Facile synthesis of magnetic covalent organic framework nanobeads and application to magnetic solid-phase extraction of trace estrogens from human urine

Functionalized magnetic covalent organic frameworks with refining tunable cores for highly selective adsorption of immunosuppressive drugs

Immunosuppressant drugs (ISDs) are widely used in the treatment of organ rejection following human transplantation and in autoimmune diseases. Herein, this study demonstrates that carbonylated covalent organic frameworks (COFs) with pore-matching capabilities can serve as promising interference-resistant adsorbents for the rapid and efficient capture of ISDs (cyclosporin A (CsA), tacrolimus (FK-506), and rapamycin (RPM)) from complex whole blood matrices. Under optimized conditions, MCOF-2-COOH, with a pore size 1.5 times the diameter of the drug molecule, demonstrated superior ISDs adsorption performance, achieving an adsorption capacity of up to 84.95 mg g-1 in 10 min. Instrumental characterization and theoretical calculations elucidated the potential adsorption matrix, revealing that the COF provides multiple forces, including hydrogen bonding, electrostatics, and π-π interactions, with the carboxyl site playing a crucial role. This study provides both a theoretical basis and experimental evidence for the use of COF materials in the selective adsorption of drugs from complex matrices, as well as a strategy for designing functionally customized COFs for drug therapy monitoring applications.

Next-Generation Chromatography: Covalent Organic Frameworks in Biomedical Analysis

Chromatography, a cornerstone technique in analytical chemistry, continues to evolve with the emergence of novel stationary phases. Covalent organic frameworks (COFs) have garnered significant attention due to their unique properties and versatile applications. COFs, composed of covalently linked organic building blocks, exhibit high surface area, tunable porosity, and exceptional chemical stability. These attributes make them next-generation chromatographic techniques that leverage novel materials and methodologies to achieve significant improvements in separation efficiency, selectivity, speed, and/or sensitivity compared to traditional methods. COF stationary phases demonstrate remarkable selectivity for small molecules, peptides, proteins, and nucleic acids. Their use in drug discovery, metabolomics, proteomics, and clinical diagnostics is gaining momentum. In this review, we explored their synthesis strategies, emphasizing the design principles that enable tailoring of their physicochemical properties. Further, we discuss the immobilization of COFs onto solid supports, ensuring their compatibility with existing chromatographic systems. Furthermore, we highlighted case studies where COFs outperformed traditional stationary phases, improving sensitivity and resolution. We delve into the integration of COFs as stationary phases in biomedical analysis and explore various strategies for utilizing COFs as stationary phases in chromatographic separations.

Magnetic conjugated microporous polymer for rapid extraction and sensitive analysis of environmental endocrine disruptors in environmental waters and dairy products

BACKGROUND

Environmental endocrine disruptors (EEDs) are a class of new pollutants that are diffusely used in the medical industry and animal husbandry. In view of toxicity concerns, elevated levels of EEDs in the environment and food, which cause potential harm to human beings and ecosystems, must be monitored. Determination of EEDs contaminants to ensure environment and food safety has became a major concern worldwide, it is also a challenging task because of their trace level and probable matrices interference. Thus, developing rapid adsorption and efficient analysis methods for EEDs is apparently necessary.

RESULTS

A magnetic conjugated micro-porous polymer (Fe3O4@TbDt) was designed and synthesized, which was endowed with large specific surface area, rich functional groups and magnetic responsiveness. The material showed high extraction efficiency for EEDs via magnetic solid-phase extraction (MSPE). The quantum chemistry calculations showed the adsorption mechanism of Fe3O4@TbDt on EEDs mainly included electrostatic interactions, van der waals forces (N-H … π interaction, C-H … π interaction), and multiple hydrogen bonds. Finally, a trace analysis method for nine EEDs was established combined with HPLC-MS/MS under optimized MSPE conditions. The method showed a good linearity (R2 ≥ 0.996), low limits of detection (0.25-5.1 ng L-1), high precision (RSD of 1.1-8.2 %, n = 6). The applicability of this method was investigated by analyzing four water samples and two dairy products, and satisfactory recovery rates (82.1-100.7 %) were obtained. The proposed method showed the potential for the analysis of EEDs residues in food and environmental samples.

SIGNIFICANCE

The developed MSPE method based on conjugated micro-porous polymers (CMPs) is simple, green, and efficient compared to existing techniques. The application of CMPs provides a new idea for preparing versatile sample pre-treatment materials. What's more, this work has certain reference value for addressing of EEDs residues in the environment and food.

Ionic liquid-functionalized covalent organic frameworks on the surface of silica for online solid-phase extraction

A covalent organic framework (COF) was gown on porous silica with 1,3,5-tri(4-aminophenyl)benzene and 2,5-divinyl-1,4-phenyldiformaldehyde as monomers, and two ionic liquids were grafted to COF by a click reaction. The materials before and after the modification of ionic liquids were separately packed into solid-phase extraction columns (10 × 4.6 mm, i.d.), which were coupled with liquid chromatography to construct online analysis systems. The extraction mechanisms of polycyclic aromatic hydrocarbons, bisphenols, diphenylalkanes and benzoic acids were investigated on these materials. There were π-π, hydrogen-bond and electrostatic interactions on ionic liquid-functionalized sorbents. After the comparison among these materials, the best sorbent was used, and the analytical method was established and successfully applied to the detection of some estrogens from actual samples. For the analytical method, the detection limit was as low as 0.005 μg L-1, linear range was as wide as 0.017-10.0 μg L-1, and enrichment ratio was as high as 3635. The recoveries in actual samples were 70 %-129 %.

Solvent and monomer regulation synthesis of core-shelled magnetic β-cyclodextrin microporous organic network for efficient extraction of estrogens in biological samples prior to HPLC analysis

The abnormal estrogens levels in human body can cause many side effects and diseases, but the quantitative detection of the trace estrogens in complex biological samples still remains great challenge. Here we reported the fabrication of a novel core-shell structured magnetic cyclodextrin microporous organic network (Fe3O4@CD-MON) for rapid magnetic solid phase extraction (MSPE) of four estrogens in human serum and urine samples prior to HPLC-UV determination. The uniform spherical core-shell Fe3O4@CD-MONs was successfully regulated by altering the reactive monomers and solvents. The Fe3O4@CD-MONs owned high specific surface area, good hydrophobicity, large superparamagnetism, and abundant extraction sites for estrogens. Under optimal conditions, the proposed MSPE-HPLC-UV method provided wide linearity range (2.0-400 μg L-1), low limits of detection (0.5-1.0 μg L-1), large enrichment factors (183-198), less adsorbent consumption (3 mg), short extraction time (3 min), and good stability and reusability (at least 8 cycles). The established method had also been successfully applied to the enrichment and detection of four estrogens in serum and urine samples with a recovery of 88.4-105.1 % and a relative standard deviation of 1.0-5.9 %. This work confirmed the feasibility of solvent and monomer regulation synthesis of Fe3O4@CD-MON composites, and revealed the great prospects of magnetic CD-MONs for efficient enrichment of trace estrogens in complex biological samples.

Magnetic Covalent Organic Frameworks-Fundamentals and Applications in Analytical Chemistry

Magnetic covalent organic frameworks are new emerging materials which, besides many other applications, have found unique applications in analytical chemistry as separating media and adsorbents. They have outstanding features such as special morphology, chemical and thermal stability, high adsorption capacity, good magnetic response, high specific surface area, uniform pore size distribution, strong π-π interactions with analytes and high reusability that makes reported studies on their properties and applications increased in the recent years. After discussing the methods of synthesis of MCOFs with different geometries that cause their special physic-chemical properties, this review focuses on their high potential which has been exhibited in various applications in extraction and pre-concentration of different analytes such as organic compounds, heavy metal ions and biological samples. The article also highlights the applications of magnetic covalent organic frameworks in other chemical analysis such as adsorbent and being used in sensors.

The determination of 11 sulfonamide antibiotics in water and foods by developing a N-rich magnetic covalent organic framework combined with ultra-high performance liquid chromatography-tandem mass spectrometry

The concentration of antibiotic residues in water and animal-derived foods is low and the matrix is complex, and effective extraction of antibiotic residues in them is a key factor for accurate quantification. It is important to establish a rapid and effective method for the analytical determination of antibiotics in water and foods. In this study, a type of novel magnetic COF (Fe3O4@SiO2@PDE-TAPB-COF) was synthesized and characterized. Moreover, Fe3O4@SiO2@PDE-TAPB-COF combined with ultra-high performance liquid chromatography-tandem mass spectrometry was used to determine the 11 sulfonamide antibiotics (SAs) in water and food. The parameters including pH, adsorption amount, adsorption time, type of elution solvent and elution time were optimized. Under the optimal conditions, the standard curves of 11 SAs showed good linearity (R 2 > 0.999) in their respective concentration ranges and had lower detection and quantification limits. The spiked recoveries of the developed MSPE-UPLC-MS/MS method for the 11 SAs in water and foods were 74.3-107.2% and 75.1-102.5%, respectively. And the relative standard deviations (RSDs) were less than 9.56% (n = 7). The results indicated that the method can be used for the determination of SAs in foods and water with low detection limits and high sensitivity.

Membrane-protected magnetic covalent organic framework for efficient extraction of estrogens in dairy products

The presence of estrogens residues in dairy products is a growing concern due to their potential health risk. Herein, in this study, we have developed a membrane-protected magnetic solid-phase extraction (MP-MSPE) method that utilized a magnetic adsorbent (Fe3O4@COF-LZU1) with in-situ growth for the efficient extraction of estrone (E1), 17β-estradiol (E2), and estriol (E3). When combined with HPLC-FLD, this method allows for the efficient detection of estrogens in dairy products. The stability of the MP-MSPE was improved by the presence of a dialysis membrane, which remained a high extraction efficiency (90 %) even after ten reuse cycles. The hydrogen bonding, π-π interactions and pore size effect contribute to the excellent adsorption of three estrogens onto Fe3O4@COF-LZU1. Under optimal conditions, the method exhibits a low detection limit (0.01-0.15 μg L-1), wide linear range (0.1-800 μg L-1), and favorable recoveries (77.3 %-109.4 %) at three concentration levels (10, 50 and 100 μg L-1). This proposed method is characterized by its simplicity, high efficiency and eco-friendliness, making it a promising approach for extracting estrogens from dairy products.

Pretreatment and analysis techniques development of TKIs in biological samples for pharmacokinetic studies and therapeutic drug monitoring

Tyrosine kinase inhibitors (TKIs) have emerged as the first-line small molecule drugs in many cancer therapies, exerting their effects by impeding aberrant cell growth and proliferation through the modulation of tyrosine kinase-mediated signaling pathways. However, there exists a substantial inter-individual variability in the concentrations of certain TKIs and their metabolites, which may render patients with compromised immune function susceptible to diverse infections despite receiving theoretically efficacious anticancer treatments, alongside other potential side effects or adverse reactions. Therefore, an urgent need exists for an up-to-date review concerning the biological matrices relevant to bioanalysis and the sampling methods, clinical pharmacokinetics, and therapeutic drug monitoring of different TKIs. This paper provides a comprehensive overview of the advancements in pretreatment methods, such as protein precipitation (PPT), liquid-liquid extraction (LLE), solid-phase extraction (SPE), micro-SPE (μ-SPE), magnetic SPE (MSPE), and vortex-assisted dispersive SPE (VA-DSPE) achieved since 2017. It also highlights the latest analysis techniques such as newly developed high performance liquid chromatography (HPLC) and high-resolution mass spectrometry (HRMS) methods, capillary electrophoresis (CE), gas chromatography (GC), supercritical fluid chromatography (SFC) procedures, surface plasmon resonance (SPR) assays as well as novel nanoprobes-based biosensing techniques. In addition, a comparison is made between the advantages and disadvantages of different approaches while presenting critical challenges and prospects in pharmacokinetic studies and therapeutic drug monitoring.

Effective extraction and determination of 24 quinolones in water and egg samples using a novel magnetic covalent organic framework combined with UPLC-MS/MS

The excessive use of quinolones (QNs) has seriously threatened human health. In this study, a novel functionalized magnetic covalent organic framework Fe3O4@SiO2@Ah-COF was fabricated with biphenyl-3,3',5,5'-tetracarbaldehyde and hydrazine hydrate (85%) as monomers and was used as a magnetic solid-phase extraction (MSPE) absorbent for the determination of 24 QNs in water and egg samples through ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The extraction parameters of MSPE were optimized, including pH, adsorbent dosage, adsorption time, and eluent type. An effective and rapid detection method was then established, which showed good linearity (R2 ≥ 0.9990), low limits of detection (0.003-0.036 μg L-1) and low limits of quantitation (0.008-0.110 μg L-1) for QNs. The good recoveries of 24 QNs in water and egg samples were in the range of 70.3-106.1% and 70.4-119.7%, respectively, with relative standard deviations lower than 10% (n = 5). As a result, Fe3O4@SiO2@Ah-COF is a promising magnetic adsorbent, and the established method was successfully applied for the determination of 24 QNs in water and egg samples.

Recent progress in the synthesis and applications of covalent organic framework-based composites

Covalent organic frameworks (COFs) have historically been of interest to researchers in different areas due to their distinctive characteristics, including well-ordered pores, large specific surface area, and structural tunability. In the past few years, as COF synthesis techniques developed, COF-based composites fabricated by integrating COFs and other functional materials including various kinds of metal or metal oxide nanoparticles, ionic liquids, metal-organic frameworks, silica, polymers, enzymes and carbon nanomaterials have emerged as a novel kind of porous hybrid material. Herein, we first provide a thorough summary of advanced strategies for preparing COF-based composites; then, the emerging applications of COF-based composites in diverse fields due to their synergistic effects are systematically highlighted, including analytical chemistry (sensing, extraction, membrane separation, and chromatographic separation) and catalysis. Finally, the current challenges associated with future perspectives of COF-based composites are also briefly discussed to inspire the advancement of more COF-based composites with excellent properties.

Synthesis of a core-shell magnetic covalent organic framework for the enrichment and detection of aflatoxin in food using HPLC-MS/MS

A porous magnetic covalent organic framework, Fe3O4@TPBD-TPA (terephthalaldehyde (TPA) , N, N, N', N'-tetrakis(p-aminophenyl)-p-phenylenediamine (TPBD)), was synthesized using the Schiff base reaction under mild reaction conditions. This adsorbent exhibited excellent adsorption performance for aflatoxins. The adsorption capacity of Fe3O4@TPBD-TPA for aflatoxins ranged from 64.4 to 84.4 mg/g. A magnetic solid-phase extraction combined with high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method based on Fe3O4@TPBD-TPA was developed for the efficient determination of four types of aflatoxins in food samples (maize, maize oil, peanut, and peanut oil). The determination coefficients (R2) were ≥0.9972. The method exhibited detection limits ranging from 0.01 to 0.06 μg/kg and spiked recoveries of 80.0 to 113.1%. The intra-day and inter-day precision were less than 6.77%, indicating good repeatability. The adsorbent showed promising prospects for the efficient enrichment of trace amounts of aflatoxins in complex food matrices.

Advanced porous organic materials for sample preparation in pharmaceutical analysis

The development of novel sample preparation media plays a crucial role in pharmaceutical analysis. To facilitate the extraction and enrichment of pharmaceutical molecules in complex samples, various functionalized materials have been developed and prepared as adsorbents. Recently, some functionalized porous organic materials have become adsorbents for pharmaceutical analysis due to their unique properties of adsorption and recognition. These advanced porous organic materials, combined with consequent analytical techniques, have been successfully used for pharmaceutical analysis in complex samples such as environmental and biological samples. This review encapsulates the progress of advanced porous materials for pharmaceutical analysis including pesticides, antibiotics, chiral drugs, and other compounds in the past decade. In addition, we also address the limitations and future trends of these porous organic materials in pharmaceutical analysis.

Fabrication of magnetic magnesium oxide cleanup adsorbent for high-throughput pesticides residue analysis coupled with supercritical fluid chromatography-tandem mass spectrometry

A rapid and accurate analytical method was established for multiple pesticide residues in complex matrices based on magnetic dispersive solid phase extraction (d-SPE) and supercritical fluid chromatography-tandem mass spectrometry (SFC-MS/MS). To develop an efficient magnetic d-SPE method, magnetic adsorbent modified with magnesium oxide (Fe₃O₄-MgO) was prepared via layer-by-layer modification and used as cleanup adsorbent for removal of interferences that contain a large number of hydroxyl or carboxyl groups in the complex matrix. The obtained Fe₃O₄-MgO coupled with 3-(N,N-Diethylamino)-propyltrimethoxysilane (PSA) and octadecyl (C18) were used as d-SPE purification adsorbents and their dosages were systematically optimized with Paeoniae radix alba as the matrix model. Combined with SFC-MS/MS, rapid and accurate determination of 126 pesticide residues in the complex matrix was achieved. Further systematic method validation showed good linearity, satisfactory recovery, and wide applicability. The average recoveries of the pesticides at 20, 50, 80, and 200 μg kg^-1 were 110, 105, 108, and 109%, respectively. The proposed method was applied to complex medicinal and edible root plants, such as Puerariae lobate radix, Platycodonis radix, Polygonati odorati rhizoma, Glycyrrhizae radix, and Codonopsis radix. The average recoveries of the pesticides at 80 μg kg^-1 in these matrices were 106, 106, 105, 103, and 105%, respectively with an average relative standard deviation range of 8.24-10.2%. The results demonstrated the feasibility and wide matrix applicability of the proposed method, which is promising for pesticide residue analysis in complex samples.

Synthesis of a magnetic covalent organic framework for extraction and separation of ultraviolet filters in beverage samples

In this study, a novel magnetic covalent organic framework (Fe₃O₄@TAPB-BTT) was successfully synthesized under mild conditions. The prepared magnetic COF exhibited large surface area (876.3 m² g^-1), porous feature as well as sizeable π-conjugated network structure. Due to the above advantages, Fe₃O₄@TAPB-BTT showed good adsorptive performance for ultraviolet (UV) filters with adsorption capacities ranging from 80.8 to 120.1 mg g^-1. Then the adsorbent was applied to magnetic solid phase extraction (MSPE) of UV filters in beverage samples, followed by UHPLC-MS/MS analysis. The established method showed good accuracy, precision, and reproducibility with satisfactory recoveries (76.9-95.6 %), low limits of detection (0.001-0.15 µg/L), and low relative standard deviations (<9.8 %). Besides, the adsorbent can be reutilized at least ten times, demonstrating satisfactory reusability. This work provided an effective method for the analysis and determination of UV filters in drinks.

Composite materials based on covalent organic frameworks for multiple advanced applications

Covalent organic frameworks (COFs) stand for a class of emerging crystalline porous organic materials, which are ingeniously constructed with organic units through strong covalent bonds. Their excellent design capabilities, and uniform and tunable pore structure make them potential materials for various applications. With the continuous development of synthesis technique and nanoscience, COFs have been successfully combined with a variety of functional materials to form COFs-based composites with superior performance than individual components. This paper offers an overview of the development of different types of COFs-based composites reported so far, with particular focus on the applications of COFs-based composites. Moreover, the challenges and future development prospects of COFs-based composites are presented. We anticipate that the review will provide some inspiration for the further development of COFs-based composites.

Highly efficient nanocomposites based on molecularly imprinted magnetic covalent organic frameworks for selective extraction of bisphenol A from liquid matrices

Highly efficient nanocomposites, hydrophobic molecularly imprinted magnetic covalent organic frameworks (MI-MCOF), have been farbricated by a facile Schiff-base reaction. The MI-MCOF was based on terephthalaldehyde (TPA) and 1,3,5-tris(4-aminophenyl) benzene (TAPB) as functional monomer and crosslinker, anhydrous acetic acid as catalyst, bisphenol AF as dummy template, and NiFe₂O₄ as magnetic core. This organic framework significantly reduced the time consumption of conventional imprinted polymerization and avoided the use of traditional initiator and cross-linking agents. The synthesized MI-MCOF exhibited superior magnetic responsivity and affinity, as well as high selectivity and kinetics for bisphenol A (BPA) in water and urine samples. The equilibrium adsorption capacity (Q_e) of BPA on the MI-MCOF was 50.65 mg g^-1, which was 3-7-fold higher than of its three structural analogues. The imprinting factor of BPA reached up to 3.17, and the selective coefficients of three analogues were all > 2.0, evidencing the excellent selectivity of fabricated nanocomposites to BPA. Based on the MI-MCOF nanocomposites, the magnetic solid-phase extraction (MSPE), combined with HPLC and fluorescence detection (HPLC-FLD), offered superior analytical performance: wide linear range of 0.1-100 μg L^-1, high correlation coefficient of 0.9996, low limit of detection of 0.020 μg L^-1, good recoveries of 83.5-110%, and relative standard deviations (RSDs) of 0.5-5.7% in environmental water, beverage, and human urine samples. Consequently, the MI-MCOF-MSPE/HPLC-FLD method provides a good prospect in selective extraction of BPA from complex matrices while replacing traditional magnetic separation and adsorption materials.

Methacrylate bonded covalent organic framework monolithic column online coupling with high-performance liquid chromatography for analysis of trace estrogens in food

Covalent organic frameworks (COFs) are a burgeoning class of crystalline porous materials with unique properties and have been considered as a promising functional extraction medium in sample pretreatment. In this study, a new methacrylate-bonded COF (TpTh-MA) was well designed and synthesized via the aldehyde-amine condensation reaction, and the TpTh-MA was incorporated into poly (ethylene dimethacrylate) porous monolith by a facile polymerization reaction inside capillary to prepare a novel TpTh-MA monolithic column. The fabricated TpTh-MA monolithic column was characterized with scanning electron microscope, Fourier transform infrared spectrometer, X-ray diffraction, and N₂ adsorption-desorption experiments. Then, the homogeneous porous structure, good permeability and high mechanical stability of TpTh-MA monolithic column was used as separation and enrichment media of capillary microextraction, which was coupled with high-performance liquid chromatography fluorescence detection for online enrichment and analysis of trace estrogens. The main experimental parameters influencing the extraction efficiency were systematically investigated. The adsorption mechanism for three estrogens was also explored and discussed based on hydrophobic effect, π-π affinity and hydrogen bonding interaction, which contributed to its strong recognition affinity to target compounds. The enrichment factors of the TpTh-MA monolithic column micro extraction method for the three estrogens were 107-114, indicating a significant preconcentration ability. Under optimal conditions, a new online analysis method was developed and exhibited good sensitivity and wide linearity range of 0.25-100.0 µg·L^-1 with a coefficient of determination (R²) higher than 0.9990 and a low limit of detection with 0.05-0.07 µg·L^-1. The method was successfully applied for online analysis of three estrogens of milk and shrimp samples and the recoveries obtained from spiking experiments were in range of 81.4-113% and 77.9-111%, with the relative standard deviations of 2.6-7.9% and 2.1-8.3% (n = 5), respectively. The results revealed the great potential for the application of the COFs-bonded monolithic column in the field of sample pretreatment.

Recent advances and applications of magnetic covalent organic frameworks in food analysis

Recently, covalent organic frameworks (COFs) have been widely used to prepare magnetic adsorbents for food analysis due to their highly tunable porosity, large specific surface area, excellent chemical and thermal stability and large delocalised π-electron system. This review summarises the main types and preparation methods of magnetic COFs and their applications in food analysis for the detection of pesticide residues, veterinary drugs, endocrine-disrupting phenols and estrogens, plasticisers and other food contaminants. Furthermore, challenges and future outlook in the development of magnetic COFs for food analysis are discussed.

[Analysis of parabens in environmental water samples by covalent organic framework-based magnetic solid-phase extraction-high performance liquid chromatography]

Parabens are a class of antimicrobial preservatives that are widely used in cosmetics, pharmaceuticals, and food products because of their ease of production, antimicrobial effect, and low price. The widespread use of these parabens, poses potential risks to human health. Therefore, it is necessary to establish a simple and rapid method for the detection of parabens. The large number of substrate interferences in complex samples is an important factor affecting the sensitivity of analytical methods. Magnetic solid-phase extraction (MSPE) has received much attention because of its advantages of easy operation, short extraction time, small sample amount, low cost, and environmental friendliness. Covalent organic frameworks (COFs) with high crystallinity, high specific surface area, adjustable pore size, regular porosity, as well as high chemical and thermal stability are now widely used in separation and analysis. Therefore, a sample pretreatment method combining MSPE and COF for the analysis of parabens in complex matrices is very promising. A magnetic covalent organic framework, Fe₃O₄@TbBd, was successfully synthesized by the Schiff base reaction of 1,3,5-triformylbenzene (Tb) and benzidine (Bd) at room temperature using Fe₃O₄ nanoparticles as magnetic cores. Characterization by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD), vibrating sample magnetometer (VSM) measurements, etc. revealed that the magnetic COF has high magnetic responsiveness, as well as good thermal and chemical stability, which make it an ideal adsorbent for the MSPE of parabens. Some factors related to the extraction efficiency, including the amount of adsorbent, extraction time, pH, desorption solvent, desorption time, and number of desorption were systematically investigated. A method involving MSPE and high performance liquid chromatography-ultraviolet detection (HPLC-UV) based on the Fe₃O₄@TbBd was developed for the determination of four parabens (ethylparaben, propylparaben, butylparaben, and benzylparaben) in environmental water samples. Under the optimal extraction conditions, the method showed good linearities. The limits of detection and limits of quantification were 0.2-0.4 μg/L and 0.7-1.4 μg/L for the four analytes, respectively. The recoveries at three spiked levels were in the range of 86.1%-110.8% with intra-day and inter-day RSDs of less than 5.5% and 4.9%, respectively. The method was successfully applied to the determination of parabens in East Lake water, Yangtze water, and domestic wastewater. Ethyl paraben and propyl paraben were detected in domestic wastewater at the levels of 1.8 μg/L and 0.4 μg/L, respectively. The recoveries of the parabens at different spiked levels ranged from 80.7% to 117.5%, with RSDs of 0.2%-8.8%. The method has good potential for the determination of parabens in environmental water samples because of its operational simplicity, short extraction time, high sensitivity, and environmental friendliness.

Fabrication of Ce-doped DUT-52 as a sorbent for dispersive solid phase extraction of estrogens in human urine samples

A cerium (Ce)-doped metal-organic framework composite (Ce/DUT-52) was prepared by using a solvothermal method and was explored as a sorbent for dispersive solid phase extraction (DSPE) of three estrogens (α-estradiol, estrone, and hexestrol) in human urine samples. After doping with Ce(III), Ce/DUT-52 exhibited more attractive features involving a higher specific surface area (774.7 m² g^-1) and zeta potential (31.4 mV), which made it an efficient adsorbent for the separation and enrichment of estrogens. The factors influencing DSPE efficiency such as the adsorbent amount, extraction time, pH, NaCl concentration, elution solvent and elution volume were investigated in detail. Under the evaluated conditions, Ce/DUT-52 showed good reusability (n = 6, RSDs ≤ 4.8%). Notably, the cofunction of electrostatic interaction, hydrophobic interaction, hydrogen bonding and π-π interaction might play major roles between estrogens and Ce/DUT-52. Finally, coupled with high-performance liquid chromatography (HPLC), a fast and sensitive method was established, which provided low limits of detection (1.5-2.0 ng mL^-1), wide linear ranges (3-500 ng mL^-1) and satisfactory recoveries (79.8-96.1%). The results demonstrated that Ce/DUT-52 had excellent adsorption ability to the targets and the developed method provided an alternative strategy for the determination of trace estrogens or other compounds with similar chemical structures in urine samples.

A membrane solid-phase extraction method based on MIL-53-mixed-matrix membrane for the determination of estrogens and parabens: polyvinylidene difluoride membrane vs. polystyrene-block-polybutadiene membrane

In this work, MIL-53(Al), as an inorganic 'filler' component, was embedded in polyvinylidene difluoride (PVDF) and polystyrene-block-polybutadiene (SBS) matrices to prepare two mixed-matrix membranes (MMMs), using a simpler method than that previously reported. The PVDF and SBS membranes retained much of the properties of PVDF, SBS, and native MIL-53(Al). The prepared MMMs were then placed in a vortex-stirred sample solution to develop a membrane solid-phase extraction method to extract estrogens and parabens which were determined by high-performance liquid chromatography with fluorescence detection. The extraction efficiencies of the two membranes were compared, with the PVDF membrane exhibiting superior performance. In addition, the PVDF membrane was more free-standing and flexible, and its preparation method was also more facile and simple. The extraction conditions were optimized, and the analytical method showed low limits of detection (0.005-0.18 ng/mL), good linearity, and high accuracy, with recoveries ranging from 90.7 to 102.5%. As a result, this membrane solid-phase extraction method indicated its potential for application in aqueous sample pretreatment. For metal-organic framework based MMM used in this method, in addition to being durable, free-standing, mechanically stable, and possessing a large area, it should also exhibit high MOF incorporation, good flexibility, and appropriate thickness and weight.

Recent Advances in the Application of Covalent Organic Frameworks in Extraction: A Review

Covalent organic frameworks (COFs) are a class of emerging materials that are synthesized based on the covalent bonds between different building blocks. COFs possess unique attributes in terms of high porosity, tunable structure, ordered channels, easy modification, large surface area, and great physical and chemical stability. Due to these features, COFs have been extensively applied as adsorbents in various extraction modes. Enhanced extraction performance could be reached with modified COFs, where COFs are presented as composites with other materials including nanomaterials, carbon and its derivatives, silica, metal-organic frameworks, molecularly imprinted polymers, etc. This review article describes the recent advances, developments, and applications of COF-based materials being utilized as adsorbents in the extraction methods. The COFs, their properties, their synthesis approaches as well as their composite structures are reviewed. Most importantly, suggested mechanisms for the extraction of analyte(s) by COF-based materials are also discussed. Finally, the current challenges and future prospects of COF-based materials in extraction methods are summarized and considered in order to provide more insights into this field.

Portable and on-site electrochemical sensor based on surface molecularly imprinted magnetic covalent organic framework for the rapid detection of tetracycline in food

In this study, for the first time, surface molecularly imprinted magnetic covalent organic frameworks (Fe₃O₄@COFs@MIPs) were combined with disposable screen-printed electrode (SPE) to construct a portable and on-site electrochemical sensor for the rapid detection of tetracycline (TC). The Fe₃O₄@COFs@MIPs, which was prepared by layer-by-layer modification method, had good magnetism and excellent adsorption ability. With the help of disposable SPE, equipped with a magnet, the electrode modification process was simplified and the detection efficiency was improved. Under optimal conditions, the fabricated electrochemical sensor exhibited linearity ranging from 1 × 10^-10 to 1 × 10^-4 g mL^-1. It had good selectivity, excellent reproducibility, desirable stability and remarkable applicability. The fabricated sensor was successfully applied to detect TC in real samples with satisfactory recoveries (96.15-106.20%). The detection strategy separated the recognition and adsorption process from the electrochemical detection process, providing a design idea for the application of COFs in the construction of high-efficiency molecularly imprinted electrochemical sensors.

Construction of a magnetic covalent organic framework for magnetic solid-phase extraction of AFM1 and AFM2 in milk prior to quantification by LC-MS/MS

A magnetic covalent organic framework (M-COF) was designed and selected as sorbent for magnetic solid-phase extraction (MSPE) of AFM1 and AFM2 in milk, followed by LC-MS/MS analysis. The application of 2,5-Dihydroxy-1,4-benzenedicarboxaldehyde (Dt) and 4',5'-bis(4-aminophenyl)-[1,1':2',1″-terphenyl]-4,4″-diamine (BAPTPDA) as monomers endows M-COF excellent properties for adsorbing AFM1 and AFM2. The morphology, structure, stability, and magnetism of the Fe₃O₄@COF(BAPTPDA-Dt) were characterized by various techniques including scanning electron microscopy, transmission electron microscopy, FTIR, thermogravimetric analysis, and vibrating sample magnetometer. The Fe₃O₄ microspheres were covered by COF shells. Fe₃O₄@COF exhibited excellent magnetism and stability. Some parameters that may influence the adsorption efficiency of MSPE were also optimized, making the extraction process more effective, time-saving (about 3 min), and less organic-reagent-consuming (only 4 mL of acetonitrile required). It is noteworthy that the Fe₃O₄@COF(BAPTPDA-Dt) can be reutilized more than 8 times. The AFM1 and AFM2 were determined by LC-MS/MS. The LODs for AFM1 and AFM2 were in the range 0.0069 to 0.0078 μg kg^-1. A wide linearity range (0.01-100 μg kg^-1) with coefficients of determination (R²) ranging from 0.9998 to 0.9999 was obtained. The recoveries at four spiked concentrations (0.05, 0.5, 5, and 50 μg kg^-1) in the milk matrix ranged from 85.2 to 106.5%. The intraday RSDs and the interday RSDs were in the range 1.74-4.58% and 2.65-6.69%, respectively. The matrix effect (9.3% for AFM1 and 6.7% for AFM2) was also significantly lower than that observed in other work . Overall, the established method has provided a powerful tool for rapid pretreatment and sensitive determination of AFM1 and AFM2 in milk with negligible matrix effect, presenting important value in toxicant determination.

Magnetic nanoparticles covalently immobilizing epidermal growth factor receptor by SNAP-Tag protein as a platform for drug discovery

Magnetic nanoparticles (NPs) cloaked with cell membranes expressing high levels of the epidermal growth factor receptor (EGFR) have been used to screen for EGFR-targeting active compounds in traditional Chinese medicine (TCM) formulations. However, previous strategies involved physical immobilization of the biomaterials on the surface of the nanocarrier, resulting in highly unstable platforms since the biological materials could dislodge easily. Chemical bonding of biomaterials to the nanoparticles surface can improve the stability of the biomimetic platforms. In this study, membrane fragments from cells expressing SNAP-Tag-EGFR (ST-EGFR) were immobilized on the surface of magnetic NPs. The ST-EGFR magnetic cell membrane nanoparticles (ST-EGFR/MCMNs) showed greater stability, and higher binding capacity, selectivity adsorption of gefitinib after 7 days compared to the un-immobilized magnetic cell membrane nanoparticles (EGFR/MCMNs). The ST-EGFR/MCMNs were used to screen for the EGFR-targeting active compounds of Zanthoxyli Radix (ZR), and identified toddalolactone and nitidine chloride. The latter significantly inhibited the proliferation of EGFR-overexpressing cancer cells, and was more effective compared to gefitinib. This innovative technology can be used to rapidly screen for active compounds from complex extracts, and aid in drug discovery.

Analysis of aristolochic acid I in mouse serum and tissues by using magnetic solid-phase extraction and UHPLC-MS/MS

A method combining magnetic solid-phase extraction (MSPE) and ultra-high-pressure liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) was developed for the analysis of aristolochic acids I (AAI) in mouse serum and tissues. The magnetic covalent organic frameworks (MNP@COF)-based MSPE exhibited high adsorption capacity towards AAI (93.1 mg/g) in optimal conditions. After MSPE extraction, AAI was separated with C18 column using gradient elution and quantified (m/z 342.21 → 298.13) by UHPLC-MS/MS with monitor reaction monitoring (MRM) mode. This MSPE-based UHPLC-MS/MS method was validated with respected to lower limit of quantification (LLOQ), linearity, recovery, precision and accuracy of intra- and inter-day, and matrix effect. Good calibration linearities at the range of 1-500 ng/L for AAI in biological matrices (serum, kidney, and liver) with high correlation coefficient (R²) > 0.9970, and high enrichment factors (mean values from 1038 to 1045) were obtained. This method was highly sensitive to determine AAI with LLOQ within the range of 4.62-5.24 ng/L in extracted serum, kidney, and liver samples. Recoveries at 5, 50, 100 and 300 ng/L in biological samples ranged from 93.2 to 104.0%, and intra- and inter day accuracy and precision (defined as bias and coefficient of variation, respectively) were below ± 15%. The method was successfully applied in the analysis of biological samples collected from mice exposed with AAI with concentrations range of 0.007-0.041 μg/L for consecutive four days. The established method might be applied for the investigation of risk assessment and toxicity induced by long-time use of AAI-containing herbs or dietary supplements.

Recognition and Selectivity Analysis Monitoring of Multicomponent Steroid Estrogen Mixtures in Complex Systems Using a Group-Targeting Environmental Sensor

The same class of steroid estrogen mixtures, coexisting in the environment of 17β-estradiol, estrone (E1), and ethinyl estradiol (EE2), have strong ability to disrupt the human endocrine system and are seriously prejudicial to the health of the organism and environmental safety. Herein, a highly sensitive and group-targeting environmental monitoring sensor was fabricated for a comprehensive analysis of multicomponent steroid estrogens (multi-SEs) in complex systems. This breakthrough was based on the highly sensitive photoelectrochemical response composite material CdSe NPs-TiO₂ nanotube and highly group-specific aptamers. The optimized procedure exhibited not only high sensitivity in a wide range of concentrations from 0.1 to 50 nM, indeed, the minimum detection limit was 33 pM, but also strong resistance to interference. The affinity and consistent action pockets of this sensor enable selective detection of multi-SEs in complex systems. It subsequently was applied for the analysis of multi-SEs from three real samples in the environment including medical wastewater, river water, and tap water to provide a means to clarify the fate of multi-SEs in the process of migration and transformation. This monitoring sensor has a brilliant application prospect for the identification and monitoring of the same class of endocrine-disrupting chemical mixtures in environmental complex systems.

Nanoplatform-Integrated Miniaturized Solid-Phase Extraction Techniques: A Critical Review

Preparation of the biological samples is one of the most critical steps in sample analysis. In past decades, the liquid-liquid extraction technique has been used to extract the desired analytes from complex biological matrices. However, solid-phase extraction (SPE) gained popularity due to versatility, simplicity, selectivity, reproducibility, high sample recovery %, solvent economy, and time-saving nature. The superior extraction efficiency of SPE can be attributed to the development of advanced techniques, including the nanosorbents technology. The nanosorbent technology significantly simplified the sample preparation, improved the selectivity, diversified the application, and accelerated the sample analysis. This review critically expands on the to-date advancements reported in SPE with particular regards to the nanosorbent technology.

Covalent Organic Frameworks: Synthesis, Properties and Applications-An Overview

Covalent Organic Frameworks (COFs) are an exciting new class of microporous polymers with unprecedented properties in organic material chemistry. They are generally built from rigid, geometrically defined organic building blocks resulting in robust, covalently bonded crystalline networks that extend in two or three dimensions. By strategically combining monomers with specific structures and properties, synthesized COF materials can be fine-tuned and controlled at the atomic level, with unparalleled precision on intrapore chemical environment; moreover, the unusually high pore accessibility allows for easy post-synthetic pore wall modification after the COF is synthesized. Overall, COFs combine high, permanent porosity and surface area with high thermal and chemical stability, crystallinity and customizability, making them ideal candidates for a myriad of promising new solutions in a vast number of scientific fields, with widely varying applications such as gas adsorption and storage, pollutant removal, degradation and separation, advanced filtration, heterogeneous catalysis, chemical sensing, biomedical applications, energy storage and production and a vast array of optoelectronic solutions. This review attempts to give a brief insight on COF history, the overall strategies and techniques for rational COF synthesis and post-synthetic functionalization, as well as a glance at the exponentially growing field of COF research, summarizing their main properties and introducing the numerous technological and industrial state of the art applications, with noteworthy examples found in the literature.

Facile fabrication of magnetic covalent organic frameworks and their application in selective enrichment of polychlorinated naphthalenes from fine particulate matter

Magnetic covalent organic frameworks (Fe₃O₄@TPPCl₄) were synthesized via a one-pot process in which magnetic nanoparticles (Fe₃O₄@MNP) served as a magnetic core and 2,4,6-trihydroxy-1,3,5-benzenetricarbaldehyde (TP) and 2,2',5,5'-tetrachlorobenzidine (PCl₄) as two building blocks to form a shell. The as-prepared Fe₃O₄@TPPCl₄ nanoparticles have superior features, including large surface area (186.5 m² g^-1), high porosity, strong magnetic responsiveness (42.6 emu g^-1), high chlorine content, and outstanding thermal stability, which make them an ideal adsorbent for highly selective enrichment of polychlorinated naphthalenes (PCNs). Combining with atmospheric pressure gas chromatography tandem mass spectrometry (APGC-MS/MS), a simple analytical method of Fe₃O₄@TPPCl₄-based magnetic solid-phase extraction (MSPE)-APGC-MS/MS was developed, which exhibited good linearity (r ≥ 0.9991) for eight PCNs in the concentration range 0.1-100 ng L^-1. Moreover, low detection limits (0.005-0.325 ng L^-1), high enrichment factors (46.62-81.97-fold), and good relative standard deviations (RSDs) of inter-day (n = 3, 1.64 to 7.44%) and day-to-day (n = 3, 2.62 to 8.23%) were achieved. This method was successfully applied to the selective enrichment of PCNs in fine particulate matter (PM)_2.5 samples, and ultra-trace PCNs were found in the range 1.56-3.75 ng kg^-1 with satisfactory recoveries (93.11-105.81%). The successful application demonstrated the great potential of Fe₃O₄@TPPCl₄ nanoparticles as an adsorbent for enrichment of halogenated compounds. Schematic presented one-pot synthesis of magnetic covalent organic framework nanocomposites (Fe₃O₄@TPPCl₄) and their application in the selective enrichment of PCNs from PM_2.5 prior to APGC-MS/MS analysis.

Recent development of nanoparticle-assisted metabolites analysis with mass spectrometry

Metabolomics systematically studies the changes of metabolites in biological systems in the temporal or spatial dimensions. It is a challenging task for comprehensive analysis of metabolomics because of diverse physicochemical properties and wide concentration distribution of metabolites. Used as enrichment sorbents, chemoselective probes, chromatographic stationary phases, MS ionization matrix, nanomaterials play excellent roles in improving the selectivity, separation performance, detection sensitivity and identification efficiency of metabolites when mass spectrometry is employed as the detection technique. This review summarized the recent development of nanoparticle-assisted metabolites analysis in terms of assisting the pretreatment of biological samples, improving the separation performance and enhancing the MALDI-MS detection.

Preparation of sheet-like covalent organic frameworks and their application for efficient preconcentration of 4-(tert-octyl)-phenol and 4-nonylphenol in textiles

In the design of highly ordered (covalent organic frameworks) COFs with "ordered domains size and orientation" construction in a well-defined arrangement, the molecular monomers are the key factors. Here, the effect of molecular monomers on the construction of COFs has been studied, and two kinds of molecular monomers, i.e., ethanediamine (flexible amine ligand) and 4,4'-diaminobiphenyl (rigid amine ligand) have been used for developing sheet-like COFs-I and sheet-like COFs-II, respectively. Furthermore, they have been evaluated in the dispersive solid phase extraction (dSPE) procedure for textiles prior to the analysis of alkylphenol by liquid chromatography-tandem quadrupole mass spectrometry (LC-MS/MS). The results showed that, the optimal usage amount of sheet-like COFs-II used in the dSPE procedure was less than that of sheet-like COFs-I, which may be explained by much higher adsorption capacity of sheet-like COFs via hydrogen-bonding and π-π stacking interactions. Rectilinear calibration graphs were obtained for 4-(tert-octyl)-phenol (4-tOP) and 4-nonylphenol (4-NP) in the range 0.2-20 µg/kg with determination coefficient (r²) higher than 0.9990, and the limits of detection (LODs) of 4-tOP and 4-NP were 0.039 µg/kg and 0.048 µg/kg, respectively. The developed method has been successfully applied to analysis of 50 textile samples, in which 4-tOP and 4-NP were found in six samples with concentrations in the range of 1.6 μg/kg-20.9 μg/kg.

Covalent Organic Framework Composites: Synthesis and Analytical Applications

In the recent years, composite materials containing covalent organic frameworks (COFs) have raised increasing interest for analytical applications. To date, various synthesis techniques have emerged that allow for the preparation of crystalline and porous COF composites with various materials. Herein, we summarize the most common methods used to gain access to crystalline COF composites with magnetic nanoparticles, other oxide materials, graphene and graphene oxide, and metal nanoparticles. Additionally, some examples of stainless steel, polymer, and metal-organic framework composites are presented. Thereafter, we discuss the use of these composites for chromatographic separation, environmental remediation, and sensing.

Magnetic solid-phase extraction for speciation of mercury based on thiol and thioether-functionalized magnetic covalent organic frameworks nanocomposite synthesized at room temperature

A simple and practical magnetic solid-phase extraction high-performance liquid chromatography-inductively coupled plasma mass spectrometry (MSPE-HPLC-ICP-MS) method for extraction and determination of trace mercury species, including inorganic mercury (IHg), monomethylmercury (MeHg) and ethylmercury (EtHg), was developed. The MSPE adsorbent, urchin-like thiol and thioether-functionalized magnetic covalent organic frameworks (Fe₃O₄@COF-S-SH), was synthesized by coating covalent organic frameworks (COFs) on the surface of Fe₃O₄ nanoparticles at room temperature and then easily grafting 1,2-Ethanedithiol on the COFs. The as-prepared Fe₃O₄@COF-S-SH has strong adsorption capacity for IHg, MeHg and EtHg, with excellent static adsorption capacity: 571, 559 and 564 mg g^-1, respectively. The parameters influencing the extraction and enrichment had been optimized, including pH, adsorption and desorption time, composition and amount of the eluent, co-existing ions and dissolved organic materials etc. Under the optimized condition, the limit of detection (3δ) of the proposed method were 0.96, 0.17 and 0.47 ng L^-1 for IHg, MeHg and EtHg, and the developed method has high actual enrichment factors of 370, 395, 365-fold for IHg, MeHg and EtHg based on 200 mL samples, respectively. The high accuracy and reproducibility has been proved by the spiked recoveries (96.0‒108 %) in real water samples and determination of the certified reference material. Both the adsorption and desorption process can be completed within 5 min. The proposed method with simple operation, short pre-concentration time and high sensitivity has been successfully applied to mercury speciation at trace levels in the samples with complicated matrices, including underground water, surface water, sea water and fish samples.