System and method for quantitatively determining nanoplastics in aqueous solutions

Abstract

The application provides a system and method for quantitatively determining nanometer plastics in an aqueous solution, and belongs to the technical field of environmental analysis and detection. The system comprises: a carrier gas supply unit for providing carrier gas and regulating the flow rate of the carrier gas, a programmed heat treatment unit, a three-way valve, a drying unit, a microplasma excitation and spectrum detection unit, a data processing unit and a control unit. The entire system is built based on miniaturized electrothermal evaporation and microplasma excitation technology, has the characteristics of low energy consumption and compact structure, has the potential to develop into a field quantitative screening device, and provides a new practical technical scheme for accurate quantitative monitoring of nanometer plastics in environmental water.

Description

Technical Field

[0001] This invention relates to the field of environmental analysis and testing technology, and in particular to a system and method for quantitatively determining nanoplastics in aqueous solutions. Background Technology

[0002] Plastic pollution has become a global environmental problem. Under the long-term effects of physical, chemical, and biological processes, plastic waste in the environment continuously breaks down into microplastics with a particle size of less than 5 mm, which further degrade into nanoplastics with a particle size of less than 1000 nm. Nanoplastics can be continuously generated through natural processes such as weathering, sunlight, mechanical wear, and biodegradation. They are highly mobile, widely diffused in the atmosphere, water, and soil, and can penetrate the cell barriers of organisms, accumulating within them through the food chain. Simultaneously, due to their large specific surface area, nanoplastics readily adsorb toxic substances such as heavy metals and persistent organic pollutants, becoming important carriers of complex pollution. However, due to limitations in current detection technologies regarding pretreatment complexity, analytical sensitivity, and real-time monitoring capabilities, accurate quantitative analysis of nanoplastics in the environment remains a challenge. Summary of the Invention

[0003] In view of the above, the present invention provides a system and method for quantitatively determining nanoplastics in aqueous solutions, aiming to partially solve at least one of the aforementioned technical problems. The technical solution provided by the present invention is as follows.

[0004] According to one aspect of the present invention, a system for quantitatively determining nanoplastics in an aqueous solution is provided, comprising:

[0005] The carrier gas supply unit is used to provide carrier gas and regulate its flow rate.

[0006] The programmed heat treatment unit, located downstream of the carrier gas supply unit, is used to sequentially execute a first heating program and a second heating program on the loaded aqueous solution sample containing nanoplastics. The first heating program is used to evaporate the water in the aqueous solution sample to generate water vapor. The second heating program is used to pyrolyze the aqueous solution sample after the water has been removed to generate pyrolysis gas products.

[0007] The three-way valve is equipped with an inlet connected to the programmed heat treatment unit for the carrier gas to carry pyrolysis gas products and water vapor into the unit, a first outlet for the carrier gas to carry water vapor out of the unit, and a second outlet for the carrier gas to carry pyrolysis gas products out of the unit.

[0008] The drying unit, connected to the second outlet, is used to dry the pyrolysis gas products carried by the carrier gas.

[0009] The micro-plasma excitation and spectral detection unit, located downstream of the drying unit, is used to excite the dried pyrolysis gas products using the generated micro-plasma to produce atomic emission spectra and to collect the atomic emission spectra.

[0010] The data processing unit, connected to the micro-plasma excitation and spectral detection unit, is used to extract carbon atom characteristic spectral lines from the received atomic emission spectra and to perform quantitative analysis of nanoplastics based on the signal intensity of the carbon atom characteristic spectral lines.

[0011] The control unit, connected to the three-way valve, is used to control the flow path switching between the first outlet and the second outlet.

[0012] In some embodiments, the carrier gas supply unit includes a carrier gas cylinder and a gas flow meter. The carrier gas cylinder provides inert gas; the gas flow meter is connected to the carrier gas cylinder via a carrier gas pipeline and is used to regulate the flow rate of the carrier gas within the pipeline.

[0013] In some embodiments, the programmed heat treatment unit includes: a quartz reaction tube, a metal sample boat, a ceramic heating rod, and a temperature controller. The quartz reaction tube serves as the reaction vessel, with a carrier gas pipe inserted inside. The metal sample boat is disposed inside the quartz reaction tube and is used to hold the aqueous solution sample containing nanoplastics. The ceramic heating rod is connected to the metal sample boat and is used to heat the aqueous solution sample containing nanoplastics. The temperature controller is connected to the ceramic heating rod and is used to control the heating temperature of the ceramic heating rod.

[0014] In some embodiments, the drying unit is a drying tube filled with a desiccant; wherein the desiccant is color-changing silica gel.

[0015] In some embodiments, the micro-plasma excitation and spectral detection unit includes: a micro-plasma excitation source, an emission spectrometer, and a high-voltage power supply. The micro-plasma excitation source is connected to the drying unit and is used to excite the dried pyrolysis gas products using the generated micro-plasma. The emission spectrometer is connected to the micro-plasma excitation source and is used to collect the atomic emission spectra generated by the excited pyrolysis product gases. The high-voltage power supply is connected to the micro-plasma excitation source and is used to provide a discharge voltage to enable the micro-plasma excitation source to generate micro-plasma.

[0016] In some embodiments, the control unit is also connected to a gas flow meter, a temperature controller, and a high-voltage power supply, respectively, for performing the following operations: controlling the gas flow meter to adjust the flow rate of the carrier gas; controlling the temperature controller to execute a first heating program and a second heating program; and controlling the high-voltage power supply to adjust the discharge voltage.

[0017] According to another embodiment of the present invention, a method for quantitatively determining nanoplastics in an aqueous solution is also provided, comprising:

[0018] The aqueous solution sample containing nanoplastics was loaded into the programmed heat treatment unit, and the carrier gas supply unit was turned on to introduce carrier gas into the system to purge the flow path.

[0019] Switch the outlet of the three-way valve to the first outlet and keep it open; at the same time, control the programmed heat treatment unit to execute the first heating program, so that the water in the aqueous sample containing nanoplastics evaporates to generate water vapor, and the water vapor is carried by the carrier gas through the first outlet to be discharged from the system.

[0020] Switch the outlet of the three-way valve to the second outlet and keep it open; at the same time, control the programmed heat treatment unit to execute the second heating program, so that the aqueous solution sample after moisture removal is pyrolyzed to generate pyrolysis gas products, and the pyrolysis gas products are carried by the carrier gas through the second outlet into the drying unit for drying.

[0021] The dried pyrolysis product gas enters the micro-plasma excitation and spectral detection unit. The generated micro-plasma is used to excite the dried pyrolysis gas products to produce atomic emission spectra, and the atomic emission spectra are collected.

[0022] The data processing unit extracts the characteristic spectral lines of carbon atoms from the received atomic emission spectra and performs quantitative analysis of the nanoplastics based on the signal intensity of the characteristic spectral lines of carbon atoms.

[0023] In some embodiments, the nanoplastic is any one of polystyrene nanoplastic, polymethyl methacrylate nanoplastic, polylactic acid nanoplastic, and polyvinyl chloride nanoplastic.

[0024] In some implementations, the end temperature of the first heating process does not exceed 300°C; the end temperature of the second heating process is not lower than 600°C.

[0025] In some implementations, the discharge voltage required to generate microplasma is 100-150V; the flow rate of the carrier gas is 75-125mL / min.

[0026] According to embodiments of the present invention, the system and method for quantitative determination of nanoplastics in aqueous solutions provided by the present invention, based on a stepwise "evaporation-pyrolysis" design and automated integrated control, achieves direct, rapid, and accurate quantitative analysis of aqueous nanoplastics without relying on traditional time-consuming "filtration-drying" pretreatment, avoiding sample loss and operational complexity. While ensuring excellent repeatability and quantitative reliability, it improves analytical efficiency and accuracy. Specifically, the system controls the programmed heat treatment unit to sequentially execute a first heating program and a second heating program via a control unit: In the first heating program stage, a three-way valve is used to promptly discharge water from the aqueous sample in the form of water vapor, which not only reduces the processing load of the subsequent drying unit but also effectively reduces the quenching interference of water vapor on the micro-plasma; in the second heating program stage, the control unit switches the flow path of the three-way valve to directionally introduce the pyrolysis product gas into the drying unit for further dehumidification, and then it enters the micro-plasma excitation and spectral detection unit for quantitative detection. The entire system is built based on miniaturized electrothermal volatilization and micro-plasma excitation technology. It features low energy consumption and compact structure, and has the potential to be developed into an on-site quantitative screening device. It provides a new and practical technical solution for the accurate quantitative monitoring of nanoplastics in environmental water bodies. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the system structure for the quantitative determination of nanoplastics in aqueous solution according to the present invention;

[0028] Figure 2 This diagram illustrates the effect of different evaporation times on the intensity of characteristic spectral lines of carbon atoms in the polystyrene (PS), polymethyl methacrylate (PMMA), and polylactic acid (PLA) nanoplastics of this invention.

[0029] Figure 3 This is a graph showing the effect of different evaporation times of the polyvinyl chloride (PVC) nanoplastics of this invention on the intensity of characteristic spectral lines of carbon atoms;

[0030] Figure 4 This is a graph showing the effect of different discharge voltages on the intensity of characteristic spectral lines of carbon atoms in this invention;

[0031] Figure 5 This is a diagram showing the effect of different carrier gas flow rates on the intensity of characteristic spectral lines of carbon atoms in this invention;

[0032] Figure 6 This diagram illustrates the effect of different injection volumes of the aqueous solution sample on the intensity of characteristic spectral lines of carbon atoms.

[0033] [Attached image labels]

[0034] 100 - Carrier gas supply unit, 101 - Carrier gas cylinder, 102 - Gas flow meter;

[0035] 200-Programmed heat treatment unit, 201-Quartz reaction tube, 202-Metal sample boat, 203-Ceramic heating rod, 204-Temperature controller;

[0036] 300 - Three-way valve, 301 - Inlet, 302 - First outlet, 303 - Second outlet;

[0037] 400-Drying Unit;

[0038] 500 - Micro-plasma excitation and spectral detection unit, 501 - Micro-plasma excitation source, 502 - Emission spectroscopy detector, 503 - High voltage power supply. Detailed Implementation

[0039] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the invention. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of the invention for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0040] Currently, the detection of microplastics mainly relies on techniques such as optical microscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy. However, these methods are limited by resolution and cannot be directly applied to the analysis and detection of nanoplastics. Pyrolysis-gas chromatography / mass spectrometry is currently the main method for quantitative analysis of nanoplastics, but it suffers from problems such as large instrument size, high energy consumption, and high cost, and it is difficult to achieve rapid on-site monitoring, thus limiting its application in real-time environmental monitoring. Against this backdrop, developing miniaturized, low-energy-consumption, and suitable quantitative detection techniques for nanoplastics in on-site environmental monitoring is particularly important.

[0041] Microplasma point discharge emission spectroscopy offers advantages such as low power consumption, miniaturization, and low sample consumption, providing new possibilities for the development of this technology. Since carbon is a major component of plastic polymers, quantitative analysis of nanoplastics can be achieved by detecting carbon. However, in practical applications, traditional sample pretreatment methods such as filtration and drying are not only cumbersome but also prone to sample loss. Furthermore, directly introducing liquid samples can cause water vapor to quench the microplasma, severely interfering with its excitation stability and detection sensitivity, thus limiting its application in the direct quantitative analysis of nanoplastics in water samples.

[0042] In view of this, and addressing the problems of easy plasma quenching, complex pretreatment, and difficulty in on-site application of instruments in the direct analysis of nanoplastics in water samples, this invention provides a system and method for the quantitative determination of nanoplastics in aqueous solutions. This scheme is based on a stepwise "evaporation-pyrolysis" design and automated control, and achieves direct, pretreatment-free quantitative analysis of nanoplastics in water samples by coupling dual-channel electrothermal volatilization and micro-plasma point discharge emission spectroscopy. The system features a compact structure, low energy consumption, simple operation, and stable operation, making it suitable for on-site quantitative screening of nanoplastics in environmental water bodies and possessing good practical application prospects.

[0043] Figure 1 This is a schematic diagram of the system structure for the quantitative determination of nanoplastics in aqueous solution according to the present invention.

[0044] like Figure 1 As shown, the system for quantitative determination of nanoplastics in aqueous solution provided by the present invention includes: a carrier gas supply unit 100, a programmed heat treatment unit 200, a three-way valve 300, a drying unit 400, a micro-plasma excitation and spectral detection unit 500, a data processing unit, and a control unit.

[0045] The carrier gas supply unit 100 is used to provide carrier gas and regulate its flow rate. It includes a carrier gas cylinder 101, a carrier gas pipeline, and a gas flow meter 102. The carrier gas cylinder 101 provides inert gas, and the gas flow meter 102 is connected to the carrier gas cylinder 101 via the carrier gas pipeline to regulate the carrier gas flow rate in real time. The inert gas used in this invention can be at least one of nitrogen and argon. Inert gases (especially argon) are chemically stable and do not readily participate in reactions, providing a stable medium for the subsequent excitation and maintenance of microplasma. This helps to form a uniform and continuous microplasma, thereby improving the signal-to-noise ratio and measurement reproducibility of atomic emission spectra.

[0046] The programmed heat treatment unit 200 is located downstream of the carrier gas supply unit 100 and is used to sequentially execute a first heating program and a second heating program on the loaded aqueous solution sample. The first heating program evaporates water in the aqueous solution sample to generate water vapor; the second heating program pyrolyzes the dehydrated aqueous solution sample to generate pyrolysis gas products. The programmed heat treatment unit 200 includes a quartz reaction tube 201, a metal sample boat 202, a ceramic heating rod 203, and a temperature controller 204. The quartz reaction tube 201 serves as the reaction vessel, and the carrier gas pipe is inserted into the quartz reaction tube 201. The metal sample boat 202 is disposed inside the quartz reaction tube 201 and is used to hold the aqueous solution sample. The metal sample boat 202 can be made of thermally conductive materials such as copper. The ceramic heating rod 203 is connected to the metal sample boat 202 and is used to heat the aqueous solution sample. The temperature controller 204 is connected to the ceramic heating rod 203 and is used to control the heating temperature of the ceramic heating rod 203. It can be equipped with a programmable DC power supply to achieve programmed heating, such as executing the first heating program and the second heating program.

[0047] The three-way valve 300 is equipped with an inlet 301, a first outlet 302, and a second outlet 303. The inlet 301 is connected to the programmed heat treatment unit 200, allowing the carrier gas to carry pyrolysis gas products and water vapor into the system. The first outlet 302 allows the carrier gas to carry water vapor out of the system, and the second outlet 303 allows the carrier gas to carry pyrolysis gas products out to the drying unit 400. The introduction of the three-way valve 300 enables real-time, directional separation of the water vapor and pyrolysis product gases generated sequentially in the process. By directly discharging the large amount of water vapor generated in the first heating process through the first outlet 302, the interference of water vapor on the downstream drying unit 400 and the micro-plasma excitation process can be mitigated at the source. This not only reduces the processing load of the drying unit 400 but, more importantly, creates a dry and stable working environment for the micro-plasma, effectively avoiding the quenching effect of water vapor on the micro-plasma, ensuring excitation efficiency and spectral signal stability, and thus improving the accuracy and repeatability of the system's quantitative analysis of nanoplastics.

[0048] The drying unit 400 is connected to the second outlet 303 and is used to dry the pyrolysis gas products carried by the carrier gas. The drying unit 400 uses a drying tube filled with color-changing silica gel, which can effectively remove residual trace moisture in the pyrolysis product gas, ensuring that the pyrolysis product gas entering the subsequent micro-plasma excitation and spectral detection unit 500 is in a fully dry state. Because the color-changing silica gel is chemically stable, it is not easy to react chemically with the pyrolysis product gas during the drying process, which can avoid the introduction of additional impurities or loss of pyrolysis product gas, thereby improving the specificity and accuracy of the detection results.

[0049] The micro-plasma excitation and spectral detection unit 500 is located downstream of the drying unit 400. It is used to excite the dried pyrolysis gas products using generated micro-plasma, causing them to produce atomic emission spectra, and to collect these atomic emission spectra. The micro-plasma excitation and spectral detection unit 500 includes a micro-plasma excitation source 501, an emission spectrometer 502, and a high-voltage power supply 503. The high-voltage power supply 503 is connected to the micro-plasma excitation source 501, providing it with a discharge voltage to generate micro-plasma. The micro-plasma excitation source 501 is connected to the drying unit 400 and is used to generate micro-plasma to excite the dried pyrolysis gas products. The emission spectrometer 502 is connected to the micro-plasma excitation source 501 and is used to collect the atomic emission spectra generated by the excited dried pyrolysis product gas. The micro-plasma excitation source 501 is a tip discharge micro-plasma excitation source, which includes a pair of opposing tungsten needle electrodes and a power supply providing the required voltage to these tungsten needle electrodes. The discharge gap between the tips of the two tungsten needle electrodes is 2-3 mm. The atomic emission spectrometer 502 includes a lens, an optical fiber, and a charge-coupled device (CCD) spectrometer. The lens is used to collect atomic emission spectral signals generated by the micro-plasma excitation source 501; the optical fiber is used to transmit the collected atomic emission spectral signals to the charge-coupled device spectrometer; the charge-coupled device spectrometer is used to receive atomic emission spectra and perform spectral dispersion and photoelectric conversion, with a spectral detection range of 177.0-864.0 nm to meet the detection requirements of carbon atom characteristic spectral lines and other related spectral lines.

[0050] The data processing unit, connected to the micro-plasma excitation and spectral detection unit 500, is used to extract carbon atom characteristic spectral lines from the received atomic emission spectra and to perform quantitative analysis of the nanoplastics based on the signal intensity of the carbon atom characteristic spectral lines. Specifically, the data processing unit simultaneously acquires the carbon atom characteristic spectral lines (e.g., 192.1 nm) and the background signal at adjacent wavelengths (e.g., 194.9 nm). By calculating the difference in signal intensity between the two (i.e., the carbon atom characteristic spectral line signal intensity minus the background signal intensity), the background-corrected carbon atom characteristic spectral line signal intensity is obtained, thereby eliminating spectral interference caused by matrix interference, instrument noise, and micro-plasma instability. After background correction, the data processing unit uses a preset quantitative analysis algorithm—typically employing a calibration curve and its corresponding equation constructed with carbon concentration as the abscissa and the corrected carbon atom characteristic spectral line signal intensity as the ordinate—to substitute the corrected carbon atom characteristic spectral line signal intensity into the algorithm to calculate the carbon content of the nanoplastics. Finally, based on the carbon mass fraction of the nanoplastics, the concentration of the nanoplastics is calculated.

[0051] Taking polystyrene (PS) nanoplastics as an example, the quantitative analysis algorithm is established as follows: A certain amount of PS emulsion is taken and serially diluted with ultrapure water to prepare standard solutions of different concentrations. The intensity of the characteristic carbon atom spectral lines is then measured. A linear fitting curve is plotted with carbon concentration on the x-axis and the measured intensity of the characteristic carbon atom spectral lines on the y-axis, and the corresponding equation is obtained, thus establishing the quantitative algorithm for this analytical method. In actual testing, the aqueous solution sample containing PS nanoplastics is placed in a metal sample boat 202 for quantitative analysis. The measured intensity of the characteristic carbon atom spectral lines is substituted into the above equation to calculate the carbon content. Then, based on the carbon mass fraction of the PS nanoplastics, the concentration of the PS nanoplastics can be calculated.

[0052] In some implementations, the data processing unit can be implemented using conventional hardware, software, or a combination thereof. For example, it can use a dedicated processor (such as a digital signal processor), a general-purpose processor (such as a central processing unit) running custom software modules, or a hybrid mode of both working together. The data processing unit can also be expanded into a programmable computer-based system equipped with input devices (such as a keyboard and mouse) for receiving user instructions and parameters, and output devices (such as a monitor and printer) for displaying analysis reports and quantitative results.

[0053] The control unit is connected to the three-way valve 300 and is used to control the flow path between the first outlet 302 and the second outlet 303 according to the stage switching of the heating program, thereby achieving directional separation of water vapor and pyrolysis product gases. In addition, the control unit is also connected to the gas flow meter 102, the temperature controller 204, and the high-voltage power supply 503 to coordinate the operation of various parts of the system. The control unit can control the gas flow meter 102 to adjust the carrier gas flow rate; control the temperature controller 204 to execute the first heating program and the second heating program sequentially according to a preset program; and control the high-voltage power supply 503 to adjust the discharge voltage required for micro-plasma excitation.

[0054] According to embodiments of the present invention, the system provided by the present invention is based on a stepwise "evaporation-pyrolysis" design and automated integrated control, realizing direct, rapid, and accurate quantitative analysis of aqueous nanoplastics. It eliminates the need for traditional time-consuming "filtration-drying" pretreatment, avoiding sample loss and operational complexity, and improving analytical efficiency and accuracy while ensuring excellent repeatability and quantitative reliability. Specifically, the system controls the programmed heat treatment unit 200 via the control unit to sequentially execute the first and second heating programs. In the first heating program, a three-way valve 300 removes moisture from the aqueous sample as water vapor, reducing the processing load on the subsequent drying unit 400 and providing a dry and stable working environment for the micro-plasma. This effectively avoids the quenching effect of water vapor, ensuring excitation efficiency and spectral signal stability, thereby improving the accuracy and repeatability of quantitative analysis. In the second heating program, the control unit switches the flow path of the three-way valve 300, directing the pyrolysis product gas into the drying unit 400 for deep dehumidification. The gas then enters the micro-plasma excitation and spectral detection unit 500, where it is excited by the micro-plasma to generate atomic emission spectra, which are collected by the emission spectrometer detector 502. The data processing unit extracts carbon atom characteristic spectral lines from the received atomic emission spectra and quantitatively analyzes the nanoplastics based on the signal intensity of these lines to determine their content. The quantitative analysis method is based on low-power, ambient-pressure stable micro-plasma excitation-atomic emission spectroscopy, which can efficiently excite pyrolysis products and collect characteristic emission spectra. By specifically extracting characteristic carbon atom spectral lines, linear quantitative analysis is achieved within a concentration range of 5-227 mg C / L with a low detection limit. The entire system is built based on miniaturized electrothermal volatilization and micro-plasma technology, featuring a compact structure and low energy consumption. It has the potential to be developed into a rapid on-site screening device, providing a practical new technological solution for the accurate quantitative monitoring of nanoplastics in environmental water bodies.

[0055] According to another embodiment of the present invention, a method for quantitatively determining nanoplastics in an aqueous solution is also provided, comprising: loading an aqueous solution sample containing nanoplastics into a programmed heat treatment unit 200, turning on a carrier gas supply unit 100, and supplying the carrier gas to a solution containing nanoplastics. Figure 1In the system for quantitative determination of nanoplastics in aqueous solution, a carrier gas is introduced to purge the flow path. The outlet of the three-way valve 301 is switched to the first outlet 302 and kept open; simultaneously, the programmed heat treatment unit 200 is controlled to execute the first heating program, causing the water in the aqueous sample containing nanoplastics to evaporate, generating water vapor, which is carried by the carrier gas and discharged from the system through the first outlet 302. The outlet of the three-way valve 301 is switched to the second outlet 303 and kept open; simultaneously, the programmed heat treatment unit 200 is controlled to execute the second heating program, causing the aqueous sample after water removal to pyrolyze, generating pyrolysis gas products, which are carried by the carrier gas through the second outlet 204 into the drying unit 400 for drying. The dried pyrolysis product gas enters the micro-plasma excitation and spectral detection unit 500, where the generated micro-plasma excites the dried pyrolysis gas products to generate atomic emission spectra, which are then acquired. The data processing unit extracts the characteristic carbon atom spectral lines from the received atomic emission spectra and performs quantitative analysis of the nanoplastics based on the signal intensity of the carbon atom characteristic spectral lines.

[0056] In some embodiments, the nanoplastic is any one of polystyrene nanoplastic (PS), polymethyl methacrylate nanoplastic (PMMA), polylactic acid nanoplastic (PLA), and polyvinyl chloride nanoplastic (PVC).

[0057] In some embodiments, the loading volume of the aqueous solution sample containing nanoplastics in the programmed heat treatment unit 200 is 20-40 μL. This loading volume ensures that the carbon content of the pyrolysis product gas generated from the pyrolysis of nanoplastics meets the detection requirements, resulting in good intensity and signal-to-noise ratio of the carbon atom characteristic spectral lines, thus guaranteeing sufficient sensitivity for quantitative analysis. Simultaneously, this loading volume effectively saves on the consumption of aqueous solution samples and detection reagents while maintaining analytical performance. It is particularly suitable for applications with limited sample volume or requiring continuous, batch detection, thereby improving the practicality and economy of the method.

[0058] In some embodiments, the parameters of the first heating program are set as follows: its endpoint temperature does not exceed 300°C, and the first heating program is achieved by the control unit controlling the high-voltage power supply 503 to apply a DC voltage of 8-12V. This temperature range can efficiently promote the evaporation of water in the aqueous sample and eliminate water vapor interference, while avoiding premature pyrolysis of the nanoplastics, thus laying the foundation for the specific and accurate detection of the subsequent carbon atom characteristic spectral lines. The control parameters of the second heating program are set as follows: its endpoint temperature is not lower than 600°C, and the second heating program is achieved by the control unit controlling the high-voltage power supply 503 to apply a DC voltage of 20-24V. This temperature condition ensures that various nanoplastics (such as polystyrene, polymethyl methacrylate, polylactic acid, polyvinyl chloride, etc.) are fully and completely pyrolyzed, transforming into stable pyrolysis product gases (such as methyl methacrylate, lactide, octadecyl alcohol, eicosanool, monocyclic aromatic hydrocarbons and their derivatives, etc.). This helps to achieve consistency in the pyrolysis process of different types and batches of aqueous solution samples, thereby improving the stability and reproducibility of the correspondence between the intensity of carbon atom characteristic spectral lines and the concentration of nanoplastics, providing a key guarantee for the reliability of quantitative results.

[0059] In some implementations, the duration of the first heating procedure is specifically set according to the type of nanoplastic. For polystyrene nanoplastics, the duration is 50-70 seconds; for polymethyl methacrylate and polylactic acid nanoplastics, the duration is 25-35 seconds; and for polyvinyl chloride nanoplastics, the duration is 400-440 seconds. These differentiated time settings aim to optimize the pyrolysis pretreatment process by combining the physicochemical properties of different types of nanoplastics, ensuring sufficient evaporation of moisture and complete elimination of interference, thereby providing effective assurance for the accurate and stable detection of subsequent nanoplastics.

[0060] In some implementations, the discharge voltage required to generate microplasma is 100-150V. This voltage range allows for stable microplasma discharge under ambient pressure, characterized by high discharge efficiency and low energy consumption. The carrier gas flow rate in the system is 75-125mL / min. A stable gas flow helps maintain the stability of the plasma discharge and reduces the residence time of gases (such as water vapor and pyrolysis product gases) in the system, thereby improving the overall detection efficiency.

[0061] The present invention will be described in detail below with reference to specific embodiments. It should be noted that the described embodiments are merely some, not all, of the embodiments of the present invention. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0062] Example 1:

[0063] Build as Figure 1 The system shown is for the quantitative determination of nanoplastics in aqueous solution. The specific process is as follows.

[0064] The outlet of the carrier gas cylinder 101 is connected to the inlet of the gas flow meter 102 via a carrier gas pipeline, forming a carrier gas supply unit 100. Next, the outlet of the gas flow meter 102 is connected to the inlet of the quartz reaction tube 201. A metal sample boat 202 is placed inside the quartz reaction tube 201, and a ceramic heating rod 203 is mounted below the metal sample boat 202. The electrical connection of the ceramic heating rod 203 is connected to a temperature controller 204, thus constructing a programmed heat treatment unit 200. The outlet of the quartz reaction tube 201 is connected to the inlet 301 of a three-way valve 300 via a pipeline. The three-way valve 300 also has a first outlet 302 and a second outlet 303. A drying unit 400 is connected to the second outlet 303, and the drying unit 400 is a drying tube containing color-changing silica gel. The micro-plasma excitation and spectral detection unit 500 is located downstream of the drying unit 400. The unit includes a micro-plasma excitation source 501, an emission spectrometer 502, and a high-voltage power supply 503. The micro-plasma excitation source 501 is a polytetrafluoroethylene (PTFE) cavity containing a pair of opposing tungsten needle electrodes with a 3 mm gap. The micro-plasma excitation source 501 is connected to both the high-voltage power supply 503 and the emission spectrometer 502. The emission spectrometer 502 includes a collecting lens, an optical fiber, and a portable charge-coupled device (CCD) spectrometer with a spectral range of 177.0-864.0 nm, used to acquire atomic spectral data in real time and connect it to the data processing unit. Simultaneously, the control interfaces of the gas flow meter 102, temperature controller 204, three-way valve 300, and high-voltage power supply 503 are connected to the control unit, forming a centralized control system that coordinates and controls the carrier gas flow rate, heating program, flow path switching, and discharge voltage, achieving automated system operation.

[0065] Quantitative analysis method flow

[0066] Using the system constructed in Example 1, taking the quantitative detection of polystyrene (PS) nanoplastics in water samples as an example, the specific steps are as follows:

[0067] 1. Initialization: Switch the three-way valve 300 to the first outlet 301. Use argon as the carrier gas, set the flow rate to 100 mL / min, turn on the carrier gas supply unit 100, and purge the system flow path for about 10 seconds to remove air.

[0068] 2. Sample Injection and Evaporation: 30 μL of PS nanoplastic water sample is taken using a microsyringe and injected into the metal sample boat 202 located inside the quartz reaction tube 201. The first heating program is initiated via the control unit: the temperature controller 204 outputs approximately 10V DC voltage, heating the metal sample boat 202 at 10V DC voltage for 60 seconds. During this process, the water vapor formed by the evaporation of water in the sample is carried by argon gas and discharged from the system through the first outlet 301.

[0069] 3. Switching and Pyrolysis: After the first heating program ends, the control unit automatically switches the three-way valve to the second outlet 302. The second heating program then begins: the temperature controller 204 outputs approximately 22V, causing the temperature of the metal sample boat 202 to rapidly rise to approximately 630℃ within seconds and remain at that temperature for approximately 90 seconds. At this time, the dried PS nanoplastic undergoes pyrolysis, generating pyrolysis product gases mainly composed of small-molecule hydrocarbons.

[0070] 4. Excitation and Detection: The pyrolysis product gas, carried by argon gas, enters a drying tube containing color-changing silica gel through the second outlet 302 for deep dehumidification. The dried pyrolysis product gas then continues into the micro-plasma excitation source 501. At this time, the control unit controls the high-voltage power supply 503 to output a discharge voltage of approximately 125V, generating a stable micro-plasma between the tungsten needle electrodes. The pyrolysis product gas is atomized and excited in the micro-plasma, producing an atomic emission spectrum. A CCD spectrometer acquires the full spectrum with an integration time of 100 ms.

[0071] 5. Data Processing and Quantitative Analysis: The data processing unit receives the acquired spectral data. The software automatically extracts the signal intensity of the characteristic emission lines of carbon atoms (the center wavelength of the CCD spectrometer is approximately 192.1 nm). Simultaneously, background wavelengths without characteristic emission (e.g., 194.9 nm) near the characteristic emission lines of carbon atoms are selected for signal acquisition, and background correction is performed on the carbon atom characteristic emission line signals to obtain the net signal intensity. Finally, based on a pre-established calibration curve between the PS nanoplastic concentration and the net signal intensity, the concentration of PS nanoplastics in the aqueous sample is calculated.

[0072] Based on the above quantitative analysis method, the effect of the first heating program setting time (i.e., evaporation time) on the detection results of different types of nanoplastics was investigated. Specific experimental results are as follows: Figure 2 , Figure 3 As shown.

[0073] Figure 2 This diagram illustrates the effect of different evaporation times of polystyrene (PS), polymethyl methacrylate (PMMA), and polylactic acid (PLA) nanoplastics on the intensity of characteristic spectral lines of carbon atoms.

[0074] like Figure 2As shown, for the three nanoplastics polystyrene (PS), polymethyl methacrylate (PMMA), and polylactic acid (PLA), the relative intensities of the carbon atom characteristic spectral lines all reached their maximum values ​​when the evaporation time was set to 30 s. When the evaporation time was too short (e.g., 0 s or 20 s), the signal intensity was significantly lower. This indicates that the moisture was not completely evaporated, and the residual water vapor may have interfered with the stability of the microplasma, leading to a decrease in detection sensitivity.

[0075] Figure 3 This diagram illustrates the effect of different evaporation times of the polyvinyl chloride (PVC) nanoplastics of this invention on the intensity of characteristic spectral lines of carbon atoms.

[0076] like Figure 3 As shown, PVC exhibits extremely high sensitivity to evaporation time. When the evaporation time is set to 30s or 180s, the relative intensity is close to 0. This indicates that within these short timeframes, moisture cannot be effectively removed, severely inhibiting subsequent pyrolysis and excitation processes. As the evaporation time is extended to 420s, the signal intensity rises sharply and reaches a peak. This suggests that PVC nanoplastics require a longer evaporation time to completely remove moisture in order to ensure the effective generation and detection of subsequent pyrolysis product gases.

[0077] Furthermore, polystyrene (PS) was selected as the research object, and three parameters—discharge voltage, carrier gas flow rate, and injection volume of aqueous solution samples—were systematically optimized. The results are as follows: Figures 4-6 As shown.

[0078] Figure 4 This diagram illustrates the effect of different discharge voltages on the intensity of characteristic spectral lines of carbon atoms.

[0079] like Figure 4 As shown, at lower discharge voltages (e.g., 50V), the signal strength is weak due to insufficient micro-plasma energy. With increasing discharge voltage, the signal strength increases significantly, reaching a peak at 125V. However, when the discharge voltage continues to rise to 150V and 175V, the signal strength decreases. This may be because excessively high discharge voltages (e.g., greater than 150V) affect plasma stability, leading to reduced excitation efficiency. Therefore, the preferred operating range for the discharge voltage can be set to 100-150V.

[0080] Figure 5 This diagram illustrates the effect of different carrier gas flow rates on the intensity of characteristic spectral lines of carbon atoms.

[0081] like Figure 5As shown, the signal intensity is weak at lower carrier gas flow rates (e.g., 75 mL / min); as the carrier gas flow rate increases, the signal intensity rises significantly, reaching a peak at 100 mL / min; when the carrier gas flow rate continues to increase to 125 mL / min and above, the signal intensity decreases instead. This may be because excessively high carrier gas flow rates (e.g., greater than 125 mL / min) result in a short residence time of the pyrolysis product gas in the excitation region, affecting the full excitation of atoms. Based on this, the preferred carrier gas flow rate range can be set to 75-125 mL / min.

[0082] Figure 6 This diagram illustrates the effect of different injection volumes of the aqueous solution sample on the intensity of characteristic spectral lines of carbon atoms.

[0083] like Figure 6 As shown, the signal intensity is weak at smaller injection volumes (e.g., 10 μL); the signal intensity increases significantly with increasing injection volume, reaching a peak at 30 μL; when the volume continues to increase to 40 μL, the increase in signal intensity slows down, which may be due to insufficient pyrolysis and liquid overflow caused by excessive sample volume (e.g., 40 μL). Based on this, the preferred injection volume range is 20-40 μL.

[0084] Performance evaluation

[0085] Using the quantitative analysis method described above, the quantitative properties of four common nanoplastics—polystyrene (PS), polymethyl methacrylate (PMMA), polylactic acid (PLA), and polyvinyl chloride (PVC)—were evaluated. The results are as follows:

[0086] 1. Linear range and detection limit

[0087] Within a concentration range of 5–227 mg C / L, the intensity of the characteristic carbon atom spectral lines of the four nanoplastics all exhibited a good linear response relationship with their concentration (R0). 2 > 0.998). Based on a signal-to-noise ratio of three times, the detection limits of the method were calculated to be: PS 4.08 mg C / L, PMMA 11.02 mg C / L, PLA 5.42 mg C / L, and PVC 8.14 mg C / L, indicating that the method has high detection sensitivity for different types of nanoplastics.

[0088] 2. Precision

[0089] By performing seven consecutive measurements on the standard solutions of each nanoplastic, the relative standard deviation (RSD) of the intensity of the characteristic spectral lines of carbon atoms was less than 4%, indicating that the method has good reproducibility.

[0090] 3. Actual water sample spiked recovery

[0091] To further verify the applicability of the method in real samples, spiked recovery experiments were conducted on tap water and reservoir surface water. The results showed that the spiked recoveries of the four nanoplastics in the two water samples ranged from 84.6% to 109.1%, indicating that the method can maintain high accuracy and reliability in real environmental water sample matrices and is suitable for quantitative analysis of real environmental water samples.

[0092] In summary, this invention, through its unique dual-channel design and integrated automated control process, enables direct, rapid, and stable quantitative determination of nanoplastics in the aquatic environment, providing a reliable tool for monitoring and research in related fields.

[0093] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A system for quantitatively determining nanoplastics in aqueous solution, characterized in that, include: A carrier gas supply unit is used to provide carrier gas and regulate the flow rate of the carrier gas; A programmed heat treatment unit, located downstream of the carrier gas supply unit, is used to sequentially execute a first heating program and a second heating program on the loaded aqueous solution sample containing nanoplastics; wherein, the first heating program is used to evaporate the water in the aqueous solution sample to generate water vapor; and the second heating program is used to pyrolyze the aqueous solution sample after the water has been removed to generate pyrolysis gas products. A three-way valve is provided with an inlet connected to the programmed heat treatment unit for the carrier gas to carry the pyrolysis gas products and water vapor into it, a first outlet for the carrier gas to carry the water vapor out, and a second outlet for the carrier gas to carry the pyrolysis gas products out. A drying unit, connected to the second outlet, is used to dry the pyrolysis gas products carried by the carrier gas; The micro-plasma excitation and spectral detection unit, located downstream of the drying unit, is used to excite the dried pyrolysis gas products with the generated micro-plasma to produce atomic emission spectra and to collect the atomic emission spectra. The data processing unit, connected to the micro-plasma excitation and spectral detection unit, is used to extract carbon atom characteristic spectral lines from the received atomic emission spectrum and to perform quantitative analysis of the nanoplastics based on the signal intensity of the carbon atom characteristic spectral lines. The control unit, connected to the three-way valve, is used to control the flow path switching between the first outlet and the second outlet.

2. The system according to claim 1, characterized in that, The carrier gas supply unit includes: Carrier gas cylinders are used to supply inert gases; and A gas flow meter, connected to the carrier gas cylinder via a carrier gas pipeline, is used to regulate the flow rate of the carrier gas within the carrier gas pipeline.

3. The system according to claim 2, characterized in that, The programmed heat treatment unit includes: A quartz reaction tube serves as a reaction vessel, and the carrier gas pipe is inserted into the quartz reaction tube; A metal sample boat is placed inside the quartz reaction tube to hold the aqueous solution sample containing nanoplastics; A ceramic heating rod, connected to the metal sample boat, is used to heat the aqueous solution sample containing nanoplastics; and A temperature controller, connected to the ceramic heating rod, is used to control the heating temperature of the ceramic heating rod.

4. The system according to claim 1, characterized in that, The drying unit is a drying tube filled with desiccant; The desiccant is color-changing silica gel.

5. The system according to claim 1, characterized in that, The micro-plasma excitation and spectral detection unit includes: A micro-plasma excitation source is connected to the drying unit and is used to excite the dried pyrolysis gas products using the generated micro-plasma. An emission spectrometer, connected to the microplasma excitation source, is used to collect the atomic emission spectra generated by the excited pyrolysis product gas after drying; and A high-voltage power supply, connected to the micro-plasma excitation source, is used to provide a discharge voltage to enable the micro-plasma excitation source to generate the micro-plasma.

6. The system according to claim 1, characterized in that, The control unit is also connected to a gas flow meter, a temperature controller, and a high-voltage power supply, respectively, and is used to perform the following operations: Control the gas flow meter to adjust the flow rate of the carrier gas; Control the temperature controller to execute the first heating program and the second heating program; and Control the high-voltage power supply to adjust the discharge voltage.

7. A method for quantitatively determining nanoplastics in an aqueous solution, characterized in that, include: An aqueous sample containing nanoplastics is loaded into a programmed heat treatment unit, and a carrier gas supply unit is turned on to purge the flow path into the system as described in any one of claims 1 to 6. Switch the outlet of the three-way valve to the first outlet and keep it open; at the same time, control the programmed heat treatment unit to execute the first heating program, so that the water in the aqueous solution sample containing nanoplastics evaporates to generate water vapor, and the water vapor is carried by the carrier gas through the first outlet to be discharged from the system. The outlet of the three-way valve is switched to the second outlet and kept open; at the same time, the programmed heat treatment unit is controlled to execute the second heating program, so that the aqueous solution sample after the moisture is removed is pyrolyzed to generate pyrolysis gas products, and the pyrolysis gas products are carried by the carrier gas through the second outlet into the drying unit for drying. The dried pyrolysis product gas enters the micro-plasma excitation and spectral detection unit, where the generated micro-plasma excites the dried pyrolysis gas product to produce an atomic emission spectrum, and the atomic emission spectrum is collected. The data processing unit extracts carbon atom characteristic spectral lines from the received atomic emission spectrum and performs quantitative analysis of the nanoplastics based on the signal intensity of the carbon atom characteristic spectral lines.

8. The method according to claim 7, characterized in that, The nanoplastic is any one of polystyrene nanoplastic, polymethyl methacrylate nanoplastic, polylactic acid nanoplastic, and polyvinyl chloride nanoplastic.

9. The method according to claim 7, characterized in that, The final temperature of the first heating process does not exceed 300°C; The final temperature of the second heating process shall not be lower than 600°C.

10. The method according to claim 7, characterized in that, The discharge voltage required to generate the microplasma is 100-150V; The flow rate of the carrier gas is 75-125 mL / min.

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