Method for analyzing volatile PFAS in stationary pollution source waste gas

Abstract

The invention discloses a method for analyzing volatile PFAS in waste gas of a stationary pollution source. The method comprises the following steps: S1, collecting the waste gas; s2, water and CO2 are removed from a part of the waste gas, pre-concentration trapping is carried out at the temperature lower than-150 DEG C, and focusing is carried out by using a cold focusing trap at the temperature lower than-190 DEG C; s3, performing gas chromatography-mass spectrometry analysis on the waste gas sample, and extracting quantitative data of a low-boiling-point PFAS component; s4, the other part of waste gas is subjected to pre-concentration trapping at the temperature of minus 50 DEG C to minus 80 DEG C, and focusing is conducted through a cold focusing trap at the temperature of minus 160 DEG C to minus 180 DEG C; s5, performing gas chromatography-mass spectrometry analysis on the waste gas sample, and extracting quantitative data of medium and high boiling point PFAS components; and S6, combining quantitative data results of S3 and S5. According to the method disclosed by the invention, the detection precision of low-boiling-point components such as CF4 in the volatile PFAS is remarkably improved in a manner of graded trapping and differentiated focusing.

Description

Technical Field

[0001] This invention relates to the field of volatile gas composition analysis and detection technology, specifically to a method for analyzing volatile PFAS in waste gas from stationary pollution sources. Background Technology

[0002] Per- and polyfluoroalkyl substances (PFAS) are a new class of persistent organic pollutants with strong chemical stability, bioaccumulation, and potential ecotoxicity. Currently, detection methods for PFAS in water and soil are relatively mature, but efficient and standardized analytical methods are still lacking for monitoring volatile PFAS in exhaust gases from stationary pollution sources. Exhaust gases often contain high concentrations of CO2 and water vapor. CO2 easily forms interfering peaks in gas chromatography, covering the signals of low-boiling-point PFAS. Simultaneously, low-boiling-point PFAS (such as CF4, boiling point -127.8℃) easily penetrate the trap during conventional pre-concentration processes, leading to low detection sensitivity or even missed detection. Summary of the Invention

[0003] The technical problem to be solved by this invention is to address the issues of low detection sensitivity or even missed detection of low-boiling-point components such as CF4 and severe interference from high-concentration CO2 in the existing monitoring of volatile PFAS in stationary pollution source exhaust gas. This invention provides a compact, easy-to-operate method for analyzing volatile PFAS in stationary pollution source exhaust gas that is conducive to improving production capacity.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A method for analyzing volatile PFAS in exhaust gas from stationary pollution sources includes the following steps: Step S1: Collect exhaust gas from stationary pollution sources using a sampling tank; Step S2: First, a portion of the exhaust gas in the sampling tank is treated to remove water and CO2, then pre-concentrated and captured at a temperature below -150°C, and then focused using a cold focusing trap at a temperature below -190°C. Step S3: Perform gas chromatography-mass spectrometry (GC-MS) analysis on the waste gas sample obtained in step S2, and extract quantitative data of low-boiling-point PFAS components from the analysis results. Step S4: First, remove water from the other part of the waste gas in the sampling tank, then pre-concentrate and capture it at a temperature of -50℃ to -80℃, and then focus it using a cold focusing trap at a temperature of -160℃ to -180℃. Step S5: Perform gas chromatography-mass spectrometry (GC-MS) analysis on the waste gas sample obtained in step S4, and extract quantitative data of medium and high boiling point PFAS components from the analysis results. Step S6: Combine the quantitative data of low-boiling-point PFAS components obtained in step S3 with the quantitative data of medium- and high-boiling-point PFAS components obtained in step S5 to obtain the quantitative results of all target PFAS components in the stationary pollution source exhaust gas sample.

[0005] As a further improvement of the present invention, the low-boiling-point PFAS component includes: carbon tetrafluoride (CF4), hexafluoroethane (C2F6), trifluorochloromethane (CClF3), tetrafluoroethylene (C2F4), trifluoromethane (CHF3), octafluoropropane (C3F8), difluoromethane (CH2F2), and fluoromethane (CH3F).

[0006] As a further improvement of the present invention, the medium-high boiling point PFAS components include: pentafluoroethane, trifluoroethane, hexafluoropropylene, hexafluoropropylene oxide, difluorochloromethane, octafluorocyclobutane, perfluorobutane, tetrafluoroethane, heptafluoropropane, perfluoropentane, chlorofluoromethane, octafluorocyclopentene, nonafluorobutane, perfluorohexane, undecylfluoropentane, heptafluoropropyl, tetrafluoroethyl ether, perfluoroheptane, tridecylfluorohexane, perfluorooctane, pentadecylfluoroheptane, 2H-perfluoro-5-methyl-3,6-dioxane, and heptadecafluorooctane.

[0007] As a further improvement of the present invention, in step S2, the waste gas sample is passed through the drying tube and the selective CO2 adsorbent module in sequence to achieve water and CO2 removal; in step S4, the waste gas sample is passed into the drying tube for water removal.

[0008] As a further improvement of the present invention, in steps S2 and S4, both the pre-concentration trapping and the cold focusing trap focusing are performed in a pre-concentrator, which includes a trapping trap, a cold focusing trap Focus1, and a cold focusing trap Focus2.

[0009] As a further improvement of the present invention, in step S2, the parameters of the pre-concentrator are set as follows: the freezing temperature of the trap is -160℃ to -170℃, the purge flow rate is 100mL / min, the purge time is 110s to 130s, the trap flow rate is 80mL / min, the preheating temperature is 20℃, the preheating time is 10s to 15s, the desorption temperature is 220℃ to 230℃, and the desorption time is 80s to 100s; the freezing temperature of the cold focusing trap is -190℃ to -200℃, the freezing stabilization time is 50s to 70s, and the flash evaporation time is 15s to 25s.

[0010] As a further improvement of the present invention, in step S4, the parameters of the pre-concentrator are set as follows: the freezing temperature of the trap is -50℃ to -60℃, the purge flow rate is 120mL / min, the purge time is 110s to 130s, the trap flow rate is 80mL / min, the preheating temperature is 20℃, the preheating time is 10s to 15s, the desorption temperature is 220℃ to 230℃, and the desorption time is 20s to 40s; the freezing temperature of the cold focusing trap is -160℃ to -170℃, the freezing stabilization time is 30s to 40s, and the flash evaporation time is 15s to 25s.

[0011] As a further improvement of the present invention, in step S3, the GC parameters are set as follows: the initial column flow rate is 0.75 mL / min, and after maintaining it for 0.1 min to 0.2 min, the column flow rate is increased to 1.5 mL / min at a rate of 5 mL / min and maintained until the end; The heating program is as follows: initial temperature 35℃, hold for 8 min to 10 min, increase to 70℃ at a rate of 5℃ / min, and then increase to 230℃ at a rate of 20℃ / min.

[0012] As a further improvement of the present invention, in step S5, the GC parameters are set as follows: the column flow rate is constant at 1.5 mL / min; the temperature program is as follows: initial temperature 35℃, hold for 8 min to 10 min, increase to 220℃ at a rate of 5℃ / min, then increase to 235℃ at a rate of 15℃ / min, and hold for 4 min to 6 min.

[0013] As a further improvement of the present invention, the ability of the cold focusing trap to focus low-boiling-point components in step S2 is greater than the ability of the cold focusing trap to focus low-boiling-point components in step S4.

[0014] Compared with the prior art, the advantages of the present invention are as follows: 1. The present invention provides an analytical method for volatile PFAS in stationary source exhaust gas. For the same exhaust gas sample, two independent and specifically optimized analytical procedures are executed sequentially. The two analyses use the same core instruments (such as a pre-concentrator and GC-MS), but the flow path and parameters are switched by program control, achieving physical "gradation" and functional "differentiation". This fundamentally solves the core contradiction that the two contradictory requirements of "capturing ultralight components" and "avoiding matrix interference" cannot be simultaneously optimized under a single condition. It achieves full-spectrum coverage and high-sensitivity detection of 30 volatile PFAS components with a wide boiling point range (-127.8℃ to 100℃). The detection limit for the most difficult-to-analyze carbon tetrafluoride (CF4) is as low as 0.03 nmol / mol, and the detection limits for the remaining 29 PFAS components are as low as 0.0021 to 0.0077 nmol / mol. The sensitivity meets the requirements for environmental trace monitoring and source tracing.

[0015] 2. The method for analyzing volatile PFAS in stationary pollution source exhaust gas of the present invention improves the anti-interference ability by adopting two strategies: "CO2 removal first" and "selective non-condensation". It removes CO2 in the pretreatment and excludes chromatographic separation from two aspects, effectively dealing with complex exhaust gas matrices, completely avoiding the coverage and interference of high concentration CO2 on PFAS chromatographic peaks, resulting in a clean chromatographic background and ensuring the reproducibility of the analysis. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the process for analyzing volatile PFAS in stationary pollution source exhaust gas in a specific embodiment of the present invention; Figure 2 This is a chromatogram of the low-boiling-point PFAS component in a specific embodiment of the present invention; Figure 3 This is a chromatogram of the high-boiling-point PFAS component in a specific embodiment of the present invention. Detailed Implementation

[0017] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but this does not limit the scope of protection of the present invention.

[0018] In the description of this invention, it should be understood that the terms "side", "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0019] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more unless otherwise explicitly specified.

[0020] Example Instruments: Nutech sampling vessel, Nutech 8910F atmospheric pre-concentrator, Nutech 2208 high-precision dilution instrument, CO2 module for water removal, gas chromatography-mass spectrometry (Agilent 8890 / 5977B, Agilent Technologies, USA), chromatographic column: GS-GasPro capillary column.

[0021] Reagents: PFAS standard gases: 30 kinds of PFAS standard gases, 200 nmol / mol, of which the concentration of carbon tetrafluoride is 2000 nmol / mol, provided by the US EPA.

[0022] like Figure 1 As shown, the method for analyzing volatile PFAS in stationary pollution source exhaust gas of the present invention includes the following steps: Step S1: Nutech sampling canisters are used to collect waste gas from stationary pollution sources. Specifically, a dynamic dilution apparatus is used to dilute the PFAS standard gas with high-purity nitrogen to prepare a working standard gas with a concentration of 0.25 nmol / mol (CF4 is 2.5 nmol / mol). The working standard gas is then filled into a pre-vacuumed 6L sampling canister. High-purity CO2 gas and vaporized deionized water are quantitatively added to the sampling canister to prepare a standard working gas containing 4% CO2 and 50% relative humidity. This gas sample is used as the "same waste gas sample" to be analyzed.

[0023] Step S2: Accurately extract 200 mL of simulated waste gas sample from the sampling container in Step S1, introduce it into the Nafion drying tube and selective CO2 adsorbent module, remove >95% of CO2 online, and then introduce it into the pre-concentrator. The pre-concentrator includes a trap, a cold focusing trap (Focus1), and a conventional cold focusing trap (Focus2). Cold focusing trap (Focus1) is a dedicated focusing trap for extremely low boiling point components, while cold focusing trap (Focus2) is a conventional cold focusing trap. The parameters of the pre-concentrator are set as follows: purge flow rate 100 mL / min, purge time 120 s, trap flow rate 80 mL / min, preheating temperature 20℃, and preheating time 10 s. In the pre-concentrator, the waste gas sample first enters the main trap, which is cooled to -165℃. At this temperature, all target PFAS, including CF4, are condensed and captured. After capture, the trap is preheated to 20°C for 10 seconds, then heated to 225°C for 90 seconds to decompose the target compound, which is then transferred to a dedicated cold focusing trap, Focus1. Focus1 is pre-cooled to -196°C with a freezing stabilization time of 60 seconds, and a dedicated focusing trap for extremely low-boiling-point components is used for secondary enrichment and focusing of low-boiling-point components. Finally, Focus1 is rapidly heated from -196°C to 80°C within 15 seconds and injected into GC-MS to complete the sample introduction.

[0024] In this embodiment, for low-boiling-point PFAS components, before the sample enters the pre-concentration system, a Nafion drying tube (such as a Perma Pure Nafion tube) and a high-efficiency CO2 selective adsorbent (such as AlphaSolve® II) module are integrated to increase the removal rate of high-concentration CO2 in the exhaust gas to >95% without adsorbing the target PFAS components. This avoids CO2 clogging the pipeline in the subsequent cryogenic steps from the source and completely eliminates the coverage and interference of its huge chromatographic peak on the low-boiling-point PFAS component peaks.

[0025] Step S3: The waste gas sample obtained in Step S2 is analyzed by gas chromatography-mass spectrometry (GC-MS), and quantitative data of low-boiling-point PFAS components are extracted from the analysis results. Specifically: In Step S2, after the waste gas sample undergoes secondary enrichment and focusing, Focus1 performs a 20-second flash evaporation, and the waste gas sample is rapidly injected into the GC-MS system. The GC parameters are set as follows: initial column flow rate 0.75 mL / min, hold for 0.1 min, increase the column flow rate to 1.5 mL / min at a rate of 5 mL / min, and hold until the end; the temperature program is as follows: initial column temperature 35℃, hold for 8 min, increase to 70℃ at a rate of 5℃ / min, and then increase to 230℃ at a rate of 20℃ / min. MS conditions are EI source, SIM scan mode, monitoring the characteristic ions of the first 8 low-boiling-point PFAS components.

[0026] The system acquired complete chromatographic-mass spectrometry data. The data processing software automatically identified and extracted the peak areas of the first eight low-boiling-point PFAS components (numbered 1-8) in the exhaust gas sample, and performed quantitative calculations using the external standard method. It should be noted that although the full spectrum was obtained in this analysis, only the data for the first eight low-boiling-point components were adopted.

[0027] Step S4: Accurately extract 200 mL of simulated waste gas sample from the sampling container in Step S1, introduce it into a Nafion drying tube for dehydration, and then introduce it into a pre-concentrator. The parameters of the pre-concentrator are set as follows: purge flow rate 100 mL / min, purge time 120 s, trap flow rate 80 mL / min, preheating temperature 20℃, and preheating time 10 s. In the pre-concentrator, the waste gas sample first enters the main trap, which is cooled to -50℃. At this temperature, the last 22 medium-to-high boiling point PFAS components in the waste gas sample are effectively condensed and trapped, while CO2 with a lower boiling point (-78.5℃) is not condensed and is purged out of the system with the carrier gas. After trapping, the trap is heated to 228℃ for 30 seconds to decompose, and the target compound is transferred to another conventional cold focusing trap, Focus2. Focus2 is pre-cooled to -170℃ and frozen for 30 s.

[0028] In this embodiment, for medium- and high-boiling-point PFAS components, the exhaust gas sample flow path bypasses the CO2 adsorption module directly after water removal, avoiding irreversible adsorption loss of medium- and high-boiling-point PFAS components on the CO2 adsorbent and ensuring complete recovery of the target analytes. Furthermore, the collection temperature is precisely set at -50°C. This temperature is higher than the boiling point of CO2 (-78.5°C) but lower than the condensation point of most medium- and high-boiling-point PFAS. The collected analytes are transferred to a conventional cold focusing trap (Focus2) at -170°C. Utilizing the boiling point difference between CO2 and the target analytes, the CO2 is not condensed at -50°C and is purged out with the carrier gas, achieving physical separation. Figure 3 The chromatogram showed no CO2 interference peaks and a clean background. By using a conventional cold focusing trap (Focus2) for focusing, the incomplete desorption of medium- and high-boiling-point components that might occur with a dedicated cold focusing trap (Focus1) was avoided, ensuring the reproducibility of the analysis.

[0029] Step S5: The waste gas sample obtained in Step S4 is analyzed by gas chromatography-mass spectrometry (GC-MS), and quantitative data of medium- and high-boiling-point PFAS components are extracted from the analysis results. Specifically: In Step S4, after the waste gas sample undergoes secondary enrichment and focusing, Focus2 is used for 20-second flash evaporation, and then the waste gas sample is rapidly injected into the GC-MS system. The GC parameters are set as follows: column flow rate constant at 1.5 mL / min; temperature program: initial temperature 35℃, hold for 8 min, increase to 220℃ at a rate of 5℃ / min, then increase to 235℃ at a rate of 15℃ / min, hold for 4 min. MS conditions are EI source, SIM scan mode, monitoring 22 PFAS components.

[0030] The system acquired complete chromatographic-mass spectrometry data. The data processing software automatically identified and extracted the peak areas of PFAS components 9 to 30. This analysis used the internal standard method (based on chlorobenzene-d5) to quantify these 22 compounds. It should be noted that while the full spectrum was obtained, only the data for the last 22 high-boiling-point compounds were adopted.

[0031] Step S6: Combine the quantitative data of the first 8 low-boiling-point PFAS components obtained in step S3 with the quantitative data of the last 22 medium- and high-boiling-point PFAS components obtained in step S5 to obtain the quantitative results of all target PFAS components in the stationary pollution source exhaust gas sample.

[0032] like Figure 2 As shown, the low-boiling-point PFAS components include: carbon tetrafluoride (CF4), hexafluoroethane (C2F6), trifluorochloromethane (CClF3), tetrafluoroethylene (C2F4), trifluoromethane (CHF3), octafluoropropane (C3F8), difluoromethane (CH2F2), and fluoromethane (CH3F). From Figure 2 As can be seen, the peaks of the eight low-boiling-point PFAS target compounds, including CF4, C2F6, and CClF3, are sharp and symmetrical, with good baseline separation. Among them, CF4 (retention time approximately 3.47 minutes), which was previously difficult to capture, exhibited a clear chromatographic peak with a high signal-to-noise ratio, without tailing or diffusion. This indicates that the extremely low temperature of -165℃ ensured the effective condensation of ultralight components such as CF4 (boiling point -127.8℃), and the dedicated cold focusing trap Focus1 at -196℃ maximized the capture and transfer efficiency of these easily penetrating components, significantly enhancing the capture and enrichment efficiency of low-boiling-point components such as CF4. Furthermore, the detection limit for CF4 reached an advanced level of 0.03 nmol / mol.

[0033] like Figure 3 As shown, the medium-to-high boiling point PFAS components include: pentafluoroethane, trifluoroethane, hexafluoropropylene, hexafluoropropylene oxide, difluorochloromethane, octafluorocyclobutane, perfluorobutane, tetrafluoroethane, heptafluoropropane, perfluoropentane, chloroform, octafluorocyclopentene, nonafluorobutane, perfluorohexane, undecylfluoropentane, heptafluoropropyl, tetrafluoroethyl ether, perfluoroheptane, tridecafluorohexane, perfluorooctane, pentadecylfluoroheptane, 2H-perfluoro-5-methyl-3,6-dioxane, and heptadecafluorooctane. Figure 3 As can be seen, all 22 medium- and high-boiling-point PFAS components were effectively detected, and the chromatographic separation was ideal. Particularly noteworthy is the region where large CO2 interference peaks would typically occur in routine analyses (approximately 10–12 minutes). Figure 3 The chromatogram background was clean, with no obvious interference. This indicates that at the selective trapping temperature of -50°C, the target PFAS was effectively condensed and trapped, while CO2 with a lower boiling point (-78.5°C) was not trapped, thus eliminating its main chromatographic interference at the source without the use of additional purification steps.

[0034] In this embodiment, two independently optimized analysis modes were used sequentially for the same exhaust gas sample: first, CO2 was removed and ultra-low temperature strong adsorption focusing was used to capture low-boiling-point PFAS components; then, CO2 was bypassed and CO2 was removed and medium-temperature selective collection was used to analyze medium- and high-boiling-point PFAS components. Finally, the data were combined, and the results of the two analysis modes complemented each other, together forming a complete and interference-free chromatogram of 30 volatile PFAS components under complex matrix, realizing full-spectrum, high-sensitivity, and interference-resistant quantitative detection.

[0035] Following the same steps described above, a standard working gas with a concentration of 0.0625 nmol / mol (CF4: 0.625 nmol / mol) was used as the spiked sample. Multiple parallel spiked samples were tested against a "blank" background (i.e., a sampling container filled with high-purity nitrogen as the matrix). The standard deviation s was calculated, and the limit of detection (MDL) was calculated using the formula MDL = t(n-1, 99) × s (t value taken as 3.143). The results are shown in Table 1. It should be noted that the calculation methods for both the standard deviation s and the limit of detection (MDL) can employ conventional techniques in this field and will not be elaborated upon here.

[0036] Table 1. Linearity test data for 30 volatile PFAS

[0037] As shown in Table 1, the detection limits for all target compounds are below 0.01 nmol / mol (the detection limit for carbon tetrafluoride is below 0.1 nmol / mol). Except for CF4, the method detection limits for the other 29 PFAS components are between 0.0021 and 0.0077 nmol / mol, demonstrating the extremely high sensitivity of the analytical method used in this embodiment.

[0038] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for analyzing volatile PFAS in exhaust gas from stationary pollution sources, characterized in that, Includes the following steps: Step S1: Collect exhaust gas from stationary pollution sources using a sampling tank; Step S2: First, a portion of the exhaust gas in the sampling tank is treated to remove water and CO2, then pre-concentrated and captured at a temperature below -150°C, and then focused using a cold focusing trap at a temperature below -190°C. Step S3: Perform gas chromatography-mass spectrometry (GC-MS) analysis on the waste gas sample obtained in step S2, and extract quantitative data of low-boiling-point PFAS components from the analysis results. Step S4: First, remove water from the other part of the waste gas in the sampling tank, then pre-concentrate and capture it at a temperature of -50℃ to -80℃, and then focus it using a cold focusing trap at a temperature of -160℃ to -180℃. Step S5: Perform gas chromatography-mass spectrometry (GC-MS) analysis on the waste gas sample obtained in step S4, and extract quantitative data of medium and high boiling point PFAS components from the analysis results. Step S6: Combine the quantitative data of low-boiling-point PFAS components obtained in step S3 with the quantitative data of medium- and high-boiling-point PFAS components obtained in step S5 to obtain the quantitative results of all target PFAS components in the stationary pollution source exhaust gas sample.

2. The method for analyzing volatile PFAS in stationary pollution source exhaust gas according to claim 1, characterized in that, The low-boiling-point PFAS components include: carbon tetrafluoride (CF4), hexafluoroethane (C2F6), trifluorochloromethane (CClF3), tetrafluoroethylene (C2F4), trifluoromethane (CHF3), octafluoropropane (C3F8), difluoromethane (CH2F2), and fluoromethane (CH3F).

3. The method for analyzing volatile PFAS in stationary pollution source exhaust gas according to claim 2, characterized in that, The medium-to-high boiling point PFAS components include: pentafluoroethane, trifluoroethane, hexafluoropropylene, hexafluoropropylene oxide, difluorochloromethane, octafluorocyclobutane, perfluorobutane, tetrafluoroethane, heptafluoropropane, perfluoropentane, chlorofluoromethane, octafluorocyclopentene, nonafluorobutane, perfluorohexane, undecylfluoropentane, heptafluoropropyl, tetrafluoroethyl ether, perfluoroheptane, tridecylfluorohexane, perfluorooctane, pentadecylfluoroheptane, 2H-perfluoro-5-methyl-3,6-dioxane, and heptadecafluorooctane.

4. The method for analyzing volatile PFAS in stationary source exhaust gas according to claim 3, characterized in that, In step S2, the waste gas sample is passed sequentially through a drying tube and a selective CO2 adsorbent module to remove water and CO2; in step S4, the waste gas sample is passed through a drying tube to remove water.

5. The method for analyzing volatile PFAS in stationary source exhaust gas according to claim 3, characterized in that, In steps S2 and S4, both pre-concentration trapping and cold focusing trap focusing are performed in a pre-concentrator, which includes a trapping trap, a cold focusing trap Focus1, and a cold focusing trap Focus2.

6. The method for analyzing volatile PFAS in stationary source exhaust gas according to claim 5, characterized in that, In step S2, the parameters of the pre-concentrator are set as follows: the freezing temperature of the trap is -160℃ to -170℃, the purge flow rate is 100mL / min, the purge time is 110s to 130s, the trap flow rate is 80mL / min, the preheating temperature is 20℃, the preheating time is 10s to 15s, the desorption temperature is 220℃ to 230℃, and the desorption time is 80s to 100s; the freezing temperature of the cold focusing trap (Focus1) is -190℃ to -200℃, the freezing stabilization time is 50s to 70s, and the heating flash evaporation time is 15s to 25s.

7. The method for analyzing volatile PFAS in stationary source exhaust gas according to claim 5, characterized in that, In step S4, the parameters of the pre-concentrator are set as follows: the freezing temperature of the trap is -50℃ to -60℃, the purge flow rate is 120mL / min, the purge time is 110s to 130s, the trap flow rate is 80mL / min, the preheating temperature is 20℃, the preheating time is 10s to 15s, the desorption temperature is 220℃ to 230℃, and the desorption time is 20s to 40s; the freezing temperature of the cold focusing trap is -160℃ to -170℃, the freezing stabilization time is 30s to 40s, and the flash evaporation time is 15s to 25s.

8. The method for analyzing volatile PFAS in stationary source exhaust gas according to any one of claims 1 to 7, characterized in that, In step S3, the GC parameters are set as follows: the initial column flow rate is 0.75 mL / min, and after maintaining it for 0.1 min to 0.2 min, the column flow rate is increased to 1.5 mL / min at a rate of 5 mL / min and maintained until the end. The heating program is as follows: initial temperature 35℃, hold for 8 min to 10 min, increase to 70℃ at a rate of 5℃ / min, and then increase to 230℃ at a rate of 20℃ / min.

9. The method for analyzing volatile PFAS in stationary source exhaust gas according to any one of claims 1 to 7, characterized in that, In step S5, the GC parameters are set as follows: the column flow rate is constant at 1.5 mL / min; the temperature program is as follows: initial temperature 35℃, hold for 8 min to 10 min, increase to 220℃ at a rate of 5℃ / min, then increase to 235℃ at a rate of 15℃ / min, and hold for 4 min to 6 min.

10. The method for analyzing volatile PFAS in stationary source exhaust gas according to any one of claims 1 to 7, characterized in that, In step S2, the cold focusing trap's ability to focus low-boiling-point components is greater than that in step S4.

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