 3-2, about 7 percentage points lower than that of Examples 1-2, and about 10 percentage points lower than that of the prior art in Example 1-1; (6) Standard curve: linear correlation coefficient R of polyethylene 2 = 0.9994, the linear correlation coefficient R of polypropylene 2 =0.9992, the linear correlation coefficient R of PET 2 = 0.9993, all satisfying R 2 The requirement is ≥0.999; Conclusion: This embodiment is suitable for the detection needs of wheat leaf and fruit tissues. The parameter settings are reasonable, and the detection effect is basically the same as that of Embodiment 4-1, and significantly better than Embodiments 1-2, 3-1 and 3-2. It completely breaks through the existing technical bottlenecks and can realize accurate and efficient detection of various types of microplastics, which is suitable for batch sample detection needs.

[0055] In summary, the comparison of test results from various embodiments clearly demonstrates the following progressive relationship: The effects of existing technologies are: < the effects of basic technical solution one, i.e., examples 1-1 and 1-2 < the effects of optimized technical solutions, i.e., examples 2-1, 2-2, 3-1, and 3-2 < the effects of optimal technical solutions, i.e., examples 4-1 and 4-2; taking polyethylene test results as an example, the specific data are summarized as follows: (1) Organic matter removal rate: Existing technology: 75.2% < Examples 1-1, 1-2: 86.8% ~ 89.1% < Examples 2-1, 2-2, 3-1, 3-2: 92.3% ~ 93.5% < Examples 4-1, 4-2: 98.3% ~ 98.9%; (2) Microplastic recovery rate: Existing technology 60.3% < Examples 1-1, 1-2: 70.5% ~ 73.2% < Examples 2-1, 2-2, 3-1, 3-2: 80.3% ~ 82.5% < Examples 4-1, 4-2: 93.8% ~ 95.8%; (3) Detection limit: Existing technology 12.5 ng / g < Examples 1-1, 1-2: 6.2 ng / g ~ 6.8 ng / g < Examples 2-1, 2-2, 3-1, 3-2: 4.2 ng / g ~ 4.9 ng / g < Examples 4-1, 4-2: 1.2 ng / g ~ 1.3 ng / g; (4) Detection error: Existing technology ±12.5% ​​< Examples 1-1, 1-2: ±8.3% ~ ±9.5% < Examples 2-1, 2-2, 3-1, 3-2: ±5.1% ~ ±6.5% < Examples 4-1, 4-2: ±1.8% ~ ±2.7%.

[0056] All embodiments were free of exogenous microplastic contamination. The operation steps were clear and the parameters were well-defined. Colleagues could repeat the implementation without further research or experimentation, which fully demonstrates that the method described in this invention can achieve accurate detection of microplastics in plant tissues. The most preferred technical solutions are Examples 4-1 and 4-2, which have the best technical effects and can meet the core needs of environmental monitoring, ecological assessment and food safety.

Claims

1. A method for analyzing microplastics in plant tissues using high-temperature anaerobic heating-pyrolysis gas chromatography-mass spectrometry, characterized in that: Plant tissues were pretreated without plastic, then heated to 350 ℃~400 ℃ for anaerobic heat treatment. The samples obtained from the anaerobic heat treatment were then analyzed by thermal pyrolysis-gas chromatography-mass spectrometry. The temperature program was used: the initial temperature was 60 ℃, and the temperature was increased to 350 ℃~400 ℃ at a rate of 10 ℃ / min, and held for 10 min~60 min.

2. The method for analyzing microplastics in plant tissues using high-temperature anaerobic heating-pyrolysis gas chromatography-mass spectrometry according to claim 1, characterized in that: The root and stem tissues of the plant were subjected to constant temperature anaerobic heat treatment at 400 ℃ for 30 min to 60 min, while the leaf, flower, and fruit tissues were subjected to constant temperature anaerobic heat treatment at 350 ℃ for 10 min to 30 min.

3. A method for analyzing microplastics in plant tissues using high-temperature anaerobic heating-pyrolysis gas chromatography-mass spectrometry according to claim 1 or 2, characterized in that: The samples obtained after anaerobic heat treatment were digested with Fenton's reagent to remove impurities. The ratio of the sample obtained after plastic-free pretreatment to Fenton's reagent was 10 mg ~ 500 mg : 10 mL ~ 50 mL. The samples were then enriched, dried, and analyzed using thermal pyrolysis-gas chromatography-mass spectrometry. The sample obtained after anaerobic heat treatment was dissolved in dilute acid, then washed until neutral, enriched and dried, and then detected and analyzed by thermal pyrolysis-gas chromatography-mass spectrometry; the dilute acid was one of dilute nitric acid, dilute hydrochloric acid and dilute sulfuric acid with a mass fraction of 5% to 10%.

4. The method for analyzing microplastics in plant tissues using high-temperature anaerobic heating-pyrolysis gas chromatography-mass spectrometry according to claim 3, characterized in that: The ratio of sample to dilute acid is 1 g : 1 mL ~ 10 mL.

5. A method for analyzing microplastics in plant tissues using high-temperature anaerobic heating-pyrolysis gas chromatography-mass spectrometry according to claim 1 or 2, characterized in that: (1) Plastic-free pretreatment of plant tissues; (2) The temperature was increased to 350 ℃~ 400 ℃ by programmed heating and constant temperature for oxygen-free heat treatment; (3) Use Fenton's reagent to remove residual non-plastic impurities, then enrich and dry; (4) Dissolve the sample in dilute acid, then wash until neutral, enrich and dry. (5) The detection and analysis were performed using a thermal pyrolysis-gas chromatography-mass spectrometry system.

6. The method for analyzing microplastics in plant tissues using high-temperature anaerobic heating-pyrolysis gas chromatography-mass spectrometry according to claim 5, characterized in that: The specific steps for plastic-free pretreatment of plant tissues are as follows: The plant tissue to be tested was cleaned to remove dirt and microplastics adhering to the surface of the tissue, dried to constant weight, crushed, and sieved to obtain a plastic-free pretreated sample. Plastic-free equipment was used throughout the process, and a blank control was set up simultaneously to eliminate contamination. The plant tissue to be tested is one or more of the following: root, stem, leaf, flower, and fruit. The cleaning method is to rinse repeatedly with pure water more than 3 times and wipe away dirt and exogenous microplastics attached to the surface. Dry to constant weight using a plastic-free oven; The dried sample was crushed using a high-speed tissue homogenizer or cryogenic grinder with quartz or stainless steel grinding components. After sieving, plant tissue particles with a particle size of less than 1 mm were obtained, which were samples after plastic-free pretreatment.

7. The method for analyzing microplastics in plant tissues using high-temperature anaerobic heating-pyrolysis gas chromatography-mass spectrometry according to claim 5, characterized in that: The specific steps of the method for oxygen-free heat treatment by programmed heating to a constant temperature of 350 ℃~400 ℃ are as follows: Weigh out the plastic-free pretreated sample and place it in an oxygen-free heating furnace. Purge the air in the heating furnace with nitrogen or helium gas with a purity of ≥99.999% to create an oxygen-free environment. Heat the sample to 350 ℃~400 ℃ and maintain the temperature for heat treatment. The rate of nitrogen or helium purging is 50 mL / min to 100 mL / min, and the time for purging and removing all air is 15 min to 30 min.

8. The method for analyzing microplastics in plant tissues using high-temperature anaerobic heating-pyrolysis gas chromatography-mass spectrometry according to claim 5, characterized in that: The specific steps of the method of treating with Fenton's reagent to remove residual non-plastic impurities, followed by enrichment and drying, are as follows: Add Fenton's reagent to the sample after anaerobic heat treatment, and shake at room temperature for 60 min to 300 min until the solution becomes a clear and transparent liquid; filter and enrich the entire mixture after shaking and dissolving, and then dry it to constant weight to obtain the sample enriched with microplastics. The specific steps of the method involving dissolving in dilute acid, washing until neutral, enriching, and drying are as follows: Add dilute acid solution to the sample and mix thoroughly to fully dissolve the inorganic minerals, metal salts and incompletely decomposed organic residues in the residue. After dissolution, a dilute acid mixture system is obtained. The entire dilute acid mixture was filtered under negative pressure to trap microplastics. The filter membrane surface was rinsed with pure water until the pH value of the filter membrane and the trapped material was neutral to remove residual dilute acid on the surface. The trapped material on the filter membrane was collected and transferred to a concentration tube. The material was dried to obtain the enriched microplastic sample. The specific steps for detection and analysis using a thermal pyrolysis-gas chromatography-mass spectrometry (PCMS) system are as follows: The enriched microplastic sample was placed in the pyrolysis tube of a thermal pyrolysis-gas chromatography-mass spectrometry system. The pyrolysis temperature was set to 500 ℃~650 ℃ and the pyrolysis time was 10 s~20 s. The microplastic was pyrolyzed into characteristic small molecule products at high temperature. The pyrolysis products were fed into a gas chromatograph via a transfer line and separated using a DB-5MS or equivalent capillary column. The chromatographic temperature program was as follows: initial temperature 40 ℃, held for 3 min, then increased to 320 ℃ at a rate of 10 ℃ / min and held for 15 min to obtain the separated characteristic components. The separated characteristic components are introduced into a mass spectrometer. The mass spectrometer uses an electron impact ion source with an ion source temperature of 230 °C and adopts a full scan mode with a scan range of m / z 50 ~ 500 amu, or it adopts an ion monitoring mode for detection. Qualitative analysis of microplastics is achieved by comparing the detected characteristic ion peaks with a standard spectral library; quantitative analysis of microplastics is achieved by fitting the characteristic peak area with a standard curve.

9. The method for analyzing microplastics in plant tissues using high-temperature anaerobic heating-pyrolysis gas chromatography-mass spectrometry according to claim 8, characterized in that: In step (3), the filtering and enrichment steps are as follows: The mixture after shaking and dissolving was added to a vacuum filtration device and filtered using a plastic-free glass fiber filter membrane with a diameter of 0.22 μm or less. Microplastics and insoluble residues were retained on the filter membrane. The container holding the mixture was rinsed 2 to 3 times with 10 mL to 50 mL of pure water. All the rinsing liquid was poured into the vacuum filtration device for simultaneous filtration to ensure that the sample to be tested was free of residues. The sample enriched with microplastics was obtained by filtration. In step (4), the negative pressure value during negative pressure filtration is 0.05 MPa ~ 0.08 MPa. Negative pressure filtration is performed through a quartz filter membrane with a pore size of less than or equal to 0.22 μm, and the surface of the filter membrane is rinsed with pure water 2 to 3 times.

10. The method for analyzing microplastics in plant tissues using high-temperature anaerobic heating-pyrolysis gas chromatography-mass spectrometry according to claim 8, characterized in that: In step (5), the gas chromatography conditions are as follows: the column used is a DB-5MS capillary column with dimensions of 30 m × 0.25 mm × 0.25 μm; the carrier gas is helium with a purity of ≥99.999% and a flow rate of 1 mL / min; the temperature program is as follows: the initial temperature is 40 ℃, held for 3 min, then increased to 320 ℃ at a rate of 10 ℃ / min and held for 15 min; the split ratio is 50:

1. Mass spectrometry conditions: EI source, electron energy 70 eV, ion source temperature 230 ℃, transfer line temperature 280 ℃; scanning mode: full scan or selected ion scan, scanning range: m / z 50 ~ 500 amu, scanning period: 0.5 s; The specific steps for qualitative and quantitative analysis of microplastics are as follows: Qualitative analysis: The mass spectrum obtained from the sample is compared with a standard plastic spectral library. Characteristic pyrolysis products are used as the basis for qualitative determination of microplastics to identify the types of microplastics. Quantitative analysis: Prepare standard microplastic solutions of a series of concentrations according to the method described in claim 8, and plot a standard curve with the peak area of ​​characteristic lysis products as the ordinate and the mass of microplastics as the abscissa; substitute the peak area of ​​the characteristic lysis products of microplastics in the sample into the corresponding standard curve to calculate the specific content of microplastics in the plant tissue; The linear correlation coefficient R of the standard curve 2 ≥0.99, the method detection limit is 1 ng / g ~ 8 ng / g dry weight, and the quantitation limit is 4 ng / g ~ 25 ng / g dry weight.