A solid phase microextraction probe, a preparation method and application thereof in alkyl phenol detection

Abstract

This invention discloses a solid-phase microextraction probe, its preparation method, and its application in the detection of alkylphenols. The solid-phase microextraction probe comprises a rod body and a coating located on the outer periphery of the rod body. The coating is made by electrospinning a mixture of 4-meso-UiO-66, DMF, and PAN onto the outer periphery of the rod body. The solid-phase microextraction probe of this invention maintains its extraction performance after 80 adsorption-desorption cycles, and this probe exhibits excellent applicability for the selective detection of alkylphenols (APs) in milk.

Description

Technical Field

[0001] This invention belongs to the field of alkylphenol detection technology, specifically relating to a solid-phase microextraction probe, its preparation method, and its application in alkylphenol detection. Background Technology

[0002] Alkylphenols (APs) are a class of compounds with substituted phenolic rings and alkyl chains, ranging in carbon chain length from 1 to 12. They are widely used in textiles, detergents, and food packaging. Alkylphenols (APs) include bisphenol A (BPA), nonylphenol (NPs), and octylphenol (OPs). Bisphenol A (BPA) is an important component of epoxy resins and polycarbonate products, used in the production of plastic packaging for food and beverages. Nonylphenol (NPs) and octylphenol (OPs) are industrial surfactants and plastic additives, and are also used in personal care products and pesticide formulations. They are the main degradation products of alkylphenol ethoxylation and are more toxic than the parent compound. APs are generally stable and can enter organisms through the food chain, disrupting normal endocrine function, altering genetic information, and leading to carcinogenic, teratogenic, and mutagenic effects in humans. The European Food Safety Authority has reassessed the risks of BPA in food and recommended reducing its tolerable daily intake to 50 ng / g. –1 (Body weight). Furthermore, BPA, NPs, and OPs are on the regulatory lists of the European Union and China. In China, the maximum residue limit (MRL) for BPA in drinking water is 10 ng / mL. –1 The maximum permitted concentrations (MRLs) of p-tert-butylphenol (PTBP) and BPA in food packaging materials were 50 and 600 ng / mL, respectively. –1 (Chinese National Standards: GB 5749-2022 and GB 9685-2016). Because adenosine depressants (APs) are present in many biological and food samples (e.g., human urine, blood, groundwater, beverages, and milk), scientists are increasingly interested in their detection. However, there is still a need to develop more selective and sensitive methods to simultaneously determine APs in complex sample matrices (e.g., milk).

[0003] Effective separation and enrichment of target compounds through appropriate sample pretreatment methods are crucial before instrumental analysis. Various sample pretreatment methods have been used to separate and enrich trace amounts of analytical compounds (APs), including solid-phase extraction (SPE), solid-phase microextraction (SPME), and dispersion-liquid-microextraction (DLLME). SPME has significant advantages over other methods due to its sensitivity, speed, and ease of operation. However, the widespread use of typical SPME fibers faces two main obstacles: firstly, commercial fibers are expensive, fragile, and unstable under extreme conditions; secondly, there is a limited selection of adsorbents with specific properties, unique interactions, or selectivity for the target analyte. The SPME Arrow, a novel SPME device commercialized in 2015, avoids the drawbacks of traditional SPME fibers. Using a stainless steel rod as the substrate and increasing the adsorbent volume significantly improves its robustness and extraction capacity. Therefore, developing functional materials with excellent selectivity as coating materials for the SPME Arrow is essential.

[0004] In recent years, researchers have explored and introduced many highly efficient adsorbents, such as graphene, metal-organic frameworks (MOFs), and template-printed polymers. MOFs are porous materials composed of metal ions or clusters and organic ligands. The crystalline structure of MOFs has a porosity exceeding 50%, while the surface area of ​​MOFs ranges from 500 to 10,000 m². 2 g –1 Between these microporous surfaces, their surface area is larger than that of typical porous materials such as carbon and zeolites. Their unique structure and characteristics, such as high specific surface area, superior thermal stability, and chemical stability, make them attractive for separating bisphenol A (BPA). For example, Sánchez-Sánchez et al. used NH2-MIL-53(Al) mesoporous material to effectively remove BPA from water; the mesoporous structure of NH2-MIL-53(Al) was key to improving BPA removal efficiency. MIL-101(Cr) and MIL-53 were used for efficient BPA extraction. UiO-66-NH2 is a representative example of zirconium-based MOFs, providing abundant adsorption sites due to the addition of amino groups. However, due to its microporous structure, the adsorption capacity of UiO-66-NH2 for large organic molecules needs to be improved.

[0005] Expanding microporous MOFs into mesoporous ones is a promising strategy for increasing pore accessibility. However, obtaining structurally stable mesoporous UiO-66 with tunable properties is crucial. Mesoporous UiO-66 particles can be obtained by using etching techniques during synthesis, leading to the rapid formation of hierarchical pores within UiO-66. However, precisely controlling the distribution of these hierarchical pores remains a challenging task. Pyrolysis is a simple, controllable, and applicable method for synthesizing mesoporous MOFs. First, defective pores are introduced into UiO-66, and its pore size is expanded from the microporous scale to the mesoporous scale through pyrolysis. However, pyrolysis triggers decarboxylation, exposing the hydrophilic Zr6O4(OH)4 clusters to a polar / ionic environment, causing them to lose adsorption sites.

[0006] Therefore, it is necessary to explore the synthesis of functionalized mesoporous UiO-66 materials with high adsorption capacity, high selectivity and fast extraction kinetics. Summary of the Invention

[0007] The first technical problem to be solved by the present invention is to provide a solid-phase microextraction probe in light of the current state of the prior art.

[0008] The second technical problem to be solved by the present invention is to provide a method for preparing a solid-phase microextraction probe.

[0009] The third technical problem to be solved by the present invention is to provide an application of a solid-phase microextraction probe in the detection of alkylphenols.

[0010] The technical solution adopted by the present invention to solve the first technical problem mentioned above is: a solid-phase microextraction probe, characterized in that: it includes a rod body and a coating located on the outer periphery of the rod body; the coating is made by electrospinning a mixture of 4-meso-UiO-66, DMF and PAN onto the outer periphery of the rod body.

[0011] The technical solution adopted by the present invention to solve the second technical problem mentioned above is as follows: a method for preparing a solid-phase microextraction probe as described above, characterized in that the 4-meso-UiO-66 is prepared by the following steps:

[0012] Preparation of UiO-66-NH2-50%: 320 mg ZrCl4, 125 mg NH2-BDC, 125 mg H2BDC, 9.864 g acetic acid and 270 mg HCl were dispersed in 50 mL DMF; then, the reaction was carried out at 120 °C for 24 hours; after washing with DMF and ethanol, UiO-66-NH2-50% was obtained and dried under vacuum at 150 °C for 12 hours.

[0013] Preparation of Meso-UiO-66: 100 mg of the UiO-66-NH2-50% sample obtained above was treated at 350℃ for 2 hours, and then cooled to 25±2℃ to obtain meso-UiO-66 nanoparticles.

[0014] Preparation of HCl-meso-UiO-66: The meso-UiO-66 obtained above was acidified with 37% HCl for 12 h to obtain HCl-meso-UiO-66;

[0015] Preparation of 4-meso-UiO-66: 45 mg of the above-mentioned HCl-meso-UiO-66, 60 mg of 4-n-pentylbenzoic acid and 3 mL of DMF were added to a glass bottle, the bottle was capped, and the mixture was stirred and heated at 80 °C for 24 hours. After washing three times with DMF, the new material was centrifuged and dried in a vacuum at 150 °C for 12 hours. It was named 4-meso-UiO-66.

[0016] Preferably, the electrospinning steps are as follows: 350 mg of 4-meso-UiO-66 is mixed with 3 mL of DMF; then, 150 mg of PAN is added, and the mixture is stirred at room temperature for 24 hours;

[0017] The rod is connected to an electric motor and rotated at 500 revolutions per minute during electrospinning. The electrospinning voltage is 18 kV, and the flow rate is 1 mL / h. –1 An electrospinning nozzle with an inner diameter of 0.6 mm and a distance of 20 cm between it and the rod were used; after 50 min of electrospinning, a coating with a thickness of 53.6 μm and a length of 1 cm was obtained.

[0018] The rod and coating were then immersed in 10 mL of ethanol for a solvent exchange reaction for 1 h, and dried in a vacuum oven at 80 °C for 12 h to finally obtain a solid-phase microextraction probe.

[0019] The technical solution adopted by the present invention to solve the third technical problem mentioned above is: the application of the solid-phase microextraction probe in the detection of alkylphenols as described above.

[0020] Preferably, the alkylphenol detection is performed using liquid chromatography-ultraviolet detection.

[0021] Preferably, the detection steps are as follows:

[0022] First, add 800 mg of zinc sulfate and 800 mg of K₄[Fe(CN)₆]·3H₂O to 80 mL of milk; vortex the mixture in a vortex mixer for 20 s; then, simmer the mixture at 10000 rpm for 1 min. –1Centrifuge for 10 min to remove precipitate; repeat the above process 3 times; filter the resulting supernatant through a 0.22 μm membrane and collect the filtrate;

[0023] Then, take 15 mL of the filtrate obtained above and immerse the solid-phase microextraction probe in it to enrich alkylphenols. The extraction temperature is 25 °C and the stirring speed is 1000 rpm. –1 Extraction time: 40 min;

[0024] The solid-phase microextraction probe was then immersed in 0.2 mL of methanol at room temperature for static desorption for 40 min.

[0025] Finally, the desorbed analytes were analyzed by liquid chromatography-ultraviolet (LC-UV) at a detection wavelength of 225 nm.

[0026] Compared with existing technologies, the advantages of this invention are as follows: The solid-phase microextraction probe of this invention uses mesoporous UiO-66 modified with 4-n-pentylbenzoic acid (4-meso-UiO-66), combining the hydrophobicity of 4-n-pentylbenzoic acid with the high pore accessibility of mesoporous UiO-66, facilitating the adsorption of Aps and thus achieving high extraction efficiency. The coating is prepared by electrospinning, and electrospun nanofibers possess high specific surface area, porous structure, and rapid mass transfer kinetics. Therefore, electrospun nanofibers have a high aspect ratio and a three-dimensional network structure, which can improve the dispersibility of MOF particles, thereby significantly increasing their active adsorption sites. Thus, electrospun nanofibers are an excellent substrate for carrying MOF particles. The prepared coating is relatively uniform, reusable, and stable, with a fast preparation time and is relatively economical. The solid-phase microextraction probe can withstand up to 80 extraction and desorption cycles and is suitable for the detection of nine Aps in milk, with a detection limit of 0.05-1 μg / L. –1 . Attached Figure Description

[0027] Figure 1 (a) is a schematic diagram of the synthesis of 4-meso-UiO-66, including the hydrothermal synthesis of UiO-66-NH2-50%, the thermal decomposition of UiO-66-NH2-50% (meso-UiO-66), the acidification treatment of meso-UiO-66 (HCl-meso-UiO-66), and the esterification of HCl-meso-UiO-66 (4-meso-UiO-66); (b) is a schematic diagram of the determination of nine APs by SPME Arrow-HPLC-UV method;

[0028] Figure 2 (a) SEM image, (b) TEM image, (c) XRD pattern, (d) FI-IR spectrum, (e) N2 adsorption-desorption isotherm and (f) pore size distribution diagram of UiO-66 series materials;

[0029] Figure 3 To optimize (a) the mass ratio of 4-meso-UiO-66 / PAN and (b) the electrospinning time when manufacturing SPME Arrow;

[0030] Figure 4 SEM images of 4-meso-UiO-66-SPME Arrows at different electrospinning times: (a) bare SPME Arrow (diameter = 1.007 mm); (b) 20 min (coating thickness = 14.4 μm); (c) 30 min (coating thickness = 22.8 μm); (d) 40 min (coating thickness = 31.5 μm); (e) 50 min (coating thickness = 53.6 μm); (f) 60 min (coating thickness = 75.2 μm).

[0031] Figure 5 A comparison of the extraction capabilities of SPME Arrow, coated with UiO-66 series materials, 4-n-pentylbenzoic acid and PAN nanofibers, for nine APs;

[0032] Figure 6 XPS plot of (a) 4-meso-UiO-66, (b) C1s spectrum and (c) Zr3d spectrum before and after adsorption of APs;

[0033] Figure 7 The absolute recoveries (%) of nine adrenal agents and three estrogens using 4-meso-UiO-66-SPME Arrow were determined; the standard solution was diluted with ultrapure water and contained 1 μg / mL. -1 APs and 10 μg mL -1 E1, E2, and DES were adsorbed using a 4-meso-UiO-66-SPME arrow at 25°C (15 mL) for 40 min. The extract was desorbed in 200 μL methanol at 1000 rpm for 40 min. Chromatographic conditions: C18 column (ZORBAX SB-C18, 250 mm × 4.6 mm, 5 μm) (Agilent Technologies, USA); column temperature 40°C; gradient mode; mobile phase: acetonitrile and ultrapure water; acetonitrile concentration increased from 70% to 95% within 0-20 min, then decreased to 70% within 1 min, followed by equilibration for 6 min; flow rate 1 mL / min. -1 The injection volume was 30 μL, the column temperature was maintained at 40℃, and the detection wavelength was 225 nm.

[0034] Figure 8For the selectional comparison of APs in enriched whole milk samples by HCl-meso-UiO-66-SPME Arrow and 4-meso-UiO-66-SPME Arrow; 1 mg L -1 Mixed standard solution (A), 1 mg / L -1 HPLC-UV chromatogram (B) of spiked whole milk sample after adsorption with HCl-meso-UiO-66-SPME Arrow; 1 mg L -1 HPLC-UV chromatogram (C) of spiked whole milk sample after extraction with 4-meso-UiO-66-SPME Arrow; (1) BPA, (2) PTBP, (3) 4-BP, (4) PP, (5) 4-HP, (6) 4-t-OP, (7) 4-N-HP, (8) 4-NP, (9) 4-OP. The injection volume of standard solution and spiked sample solution was 30 μL, and the detection wavelength was 225 nm.

[0035] Figure 9 The optimization of (a) sample volume, (b) stirring speed, (c) adsorption time, (d) elution solvents (1. acetonitrile, 2. acetone, 3. methanol, 4. methanol:water (9:1, v / v), 5. methanol:water (7:3, v / v), 6. methanol:water (1:9, v / v)), (e) sodium chloride concentration, (f) extraction temperature, and (g) elution time was carried out. Standard solution: a mixture of nine APs at a concentration of 1 mg / L. –1 ;

[0036] Figure 10 This study investigated the residual adsorption of nine active ingredients (APs) using a 4-meso-UiO-66-SPME arrow. The test used 1 μg / mL diluted form. -1 Ultrapure water for APs; extraction of the working solution (15 mL) using a 4-meso-UiO-66-SPME arrow at 25 °C for 40 min; stirring speed 1000 rpm min. -1 The APs were desorbed in 200 μL of methanol for 40 min. Then, the APs were desorbed sequentially in three test tubes, each containing 200 μL of methanol, for 20 min in each tube. The desorbed APs were analyzed using an HPLC-UV system; the residual rate was calculated by dividing the mass of APs desorbed in the last three desorbed APs by the mass of APs desorbed in the first 40 min; the chromatographic conditions were as follows: C18 column (ZORBAX SB-C18, 250 mm × 4.6 mm, 5 μm) (Agilent Technologies, USA), column temperature 40 °C, gradient mode, mobile phase of acetonitrile and ultrapure water, acetonitrile concentration increased from 70% to 95% in 0-20 min, decreased to 70% in 1 min, and then equilibrated for 6 min; flow rate 1 mL / min. -1The injection volume was 30 μL, the column temperature was maintained at 40℃, and the detection wavelength was 225 nm.

[0037] Figure 11 (a) A newly manufactured 4-meso-UiO-66-SPME Arrow; (b) A SEM image of a 4-meso-UiO-66-SPME Arrow after 80 uses; (c) Photographs of the newly manufactured 4-meso-UiO-66-SPME Arrow and the 4-meso-UiO-66-SPME Arrow after 80 uses; (d) The number of uses of the 4-meso-UiO-66-SPME Arrow;

[0038] Figure 12 The extraction capabilities of (1) 4-meso-UiO-66-SPME Arrow, (2) PDMS, (3) PA, (4) PDMS / DVB and (5) PDMS / CAR / DVB SPME Arrow for nine APs were compared.

[0039] Figure 13 1 μg mL -1 APs mixed standard solution, with 1 μg mL added -1 APs were diluted with 5% whole milk and 1 μg mL was added. -1 Adsorption curves of APs in pure whole milk were obtained. The mixture (15 mL) was adsorbed using a 4-meso-UiO-66-SPME arrow at 25 °C for 40 min. The stirring speed was 1000 rpm. -1 The extract was desorbed in 200 μL methanol for 40 min; chromatographic conditions: C18 column (ZORBAX SB-C18, 250 mm × 4.6 mm, 5 μm) (Agilent Technologies, USA); column temperature 40 °C; gradient mode; mobile phase: acetonitrile and ultrapure water; acetonitrile concentration increased from 70% to 95% within 0-20 min, then decreased to 70% within 1 min, followed by equilibration for 6 min; flow rate 1 mL / min. -1 The injection volume was 30 μL, and the column temperature was maintained at 40℃. The detection wavelength was 225 nm.

[0040] Figure 14 (a) HPLC-UV chromatogram and (b) UPLC-ESI-Q-ToF / MS total ion chromatogram, 0.5 mg L -1 Mixed standard solution (A), with 0.5 mg / L added -1 Chromatograms of skim milk (B), low-fat milk (C), and whole milk (D) sample solutions containing APs after adsorption with a 4-meso-UiO-66-SPME Arrow; 0.5 mg L-1 Chromatograms of skim milk (E), low-fat milk (F), and whole milk (G) sample solutions of APs after precipitation pretreatment; (1) BPA, (2) PTBP, (3) 4-BP, (4) PP, (5) 4-HP, (6) 4-t-OP, (7) 4-n-HP, (8) 4-NP, (9) 4-OP; the injection volumes of HPLC-UV and UPLC-ESI-Q-ToF / MS were 30 and 10 μL, respectively; the detection wavelength was 225 nm, and the scanning range of ToF / MS was 50–500 (m / z). Detailed Implementation

[0041] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0042] 1. Experimental materials and preparation methods

[0043] 1.1. Chemicals and standard solutions

[0044] Zirconium chloride (ZrCl4, 98%), phthalic acid (H2BDC, 99%), 4-n-pentylbenzoic acid (98%), N-dimethylformamide (DMF, 99.5%), acetic acid (analytical grade), ethanol (analytical grade), 2-aminophthalic acid (NH2-BDC, 99%), and polyacrylonitrile (PAN, average molecular weight: 85,000) were all purchased from Maclean Company (Shanghai, China). Bisphenol A (BPA, 99%), 4-pentylphenol (PP, 99%), estrone (E1, 98%), 17-β-estradiol (E2, 99%), and benzyl isopropylbenzene (DES, 99%) were provided by Aladdin Biochemical Technology Co., Ltd. (Shanghai, China). Standards such as 4-tert-octylphenol (4-t-OP, 99.5%), p-tert-butylphenol (PTBP, 99%), and 4-octylphenol (4-OP, 98%) were supplied by Enhua Chemical Technology Co., Ltd. (Shanghai, China) and Ambizo Biochemical Co., Ltd. (Shanghai, China). Stock solutions of all APs were prepared by dissolving 50 mg of each AP in 50 mL of acetonitrile, and mixed standard solutions were prepared by diluting the stock solutions with ultrapure water.

[0045] 1.2. Instruments and HPLC conditions

[0046] The separation and detection of APs were performed using an Agilent 1260 high-performance liquid chromatography (HPLC) system equipped with a UV detector. APs were separated using a C18 column (ZORBAX SB-C18, 250 mm × 4.6 mm, 5 μm) (Agilent Technologies, USA). The mobile phase was acetonitrile and ultrapure water. In a gradient elution program, the concentration of acetonitrile was systematically increased from 70% to 95% over 0–20 min. Subsequently, the concentration was rapidly reduced to 70% over 1 min, followed by reequilibration for 6 min. The flow rate used in the experiment was 1 mL / min. –1 The injection volume was 30 μL, and the column temperature was maintained at 40 °C. Target analytes were analyzed at a detection wavelength of 225 nm. The morphology and size of the UiO-66 series materials were determined using scanning electron microscopy (SEM) (ZEISS Sigma 300, Germany) and transmission electron microscopy (TEM) (JEOL JEM 2100F, Japan). Functional groups of the UiO-66 series materials were characterized using Fourier transform infrared spectroscopy (FT-IR) (Nicolet 6700, Thermo Fisher Scientific, USA). Specific surface area and pore size were determined using a physical adsorption analyzer (Micromeritics ASAP 2460, USA). X-ray diffraction patterns (XRD) were determined using Rigaku Ultima IV (Japan). The interaction between APs and 4-meso-UiO-66 was analyzed using X-ray photoelectron spectroscopy (XPS) (Thermo Scientific K-Alpha, USA). The ultrapure water system was supplied by British Airways Water Treatment Equipment Co., Ltd. (China).

[0047] 1.3. Synthesis of 4-meso-UiO-66

[0048] The synthesis process of 4-meso-UiO-66 is as follows: Figure 1 As shown in Figure a. First, UiO-66-NH2-50% was synthesized. Mesoporous UiO-66 (meso-UiO-66) was obtained by thermal decomposition of UiO-66-NH2-50%. meso-UiO-66 was then acidified with concentrated hydrochloric acid (37% HCl) to obtain HCl-meso-UiO-66. Finally, HCl-meso-UiO-66 was esterified with 4-n-pentylbenzoic acid to obtain 4-meso-UiO-66. Details are as follows.

[0049] The synthesis of UiO-66-NH2-50% was as follows: ZrCl4 (320 mg), NH2-BDC (125 mg), H2BDC (125 mg), acetic acid (9.864 g), and HCl (270 mg) were dispersed in DMF (50 mL). The reaction was then carried out at 120 °C for 24 hours. UiO-66-NH2-50% was obtained by five washing steps with DMF and ethanol, and then dried under vacuum at 150 °C for 12 hours. The yield of UiO-66-NH2-50% was 85.8 ± 5.4% (n = 3).

[0050] The synthesis steps of mesoporous UiO-66 (Meso-UiO-66) are as follows: 100 mg of UiO-66-NH2-50% sample was treated at 350 °C for 2 hours. After cooling to room temperature, meso-UiO-66 nanoparticles were obtained. The yield of Meso-UiO-66 was 70.6 ± 11.9% (n = 3).

[0051] The synthesis steps of 4-meso-UiO-66 are as follows: 45 mg of HCl-meso-UiO-66, 60 mg of 4-n-pentylbenzoic acid, and 3 mL of DMF were added to a glass bottle, the bottle was capped, and the mixture was stirred and heated at 80 °C for 24 hours. The mixture was then washed three times with DMF. After centrifugation, the resulting material was dried under vacuum at 150 °C for 12 hours and named 4-meso-UiO-66. The yield of 4-meso-UiO-66 was 89.6 ± 3.8% (n = 3).

[0052] The 4-n-pentylbenzoic acid-modified UiO-66-NH2-50% was synthesized under the same conditions as 4-meso-UiO-66.

[0053] 4-n-Pentylbenzoic acid (containing an alkyl chain and a benzene ring) is a promising capping agent that can synergistically bind to free -OH / -OH2 groups on the Zr6O4(OH)4 cluster to maintain the adsorption properties of mesoporous UiO-66 and reduce interference. Simultaneously, controlling the number of hydroxyl groups and benzene rings can effectively influence the physical and chemical stability of mesoporous UiO-66. 4-n-Pentylbenzoic acid-modified mesoporous UiO-66 (4-meso-UiO-66) combines the hydrophobicity of 4-n-pentylbenzoic acid with the high pore accessibility of mesoporous UiO-66.

[0054] 1.4. Preparation of 4-meso-UiO-66 coating

[0055] The steps for preparing the solid-phase microextraction probe coated with 4-meso-UiO-66 are as follows: First, 350 mg of 4-meso-UiO-66 was mixed with 3 mL of DMF. Then, 150 mg of PAN was added, and the mixture was stirred at room temperature for 24 hours (the mixture contained 70% 4-meso-UiO-66). The bare probe was connected to a compact electric motor and rotated at 500 rpm during electrospinning. The electrospinning voltage was 18 kV, and the flow rate was 1 mL / h. –1 The distance between the electrospinning nozzle (0.6 mm inner diameter) and the rod was 20 cm. After 50 min of electrospinning, a coating of the desired thickness was obtained. The coating length was 1 cm, and excess coating was scraped off with a blade. Finally, the prepared SPME Arrow was immersed in 10 mL of ethanol for solvent exchange and dried in a vacuum oven at 80 °C for 12 h.

[0056] 1.5. SPME Arrow-HPLC-UV Program

[0057] Figure 1 b shows the SPME Arrow-HPLC-UV program. First, 15 mL of pure aqueous solution (containing a total concentration of 1 mg / L of the nine alkylphenols) was added to the sample vial. -1 Alternatively, milk samples pretreated according to procedure 1.6 below can be used. Then, solid-phase microextraction probes (SPMPs) are enriched via direct immersion. The extraction temperature is 25°C, and the stirring speed is 1000 rpm. –1 The solid-phase microextraction probe was then statically desorbed by immersing it in 0.2 mL of methanol at room temperature. Finally, the desorbed analytes were analyzed by HPLC-UV at a detection wavelength of 225 nm. After each extraction / desorption cycle, the solid-phase microextraction probe was pretreated with 20 mL of methanol for 20 min to prevent any potential memory effects.

[0058] 1.6. Real Sample

[0059] Three types of commercially available dairy products, including whole milk, low-fat milk, and skim milk samples, were ordered from a local supermarket in Ningbo. The samples were processed by adding 800 mg of zinc sulfate and 800 mg of K₄[Fe(CN)₆]·3H₂O to 80 mL of milk to remove matrix interferences such as proteins. The mixed samples were vortexed in a vortex mixer for 20 s. Then, the mixture was centrifuged (10000 rpm min). –1 Remove the precipitate after 10 min. Repeat the above process 3 times until the precipitate is almost negligible. Filter the resulting supernatant through a 0.22 μm membrane and collect the filtrate. Subsequently, store the pretreated sample at 4 °C, and enrich alkylphenols using the prepared solid-phase microextraction probe.

[0060] 2. Results and Discussion

[0061] 2.1. Characterization

[0062] Through SEM ( Figure 2 a) and TEM Figure 2 (b) The surface morphology of functionalized UiO-66 was investigated. UiO-66-NH2-50% exhibited an octahedral shape with a smooth surface. After thermal decomposition and acidification treatment, the surfaces of meso-UiO-66 and HCl-meso-UiO-66 tended to become rougher, which was due to the partial collapse of the MOF framework during the heat treatment, resulting in mesoporous structures. Figure 2 As shown in b, compared to UiO-66-NH2-50%, meso-UiO-66, HCl-meso-UiO-66, and 4-meso-UiO-66 show visible mesoporous defects (areas circled in red). Since 4-n-pentylbenzoic acid has been successfully modified onto the surface of HCl-meso-UiO-66, the surface of 4-meso-UiO-66 is smoother. However, the octahedral structure and average size of the UiO-66 series materials remain unchanged. The crystallinity and chemical stability of the UiO-66 series materials are still preserved, as confirmed by XRD (…). Figure 2 c) Characterization, wherein the post-treated UiO-66 material has the same diffraction pattern as UiO-66-NH2-50%.

[0063] Figure 2 Image d shows the FT-IR spectra of UiO-66-NH2-50%, meso-UiO-66, HCl-meso-UiO-66, 4-meso-UiO-66, and 4-n-pentylbenzoic acid. 489 cm⁻¹ –1 and 1255cm –1 The two peaks at [value] are attributed to the stretching vibrations of the Zr-O and NH bonds. The characteristic vibrational bands of UiO-66-NH2-50% CH3COO- appear at 1384, 1425, and 1565 cm⁻¹. –1 This indicates the successful synthesis of UiO-66-NH2-50%. In the spectra of HCl-meso-UiO-66 and meso-UiO-66, the 1655 cm⁻¹... –1 The peak at (and Zr4) + The disappearance of the coordinated carboxyl group is due to the decarboxylation reaction within MOFs during thermal decomposition. (1255cm) –1 The disappearance of the (NH bond) is due to the lower thermal stability of H₂BDC-NH₂ compared to H₂BDC. Compared to the spectra of HCl-meso-UiO-66 and 4-meso-UiO-66, the stretching vibration peak of the ester group (C=O-) is at 1715 cm⁻¹. –1At this point, the tensile vibration peak of CH is between 2850-3000 cm⁻¹. –1 These results indicate that 4-n-pentylbenzoic acid has been successfully grafted onto HCl-meso-UiO-66.

[0064] N2 adsorption-desorption isotherm diagram Figure 2 e) indicates that the UiO-66-NH2-50% sample possesses a microporous structure. On the other hand, the isotherm patterns of meso-UiO-66, HCl-meso-UiO-66, and 4-meso-UiO-66 show distinct hysteresis loops, indicating that they possess mesoporous structures. Furthermore, the mesopore diameters of meso-UiO-66, HCl-meso-UiO-66, and 4-meso-UiO-66 range from 2–20 nm. Figure 2 f). Due to structural collapse caused by thermal decomposition, the total pore volume and specific surface area of ​​meso-UiO-66 materials decreased (Table 1), and a reduction was observed in meso-UiO-66. Meso-UiO-66 has an average pore size of 3.8 nm and a pore volume of 0.40 cm³. 3 g –1 Specific surface area 422.9 cm² 2 g –1 Surface grafting reduced the pore size and pore volume of HCl-meso-UiO-66 (the average pore size, pore volume, and specific surface area of ​​4-meso-UiO-66 were 4.88 nm, 0.41 cm², and 4.88 nm, respectively). 3 g –1 and 338.1cm 2 g –1 (Table 1)). The above results indicate that functionalized 4-meso-UiO-66 with large pore size (2–20 nm) was successfully synthesized.

[0065] Table 1 Structural properties of UiO-66 series materials

[0066]

[0067] 2.2. Optimization of SPME Arrow Coating

[0068] Electrospinning solutions containing 4-meso-UiO-66 in polyacrylonitrile / DMF solutions at different weight ratios were prepared. Figure 3a) When the solution contains more than 70% (wt) of 4-meso-UiO-66, it is difficult to obtain a uniform coating, possibly due to the high viscosity of the solution causing condensation within the electrospinner. The adsorption capacity of the 4-meso-UiO-66 coating for APs increases with increasing 4-meso-UiO-66 mass ratio. Therefore, a solution containing 70% (wt) of 4-meso-UiO-66 was selected as the raw material for preparing the 4-meso-UiO-66-SPME Arrow.

[0069] When the electrospinning time was increased from 20 min to 60 min, the thickness of the 4-meso-UiO-66 / PAN coating increased from 14.4 μm to 75.2 μm. Figure 4 Therefore, the 4-meso-UiO-66-SPME Arrow significantly improves the extraction capability of APs. Figure 3 (b) However, further increasing the electrospinning time did not improve its extraction capacity because the high adsorption affinity between the coating and APs made the desorption step challenging. On the other hand, an excessively thick SPME Arrow coating may hinder the diffusion path and slow down its adsorption kinetics. Therefore, a 50-min electrospinning time was chosen to prepare 4-meso-UiO-66-SPMEArrow.

[0070] In summary, electrospinning is relatively time-consuming and more cumbersome compared to other techniques used in our previous work, such as dip-coating and electrodeposition. However, the coatings prepared in this study are more uniform and reproducible. Furthermore, electrospinning of SPME Arrow coatings remains faster and more economical than more controllable techniques such as atomic layer deposition.

[0071] 2.3. Comparison of UiO-66 series materials

[0072] We compared the extraction capabilities of the UiO-66 series materials for APs. Figure 5 Compared to other UiO-66 series materials, 4-n-pentylbenzoic acid, and PAN, 4-meso-UiO-66 exhibited the best adsorption capacity for APs. Furthermore, the extraction capacity of 4-n-pentylbenzoic acid-modified UiO-66-NH2-50% was significantly lower than that of 4-meso-UiO-66. According to Table 1, the average pore size of 4-meso-UiO-66 (4.88 nm) is larger than that of UiO-66-NH2-50% (2.37 nm), making it easier for target analytes to enter. UiO-66-NH2-50%, on the other hand, prevents APs from entering its internal micropores. Figure 5(See Table 1). Compared with HCl-meso-UiO-66, 4-meso-UiO-66 exhibited higher extraction efficiency for APs, indicating that the chemical affinity of HCl-meso-UiO-66 modified with 4-n-pentylbenzoic acid was improved with APs. Furthermore, the specific surface area of ​​4-meso-UiO-66 (338.1 m²) was significantly higher. 2 g –1 Approximately lower than meso-UiO-66 (422.9m) 2 g –1 ) is 20% of that of other parts, but their total pore volume is almost the same (0.40 cm). 3 g –1 vs 0.41cm 3 g –1 Therefore, the more accessible mesoporous structure and relatively low specific surface area play a decisive role in the extraction of these nine APs. 4-n-pentylbenzoic acid and PAN-coated SPME Arrow exhibit relatively low extraction capabilities for APs, implying that their affinity for APs is limited.

[0073] XPS analysis was performed to investigate the adsorption mechanism of APs by 4-meso-UiO-66. Figure 6 a shows the complete XPS spectra of 4-meso-UiO-66 before and after APs adsorption, displaying four characteristic peaks corresponding to Zr 3d, C1s, O 1s, and N1s. Abundant benzene rings are present in both 4-meso-UiO-66 and APs. After APs adsorption ( Figure 6 (b) Due to the adsorption of APs, the C=C group region expands. The binding energy of CO shifts from 283.16 eV to 285.9 eV, and the peak intensity changes significantly, which is attributed to the electronic interaction between APs and oxygen-containing groups. The oxygen atom shares electrons with the hydrogen atom in the AP molecule, increasing the electron density of adjacent carbon atoms and decreasing the carbon binding energy. Therefore, the possible adsorption mechanism is the electronic interaction between the hydroxyl group of 4-meso-UiO-66 and APs. Zr 3d spectrum ( Figure 6 XPS analysis of c) revealed two distinct Zr-O bonds and two distinct Zr-Zr bonds. The Zr-O bond at 185.43 eV corresponds to a bridge between Zr-O-Zr zirconium centers in the UiO-66 frame element, while the Zr-O bond at 182.2 eV is a connection between Zr and H2BDC. Figure 6 c shows that the binding energy of Zr-O shifts from 185.43 eV to 184.82 eV after adsorption of APs. This observation indicates that Zr-O plays a crucial role in APs adsorption.

[0074] Compounds with similar chemical structures, molecular weights, and functional groups in real samples (e.g., estrogens, alkylphenol ethoxy ethers, and methylphenols) may be co-extracted by 4-meso-UiO-66. Therefore, selectivity tests were conducted in the presence of three coexisting estrogens (E1, E2, and DES). The results showed that these estrogens did not significantly affect the adsorption of APs, even when their concentrations were ten times that of the APs. Figure 7 The three estrogens with hydroxyl groups can also interact with Zr-O bonds. Figure 6 The low adsorption capacity they result in may be due to their relatively large molecular size limiting their accessibility to the pores of 4-meso-UiO-66 (Table 1). Based on the texture properties of the UiO-66 series materials (Table 1) and XPS analysis results (…), Figure 6 ), selective test results ( Figure 7 The high selectivity of 4-meso-UiO-66 for APs is mainly due to the synergistic effect of size exclusion effect and electrostatic interaction, as well as the structures of nine APs and three estrogens.

[0075] We compared the selectivity of HCl-meso-UiO-66 and 4-meso-UiO-66 coated SPME arrows for active ingredients (APs) in whole milk samples. Figure 8 As shown, 4-meso-UiO-66 exhibited higher adsorption capacity for nine APs compared to HCl-meso-UiO-66. Furthermore, the chromatograms of whole milk samples pretreated with 4-meso-UiO-66-SPME Arrow were clearer than those pretreated with HCl-meso-UiO-66-SPME Arrow, indicating the high selectivity and matrix elimination ability of 4-meso-UiO-66-SPME Arrow.

[0076] 2.4. Optimization of the SPME program

[0077] The SPME program was optimized, including sample volume, stirring speed, ionic strength, extraction temperature and time, desorption solvent and desorption time.

[0078] 2.4.1. Sample volume

[0079] Different volumes of 1 μg mL were tested in 20 mL sample vials. –1 Nine alkylphenols were prepared in pure aqueous solutions (5, 10, and 15 mL). The concentration of APs in all samples was 1 μg / mL. –1 The effect of sample volume on the adsorption response is as follows: Figure 9As shown in figure a, it was observed that the extraction efficiency of APs increased with increasing sample volume. Therefore, 15 mL was chosen for further experiments to obtain appropriate sensitivity.

[0080] 2.4.2. Stirring speed

[0081] The effect of stirring speed (0, 250, 500, 750, 1000, 1250 and 1500 rpm) was investigated. –1 It was observed that when the stirring speed was increased from 0 to 1000 r / min... –1 When the peak intensity of all analytes increases, Figure 9 b). According to SPME theory, the thickness of the boundary layer between the coating and the solution can be reduced by increasing the stirring speed. When the solution stirring speed exceeds 1250 rpm... –1 At that time, due to the formation of eddies in the solution, the extraction capacity of some analytes decreased slightly. Therefore, in further studies, 1000 rpm was used. –1 .

[0082] 2.4.3. Extraction Time

[0083] The effects of extraction times of 2–60 min were evaluated. Figure 9 c) Extraction of 4-BP, PP, BPA, 4-t-OP, and PTBP reached equilibrium within 20 min, while extraction of 4-HP and 4-NP reached equilibrium within 40 min. 4-OP and 4-n-HP required more than 60 min to reach extraction equilibrium. Further increasing the extraction time did not substantially improve the extraction efficiency of most analytes, especially PP, 4-BP, and BPA, which decreased after 40 min, possibly due to competitive extraction effects. Considering the extraction time effect of all APs, 40 min was selected as the extraction time.

[0084] 2.4.4. Desorption Solvent

[0085] Desorption from the adsorbed analyte should be attempted whenever possible. Several desorption solvents were first compared: methanol, acetone, acetonitrile, methanol / water (9:1 v / v), methanol / water (7:3 v / v), and methanol / water (1:9 v / v). Figure 9 d). Methanol exhibited the highest desorption capacity. This is likely because, of the three solvents, methanol is the most polar organic solvent, and APs are polar compounds. Following the rule of similar dissolution, methanol provided the highest desorption efficiency. Therefore, pure methanol was chosen as the optimal desorption solvent for subsequent experiments.

[0086] 2.4.5. Ionic strength

[0087] The effect of ionic strength on the adsorption of APs by 4-meso-UiO-66-SPME arrow was investigated using NaCl. When the NaCl concentration increased from 0% to 20%, the extraction efficiencies of 4-HP, 4-t-OP, 4-N-HP, 4-NP, and 4-OP significantly decreased. Figure 9 e). In contrast, the extraction efficiencies of BPA, PTBP, 4-BP, and PP increased dramatically. This is likely because the increased ionic strength leads to a decrease in the solubility of organic analytes in aqueous solution, thereby increasing the partition constant between the coating and the aqueous phase. These results indicate that salts have a dual effect on the adsorption of APs. Therefore, salts were excluded from the samples in subsequent studies.

[0088] 2.4.6. Extraction temperature

[0089] The effect of temperature on analyte extraction in DI-SPME depends on the exothermic or endothermic nature of the extraction process and the volatility of the analyte. The effect of extraction temperature was investigated within the range of 25–60 °C. Figure 9 f). The peak areas of most APs gradually decreased with increasing extraction temperature. This may be because higher extraction temperatures are detrimental to the exothermic adsorption process of the analytes on the SPME Arrow. Therefore, 25℃ was chosen as the optimal extraction temperature for subsequent experimental studies.

[0090] 2.4.7. Desorption time

[0091] The effect of desorption time was examined within the range of 2–90 min. 40 min was considered sufficient for complete desorption of the analyte. Figure 9 g). Furthermore, continuous testing was conducted under optimal extraction and desorption conditions. For example... Figure 10 As shown, there is almost no memory effect.

[0092] Extraction performance of 2.5.4-meso-UiO-66-SPME Arrow

[0093] The repeatability of the method upon which SPME Arrow is based is significantly affected by the reusability of the coating. Figure 11 ab shows SEM images of the SPME Arrow after 0 and 80 extraction-desorption cycles. After 80 extraction-desorption cycles, the coating morphology and internal structure of the SPME Arrow showed no significant damage. Figure 11 c). Excellent extraction efficiency was maintained after 80 extraction-desorption cycles in the SPME process. Figure 11d) demonstrates that the 4-meso-UiO-66-SPME Arrow exhibits good reproducibility. We also performed reproducibility tests on the 4-meso-UiO-66-SPME Arrow between the same batch and different batches. The results showed that the RSD of reproducibility between the same batch was less than 14.7% (N=3), and the RSD of reproducibility between different batches was less than 15.2% (N=3). The extraction performance of the 4-meso-UiO-66-SPME Arrow was compared with that of commercial SPME Arrows (coated with PDMS, PDMS / DVB, PDMS / CAR / DVB, and PA, respectively) for APs. Figure 12 First, the extraction and desorption conditions of commercial SPME Arrows were optimized. Then, comparisons were made under their optimal extraction and desorption conditions. The volumes of PDMS, PA, PDMS / DVB, and PDMS / CAR / DVB coatings were approximately 6.28–7.39 μL (calculated based on manufacturer-provided data), and the volume of the 4-meso-UiO-66 coating was 1.79 μL (based on...). Figure 4 a and 4d calculations). However, the 4-meso-UiO-66-SPME Arrow still exhibits superior extraction capabilities for nine APs (a and 4d calculations). Figure 13 The reasons may be: 1) Due to the grafting of 4-n-pentylbenzoic acid, 4-meso-UiO-66 is hydrophobic, thereby reducing the interference of water molecules; 2) 4-meso-UiO-66 has better chemical affinity with APs; 3) The mesoporous structure in 4-meso-UiO-66 is more easily penetrated by APs; 4) PAN nanofibers have stronger permeability than PDMS.

[0094] 2.6. Method Validation

[0095] Matrix effects can significantly influence analyte signals caused by co-extraction and co-elution of matrix substances. The analyte response may be enhanced or suppressed. For example... Figure 14 As shown in Table 2, the release rate constant (k2) differed significantly among the standard solution, 5% whole milk, and 100% whole milk samples, indicating a severe matrix effect. The maximum concentration of APs in the coating was significantly affected. Therefore, to compensate for the observed matrix effect, quantitative analysis was performed using a matrix-matched calibration curve. Nine APs were analyzed using a combination of SPME Arrow and HPLC-UV on the 4-meso-UiO-66 coating (4-meso-UiO-66-SPME Arrow-HPLC-UV) at a detection wavelength of 225 nm. This method was used to analyze APs in concentration ranges from 0.2–1000 μg / L. –1Whole milk samples were added to the APs for calibration. The validation results of this method are listed in Table 3. The correlation coefficients (R) for all nine APs were greater than 0.9989. The limits of detection (LODs) for the nine APs were detected at a signal-to-noise ratio (S / N) of 3, ranging from 0.05–1 μg L⁻¹. –1 The intraday and interday precision were 2.8%–9.7% and 3.2%–11.5%, respectively.

[0096] Table 2 Kinetic constants of adsorption curves of nine APs in milk at different concentrations

[0097]

[0098]

[0099] Note: k2 is the release rate constant; ff is the free fraction, ff = 1; k1 is the absorption rate constant. The percentage loss of sample after a single extraction is calculated as follows: at 60 min, 100% × [(k1v] f ) / (k2v a )](1–e –k 2 t ).

[0100]

[0101] 2.7. Comparison of Method Performance

[0102] Numerous analytical methods for determining endocrine disruptors (APs) have been reported to date (Table 4). However, most methods focus on BPAs due to their regulatory nature in both the EU and China. In this study, nine APs were selected as targets because their endocrine disrupting effects are not negligible. Compared to SPME-GC-MS methods, HPLC-based methods, such as our method, SPE-HPLC-PAD, and MSPE-HPLC-UV methods, offer higher limits of detection (which can be improved by using advanced instruments, such as ultra-high performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight mass spectrometry (UPLC-ESI-Q-ToF / MS),) without requiring complex derivatization. Furthermore, our method exhibits a comparable linear range compared to other HPLC-based methods. Additionally, limited methods focus on milk sample preparation. On the other hand, this method leverages the ease of operation of SPME technology, making sample preparation more convenient than SPE-based methods. Compared to the National Food Safety Standard Method 2-5.6.6 Determination of parabens in milk and dairy products by gas chromatography-mass spectrometry (GB31660.2-2019), our method offers shorter sample preparation time (80 min vs. >120 min) and is easier to operate. The National Food Safety Standard Method requires complex gel purification, solid-phase extraction, and derivatization. Furthermore, our method demonstrates comparable sensitivity, accuracy, and precision for the detection of PTBP, 4-OP, and BPA.

[0103]

[0104] 2.8. Analysis of actual samples

[0105] Whole milk, low-fat milk, and skim milk samples were used to evaluate the suitability of the SPME Arrow-HPLC-UV method at an adsorption wavelength of 225 nm. Since APs were not detected in these samples, they were added at three concentration levels. According to Chinese national standards (GB 5749-2022 and GB 9685-2016), the maximum residue limits for BPA and PTBP in drinking water and food packaging materials are 10-600 ng / mL. –1 Within the range. Furthermore, Boti et al. detected four APs in 27 milk samples, with concentrations of 9.4 ± 4.2 (BPA), 174.1 ± 128.0 (4-t-OP), 137.7 ± 93.0 (NP), and 196.7 ± 130.3 (4-NP). Therefore, the recommended addition levels of APs in milk samples were 20, 100, and 500 ng / mL. –1 APs were enriched using optimal SPME Arrow conditions and then detected by HPLC-UV. Typical chromatograms of the nine APs are shown below. Figure 14As shown in Table 5, the recoveries of whole milk samples were 83.6%–112%, low-fat milk samples were 84.3%–106%, and skim milk samples were 85.3%–105%, with all RSDs ranging from 2.2% to 14.6%. The developed SPME Arrow-HPLC-UV method demonstrated satisfactory accuracy and reproducibility in the quantitative and qualitative analysis of nine active ingredients (APs) in complex milk samples. Further comparative experiments with UPLC-ESI-Q-ToF / MS were conducted to evaluate the high selectivity and anti-interference capability of the 4-meso-UiO-66-SPME Arrow-HPLC-UV method. The total ion chromatogram of milk samples pretreated with 4-meso-UiO-SPME Arrow is shown in Table 5. Figure 14 (b) The method exhibits a good baseline and limited matrix effects, indicating that it has high selectivity and robustness. Specifically, Aps in whole milk, low-fat milk, and skim milk can be enriched using the solid-phase microextraction probe of this application and detected using the method described herein.

[0106]

[0107] in conclusion

[0108] This study successfully synthesized 4-meso-UiO-66 using a post-modification strategy. The high specific surface area and mesoporous structure of 4-meso-UiO-66 were directly electrospun onto rods using electrospinning. This novel solid-phase microextraction probe, while maintaining its structural integrity and excellent adsorption performance, can withstand up to 80 extraction and desorption cycles. XPS and N2 adsorption-desorption results showed that the extraction mechanism of APs by 4-meso-UiO-66 is the electrostatic interaction and size repulsion effect between APs and Zr-O. The optimized and validated SPME Arrow-HPLC-UV method demonstrated high sensitivity and good reproducibility for the detection of APs in milk. This work established a selective and sensitive SPME Arrow-HPLC-UV method for the determination of nine APs in milk and expanded the applicability of mesoporous MOFs. Overall, the 4-meso-UiO-66 adsorbent shows great potential for the selective adsorption of APs.

Claims

1. A solid-phase microextraction probe, characterized in that: Includes the rod body and the coating located on the outer periphery of the rod body; The coating is made by electrospinning a mixture of 4-n-pentylbenzoic acid-modified mesoporous UiO-66, DMF, and PAN onto the outer periphery of the rod.

2. A method for preparing a solid-phase microextraction probe as described in claim 1, characterized in that, The 4-n-n-pentylbenzoic acid-modified mesoporous UiO-66 was prepared by the following steps: Preparation of UiO-66-NH2-50%: 320 mg ZrCl4, 125 mg NH2-BDC, 125 mg H2BDC, 9.864 g acetic acid and 270 mg HCl were dispersed in 50 mL DMF; then, the reaction was carried out at 120 °C for 24 hours; after washing with DMF and ethanol, UiO-66-NH2-50% was obtained and dried under vacuum at 150 °C for 12 hours. Preparation of meso-UiO-66: 100 mg of the UiO-66-NH2-50% sample obtained above was treated at 350℃ for 2 hours, and then cooled to 25±2℃ to obtain meso-UiO-66 nanoparticles. Preparation of HCl-meso-UiO-66: The meso-UiO-66 obtained above was acidified with 37% HCl for 12 h to obtain HCl-meso-UiO-66; Preparation of 4-n-pentylbenzoic acid modified mesoporous UiO-66: 45 mg of the above-mentioned HCl-meso-UiO-66, 60 mg of 4-n-pentylbenzoic acid and 3 mL of DMF were added to a glass bottle, stirred and heated at 80 °C for 24 hours, and then washed three times with DMF; after centrifugation, the new material was dried in vacuum at 150 °C for 12 hours and named 4-n-pentylbenzoic acid modified mesoporous UiO-66.

3. The method according to claim 2, characterized in that: The electrospinning steps are as follows: 350 mg of 4-n-pentylbenzoic acid-modified mesoporous UiO-66 is mixed with 3 mL of DMF; 150 mg of PAN is added, and the mixture is stirred at 25±2℃ for 24 hours; The rod was attached to a motor and rotated at 500 rpm during electrospinning, with an electrospinning voltage of 18 kV and a flow rate of 1 mL h –1 An electrospinning nozzle with an internal diameter of 0.6 mm was used, with a distance of 20 cm between the nozzle and the rod; a coating with a desired thickness of 53.6 μm was obtained after 50 min of electrospinning, with a coating length of 1 cm; The rod and coating were then immersed in 10 mL of ethanol for a solvent exchange reaction for 1 h, and dried in a vacuum oven at 80 °C for 12 h to finally obtain a solid-phase microextraction probe.

4. The application of the solid-phase microextraction probe as described in claim 1 in the detection of alkylphenols.

5. The application according to claim 4, characterized in that: The alkylphenol was detected using liquid chromatography-ultraviolet (LC-UV) detection.

6. The application according to claim 5, characterized in that: The detection step is as follows: first, 800 mg of zinc sulfate and 800 mg of K4[Fe (CN)6] 3H2O are added to 80 mL of milk; the mixed sample is vortexed in a vortexer for 20 s; the mixture is centrifuged at 10000 rpm min –1 for 10 min to remove the precipitate; the above process is repeated 3 times; the obtained supernatant is filtered through a 0.22 μm membrane, and the filtrate is taken; Take 15 mL of the above obtained filtrate, immerse the solid phase microextraction probe therein to enrich the alkylphenol, the extraction temperature is 25°C, the stirring speed is 1000 rpm min –1 , the extraction time is 40 min; The solid-phase microextraction probe was then immersed in 0.2 mL of methanol at 25±2℃ for static desorption for 40 min. Finally, the desorbed analytes were analyzed by liquid chromatography-ultraviolet (LC-UV) at a detection wavelength of 225 nm.

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