A method for monitoring semi-volatile organic compounds in ambient air and exhaust gas

Abstract

The present invention discloses a method for monitoring semi-volatile organic compounds in ambient air and waste gas, and belongs to the technical field of environmental monitoring. The present invention collects samples of ambient air or waste gas through a sampling chamber, and collects semi-volatile organic compounds in the sample using a filter membrane and a solid-phase adsorbent; then an organic solvent is added and the sampling chamber is heated, pressurized or ultrasonicated to dissolve the collected semi-volatile organic compounds in the organic solvent; then most of the solvent in the extract is blown away by an inert gas; then the semi-volatile organic compounds are vaporized at high temperature, and the vaporized substances to be tested are brought into a cold trap with the inert gas for condensation and enrichment; finally, the temperature is quickly raised to desorb the enriched semi-volatile organic compounds from the cold trap, and brought into a gas chromatograph by a carrier gas for separation and detection. The present invention greatly increases the injection amount of the target object to be tested, thereby reducing the detection limit and improving the sensitivity of the method; at the same time, it is easy to realize automation and reduce manpower.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental monitoring, and in particular relates to a method for monitoring semi-volatile organic compounds in ambient air and waste gas. Background Art

[0002] Semi-volatile organic pollutants (SVOCs) usually refer to organic substances with boiling points between 170 and 350 ° C and low vapor pressure. Due to the vague classification basis, they often overlap with volatile organic compounds. The SVOCs that environmental monitoring focuses on now mainly include dioxins, polycyclic aromatic hydrocarbons, organic pesticides, chlorobenzenes, polychlorinated biphenyls, pyridines, quinolines, nitrobenzenes, phthalates, nitrosamines, anilines, phenols, polychlorinated naphthalenes and polybrominated diphenyl ethers, etc., which actually include substances with boiling points exceeding 350 ° C. Among them, some SVOCs with high boiling points or strong polarity or high viscosity are easily adsorbed on particulate matter. Many SVOCs substances have direct hazards to the ecological environment or human health. Specific examples include dioxins, polycyclic aromatic hydrocarbons, organic pesticides, etc. They exist in the ambient air in gaseous state, aerosol, or attached to particulate matter. Therefore, it is necessary to monitor SVOCs in ambient air and exhaust gas.

[0003] The existing monitoring method is basically that the sampling personnel collect the samples on site and transport them to the laboratory for analysis. The existing online monitoring equipment mainly monitors SVOCs in the gas phase and is difficult to be used for monitoring SVOCs with higher boiling points in particulate matter.

[0004] Existing monitoring technologies:

[0005] 1. Mainstream analysis methods at home and abroad: Use filter membrane (collection of particle state) + solid phase adsorbent (enrichment of gas state), adopt rapid solvent extraction or Soxhlet extraction, extract with organic solvent, and then concentrate the extract to 0.1~1mL by nitrogen blowing. The final concentrate is then injected into the gas chromatograph for analysis through a liquid injector (the injection volume is generally 1μL, basically not more than 2μL).

[0006] For details, please refer to: HJ 646-2013 "Determination of Polycyclic Aromatic Hydrocarbons in Gas Phase and Particles of Ambient Air and Exhaust Gas by Gas Chromatography-Mass Spectrometry" and HJ 691-2014 "Technical Guidelines for Sampling Semi-volatile Organic Compounds in Ambient Air".

[0007] 2. New methods such as the US EPA: Use solid-phase adsorption materials to collect, then use high temperature to vaporize semi-volatile organic compounds, and then use inert gas to enrich them in a cold trap, and then use the cold trap for thermal desorption and gas chromatography analysis.

[0008] The disadvantages of the first monitoring technology are: (1) The degree of automation is not high. After concentration, the concentrate needs to be manually transferred to the instrument for analysis; (2) The injection volume is only 0.1%~1% of the concentrate. The injection volume is too small and the monitoring sensitivity is low, which makes it difficult to accurately analyze certain trace semi-volatile organic compounds.

[0009] Disadvantages of the second monitoring technology: it is difficult to completely vaporize and remove the collected semi-volatile organic compounds by heating, the recovery rate of some substances with high boiling points or substances with strong adsorbent binding is low, and the monitoring cost is high. Summary of the invention

[0010] The object of the present invention is to provide a method for monitoring semi-volatile organic compounds in ambient air and exhaust gas to solve the problems existing in the background technology.

[0011] The objective of the present invention is achieved through the following technical solutions:

[0012] A method for monitoring semi-volatile organic compounds in ambient air and exhaust gas comprises the following steps:

[0013] S1, collecting samples: collecting samples of ambient air or exhaust gas through a sampling chamber, wherein a filter membrane and a solid phase adsorbent are arranged in the sampling chamber, and adsorption of SVOCs in ambient air or exhaust gas is achieved through passive sampling;

[0014] S2, solvent extraction: adding an organic solvent into the sampling chamber and heating, pressurizing or ultrasonicating the sampling chamber at the same time, the organic solvent immerses the filter membrane and the adsorbent, and the SVOCs in the sampling chamber are fully dissolved in the organic solvent, and an extract is obtained at this time;

[0015] S3, blowing off the solvent: transferring the extract to a solvent-driving chamber, introducing an inert gas into the solvent-driving chamber, and blowing off the solvent in the extract by blowing off the inert gas;

[0016] S4, high temperature vaporization of target: the whole solvent chamber is heated and inert gas is continuously introduced, and the SVOCs in the solvent chamber are vaporized and carried into the cold trap by the inert gas;

[0017] S5, cold trap enrichment of target substances: the temperature of the cold trap is kept below -20°C, and SVOCs condense on the inner surface of the cold trap;

[0018] S6, thermal desorption target: rapidly heating the cold trap to desorb SVOCs;

[0019] S7, gas chromatography separation and detection: the desorbed SVOCs enter the gas chromatograph through the carrier gas, are separated by the capillary chromatographic column in the gas chromatograph, and then are detected by the detector in the gas chromatograph.

[0020] Furthermore, in step S1, the sampling temperature of the sampling chamber is controlled at 5-10°C, the filter membrane is made of polytetrafluoroethylene or quartz, the solid-phase adsorbent is located at the rear end of the filter membrane, the solid-phase adsorbent is made of organic solvent-resistant material, the solid-phase adsorbent is made of a single filler or a mixed filler, and the particle size in the solid-phase adsorbent is 20-80 meshes.

[0021] Furthermore, anhydrous sodium sulfate is contained at the bottom of the sampling chamber.

[0022] Furthermore, step S1 also includes sub-step S11: adding a process substitute.

[0023] Furthermore, in step S2, the organic solvent may be dichloromethane, n-hexane, acetone, methanol, acetonitrile, etc., or a mixture of multiple organic solvents; the sampling cavity is sealed before heating, pressurizing or ultrasonication.

[0024] Furthermore, step S2 is further provided with a sub-step S21: adding an internal standard, and sub-step S21 is performed before heating, pressurizing or ultrasonication.

[0025] Furthermore, in step S3, the solvent-driving chamber is made of a high temperature resistant material, and while an inert gas is introduced into the solvent-driving chamber, auxiliary heating is performed on the solvent-driving chamber, and the heating temperature is lower than the boiling point of the organic solvent.

[0026] Furthermore, the heating temperature in step S4 is not less than 400°C.

[0027] Furthermore, in step S6, when there is no stationary phase, the temperature of the cold trap is raised to 400° C.; when there is a stationary phase, the temperature of the cold trap is raised to the upper limit temperature at which the stationary phase can be normally used.

[0028] The beneficial effects of the present invention are:

[0029] 1) The injection volume of the target object is greatly increased, thereby reducing the detection limit and improving the sensitivity of the method. It can detect substances with very low concentrations but need special attention, allowing for less sampling volume and sampling time, improving analysis efficiency, etc. In this case, some substances with very low concentrations but high toxicity can be detected, which is of great significance for environmental monitoring. Moreover, the shortening of sampling time means higher monitoring "resolution". Multiple analyses can be performed in the same time. For example, the original method requires one sample and one set of data for 24 hours, but now it can achieve one sample for 2 hours and 12 sets of data for 24 hours. More precise data analysis can be achieved, and the judgment of air pollution conditions is more accurate.

[0030] 2) This method does not require volume setting steps, which facilitates fully automatic unmanned operation. It can completely free up manpower, reduce the contact between people and toxic and harmful reagents, and facilitate the realization of IoT and cloud data. It can not only be used for unmanned laboratories, but also facilitate the development of automatic monitoring devices for fixed pollution source exhaust gas or ambient air points.

[0031] 3) It is convenient to dispose of thermally unstable substances and substances that are easily deposited on the quartz surface and difficult to vaporize, avoiding them from entering the cold trap. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of the monitoring method of the present invention; DETAILED DESCRIPTION

[0033] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0034] See also Figure 1 , the present invention provides a technical solution:

[0035] A method for monitoring semi-volatile organic compounds in ambient air and exhaust gas comprises the following steps:

[0036] S1, collecting samples: collecting samples from ambient air or exhaust gas through a sampling chamber, wherein a filter membrane and a solid-phase adsorbent are arranged in the sampling chamber, and SVOCs in the ambient air or exhaust gas are adsorbed by the solid-phase adsorbent;

[0037] S2, solvent extraction: adding an organic solvent into the sampling chamber and heating, pressurizing or ultrasonicating the sampling chamber at the same time, the organic solvent immerses the filter membrane and the adsorbent, and the SVOCs in the sampling chamber are fully dissolved in the organic solvent, and an extract is obtained at this time;

[0038] S3, blowing off the solvent: transferring the extract to a solvent-driving chamber, introducing an inert gas into the solvent-driving chamber, and blowing off the solvent in the extract by the inert gas;

[0039] S4, high temperature vaporization of target: the whole solvent chamber is heated and inert gas is continuously introduced, and the SVOCs in the solvent chamber are vaporized and carried into the cold trap by the inert gas;

[0040] S5, cold trap enrichment of target substances: the temperature of the cold trap is kept below -20°C, and SVOCs condense on the inner surface of the cold trap;

[0041] S6, thermal desorption target: rapidly heating the cold trap to desorb SVOCs;

[0042] S7, gas chromatography separation and detection: the desorbed SVOCs enter the gas chromatograph through the carrier gas, are separated by the capillary chromatographic column in the gas chromatograph, and then are detected by the detector in the gas chromatograph.

[0043] Through the above technical scheme: ambient air or waste gas samples are collected through a sampling cavity, and semi-volatile organic matter in the sample is collected by using a filter membrane and a solid phase adsorbent; then an organic solvent is added and the sampling cavity is heated, pressurized or ultrasonicated to dissolve the collected semi-volatile organic matter in the organic solvent; then most of the solvent in the extract is blown away by an inert gas; then the semi-volatile organic matter is vaporized at high temperature and brought into a cold trap by the inert gas for condensation and enrichment; finally, the enriched semi-volatile organic matter is quickly heated and brought into a gas chromatograph by a gas chromatograph carrier gas for separation and analysis.

[0044] It can be known that, through the above technical solution, the sample that finally enters the gas chromatograph is gas, while the sample that enters the gas chromatograph in the traditional detection method is liquid. The advantages of gas injection in this method include the following points:

[0045] (1) The injection volume of the target substance is greatly increased, thereby reducing the detection limit of the method and improving the sensitivity of the method. This brings about method innovation, which can detect substances with very low concentrations but require special attention, and can allow for a smaller sampling volume and sampling time.

[0046] (2) Easy to automate. In the traditional semi-automated method, volume determination is an essential operation step in the process of processing SVOCs samples. However, most of the current intermediate pre-processing equipment requires analysts to manually determine the volume and then load the sample into the machine by themselves. This method does not require steps such as volume determination, which makes it easy to achieve fully automatic unmanned operation.

[0047] (3) In traditional detection methods, thermally unstable substances and substances that are easily deposited on the quartz surface and difficult to vaporize usually need to be purified before the purified liquid sample can be loaded onto the machine. In this method, filtering is performed in step 1, and the target object is obtained in steps 2-4, making it difficult for the above unstable substances to enter the cold trap, thereby ensuring the accuracy of the detection results and extending the life of the cold trap.

[0048] Specifically: in step S1, the sampling container can refer to HJ 691-2014 "Technical Guidelines for Sampling Semi-volatile Organic Compounds in Ambient Air", and preferably, the shape of the sampling cavity is a tubular sampling cavity. The filter membrane and the solid phase adsorbent are connected in series for collection, and the solid phase adsorbent is located at the rear end of the filter membrane. The SVOCs on the particulate matter are collected through the filter membrane, and the gaseous SVOCs are collected through the solid phase adsorbent.

[0049] Preferably, the filter membrane is generally 0.22μm or 0.45μm, and the filter membrane is made of polytetrafluoroethylene or quartz. The filter membrane collects the particles and also collects the SVOCs adsorbed on the particles; generally, water is not expected to enter the solvent cavity, so the water in the sample needs to be removed as much as possible. Therefore, when the water content in the sample is high, the filter membrane is made of polytetrafluoroethylene, which uses its hydrophobicity to make it difficult for liquid water to pass through.

[0050] Preferably, the volume of the solid phase adsorbent stack for ambient air samples should not be less than 350 mL, and the volume of the solid phase adsorbent stack for exhaust gas samples should not be less than 30 mL;

[0051] Preferably, the solid phase adsorbent adopts an adsorption material resistant to organic solvents, which can be a single filler or a mixed filler. The adsorption material can be selected from quartz glass porous microbeads, polyurethane foam (PUF), macroporous resin, etc. If the adsorption material is granular, the size is generally 20~80 mesh; if the water content of the sample is very high (it is difficult to remove it by polytetrafluoroethylene filter membrane), a small amount of anhydrous sodium sulfate is filled under the solid phase adsorbent.

[0052] Furthermore, in step S1, the sampling volume and sampling time are determined according to the monitoring requirements. The sampling time and flow rate of the exhaust gas sample are generally lower than the sampling of the ambient air. In one embodiment, the sampling chamber controls the air flow rate of the sampled gas to be 0.45m / s, and the resistance of a single filter membrane is no more than 3.5kPa.

[0053] It can be known that sub-step S11 of adding process substitutes is carried out during the sampling process. The purpose of adding substitutes is to characterize the loss or recovery rate of the entire pre-treatment process and to judge the sampling accuracy.

[0054] It can be known that if the temperature and humidity of the gas sample are high, the supersaturated water will condense into liquid due to the decrease in temperature after entering the sampling chamber. The filter membrane made of polytetrafluoroethylene will block most of the condensed water and prevent it from entering the area behind the sampling chamber. The gas sample that passes through the filter membrane, the gaseous and aerosol semi-volatile organic compounds (SVOCs) therein, will be adsorbed by the solid adsorbent.

[0055] By controlling the sampling chamber at a relatively low temperature above 0°C, ice will not form due to excessively low temperatures, and the effect of the solid phase adsorbent will be improved, and even volatile organic compounds (VOCs) with higher boiling points will be adsorbed. Preferably, the temperature of the sampling chamber is controlled at 5-10°C to improve the adsorption rate of SVOCs.

[0056] When the sample humidity is particularly high or the total collected volume is particularly large, causing the total amount of water entering the solid phase adsorbent area to be non-negligible, a small amount of dehydrating agent can be added after the solid phase adsorbent. Preferably, the dehydrating agent is anhydrous sodium sulfate, which can further remove water through the dehydrating agent, and will not adsorb SVOCs in the presence of organic solvents; at this time, the remaining part of the gas sample, including nitrogen, oxygen, carbon dioxide, most VOCs, etc., is discharged.

[0057] Furthermore, in step S2, the organic solvent can be dichloromethane, n-hexane, acetone, methanol, acetonitrile, etc., or a mixture of multiple organic solvents; the organic solvent immerses the filter membrane and the solid phase adsorbent, and after the sampling cavity is completely sealed, the SVOCs are fully dissolved in the organic solvent by extraction under high temperature and high pressure or thermal ultrasound.

[0058] Step S21, adding an internal standard must be performed before heating, pressurizing or ultrasonication. By adding an internal standard, the target and substitute are quantified by the internal standard method, and the base effect is reflected, which improves the accuracy of the analysis. It should be noted that heating or ultrasonication will cause the organic solvent in the closed container to vaporize, thereby increasing the pressure in the closed area; when the water content in the sample is high, it is generally not advisable to use organic solvents that are miscible with water, such as acetone, methanol, acetonitrile, etc., because they will reduce the water removal effect of anhydrous sodium sulfate and may eventually bring water into the solvent removal cavity.

[0059] Furthermore, in step S3, an inert gas is introduced into the solvent-removing chamber, and the solvent-removing chamber is auxiliary heated at the same time, and the heating temperature is lower than the boiling point of the organic solvent. The inert gas is high-purity nitrogen.

[0060] It can be known that all or most of the solvent in the extract is blown away by the inert gas. Even if there is residual solvent, it is generally less than 0.1 mL. When the residual solvent amount is low, the solvent-driving chamber does not need to be heated. By blowing at room temperature or even low temperature, SVOCs will eventually condense on the inner surface of the solvent-driving chamber.

[0061] Preferably, the solvent-removing cavity needs to be made of a material that can withstand a high temperature of at least 400°C, and the dead volume of the solvent-removing cavity is small, and the inner surface is smooth, and has no adsorption effect on SVOCs. Specifically, quartz material can be used.

[0062] In one embodiment, in order to ensure the recovery rate of SVOCs with relatively low boiling points (such as boiling points of 170-260°C), only the lower part of the solvent chamber is heated when the solvent is purged, and the upper temperature is relatively low to ensure that even if the SVOCs evaporate, they will condense in other areas of the chamber. Further, the heating temperature in step S4 is not less than 400°C, wherein the flow rate of the inert gas introduced in step S4 is generally not higher than 40mL / min, so that the SVOCs on the inner surface are vaporized and brought into the cold trap.

[0063] It is known that even if some SVOCs have a boiling point higher than 400°C, they will vaporize and be carried away due to the principle of saturated vapor pressure and the flow of inert gas.

[0064] Take benzo[a]pyrene as an example: due to its high toxicity, it is a substance of great concern in both ambient air and exhaust gas, and has corresponding standard limits. According to its properties, it is considered to be a substance between SVOCs and low-volatile organic compounds. Its boiling point is 495°C, and its saturated vapor pressure at 25°C is 7.3×10 -10 kPa, which means that its saturated mole fraction at standard atmospheric pressure at this temperature is 7.2 × 10 -12 mol / mol, but when the temperature reaches 300℃, its saturated vapor pressure reaches 1.2 kPa, and the saturated concentration can reach 0.01 mol / mol at standard atmospheric pressure; if the solvent chamber is measured with a volume of 200mL, even if the gas flow is not considered (set as a closed space), about 11 mg of benzo[a]pyrene can be converted into gas at 300℃, and the ambient air concentration can be 0.074 μg / m 3 Calculate, collect 24h, 200m 3 The above data show that the collected benzo[a]pyrene is about 15 μg; the limit value of fixed source exhaust gas (GB31571-2015) is 0.3 μg / m 3 , even if the collection time is 1h and more than 400L, the benzo[a]pyrene is only 0.036 μg; all of the above are far below 11 mg. In summary, in theory, in a closed space at 300℃, all the collected benzo[a]pyrene can be vaporized, and this is even more true when the gas is flowing. Therefore, when the heating temperature is 400℃, SVOCs and even a few non-volatile organic compounds can basically be vaporized and taken away by the inert gas.

[0065] Furthermore, the cold trap can use an inert pipeline with an inner diameter of 0.5~1.0mm, such as a quartz capillary or a silanized stainless steel tube. The length is determined according to the experimental results and generally should not be less than 5m. The inner wall of the pipeline can be coated or loaded with a stationary phase, such as polydimethylsiloxane (PDMS), according to the principle of a chromatographic column to enhance the adsorption effect.

[0066] Since the boiling point of SVOCs is not low, the cold trap temperature is not lower than -20°C. At this temperature, SVOCs will condense on the inner surface of the cold trap (or adsorb to the stationary phase of the cold trap). At the same time, the duration of cold trap enrichment in step 5 is generally not less than 5 minutes to ensure that all SVOCs are vaporized and enriched.

[0067] It can be known that if it is necessary to analyze highly volatile substances, such as substances between volatile organic compounds and SVOCs, the temperature can be lowered to a lower level, but if there is a stationary phase, its temperature should not be lower than the good working temperature of the stationary phase, such as PDMS, not lower than -30°C.

[0068] Furthermore, in step S6, when there is no stationary phase, the temperature of the cold trap is raised to 400° C.; when there is a stationary phase, the temperature of the cold trap is raised to the upper limit temperature of normal use of the stationary phase.

[0069] Furthermore, the flow paths (including pipelines, adapters, valves, etc.) in this method need to be inertized and withstand temperatures above 300° C. During operation, they are kept at 300° C. for a long time to prevent SVOCs from being adsorbed or condensed.

[0070] The above is only a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the concept described herein through the above teachings or the technology or knowledge of the relevant field. The changes and modifications made by those skilled in the art do not depart from the spirit and scope of the present invention, and should be within the scope of protection of the claims attached to the present invention.

Claims

1. A method for monitoring semi-volatile organic compounds in ambient air and exhaust gas, characterized in that: The following steps are involved: S1, collecting samples: collecting samples from ambient air or exhaust gas through a sampling chamber, wherein a filter membrane and a solid phase adsorbent are arranged in the sampling chamber, and SVOCs in the ambient air or exhaust gas are adsorbed through passive sampling; S2, solvent extraction: adding an organic solvent into the sampling chamber and heating and pressurizing the sampling chamber at the same time, the organic solvent immerses the filter membrane and the adsorbent, and the SVOCs in the sampling chamber are fully dissolved in the organic solvent, and an extract is obtained at this time; S3, blowing off the solvent: transferring the extract to a solvent-driving chamber, introducing an inert gas into the solvent-driving chamber, and blowing off the solvent in the extract by the inert gas; S4, high temperature vaporization of target: the whole solvent chamber is heated and inert gas is continuously introduced, and the SVOCs in the solvent chamber are vaporized and carried into the cold trap by the inert gas; S5, cold trap enrichment of target substances: the temperature of the cold trap is kept below -20°C, and SVOCs condense on the inner surface of the cold trap; S6, thermal desorption target: rapidly heating the cold trap to desorb SVOCs; S7, gas chromatography separation and detection: the desorbed SVOCs enter the gas chromatograph through the carrier gas, are separated by the capillary chromatographic column in the gas chromatograph, and then are detected by the detector in the gas chromatograph.

2. The method for monitoring semi-volatile organic compounds in ambient air and exhaust gas according to claim 1, characterized in that: In step S1, the sampling temperature of the sampling cavity is controlled at 5-10°C, the filter membrane is made of polytetrafluoroethylene or quartz, the solid phase adsorbent is located at the rear end of the filter membrane, the solid phase adsorbent is made of a material resistant to organic solvents, the solid phase adsorbent is made of a single filler or a mixed filler, and the particle size in the solid phase adsorbent is 20-80 meshes.

3. The method for monitoring semi-volatile organic compounds in ambient air and exhaust gas according to claim 1, characterized in that: Anhydrous sodium sulfate is arranged at the bottom of the sampling cavity.

4. The method for monitoring semi-volatile organic compounds in ambient air and exhaust gas according to claim 1, characterized in that: Step S1 also includes sub-step S11: adding process substitutes.

5. The method for monitoring semi-volatile organic compounds in ambient air and exhaust gas according to claim 1, characterized in that: In step S2, the organic solvent is dichloromethane, n-hexane, acetone, methanol, acetonitrile or a mixture of two or more thereof; the sampling cavity is sealed before heating and pressurizing.

6. The method for monitoring semi-volatile organic compounds in ambient air and exhaust gas according to claim 1, characterized in that: Step S2 also includes a sub-step S21: adding an internal standard, and sub-step S21 is performed before heating and pressurizing.

7. The method for monitoring semi-volatile organic compounds in ambient air and exhaust gas according to claim 1, characterized in that: In step S3, the solvent-driving chamber is made of high-temperature resistant material, and while an inert gas is introduced into the solvent-driving chamber, auxiliary heating is performed on the solvent-driving chamber, and the heating temperature is lower than the boiling point of the organic solvent.

8. The method for monitoring semi-volatile organic compounds in ambient air and exhaust gas according to claim 1, characterized in that: The heating temperature in step S4 is not less than 400°C.

9. The method for monitoring semi-volatile organic compounds in ambient air and exhaust gas according to claim 1, characterized in that: In step S6, when there is no stationary phase, the temperature of the cold trap is raised to 400° C.; when there is a stationary phase, the temperature of the cold trap is raised to the upper limit temperature at which the stationary phase can be normally used.

Images