Application of Chinese tree flower in monitoring dioxin-like air pollutants and monitoring methods

Abstract

The present invention relates to the technical field of environmental monitoring, and specifically discloses the application of Chinese tree flowers in monitoring dioxin-type atmospheric pollutants and a monitoring method. The method for monitoring dioxin-type atmospheric pollutants provided by the present invention uses Chinese tree flowers as dioxin biological monitors, which have strong dioxin accumulation capabilities, and uses lichen transplantation monitoring methods, uses Chinese tree flowers as atmospheric deposition receivers, and analyzes the dioxin content accumulated in Chinese tree flowers, which can realize the monitoring of dioxin-type pollutants in the atmosphere of remote areas, and provide a basis for studying the level, source and spatiotemporal pattern of atmospheric pollutant deposition. The operation method is simple, and is suitable for high spatial resolution research on atmospheric pollutant deposition at multiple scales, which makes up for the shortcomings of expensive instrument monitoring methods, cumbersome operations, and high technical requirements for operation, and provides a new technology for atmospheric dioxin deposition monitoring, which has important application value.

Description

Technical Field

[0001] The invention relates to the technical field of environmental monitoring, and in particular to an application of Chinese tree flower in monitoring dioxin-type air pollutants and a monitoring method. Background Art

[0002] Dioxins are a class of highly toxic synthetic chemicals that are extremely difficult to decompose in nature. They can migrate over long distances in the atmosphere and accumulate in organisms, harming the ecological environment and human health. Therefore, it is of great significance to study the source, migration and deposition level of dioxins in the atmosphere.

[0003] At present, the monitoring of dioxin pollution in the atmosphere of my country is mainly based on instrument monitoring, including manual sampling method and instrument continuous sampling method. Both methods require the placement of large-flow ambient air samplers at the sampling points, with glass fiber membrane (GFF) and polyurethane foam (PUF) as sampling media, and quantitative analysis of dioxins in the atmosphere after sampling. The instrument monitoring method has the advantages of directness, speed and accuracy in the early warning and prevention and control of atmospheric dioxin pollution. However, its defects are also obvious: the manual sampling method can only obtain instantaneous value data of atmospheric dioxin components, and the instrument continuous sampling method depends on the deployment, maintenance, power supply and manual attendance of environmental monitoring stations and atmospheric monitoring samplers. Both require elution and separation of dioxins from the collection medium, which is cumbersome to operate and has high technical requirements, which can easily cause distortion of results. Therefore, this method is often used in densely populated towns and industrial areas, and it is difficult to implement monitoring in areas with insufficient transportation and electricity, where it is difficult to deploy environmental monitoring stations and samplers.

[0004] In view of the above problems, there is an urgent need to develop a monitoring method for dioxin pollutants in the atmosphere that can permanently monitor dioxin pollutants and has a simple detection and analysis method and high monitoring accuracy. Summary of the invention

[0005] In view of the above technical problems, the present invention provides an application of Chinese tree flower in monitoring dioxin-type air pollutants and a monitoring method. The monitoring method can monitor the long-term accumulation of dioxin deposition in the atmosphere at any site, and the detection and analysis method is simple and the distortion of the monitoring results is small.

[0006] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0007] Application of Chinese tree flowers in monitoring dioxin-like air pollutants.

[0008] The present invention also provides a method for monitoring dioxin-type air pollutants, comprising the following steps:

[0009] Step a, dividing the target monitoring area into grids to obtain the target monitoring grid area;

[0010] Step b, packing the Chinese tree flower into mesh bags and transporting them to the target monitoring grid area, suspending them on a bracket, exposing them to the atmosphere for a predetermined time, taking back the mesh bags, removing impurities attached to the surface of the Chinese tree flower, drying, crushing, and sieving to obtain a Chinese tree flower powder sample;

[0011] Step c, extracting the Chinese tree flower powder sample, and purifying the extract by passing through a multi-layer silica gel column and an activated carbon silica gel column in sequence to obtain a purified solution;

[0012] Step d, determining the content of dioxins in the purified liquid by isotope dilution high-resolution gas chromatography-high-resolution mass spectrometry.

[0013] Compared with the prior art, the method for monitoring dioxin-like air pollutants provided by the present invention uses Chinese tree flowers as dioxin biological monitors, which have a strong dioxin accumulation capacity. Through the lichen transplantation monitoring method, Chinese tree flowers are used as atmospheric deposition receivers, and the dioxin content accumulated in the Chinese tree flowers is analyzed, so that the monitoring of dioxin-like pollutants in the atmosphere of remote areas can be realized, and a basis is provided for studying the level, source and spatiotemporal pattern of atmospheric pollutant deposition. The operation method is simple and suitable for conducting high spatial resolution research on atmospheric pollutant deposition at multiple scales, making up for the shortcomings of the instrument monitoring method, such as high cost, cumbersome operation and high technical level requirements. Moreover, the method for monitoring dioxin-like air pollutants provided by the present invention can break through the geographical distribution limitations of lichen species, and realize the purpose of detecting dioxin-like air pollutants anywhere on the land surface, providing a new technology for atmospheric dioxin deposition monitoring, and having important application value.

[0014] Specifically, the Chinese tree flower is the Chinese tree flower in the mountain forest ecosystem at the northern end of Yanshan Mountain. The initial dioxin content (i.e., the content before transplantation) in the Chinese tree flower samples in this area is extremely low, which can realize accurate monitoring of dioxin-type air pollutants in the monitoring area.

[0015] Specifically, when selecting Chinese tree flowers, select Chinese tree flowers with a diameter of 3mm-5mm, wear clean plastic gloves, gently break the Chinese tree flowers from the bark, place them in a kraft paper bag, and dry them naturally in a dark place at room temperature.

[0016] Preferably, the size of each target monitoring grid area is 5×5km 2 -30×30km 2 The size of each monitoring point in the target monitoring grid area is 0.5×0.5km 2 -1×1km 2 .

[0017] Preferably, 1-3 sub-sample points are set in each monitoring point, and a mesh bag is suspended in each sub-sample point, and the hanging height of the mesh bag is 2m-3m from the ground.

[0018] Preferably, 3-5 Chinese tree flowers are loaded in each mesh bag, and the mesh bag is made of a nylon mesh sleeve, and a plurality of mesh holes with a hole diameter of 1mm-2mm are provided on the mesh bag.

[0019] Furthermore, the diameter of the Chinese tree flower is greater than 3 cm.

[0020] It should be noted that when loading Chinese tree flowers, ensure that they do not overlap and transplant them immediately after loading.

[0021] Preferably, in step b, the predetermined time is 1-3 months.

[0022] Preferably, in step b, the drying temperature is 40° C.-50° C., and the mesh size of the sieve is 100-200 mesh.

[0023] It should be noted that after the monitoring is completed, the Chinese tree flowers are collected and stored using cowhide bags, stainless steel or aluminum alloy utensils that have no adsorption effect on dioxins, and transported back to the laboratory. Under a dissecting microscope, tweezers and a small brush are used to remove biological debris, soil, rock particles and other debris attached to the surface of the Chinese tree flowers, and then they are dried, crushed, ground and sieved through a 100-200 mesh sieve.

[0024] Preferably, in step d, the extraction solvent is a mixed solution of n-hexane, dichloromethane and acetone.

[0025] Furthermore, in step d, the extraction solvent is a mixed solution of n-hexane, dichloromethane and acetone in a volume ratio of 40:40:20.

[0026] Preferably, in step d, the fillers of the multilayer silica gel column are, from bottom to top, anhydrous sodium sulfate, silica gel, 1%-3% potassium hydroxide silica gel, silica gel, 43%-45% sulfuric acid silica gel, 21%-23% sulfuric acid silica gel, silica gel, 9%-11% silver nitrate silica gel and anhydrous sodium sulfate.

[0027] Specifically, the 1%-3% potassium hydroxide silica gel is obtained by mixing potassium hydroxide and silica gel, wherein the mass content of potassium hydroxide is 1%-3%. The 43%-45% sulfuric acid silica gel is obtained by mixing 98% concentrated sulfuric acid and silica gel, wherein the mass content of 98% concentrated sulfuric acid is 43%-45%. The 21%-23% sulfuric acid silica gel is obtained by mixing 98% concentrated sulfuric acid and silica gel, wherein the mass content of 98% concentrated sulfuric acid is 21%-23%. The 9%-11% silver nitrate silica gel is obtained by mixing silver nitrate and silica gel, wherein the mass content of silver nitrate is 9%-11%.

[0028] Preferably, in step d, the fillers of the activated carbon silica gel column are anhydrous sodium sulfate, 9%-11% activated carbon silica gel and anhydrous sodium sulfate from bottom to top.

[0029] Specifically, the 9%-11% activated carbon silica gel is obtained by mixing activated carbon and silica gel, wherein the mass content of the activated carbon is 9%-11%.

[0030] Preferably, the specific steps of extraction in step c are:

[0031] Fill the extraction cell with silica gel and florisil in sequence from bottom to top, mix the Chinese tree flower powder sample and diatomaceous earth evenly, add them into the extraction cell, add the extraction internal standard and the extraction solvent, and use an accelerated solvent extractor for extraction, the heating temperature is 148°C-152°C, the extraction time is 7min-9min, the extraction pressure is 10MPa-10.5MPa, and after the extraction is completed, the extract is concentrated to 1mL-2mL to obtain a concentrated solution.

[0032] Accelerated solvent extraction is used, with a short extraction time (30 minutes), a small amount of organic solvent (extraction volume 30 mL), and a high degree of automation; the Chinese tree flower sample is mixed with diatomaceous earth, and silica gel and floral silica are filled from bottom to top in the extraction pool. The dioxins in the Chinese tree flower sample containing a large amount of pigment can be better extracted and purified. The extraction and partial purification steps are combined into one, and a large amount of interferences in the matrix are removed during the extraction process, which greatly saves pre-treatment time and reduces the use of organic solvents, opening up a fast, efficient and convenient method for the future detection of dioxins.

[0033] Preferably, in step c, the specific steps of purification by multilayer silica gel column and activated carbon silica gel column are:

[0034] The concentrated solution is added to a multi-layer silica gel column, eluted with n-hexane, and the eluate is concentrated to 1 mL-2 mL to obtain a primary purified solution;

[0035] The primary purification liquid is added to an activated carbon silica gel column, eluted with a mixed solution of n-hexane and dichloromethane, the eluent is discarded, the activated carbon silica gel column is inverted, eluted with toluene, the eluent is collected, and the eluent is concentrated to 1 mL-2 mL, blown dry with nitrogen, and the injection internal standard and decane are added, mixed evenly to obtain a purified liquid.

[0036] The preferred purification method can remove a large amount of pigments contained in the Chinese tree flowers and a large amount of interferences in the matrix, so that the dioxins accumulated in the Chinese tree flowers can be effectively enriched, thereby improving the accuracy and reliability of subsequent analysis and detection results.

[0037] Preferably, the high-resolution gas chromatography conditions are:

[0038] Chromatographic column: ThermoTR-Dioxin-5MS capillary column, 60m×0.25mm×0.25μm;

[0039] Column temperature: 138℃-142℃, maintain for 1min-2min, then increase the temperature to 198℃-202℃ at a rate of 19℃ / min-21℃ / min, maintain for 1min-2min, then increase the temperature to 218℃-222℃ at a rate of 4℃ / min-6℃ / min, maintain for 15min-17min, then increase the temperature to 233℃-237℃ at a rate of 4℃ / min-6℃ / min, maintain for 6min-8min, finally increase the temperature to 308℃-312℃ at a rate of 4℃ / min-6℃ / min, maintain for 9min-11min;

[0040] Inlet temperature: 268℃-272℃;

[0041] Transmission line temperature: 278℃-282℃;

[0042] Injection method: splitless;

[0043] Carrier gas flow rate: 0.9mL / min-1.1mL / min.

[0044] Preferably, the high-resolution mass spectrometry conditions are: ionization mode: electron bombardment ion source; electron energy: 45eV; ion source temperature: 250°C; acceleration voltage: 4800V; resolution ≥ 10000; acquisition mode is selected ion monitoring mode; dioxin [M] + , [M+2] + , [M+4] + The characteristic ions are as follows:

[0045]

[0046]

[0047] The preferred high-resolution gas chromatography-high-resolution mass spectrometry detection conditions can realize the accurate detection of multiple dioxin substances (17 species) in Chinese tree flowers, and can qualitatively and quantitatively detect 2,3,7,8-chloro dioxins, tetrachloro-octachloro polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). The methodological validation shows that the detection method has good accuracy, sensitivity and stability. When the sampling amount of Chinese tree flowers is 2.0g, 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8- The detection limits of octachlorodibenzodioxin (OCDD) and octachlorodibenzofuran (OCDF) are 0.50 ng / kg, and the detection limits of other PCDD / Fs are 0.20 ng / kg.

[0048] The method of the present invention uses Chinese tree flowers as lichens, monitors dioxin-like atmospheric pollutants through lichen transplantation detection methods, and can implement gridded monitoring of the long-term accumulation degree of atmospheric dioxin deposition at multiple spatial resolutions and time resolutions at any place on the land surface. By extracting and purifying the dioxin-like substances accumulated in the Chinese tree flowers and adopting isotope dilution high-resolution gas chromatography-high-resolution mass spectrometry under specific detection conditions, qualitative and quantitative detection of 17 dioxin-like substances in the Chinese tree flowers is achieved, and the detection limits of the 17 dioxin-like substances are between 0.05-0.2 ng / kg, and the average recovery rate of the actual sample internal standard is 42%-89%, which is of great significance for further studying the source, distribution, migration and deposition level of atmospheric dioxins. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 is a schematic diagram of the target monitoring grid area in Example 1, wherein: Represents a monitoring point, each square represents a target monitoring grid area, the size of which is 5×5km 2 -30×30km 2 ;

[0050] Figure 2 This is a comparison chart of dioxin toxicity equivalents before and after 3 months of monitoring of Chinese tree flowers in Example 1. DETAILED DESCRIPTION

[0051] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0052] Example 1

[0053] 1.1 Main instruments and reagents

[0054] Thermo ASE 350 accelerated solvent extractor, Thermo Fisher, USA. BUCHI R300 rotary evaporator, BUCHI, Switzerland. Manual nitrogen blow-through concentrator, Shanghai Anpu Technology Co., Ltd. ThermoTRACE1310-DFS high-resolution gas chromatograph-high-resolution mass spectrometer, Thermo Fisher, USA. Thermo TR-Dioxin-5MS capillary column: 60m×0.25mm×0.25μm, Thermo Fisher, USA.

[0055] Acetone, toluene, n-hexane, dichloromethane, and decane are all pesticide-grade reagents, from Thermo Fisher, USA. Hydrochloric acid, concentrated sulfuric acid, anhydrous sodium sulfate, potassium hydroxide, and silver nitrate are all high-grade pure, from Sinopharm Chemical Reagent Company. Silica gel and activated carbon silica gel for chromatography columns, from Wako Reagent Company, Japan. Dioxin standard solution (1613-CS), extraction internal standard (1613-LCS), and injection internal standard (1613-ISS), with nonane as the medium, 1 mL, from Wellington, USA. Mass calibration material (PFK), from Wellington, USA. Diatomaceous earth and Florisil, from Shanghai Anpu Technology Co., Ltd.

[0056] 1.2 Instrument conditions

[0057] High-resolution gas chromatography conditions: injection mode: splitless injection; injection volume: 1.0 μL; injection port temperature: 270°C; transfer line temperature: 280°C; carrier gas flow rate: 1.0 mL / min; programmed temperature: initial temperature 140°C, hold for 1 min, increase the temperature to 200°C at a rate of 20°C / min, hold for 1 min, then increase the temperature to 220°C at a rate of 5°C / min, hold for 16 min, then increase the temperature to 235°C at a rate of 5°C / min, hold for 7 min, and then increase the temperature to 310°C at a rate of 5°C / min and hold for 10 min.

[0058] Mass spectrometry conditions: electron impact ion source (EI), electron energy 45 eV; ion source temperature 250°C; acceleration voltage 4800 V; selected ion detection, mass spectrometry resolution ≥10000; the monitoring peaks of each compound to be tested are shown in Table 1, and the isotope dilution internal standard method and chromatographic retention law are used for qualitative and quantitative analysis.

[0059] Table 1 Mass number setting (monitoring ions and lock mass numbers)

[0060]

[0061]

[0062] 1.3 Experimental methods

[0063] 1.3.1 Sample collection and preparation

[0064] 1) Select monitoring points:

[0065] Select the target monitoring area, divide the target monitoring area into grids, and obtain the target monitoring grid area (such as Figure 1 The size of each target monitoring grid area is set to 5×5km 2 -30×30km 2The size of each monitoring point in the target monitoring grid area is 0.5×0.5km 2 -1×1km 2 ;

[0066] 2) Collecting Chinese tree flowers:

[0067] Select Chinese tree flowers with a diameter of 3mm-5mm from Saihanba, Weichang, Hebei (background area), wear clean plastic gloves, gently break off the Chinese tree flowers from the bark, put them in a kraft paper bag, transport them back to the laboratory, and dry them naturally in the dark at room temperature;

[0068] 3) Packaging of Chinese tree flowers:

[0069] Randomly select Chinese tree flowers and place them in a 10cm×10cm nylon mesh bag with a pore size of 1mm-2mm. Each mesh bag is loaded with 3-5 Chinese tree flowers with a diameter of more than 3cm (dry weight 5-10g). When loading, make sure that they do not overlap each other and transplant them immediately after loading.

[0070] 4) Transplantation of Chinese tree flowers:

[0071] At each monitoring point, randomly select 2-3 sub-sample points with a distance of 10m-100m from each other. On the monitoring start date, hang a nylon mesh bag containing Chinese tree flowers at a height of 2m-3m above the ground in each small sample point;

[0072] 5) Chinese tree flower recycling:

[0073] After 3 months of atmospheric exposure, the nylon mesh bag was removed, and the Chinese tree flower was transplanted into a clean cowhide bag, which was sealed and transported back to the laboratory. Under a dissecting microscope, biological debris, soil, rock particles and other debris attached to the surface of the Chinese tree flower were removed with tweezers and a small brush, and then dried, crushed, ground, and passed through a 100-200 mesh sieve to obtain a Chinese tree flower powder sample;

[0074] 6) Sample pretreatment:

[0075] First, add 5g silica gel and 5g Florisil from bottom to top at the bottom of the extraction pool, weigh 2.00g of Chinese tree flower powder sample and mix it with diatomaceous earth, place it in the extraction pool, add 5μL of extraction internal standard (1613- LCS), and use accelerated solvent extraction instrument for extraction. The accelerated solvent extraction conditions are as follows: extraction solvent: a mixed solution of n-hexane, dichloromethane and acetone with a volume ratio of 40:40:20; heating temperature: 150℃; heating time: 7min; static extraction time: 8min; pressure: 10.3MPa (1500psi); cycle twice; nitrogen purge time: 120s, after the extraction is completed, the extract is concentrated to 1mL-2mL to obtain a concentrated solution;

[0076] 7) Multi-layer silica gel column purification:

[0077] The multilayer silica gel column is sequentially filled with 4 g of anhydrous sodium sulfate, 0.9 g of silica gel, 3 g of 2% potassium hydroxide silica gel, 0.9 g of silica gel, 4.5 g of 44% sulfuric acid silica gel, 6 g of 22% sulfuric acid silica gel, 0.9 g of silica gel, 3 g of 10% silver nitrate silica gel, and 6 g of anhydrous sodium sulfate, and the multilayer silica gel column is eluted with 100 mL of n-hexane, and then the above-mentioned concentrated solution is quantitatively transferred to the multilayer silica gel column, and eluted with 200 mL of n-hexane, and the eluate is concentrated to 1 mL-2 mL to obtain a primary purified solution;

[0078] 8) Activated carbon silica gel column purification:

[0079] The activated carbon silica gel column is filled with anhydrous sodium sulfate about 10 mm thick, 1.0 g of 10% activated carbon silica gel, and anhydrous sodium sulfate about 10 mm thick in sequence, and the activated carbon silica gel column is eluted with 20 mL of n-hexane. The sample concentrate purified by the multi-layer silica gel column is quantitatively transferred to the activated carbon silica gel column. Elute with a mixed solution of 30 mL of n-hexane and 10 mL of dichloromethane, discard the eluent, flip the activated carbon column, elute with 60 mL of toluene, collect the eluent and concentrate it to 1-2 mL, blow it with nitrogen until it is nearly dry, add 5 μL of injection internal standard (1613-ISS) and 45 μL of decane, vortex and oscillate to mix, and obtain the purified solution.

[0080] 9) The above purified solution was tested according to the instrument conditions in 1.2, and the dioxin toxicity equivalent was calculated based on the dioxin content in the flowers of the Chinese tree. The results are as follows: Figure 2 shown.

[0081] The calculation formula for the toxic equivalent of dioxins is:

[0082] TEQ=Σ(dioxin isomer concentration)×TEF

[0083] In the formula, TEF is the Toxic Equivalency Factor of dioxin compounds, that is, the Toxic Equivalency Factor of the most toxic 2,3,7,8-TCDD is set to 1, and TEF is the toxicity coefficient of the toxicity of dioxin isomers compared with the toxicity of 2,3,7,8-TCDD.

[0084] Example 2

[0085] Methodological validation of isotope dilution high-resolution gas chromatography-high-resolution mass spectrometry:

[0086] 2.1 Relative response factor

[0087] The determination has more than 5 mass concentration standard solution sequences. The ion abundance ratio of the detection ion corresponding to the compound in the standard solution should be roughly consistent with the theoretical ion abundance ratio (see Table 2), and the variation range should be within ±15%. Calculate the relative response factor (RRFes) of the test compound relative to the extracted internal standard at each mass concentration point. Then perform sample determination to obtain the chromatogram of each monitoring ion of dioxins.

[0088] Table 2 Theoretical ion abundance ratios calculated based on the isotope abundance ratios of chlorine atoms

[0089]

[0090]

[0091] 2.2 Results and calculations

[0092] 2.2.1 Qualitative analysis

[0093] The two monitoring ions of dioxin analogs exist simultaneously within the specified retention time window, and their ion abundance ratio is consistent with the theoretical ion abundance ratio listed in Table 2, with a relative deviation of less than 15%. The chromatographic peaks that meet the above conditions are qualitatively identified as dioxin substances. In addition to meeting the above requirements, the retention time of the chromatographic peak should be consistent with that of the standard solution (within 3s), and the relative retention time of the internal standard is also consistent with that of the standard solution (within 0.5%). The chromatographic peaks that meet the above conditions are qualitatively identified as 2,3,7,,8-chlorodioxins.

[0094] 2.2.2 Quantitative analysis

[0095] The absolute amount (Q) of dioxins detected in the sample was calculated by the internal standard method, and the Q of 2,3,7,8-chloro dioxins was calculated by the following formula. For non-2,3,7,8-chloro dioxins, the average RRFes of 2,3,7,8-chloro dioxins with the same number of chlorine atoms were used.

[0096]

[0097] Where: Q—the amount of the compound to be tested in the sample, ng;

[0098] A—the sum of the monitoring ion peak areas of the compound to be tested in the chromatogram;

[0099] Aes—sum of the peak areas of the monitored ions extracted from the internal standard;

[0100] Qes—the amount of internal standard added for extraction, ng;

[0101] RRFes—Relative response factors of the test compound relative to the extracted internal standard.

[0102] The mass fraction of the compound to be tested in the sample was calculated using the following formula.

[0103]

[0104] Where: ω—mass fraction of the compound to be tested in the sample, ng / kg;

[0105] Q—total amount of the compound to be tested in the sample, ng;

[0106] m—sample weight, kg;

[0107] w—moisture content, %.

[0108] 2.3 Standard curve and detection limit

[0109] A series of different concentrations of PCDDs and PCDFs standard solutions CS1-CS5 were injected respectively, and a standard curve was drawn with the mass concentration of each PCDDs and PCDFs compound versus the corresponding peak area.

[12] , the relative response factor of the test compound at each mass concentration point relative to the extracted internal standard was calculated, and its relative standard deviation was calculated. The detection limit of each compound monomer was determined using a 3-fold signal-to-noise ratio. The results are shown in Table 3.

[0110] Table 3 Average relative response factors and method detection limits of 17 PCDD / Fs

[0111]

[0112]

[0113] 2.4 Precision and Accuracy

[0114] Actual lichen samples were selected, dioxin isotope internal standard substances were added, and the actual spiked samples were measured repeatedly (n=6), and the results are shown in Table 4. Through the actual sample spiked determination, the average recovery rate of the internal standard was 42% to 89%, which met the requirements of the international standard method US EPA1613 for the recovery rate of isotope internal standard.

[0115] Table 4 Analysis results of internal standard recovery of actual samples

[0116]

[0117]

[0118] In summary, the present invention provides a method for analyzing 17 PCDD / Fs in lichens by high-resolution gas chromatography / high-resolution mass spectrometry. After the samples are extracted, purified and concentrated by accelerated solvent, the PCDD / Fs in the lichen samples are qualitatively and quantitatively analyzed by HRGC / HRMS. The results show that the average recovery rate of the internal standard of this method is 42% to 89%, and the analysis results are accurate and reliable, which meets the requirements of the international standard method US EPA1613 for the recovery rate of isotope internal standards. This method has a wide range of application prospects in the detection of dioxins in Chinese tree flower samples, and can provide data support for the study of the source, distribution, migration and deposition level of atmospheric dioxins.

[0119] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent substitution or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for monitoring dioxin-type air pollutants, characterized in that: The steps include: Step a, dividing the target monitoring area into grids to obtain the target monitoring grid area; Step b, packing the Chinese tree flower into mesh bags and transporting them to the target monitoring grid area, suspending them on a bracket, exposing them to the atmosphere for a predetermined time, taking back the mesh bags, removing impurities attached to the surface of the Chinese tree flower, drying, crushing, and sieving to obtain a Chinese tree flower powder sample; Step c, filling the extraction pool with silica gel and florisil from bottom to top in sequence, mixing the Chinese tree flower powder sample and diatomaceous earth evenly, adding the mixture into the extraction pool, adding the extraction internal standard and the extraction solvent, extracting with an accelerated solvent extractor, heating at 148° C.-152° C., extracting for 7 min.-9 min., extracting at a pressure of 10 MPa-10.5 MPa, concentrating the extract to 1 mL-2 mL after the extraction to obtain a concentrated solution, and purifying the concentrated solution by passing through a multi-layer silica gel column and an activated carbon silica gel column in sequence to obtain a purified solution; The extraction solvent is a mixed solution of n-hexane, dichloromethane and acetone; Step d, using isotope dilution high-resolution gas chromatography-high-resolution mass spectrometry to determine the content of dioxins in the purified liquid; the dioxins are the following 17 substances: 2378-T4CDD, 12378-P5CDD, 123478-H6CDD, 123678-H6CDD, 123789-H6CDD, 1234678-H7CDD, O8CDD, 2378-T4CDF, 12378-P5 CDF, 23478-P5CDF, 123478-H6CDF, 123678-H6CDF, 234678-H6CDF, 123789-H6CDF, 1234678-H7CDF, 1234789-H7CDF, O8CDF; Wherein, in step c, the fillers of the multilayer silica gel column are, from bottom to top, anhydrous sodium sulfate, silica gel, 1%-3% potassium hydroxide silica gel, silica gel, 43%-45% sulfuric acid silica gel, 21%-23% sulfuric acid silica gel, silica gel, 9%-11% silver nitrate silica gel and anhydrous sodium sulfate; In step c, the fillers of the activated carbon silica gel column are anhydrous sodium sulfate, 9%-11% activated carbon silica gel and anhydrous sodium sulfate from bottom to top; In step c, the specific steps of purification by multilayer silica gel column and activated carbon silica gel column are: The concentrated solution is added to a multilayer silica gel column, eluted with n-hexane, and the eluate is concentrated to 1 mL-2 mL to obtain a primary purified solution; Add the primary purification liquid to an activated carbon silica gel column, elute with a mixed solution of n-hexane and dichloromethane, discard the eluent, invert the activated carbon silica gel column, elute with toluene, collect the eluent, and concentrate the eluent to 1 mL-2 mL, blow dry with nitrogen, add the injection internal standard and decane, mix well, and obtain a purified liquid; High resolution gas chromatography conditions are: Chromatographic column: ThermoTR-Dioxin-5MS capillary column, 60m×0.25mm×0.25μm; Column temperature: 138℃-142℃, maintain for 1min-2min, then increase the temperature to 198℃-202℃ at a rate of 19℃ / min-21℃ / min, maintain for 1min-2min, then increase the temperature to 218℃-222℃ at a rate of 4℃ / min-6℃ / min, maintain for 15min-17min, then increase the temperature to 233℃-237℃ at a rate of 4℃ / min-6℃ / min, maintain for 6min-8min, finally increase the temperature to 308℃-312℃ at a rate of 4℃ / min-6℃ / min, maintain for 9min-11min.

2. The method for monitoring dioxin-type air pollutants according to claim 1, characterized in that: The size of each target monitoring grid area is 5×5km 2 -30×30km 2 The size of each monitoring point in the target monitoring grid area is 0.5×0.5km 2 -1×1km 2 .

3. The method for monitoring dioxin-type air pollutants according to claim 2, characterized in that: 1-3 sub-sample points are set in each monitoring point, and a mesh bag is suspended in each sub-sample point. The hanging height of the mesh bag is 2m-3m from the ground.

4. The method for monitoring dioxin-type air pollutants according to claim 1 or 2, characterized in that: Each mesh bag is loaded with 3-5 Chinese tree flowers. The mesh bag is made of a nylon mesh sleeve and is provided with a plurality of mesh holes with a hole diameter of 1mm-2mm.

5. The method for monitoring dioxin-type air pollutants according to claim 1, characterized in that: Inlet temperature: 268℃-272℃; Transmission line temperature: 278℃-282℃; Injection method: splitless; Carrier gas flow rate: 0.9mL / min-1.1mL / min.

6. The method for monitoring dioxin-type air pollutants according to claim 5, characterized in that: The high-resolution mass spectrometry conditions were as follows: ionization mode: electron bombardment ion source; electron energy: 45 eV; ion source temperature: 250 °C; acceleration voltage: 4800 V; resolution ≥ 10000; acquisition mode: selected ion monitoring mode; dioxin [M] + , [M+2] + , [M+4] + The characteristic ions are as follows: T4CDDs[M] + is 319.8965, [M+2] + is 321.8936, 13 C 12 -T4CDDs[M] + is 331.9368, [M+2] + is 333.9339, 37 Cl4-T4CDD[M] + is 327.8847; P5CDDs[M+2] + is 355.8546, [M+4] + is 357.8517, 13 C 12 -P5CDDs[M+2] + is 367.8949, [M+4] + is 369.8919; [M+2] of H6CDDs + is 389.8157, [M+4] + is 391.8127, 13 C 12 -H6CDDs[M+2] + is 401.8559, [M+4] + is 403.8530; [M+2] of H7CDDs + is 423.7767, [M+4] + is 425.7737, 13 C 12 -H7CDDs[M+2] + is 435.8169, [M+4] + is 437.8140; O8CDD's [M+2] + is 457.7377, [M+4] + is 459.7348, 13 C 12 -O8CDD's [M+2] + is 469.7780, [M+4] + is 471.7750; T4CDFs[M] + is 303.9016, [M+2] + is 305.8987, 13 C 12 -T4CDFs[M] + is 315.9419, [M+2] + is 317.9389; [M+2] of P5CDFs + is 339.8597, [M+4] + is 341.8568, 13 C 12 -P5CDFs[M+2] + is 351.9000, [M+4] + is 353.8970; [M+2] of H6CDFs + is 373.8207, [M+4] + is 375.8178, 13 C 12 -[M+2] of H6CDFs + is 383.8369, [M+4] + is 385.8610; [M+2] of H7CDFs + is 407.7818, [M+4] + is 409.7788, 13 C 12 -[M+2] of H7CDFs + is 417.8253, [M+4] + is 419.8220; O8CDF[M+2] + is 441.7428, [M+4] + is 443.7398, 13 C 12 -O8CDF[M+2] + is 451.7860, [M+4] + It is 453.7830.

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