Fluorine-functionalized covalent organic framework material, solid-phase microextraction probe and method for detecting LCMs in complex matrix

Abstract

The invention discloses a fluorine-functionalized covalent organic framework material, a solid-phase microextraction probe and a method for detecting LCMs in a complex matrix, and the fluorine-functionalized covalent organic framework material is formed by copolymerizing three monomers, namely tetraaminophenyl porphyrin, tetraaldehyde phenyl porphyrin and 3, 5-bis (trifluoromethyl) phenylacetylene by adopting a solvothermal method. The synthesized Por-CF3-COF has a quinoline-connected nitrogen heterocyclic ring, a trifluoromethyl functionalized site and a porphyrin ring cavity, and a functionalized modified fluorinated electron donor region, a large conjugate system and a hydrophobic site, so that the Por-CF3-COF is directionally combined with LCMs through lone pair electron-pi interaction and pi-pi interaction; the hydrogen bond interaction between the H atom of the Por-CF3-COF aromatic ring and the F of the LCMs further promotes the molecular contact of the fluorescent probe and the LCMs, so that the quantitative detection of trace LCMs in a complex environment system is realized.

Description

Technical Field

[0001] The present invention relates to the field of environment, and in particular to a fluorine-functionalized covalent organic framework material, a solid-phase microextraction probe, and a method for detecting LCMs in complex matrices. Background Art

[0002] LCMs (i.e., Liquid Crystal Monomers) are a class of organic molecules with a biphenyl or bicyclohexyl backbone, usually containing substituents such as esters, alkynes, cyclohexyl groups, cyano groups, and fluorine, and are widely used in various liquid crystal displays (such as televisions, computer monitors, and mobile phone screens), and are the core materials for liquid crystal displays to achieve image display. Research shows that most LCMs are persistent, bioaccumulative, and biotoxic, and are considered a new type of emerging organic pollutants. During the production, use, disposal, and recycling of liquid crystal displays, LCMs will inevitably be released into the environment. Therefore, the detection of LCMs (especially LCMs in food) is crucial.

[0003] In the field of sample analysis, due to the low content in actual samples and the interference of complex matrices, it is difficult to directly detect low-concentration micro-pollutants in environmental matrices by chromatography or mass spectrometry. Therefore, it is usually necessary to pretreat the actual samples before chromatographic or mass spectrometric detection.

[0004] Solid-phase microextraction (i.e., SPME) is a solvent-free sample pretreatment method that uses a fiber as an absorption or adsorption medium to extract and concentrate target analytes, and has advantages such as sensitivity, selectivity, and repeatability. The solid-phase microextraction process is a process of dynamic adsorption equilibrium between the adsorption layer and the sample solvent. Therefore, the fiber coating plays an important role in the SPME process. In recent years, fibers such as polyacrylate (PA), poly(dimethylsiloxane) / divinylbenzene (PDMS / DVB), divinylbenzene / carbon / polydimethylsiloxane (DVB / CAR / PDMS), and polydimethylsiloxane (PDMS) have been commercialized and successfully used for the analysis of trace target substances, but these fibers usually have disadvantages such as limited lifespan, poor thermal stability, and low selectivity. Therefore, it is crucial to develop new materials as stable and effective coatings for SPME fibers.

[0005] At present, new coating materials such as molecular imprinting polymers, ionic liquids, covalent organic frameworks (COFs) and metal organic frameworks (MOFs) are constantly developing and showing great potential for the adsorption and removal of organic pollutants. Among them, COFs stand out among these materials due to their superb thermal stability, high porosity and huge specific surface area, and have excellent molecular adsorption and separation capabilities. However, there are no reports on the use of COFs as SPME coatings to capture LCMs, and the detection of trace LCMs in food is still a problem that plagues the industry. Summary of the invention

[0006] In view of this, the present invention proposes a fluorine-functionalized covalent organic framework material, a solid phase microextraction probe, and a method for detecting LCMs in food, which can achieve accurate detection of trace LCMs in food and provide new ideas for the quantitative analysis of trace LCMs in complex matrices.

[0007] To achieve the above object, the present invention adopts the following technical solutions: The fluorine-functionalized covalent organic framework material of the present invention is copolymerized by tetraaminophenylporphyrin, tetraaldehydephenylporphyrin and 3,5-bis(trifluoromethyl)phenylacetylene, and specifically comprises: In the first step, tetraaminophenylporphyrin, tetraaldehydephenylporphyrin and 3,5-bis(trifluoromethyl)phenylacetylene are added to a first solvent for a first mixing, and then acetic acid solution, boron trifluoride-ether and tetrachloro-1,4-benzoquinone chloro-1,4-benzoquinone are added for a second mixing, and then a freeze-vacuum-thaw cycle is performed for degassing; In the second step, the degassed reaction solution is sealed and heated to cause the three monomers in the reaction solution to undergo Schiff base reaction and Povarov reaction; after the reaction, the reaction is filtered, washed, and dried to obtain a black powdery fluorine-functionalized covalent organic framework material, which is recorded as Por-CF3-COF and has the following structural formula: .

[0008] The beneficial effect is that the fluorine-functionalized covalent organic framework material of the present invention has a functionally modified fluorinated electron donor region, a large conjugated system and a hydrophobic site, so that it can be directionally combined with LCMs through lone pair electron-π interaction and π-π interaction. The hydrogen bond interaction between the H of the aromatic ring in the material and the F of the LCMs can further strengthen the molecular contact between Por-CF3-COF and LCMs, thereby promoting the adsorption of the material to LCMs.

[0009] Preferably, the first solvent in the first step is n-butanol / o-dichlorobenzene in a volume ratio of 1:1; the first mixing in the first step is ultrasonic mixing for 10 min or more; and the second mixing is ultrasonic mixing for 4 min to 6 min.

[0010] Preferably, the heating in the second step is carried out in a programmed heating manner: first, the reaction solution is placed in an environment of 100 °C for 1 day, and then in an environment of 120 °C for 3 to 6 days (preferably 5 days); The washing in the second step is to first wash with a saturated NaHCO3 solution to neutralize the unreacted acid and quench the reaction, and then perform Soxhlet extraction with tetrahydrofuran (extraction for 24 h) to remove the unreacted small molecule monomers and organic solvents; the drying is carried out under vacuum at 50 °C to 70 °C for 10 h to 12 h.

[0011] Preferably, the molar ratio of the three comonomers of tetraminophenyl porphyrin, tetraaldehyde phenyl porphyrin and 3,5-bis(trifluoromethyl)phenylacetylene in the first step is 0.12:0.12:1.6.

[0012] The present invention also provides a solid-phase microextraction probe, which includes a stainless steel wire and a coating adhered to the stainless steel wire, and the coating is made of the fluorine-functionalized covalent organic framework material of the present invention.

[0013] The beneficial effects are as follows: The synthesized Por-CF3-COF of the invention has quinoline-linked nitrogen heterocycles, trifluoromethyl functionalized sites and porphyrin ring cavities, which together construct a unique framework structure, thereby endowing it with rich molecular recognition sites. When performing SPME, the functionalized fluorinated electron donor region, large conjugated system and hydrophobic sites of the present invention enable Por-CF3-COF of the present invention to be directionally bound to LCMs through lone pair electron-π interaction and π-π interaction; the hydrogen bond interaction between the H atom of the aromatic ring of Por-CF3-COF and the F atom of LCMs will further strengthen the molecular contact between the functionalized Por-CF3-COF and LCMs.

[0014] Based on the Por-CF3-COF probe and SPME-GC-MS / MS, the present invention proposes a detection method for trace LCMs in complex matrices. The detection method uses the solid-phase microextraction probe of the present invention (Por-CF3-COF coating adhered to the stainless steel wire) to perform solid-phase extraction on actual samples or standards, and uses GC-MS to desorb and quantitatively analyze the probe, specifically including the following contents: In the first step, when the actual sample is a solid, first crush the actual sample, and then add an internal standard 13 C 12 -(PCB)-180, 13 C 12 -(PCB)-52 and a certain volume of ultrapure water to obtain a sample working solution; When the actual sample is a liquid, take a certain volume of the actual sample, and add an internal standard 13C 12 -(PCB)-180 and 13 C 12 -(PCB)-52 to obtain a sample working solution; In the second step, insert the solid-phase microextraction probe into the sample working solution for extraction. The extraction conditions are as follows: the extraction time is 30 min to 60 min, the extraction temperature is 90°C to 100°C, and the stirring speed is 300 rpm to 700 rpm; In the third step, after the extraction is completed, analyze the probe adsorbed with the analyte by GC-MS. The inlet temperature is 260°C to 290°C, and the oven temperature uses a programmed temperature rise. Its initial temperature is 40°C, rising to 145°C at a rate of 30°C / min and holding for 3 min; rising to 250°C at a rate of 3°C / min; rising to 300°C at a rate of 10°C / min; In the fourth step, confirm the concentration of LCMs in the actual sample according to the linear regression equation of each LCM.

[0015] In the present invention, the LCMs include 2CB, EDPdB, DMPMB, BDPdB, DECB, DTMDEB, PCTB, TePdB, DPdB, TePT, TpeCB, EFPT, and EDPB.

[0016] The beneficial effects are as follows: The detection method of the present invention has high sensitivity and a wide linear range. The RSDs between the Por-CF3-COF probes are 0.83 - 9.84%, further proving that the detection method of the present invention has good reproducibility and reliability, can be applied to the accurate detection of LCMs in water bodies, and can also achieve the accurate detection of LCMs in complex matrices. In addition, the probe of the present invention can be reused more than 70 times, reducing the detection cost, being economical and environmentally friendly, and further illustrating the potential application prospects and value of the present invention. Description of the Drawings

[0017] Figure 1 is the synthesis route diagram of the fluorine-functionalized covalent organic framework material of the present invention.

[0018] Figure 2 is the TGA characterization diagram of Por-COF and Por-CF3-COF.

[0019] Figure 3 is the FT-IR characterization diagram of Por-COF and Por-CF3-COF.

[0020] Figure 4 is the XPS characterization diagram of Por-CF3-COF of the present invention.

[0021] Figure 5SEM and TEM characterization diagrams of Por-CF3-COF and Por-CF3-COF probes. In Figure 5 , (a) is the SEM diagram of the stainless steel wire, (b) is the planar SEM diagram of the Por-CF3-COF probe, (c) is the cross-sectional SEM diagram of the Por-CF3-COF probe, (d) is the SEM diagram of Por-CF3-COF, (e) is the TEM diagram of Por-CF3-COF, and (f)-(h) are the EDS diagrams of Por-CF3-COF.

[0022] Figure 6 GC-MS / MS chromatograms after spiking actual samples. In Figure 6 , (a) is the wheat flour sample, (b) is the red bean sample, (c) is the meat sample, and (d) is the vegetable sample. Among them, the substances corresponding to peaks 1-15 in (a)-(d) are PCB-52 (i.e., internal standard 13 C 12 -(PCB)-52), 2CB, EDPrB, DMPMB, BDPrB, DECB, DTMDEB, PCTB, TePrB, DPrB, TePT, PCB-180 (i.e., internal standard 13 C 12 -(PCB)-180), TpeCB, EFPT, and EDPB.

[0023] Figure 7 GC-MS / MS chromatograms after spiking juice samples. The substances corresponding to peaks 1-15 in the figure are PCB-52 (i.e., internal standard 13 C 12 -(PCB)-52), 2CB, EDPrB, DMPMB, BDPrB, DECB, DTMDEB, PCTB, TePrB, DPrB, TePT, PCB-180 (i.e., internal standard 13 C 12 -(PCB)-180), TpeCB, EFPT, and EDPB.

[0024] Figure 8 Spiked recovery rates of actual samples. In Figure 8 , (a) is the wheat flour sample, (b) is the red bean sample, (c) is the meat sample, (d) is the vegetable sample; (e) is the juice.

[0025] Figure 9 Adsorption comparison diagrams of Por-CF3-COF probes, comparative probes, and commercially available fibers for LCMs and the repeatability diagram of Por-CF3-COF probes.

[0026] Figure 10 High-resolution F1s and N1s diagrams of Por-CF3-COF before and after adsorption.

[0027] Figure 11 It is an analysis diagram of non-covalent intermolecular interactions between Por-CF3-COF and LCMs. Specific implementation manners

[0028] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Among them, the reagents used in the present invention are all commercially available reagents, and the experimental instruments used in the present invention are all commonly used laboratory instruments. It should be noted that the LCMs in the embodiments of the present invention include 2CB, EDPrB, DMPMB, BDPrB, DECB, DTMDEB, PCTB, TePrB, DPrB, TePT, TpeCB, EFPT and EDPB, and the structural formulas are shown in Table 1.

[0029] Table 1 Target analytes LCMs of the present invention and their structural formulas It should be noted that the actual samples of the present invention include wheat flour, wheat flour, red beans, vegetables, chicken, and fruit juice purchased from a certain farmers' market. The solid foods are stored frozen before detection, and the fruit juice is stored sealed.

[0030] Example 1 Fluorine-functionalized covalent organic framework material of the present invention I. The present invention provides a fluorine-functionalized covalent organic framework material, which is copolymerized by using tetraaminophenyl porphyrin, tetraaldehyde phenyl porphyrin and 3,5-bis(trifluoromethyl)phenylacetylene as comonomers by a solvent method. Combining Figure 1 It can be seen that the synthesis process of the fluorine-functionalized covalent organic framework material of the present invention is as follows: In the first step, 0.12 mol of tetraaminophenyl porphyrin, 0.12 mol of tetraaldehyde phenyl porphyrin and 1.6 mol of 3,5-bis(trifluoromethyl)phenylacetylene are added to 1.2 ml of a first solvent (preferably n-butanol and o-dichlorobenzene with a volume ratio of 1:1), ultrasonically mixed for 10 min to 15 min, then 0.2 ml of acetic acid solution (6M), 8 μl of boron trifluoride-ether and 19 mg of tetrachloro-1,4-benzoquinone are added, and ultrasonically mixed again for 5 min. Finally, the reaction solution is subjected to three cycles of freezing (using liquid nitrogen freezing)-vacuum pumping-thawing for degassing; Step 2: Seal the degassed reaction solution (using flame sealing) and heat it to cause the Schiff base reaction and Povarov reaction among the three comonomers in the reaction solution. After the reaction is completed, filter and wash (first wash with saturated NaHCO3 solution to neutralize the unreacted acid and quench the reaction; then perform Soxhlet extraction with tetrahydrofuran to remove the unreacted small molecule monomers and organic solvents), and dry in vacuum at 70 °C overnight to obtain a black powdery fluorine-functionalized covalent organic framework material, denoted as Por-CF3-COF, whose structural formula is as follows: 。

[0031] In the present invention, programmed heating is adopted during the copolymerization process. First, the reaction solution is placed in an environment of 100 °C for 1 day, and then in an environment of 120 °C for 3 to 6 days (preferably 5 days or more).

[0032] II. In the present invention, Por-COF is used as a comparison. Por-COF is prepared by dissolving tetraaminophenyl porphyrin and tetraaldehyde phenyl porphyrin in 6M aqueous acetic acid solution, using ortho-dichlorobenzene and n-butanol (v / v = 1:1) as solvents, mixing evenly by ultrasonic, then performing three cycles of liquid nitrogen freezing - vacuum pumping - thawing degassing, and then flame sealing. It is placed in an environment of 120 °C (generally using a constant temperature drying oven) for constant temperature reaction for 3 days; after the reaction is completed, it is washed thoroughly with 100 ml of tetrahydrofuran, filtered, and dried in vacuum at 70 °C for 10 h to obtain a dark purple powder, which is Por-COF.

[0033] III. Characterization of Por-CF3-COF and Por-COF 1. The XPS characterization of Por-CF3-COF is shown in Figure 2 。From Figure 2 it can be seen that the total spectra of C1s, N1s, O1s, and F1s correspond to 285 eV, 399 eV, 532 eV, and 688 eV respectively; the high-resolution N1s spectrum can be divided into two peaks. The peak at 400.1 eV belongs to the non-protonated porphyrin N and quinoline N, and the peak at 398.1 eV belongs to the protonated porphyrin N; compared with Por-COF, the content of F increases from 0 to 2.47%, proving the successful synthesis of Por-CF3-COF.

[0034] 2. The FT-IR characterization of Por-COF and Por-CF3-COF is shown in Figure 3 。Combined with Figure 3 it can be known that Por-COF shows a stretching vibration peak of C=N at 1625 cm -1 ; compared with Por-COF, Por-CF3-COF shows a strong stretching vibration peak of C-F at 1278 cm -1 and its peak at 1625 cm-1 The disappearance of the stretching vibration peak of C=N also indicates the successful synthesis of Por-CF3-COF.

[0035] 3. Adsorption-desorption characterization was carried out on Por-COF and Por-CF3-COF. The results show that the isotherm types of both Por-CF3-COF and Por-COF are type IV isotherms. The BET specific surface areas of Por-COF and Por-CF3-COF are 1129 m 2 / g and 702 m 2 / g respectively, and the pore diameters are 1.0 nm and 0.5 nm respectively. It can be seen that the Por-CF3-COF of the present invention has a larger specific surface area, laying a foundation for its adsorption of LCMs.

[0036] 4. The thermogravimetric characterization results of Por-COF and Por-CF3-COF are shown in Figure 4 . It can be seen from Figure 4 that Por-CF3-COF has better thermal stability than Por-COF, which is beneficial to thermal desorption.

[0037] 5. The contact angles of Por-COF and Por-CF3-COF are 73.1° and 123.1° respectively, indicating that the introduction of trifluoromethyl group makes Por-CF3-COF have a stronger hydrophobic surface.

[0038] Example 2 Preparation of the solid-phase microextraction probe and the comparative probe of the present invention I. The present invention uses a physical gluing method to adhere and cure Por-CF3-COF on the surface of a stainless steel wire, which is specifically described as follows: The stainless steel wire (with a diameter of about 150 μm and a length of about 5 cm) is first ultrasonically assisted cleaned with water, methanol and acetone to remove impurities, and dried at room temperature for 12 h; Organosilicon curing agent and cyclohexane are added to polydimethylsiloxane rubber (PDMS), and ultrasonic treatment is carried out to make them uniformly mixed until there are no bubbles in the mixed solution, obtaining the gluing agent for adhesion; The dried stainless steel wire is inserted into the glue, and after pulling out, it is rotated in the Por-CF3-COF powder to obtain a coating, and vacuum dried at 150°C for 30 min; Then it is inserted into the glue again, and this adhesion is repeated three times to obtain the Por-CF3-COF probe. Before use, the probe of the present invention is aged for 20 min in the injection port of a gas chromatograph (temperature is 300°C, nitrogen environment).

[0039] II. Repeat the above manufacturing steps to make a Por-COF probe with a Por-COF coating, and perform aging treatment according to the aging steps of the Por-CF3-COF probe before use to obtain an activated Por-COF probe.

[0040] III. SEM and TEM characterizations were performed on Por-CF3-COF, Por-CF3-COF probe and stainless steel wire, and the results are shown in Figure 5 . As can be seen from Figure 5 d-5e, Por-CF3-COF is a uniform sheet-like structure; Figure 5 f-5h are the C, F, N element mapping diagrams of Por-CF3-COF, further proving the successful synthesis of Por-CF3-COF. As can be seen from Figure 5 a-5c, the diameter of the stainless steel coating is about 147 μm, Por-CF3-COF is uniformly coated on the stainless steel wire, and the thickness of the Por-CF3-COF coating is 100 μm.

[0041] Example 3 The present invention constructs a SPME-GC-MS / MS detection method for LCMs in complex matrices Based on the solid-phase microextraction probe and GC-MS / MS in Example 2, the present invention constructs a quantitative detection method for LCMs in complex matrices, and this method includes the following steps: The first step, when the actual sample is solid, first crush and freeze-dry the actual sample, and then add internal standards 13 C 12 -(PCB)-180, 13 C 12 -(PCB)-52 and ultrapure water to obtain a sample working solution; When the actual sample is liquid, take a certain volume of the actual sample, and add internal standards 13 C 12 -(PCB)-180 and 13 C 12 -(PCB)-52 to obtain a sample working solution; The second step, insert the solid-phase microextraction probe into the sample working solution for SPME, and the SPME conditions are: the extraction time is 30 min to 60 min, the extraction temperature is 90°C to 100°C, and the stirring speed is 300 rpm to 700 rpm; more preferably, the extraction time is 50 min, the extraction temperature is 90°C, and the stirring speed is 700 rpm; The third step, after the extraction is completed, analyze the probe adsorbed with the analyte by GC-MS. The inlet temperature is 260°C to 290°C (the optimal is 290°C, and the desorption time is controlled within 5 min). The oven temperature uses programmed temperature rise. Its initial temperature is 40°C, rises to 145°C at a rate of 30°C / min, and is held for 3 min; rises to 250°C at a rate of 3°C / min; rises to 300°C at a rate of 10°C / min; The fourth step, confirm the concentration of LCMs in the actual sample according to the linear regression equation of each LCM.

[0042] Example 4 Reliability Analysis of the Detection Method Constructed in Example 3 of the Present Invention 1. Reliability Analysis of the Detection Method of the Present Invention for Detecting LCMs in Water To further investigate the enrichment performance of Por-CF3-COF for LCMs, based on the solid-phase microextraction probe and GC-MS in Example 2, the present invention established a quantitative detection method for LCMs in complex matrices. Using this method, the linear range, linear correlation coefficient (R 2 ), detection limits (LODs), quantification limits (LOQs), repeatability, reproducibility, and enrichment factors (EFs) of each LCM were investigated, specifically including the following: In the first step, a mixed stock solution of 13 LCMs was prepared with ultrapure water, and the mixed stock solution was diluted to obtain mixed working solutions with different concentration gradients; 10 mL of the mixed working solution (equilibrated three times at each concentration) was taken, and 40 ng 13 C 12 -(PCB)-180 and 40 ng 13 C 12 -(PCB)-52 were added to obtain the sample working solution; In the second step, headspace solid-phase microextraction (HS-SPME) was used to extract the target analytes in the sample working solution. The SPME conditions were: extraction time was 50 min, extraction temperature was 90 °C, and stirring speed was 700 rpm; In the third step, after extraction, the probe adsorbed with the analyte was desorbed and detected by GC-MS. The inlet temperature was 290 °C (desorption time was controlled at 5 min, nitrogen environment), and the oven temperature was programmed. Its initial temperature was 40 °C, which was increased to 145 °C at a rate of 30 °C / min and held for 3 min; then it was increased to 250 °C at a rate of 3 °C / min; and then it was increased to 300 °C at a rate of 10 °C / min. The results are shown in Table 2.

[0043] Table 2 Linear Range, R 2 , LODs, LOQs, Repeatability, Reproducibility, and EFs As can be seen from Table 2, the R 2 of the detection method of the present invention is between 0.990 - 0.998, showing a good linear relationship for 13 LCMs in the range of 0.05 - 1000 ng / L. Moreover, the LODs and LOQs of LCMs are 0.011 - 16.72 ng / L and 0.037 - 55.74 ng / L respectively, with low detection limits and low quantification limits, and thus accurate quantitative analysis of trace LCMs can be achieved.

[0044] As can be seen from Table 2, the intra-day and inter-day RSDs of the 13 LCMs were 1.96 - 9.29% and 0.87 - 8.50%, respectively, indicating that the method has extremely high repeatability and consistency within a single day and on different days. In addition, the RSDs among the probes (i.e., multiple Por-CF3-COF probes were used) were 0.83 - 9.84%, further demonstrating the good reproducibility of the method. The results prove that the detection method of the present invention has excellent repeatability and reliability.

[0045] As can be seen from Table 2, the EFs values of the LCMs of the present invention ranged from 10051 to 50402, indicating that the Por-CF3-COF probe has a significant enrichment ability for LCMs. This enrichment amplifies the detectability and lays a foundation for the high-sensitivity quantitative detection of trace LCMs in complex matrices.

[0046] 2. Reliability analysis of the detection method of the present invention for LCMs in food matrices Since the compositions of different types of food samples are very complex and diverse, there is a strong matrix effect. Therefore, on the premise of not changing the optimal extraction conditions, the present invention further investigated the reliability of the present invention in detecting LCMs in complex matrices, specifically including the following: First, when the food is solid (such as fruits, vegetables, meats, and grains), the actual sample is first broken or crushed, and then freeze-dried. If it cannot be detected in time, it is stored frozen at -20 °C. Take a certain amount of the actual sample, add a certain volume of ultrapure water to the actual sample to obtain a complex sample matrix (when the sample is a liquid such as fruit and vegetable juice, it can be directly used as a complex matrix), and prepare LCMs standard solutions with a certain concentration gradient using the sample matrix; take 10 ml of the LCMs standard solution (equilibrated three times for each concentration), and add 40 ng 13 C 12 -(PCB)-180 and 40 ng 13 C 12 -(PCB)-52; Second step, the same as the second step of item 1 of this example; Third step, the same as the third step of item 1 of this example, and the detection results are shown in Table 3 and Table 4.

[0047] Table 3 Linear ranges, R 2 , LODs and LOQs of LCMs in wheat and red bean matrices Table 4 Linear ranges, R2, LODs and LOQs of LCMs in meat, vegetable and juice matrices As can be seen from Table 3 to Table 4, the detection method of the present invention still shows a good linear relationship for LCMs in complex matrices, with a wide linear range, low detection limit and quantification limit. The results prove that the detection method of the present invention can be used for the quantitative detection of LCMs in complex food matrices.

[0048] 3. Spiking recovery test of actual samples To further confirm the accuracy and applicability of the detection method of the present invention in actual complex matrices, in this example, LCMs standard solutions at three concentration levels of low, medium and high were added to each food matrix for spiking recovery experiments, and the results are shown in Figure 6 , Figure 7 and Table 5 to Table 9.

[0049] Table 5 Spiking recovery of LCMs in wheat flour Table 6 Spiking recovery of LCMs in red bean samples Table 7 Spiking recovery of LCMs in meat Table 8 Spiking recovery of LCMs in vegetable samples Table 9 Spiking recovery of LCMs in juice samples From Figure 6 a-d and Figure 7 it can be seen that in five different matrices, obvious absorption peaks of the target LCMs appear in the chromatograms obtained by the method of the present invention. From Figure 8 a-e and Table 5 to Table 9, it can be seen that the spiking recovery rates of the five food samples of wheat flour samples, red bean samples, meat samples, vegetable samples and juice samples are 83.74 - 108.7% (RSDs are 1.21 - 18.5%), 80.67 - 126.4% (RSDs are 0.04 - 16.5%), 87.04 - 130.0% (RSDs are 0.47 - 18.3%), 83.94 - 112.2% (RSDs are 0.17 - 18.6%), 85.86 - 115.4% (RSDs are 0.23 - 17.3%) respectively, further confirming the accuracy and applicability of the detection method of the present invention for the quantitative detection of LCMs in complex food sample matrices.

[0050] Example 5 Repeatability of the solid-phase microextraction probe of the present invention In this example, commercial fibers PDMS / DVB, PDMS, DVB / CAR / PDMS, and Por-COF probes were used as comparisons to investigate the repeatability of the Por-CF3-COF probe. The specific contents are as follows: The probe of the present invention, the comparative probe, and the commercial fiber were respectively inserted into the working solution of LCMs for SPME and GC-MS detection and analysis. The results are shown in Figure 8 . As can be seen from Figure 8 a, the enrichment efficiency of the Por-CF3-COF probe of the present invention for the target LCMs is 2.78 - 21.32 times that of PDMS, 1.28 - 3.50 times that of PDMS / DVB, and 1.68 - 15.40 times that of DVB / CRA / PDMS. Compared with the Por-COF probe, the extraction rate of the Por-CF3-COF probe of the present invention for other target analytes except 2CB is significantly better than that of the Por-COF probe, indicating that the Por-CF3-COF probe of the present invention has better application prospects.

[0051] Compared with existing fibers, the inherent framework of Por-CF3-COF has good stability. Its building blocks are connected by strong covalent bonds, which in turn fixes the COF together. Even after repeated adsorption-desorption cycles, the integrity of its structure can be ensured. In addition, the material of the present invention can self-assemble into a highly ordered honeycomb structure, forming pores with uniform size and distribution, thereby capturing LCMs. During the adsorption process, the hydrophobic π-conjugated system between LCMs and the porphyrin macrocycle interacts to achieve the enrichment and extraction of LCMs. Under high-temperature conditions, the desorption of LCMs and the probe can be realized, and then the captured LCMs are released and enter the instrument for analysis, thus ensuring the repeatability of the adsorption sites. As can be seen from Figure 8 b, the Por-CF3-COF probe of the present invention still shows good extraction ability for the target analyte after being reused 70 times, proving that the probe of the present invention has good repeatability and making it a more sustainable analysis method.

[0052] Example 6 Adsorption mechanism of Por-CF3-COF of the present invention for target LCMs The quinoline-linked azacycle, trifluoromethyl-functionalized site, and porphyrin ring cavity of Por-CF3-COF of the present invention jointly construct a unique framework structure, which in turn endows it with rich molecular recognition sites. The chemical structure of the target LCMs contains multiple fluorine atoms and aromatic rings, so it exhibits obvious hydrophobicity and electron induction effect. Therefore, the different adsorption properties, high selectivity of Por-CF3-COF for LCMs are closely related to fluorine-fluorine interaction, hydrophobic interaction, π-π interaction, and p-orbital-π (p-π) interaction.

[0053] Specifically, the adsorption mechanism of the present invention was analyzed by XPS, and the results are shown in Figure 10 and Figure 11 . It can be seen from Figure 10 that in the Por-CF3-COF adsorbed with the target LCMs, the peak of F1s of F-C correspondingly shifted from 688.9 eV to 687.7 eV; the peaks of quinoline ring N and unprotonated porphyrin N shifted from 399.8 eV to 399.5 eV, and the peak of protonated porphyrin N shifted from 397.9 eV to 397.7 eV. This indicates that the nitrogen atom sites and modified trifluoromethyl groups in this material play a key role in the enrichment of LCMs.

[0054] The adsorption mechanism was studied by DFT theoretical simulation. Taking Por-CF3-COF as the basic unit of COF and DFT-B3LYP / 6–31G(d,p) as the basis set, the optimal complex structure of LCMs-Por-CF3-COF with the lowest energy was analyzed, and the stable energy displacement Δen during the simultaneous synthesis of LCMs-Por-CF3-COF supramolecules was estimated. The results are shown in Figure 11 . It can be seen from Figure 11 that the ΔEn values of LCMs-Por-CF3-COF are all negative, indicating that these supramolecules are stable and the adsorption of LCMs by COF is a spontaneous process.

[0055] The present invention is based on the non-covalent interaction (NCI) theory to desorb the molecular recognition mechanism between Por-CF3-COF and LCMs. The results are shown in Figure 11 . It can be seen from Figure 11 that the functionalized Por-CF3-COF with functionalized fluorinated electron donor regions, large conjugated systems and hydrophobic sites binds to LCMs directionally through lone pair electron-π interaction and π-π interaction; the hydrogen bond interaction between the H atom of the aromatic ring of Por-CF3-COF and the F atom of LCMs will further strengthen the molecular contact between the functionalized Por-CF3-COF and LCMs.

[0056] In summary, the Por-CF3-COF probe of the present invention has a large specific surface area and provides many binding sites. There are lone pair electron-π interaction, π-π interaction and hydrogen bond interaction between it and LCMs, which promotes the adsorption of LCMs, and can realize the quantitative detection of trace LCMs in water bodies and complex matrices. Moreover, the detection method of the present invention has a wide linear range, low detection limit and quantification limit, high sensitivity and good reproducibility, and can be used repeatedly for many times. It is economical and environmentally friendly and has promotional significance.

Claims

1. A fluorine-functionalized covalent organic framework material, characterized in that: It is copolymerized from three monomers: tetraminophenyl porphyrin, tetraaldehyde phenyl porphyrin and 3,5-bis(trifluoromethyl)phenylacetylene, specifically including: In the first step, tetraminophenyl porphyrin, tetraaldehyde phenyl porphyrin and 3,5-bis(trifluoromethyl)phenylacetylene are added to the first solvent for primary mixing, then acetic acid solution, boron trifluoride-ether and tetrachloro-1,4-benzoquinone are added for secondary mixing. After mixing, freeze-pump-thaw cycling degassing is carried out. In the second step, the degassed reaction solution is sealed and heated to cause Schiff base reaction and Povarov reaction among the three monomers in the reaction solution. After the reaction is completed, filtration, washing and drying are carried out to obtain a black powdery fluorine-functionalized covalent organic framework material, denoted as Por-CF3-COF, and its structural formula is as follows: 。 2. The fluorine-functionalized covalent organic framework material according to claim 1, wherein: The first solvent in the first step is n-butanol / o-dichlorobenzene with a volume ratio of 1:1; the primary mixing in the first step is ultrasonic for 10 min to 15 min; the secondary mixing is ultrasonic for 4 min to 6 min.

3. The fluorine-functionalized covalent organic framework material according to claim 1, characterized in that: The heating in the second step is programmed heating: first, the reaction solution is placed in an environment of 100 °C for 1 day, and then in an environment of 120 °C for 3 days to 6 days; the washing in the second step is to wash with saturated NaHCO3 solution first, and then carry out Soxhlet extraction with tetrahydrofuran; the drying is vacuum drying at 50 °C to 70 °C for 10 h to 12 h.

4. The fluorine-functionalized covalent organic framework material according to claim 1, wherein: The molar ratio of the three copolymerization monomers of tetraminophenyl porphyrin, tetraaldehyde phenyl porphyrin and 3,5-bis(trifluoromethyl)phenylacetylene in the first step is 0.12:0.12:1.

6.

5. A solid-phase microextraction probe, comprising a stainless steel wire and a coating adhered to the stainless steel wire, characterized in that: The coating is the fluorine-functionalized covalent organic framework material described in any one of claims 1-4.

6. A method for detecting LCMs in a complex matrix, characterized in that: The detection method uses the solid-phase microextraction probe described in claim 5 to carry out solid-phase extraction on the actual sample or standard product, and uses GC-MS for desorption and quantitative analysis, specifically including the following content: First step, when the actual sample is solid, first crush the actual sample, and then add an internal standard to the actual sample 13 C 12 -(PCB)-180, 13 C 12 -(PCB)-52 and a certain volume of ultrapure water to obtain a sample working solution; When the actual sample is a liquid, take a certain volume of the actual sample and add an internal standard to the actual sample 13 C 12 -(PCB)-180 and 13 C 12 -(PCB)-52 to obtain a sample working solution; In the second step, the solid-phase microextraction probe is inserted into the sample working solution for extraction, and the extraction conditions are: the extraction time is 30 min to 60 min, the extraction temperature is 90 °C to 100 °C, and the stirring speed is 300 rpm to 700 rpm. In the third step, after the extraction is completed, the probe adsorbed with the analyte is analyzed by GC-MS. The inlet temperature is 260 °C to 290 °C, and the oven temperature is programmed heating. Its initial temperature is 40 °C, which is raised to 145 °C at a rate of 30 °C / min and maintained for 3 min; it is raised to 250 °C at a rate of 3 °C / min; it is raised to 300 °C at a rate of 10 °C / min. In the fourth step, the concentration of LCMs in the actual sample is confirmed according to the linear regression equation.

7. The detection method of LCMs in a complex matrix according to claim 6, characterized in that: The LCMs include any one or more of 2CB, EDPdB, DMPMB, BDPdB, DECB, DTMDEB, PCTB, TePrB, DPrB, TePT, TpeCB, EFPT and EDPB.

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