A polycyclic aromatic hydrocarbon gas chromatography-mass spectrometry detection technology method based on hydrophobic covalent organic framework solid-phase microextraction

Abstract

The present application relates to the technical field of persistent organic pollutants enrichment detection, and discloses a polycyclic aromatic hydrocarbon gas chromatography detection technology method based on hydrophobic covalent organic framework solid-phase microextraction fiber.The solid-phase microextraction fiber comprises a metal fiber as a core, is wrapped with polydopamine, and is obtained by growing a trifluoromethyl covalent organic framework in situ layer by layer; when 16 kinds of polycyclic aromatic hydrocarbons are enriched, the extraction time is as low as 12-19 min, and the desorption time is as low as 3-5 min.The solid-phase microextraction fiber cooperates with headspace sampling-gas chromatography-mass spectrometry to achieve a polycyclic aromatic hydrocarbon detection limit as low as 0.16 ng mL ‑1 The following has the advantages of precision RSD < 5.98%, wide detection range, and high polycyclic aromatic hydrocarbon substance detection rate.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of persistent organic pollutants extraction detection, and particularly relates to a polycyclic aromatic hydrocarbon gas chromatography detection technology method based on hydrophobic covalent organic framework solid phase microextraction. BACKGROUND

[0002] Solid phase microextraction (SPME) is a sample pretreatment technology introduced in the 1990s. It has been considered as a very promising sample enrichment method. Solid phase microextraction consumes less solvent, can integrate multiple steps such as sampling, enrichment and sampling together, and has been widely used in food, biology, environment and many other fields. Among them, the coating material coated on the fiber plays a key role in the extraction process. The adsorption effect of the target is mainly related to the physical and chemical properties of the specific surface area, pore size distribution and chemical functional groups of the adsorption material. The improvement of suitable and targeted adsorption effect of certain chemical substances is one of the effective strategies to significantly improve the detection effect of trace chemicals.

[0003] Polycyclic aromatic hydrocarbons (PAHs) are a typical class of persistent organic pollutants, which are stable in physical and chemical properties and cause unpredictable harm to the ecological environment and human health. They are one of the earliest organic pollutants discovered by humans, which can cause deformity, cancer and mutation effect, and have long-term malignant effect. In addition to direct combustion, polycyclic aromatic hydrocarbons are also easily deposited into food through volatilization. Because of the low concentration in the actual food matrix, it is difficult to directly use instrumental analysis, so effective enrichment of trace polycyclic aromatic hydrocarbons to achieve accurate detection is currently a hot topic of concern.

[0004] Chinese patent application No. 201810397374.X discloses a solid phase microextraction fiber for polycyclic aromatic hydrocarbon enrichment and detection and a manufacturing method. The method can manufacture a solid phase microextraction coating on different fiber substrates and be used with gas chromatography or gas chromatography-mass spectrometry. The method is used for detection of polycyclic aromatic hydrocarbon pollutants and reduces the detection limit of aromatic hydrocarbon pollutants. A metal fiber is used as a substrate, dopamine is polymerized on the substrate surface to provide a functional group, and the functional group is combined with a single ligand of COF material to provide an anchor point. Finally, a PDA-COF composite layer is synthesized for solid phase microextraction. However, the enrichment time of this method is as high as 50 min, which is not user-friendly. SUMMARY

[0005] In view of the fact that the enrichment time of the solid phase microextraction fiber of the prior art for the target detection object is too long and not user-friendly, the application provides a high-efficiency solid phase microextraction fiber for adsorbing trace polycyclic aromatic hydrocarbons in a liquid sample, and the extraction time is as low as 12-19 min, and the recovery rate reaches 80-120%; the application also provides a preparation method of the high-efficiency solid phase microextraction fiber, and the prepared solid phase microextraction fiber is used for adsorbing trace polycyclic aromatic hydrocarbons in a liquid sample, the extraction time is as low as 12-19 min, and the recovery rate reaches 80-120%; and the application also provides an application of the high-efficiency solid phase microextraction fiber in detecting the content of polycyclic aromatic hydrocarbons in a sample liquid, and the high-efficiency solid phase microextraction fiber is used for adsorbing trace polycyclic aromatic hydrocarbons in a liquid sample, the extraction time is as low as 12-19 min, and the recovery rate reaches 80-120%.

[0006] The application is implemented by the following technical solutions:

[0007] A hydrophobic covalent organic framework solid phase microextraction fiber, which comprises a metal fiber as a core, is wrapped with polydopamine, and then a trifluoromethyl covalent organic framework is grown in situ layer by layer to obtain the solid phase microextraction fiber.

[0008] Preferably, the metal fiber is a stainless steel fiber, the length of which is 8-12 cm, and the inner diameter of which is 0.2-0.5 mm.

[0009] Preferably, the metal fiber is corroded by an oxidizing solution for 12-18 min before being wrapped with polydopamine.

[0010] Preferably, the oxidizing solution is obtained by mixing concentrated sulfuric acid and a perhydrogenated oxygen solution with a mass concentration of 30% at a volume ratio of 1.5-2.5:1.

[0011] A preparation method of a hydrophobic covalent organic framework solid phase microextraction fiber, comprising the following steps:

[0012] 1) The metal fiber corroded by the oxidizing solution is cleaned and dried with deionized water, and then immersed in a polydopamine solution for more than 10 h;

[0013] 2) The metal fiber wrapped with polydopamine prepared in step 1) is immersed in an aldehyde organic ligand organic solution for several hours, and a mixture containing a trifluoromethyl amine organic ligand and a catalyst is added;

[0014] 3) The mixture prepared in step 2) is stirred at room temperature for more than 10 h, and the precipitate is collected by centrifugation, washed with an organic solvent, and vacuum dried to obtain the solid phase microextraction fiber.

[0015] Preferably, the metal fiber in step 1) is immersed in the polydopamine solution for 10-14 hours, and the polydopamine solution is obtained by mixing 2-4 mg of dopamine hydrochloride with 1 mL of Tris buffer solution at a mixing ratio of 2-4 mg:1 mL, and the Tris buffer solution has a pH of 8-9.

[0016] Preferably, the aldehyde organic ligand in step 2) is one or more of p-xylylene, 4,4'-diphenyl xlylene and 1,3,5-tris(p-formylphenyl) benzene, and the mixing ratio of the aldehyde organic ligand and the organic solvent is 0.3-0.4 mmol:5 mL, and the immersion time is 3-8 hours; the organic solvent of the aldehyde organic ligand solution is obtained by mixing 1,4-dioxane and n-butanol at a volume ratio of 4:1; the amine organic ligand is one or more of 2-(trifluoromethyl)-1,4-phenylenediamine and 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl; and the catalyst is acetic acid, and the mixing ratio of the amine organic ligand and the acetic acid is 0.1-0.15 mmol:1 mL.

[0017] Preferably, the organic solvent used for washing in step 3) is 1,4-dioxane and acetone, the vacuum drying temperature is 55-65°C, and the time is 10-18 hours.

[0018] The hydrophobic covalent organic framework solid-phase microextraction fiber or the solid-phase microextraction fiber prepared by the preparation method of the hydrophobic covalent organic framework solid-phase microextraction fiber is used for detecting the content of polycyclic aromatic hydrocarbons in a sample, and the method comprises the following steps:

[0019] a) inserting the solid-phase microextraction fiber into an extraction bottle containing a fixed volume of sample liquid, so that the solid-phase microextraction fiber is partially immersed in the liquid and the other part is above the liquid surface, heating and magnetic stirring are performed;

[0020] b) adjusting the ionic concentration of the liquid by using NaCl;

[0021] c) inserting the solid-phase microextraction fiber obtained in step b) into a gas chromatography injection port for desorption.

[0022] Preferably, the extraction temperature in step a) is 40-60°C, and the stirring speed is 0-1000 rpm; the NaCl solution in step b) is a 10% NaCl solution in terms of ionic volume concentration; and the desorption temperature in step c) is 240-320°C.

[0023] The beneficial effects of the present application are as follows:

[0024] (1) The solid-phase microextraction fiber of the present application can achieve a polycyclic aromatic hydrocarbon detection limit as low as 0.16 ng mL -1The precision RSD is less than 5.98%, the detection range is wide, the detection rate of polycyclic aromatic hydrocarbon substances is high, and if more precise instruments are used, the above-mentioned index effect is more significantly improved.

[0025] (2) The extraction time of the solid-phase microextraction fiber prepared by the application is as low as 12-19 min, the polycyclic aromatic hydrocarbon recovery rate is 80-120%, the extraction time is short, the user is friendly, the recovery rate is high, and the enrichment efficiency of polycyclic aromatic hydrocarbons is effectively improved.

[0026] (3) The preparation method is simple and low in cost, and is conducive to large-scale industrial promotion. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a scanning electron microscope (SEM) of the trifluoromethyl covalent organic framework coating layer obtained by layer-by-layer in-situ growth.

[0028] Figure 2 is an X-ray powder diffraction (XRD) of the fiber coating material.

[0029] Figure 3 is a thermogravimetric diagram of the fiber coating material.

[0030] Figure 4 is a water contact angle measurement of the fiber coating material.

[0031] Figure 5 is a chromatogram of the fiber coating material for the enrichment detection of polycyclic aromatic hydrocarbons in the spiked water sample, the actual water sample and the actual barbecue sample.

[0032] Figure 6 is the adsorption of Examples 1-6 on various polycyclic aromatic hydrocarbons. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical scheme and advantages of the application clearer and more apparent, the application will be further described in detail below with reference to examples; it should be understood that the specific examples described herein are only used to explain the application and not to limit the application; in the examples, unless otherwise specified, the means used are conventional means in the art; the terms "comprise", "include" or any other variation thereof used herein are intended to cover non-exclusive inclusion; for example, a composition, step, method, article or device comprising the listed elements does not necessarily limit to only those elements, but can include other elements not explicitly listed or inherent to such composition, step, method, article or device; in addition, the technical features involved in each embodiment of the application described below can be combined with each other as long as there is no conflict; the experimental raw materials used in the examples and comparative examples of the application are commercially available products.

[0034] Example 1

[0035] 1. A method for preparing a hydrophobic covalent organic framework compound solid-phase microextraction coating, comprising the following steps:

[0036] 1) Take a stainless steel fiber with a length of 10 cm and an inner diameter of 0.35 mm, immerse the front end 5.5 cm part into the piranha solution for 15 min, etch the stainless steel fiber to form a rough surface, wash with deionized water for three times, and dry for standby, the piranha solution is concentrated sulfuric acid: 30% hydrogen peroxide = 2:1;

[0037] 2) Immerse the pretreated stainless steel fiber in step 1) into the polydopamine solution for 12 h to obtain a large number of amino and hydroxyl groups on the surface, and vacuum dry for 2 h for standby, the polydopamine solution is formed by 30 mg of dopamine hydrochloride in 10 mL of Tris buffer (pH 8.5);

[0038] 3) (a): immerse the modified stainless steel fiber in step 2) into the mixed solution of aldehyde organic ligand (p-xylylene Ta, 4, 4'-diphenyl dicarboxylic acid) and 1, 4-dioxane, n-butanol organic solvent for 4 h, the mixing ratio of the aldehyde organic ligand and the organic solvent is 0.33 mmol: 5 mL, and the volume ratio of the mixed solution of 1, 4-dioxane and n-butanol is 4:1; (b) add amine organic ligand (2-(trifluoromethyl)-1, 4-phenylenediamine Pa) catalyst acetic acid into the mixed solution of step 2(a), the mixing ratio is 0.375 mmol: 3 mL; (c) stir the mixture of step 2(b)) and the stainless steel fiber at 25°C for 12 h. Collect the yellow powder by centrifugation and wash with 1, 4-dioxane and acetone; after vacuum drying at 60°C for 24 hours, a trifluoromethyl covalent organic framework coating is obtained.

[0039] 2. Actual food sample extraction detection:

[0040] Pre-treatment: insert the prepared solid-phase microextraction fiber into the sample inlet of the gas chromatograph at 300°C for aging until the baseline is stable, the purpose is to exclude the interference of impurities in the coating material.

[0041] a) insert the solid-phase microextraction coating into the extraction bottle containing 10 mL of sample solution, so that half of the coating is immersed in the solution and the other half is in the headspace. Heat and perform magnetic stirring;

[0042] b) adjust the ion concentration of the solution with NaCl;

[0043] c) insert the solid-phase microextraction coating obtained in step b) into the gas chromatograph sample inlet for desorption.

[0044] Gas chromatography conditions: Agilent 19091S-433UI, HP-5ms Ultra Inert (30 m x 250 μm x 0.25 μm), column initial temperature 60℃, hold for 1 min, then increase the temperature to 170℃ at the rate of 40℃ / min, then increase the temperature to 300℃ at the rate of 10℃ / min, hold for 10 min. The injection port temperature is 300℃. The carrier gas is high-purity helium (purity greater than 99.999%), the flow rate is 1.0 mL / min. The pulse injection, the pulse pressure is 168.24 kPa, the pulse time is 0.9 min, the injection is 1 uL. The split valve is opened after 0.50 min, the split flow is 30 mL / min.

[0045] Mass spectrometry conditions: ion source: EI source; ion source temperature: 230℃; ionization energy: 70 eV; electron multiplier voltage 500 V; solvent delay 6 min; full scan m / z 45-450. The data acquisition of the quantitative part is in the multiple reaction monitoring mode (MRM).

[0046] Optimal extraction conditions: extraction temperature 50℃; extraction time 15 min; ion concentration 10% NaCl (V / V); stirring speed 400 rpm; desorption time 3 min and desorption temperature 300℃.

[0047] The detection linear range is between 0.25-500 ng mL -1 ; the detection limit is between 0.008-0.16 ng mL -1 , and the precision RSD is less than 5.98%.

[0048] Example 2

[0049] A method for preparing a hydrophobic covalent organic framework compound solid-phase microextraction coating, the aldehyde ligand used is 4,4'-diphenyl-dimethylaldehyde Bd, and the remaining steps are the same as in Example 1.

[0050] Example 3

[0051] A method for preparing a hydrophobic covalent organic framework compound solid-phase microextraction coating, the aldehyde ligand used is 1,3,5-tris(p-formylphenyl) benzene Tb, and the remaining steps are the same as in Example 1.

[0052] Example 4

[0053] A method for preparing a hydrophobic covalent organic framework compound solid-phase microextraction coating, the trifluoromethyl-containing amine ligand used is 2,2'-bis-trifluoromethyl-4,4'-diaminobiphenyl Tf, and the remaining steps are the same as in Example 1.

[0054] Example 5

[0055] A method for preparing a hydrophobic covalent organic framework compound solid phase microextraction coating, the trifluoromethyl-containing amine ligand used is 2,2'-bis-trifluoromethyl-4,4'-diaminobiphenyl, and the remaining steps are the same as in Example 2.

[0056] Example 6

[0057] A method for preparing a hydrophobic covalent organic framework compound solid phase microextraction coating, the trifluoromethyl-containing amine ligand used is 2,2'-bis-trifluoromethyl-4,4'-diaminobiphenyl Tf, and the remaining steps are the same as in Example 3.

[0058] Example 7

[0059] A method for preparing a hydrophobic covalent organic framework compound solid phase microextraction coating, the food sample used in step 2.2a) is water sample, and the remaining steps are the same as in Example 5.

[0060] Example 8

[0061] A method for preparing a hydrophobic covalent organic framework compound solid phase microextraction coating, the food sample used in step 2.2a) is roast meat, and the remaining steps are the same as in Example 5.

[0062] Table 1 Detection conditions of gas chromatography-mass spectrometry

[0063]

[0064] Table 1 continued

[0065]

[0066] Table 2 Methodology analytical performance

[0067]

[0068] Table 2 shows that the linearity (≥ 7 points, n = 3) of the method ranges from 0.25 to 500 ng mL for each analyte -1 , with good determination coefficients (R 2 ) between 0.995 and 0.998. The limits of detection (LOD) (S / N = 3) of the three replicate extractions range from 0.008 to 0.16 ng mL -1 . The limits of quantification (LOQ) (S / N = 10) of the three replicate extractions range from 0.029 to 0.47 ng mL -1 . Therefore, the analytical method has sufficient sensitivity for the detection of trace amounts of polycyclic aromatic hydrocarbons. The relative standard deviation (RSD) of the three replicate experiments ranges from 1.64% to 5.94%. The inter-fiber reproducibility of the three fibers of the three replicate extractions ranges from 3.29% to 5.98%. The method meets the requirements of the methodology.

[0069] Table 3 shows the results of the analysis of the actual water samples and barbecue samples

[0070]

[0071] Table 3 shows that four polycyclic aromatic hydrocarbons, naphthalene, acenaphthene, fluorene and pyrene, were detected in the actual water samples of Example 7, and the polycyclic aromatic hydrocarbons in the samples were calculated according to the standard regression equation prepared in Table 2, with contents of 4.21, 3.51, 4.01 and 5.09 ng / mg, respectively -1 , with a standard addition recovery of 86.01%-117.67%. Among the polycyclic aromatic hydrocarbons detected in this work, three are light polycyclic aromatic hydrocarbons, which are more likely to be detected in water due to their high volatility. In the actual barbecue samples of Example 8, a total of 16 polycyclic aromatic hydrocarbons were detected, with contents of 1.38-23.82 ng / mg -1 , with a recovery of 84.23%-118.53%, and all the results show that the trifluoromethyl covalent organic framework as a new type of solid phase microextraction coating material is feasible for the enrichment and determination of polycyclic aromatic hydrocarbon compounds in actual food samples.

[0072] As shown in Figure 1 (a), the solid phase microextraction coating outside the metal fiber has a thickness of 35 μm and is tightly and uniformly distributed, and further magnification shows Figure 1 (b) that the microstructure is loose and porous. Such structure of the coating can be wrapped on the rough surface of the core and is not easy to peel off, but the loose and porous internal structure enlarges the effective adsorption area, so that the polycyclic aromatic hydrocarbons in the liquid are more easily adsorbed on the surface of the coating.

[0073] As shown in Figure 2 , the XRD spectrum of the solid phase microextraction material shows that the CF3-COF SPME coating material prepared at room temperature has three main peaks at 2.77, 5.69 and 7.43, corresponding to (100), (020) and (210) surfaces, respectively, which is consistent with the literature and indicates that the material synthesis is successful.

[0074] As shown in Figure 3 , the thermogravimetric experiment of the solid phase microextraction material shows that the total weight of the coating surface decreases slightly at 100-150°C due to the evaporation of water, and the total weight decreases slowly and steadily at 200-450°C, indicating that less than 10% of the weight of the solid phase microextraction material is lost at this temperature. When the temperature reaches 450-600°C, the weight of the solid phase microextraction material decreases by more than 40%, indicating that half of the solid phase microextraction material is pyrolyzed at this temperature. The coating mainly pyrolyzes at this temperature, and the remaining core material pyrolyzes at a temperature higher than 600°C. The core material continues to melt and pyrolyze at 600-800°C, and the mass decreases much more slowly than the coating.

[0075] As Figure 4 It can be seen that the water droplet contact angle is about 120℃, and the spherical water droplet only wets a small part of the coating surface, indicating that the hydrophobicity of the coating is very strong and has higher affinity with polycyclic aromatic substances.

[0076] As Figure 5 As

[0077] As Figure 6 Two kinds of monomers grafted with-CF3, namely 2-(trifluoromethyl)-1,4-phenylenediamine (Pa), 2,2'-bis-trifluoromethyl-4,4'-diaminobiphenyl (Tf) were selected. According to the number of benzene rings, three types of-CHO monomers, terephthaldehyde (Ta), 4,4'-biphenyldialdehyde (Bd) and 1,3,5-tris (p-formylphenyl) benzene (Tb) were selected, each ring containing 1-3 benzene rings. The two types of monomers were combined into six kinds of monomers with CF3-COF imine bond connection, synthesized according to the method in the literature, and the adsorption of polycyclic aromatic hydrocarbons was discussed. The material synthesized by Bd and Tf monomers has the best extraction effect on polycyclic aromatic hydrocarbons. This may be because a large number of benzene rings in the monomer may cause steric hindrance to the adsorption of polycyclic aromatic hydrocarbons, and a small number of benzene rings may make the pore size of the coating material formed smaller, which is not conducive to adsorption. Bd and Tf were selected as the coating material for this work. Figure 6 Terephthaldehyde (Ta), 4,4'-biphenyldialdehyde (Bd), 1,3,5-tris (p-formylphenyl) benzene (Tb), 2-(trifluoromethyl)-1,4-phenylenediamine (Pa), 2,2'-bis-trifluoromethyl-4,4'-diaminobiphenyl (Tf), naphthalene NAP, acenaphthylene ACP, acenaphthene ACPY, fluorene FLU, phenanthrene ANT, anthracene PHE, fluoranthene FLT, pyrene PYR, benz(a) anthracene BaA, HR, benzo[b]fluoranthene BbP, benzo[k]fluoranthene BbF, benzo[a]pyrene BKF, indenophenanthrene [1,2,3-c,d]pyrene IcdP, dibenzo[a,h]anthracene DBA, benzo(ghi)perylene (picene) ICP.

[0078] The above examples only express several embodiments of the present application, which are described in detail and specifically, but cannot be understood as a limitation on the scope of the patent.

[0079] For those skilled in the art, without departing from the concept of the present application, several modifications and improvements can be made, which are within the scope of the present application, therefore, the protection scope of the present application patent should be subject to the appended claims.

Claims

1. A hydrophobic covalent organic framework solid-phase microextraction fiber, comprising a core with a rough surface and a microextraction coating, characterized in that, The microextraction coating refers to polydopamine wrapped around a core with a rough surface, which is then grown in situ layer by layer to form a trifluoromethyl covalent organic framework. When the solid-phase microextraction fiber extracts polycyclic aromatic hydrocarbons, the extraction time is as low as 12 to 19 minutes and the desorption time is as low as 3 to 5 minutes. The solid-phase microextraction fiber is prepared through the following steps: Step 1) Clean the core with a rough surface with deionized water and dry it. Then immerse it in a polydopamine solution for more than 10 hours to obtain a core coated with polydopamine. Step 2) Immerse the polydopamine core prepared in Step 1) in an organic solution of aldehyde organic ligands for several hours, and add amine organic ligands containing trifluoromethyl and catalyst to obtain a mixture; Step 3) Stir the mixture prepared in Step 2) at room temperature for more than 10 hours, collect the precipitate by centrifugation, wash with organic solvent, and vacuum dry to obtain the solid-phase microextraction fiber; In step 2), the aldehyde organic ligand is 4,4'-biphenyldicarboxaldehyde, wherein the mixing ratio of the aldehyde organic ligand to the organic solvent is 0.3–0.4 mmol:5 mL, and the immersion time is 3–8 h; the organic solvent of the organic solution of the aldehyde organic ligand is a mixture of 1,4-dioxane and n-butanol at a volume ratio of 4:1; the amine organic ligand is 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl; and the catalyst is acetic acid, wherein the mixing ratio of the amine organic ligand to acetic acid is 0.1–0.15 mmol:1 mL.

2. The hydrophobic covalent organic framework solid-phase microextraction fiber according to claim 1, characterized in that, The core is made of stainless steel fiber with a length of 8-12 cm and an inner diameter of 0.2-0.5 mm.

3. The hydrophobic covalent organic framework solid-phase microextraction fiber according to claim 2, characterized in that, Before being coated with polydopamine, the stainless steel fibers are first corroded by an oxidizing solution for 12 to 18 minutes.

4. The hydrophobic covalent organic framework solid-phase microextraction fiber according to claim 3, characterized in that, The oxidizing solution is obtained by mixing concentrated sulfuric acid and a 30% (w / w) perhydrogenated oxygen solution at a volume ratio of 1.5 to 2.5:

1.

5. The hydrophobic covalent organic framework solid-phase microextraction fiber according to claim 1, characterized in that, Step 1) The core with the rough surface is immersed in the polydopamine solution for 10-14 hours. The polydopamine solution is obtained by mixing dopamine hydrochloride and Tris buffer at a mixing ratio of 2-4 mg:1 mL. The pH of the Tris buffer is 8-9.

6. The hydrophobic covalent organic framework solid-phase microextraction fiber according to claim 1, characterized in that, The organic solvents used for washing in step 3) are 1,4-dioxane and acetone, and the vacuum drying temperature is 55-65°C for 10-18 hours.

7. An application of the hydrophobic covalent organic framework solid-phase microextraction fiber according to any one of claims 1 to 6 in detecting the content of polycyclic aromatic hydrocarbons in a sample liquid, characterized in that, Includes the following steps: Step a) Insert the solid-phase microextraction fiber into an extraction bottle containing a fixed volume of sample liquid, so that part of the solid-phase microextraction fiber is immersed in the liquid and the other part is above the liquid surface, and heat and magnetically stir. Step b) Adjust the ion concentration of the liquid with NaCl; Step c) Insert the solid-phase microextraction fiber obtained in step b) into the gas chromatograph inlet for desorption.

8. The application according to claim 7, characterized in that, The extraction temperature in step a) is 40–60°C, and the stirring speed is 0–1000 rpm; the NaCl solution in step b) is a 10% NaCl solution with an ion volume concentration; and the desorption temperature in step c) is 240–320°C.

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