MALDI-TOF (matrix-assisted laser desorption / ionization-time of flight) mass spectrometry-based nano micro-plastic rapid screening method
By using MALDI-TOF mass spectrometry to pretreat and mix waste, soil, leachate, and groundwater samples with specific solutions, the limitations of existing technologies in detecting nanoscale microplastics have been overcome, enabling rapid and accurate screening of nanoscale microplastics and breaking through the detection bottleneck of traditional methods.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- EAST CHINA UNIV OF SCI & TECH
- Filing Date
- 2026-01-20
- Publication Date
- 2026-05-12
AI Technical Summary
Existing technologies for detecting microplastics have long analysis cycles, narrow applicability, and cannot accurately screen for nanoscale microplastics. In particular, they have a high false positive rate in samples from complex environments, making it difficult to meet the needs for rapid screening and accurate evaluation of large batches of samples.
A rapid screening method for nanoplastics based on MALDI-TOF mass spectrometry was adopted. By pretreating waste, soil, leachate and groundwater samples from historical non-standard landfills, and combining organic solvent dissolution with a specific ratio of matrix solution and cationizing agent solution, the MALDI-TOF mass spectrometer was used for spectral acquisition to achieve rapid identification of nanoscale microplastics.
It enables accurate identification of nanoscale microplastics with a particle size of less than 1 micrometer, broadens the applicable range of media, shortens the analysis cycle, and meets the need for rapid and accurate screening of nanoscale microplastics in samples from complex environments.
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Figure CN122016995A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the detection of microplastics in environmental monitoring, and more specifically to a rapid screening method for nanoplastics based on MALDI-TOF mass spectrometry. Background Technology
[0002] Microplastics (MPs), as a new type of pollutant that has attracted widespread attention, have made source identification and risk management one of the core tasks in the field of new pollutant remediation. Historically unregulated landfills, due to the accumulation of large amounts of plastic waste and the general lack of effective anti-seepage systems, have led to the gradual degradation of plastics into microplastics under long-term environmental influences. These microplastics then continuously migrate into the soil-groundwater environment with leachate, causing multi-media complex pollution and becoming a major contributor to soil-groundwater microplastic pollution.
[0003] Statistics show that as of 2020, my country had 24,000 historically unregulated landfills, with a stockpile of approximately 8 billion tons of waste, equivalent to 30 times the annual volume of municipal solid waste collected nationwide. These landfills are widely distributed, their pollution levels are unclear, and their remediation is extremely difficult. However, current research on microplastic pollution from historically unregulated landfills still has significant shortcomings: the formation mechanism of nanoscale microplastics in the multi-media system of waste-leachate-soil-groundwater remains unclear, the migration and transformation patterns lack systematic understanding, and environmental health risk assessment technologies urgently need improvement. Therefore, developing rapid microplastic screening technologies applicable to this complex multi-media system is of significant practical and scientific value for revealing the characteristics of microplastic occurrence, clarifying pollution migration pathways, and assessing environmental health risks.
[0004] Developing rapid and accurate quantitative analysis methods is fundamental to the effective identification of microplastics in multi-media systems. In the development of microplastic detection technology, traditional methods often employ pretreatment techniques such as density separation and digestion, followed by visual observation or infrared spectroscopy for sampling and detection. However, these methods have a high false positive rate, especially in complex environmental samples where microplastics are difficult to distinguish from other impurities, thus limiting accurate identification.
[0005] To address this issue, research teams both domestically and internationally have developed qualitative and quantitative methods such as pyrolysis-gas chromatography-mass spectrometry (PCMS) and spectral image recognition. These technologies have made progress in improving the analytical accuracy of specific types of microplastics, such as polystyrene and polyvinyl chloride, providing new insights for the identification of microplastics in complex environmental samples. However, these improved technologies still have significant drawbacks: First, the analysis cycle is too long. The PCMS analysis cycle for a single sample can be as long as 3-5 hours, and the spectral image recognition analysis cycle also requires 1-2 hours, making it difficult to meet the needs of rapid screening of large batches of samples. Second, the scope of application is narrow. Spectral image recognition can only detect microplastics larger than 50 μm, and cannot effectively identify microplastics smaller than 50 μm or nanoscale microplastics. Third, the detection error is still relatively high. The error rate of spectral image recognition is approximately 10%-15%, which is insufficient to meet the requirements of accurate pollution assessment. Summary of the Invention
[0006] To address the problems of long analysis cycles, narrow applicability, and inability to accurately screen nanoscale microplastics in existing technologies, this invention aims to provide a rapid screening method for nanoscale microplastics based on MALDI-TOF mass spectrometry.
[0007] The rapid screening method for nanoplastics based on MALDI-TOF mass spectrometry according to the present invention includes the following steps: S1, pre-treating solid and liquid samples from historical non-standard landfills to obtain solid particles enriched with nanoscale microplastics, wherein the solid sample is a waste sample or soil sample, and the liquid sample is a leachate sample or groundwater sample; S2, taking the solid particles, adding an organic solvent to dissolve them to obtain a microplastic sample solution; S3, dissolving the imaging matrix in the organic solvent to form a matrix solution, dissolving the cationizing agent in the organic solvent to form a cationizing agent solution, and mixing them at a mass ratio of matrix solution: microplastic sample solution: cationizing agent solution = (9-11):(9-11):1 to obtain a mixed solution; S4, spotting the mixed solution onto a target plate and allowing it to crystallize naturally under environmental conditions; S5, placing the crystallized target plate into a MALDI-TOF mass spectrometer for spectral acquisition, and determining the presence of nanoscale microplastics in the sample by analyzing the mass spectrometry characteristic signals.
[0008] In a preferred embodiment, step S1, the pretreatment of the solid sample includes: setting up sampling points by planar and / or vertical point layout, and collecting samples by profiling or drilling; reducing the size of the collected samples; drying the reduced samples to constant weight at room temperature to 60°C; and sieving the dried samples using a 5-20 mesh sieve to collect the solid particles that pass through the sieve.
[0009] In a preferred embodiment, the planar sampling points are arranged using a grid method or a zoning method; the vertical sampling points collect surface, middle, and deep samples at different depths, with surface samples collected at a depth of 0-0.8 meters, middle samples at a depth of 0.5-6 meters, and deep samples at a depth greater than 6 meters.
[0010] In a preferred embodiment, the reduction is performed using a quartering method.
[0011] In a preferred embodiment, step S1, the pretreatment of the liquid sample includes the following steps: collecting liquid samples by setting up sampling points through the collection system sampling points, processing facility sampling points, or environmental monitoring points; sieving the liquid sample through a 500-700 mesh sieve to retain solid particles; rinsing the sieve with a saturated sodium chloride solution and collecting the mixture of the rinsed solid particles and the rinsing solution; separating the solid particles from the liquid in the mixture and drying it to constant weight to obtain the solid particles.
[0012] In a preferred embodiment, the sampling points of the collection system include an adjustment pool, a collection well, or an observation well and outlet of a drainage blind ditch; the sampling points of the treatment facility include the inlet and outlet of the leachate treatment facility; and the environmental monitoring points include groundwater monitoring wells or surface water discharge outlets.
[0013] In a preferred embodiment, the organic solvent is tetrahydrofuran, and the concentration of the microplastic sample solution is 3-8 mg / mL.
[0014] In a preferred embodiment, the imaging matrix is DCTB, and the concentration of the matrix solution is 15-25 mg / mL.
[0015] In a preferred embodiment, the cationizing agent is silver trifluoroacetate, and the concentration of the cationizing agent solution is 3-8 mg / mL.
[0016] In a preferred embodiment, the mass ratio of the matrix solution, the microplastic sample solution, and the cationizing agent solution is 10:10:1, and the nanoscale microplastics are plastic particles with a particle size of less than 1 micrometer.
[0017] This invention enriches nanoscale microplastic solid particles by targeted pretreatment of multi-media samples, including waste, soil, leachate, and groundwater from historically non-standard landfills. Combined with organic solvent dissolution and a synergistic ratio of matrix solution and cationizing agent solution, and leveraging the high sensitivity of MALDI-TOF mass spectrometry, this invention not only overcomes the limitation of existing technologies that can only detect larger-diameter microplastics, achieving accurate identification of nanoscale microplastics with a particle size of less than 1 micrometer, but also broadens the applicable media range for microplastic screening, significantly shortens the analysis cycle, and effectively meets the practical needs for rapid and accurate screening of nanoscale microplastics in the risk prevention and control of new pollutants. Attached Figure Description
[0018] Figure 1 This is a flowchart of a rapid screening method for nanoplastics based on MALDI-TOF mass spectrometry according to the present invention.
[0019] Figure 2 This is the MALDI-TOF mass spectrum of the nanoscale polystyrene (PS) microplastics of the present invention. Detailed Implementation
[0020] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.
[0021] This invention is applicable to the rapid screening of nanoscale microplastics (MPs) in multi-media systems of waste, leachate, soil, and groundwater in historically non-standard landfills. Here, MPs refer to plastic particles with a diameter of less than 5 mm in the environmental media, including micron-sized and nano-sized plastic particles, wherein nanoscale microplastics are plastic particles with a diameter of less than 1 micron.
[0022] like Figure 1 As shown, the rapid screening method for nanoplastics according to the present invention includes a pretreatment stage, the core of which is to obtain representative target samples. For solid samples (garbage, soil), after sampling, they are successively dried and sieved to remove moisture and large particulate impurities, laying the foundation for subsequent dissolution steps. For liquid samples (leachate, groundwater), after sampling, they are successively sieved and rinsed to retain solid particles and avoid loss of microplastics, ensuring complete retention of the target material.
[0023] The sampling point layout for solid samples includes planar and vertical point layout.
[0024] Planar sampling refers to the placement of sampling points based on the operational area distribution of historically non-standard landfills, using either a grid or zone method. The entire sampling area is divided into several grids of equal area, and a sampling point is randomly selected within each grid. For newly landfilled waste, zones can be established according to the origin of the waste trucks, with sampling points placed within each zone.
[0025] Vertical sampling refers to collecting samples from different layers at varying depths, including surface, intermediate, and deep layers, taking into account the layered structure of landfills. Surface samples are collected from 0-0.5 meters below the landfill surface. Intermediate samples are obtained by drilling to depths of 0.5-2 meters, 2-5 meters, etc., using specialized drilling equipment. Deep samples, when drilling conditions permit, are obtained using specialized drilling rigs to study the microplastic characteristics of waste at different stages of degradation.
[0026] Sampling of solid samples includes the following steps:
[0027] S1. Determine the sampling plan: Clarify the purpose of this sampling, the sampling point layout method, the sampling depth, and the required number of samples.
[0028] S2, Clean the surface of the sampling point: Remove the covering soil, vegetation or other non-representative debris from the surface of the sampling point to ensure that the sample of the target layer is collected.
[0029] S3, Sample collection: Samples are collected using either the profiling method or the drilling method. The profiling method requires digging a sufficiently deep profile and collecting samples from the profile wall at the preset strata. The drilling method involves using drilling equipment to reach the specified depth and then extracting the core sample.
[0030] S4, Sample Reduction: The initial sample volume can reach several hundred kilograms, which needs to be reduced by quartering. That is, the original sample is piled into a cone shape, flattened and divided into four equal parts with cross lines. The two diagonally opposite parts are kept and the other two parts are discarded. This process is repeated until the sample of several kilograms required for laboratory analysis is obtained.
[0031] S5, Sample Preservation and Recording: Immediately place the reduced sample into a clean container, seal it, and affix a label. The label information should include the sampling location, sampling date, sampling depth, sample number, and sampling personnel. At the same time, fill out the sampling record form to record the site conditions in detail, such as the appearance of the waste, odor, and ambient temperature.
[0032] The drying and sieving of solid samples include: placing the collected and reduced solid samples, i.e., garbage samples or soil samples, into an oven and drying them at 40°C to constant weight; after drying, the samples are sieved using a 10-mesh (2mm aperture) stainless steel sieve to remove large particle impurities; accurately weighing 0.5g of the sieved garbage sample or 1g of the sieved soil sample using an electronic balance and placing it in a 250mL beaker for later use.
[0033] The sampling points for liquid samples include sampling points for the collection system, sampling points for the processing facilities, and environmental monitoring points.
[0034] The sampling point of the collection system refers to the priority selection of the regulating pool / collection well as the sampling point. Mixed samples can be collected in the middle of the pool (well) or profile samples can be collected at different depths; samples can also be collected at the observation well or outlet of the drainage blind ditch.
[0035] Sampling points at a treatment facility refer to sampling points set up at the inlet and outlet of a leachate treatment facility to assess the facility's efficiency in removing microplastics.
[0036] Environmental monitoring points refer to groundwater monitoring wells, including groundwater background wells deployed upstream of the landfill, and pollution monitoring wells and diffusion wells deployed downstream. Before sampling, the wells are flushed until the water quality is stable. If the treated leachate is allowed to be discharged into surface water bodies, sampling points need to be set up at the surface water discharge outlet.
[0037] Sampling liquid samples involves the following steps:
[0038] S1. Preparation before sampling: Prepare sample bottles of the appropriate specifications and the required preservatives according to the list of test items; rinse the sampler and sample bottle 2-3 times with the water sample to be collected to avoid container contamination.
[0039] S2, Water Sample Collection:
[0040] Surface water sampling: Hold the bottom of the sample bottle and immerse it 20-50 cm below the water surface, with the bottle opening facing the direction of the water flow to collect the water sample;
[0041] Deep water sampling: Using a Bayle tube or submersible pump, the water sample is collected after being lowered to the predetermined depth.
[0042] Groundwater well sampling: Before sampling, the well is flushed, and the amount of water discharged is 3-5 times the volume of water stored in the well pipe. Water samples are collected after the water quality parameters (pH, conductivity, temperature, etc.) have stabilized.
[0043] S3, Sample Preservation and Recording: Inject the collected water sample into the corresponding sample bottle, add preservative as required, seal the container and ensure no air bubbles; affix a label with information consistent with the garbage / soil sample, and fill in the sampling record; at the same time, record parameters such as water temperature, pH, conductivity, dissolved oxygen, and weather conditions on site to provide a basis for the interpretation of results.
[0044] S4, Quality Control Sample Preparation:
[0045] Field blank: Ultrapure water is brought to the sampling site, put into sample bottles, and goes through all the steps of sampling, preservation, and transportation together with the real sample. This is used to check for contamination during transportation and operation.
[0046] Parallel samples: Two identical samples are collected at the same time and at the same sampling point to evaluate the precision of the sampling.
[0047] The drying and sieving of liquid samples includes: measuring 500 mL of the collected and processed liquid sample, i.e., leachate or groundwater sample, into a beaker using a graduated cylinder; sieving the sample in the beaker through a 600-mesh (approximately 20 micrometers in pore size) stainless steel metal filter to retain solid particles; taking approximately 300 mL of saturated NaCl solution (the amount can be adjusted according to the actual retention situation), carefully rinsing the filter with a wash bottle to ensure that all solid particles retained on the filter are rinsed back into the original 500 mL beaker, avoiding loss of microplastics; separating the solid particles in the beaker from the rinsing solution (e.g., through static sedimentation, filtration, etc.), collecting the separated solid particles and drying them to constant weight for later use.
[0048] like Figure 1As shown, the rapid screening method for nanoplastics according to the present invention also includes a rapid screening stage, the core of which is to achieve rapid identification of nanoscale microplastics through reagent ratio and instrument detection. Pretreated solid particles are dissolved in tetrahydrofuran to form a homogeneous sample solution. A matrix solution, sample solution, and cationizing agent solution are mixed in a preset ratio to obtain a mixed solution. The mixed solution is spotted onto a target plate and allowed to crystallize naturally. Spectra are acquired using a MALDI-TOF mass spectrometer, ultimately achieving rapid screening of nanoplastics.
[0049] Specifically, 50 mg of solid sample was collected from the above-mentioned dried and sieved garbage samples, soil samples, or leachate samples and groundwater samples that had been sieved, rinsed, separated and dried, and placed in a beaker. 10 mL of tetrahydrofuran was added to the beaker and stirred to fully dissolve the solid sample, forming a microplastic sample solution with a concentration of 5 mg / mL.
[0050] Accurately weigh 200 mg of imaging matrix DCTB, dissolve it in 10 mL of tetrahydrofuran, stir well, and prepare a matrix solution with a concentration of 20 mg / mL.
[0051] Accurately weigh 50 mg of the cationizing agent silver trifluoroacetate (AgTFA), dissolve it in 10 mL of tetrahydrofuran, stir well, and prepare a cationizing agent solution with a concentration of 5 mg / mL.
[0052] According to the mass ratio of matrix solution: sample solution: cationizing agent solution = 10:10:1, use a pipette to pipette 50 μL of matrix solution, 200 μL of sample solution and 20 μL of cationizing agent solution and add them to a 2 mL centrifuge tube in sequence; tighten the cap of the centrifuge tube and shake thoroughly to mix the three solutions evenly.
[0053] Quickly use a pipette to draw 1 μL of the mixed solution from the centrifuge tube and spot it onto the MALDI-TOF mass spectrometer target plate. Place the target plate under ambient conditions to allow it to crystallize naturally. Once crystallization is complete, it is ready for use.
[0054] The crystallized target plate was placed in a Shimadzu MALDI-TOF mass spectrometer. After setting the instrument parameters, spectral acquisition was performed. By analyzing the characteristic signals in the mass spectrum, it was determined whether there were nanoscale microplastics in the sample.
[0055] Figure 2This is a MALDI-TOF mass spectrum of the nanoscale polystyrene (PS) microplastics of this invention. The horizontal axis represents the mass-to-charge ratio (m / Z), and the vertical axis represents the relative signal intensity. The percentage value of the relative signal intensity reflects the strength of the detected signal. Multiple characteristic signal peaks can be clearly observed in the figure, with mass-to-charge ratios of 2452.4, 2556.3, 2660.3, 2764.4, 2868.6, and 2973.0, respectively. The mass-to-charge ratio difference of 104 among the characteristic peaks is consistent with the molecular weight of the repeating unit of polystyrene (PS), thus proving the presence of nanoscale polystyrene microplastics in the sample. By analyzing the distribution and difference patterns of the characteristic peaks in this mass spectrum, accurate identification of specific types of nanoscale microplastics can be achieved, thus pioneering a rapid screening method for nanoscale MPs using in-situ mass spectrometry.
[0056] This invention designs specific pretreatment processes for multi-media samples of waste, soil, leachate, and groundwater from historically non-standard landfills: solid samples undergo stratified sampling, quartering, and sieving enrichment, while liquid samples undergo targeted sampling, sieving, and rinsing enrichment. This solves the problem in the prior art of lacking a microplastic screening pretreatment scheme suitable for multi-media systems, and the difficulty in distinguishing microplastics from environmental impurities in traditional methods, thus achieving efficient enrichment of nanoscale microplastics in multi-media.
[0057] This invention further and thoroughly solves the core defects of the detection methods in the background technology through a subsequent rapid screening process: by rapidly spotting the matrix, analyte, and cationizing reagent mixed in a specific mass ratio, combined with the laser detection technology of a MALDI-TOF mass spectrometer, it not only overcomes the limitation of spectral image recognition being able to detect microplastics larger than 50 μm, achieving accurate identification of nanoscale microplastics with a particle size of less than 1 micrometer, but also avoids the high misjudgment rate and spectral image recognition of traditional visual observation and infrared spectral sampling detection by precisely matching the mass spectrometry characteristic peak difference value with the molecular weight of the repeating unit of the plastic. With a detection error of 10%-15%, compared to the detection efficiency of pyrolysis-GC-MS / MS (3-5 hours / sample) and spectral image recognition (1-2 hours / sample), this method can complete the detection of 48 sample test points within 30 minutes (adapted to the instrument's sample plate capacity of 48 test points), without the need for repeated calibration. In contrast, traditional methods require 24-48 hours to screen 48 samples, significantly shortening the analysis cycle. This method truly meets the need for rapid and accurate screening of nanoscale microplastics in complex environmental samples, pioneering a new solution for rapid screening of nanoscale MPs using in-situ mass spectrometry.
[0058] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the invention. Various variations can be made to the above embodiments of the present invention. That is, all simple and equivalent changes and modifications made based on the claims and description of this invention fall within the protection scope of the claims. All aspects not described in detail in this invention are conventional technical content.
Claims
1. A rapid screening method for nanoplastics based on MALDI-TOF mass spectrometry, characterized in that, This rapid screening method for nanoplastics includes the following steps: S1, pre-treat solid and liquid samples from historical non-standard landfills to obtain solid particles enriched with nano-sized microplastics, wherein the solid sample is a waste sample or soil sample, and the liquid sample is a leachate sample or groundwater sample. S2, take the solid particles, add an organic solvent to dissolve them, and obtain a microplastic sample solution; S3, the imaging matrix is dissolved in the organic solvent to form a matrix solution, and the cationizing agent is dissolved in the organic solvent to form a cationizing agent solution. The matrix solution: microplastic sample solution: cationizing agent solution = (9-11):(9-11):1 is mixed to obtain a mixed solution; S4, the mixed solution is spotted onto a target plate and allowed to crystallize naturally under environmental conditions; S5. The crystallized target plate is placed in a MALDI-TOF mass spectrometer for spectral acquisition. The presence of nanoscale microplastics in the sample is determined by analyzing the mass spectrometry characteristic signals.
2. The rapid screening method for nanoplastics according to claim 1, characterized in that, In step S1, the pretreatment of the solid sample includes: setting up sampling points by planar and / or vertical point layout, and collecting samples by profile method or drilling method; reducing the collected samples; drying the reduced samples to constant weight at room temperature to 60°C; and sieving the dried samples with a 5-20 mesh sieve to collect the solid particles that pass through the sieve.
3. The rapid screening method for nanoplastics according to claim 2, characterized in that, The planar sampling points are arranged using a grid method or a zoning method; the vertical sampling points collect surface, middle and deep samples at different depths, with surface samples collected at a depth of 0-0.8 meters, middle samples at a depth of 0.5-6 meters, and deep samples at a depth greater than 6 meters.
4. The rapid screening method for nanoplastics according to claim 2, characterized in that, The reduction is performed using the quartering method.
5. The rapid screening method for nanoplastics according to claim 1, characterized in that, In step S1, the pretreatment of the liquid sample includes the following steps: collecting liquid samples by setting up sampling points through the collection system, processing facility, or environmental monitoring points; sieving the liquid sample through a 500-700 mesh sieve to retain solid particles; rinsing the sieve with a saturated sodium chloride solution and collecting the mixture of the rinsed solid particles and the rinsing solution; separating the solid particles from the liquid in the mixture and drying it to constant weight to obtain the solid particles.
6. The rapid screening method for nanoplastics according to claim 5, characterized in that, The sampling points of the collection system include the regulating pool, the observation well and the outlet of the collection well or the drainage blind ditch; the sampling points of the treatment facility include the inlet and outlet of the leachate treatment facility; and the environmental monitoring points include groundwater monitoring wells or surface water discharge outlets.
7. The rapid screening method for nanoplastics according to claim 1, characterized in that, The organic solvent is tetrahydrofuran, and the concentration of the microplastic sample solution is 3-8 mg / mL.
8. The rapid screening method for nanoplastics according to claim 1, characterized in that, The imaging matrix is DCTB, and the concentration of the matrix solution is 15-25 mg / mL.
9. The rapid screening method for nanoplastics according to claim 1, characterized in that, The cationizing agent is silver trifluoroacetate, and the concentration of the cationizing agent solution is 3-8 mg / mL.
10. The rapid screening method for nanoplastics according to claim 1, characterized in that, The mass ratio of the matrix solution, the microplastic sample solution, and the cationizing agent solution is 10:10:1, and the nanoscale microplastics are plastic particles with a particle size of less than 1 micrometer.