An amino phenyl / fluorine bifunctional magnetic three-dimensional covalent organic framework material, a preparation method and application thereof

Abstract

This invention discloses an aminophenyl / fluorine bifunctional magnetic three-dimensional covalent organic framework material, its preparation method, and its applications, belonging to the fields of magnetic solid-phase adsorbent preparation and antibiotic detection technology. The preparation steps of the aminophenyl / fluorine bifunctional magnetic three-dimensional covalent organic framework material include: dissolving octasesquiaminophenyltrimethoxysilane and 2,3,5,6-tetrafluoroterephthalaldehyde in a solvent, then adding polydopamine-coated Fe3O4 magnetic nanoparticles, dispersing them evenly, adding acetic acid, and then carrying out a solvothermal reaction to obtain the aminophenyl / fluorine bifunctional magnetic three-dimensional covalent organic framework material. The prepared aminophenyl / fluorine bifunctional magnetic three-dimensional covalent organic framework material has a large specific surface area, good thermal stability, and stable crystal structure. The magnetic solid-phase extraction-high performance liquid chromatography detection method established based on this aminophenyl / fluorine bifunctional magnetic three-dimensional covalent organic framework material has high sensitivity and accuracy, and has good application prospects.

Description

Technical Field

[0001] This invention belongs to the field of magnetic solid-phase adsorbent preparation and antibiotic detection technology, specifically relating to an aminophenyl / fluorine bifunctional magnetic three-dimensional covalent organic framework material, its preparation method, and its application. Background Technology

[0002] Fluoroquinolones (FQs) are a class of broad-spectrum antibiotics widely used in livestock farming due to their potent antibacterial activity. However, excessive or improper use of FQs can lead to drug residues in animal-derived foods, posing health risks. Therefore, establishing efficient and sensitive FQs detection methods is crucial for ensuring food safety and protecting public health. Currently, the main methods for FQs detection include high-performance liquid chromatography (HPLC), liquid chromatography-mass spectrometry (LC-MS / MS), and immunoassay (ELISA). Because the concentration of FQs in food is low and complex matrix interferences (fat, protein, sugar, etc.) exist, effective sample pretreatment is essential before instrumental analysis. Magnetic solid-phase extraction (MSPE) has advantages such as low cost, low organic solvent usage, and simple operation, and is widely used for the separation and enrichment of FQs. To improve enrichment efficiency and selectivity, developing suitable porous materials as solid-phase extraction adsorbents is crucial.

[0003] In recent years, covalent organic frameworks (COFs) have demonstrated significant advantages in sample pretreatment due to their high specific surface area, controllable structure, and abundant functional groups. Compared with traditional porous materials, COFs, constructed through strong covalent bonds, possess excellent chemical stability and structural designability, allowing for functional modification for specific analytes to improve enrichment efficiency and selectivity. Three-dimensional COFs, in particular, with their multi-directional interconnected pore structure, are more conducive to mass transfer and exposure of adsorption sites, further enhancing adsorption kinetics and capacity. However, their development and application have always been limited by the lack of suitable building blocks. Polyhedral oligomeric silsesquioxanes (POSS) are a promising cage-like building block for constructing 3D COFs. Their molecules have a rigid cubic inorganic siloxane core, with organic groups attached to all eight vertices, facilitating post-synthetic modification. For example, Xu et al. developed an externally hydrophilic 3D COF material based on 8-sesquiaminophenyltrimethoxysilane (8NH2-POSS) for adsorbing bisphenol substances in milk samples, providing an effective solution for the detection of harmful pollutants in complex samples. Summary of the Invention

[0004] To further improve the enrichment efficiency and selectivity of fluoroquinones (FQs), this invention provides an aminophenyl / fluorine bifunctional magnetic three-dimensional covalent organic framework material, its preparation method, and its applications. Using 8NH₂-POSS and 2,3,5,6-tetrafluoro-p-dibenzaldehyde (TFTA) as structural units, this invention prepares an aminophenyl / fluorine bifunctional magnetic three-dimensional covalent organic framework material (F / aminophenyl@MCOF). The abundant amino groups in the 8NH₂-POSS molecule not only enhance the hydrophilicity of the COF material but also generate electrostatic and hydrogen bonding interactions with FQs molecules; its benzene ring can generate π-π interactions with FQs molecules; simultaneously, TFTA can enhance the material's selectivity for FQs through FF interactions. Using F / aminophenyl@MCOF as an adsorbent, the adsorption performance of the material for FQs was studied, the MSPE conditions were optimized, and finally, an MSPE-HPLC analysis method for FQs in pork was established, achieving good sensitivity and accuracy.

[0005] To achieve the above objectives, the present invention provides the following technical solution: One of the technical solutions of this invention is to provide a method for preparing an aminophenyl / fluorine bifunctional magnetic three-dimensional covalent organic framework material, comprising the following steps: Eight-fold sesquiaminophenyltrimethoxysilane and 2,3,5,6-tetrafluoroterephthalaldehyde were dissolved in a solvent, and then polydopamine-coated Fe3O4 magnetic nanoparticles were added. After being dispersed evenly, acetic acid was added, and then a solvothermal reaction was carried out to obtain the aminophenyl / fluorine bifunctional magnetic three-dimensional covalent organic framework material.

[0006] Preferably, the molar ratio of the octasesquiaminophenyltrimethoxysilane to the 2,3,5,6-tetrafluoroterephthalaldehyde is 1:3.

[0007] Preferably, the solvent is a mixture of mesitylene and dioxane in a volume ratio of 1:1.

[0008] Preferably, the concentration of acetic acid in the system is 6M.

[0009] Preferably, the ratio of the polydopamine-coated Fe3O4 magnetic nanoparticles to the solvent is 5 mg: 1 mL.

[0010] Preferably, the preparation steps of the polydopamine-coated Fe3O4 magnetic nanoparticles include: mixing Fe3O4 magnetic nanoparticles and dopamine in a solvent at a mass ratio of 1:1, stirring and polymerizing to obtain the polydopamine-coated Fe3O4 magnetic nanoparticles.

[0011] Preferably, the solvothermal reaction is performed at a temperature of 120°C for a time of 36 hours.

[0012] The second technical solution of the present invention provides an aminophenyl / fluorine bifunctional magnetic three-dimensional covalent organic framework material prepared according to the above-mentioned preparation method of aminophenyl / fluorine bifunctional magnetic three-dimensional covalent organic framework material.

[0013] The third technical solution of the present invention provides an application of the above-mentioned aminophenyl / fluorine bifunctional magnetic three-dimensional covalent organic framework material in the detection of fluoroquinolones.

[0014] Fourth technical solution of the present invention: A method for detecting fluoroquinolones using magnetic solid-phase extraction-high performance liquid chromatography (HPLC), comprising the following steps: The sample to be tested was extracted using acidified acetonitrile. The extract was dried and then reconstituted for magnetic solid-phase extraction. The magnetic solid-phase adsorbent after extraction was eluted. Finally, high performance liquid chromatography was used to detect the fluoroquinolone in the eluent. The content of fluoroquinolone in the sample to be tested was calculated based on the detection results. The magnetic solid-phase adsorbent is the above-mentioned aminophenyl / fluorine bifunctional magnetic three-dimensional covalent organic framework material.

[0015] Preferably, the pH value during magnetic solid-phase extraction is 6.0.

[0016] Preferably, the eluent is a 5 vol% ammonia / methanol solution (5 mL ammonia + 95 mL methanol), and the elution time is 10 min.

[0017] The beneficial technical effects of the present invention are as follows: The aminophenyl / fluorine bifunctional magnetic three-dimensional covalent organic framework material provided by this invention has a large specific surface area, good thermal stability, and stable crystal structure. The optimal adsorption pH for FQs is 6.0, the adsorption kinetics conform to the pseudo-second-order model, the adsorption equilibrium is reached in 10 minutes, the isothermal adsorption conforms to the Langmuir model, and the reusability is good.

[0018] This invention establishes a magnetic solid-phase extraction-high performance liquid chromatography (HPLC) method based on the provided aminophenyl / fluorinated bifunctional magnetic three-dimensional covalent organic framework material. Results show that the aminophenyl / fluorinated bifunctional magnetic three-dimensional covalent organic framework material has selective enrichment ability for fluorocarbons (FQs) in actual samples, with five FQs enriched in the range of 1–1500 μg·kg⁻¹. -1 The linear relationship was good within the range, and the limits of detection and quantitation were 0.1–0.5 μg·kg⁻¹, respectively. -1 and 0.3~1.5 μg·kg -1The recoveries of the five free quantity parameters (FQs) in pork ranged from 86.1% to 109.1%, with intra-day relative standard deviations (RSDs) of 2.3% to 8.5% and inter-day RSDs of 3.6% to 10.8%. In chicken samples, the recoveries of the five FQs ranged from 88.1% to 105.2%, with intra-day RSDs of 3.9% to 8.6% and inter-day RSDs of 5.2% to 9.2%. These results indicate that the method has high sensitivity, good accuracy, and promising application prospects. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a flowchart illustrating the preparation process of F / aminophenyl@MCOF in Example 1.

[0021] Figure 2 To investigate the adsorption capacity of F / aminophenyl@MCOF for three FQs under various preparation conditions.

[0022] Figure 3 The images show the SEM images of Fe3O4@PDA (a) and F / aminophenyl@MCOF (b) in Example 1, the all-element EDS spectrum of F / aminophenyl@MCOF (c), and the EDS spectra of the individual elements C (c1), O (c2), F (c3), Fe (c4), N (c5), and Si (c6) in F / aminophenyl@MCOF.

[0023] Figure 4 The following are the FT-IR spectra of Fe3O4@PDA, 8NH2-POSS, TFTA and F / aminophenyl@MCOF in Example 1 (a), the thermogravimetric analysis (b) of Fe3O4@PDA and F / aminophenyl@MCOF, the XRD spectra of Fe3O4@PDA and F / aminophenyl@MCOF (c), and the N2 adsorption-desorption isotherms of Fe3O4@PDA and F / aminophenyl@MCOF (d).

[0024] Figure 5 The adsorption capacity of F / aminophenyl@MCOF prepared in Example 1 for three FQs under different pH conditions.

[0025] Figure 6 The adsorption amounts of F / aminophenyl@MCOF prepared in Example 1 on three FQs at different adsorption times are shown in (a), and the pseudo-first-order kinetic fitting curves (b), pseudo-second-order kinetic fitting curves (c), static isothermal adsorption lines (d), Langmuir fitting curves (e), and Freundlich fitting curves (f) corresponding to each adsorption amount are shown.

[0026] Figure 7 In optimizing the magnetic solid-phase extraction efficiency of FQs, the effects of different adsorption times (a) and different amounts of F / aminophenyl@MCOF added (b) on the adsorption rate, and the effects of different eluents (c) and different elution times (d) on the elution efficiency were investigated.

[0027] Figure 8 This is a chromatographic comparison of the blank control, spiked sample, and spiked sample before and after enrichment with F / aminophenyl@MCOF when MSPE and HPLC-FLD are used to analyze FQs in pork. Detailed Implementation

[0028] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0029] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0030] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0031] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar to or equivalent to those described herein may be used in the implementation or testing of this invention.

[0032] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0033] The reagents and instruments used in this invention are as follows: Ciprofloxacin (CIP, 98%), enrofloxacin (ENR, 99.8%), lomefloxacin hydrochloride (LOM, 98%), norfloxacin (NOR, 98%), difluorofloxacin hydrochloride (DIF, 98%), dopamine hydrochloride (DA, 98%), 1,4-dioxane (AR), and 2,3,5,6-tetrafluoroterephthalaldehyde (TFTA, 98%) were purchased from Aladdin Chemical Reagent Co., Ltd. Ferric chloride hexahydrate (FeCl3·6H2O) and octasesquiaminophenyltrimethoxysilane (8NH2-POSS, 95%) were purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0034] Sigma 300 scanning electron microscope (SEM, Zeiss AG, Germany), SmartLab SE X-ray powder diffractometer (XRD, Rigaku Corporation, Japan), TENSOR 27 Fourier transform infrared (FT-IR, Bruker Corporation, USA), 660A6S surface area and pore size analyzer (BET, Best Instruments Technology Co., Ltd., China), TGA / DSC thermogravimetric analyzer (TGA, Mettler AG, Switzerland), 1260 high performance liquid chromatograph (HPLC, Agilent Technologies, USA), HC-C18 column (250mm × 4.6 mm, 5μm, Agilent Technologies, USA).

[0035] The polydopamine-coated Fe3O4 magnetic nanoparticles (Fe3O4@PDA) used in this invention were synthesized according to the literature method (He Maofang, Wang Xin, Zhang Yuzhen, et al. Analytical Chemistry, 2024, 52(03):409), and the specific steps are as follows: (1) Preparation of Fe3O4 magnetic nanoparticles by hydrothermal method 1.3 g FeCl3, 0.4 g sodium citrate, and 2.0 g anhydrous sodium acetate were dissolved in 30 mL ethylene glycol. After stirring for 30 min, the solution was transferred to a polytetrafluoroethylene reactor and reacted at 200 °C for 12 h. After the reaction was completed, the supernatant was magnetically separated and the resulting magnetic microspheres were washed sequentially with ultrapure water and ethanol.

[0036] (2) Dopamine coated on Fe3O4 surface 1.0 g of Fe3O4 magnetic nanoparticles prepared in step (1) were dispersed in 500 mL of 10 mmol / L Tris-HCl (pH 8.5), and 1.0 g of dopamine was added. The mixture was ultrasonically dispersed for 2 min. After mechanical stirring at room temperature (20±10℃) for 12 h, polydopamine-coated Fe3O4 (Fe3O4@pDA) was obtained. The product was washed several times with Tris-HCl buffer, water, and ethanol, and then vacuum dried for 6 h before use.

[0037] Example 1 Preparation of aminophenyl / fluorine bifunctional magnetic three-dimensional covalent organic framework materials: Magnetic covalent organic framework materials were prepared using Fe3O4@PDA as a matrix. First, 56 mg of 8NH2-POSS and 30 mg of TFTA (n...) were... POSS :n TFTA Dissolve 1:3 (v / v=1:1) in 20 mL of a mixed solvent of mesitylene and dioxane, then add 100 mg Fe3O4@PDA, and after ultrasonic dispersion, add 1.6 mL of acetic acid (6 mol·L⁻¹). -1 The mixture was transferred to a reactor and reacted at 120 °C for 36 h. After the reaction, the product was washed three times alternately with anhydrous ethanol and water, and dried under vacuum at 50 °C for 6 h to obtain the aminophenyl / fluorine bifunctional magnetic three-dimensional covalent organic framework material (F / aminophenyl@MCOF).

[0038] The preparation flow chart of F / aminophenyl@MCOF in Example 1 is shown below. Figure 1 .

[0039] This invention uses Fe3O4@PDA as a matrix and 8NH2-POSS and TFTA as monomers to prepare MCOF via in-situ polymerization. The surface of Fe3O4@PDA is rich in amino groups, which can provide reaction sites for the in-situ growth of COF. The amino groups in the 8NH2-POSS molecule can react with TFTA to form a stable COF structure, and can also act as anion exchange sites to bind with the carboxyl groups in the FQs molecule. At the same time, the fluorine atoms in the TFTA molecule form FF interactions with FQs, thereby endowing the material with bifunctional adsorption properties.

[0040] The testing methods used in this invention are as follows: 1. Adsorption kinetics experiment Accurately weigh approximately 5 mg of F / aminophenyl@MCOF and disperse it in 5 mL of a standard solution of NOR, CIP, or ENR (1.0 μg / mL). -1 The sample (pH=6.0) was placed in a constant-temperature reciprocating shaker (25 ℃, 150 rpm) and shaken for 5, 10, 20, 30, and 40 min. After adsorption, the supernatant was collected for HPLC-FLD analysis. The adsorption amount (Q) was determined. e μg·mg -1 Calculate according to formula (1): (1) In formula (1), C0 (μg·mL -1 ) and C e (μg·mL) -1) represent the initial concentration and the adsorption equilibrium concentration, respectively; V0 (mL) represents the volume of the solution; m (mg) represents the mass of the adsorbent.

[0041] 2. Determination of static adsorption capacity Accurately weigh approximately 5 mg of F / aminophenyl@MCOF and disperse it in 5.0 mL of different concentrations (5, 10, 30, 50, 70 μg·mL). -1 In the FQs solution, the adsorption was carried out at 25℃ and 150 rpm for 30 min with shaking. The equilibrium concentration of the solution was determined by HPLC-FLD, and Q was calculated according to formula (1). e Q e For C e Plot the static isothermal adsorption curve. Fit the isothermal adsorption curve using the Langmuir equation (Equation (2)) and the Freundlich equation (Equation (3)) to calculate the maximum adsorption capacity (Q). max μg·mg -1 ).

[0042] (2) (3) In equations (2) and (3), C e (μg·mL) -1 Q is the adsorption equilibrium concentration of the solution; e (μg·mg) -1 ) and Q max (μg·mg) -1 These represent the equilibrium adsorption capacity and the maximum adsorption capacity, respectively; K L and K F These are the Langmuir constant and the Freundlich constant, respectively.

[0043] 3. Magnetic solid-phase extraction of FQs Accurately weigh approximately 5 mg of F / aminophenyl@MCOF and disperse it in 5.0 mL of FQs solution. Adsorb the microspheres by shaking at 25 °C and 150 rpm for 10 min. Then, perform liquid-solid separation using a magnet, collect the magnetic microspheres, wash twice with 1 mL of washing buffer (50 mM phosphate buffer, pH=6.0), and then elute with 1.0 mL of eluent (5 vol% ammonia / methanol solution) for 10 min. Collect the eluent and dry it with nitrogen gas. Redissolve the microspheres in 0.1 mL of mobile phase and finally perform HPLC-FLD detection.

[0044] 4. Analysis of actual samples Chicken and pork samples were purchased from a local supermarket in Xi'an. To establish a working curve, organic pork was selected as a blank sample, and a certain amount of FQs was added before extraction and enrichment. Before extraction, the meat sample was cut into small cubes and then minced into a paste using a meat grinder. Subsequently, 1.0 g of sample was weighed, and 5 mL of acidified acetonitrile (hydrochloric acid:acetonitrile = 1:50, v / v) was added. The mixture was vortexed for 5 min, sonicated for 20 min, and then centrifuged for 10 min (10000 r·min). -1 Collect the supernatant and dry it under rotary vacuum at 40°C. Finally, dissolve the residue in 200 μL of sodium hydroxide solution (0.05 mol·L⁻¹). -1 Dissolve the sample and bring the volume to 5 mL with pH 6.0 phosphate buffer for solid-phase extraction.

[0045] According to the preparation method disclosed in Example 1, the effect of changes in preparation conditions on the adsorption performance of the product was investigated. The preparation conditions are shown in Table 1.

[0046] Table 1 Different preparation conditions of F / aminophenyl@MCOF The adsorption capacities of F / aminophenyl@MCOF for the three FQs obtained under various preparation conditions are shown in the figure. Figure 2 (Adsorption time is 30 min).

[0047] Figure 2 The display shows that when n POSS :n TFTA The material exhibits the highest adsorption capacity for FQs when the solvent ratio is 1:3 (v / v = 1:1), the reaction temperature is 120℃, and the reaction time is 36 h. Therefore, this condition (condition D, i.e., the synthesis conditions of Example 1) was determined to be the optimal synthesis process for the material, and it was used for subsequent adsorption performance studies and sample preparation.

[0048] SEM images of Fe3O4@PDA (a) and F / aminophenyl@MCOF (b) in Example 1, the all-element EDS spectrum of F / aminophenyl@MCOF (c), and the EDS spectra of individual elements C (c1), O (c2), F (c3), Fe (c4), N (c5), and Si (c6) in F / aminophenyl@MCOF are shown below. Figure 3 .

[0049] Figure 3The results showed that Fe3O4@PDA exhibited uniform, smooth, and well-dispersed spherical particles. After Schiff base reaction, the nanoparticles showed irregular morphology, blurred boundaries, and significant agglomeration. EDS elemental analysis revealed obvious signals of C, O, F, Fe, N, and Si on the F / aminophenyl@MCOF surface. Specifically, the C content was 59.93 wt%, N content was 7.64 wt%, O content was 16.57 wt%, F content was 5.89 wt%, Si content was 9.55 wt%, and Fe content was 0.42 wt%. This indicates successful modification of the Fe3O4@PDA surface with a covalent organic framework.

[0050] The FT-IR spectra of Fe3O4@PDA, 8NH2-POSS, TFTA, and F / aminophenyl@MCOF in Example 1 (a), the thermogravimetric analysis (b) of Fe3O4@PDA and F / aminophenyl@MCOF, the XRD patterns of Fe3O4@PDA and F / aminophenyl@MCOF (c), and the N2 adsorption-desorption isotherms of Fe3O4@PDA and F / aminophenyl@MCOF (d) are shown below. Figure 4 .

[0051] Figure 4 The FT-IR spectrum of Fe3O4@PDA shows that 3447 cm⁻¹ -1 and 1395 cm -1 The strong absorption peaks at 1643 cm⁻¹ correspond to the stretching vibrations of OH and NH, respectively. -1 The characteristic absorption of the benzene ring is at 1410 cm⁻¹. Compared to Fe₃O₄@PDA, F / aminophenyl@MCOF shows a higher absorption at 1410 cm⁻¹. -1 1050 cm -1 880 cm -1 New absorption peaks appear nearby, corresponding to the C=C skeletal stretching vibration of the fluorinated benzene ring, the stretching vibration of CF, and the out-of-plane bending vibration of the CH of the substituted benzene ring in the TFTA molecule, respectively; at 1086 cm⁻¹ -1 A new absorption peak appears at [location], corresponding to the stretching vibration of the Si-O-Si bond in 8NH2-POSS. These results further confirm the successful preparation of F / aminophenyl@MCOF.

[0052] Both Fe3O4@PDA and F / aminophenyl@MCOF exhibited good thermal stability. The weight loss rates of Fe3O4@PDA in the low-temperature region (<200℃) and high-temperature region (200~600℃) were 14.3% and 19.7%, respectively, mainly corresponding to the removal of surface adsorbed water and the thermal decomposition of the PDA layer. The weight loss rates of F / aminophenyl@MCOF in the same temperature range were 17.9% and 24.1%, respectively. The increased weight loss rate in the high-temperature region confirms the successful growth of the COF layer on the Fe3O4@PDA surface; while the slight increase in weight loss in the low-temperature region is consistent with the strong water absorption characteristics of the porous structure of the COF material. The large amount of inorganic residue at 800℃ further proves the stable existence of the Fe3O4 magnetic core.

[0053] The Fe3O4@PDA exhibits sharp and high-intensity diffraction peaks at 30.4°, 35.7°, 43.3°, 53.7°, 57.3°, and 62.9°, which are typical diffraction peaks for Fe3O4 crystals, indicating that the surface modification of Fe3O4 with polydopamine did not significantly affect its crystal structure. In the XRD pattern of F / aminophenyl@MCOF, the characteristic peaks of Fe3O4 remain clear, indicating that the magnetic core remains structurally stable during the recombination process.

[0054] F / aminophenyl@MCOF exhibits a typical type IV (H3) adsorption-desorption isotherm, indicating that the material possesses a distinct mesoporous structure and that multilayer nitrogen adsorption can occur within the pores. Calculations using the Brunauer-Emmett-Teller (BET) model show that the specific surface area of ​​F / aminophenyl@MCOF is 206.8 m². 2 ·g -1 The total pore volume is 0.12 cm³. 3 ·g -1 The average pore diameter is 2.4 nm. The high specific surface area and suitable pore structure provide sufficient adsorption sites and mass transfer channels for the target analyte, which is beneficial to improving the adsorption capacity and extraction efficiency of the material.

[0055] The adsorption capacities of the F / aminophenyl@MCOF prepared in Example 1 for the three FQs under different pH conditions are shown in the figure. Figure 5 (Adsorption time is 30 min).

[0056] Figure 5 The results showed that the adsorption capacity of F / aminophenyl@MCOF for FQs first increased and then decreased with increasing pH, reaching a maximum at pH=6. This phenomenon is mainly due to the synergistic change in the surface charge state of the adsorbent and the morphology of the FQs molecules: FQs, as an amphoteric compound (pK... a1 6.0~6.5, pKa2 At pH 6-7, the FQs molecules (8.5-8.7) primarily exist as zwitterions, with their negatively charged carboxyl groups forming electrostatic attraction with the protonated amino groups on the F / aminophenyl@MCOF surface. Simultaneously, multiple mechanisms, including FQs-FQs interactions and hydrophobic interactions, work synergistically to maximize adsorption. However, at pH < 6, the positively charged FQs molecules exhibit electrostatic repulsion with the positively charged amino groups on the F / aminophenyl@MCOF surface, inhibiting adsorption. At pH > 8, the FQs molecules deprotonate and exist as anions, and the deprotonation of the amino groups on the F / aminophenyl@MCOF surface reduces anion exchange sites, significantly weakening electrostatic interactions and ultimately leading to a substantial decrease in the adsorption capacity of all three FQs. Furthermore, F / aminophenyl@MCOF exhibits higher adsorption capacity for ENR than for NOR and CIP across the entire pH range. This is related to the enhanced hydrophobicity of the ethyl substituents in the ENR molecule, making it more readily interact with the hydrophobic channels of F / aminophenyl@MCOF. Therefore, pH 6.0 was chosen for subsequent experiments.

[0057] The adsorption amounts of the F / aminophenyl@MCOF prepared in Example 1 for three FQs at different adsorption times are shown in (a), and the pseudo-first-order kinetic fitting curves (b), pseudo-second-order kinetic fitting curves (c), static isotherm adsorption lines (d), Langmuir fitting curves (e), and Freundlich fitting curves (f) corresponding to each adsorption amount are shown in the figure. Figure 6 .

[0058] Figure 6 The data shows that the adsorption capacity of F / aminophenyl@MCOF for FQs increases rapidly within 5–10 min, and the increase slows down after 10 min, indicating that the adsorption of F / aminophenyl@MCOF for FQs reaches equilibrium within 10 min. Therefore, this adsorbent has a fast mass transfer efficiency, which significantly shortens the analysis time and improves the analysis efficiency. The correlation coefficient (R0) of the pseudo-second-order kinetic fitting is shown. 2 The value is approximately 0.999, significantly higher than the pseudo-first-order kinetic fit. Therefore, the adsorption of FQs by F / aminophenyl@MCOF conforms more closely to the pseudo-second-order kinetic equation, indicating that the adsorption process of FQs by F / aminophenyl@MCOF is mainly chemisorption.

[0059] The static isotherm adsorption curves indicate that the adsorption amount gradually increases with increasing FQs solution concentration. Fitting the isotherm adsorption curves using the Langmuir and Freundlich models shows that the R² value of the Langmuir fit is higher. 2The adsorption rate is significantly higher than that of the Freundlich fit, indicating that the material surface is homogeneous and the adsorption of FQs by F / aminophenyl@MCOF is monolayer adsorption. Calculations show that the adsorption capacities of F / aminophenyl@MCOF for NOR, CIP, and ENR are 7.07, 11.78, and 17.51 ​​μg·mg, respectively. -1 .

[0060] To improve the magnetic solid-phase extraction efficiency of FQs, this invention optimizes the adsorption time, adsorption capacity, eluent, and elution time. Compared to "3. Magnetic Solid-Phase Extraction of FQs", the adsorption time was adjusted to 5, 10, 20, and 30 min, with the corresponding adsorption rates shown in [reference needed]. Figure 7 The dosage of a;F / aminophenyl@MCOF was adjusted to 2.5, 5, 10, 15, and 20 mg, and the corresponding adsorption rates are shown in [reference needed]. Figure 7 b; After selecting different eluents (ammonia:ethanol = 2:98 (v / v), ammonia:ethanol = 5:95 (v / v), formic acid:ethanol = 2:98 (v / v), ammonia:methanol = 2:98 (v / v), ammonia:methanol = 5:95 (v / v), ammonia:methanol = 10:90 (v / v), formic acid:methanol = 2:98 (v / v), formic acid:methanol = 5:95 (v / v)), the corresponding elution efficiencies are shown in [reference to table]. Figure 7 c; the elution times were adjusted to 5, 10, 20, and 30 min respectively, and the corresponding elution efficiencies are shown in [reference needed]. Figure 7 d.

[0061] Figure 7 The results showed that for a 5 mL mixed solution of five FQs at a concentration of 100 ng / mL, using 5 mg of adsorbent, the maximum adsorption rate (approximately 96%) was reached within 10 minutes. Figure 7 (a) When the adsorbent dosage is increased from 5 mg to 10 mg, the adsorption rate further increases to over 99%. Figure 7 (b). Therefore, the optimal adsorption time is 10 min, and the optimal adsorbent dosage is 10 mg.

[0062] The composition of the eluent and the elution time directly affect the extraction recovery rate. The adsorption of F / aminophenyl@MCOF on FQs mainly relies on electrostatic interactions, hydrogen bonding, and hydrophobic interactions. When selecting the eluent, the electrostatic interactions can be disrupted by adjusting the pH to change the charge state of the adsorbent and FQs, or the polarity of the organic solvent can be altered to achieve the elution objective. Studies have found that the elution efficiency is highest when using 2% ammonia / methanol as the eluent. Figure 7(c) Ammonia deprotonates the amino groups on the material surface, while the carboxyl groups of FQs dissociate. Both are negatively charged, generating electrostatic repulsion, thus desorbing the FQs. Methanol dissolves the FQs through hydrogen bonding and hydrophobic interactions, enhancing the elution effect. When the elution time is 10 min, the maximum elution efficiency is 80%~98%. Figure 7 (d). Therefore, the optimal elution conditions were determined to be elution with 2% ammonia / methanol for 10 min.

[0063] Under the aforementioned optimal conditions, an analytical method for FQs in pork was established by coupling MSPE with HPLC-FLD. Using organic pork as a blank matrix, a series of working solutions were prepared, enriched with F / aminophenyl@MCOF, and then detected by HPLC-FLD. Figure 8 Chromatographic comparison of blank control, spiked sample, and spiked sample before and after enrichment with F / aminophenyl@MCOF (chromatographic peaks: 1 Norfloxacin, 2 Ciprofloxacin, 3 Normefloxacin, 4 Enrofloxacin, 5 Difluorofloxacin).

[0064] Figure 8 The results showed that no FQs peaks were detected in the organic pork, indicating that there were no target analyte residues or the content was below the detection limit in the blank control; the spiked sample (20 ng·kg) -1 Four types of free radicals (FQs) could be detected, but the signals were extremely weak, indicating that the concentration of the target analytes was low without enrichment, making accurate quantification difficult. In contrast, after enrichment with F / aminophenyl@MCOF, the chromatographic peaks of the five FQs were significantly enhanced, with symmetrical peak shapes and good separation. Therefore, F / aminophenyl@MCOF has good adsorption selectivity and enrichment ability for FQs, while effectively eliminating matrix interference, laying the foundation for quantitative detection.

[0065] To examine the feasibility and reliability of the analytical methods, the linearity, limit of detection (LOD), and limit of quantitation (LOQ) were first investigated (results are shown in Table 2). The results showed that the linear range for all five FQs was 1–500 μg·kg⁻¹. -1 Correlation coefficient (R) 2 All values ​​are greater than 0.9900. Based on S / N=3 and S / N=10, the LOD and LOQ are calculated to be 0.1~0.5 μg·kg⁻¹, respectively. -1 and 0.3~1.5 μg·kg -1 Therefore, this method has a wide linear range and high sensitivity.

[0066] Table 2. Linear equation, limit of detection, and limit of quantitation for the detection of fluoroquinolones. Spiked recovery experiments were conducted using organic pork and antibiotic-free chicken as matrices to investigate the accuracy and reproducibility of the method (results are shown in Table 3). The results showed that the recoveries of the five free radical spiking parameters (FQs) in pork ranged from 86.1% to 109.1%, with intra-day relative standard deviations (RSDs) of 2.3% to 8.5% and inter-day RSDs of 3.6% to 10.8%. In chicken samples, the recoveries of the five FQs ranged from 88.1% to 105.2%, with intra-day RSDs of 3.9% to 8.6% and inter-day RSDs of 5.2% to 9.2%. Therefore, this method exhibits high accuracy and reproducibility.

[0067] Table 3. Spiked recoveries of fluoroquinolones at three levels in pork and chicken (n=3) The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing an aminophenyl / fluorine bifunctional magnetic three-dimensional covalent organic framework material, characterized in that, Includes the following steps: Eight-fold sesquiaminophenyltrimethoxysilane and 2,3,5,6-tetrafluoroterephthalaldehyde were dissolved in a solvent, and then polydopamine-coated Fe3O4 magnetic nanoparticles were added. After being dispersed evenly, acetic acid was added, and then a solvothermal reaction was carried out to obtain the aminophenyl / fluorine bifunctional magnetic three-dimensional covalent organic framework material.

2. The method for preparing the aminophenyl / fluorine bifunctional magnetic three-dimensional covalent organic framework material according to claim 1, characterized in that, The molar ratio of the octasesquiaminophenyltrimethoxysilane to the 2,3,5,6-tetrafluoroterephthalaldehyde is 1:

3.

3. The method for preparing the aminophenyl / fluorine bifunctional magnetic three-dimensional covalent organic framework material according to claim 1, characterized in that, The solvent is a mixture of mesitylene and dioxane in a volume ratio of 1:1; and / or, the concentration of acetic acid in the system is 6M.

4. The method for preparing the aminophenyl / fluorine bifunctional magnetic three-dimensional covalent organic framework material according to claim 1, characterized in that, The ratio of the polydopamine-coated Fe3O4 magnetic nanoparticles to the solvent is 5 mg: 1 mL.

5. The method for preparing the aminophenyl / fluorine bifunctional magnetic three-dimensional covalent organic framework material according to claim 1, characterized in that, The preparation steps of the polydopamine-coated Fe3O4 magnetic nanoparticles include: mixing Fe3O4 magnetic nanoparticles and dopamine in a solvent at a mass ratio of 1:1, stirring and polymerizing to obtain the polydopamine-coated Fe3O4 magnetic nanoparticles.

6. The method for preparing the aminophenyl / fluorine bifunctional magnetic three-dimensional covalent organic framework material according to claim 1, characterized in that, The conditions for the solvothermal reaction were a temperature of 120°C and a time of 36 hours.

7. An aminophenyl / fluorine bifunctional magnetic three-dimensional covalent organic framework material prepared by the preparation method of the aminophenyl / fluorine bifunctional magnetic three-dimensional covalent organic framework material according to any one of claims 1 to 6.

8. The application of the aminophenyl / fluorine bifunctional magnetic three-dimensional covalent organic framework material of claim 7 in the detection of fluoroquinolones.

9. A method for detecting fluoroquinolones using magnetic solid-phase extraction-high performance liquid chromatography, characterized in that, Includes the following steps: The sample to be tested was extracted using acidified acetonitrile. The extract was dried and then reconstituted for magnetic solid-phase extraction. The magnetic solid-phase adsorbent after extraction was eluted. Finally, the fluoroquinolone component in the eluent was detected by high performance liquid chromatography. The content of fluoroquinolone in the sample to be tested was calculated based on the detection results. The magnetic solid-phase adsorbent is the aminophenyl / fluorine bifunctional magnetic three-dimensional covalent organic framework material as described in claim 7.

10. The method for detecting fluoroquinolones using magnetic solid-phase extraction-high performance liquid chromatography according to claim 9, characterized in that, The pH value during magnetic solid-phase extraction is 6.0; and / or the eluent is a 5 vol% ammonia / methanol solution, and the elution time is 10 min.

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