Cationic covalent organic frameworks and their preparation and use

Abstract

The application discloses a preparation method of a cationic covalent organic framework, which comprises the following steps: 1) placing 5,5'-diamino-2,2'-bipyridine and triformylphloroglucin in a reaction container, adding a mixed solvent of mesitylene / 1,4-dioxane, stirring, adding acetic acid, stirring, and then placing the reaction container in an oven for reaction to obtain a brown powder; 2) washing the brown powder with acetone, and then performing Soxhlet extraction to clean the unreacted monomers, and vacuum drying to obtain a covalent organic framework; 3) placing the covalent organic framework, nitrobenzene and 1,2-dibromoethane in a reaction container, stirring and refluxing, centrifuging after the reaction is completed, cleaning the brown-black solid with acetone, and vacuum drying overnight to obtain the cationic covalent organic framework. The application further discloses an analysis method for determining o-phthalic acid monoester compounds in urine samples quickly, sensitively and accurately by taking the cationic covalent organic framework as a solid-phase extraction adsorbent and combining with UPLC-MS / MS technology.

Description

Technical Field

[0001] This invention belongs to the field of functional materials. More specifically, this invention relates to a cationic covalent organic framework and its preparation and application. Background Technology

[0002] Phthalate esters (PAEs) are among the most produced industrial chemicals, commonly used as plasticizers in the processing and production of industrial and consumer products such as toys, food packaging, medical supplies, and personal care products. PAEs are classified as endocrine disruptors and can enter the human body through food ingestion, skin contact, and inhalation, rapidly metabolizing into mono- and mPAEs within 24 hours. mPAEs serve as biomarkers for PAEs, and their internal exposure levels in the human body are correlated with many diseases. Li's research group investigated the correlation between urinary mPAE levels and depression, identifying a positive correlation between mono(2-ethylhexyl) phthalate, mono(2-ethyl-5-hydroxyhexyl) phthalate, and mono(2-ethyl-5-carboxypentyl) phthalate and the risk of depressive symptoms in ordinary adults. Sun Hongwen's research group demonstrated through epidemiological surveys that there is a significant correlation between prenatal exposure to mPAEs and human placental gene expression, and the distribution characteristics of mPAEs in the placenta can serve as an important indicator for evaluating fetal exposure status. However, biological sample matrices are very complex, and the content of mPAEs in the human body is often at trace or even ultra-trace levels. Developing high-throughput and high-affinity sample pretreatment methods is a necessary condition for obtaining reliable analytical results.

[0003] Covalent organic frameworks (COFs) are a class of crystalline polymers formed by the covalent bonding of monomers containing light elements such as C, H, O, N, and B, exhibiting a periodic arrangement. Benefiting from their ordered porous structure and numerous active sites, COFs have demonstrated unique advantages in sample pretreatment and have been successfully applied in solid-phase extraction (SPE), dispersive solid-phase extraction (DSPE), magnetic solid-phase extraction (MSPE), stir bar extraction (SBSE), and solid-phase microextraction (SPME) to extract various target analytes from environmental, food, and biological samples. However, most reported COFs as extraction adsorbents currently rely primarily on non-specific interactions such as hydrophobic interactions, hydrogen bonds, van der Waals forces, and π-π interactions to adsorb target analytes, lacking specificity. Functionalizing COFs is an effective way to improve their selective adsorption capacity for target analytes. Currently, some functionalized COFs have been used in biological sample pretreatment and have demonstrated good adsorption performance. Xiong et al. prepared positively charged COFs using guanidine monomers for the specific enrichment of low-abundance phosphorylated peptides in HeLa cells. Gao et al. synthesized phenylboronic acid-functionalized magnetic COFs using a post-modification method and applied them to specifically enrich N-glycopeptides. Deng's group modified magnetic COFs with carboxyl groups to increase hydrophilicity, achieving efficient extraction of endogenous glycopeptides from human saliva. Jia's group prepared glutathione-functionalized thioether COFs for the simultaneous enrichment of glycosylated and phosphorylated peptides in exosomes. However, covalent organic frameworks that can effectively enrich mPAEs in human urine samples are currently lacking. Summary of the Invention

[0004] One object of the present invention is to solve at least the above-mentioned problems and to provide at least the advantages that will be described later.

[0005] One object of the present invention is to provide a cationic covalent organic framework that can adsorb a variety of phthalic acid monoesters in the sample solution to be analyzed.

[0006] To achieve these objectives and other advantages of the present invention, a method for preparing a cationic covalent organic framework is provided, comprising the following steps: 1) Place 5,5′-diamino-2,2′-bipyridine and trialdehyde phloroglucinol in a reaction vessel, add a mixed solvent of mesitylene / 1,4-dioxane, stir for 10-50 min, add acetic acid, stir for 10-30 min, and then place the reaction vessel in a high temperature environment of 110-130℃ to react and obtain a covalent organic framework (TpBPy). 2) Place the covalent organic framework, nitrobenzene, and 1,2-dibromoethane in a reaction vessel, stir, and reflux at 150-180 °C. After the reaction is complete, centrifuge to obtain a brownish-black solid, wash with acetone, and vacuum dry overnight to obtain a cationic covalent organic framework (TpBPy). 2+ ).

[0007] Preferably, in step 1), the molar ratio of 5,5′-diamino-2,2′-bipyridine to trialdehyde phloroglucinol is 1.5:1, the volume ratio of mesitylene to 1,4-dioxane in the mixed solvent is 1:1, the added volume of the mixed solvent is 10-30 times the mass of 5,5′-diamino-2,2′-bipyridine and trialdehyde phloroglucinol, the acetic acid concentration is 1-10 mol / L, and the added volume of acetic acid is 1-3 times the mass of 5,5′-diamino-2,2′-bipyridine and trialdehyde phloroglucinol.

[0008] Preferably, the covalent organic framework obtained in step 1) is further treated as follows: washed with acetone, then washed with methanol containing tetrahydrofuran by Soxhlet extraction to remove unreacted monomers, and vacuum dried to remove impurities from the covalent organic framework.

[0009] Preferably, in step 2), the volume of nitrobenzene added is 40-80 times the mass of the covalent organic framework; and the volume of 1,2-dibromoethane added is 4-8 times the mass of the covalent organic framework.

[0010] The cationic covalent organic framework is prepared by the method described above.

[0011] The application of cationic covalent organic frameworks is for solid-phase extraction of phthalic acid monoester compounds in samples to be analyzed.

[0012] Preferably, the phthalic acid monoester compounds include, but are not limited to, one or more of the following: methyl phthalate (mMP), ethyl phthalate (mEP), n-butyl phthalate (mBP), isobutyl phthalate (miBP), mono(2-ethylhexyl) phthalate (mEHP), mono(2-ethyl-5-oxohexyl) phthalate (mEOHP), and mono(2-ethyl-5-hydroxyhexyl) phthalate (mEHHP).

[0013] Preferably, the sample to be analyzed is urine.

[0014] A method for analyzing phthalic acid monoesters in human urine using a cationic covalent organic framework includes the following steps: A) Adjust the pH of the urine sample to be analyzed to 5.5-6.5, shake for 1-5 min, add the complex enzyme of β-glucuronidase and arylsulfatase, shake for 1-5 min, place in a 35-40 ℃ water bath for hydrolysis overnight, cool to room temperature, and obtain the extract to be extracted. B) Place the cationic covalent organic framework in a reaction vessel, add the urine sample to be analyzed treated in step A), disperse by ultrasonication, place in a cyclotron for solid-phase extraction, centrifuge, remove the supernatant, and obtain the solid-phase extract; C) Add methanol solvent containing ammonia to the solid extract for desorption, centrifuge, collect the supernatant and dry it with N2 to obtain the solid to be analyzed; D) The analytical solid was redissolved in an aqueous solution containing methanol, mixed, filtered through a pinhole membrane, and then analyzed by ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS / MS).

[0015] Preferably, in step A), the pH of the sample solution to be analyzed is adjusted with glacial acetic acid.

[0016] The present invention has at least the following beneficial effects: First, this invention is based on symmetry. C 2-5,5′-diamino-2,2′-bipyridine (BPy) and symmetry are C COFs (TpBPy) were prepared using 3-trialdehyde phloroglucinol (Tp) as the building block. Then, a cyclization reaction was performed between 1,2-dibromoethane and the bipyridine structure in the TpBPy skeleton to obtain positively charged TpBPy. 2+ Due to TpBPy 2+ It can specifically bind to mPAEs through electrostatic attraction, thus significantly increasing the adsorption capacity of seven mPAE target analytes. Using TpBPy... 2+ The analytical method using solid-phase extraction adsorbents has high sensitivity and can be used to determine the content of mPAEs in human urine samples.

[0017] Secondly, based on the negatively charged characteristic of mPAEs, this invention utilizes a quaternization reaction to customize cationic TpBPy. 2 + Electrostatic attraction enables specific adsorption of target analytes mPAEs, thereby increasing extraction capacity. TpBPy 2+ As a solid-phase extraction adsorbent, combined with an analytical method established using UPLC-MS / MS technology, it is possible to rapidly, sensitively, and accurately determine seven trace mPAEs in urine samples. (TpBPy) 2+ Its successful application not only demonstrates its great potential for efficient enrichment of mPAEs in sample pretreatment, but also provides a new approach for the preparation of ionic COFs.

[0018] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0019] Figure 1 TpBPy of the present invention 2+ A schematic diagram of the synthesis; Figure 2 This invention utilizes TpBPy 2+ Schematic diagram of mPAE extraction; Figure 3 For the present invention TpBPy and TpBPy 2+ Powder X-ray diffraction; Figure 4 For Tp, BPy, TpBPy and TpBPy 2+ Fourier transform infrared spectrum; Figure 5 For TpBPy and TpBPy 2+ X-ray photoelectron spectroscopy (XPS) images; where a represents TpBPy and TpBPy. 2+ XPS full spectrum; b represents TpBPy and TpBPy. 2+ Br 3d XPS plot; c is TpBPy 2+ d is the Br 3d high-resolution XPS image; d is the N 1s high-resolution XPS image of TpBPy; e is the TpBPy 2+ N 1s high-resolution XPS image; Figure 6 For TpBPy 2+ Figure 1 shows the results of the porous properties; where a is the N2 adsorption-desorption isotherm and b is the pore size distribution curve. Figure 7 For TpBPy and TpBPy 2+ The morphological results are shown in the figures; where a is the SEM image of TpBPy; b is the SEM image of TpBPy. 2+ SEM image; c is the element distribution map of TpBPy; d is the SEM image of TpBPy. 2+ Element distribution diagram; Figure 8 For TpBPy and TpBPy 2+ Figures showing the results of thermal stability and charge analysis; where a is the thermogravimetric curve and b is the Zeta potential; Figure 9 For TpBPy and TpBPy 2+ The hydrophilicity analysis results are shown in the figure; where a represents TpBPy; b represents TpBPy. 2+ ; Figure 10This is a graph showing the optimization results of solid-phase extraction conditions in this invention; where a represents the pH of the extract; and b represents TpBPy. 2+ Dosage; c is extraction time; d is desorption solvent; Figure 11 This is a chromatogram of urine analysis results; where a is mMP; b is mEP; c is miBP and mBP; d is mEHP; e is mEOHP; f is the extraction ion chromatogram of mEHHP; curve A is 25 μg·L ‒1 Mixed standard solution; Curve B is urine sample without TpBPy 2+ Extraction; curve C is the urine sample after TpBPy. 2+ Extraction; curve D is the result of 10 μg·L⁻¹ spiking. ‒1 The urine sample was processed by TpBPy 2+ Extraction (1: mMP; 2: mEP; 3: miBP; 4: mBP; 5: mEHP; 6: mEOHP; 7: mEHHP). Detailed Implementation

[0020] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0021] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0022] It should be noted that, unless otherwise specified, the experimental methods described in the following implementation plan are all conventional methods, and the reagents and materials described are all commercially available unless otherwise specified.

[0023] like Figure 1 As shown, this invention provides a method for preparing a cationic covalent organic framework, which includes the following steps: 1) Take C 2. Symmetrical 5,5′-diamino-2,2′-bipyridine C 3. A symmetrical trialdehyde phloroglucinol was placed in a reaction vessel, and a mixed solvent of mesitylene / 1,4-dioxane was added. The mixture was stirred for 10-50 min, acetic acid was added, and the mixture was stirred for 10-30 min. Then the reaction vessel was placed in a high temperature environment of 110-130 °C to react and obtain a covalent organic framework. 2) Take a covalent organic framework, nitrobenzene, and 1,2-dibromoethane into a reaction vessel, stir, and reflux at 150-180 °C. After the reaction is completed, centrifuge to obtain a brownish-black solid, wash with acetone, and vacuum dry overnight to obtain a cationic covalent organic framework.

[0024] In another technical solution, in step 1), the molar ratio of 5,5′-diamino-2,2′-bipyridine to trialdehyde phloroglucinol is 1.5:1, the volume ratio of mesitylene to 1,4-dioxane in the mixed solvent is 1:1, the added volume of the mixed solvent is 10-30 times the mass of 5,5′-diamino-2,2′-bipyridine and trialdehyde phloroglucinol, the acetic acid concentration is 1-10 mol / L, and the added volume of acetic acid is 1-3 times the mass of 5,5′-diamino-2,2′-bipyridine and trialdehyde phloroglucinol.

[0025] In another technical solution, the covalent organic framework obtained in step 1) is further treated to remove impurities by washing with acetone, followed by Soxhlet extraction with methanol containing tetrahydrofuran to remove unreacted monomers, and vacuum drying.

[0026] In another technical solution, in step 2), the volume of nitrobenzene added is 40-80 times the mass of the covalent organic framework; the volume of 1,2-dibromoethane added is 4-8 times the mass of the covalent organic framework.

[0027] This invention provides a cationic covalent organic framework, which is prepared by the method described above.

[0028] like Figure 2 As shown, this invention provides the use of a cationic covalent organic framework for solid-phase extraction of phthalic acid monoester compounds in a sample to be analyzed.

[0029] In another technical solution, the phthalic acid monoester compounds include, but are not limited to, one or more of monomethyl phthalate, monoethyl phthalate, monobutyl phthalate, monoisobutyl phthalate, mono(2-ethylhexyl) phthalate, mono(2-ethyl-5-oxohexyl) phthalate, and mono(2-ethyl-5-hydroxyhexyl) phthalate.

[0030] In another technical solution, the sample to be analyzed is urine.

[0031] This invention provides a method for analyzing phthalic acid monoesters in human urine using a cationic covalent organic framework, comprising the following steps: A) Adjust the pH of the urine sample to be analyzed to 5.5-6.5, shake for 1-5 min, add the complex enzyme of β-glucuronidase and arylsulfatase, shake for 1-5 min, place in a 35-40 ℃ water bath for hydrolysis overnight, cool to room temperature, and obtain the extract to be extracted. B) Place the cationic covalent organic framework in a reaction vessel, add the urine sample to be analyzed treated in step A), disperse by ultrasonication, place in a cyclotron for solid-phase extraction, centrifuge, remove the supernatant, and obtain the solid-phase extract; C) Add methanol solvent containing ammonia to the solid extract for desorption, centrifuge, collect the supernatant and dry it with N2 to obtain the solid to be analyzed; D) The analytical solid was redissolved in an aqueous solution containing methanol, mixed, filtered through a pinhole membrane, and then analyzed by ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS / MS).

[0032] In another technical solution, in step A), the pH of the sample solution to be analyzed is adjusted with glacial acetic acid.

[0033] <Experiment Content> 1.1 Test Materials Trialdehyde phloroglucinol (Tp) and 5,5′-diamino-2,2′-bipyridine (BPy) were purchased from Jilin Zhongke Science & Technology Co., Ltd.; 1,2-dibromoethane, mesitylene, 1,4-dioxane, acetone, tetrahydrofuran (THF), methanol, acetonitrile, acetic acid, nitrobenzene, and ammonia were purchased from Shanghai Chemical Reagent Co., Ltd. of Sinopharm Group. All reagents were of analytical grade. Methanol (HPLC grade) and formic acid (HPLC grade) were purchased from Fisher Scientific, USA; β-glucuronidase (>100,000 units / mL) and arylsulfatase (<20,000 units / mL) complex enzymes, and standards of monomethyl phthalate (mMP), monoethyl phthalate (mEP), monobutyl phthalate (mBP), monoisobutyl phthalate (miBP), mono(2-ethylhexyl) phthalate (mEHP), mono(2-ethyl-5-oxohexyl) phthalate (mEOHP), and mono(2-ethyl-5-hydroxyhexyl) phthalate (mEHHP) were purchased from Shanghai Anpu Experimental Technology Co., Ltd.; the test water was ultrapure water prepared by the Millipore pure water system.

[0034] Urine samples were collected from 10 individuals working in environments with high concentrations of PAEs (polyacrylamide emulsions) as the exposure group, and urine samples were collected from 4 individuals working in environments without high concentrations of PAEs as the control group. The urine pH was adjusted to approximately 6 with glacial acetic acid and shaken for 1 min. Then, 30 μL of a complex enzyme of β-glucuronidase and arylsulfatase was added and shaken for 1 min. The mixture was then placed in a 37 ℃ water bath for hydrolysis overnight, cooled to room temperature, and ready for extraction and analysis.

[0035] 1.2 Testing and Characterization Methods Powder X-ray diffraction (PXRD, D8 ADVANCE) determines the crystal form of materials; Fourier transform infrared spectroscopy (FT-IR, Spectrum Two) and X-ray photoelectron spectroscopy (XPS, K-Alpha) are used to determine the crystal form of materials. +The composition and chemical structure of the material were identified; N2 adsorption-desorption experiments were performed on a multi-purpose gas adsorption analyzer (3-Flex, 77 K), and the specific surface area and pore size distribution of the material were calculated using the Brunauer-Emmett-Teller (BET) model and density functional theory (DFT), respectively; the morphology of the material was characterized by field emission scanning electron microscopy (SEM, Ultra55); and a thermal comprehensive analyzer (TGA, TGA / DSC 3) was used. + The following instruments were used to determine the thermal stability of the material: a Zeta potential analyzer (Nano ZS-90) to determine the surface charge properties of the material; and a water contact angle meter (Dataphysics OCA15EC) to determine the hydrophilicity of the material.

[0036] 1.3, TpBPy 2+ Preparation Weigh Tp (0.3 mmol, 63.0 mg) and BPy (0.45 mmol, 83.7 mg) into a 25 mL reaction vessel, add 3.0 mL of a 1:1 mixture of mesitylene / 1,4-dioxane (v / v), stir magnetically for 30 min, and then add 0.3 mL of a 6 mol·L⁻¹ solution. ‒1 Acetic acid was added, and the mixture was magnetically stirred for 15 min. The reactor was then placed in an oven at 120 °C and reacted for 72 h. The resulting brownish-red powder was washed five times with acetone, and then further washed with Soxhlet extract of methanol containing 10% THF for 24 h to remove unreacted monomers. The powder was then vacuum dried overnight at 80 °C to obtain TpBPy.

[0037] Quaternization of the bipyridine structure in TpBPy was performed using 1,2-dibromoethane. 80 mg of TpBPy was weighed into a round-bottom flask, and 4.5 mL of nitrobenzene and 0.5 mL of 1,2-dibromoethane were added. The mixture was magnetically stirred and refluxed at 160 °C for 24 h. After the reaction, the resulting brownish-black solid was centrifuged, washed five times with acetone, and dried under vacuum at 80 °C overnight to obtain cationic TpBPy. 2+ .

[0038] 1.4 Solid-phase extraction process The solid-phase extraction process for the seven mPAEs in standard solutions or urine samples is as follows: Weigh 4.0 mg TpBPy 2+ Add 10 mL of mPAEs extraction buffer (using 0.1 mol·L⁻¹) to a 25 mL round-bottom centrifuge tube. ‒1Adjust the pH to 6 with HCl and sonicate for several seconds to ensure uniform dispersion of the adsorbent. Extract in a cyclotron for 10 min. After centrifugation and discarding the extract, add 5 mL of methanol solvent containing 1.5% ammonia for desorption. Centrifuge, collect the eluent, and dry with N2. Redissolve the analyte in 200 μL of methanol / water (v / v, 2:8) mixture, filter through a 0.22 μm pinhole membrane, and analyze by ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS / MS).

[0039] 1.5 UPLC-MS / MS Analysis The chromatographic system used was a Waters Acquity ultra-high performance liquid chromatograph equipped with a SCIEX triple quadrupole mass spectrometer, and the mass spectrometry system was a Qtrap 6500 tandem mass spectrometer. Separation was performed using a Waters BEH column (3.0 × 150 mm, 1.7 μm) at a flow rate of 300 μL·min. ‒1 The injection volume was 2 μL, and detection was performed using an electrospray ionization (ESI) source in negative ion mode. Mobile phase A was an aqueous phase containing 1% formic acid, and mobile phase B was methanol. A gradient elution method was used: A: 0–1 min, 90%; 1–14.5 min, 90%–15%; 14.5–16.5 min, 15%–90%; 16.5–20 min, 90%. The chromatographic and mass spectrometric detection parameters of the seven mPAE target analytes are shown in Table 1.

[0040] Table 1. Detection parameters of 7 mPAEs analytes <Experimental Results> 2.1 TpBPy 2+ The representation 2.1.1 TpBPy 2+ Crystal form In terms of appearance, TpBPy is a brownish-red powder. The cationic TpBPy... 2+ It turns into a brownish-black powder. (TpBPy) 2+ The polycrystalline structure was characterized by PXRD. Figure 3 It can be seen that TpBPy and TpBPy 2+ The shape of the PXRD spectrum is similar to the standard spectrum of TpBPy, Material 2 θ The strong diffraction peak at 3.5° corresponds to the (1,0,0) crystal plane. θ The weak diffraction peak at 6.1° corresponds to the (2,‒1,0) crystal plane. θ The broad peak at 26.6° corresponds to the (0,0,1) crystal plane, which is mainly caused by the π–π stacking effect between material layers. (TpBPy) 2+The intensity of the main diffraction peak was not significantly reduced compared to TpBPy, indicating that cation functionalization does not affect the TpBPy effect. 2+ The ordered stacking topology has a significant impact, and the material still retains a relatively complete crystal form.

[0041] 2.1.2 TpBPy 2+ Structure TpBPy confirmed via FT-IR 2+ Chemical composition and structure ( Figure 4 The strong C=O stretching vibration of the aldehyde monomer Tp and the N–H stretching vibration of the amino monomer BPy are at 1643 cm⁻¹. ‒1 and 3204-3324 cm ‒1 In TpBPy and TpBPy 2+ The absence of characteristic peaks for these two groups in the spectrum indicates that the aldehyde and amino groups are synthesized via a Schiff base reaction. (TpBPy and TpBPy) 2+ Located at 1607, 1578, 1261 cm ‒1 The strong stretching vibration peaks correspond to C=O, C=C, and C–N bonds, respectively, indicating that the material has undergone a configurational transformation from an enol form to the more stable β-ketoenamine configuration. (TpBPy) 2+ At 2984 and 2881 cm ‒1 A weak C–H bond stretching vibration peak was observed, while no C–H bond stretching vibration signal was found in the FT-IR spectrum of TpBPy. This indicates that 1,2-dibromoethane undergoes a cyclization reaction with the bipyridine structure of TpBPy, achieving cationic functionalization.

[0042] To further confirm TpBPy 2+ Cationicization was successfully achieved, and the composition of the material was characterized using XPS. It consists of TpBPy and TpBPy... 2+ XPS full spectrum ( Figure 5 -a Figure 5 -b) It can be seen that TpBPy contains C, N, and O elements, while TpBPy 2+ The presence of C, N, O, and Br elements indicates that 1,2-dibromoethane underwent a cyclization reaction with the bipyridine structure of TpBPy. (The text abruptly ends here, likely due to an incomplete sentence or missing information.) 2+ Br 3d high-resolution XPS image ( Figure 5 -c) indicates that the Br element is represented by Br ‒ It exists in two forms: (67.0 and 68.0 eV) and alkylated C–Br bonds (70.1 and 71.2 eV), and as the counterion Br of the quaternary ammonium salt. ‒ The form is the primary indicator, thus proving that CH-COF was successfully cationized. Figure 5 -d and Figure 5 -e represents TpBPy and TpBPy respectively. 2+ The N 1s high-resolution XPS image shows that the N element in TpBPy exists in both imine and pyridine forms, indicating that the connection mode of TpBPy is a topological structure formed by the Schiff base reaction between the aldehyde group of Tp and the amino group of BPy to form an imine bond. Because TpBPy 2+ The skeletal structure remained unchanged; therefore, nitrogen exists in both imine and pyridine forms. Furthermore, TpBPy 2+ The presence of quaternary ammonium salts at 402.0 eV further confirms the presence of TpBPy. 2+ Positively charged. TpBPy 2+ Positive charge is advantageous for the specific adsorption of negatively charged mPAEs in solid-phase extraction via electrostatic interactions.

[0043] 2.1.3 TpBPy 2+ Porous properties Figure 6 -a and 6-b are TpBPy 2+ The N2 adsorption-desorption isotherms and pore size distribution curves are shown. The N2 adsorption-desorption isotherms exhibit the characteristics of a Type I isotherm, with a rapid increase in N2 adsorption in the relatively low-pressure region, indicating that TpBPy 2+ It is a microporous material; the pore size calculated by the DFT model is mainly concentrated at 1.1 nm, indicating that its pore size falls within the microporous range. Thanks to its complete crystal structure, TpBPy... 2+ It has a high BET specific surface area (293.5 m²). 2 ·g ‒1 It can be used as a solid-phase extraction material for the enrichment of target analytes.

[0044] 2.1.4 TpBPy 2+ morphology SEM image of TpBPy ( Figure 7 -a) It can be seen that TpBPy exhibits an interwoven filamentous morphology and aggregates together to form a fluffy, sponge-like structure. TpBPy 2+ ( Figure 7 The surface morphology of -b) is similar to that of TpBPy, indicating that cation functionalization has almost no effect on the morphology. Elemental distribution diagram ( Figure 7 -c) clearly shows that C, N, and O elements are uniformly distributed in the framework of TpBPy. 2+ Composed of C, N, O, and Br elements ( Figure 7 -d), which is consistent with the results of XPS characterization, indicating that the reaction of 1,2-dibromoethane with bipyridine in the TpBPy skeleton successfully achieved cationic functionalization.

[0045] 2.1.5 TpBPy 2+ thermal stability Thermogravimetric analysis characterizes the thermal stability of materials. Figure 8 -a). TpBPy does not decompose below 400 °C, indicating that the material has excellent thermal stability. TpBPy 2+ There are two weight loss stages. The first stage (180–350 °C) results from the decomposition of the cyclized bipyridine moiety, and the second stage (>400 °C) is due to the decomposition of the material. The weight loss rate in the first stage indicates the composition of the prepared TpBPy. 2+ The cyclopyridine moiety accounts for approximately 15.6%.

[0046] 2.1.6 TpBPy 2+ The charge like Figure 8 As shown in -b, the Zeta potential of TpBPy is ‒7.8 mV. After the cyclization reaction with 1,2-dibromoethane, TpBPy... 2+ The Zeta potential changed to 17.9 mV, proving that TpBPy 2+ Cation was successfully achieved. Compared to the negatively charged TpBPy, the positively charged TpBPy... 2+ It is more advantageous to adsorb negatively charged mPAEs analytes by electrostatic attraction.

[0047] 2.1.7 TpBPy 2+ hydrophilicity The hydrophilicity of the material is determined by the water contact angle test. Figure 9 The water contact angle of TpBPy is 52.3°. (This refers to TpBPy that has undergone cation functionalization.) 2+ It becomes a more hydrophilic material because its water contact angle decreases to 21.6°. Dispersive solid-phase extraction is generally carried out in aqueous solution. A hydrophilic adsorbent can be uniformly dispersed in the analyte sample solution, thereby accelerating the adsorption rate and reaching adsorption equilibrium in a shorter time.

[0048] 2.1.8 TpBPy 2+ Optimization of mPAE extraction conditions In order to make TpBPy 2+ The best extraction performance was achieved for seven mPAEs (mMP, mEP, mBP, miBP, mEHP, mEOHP, and mEHHP) by optimizing conditions such as extractant pH, adsorbent dosage, extraction time, and desorption solvent. The concentration of the mixed standard solution of the seven mPAEs was 5 μg·L⁻¹. ‒1 The volume of the extract is 10 mL.

[0049] The pH of the extraction solution affects the surface charge properties of the material and the degree of dissociation of mPAEs in solution; therefore, the acidity of the extraction solution has a significant impact on the extraction efficiency. Optimization was performed within a pH range of 2–10 for the mPAEs solution, and the results are as follows: Figure 10 As shown in -a, the extraction recoveries of the seven mPAEs reached their optimum at pH 6. The pH values ​​of the seven mPAEs... K a The value is 3.32–3.38, and the pH of the extraction solution is less than p. K a A pH that is too high is unfavorable for the formation of mPAEs anions, and a pH that is too high in the extraction solution will affect TpBPy. 2+ The positive charge of the quaternary ammonium salt moiety. In summary, TpBPy is present at an extraction solution pH of 6. 2+ The highest extraction efficiency can be achieved with mPAEs through electrostatic attraction.

[0050] like Figure 10 -b shows that, with TpBPy 2+ Increasing the dosage from 1 mg to 4 mg gradually increased the extraction recoveries of mMP, mEP, mBP, miBP, mEHP, mEOHP, and mEHHP, as the increased material dosage provided more adsorption sites for the target analytes. Once extraction reached saturation, further increasing the material dosage did not improve the recovery rate. Therefore, 4 mg TpBPy was selected. 2+ Further experiments will be conducted.

[0051] The effect of extraction time on extraction recovery was investigated within the range of 2–25 min. Figure 10 -c). With increasing extraction time, the extraction recoveries of the seven mPAEs increased rapidly and reached extraction equilibrium within 10 min. Due to TpBPy 2+ It has a large specific surface area and porous structure, thus enabling it to quickly adsorb target substances.

[0052] The type of desorption solvent determines the extent to which the target analyte is desorbed from the adsorbent, thus affecting the extraction recovery rate. Therefore, we investigated the effects of methanol and acetonitrile on the extraction recovery rate. Figure 10 -d). For miBP and mEHP, the effects of using methanol and acetonitrile as desorption solvents were similar. However, for the other five mPAEs, the extraction recovery rate using methanol as the desorption solvent was higher than that using acetonitrile. This may be because methanol is a protic solvent, which can form hydrogen bonds with the target mPAEs, thereby improving desorption efficiency. (The text abruptly ends here, likely due to an incomplete sentence or a missing section.) 2+ Desorption of mPAEs requires weakening TpBPy 2+The electrostatic attraction between the ammonia and mPAEs means that alkaline conditions are beneficial for improving desorption efficiency. Adding ammonia to methanol or acetonitrile results in higher extraction efficiency than using pure methanol or pure acetonitrile as the desorption solvent, with the best extraction effect achieved at an ammonia mass fraction of 1.5%. Finally, methanol containing 1.5% ammonia was selected as the desorption solvent.

[0053] 2.1.9 Evaluation of Analytical Methods Under optimal dispersion solid-phase extraction conditions, with TpBPy 2+ The evaluation indicators for the analytical method of adsorbent-based UPLC-MS / MS detection of mMP, mEP, mBP, miBP, mEHP, mEOHP, and mEHHP are shown in Table 2. The seven target analytes exhibited wide linear ranges and good linear relationships within these ranges. r >0.99). The limit of detection (LOD) based on a 3x signal-to-noise ratio is 0.0030–0.0082 μg·L⁻¹. ‒1 The limit of quantitation (LOQ) based on a 10-fold signal-to-noise ratio is 0.035–0.16 μg·L⁻¹. ‒1 The concentration of mPAEs in human urine under normal exposure conditions is μg·L⁻¹. ‒1 The analytical method established meets the requirements of actual urine sample analysis because it is at a suitable level. (Using 5 μg·L⁻¹) ‒1 The relative standard deviation (RSD) of the seven mPAEs mixed standard solutions was 2.9–5.3% after three repeated determinations, demonstrating that the method has good reproducibility.

[0054] Table 2 TpBPy 2+ Evaluation of analytical methods for the detection of seven mPAEs by extraction combined with UPLC-MS / MS. 2.1.10 Human urine sample analysis To investigate the effects of environmental PAE concentrations on the population, we collected 10 urine samples from individuals working in high-concentration PAE environments as the exposure group and 4 urine samples from individuals working in non-PAE environments as the control group. We used the established TpBPy... 2+The contents of seven metabolites of PAEs (mPAEs) – mMP, mEP, mBP, miBP, mEHP, mEOHP, and mEHHP – in 14 urine samples were determined by solid-phase extraction combined with UPLC-MS / MS. The results are detailed in Table 3. Except for a few urine samples in the exposure and control groups where mEHP was undetectable, the other six mPAEs were detected in all urine samples. The average contents of mMP, mEP, mBP, miBP, mEHP, mEOHP, and mEHHP in the exposure group were 7.00, 15.3, 143.8, 36.3, 5.03, 5.17, and 10.29 μg·L, respectively. ‒1 The average contents of mMP, mEP, mBP, miBP, mEHP, mEOHP, and mEHHP in the control group were 4.04, 4.45, 67.8, 14.5, 6.52, 4.01, and 4.96 μg·L, respectively. ‒1 The average levels of mMP, mEP, mBP, miBP, and mEHHP in the exposure group were significantly higher than those in the control group, and can serve as biomarkers for PAEs. However, the average levels of mEHP and mEOHP did not differ significantly between the exposure and control groups. The total content of the seven mPAEs in the four control group urine samples was 7.26–23.3 μg·L. ‒1 The total content of the seven mPAEs in the urine samples of the 10 exposed groups was 4.54–89.5 μg·L. ‒1 The total concentrations of the seven mPAEs varied considerably among the exposed groups. This may be because the concentration of metabolites in the human body is related not only to the concentration of the parent pollutant in the exposed environment, but also to the absorption rate and individual differences.

[0055] Table 3-1 Content of four mPAEs in urine samples from the exposed group and the control group (n=3) Table 3-2 Content of three mPAEs in urine samples from the exposed group and the control group (n=3) Figure 11 This is a chromatogram of the seven mPAEs detected in human urine samples using the established analytical method. The urine samples were not subjected to TpBPy testing. 2+ Extraction (line b) showed that direct injection failed to detect the target analyte, but after TpBPy... 2+ After extraction (line c), all seven target analytes were detected. This indicates that TpBPy 2+ It can efficiently enrich trace amounts of mPAEs in samples, and after solid-phase extraction, it can improve the sensitivity of analytical methods.

[0056] To evaluate the accuracy of the established analytical method, we conducted a spiked recovery test using urine samples at three spiking levels (high, medium, and low). One urine sample each was used in the exposure group and the control group. The results are shown in Table 4. The recoveries of the analytes mMP, mEP, mBP, miBP, mEHP, mEOHP, and mEHHP in the urine samples were 81.5%–101.8%, with relative standard deviations (RSDs) of 1.6%–6.5%. These results indicate that the analytical method has satisfactory accuracy and can be used for the accurate determination of the seven mPAEs in human urine samples.

[0057] Table 4 TpBPy 2+ Recovery rates of seven mPAEs in spiked urine were determined by extraction combined with UPLC-MS / MS (n=3). Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. The use of cationic covalent organic frameworks, characterized in that, The method for preparing the cationic covalent organic framework for solid-phase extraction of phthalic acid monoester compounds from an analyte sample includes the following steps: 1) Place 5,5′-diamino-2,2′-bipyridine and trialdehyde phloroglucinol in a reaction vessel, add a mixed solvent of mesitylene / 1,4-dioxane, stir for 10-50 min, add acetic acid, stir for 10-30 min, and then place the reaction vessel in an environment of 110-130 °C to react and obtain a covalent organic framework. 2) Take a covalent organic framework, nitrobenzene, and 1,2-dibromoethane into a reaction vessel, stir, and reflux at 150-180 °C. After the reaction is completed, centrifuge to obtain a brownish-black solid, wash with acetone, and vacuum dry overnight to obtain a cationic covalent organic framework.

2. The use of the cationic covalent organic framework according to claim 1, characterized in that, In step 1), the molar ratio of 5,5′-diamino-2,2′-bipyridine to trialdehyde phloroglucinol is 1.5:1, the volume ratio of mesitylene to 1,4-dioxane in the mixed solvent is 1:1, and the added volume of the mixed solvent is 10-30 times the mass of 5,5′-diamino-2,2′-bipyridine and trialdehyde phloroglucinol, with a volume-to-mass ratio of mL / g; the acetic acid concentration is 1-10 mol / L, and the added volume of acetic acid is 1-3 times the mass of 5,5′-diamino-2,2′-bipyridine and trialdehyde phloroglucinol, with a volume-to-mass ratio of mL / g.

3. The use of the cationic covalent organic framework according to claim 1, characterized in that, Step 1) The covalent organic framework obtained is further processed as follows: washed with acetone, then washed with methanol containing tetrahydrofuran to remove unreacted monomers, and then dried under vacuum.

4. The use of the cationic covalent organic framework according to claim 1, characterized in that, In step 2), the volume of nitrobenzene added is 40-80 times the mass of the covalent organic framework, with a volume-to-mass ratio of mL / g; the volume of 1,2-dibromoethane added is 4-8 times the mass of the covalent organic framework, with a volume-to-mass ratio of mL / g.

5. The use of the cationic covalent organic framework according to claim 1, characterized in that, Phthalic acid monoesters are one or more of the following: monomethyl phthalate, monoethyl phthalate, monobutyl phthalate, monoisobutyl phthalate, mono(2-ethylhexyl) phthalate, mono(2-ethyl-5-oxohexyl) phthalate, and mono(2-ethyl-5-hydroxyhexyl) phthalate.

6. The use of the cationic covalent organic framework according to claim 1, characterized in that, The sample to be analyzed was urine.

7. A method for analyzing phthalic acid monoesters in human urine using a cationic covalent organic framework, characterized in that, Includes the following steps: A) Adjust the pH of the urine sample to be analyzed to 5.5-6.5, shake for 1-5 min, add the complex enzyme of β-glucuronidase and arylsulfatase, shake for 1-5 min, place in a 35-40 ℃ water bath for hydrolysis overnight, cool to room temperature, and obtain the extract to be extracted. B) Place the cationic covalent organic framework of claim 1 in a reaction vessel, add the urine sample to be analyzed treated in step A), disperse by ultrasonication, place in a cyclotron for solid-phase extraction, centrifuge, remove the supernatant, and obtain the solid-phase extract; C) Add methanol solvent containing ammonia to the solid extract for desorption, centrifuge, collect the supernatant and dry it with N2 to obtain the solid to be analyzed; D) The solid to be analyzed is redissolved in an aqueous solution containing methanol, mixed, filtered through a pinhole filter membrane, and then analyzed by ultra-high performance liquid chromatography-tandem mass spectrometry.

8. The method for analyzing phthalic acid monoesters in human urine using the cationic covalent organic framework according to claim 7, characterized in that, In step A), the pH of the sample solution to be analyzed is adjusted with glacial acetic acid.

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