A system and method for automated qualitative and quantitative analysis of organic compounds using a thermal analyzer and a gas chromatograph-mass spectrometer

Abstract

The present application relates to a kind of systems and methods for using thermal analyzer and GC-MS automatic qualitative and quantitative analysis of organic matter, the system includes thermal gravimetric analyzer (TGA), preconcentrator (PRC) and gas chromatography mass spectrometer (GC-MS);The outlet of the TGA device is connected with the inlet of the PRC device by pipeline, the pipeline is transparent glass tube or polytetrafluoroethylene tube, inert quartz wool is inserted in the inside of the pipeline, the outlet of the PRC device is connected with the GC-MS device;The qualitative and quantitative analysis is based on the development of PRC-based interface device, combined with TGA and GC / MS, builds TGA-PRC-GC / MS system, can observe the pyrolysis weight loss process of microplastic, and the characteristic of small molecule volatile product escaped from microplastic pyrolysis is analyzed in combination with GC / MS, and the method for qualitatively and quantitatively analyzing microplastic is established.The present application studies microplastic in sample, has good recognizability and accuracy, and reaches good effect for qualitative and quantitative research of microplastic.

Description

TECHNICAL FIELD

[0001] The present application relates to the detection technology of microplastics, and in particular to a system and method for automatically qualitatively and quantitatively analyzing organic matters by using a thermal analyzer and a GC-MS. BACKGROUND

[0002] Plastics, as a widely used industrial product, has increasingly rich types, continuously expanding application fields, and increasing production year by year. While bringing convenience to people's daily production and life, it also brings huge environmental pollution. Microplastics are directly produced by industrial activities, or formed in the environment by plastics under the action of hydrolysis, photodegradation, mechanical wear and tear, and biodegradation, etc. Microplastics are stable and difficult to degrade, and have been listed as one of the top ten emerging pollutants by the United Nations Environment Programme. Microplastics migrate over long distances with rivers, oceans and atmosphere, and are easily ingested by microorganisms due to their small size, which has great potential risks to the environment, ecosystem and organisms, and gradually attracts the attention and research of scholars all over the world. Therefore, the detection and monitoring of microplastics cannot be relaxed.

[0003] At present, the qualitative and quantitative analysis methods of microplastics include visual identification method, spectral analysis method and thermal analysis method, etc. The visual identification method is fast and convenient, but cannot be used to identify particles with a particle size of <500 μm, and the detection is very time-consuming. The spectral analysis method mainly includes Fourier transform infrared spectroscopy and Raman spectroscopy,

[0004] Among them, infrared spectroscopy has the advantages of rapidity, simple operation, accurate identification, etc., but it is easily disturbed by the aging degree and unevenness of the measured microplastics; the detection limit of Raman spectroscopy can reach 500 nm, but it cannot measure samples that produce fluorescence effects in laser light, and the samples need to be purified before measurement to prevent fluorescence effects. Thermal analysis method identifies microplastic components through the decomposition products of the measured sample after heating, which has the advantages of small sample size and no need for pretreatment. Thermogravimetric analysis, differential scanning calorimetry and thermal cracking are the three most common thermal analysis methods, which are usually combined with other analysis methods to improve the detection sensitivity of the target component. Among them, the combination of thermogravimetric analyzer (TGA) and gas chromatography mass spectrometry (GC-MS) is a common detection technology for qualitative and quantitative analysis of microplastics. The detection principle is to heat the microplastics in an inert gas, analyze the thermodynamic properties of the microplastics, introduce the pyrolysis products generated by heating into the GC-MS for separation and detection, identify the microplastics through their characteristic components, establish a selected ion scanning method for microplastics, and establish a calibration curve according to the standard sample. The results of the sample detection are substituted into the calibration curve to obtain the quantitative results. Although this technology is common in the chemical analysis of microplastics, there are still many shortcomings, such as 1. TGA and GC-MS are independent analysis instruments and cannot be directly connected, which requires small-volume quantitative ring transfer; or the pyrolysis products are collected by an adsorption tube and then manually introduced into the GC-MS; 2. The interface device of TGA and GC-MS uses a quantitative ring, and the sampling volume is 0.5 mL or 1 mL, which can only remove the product components at a certain temperature point or a certain time point. Small-volume sampling has many disadvantages: it cannot remove the pyrolysis products generated during the whole weight loss process; the sensitivity is low; the pyrolysis products are directly introduced into the GC-MS without purification, and the particulate matter will accumulate on the pipeline, causing pollution to the pipeline and seriously affecting the analysis results; impurity gases such as nitrogen and carbon dioxide will also interfere with the detection results of GC-MS. SUMMARY

[0005] The purpose of the present application is to overcome the technical problems of existing sampling instability, low sensitivity, pipeline pollution and interference of impurity gases, and to provide a system and method for automatic qualitative and quantitative analysis of organic matter using a thermal analyzer and a gas chromatograph mass spectrometer.

[0006] The present application is based on the development of a pre-concentrator (PRC) based interface device, combined with TGA and GC-MS, to build a TGA-PRC-GC / MS system. The method for qualitative and quantitative analysis of microplastics is established by observing the thermal decomposition weight loss of microplastics and analyzing the characteristics of small molecular volatile products released by microplastics.

[0007] The specific scheme is as follows:

[0008] The interface device of the application is designed to use PRC as the main part of the sampling device, connect TGA and GC-MS, and form a TGA-PRC-GC / MS analysis system. The PRC has a temperature control function, and the temperature control range is -190 DEG C to 200 DEG C; it has a sampling power, and can collect gas in the range of 4-2000 mL, and also can accurately sample 1.0 mL. Through the combination of adsorption filler and low temperature means, the target component is enriched and concentrated, and then the temperature is adjusted. According to the different volatilization properties of the target and impurities at low temperature, nitrogen, oxygen, carbon dioxide, water, methane and other impurities can be removed, and the characteristics of the volatile organic matter to be measured can be retained. The TGA-PRC-GC / MS analysis system can be built, and the pyrolysis weight loss of microplastics can be observed and analyzed at the same time. The pyrolysis products are automatically collected and qualitatively and quantitatively analyzed. The technical method is simple to operate, easy to maintain, high in sensitivity, small in sample amount, and does not need pretreatment. It can be used for identification and quantitative detection of microplastics or other high molecular organic matters, and the detection result is accurate.

[0009] A system and method for automatic qualitative and quantitative analysis of organic matter using a thermal analyzer and a GC-MS instrument, comprising the following contents: the system is composed of three devices, namely TGA device, PRC device and GC-MS device; the outlet of the TGA device is connected with the inlet of the PRC device through a pipeline, the pipeline is a transparent glass tube or a polytetrafluoroethylene tube, inert quartz wool is inserted into the inside of the pipeline, and the outlet of the PRC device is connected with the GC-MS device;

[0010] The specific steps of qualitative and quantitative analysis include:

[0011] (1) first, the thermal analysis parameters of microplastics are established in the TGA device, and the thermodynamic parameters of the microplastic standard decomposition are analyzed by the quality change of the microplastic standard under the conditions of inert environment and program-controlled weight loss temperature, so as to obtain the time length of weight loss;

[0012] (2) uniform sampling is carried out in the whole process of weight loss, and the sampling volume is calculated according to the sampling flow rate;

[0013] (3) the sampling flow rate, the sampling volume and other parameters of automatic collection of gas are set in advance in the PRC device, then the sample is pre-concentrated and the impurities in the gas sample to be measured are removed after the sample enters the PRC device, so as to obtain the small molecular products volatilized by the microplastic standard pyrolysis;

[0014] (4) the small molecular products volatilized by the microplastic standard pyrolysis are concentrated and introduced into the GC-MS device for detection, so as to obtain a chromatogram and proceed to the next step;

[0015] (5) according to the characteristic thermal decomposition gas components of the microplastic standard, establish the selected ion scan method of GC-MS, prepare different quality of the microplastic standard, and obtain the chromatogram of the corresponding characteristic component of the thermal decomposition product by GCMS detection, draw the standard curve according to the peak area of the chromatogram and the quality of the microplastic, and calculate the content of the microplastic;

[0016] (6) the target object to be measured is operated through the above steps (2) to (4), and the content of the microplastic in the target object is obtained according to the characteristic component calculated in step (5) according to the standard curve of the microplastic standard.

[0017] Further, the outlet of the PRC device is connected to the inlet of the GC-MS device with a No. 1 inertized metal tube connected to the carrier gas; the outlet of the PRC device is connected to the inlet of the chromatographic column in the GC-MS device with a No. 2 inertized metal tube, and the inertized metal tube refers to a metal tube with inertized material coated on the inner wall;

[0018] Preferably, the inner walls of the metal tube and the glass tube used above are treated by the inertized coating technology of molten silicon, and the inertized material is a silanized material.

[0019] Among them, the inner wall of the polytetrafluoroethylene tube does not need to be inertized, because the polytetrafluoroethylene material itself has excellent chemical stability, corrosion resistance, high lubrication and non-stickiness, electrical insulation and good aging resistance, etc., and will not have physical adsorption or chemical reaction with the components to be analyzed.

[0020] Further, in step (1), the temperature rising rate of the TGA device is ≤100℃ / min, and the temperature is ≤1000℃;

[0021] Preferably, the initial temperature is 35-45℃, and then the temperature is raised to 550-750℃ at a temperature rising rate of 80-100℃ / min, and the total time used is 5.5-6.8min;

[0022] More preferably, the initial temperature is 40℃, and then the temperature is raised to 650℃ at a temperature rising rate of 100℃ / min, and the total time used is 6.1min.

[0023] Further, in step (1), the thermal analysis parameters of the microplastic are established in the TGA device, the N2 flow rate is 55-65mL / min, preferably 60mL / min; the protective gas N2 flow rate is 10-30mL / min, preferably 20mL / min; and the weight loss temperature is 0-1000℃, preferably 200-800℃, more preferably 300-660℃;

[0024] Although most of the microplastics have a weight loss temperature range below 660℃, there are still some microplastics with a weight loss temperature greater than 660℃, distributed in the range of 660℃-1000℃;

[0025] Preferably, the protective gas is defined as a gas that protects the balance in the TGA device from being contaminated by thermal decomposition gas, including at least one of oxygen, carbon dioxide or inert gas, preferably nitrogen.

[0026] Further, in step (2), the sampling volume = the sampling time x the sampling flow rate; the sampling flow rate is set according to the carrier gas flow rate of the TGA device; the sampling time is calculated according to the TGA thermal decomposition behavior to obtain the sampling time.

[0027] Further, in step (3), the PRC device, the sampling flow rate is set to 20-120 mL / min, with an accuracy of ±1 mL / min; the sampling accuracy is 1.0±0.05 mL; the sampling gas range is 4-2000 mL, with an accuracy of ±1 mL;

[0028] Optionally, the sampling conditions: the transfer line stability is maintained at 80-120℃; the sampling time is 6-10 min;

[0029] Preferably, the transfer line stability is maintained at 100℃; the sampling time is 8 min.

[0030] Further, the pre-concentration in step (3) includes: the PRC device is divided into three-stage adsorption traps, which are first-stage cold trap, second-stage cold trap and third-stage cold trap, respectively; the PRC device functions to remove impurities and water, and to concentrate and enrich the gas; the PRC device can be selected conventionally, and in this application, it is preferably a three-stage cold trap pre-concentration instrument, which can be Nutech (8910) in particular.

[0031] The operating parameters of the three-stage adsorption traps are as follows:

[0032] The first-stage cold trap has a trapping temperature of -160 to -140℃, a preheating temperature of -40 to -20℃, an analysis temperature of 20 to 40℃, a baking temperature of 160 to 200℃, and a baking time of 5 to 15 min; preferably, the trapping temperature is -150℃, the preheating temperature is -30℃, the analysis temperature is 30℃, the baking temperature is 180℃, and the baking time is 10 min, so as to remove water in the sample;

[0033] Optionally, the second-stage cold trap: trapping temperature -30 to -10℃, preheating temperature -40 to -20℃, desorption temperature 210 to 250℃, desorption time 1.5 to 3.5min, baking temperature 215 to 255℃, baking time 2 to 6min; preferably, trapping temperature -20℃, preheating temperature 30℃, desorption temperature 230℃, desorption time 2.5min, baking temperature 235℃, baking time 4min, so as to remove rare gases, residual water, nitrogen, oxygen or methane in the sample, etc.

[0034] Optionally, the third-stage cold trap: trapping temperature -160 to -200℃, sample injection time 0.5 to 2.5min, baking time 2 to 4min; preferably, trapping temperature -180℃, sample injection time 1.5min, baking time 3min, so as to enter the GC-MS device for analysis.

[0035] Further, the volatile and semi-volatile organic compounds of polar organic compounds, non-polar organic compounds, active sulfides and active nitrogen compounds with carbon number below C18 in the sample to be tested are subjected to the pre-concentration treatment, so as to remove water, CO2, N2and inert gases in the gas sample to be tested;

[0036] Optionally, the polar organic compounds include aldehyde, alcohol, ester, ketone and ether compounds.

[0037] Further, the system and method of organic compounds, characterized in that: the GC-MS device in step (4), wherein,

[0038] Chromatographic conditions: chromatographic column: DB-624, 60m x 0.25mm x 1.4μm; injection port temperature 150-250℃; carrier gas: high-purity helium; constant pressure mode, 50-150psi; temperature rising program: 40-50℃ for 2-4min, rising to 150-210℃ at 10-20℃ / min, then rising to 220-260℃ at 20-30℃ / min, holding for 5-10min; detector: at least one of mass spectrometry MSD detector or FID detector;

[0039] Preferably, the injection port temperature is 200℃; the constant pressure mode is 100psi; the temperature rising program is 50℃ for 2min, rising to 180℃ at 10℃ / min, then rising to 240℃ at 20℃ / min, holding for 5min; the detector is at least one of mass spectrometry MSD detector or FID detector;

[0040] Mass spectrometry conditions:

[0041] Optionally, the MSD detector: ion source is EI source, energy is 70ev; solvent delay is 1.0-3.0min; transfer line temperature is 100-300℃; full scan range is 35-300amu;

[0042] Preferably, the MSD detector: ion source is an EI source with an energy of 70ev; solvent delay 2.0min; transfer line temperature 230℃; full scan range 35-300amu.

[0043] Optionally, the FID detector: detector temperature 250℃; H2 flow rate 30-60mL / min; air flow rate 150-450mL / min; tailing nitrogen 10-100mL / min.

[0044] Preferably, the FID detector: detector temperature 250℃; H2 flow rate 45mL / min; air flow rate 300mL / min; tailing nitrogen 10mL / min.

[0045] Further, the qualitative analysis in step (5) is based on the chromatogram in step (4) to obtain characteristic chromatographic peaks of each component of the microplastic, one component is selected, which is the component of the microplastic and the relative percentage content of the components is fixed during the thermal decomposition product of the microplastic during the TGA program running, and can represent the component of the microplastic, and when the GC-MS running program is unchanged, the selected ion scan mode is established according to the retention time and characteristic ion fragments of the component, and the characteristic chromatographic peak represents the microplastic.

[0046] Preferably, the characteristic component refers to a characteristic component selected from the microplastic pyrolysis products with a relatively large relative percentage content and significantly different from other microplastics.

[0047] Further, according to the calculation of three times the signal-to-noise ratio, the detection limits of PAN, PVA and PVC microplastics are 0.0748ug / g, 0.0057ug / g and 0.0100ug / g respectively.

[0048] Beneficial effects:

[0049] In the present application, the TGA-PRC connecting device is designed, which can collect volatile components in the pyrolysis products, does not affect the balance of the TGA internal balance, can prevent pipeline adsorption of samples or cross contamination, and the sampling flow rate and volume range can be set, not limited to the quantitative ring mode, compared with other thermal analysis-GC-MS technology, the TGA-PRC-GC / MS combined technology is more convenient to operate, more sample components can be collected, and the detection sensitivity is higher.

[0050] In addition, the experimental technical method based on the TGA-PRC-GC / MS analysis system has the characteristics of small sampling amount, simple operation, convenient maintenance and potential application, improves the sensitivity of the existing thermal analysis combined with GC-MS analysis method, and can comprehensively analyze the characteristics of microplastic pyrolysis small molecule volatile products, greatly saving the labor.

[0051] In summary, the use of the TGA-PRC-GC / MS analysis system and the experimental method flow are constructed, the microplastics in the sample are researched, good identification and accuracy are obtained, and the qualitative and quantitative research on the microplastics reaches good effects. Meanwhile, the PRC interface is suitable for connecting the TGA and the PRC, is simple and convenient to maintain and operate, has high purification efficiency, and is low in cost. BRIEF DESCRIPTION OF DRAWINGS

[0052] In order to more clearly illustrate the technical solutions of the present application, the following will briefly introduce the drawings. Obviously, the drawings described below only relate to some embodiments of the present application, and not limit the present application.

[0053] Figure 1 is a three-way schematic diagram for TGA-PRC-atmosphere connection provided by an embodiment 1 of the present application;

[0054] Figure 2a is a schematic diagram for connecting the PRC and the GC-MS device at the sample inlet provided by an embodiment 1 of the present application;

[0055] Figure 2b is a schematic diagram for connecting the PRC and the GC-MS device at the column inlet provided by an embodiment 1 of the present application;

[0056] Figure 3 is a schematic diagram of the GC-MS device provided by an embodiment 1 of the present application;

[0057] Figure 4 is a different microplastic weight loss curve provided by an embodiment 2 of the present application;

[0058] Figure 5 is a schematic diagram of the PRC device working process provided by an embodiment 2 of the present application;

[0059] Figure 6 is a different microplastic pyrolysis product full scan chromatogram provided by an embodiment 3 of the present application;

[0060] Figure 7 is a PVC, PAN and PVA pyrolysis product full scan chromatogram provided by an embodiment 3 of the present application

[0061] Figure 8 is a thermal analysis weight loss curve of PAN, PVA, PVC standard and sample provided by an embodiment 3 of the present application;

[0062] Figure 9 is a PAN calibration curve provided by an embodiment 3 of the present application;

[0063] Figure 10 is a PVA calibration curve provided by an embodiment 3 of the present application;

[0064] Figure 11 is a PVC calibration curve provided by one embodiment 3 of the present application. DETAILED DESCRIPTION

[0065] The following gives the definition of some terms used in the present application, and other terms not mentioned have the definition and meaning known in the art:

[0066] 1、Microplastics (MPs) are high molecular weight organic polymers polymerized from monomers, generally refers to plastic particles, cosmetics, microfibers, foam plastics or films with a diameter or length of 1 nm-5 mm, microplastics are derived from industrial manufacturing or recycling, also from the fragmentation of larger plastic fragments by mechanical force, thermal degradation, photolysis, thermal oxidation and biodegradation, with the characteristics of small size, wide distribution, easy to be ingested by organisms and accumulated in the food chain.

[0067] 2、Loop mode: is the mode of sampling with a loop, the loop is composed of a small section of pipeline, the volume in the pipe is fixed, generally 0.5 ml or 1 ml. When the loop is full of the gas to be analyzed, the excess sample is discharged from the vent, at this time the volume of the gas to be analyzed in the pipeline is equal to the volume in the loop.

[0068] 3、The characteristic thermal decomposition gas component in microplastics is a component that can represent the pyrolysis gas of the microplastics.

[0069] 4、Selected ion scan method: SIM for short

[0070] The preferred embodiments of the present application will be described in more detail below. Although the preferred embodiments of the present application are described below, it should be understood that the present application can be implemented in various forms and should not be limited by the embodiments set forth herein. If no specific technique or condition is specified in the examples, the technique or condition described in the literature in the art or according to the product manual is used. If no manufacturer of the reagent or instrument is specified, it is a conventional product that can be obtained by purchase. In the following examples, unless otherwise specified, "%" means weight percent, and parts refer to weight parts.

[0071] Example 1

[0072] A system and method for automatic qualitative and quantitative analysis of organic matter using a thermal analyzer and a GC-MS instrument, specifically including the following contents:

[0073] 1.1 Development of TGA and GC-MS interface connection device

[0074] The TGA and the GC-MS interface must meet the following conditions: 1. Provide sampling power, direct sampling, easy operation, good airtightness, realize automatic enrichment of the target object; the sampling flow rate is stable, and does not affect the flow rate balance inside and outside the TGA, and does not cause the balance of the TGA to be unbalanced; 2. The volatile pyrolysis products to be tested are not adsorbed during the transfer process, and the non-gaseous impurities such as particulate matter and oil gas are effectively reduced.

[0075] The pre-concentration (PRC) instrument in the system is used as an interface device of the TGA and the GC-MS, and has the functions of connection and import. According to the set parameters, the body gas is automatically collected, and the volume range is 4±1 mL to 2000±1 mL. The PRC sampling flow rate is controlled by using a precise mass flow meter (MFC), so that the sampling flow rate is stable, and the flow rate range is 20±1 mL / min to 120±1 mL / min.

[0076] In order to ensure that the sampling process does not affect the balance of the thermal balance inside the TGA, the sampling must meet the requirement of not affecting the flow rate of the TGA carrier gas. A three-way connector is designed to connect the TGA, PRC and atmospheric pressure environment. The products after decomposition of the TGA flow out with the carrier gas, forming a pressure difference, part of which can flow into the PRC, and part of which flows into the atmospheric pressure environment. When the sampling flow rate of the PRC is ≤ the flow rate of the TGA carrier gas, neither the balance of the thermal balance inside the TGA is affected, nor the volatile organic compounds in the atmospheric environment are adsorbed.

[0077] The stainless steel tee connecting the TGA, PRC and atmospheric pressure environment is selected to have inert treatment on the inner wall, and the pipeline through which the gas flows is selected to be a polytetrafluoroethylene pipe or a glass pipe with inert treatment on the inner wall, which can effectively prevent the adsorption interference of the inner wall of the pipe on the measured object.

[0078] The schematic diagram of the tee used for TGA-PRC-atmosphere connection is shown in Figure 1 In the pipeline at the outlet of the TGA and the inlet of the PRC, inert quartz wool is inserted Figure 1 This method does not block the gas flowing in the pipeline, effectively prevents the adsorption of volatile organic compounds in the gas, and also efficiently filters particulate matter, oil gas and other impurities in the pyrolysis products, playing a purifying role. The transparent glass pipe or polytetrafluoroethylene pipe can directly observe the color change of the quartz wool, and can reflect the pollution of the quartz wool and the pipeline in time. When the color of the quartz wool changes, it means that particulate matter, oil gas and other impurities have been adsorbed, at which time the inert treatment of the new quartz wool and the pipeline should be replaced, and the tee should be purged with inert gas. The glass pipe and the polytetrafluoroethylene pipe with inert treatment on the inner wall have the characteristics of high temperature resistance, corrosion resistance and almost insoluble in organic solvents, which are suitable for the transfer of volatile organic compounds, and the polytetrafluoroethylene pipe is low in price and can save maintenance cost. The PRC interface is suitable for connecting the TGA and the PRC, has simple maintenance and operation, high purification efficiency and low cost.

[0079] The schematic diagram of the interface between PRC and GC-MS is shown in Figure 2a and Figure 2b The PRC has two inertized metal tubes, one of which is connected to the sample inlet and connected to the carrier gas, and the flow rate is controlled by the GC flow controller to make the PRC carrier gas flow rate stable and not affected by temperature and pressure, and the other is connected to the end of the chromatographic column inlet, and the pre-concentrated components to be tested are introduced into the chromatographic column with the carrier gas for separation. All the connecting tubes have good airtightness, and the inner walls of the metal and glass tubes used are coated with inert silicon.

[0080] Based on the research of the interface device of the project, a TGA-PRC-GC / MS analysis system was built, as shown in Figure 3 Firstly, the thermal analysis parameters of microplastics were established. In an inert environment and under program-controlled temperature, the thermal analysis parameters of microplastic standard samples were analyzed by mass change, the thermal decomposition behavior of microplastics was directly analyzed, and the weight loss time was found out. Then, according to the thermal decomposition behavior of microplastics, the sampling volume was calculated by selecting the appropriate flow rate, and the sample was taken at a constant speed throughout the weight loss process. Through the physical properties of different boiling points of various components and the enrichment effect of different adsorption materials on volatile organic compounds, impurities with extremely low boiling points were first flowed out, and the target compounds were flowed out later. The volatile and semi-volatile organic compounds with carbon number below C18 in the sample, such as polar (aldehyde, alcohol, ester, ketone, ether) and non-polar, active sulfur, and nitrogen compounds, were pre-concentrated, and H2O, CO2, N2, and inert gases in the gas sample were effectively removed. Finally, the small molecular products of the collected microplastic standard sample were concentrated and quickly introduced into the GC-MS for detection under the same analysis parameters. According to the characteristics of different microplastic thermal decomposition products, the characteristic components that can be distinguished from other microplastics were found out, the qualitative scanning method was established, the calibration curve of the microplastic standard sample was configured and analyzed, and the amount of the characteristic components was calculated to reflect the amount of the microplastic. Based on this qualitative and quantitative analysis method of microplastics, the polymer and additive type and content of microplastics can be quickly and accurately analyzed.

[0081] Example 2

[0082] The improved device of Example 1 was used for processing, including the following contents:

[0083] 2.1 Establishing TGA analysis method and determining sample collection time during weight loss process

[0084] 2.1.1 TGA conditions

[0085] The maximum heating rate of TGA (Netzsch, Germany, model TG209F3) is 100℃ / min, and the maximum temperature is 1000℃. The TGA conditions are set as follows:

[0086] N2 flow rate: 60 mL / min, protective gas N2 flow rate: 20 mL / min

[0087] Temperature program: initial temperature 40°C, then 100°C / min to 650°C, the total time 6.1 min.

[0088] Different microplastics weight loss curves are shown in Figure 4 , wherein [1] represents chlorinated polyethylene (CPE), [2] represents polyamide (PA), [3] represents polyamide (PA12), [4] represents polyformaldehyde resin (POM), [5] represents polyethylene (PE), [6] represents polyethylene terephthalate (PET), [7] represents polymethyl methacrylate (PMMA), and [8] represents polypropylene (PP). It can be seen that the weight loss temperature range of most microplastics is between 300°C and 600°C, and therefore, this TGA analysis parameter can be used as the parameter of the thermal analysis method of most microplastics. If the thermal decomposition behavior of individual microplastics is obviously different, the parameters that can comprehensively analyze the sample can be set as much as possible according to the actual working capacity range of the instrument.

[0089] 2.2 Establishing sampling method and sample analysis method

[0090] According to the TGA carrier gas flow rate, set the appropriate sampling flow rate; according to the TGA thermal decomposition behavior, calculate the sample collection time, according to the sampling time, the sampling flow rate = the sampling volume, set the sampling flow rate and the sampling volume on the PRC. By designing the components and proportions of the three-stage pre-concentration inner filler of the PRC, i.e., the parameters of the three-stage cold trap, the first-stage cold trap removes water, the second-stage cold trap removes N2 and other impurities, and the third-stage cold trap enriches and concentrates the thermal decomposition product components, and then rapidly heats at a rate of 10000°C / min, and after desorption, is introduced into the GC-MS for analysis.

[0091] 2.2.1 Pre-concentration instrument (PRC) conditions

[0092] The operating parameters of the three-stage cold trap of the PRC (8910, Nutech) are as follows:

[0093] First-stage cold trap: trapping temperature -150°C; preheating temperature -30°C; desorption temperature 30°C; baking temperature 180°C, baking time 10 min;

[0094] Second-stage cold trap: trapping temperature -20°C; preheating temperature 30°C; desorption temperature 230°C; desorption time 2.5 min; baking temperature 235°C, baking time 4 min;

[0095] Third-stage cold trap: trapping temperature -180°C; sampling time 1.5 min; baking time 3 min.

[0096] Sampling conditions: Transmission line stability: 100 °C; sampling started when the TGA was running, sampling time was 8 min.

[0097] According to the TGA carrier gas 100 mL / min, the PRC sampling flow rate range is 20-100 mL / min, and above 100 mL / min flow rate, the external atmospheric sample is taken, which will pollute the actual sample, therefore, the specific sampling flow rate can be set according to the actual sample concentration.

[0098] The ultra-low temperature can pre-concentrate the volatile and semi-volatile organic compounds in the sample, such as polar (aldehyde, alcohol, ester, ketone, ether) and non-polar, active sulfur, nitrogen compounds with carbon number below C18, through the adsorption of the filler and the temperature difference, effectively removing the impurity components in the gas sample. The microplastics are decomposed into small molecular volatile organic compounds after thermal analysis, and the above PRC conditions fully meet the needs of automatic collection of pyrolysis products, and enrichment, impurity removal, concentration, and then rapid introduction into GC-MS.

[0099] The PRC working process is shown in Figure 5 The working principle of the three-stage cold trap is as follows:

[0100] The inert trap of the first-stage cold trap is filled with glass beads, and the sample passes through the first-stage cold trap (-30 °C) and the second-stage cold trap (-20 °C) in turn during sampling, and water is removed by using the principle that the lower the temperature, the lower the water saturation content. A large amount of water is removed in the first-stage cold trap.

[0101] The first-stage cold trap uses tenax to remove CO2, noble gases, water, nitrogen, oxygen, and methane at low temperature (-20 °C), and the target VOCs are enriched in the second-stage cold trap.

[0102] The third-stage cold trap is cooled to -180 °C, the second-stage cold trap is heated for desorption, the valve is switched, the sample is transferred to the third-stage cold trap, the third-stage cold trap is rapidly heated, small volume sampling, and GC-MS analysis.

[0103] 2.2.2 GC parameters

[0104] Chromatographic conditions: Chromatographic column: DB-624 (Agilent) capillary column, 60 m x 0.25 mm x 1.4 μm; injection port temperature 200 °C; carrier gas: high-purity helium; constant pressure mode, 100 psi.

[0105] Temperature program: 50 °C for 2 min, increased to 180 °C at 10 °C / min, then increased to 240 °C at 20 °C / min, and maintained for 5 min.

[0106] 2.2.3 Detector

[0107] The detector is a mass spectrometer (MSD) detector, which is commonly used to analyze volatile components and above components of C4. FID detection can also be added to assist in analyzing C2-C3, but only known components can be qualitatively and quantitatively analyzed, and unknown components cannot be qualitatively analyzed. The detector parameters are as follows:

[0108] MSD: The ion source is an EI source with an energy of 70 ev; solvent delay 2.0 min; transfer line temperature 230°C; full scan range 35-300.

[0109] The FID can refer to the following parameters: detector temperature 250°C; H2 flow rate 45 mL / min; air flow rate 300 mL / min; tail nitrogen 10 mL / min.

[0110] Example 3 Specific sample analysis application

[0111] The improved device of Example 1 and the system parameters of Example 2 are used to analyze 7 kinds of microplastics such as PP, PE, PET, PMMA, PAN, PVA and PVC.

[0112] 3.1 Qualitative analysis

[0113] According to the GC-MS detection, the characteristic chromatographic peaks of different microplastics can be analyzed by chromatogram, the characteristic components with relatively large relative percentage content in the microplastic pyrolysis products and obviously different from other microplastics are selected, and the amount of the microplastic is reflected by quantitative analysis of the characteristic pyrolysis products of the microplastic.

[0114] Taking 7 kinds of microplastics such as PP, PE, PET, PMMA, PAN, PVA and PVC as examples, the GC-MS analysis results chromatogram of the pyrolysis products are shown in Figure 6 and Figure 7 The characteristic component information of each microplastic is shown in Table 1. Among them: 2-methyl-2-propyl-oxirane is selected as the characteristic pyrolysis product of PMMA; trans-1,3-hexadiene-5-yne is selected as the characteristic pyrolysis product of PET; 1-heptene is selected as the characteristic pyrolysis product of PE; 1-methyl-2-(3-methylpentyl)cyclopropane is selected as the characteristic pyrolysis product of PP; acrylonitrile is selected as the characteristic pyrolysis product of PAN; 2-butenal is selected as the characteristic pyrolysis product of PVA; 1,3,5,7-cyclooctatetraene is selected as the characteristic pyrolysis product of PVC.

[0115] Table 1 Characteristic component information of different microplastic pyrolysis products

[0116]

[0117] 3.2 Quantitative analysis

[0118] The TGA-PRC-GC / MS analysis system was applied to quantitatively analyze polyacrylonitrile (PAN), polyvinyl alcohol (PVA) and polyvinyl chloride (PVC) microplastics.

[0119] The thermal analysis weight loss curves of PAN, PVA and PVC standard samples and samples are shown in Figure 8 The pyrolysis product full scan comparison results are shown in Figure 7 The characteristic peak of PAN is acrylonitrile (retention time 8.798 min); the characteristic peak of PVA is 2-butenal (retention time 11.760 min); and the characteristic peak of PVC is 1,3,5,7-cyclooctatetraene (retention time 16.825 min). According to the PAN, PVA and PVC microplastic standard samples, different weights were taken, and the calibration curve graph was drawn by combining the calculation of the chromatographic peak area of the characteristic components in GC-MS, as shown in Figure 9-11 The correlation coefficients r 2 of the calibration curves of the three kinds of microplastics are all greater than 0.99, wherein the correlation coefficient r 2 of PAN is 0.998; the correlation coefficient r 2 of PVA is 0.995; and the correlation coefficient r 2 of PVC is 0.991. The contents of PAN, PVA and PVC in the sample were detected, and 6 samples were analyzed, and the detection results are shown in Table 2. The contents of PAN, PVA and PVC in the sample are 420.43 μg / mg, 11.68 μg / mg and 0.72 μg / mg, respectively. The contents of PAN, PVA and PVC in 15.0 mg of alumina are 0.87 μg / mg, 1.37 μg / mg and 0.13 μg / mg, respectively. According to the calculation of three times the signal-to-noise ratio, the method detection limits of the three kinds of microplastics are 0.0748 μg / g, 0.0057 μg / g and 0.0100 μg / g, respectively. It can be seen that the sensitivity, i.e. the detection limit, of the TGA-PRC-GC / MS analysis system can reach the μg / g level.

[0120] Table 2 Detection results of PAN, PVA and PVC in samples

[0121]

[0122] From Examples 1-3, it can be seen that

[0123] (1) Based on the development of PRC-based interface device, combined with TGA and GC-MS, a TGA-PRC-GC / MS system is built, which makes the pyrolysis behavior of microplastics visualized, and at the same time, the characteristics of small molecule volatile products escaped from microplastics are analyzed by GC-MS, a method for qualitative and quantitative analysis of microplastics is established.(2) The technical method realizes automatic collection, enrichment and concentration of the target object, the collection process does not affect the balance of the TGA internal thermal balance, which can effectively prevent the adsorption of samples or cross contamination in the pipeline, and improve the detection sensitivity.(3) The experimental technical method based on the device has the characteristics of small sampling amount, simple operation, easy maintenance and potential wide application, which improves the sensitivity of the existing thermal analysis combined with GC-MS analysis method, and can comprehensively analyze the characteristics of small molecule volatile products of microplastics, which greatly saves the labor.

[0124] (4) For the use of the device and the construction of the experimental method process, the microplastics in the sample are studied, which has good recognition and accuracy, and the qualitative and quantitative research of microplastics achieves good results.

[0125] The above describes the preferred embodiments of the present application, but the present application is not limited to the specific details in the above embodiments, and within the technical concept range of the present application, the technical solutions of the present application can be variously modified, and these simple modifications all belong to the protection range of the present application.

[0126] In addition, it should be noted that each specific technical feature described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present application will not further describe various possible combinations.

[0127] In addition, various different embodiments of the present application can be combined in any manner, as long as they do not deviate from the technical concept of the present application, and they should also be considered as disclosed by the present application.

Claims

1. A system for automated qualitative and quantitative analysis of microplastics using a thermal analyzer and a gas chromatograph-mass spectrometer, characterized by: The system is composed of three devices, namely, a TGA device, a pre-concentration PRC device and a GC-MS device; the outlet of the TGA device is connected to the inlet of the PRC device through a pipeline, the pipeline is a transparent glass tube or a polytetrafluoroethylene tube, inert quartz wool is inserted into the pipeline, the outlet of the PRC device is connected to the GC-MS device; The specific steps of the qualitative and quantitative analysis include: (1) First, the thermal analysis parameters of microplastics are established in the TGA device, under the conditions of inert environment and program-controlled weight loss temperature, the thermal parameters of the microplastic standard are analyzed by analyzing the quality change of the microplastic standard, and the time length of weight loss is obtained; (2) Uniform sampling is performed during the whole process of weight loss, and the sampling volume is calculated according to the sampling flow rate; (3) The sampling flow rate, sampling volume and automatic gas collection parameters are set in the PRC device, then the sample is pre-concentrated and impurities are removed after the sample enters the PRC device, and the small molecule products of the microplastic standard pyrolysis are obtained; the sampling flow rate of the PRC device is set to 20-120 mL / min, the accuracy is ±1 mL / min; the sampling accuracy is 1.0±0.05 mL; the range of the collected gas is 4-2000 mL, and the accuracy is ±1 mL; The sampling conditions: the stability of transmission line is kept at 80-120 o C; the sampling time is 6-10 min; The pre-concentration includes that the PRC device is divided into three adsorption traps, namely, a first cold trap, a second cold trap and a third cold trap; the PRC device removes impurities and water, and realizes the concentration and enrichment of the gas; The operating parameters of the three adsorption traps are as follows: The first stage cold trap: trapping temperature -160 - -140 o C, preheating temperature -40 - -20 o C, desorption temperature 20 - 40 o C, baking temperature 160 - 200 o C, baking time 5 - 15 min, in order to remove water in the sample; The second stage cold trap: trapping temperature -30 - -10 o C, preheating temperature -40 - -20 o C, desorption temperature 210 - 250 o C, desorption time 1.5 - 3.5 min, baking temperature 215 - 255 o C, baking time 2 - 6 min, in order to remove rare gas, residual water, nitrogen, oxygen or methane in the sample; The third stage cold trap: trapping temperature -160 - -200 o C, injection time 0.5 - 2.5 min, baking time 2 - 4 min, in order to enter the GC-MS device for analysis; The volatile and semi-volatile organic compounds of the polar organic compounds, non-polar organic compounds, active sulfides and active nitrogen compounds in the sample to be tested with carbon number below C18 are pre-concentrated, and water, CO2, N2 and inert gases in the gas sample to be tested are removed; the polar organic compounds include aldehyde, alcohol, ester, ketone and ether compounds; (4) The small molecule products of the microplastic standard pyrolysis are concentrated and introduced into the GC-MS device for detection, and a chromatogram is obtained for the next step; (5) The selected ion scan method of GC-MS is established according to the characteristic thermal decomposition gas components of the microplastic standard, different qualities of the microplastic standard are prepared, and the corresponding chromatogram of the equal proportion of the characteristic components of the thermal decomposition products is obtained by GC-MS detection, and the standard curve is drawn according to the peak area of the chromatogram and the quality of the microplastic, and the content of the microplastic is calculated; (6) The target to be tested is operated through steps (2) to (4), and the content of the microplastic in the target is obtained according to the characteristic components calculated in step (5).

2. The system for automated qualitative and quantitative analysis of microplastics using a thermal analyzer and a GC-MS according to claim 1, characterized in that: The outlet of the PRC device is connected to the inlet of the GC-MS device through a No. 1 inertized metal tube and a carrier gas; the outlet of the PRC device is connected to the inlet of the chromatographic column of the GC-MS device through a No. 2 inertized metal tube, and the inertized metal tube refers to a metal tube with inertized material coated on the inner wall. The inner walls of the metal pipe and the glass pipe are treated by a fused silica inert coating technology, and the inert material is a silanized material.

3. The system for automated qualitative and quantitative analysis of microplastics using a thermal analyzer and a GC-MS according to claim 1, characterized in that: In step (1), the temperature increasing rate of the TGA device is ≤100℃ / min, and the temperature is ≤1000℃.

4. The system for automated qualitative and quantitative analysis of microplastics using a thermal analyzer and a GC-MS according to claim 3, characterized in that: Initial temperature 35-45 o C, and then ramped at a rate of 80-100°C / min to 550-750°C, for a total time of 5.5-6.8 min.

5. The system for automated qualitative and quantitative analysis of microplastics using a thermal analyzer and a GC-MS according to claim 4, characterized in that: Initial temperature 40 o C, and then ramped at 100°C / min to 650°C, for a total time of 6.1 min.

6. The system for automated qualitative and quantitative analysis of microplastics using a thermal analyzer and a GC-MS according to claim 1, characterized in that: In step (1), the thermal analysis parameters of the microplastics are established in a TGA device, N2 flow rate: 55-65 mL / min; protective gas N2 flow rate: 10-30 mL / min; the weight loss temperature: 0~1000 o C; the protective gas is defined as a gas that protects the balance in the TGA device from being contaminated by thermal decomposition gas.

7. The system for automated qualitative and quantitative analysis of microplastics using a thermal analyzer and a GC-MS according to claim 6, characterized in that: The N2 flow rate is 60 mL / min.

8. The system for automated qualitative and quantitative analysis of microplastics using a thermal analyzer and a GC-MS according to claim 6, characterized in that: The N2 flow rate of the protective gas is 20 mL / min.

9. The system for automated qualitative and quantitative analysis of microplastics using a thermal analyzer and a GC-MS according to claim 6, characterized in that: The weight loss temperature is 200-800 o C.

10. The system for automated qualitative and quantitative analysis of microplastics using a thermal analyzer and a GC-MS according to claim 9, characterized in that: The weight loss temperature is 300 to 660 o C.

11. The system for automated qualitative and quantitative analysis of microplastics using a thermal analyzer and a GC-MS according to any one of claims 1-10, characterized in that: In step (2), the sampling volume = the sampling time × the sampling flow rate; the sampling flow rate is set according to the carrier gas flow rate of the TGA device; the sampling time is calculated according to the TGA pyrolysis behavior, and the sampling time is obtained.

12. The system for automated qualitative and quantitative analysis of microplastics using a thermal analyzer and a GC-MS according to claim 1, characterized in that: The PRC device in step (3) is configured to maintain the stability of the transmission line at 100 o C; the sampling time is 8 min.

13. The system for automated qualitative and quantitative analysis of microplastics using a thermal analyzer and a GC-MS according to claim 1, characterized in that: Step (3) The operating parameters of the first cold trap are: trapping temperature -150 o C, preheating temperature -30 o C, desorption temperature 30 o C, baking temperature 180 o C, baking time 10 min, in order to remove water in the sample.

14. The system for automated qualitative and quantitative analysis of microplastics using a thermal analyzer and a GC-MS according to claim 1, characterized in that: The operating parameters of the second cold trap are: trapping temperature -20 o C, preheating temperature 30 o C, desorption temperature 230 o C, desorption time 2.5 min, baking temperature 235 o C, baking time 4 min, in order to remove the noble gases, residual water, nitrogen, oxygen or methane from the sample.

15. The system for automated qualitative and quantitative analysis of microplastics using a thermal analyzer and a GC-MS according to claim 1, characterized in that: The operating parameters of the third cold trap are: trapping temperature -180 o C, injection time 1.5 min, oven time 3 min, for analysis in the GC-MS device.

16. The system for automated qualitative and quantitative analysis of microplastics using a thermal analyzer and a GC-MS according to claim 1, characterized in that: In step (4), the GC-MS device, wherein, The chromatographic conditions are as follows: the chromatographic column is DB-624, 60 m × 0.25 mm × 1.4 µm; the injection port temperature is 150-250 ℃; the carrier gas is high-purity helium; the constant pressure mode is 50-150 psi; the temperature increasing program is 40-50 ℃ for 2-4 min, increased to 150-210 ℃ at a rate of 10-20 ℃ / min, and then increased to 220-260 ℃ at a rate of 20-30 ℃ / min, and maintained for 5-10 min; and the detector is at least one of a mass spectrometry MSD detector or an FID detector; The mass spectrometry conditions of the MSD detector are as follows: the ion source is an EI source with an energy of 70 ev; the solvent delay is 1.0-3.0 min; the transfer line temperature is 100-300 ℃; and the full scan range is 35-300 amu. The FID detector has the following conditions: the detector temperature is 250 ℃; the H2 flow rate is 30-60 mL / min; the air flow rate is 150-450 mL / min; and the tail nitrogen flow rate is 10-100 mL / min.

17. The system for automated qualitative and quantitative analysis of microplastics using a thermal analyzer and a GC-MS according to claim 16, characterized in that: The chromatographic conditions are as follows: the injection port temperature is 200 ℃; the constant pressure mode is 100 psi; and the temperature increasing program is 50 ℃ for 2 min, increased to 180 ℃ at a rate of 10 ℃ / min, and then increased to 240 ℃ at a rate of 20 ℃ / min, and maintained for 5 min. The detector is at least one of a mass spectrometry MSD detector or an FID detector.

18. The system for automated qualitative and quantitative analysis of microplastics using a thermal analyzer and a GC-MS according to claim 16, characterized in that: The MSD detector has the following conditions: the ion source is an EI source with an energy of 70 ev; the solvent delay is 2.0 min; the transfer line temperature is 230 ℃; and the full scan range is 35-300 amu.

19. The system for automated qualitative and quantitative analysis of microplastics using a thermal analyzer and a GC-MS according to claim 16, characterized in that: The FID detector has the following conditions: the detector temperature is 250 ℃; the H2 flow rate is 45 mL / min; the air flow rate is 300 mL / min; and the tail nitrogen flow rate is 10 mL / min.

20. The system for automated qualitative and quantitative analysis of microplastics using a thermal analyzer and a GC-MS according to claim 1, characterized in that: In step (5), the qualitative analysis is performed according to the chromatogram in step (4), to obtain characteristic chromatographic peaks of each component of the microplastic; one component is selected, which is a component of the microplastic with fixed thermal decomposition product components and relative percentage contents between components during the TGA program running process, and can represent the microplastic; when the GC-MS running program is unchanged, a selected ion scan mode is established according to the retention time and characteristic ion fragments of the component, and the microplastic is represented by the characteristic chromatographic peak. The characteristic component refers to a characteristic component with a relatively large relative percentage content in the microplastic pyrolysis product and obviously different from other microplastics; According to the calculation of three times signal-to-noise ratio, the detection limits of PAN, PVA and PVC microplastics are 0.0748 μg / g, 0.0057 μg / g and 0.0100 μg / g, respectively.

Images