Electro-enhanced solid-phase microextraction with covalent organic framework modified stainless steel fiber for efficient adsorption of bisphenol A

Covalent organic framework-based solid phase microextraction coupled with electrospray ionization mass spectrometry for the quantitative assessment of abnormal bile acids by triclosan exposure in mice

Bile acids, a representative diagnostic indicator of liver function, are used to visualize the extent of liver injury. Numerous studies have shown that triclosan (TCS) exposure leads to abnormal bile acid metabolism. As a result, there is a requirement to develop a fast and smart means to quantitatively monitor abnormal bile acids from exposure to triclosan in bio-sample. In this work, solid-phase microextraction (SPME) probes of sea urchin-like covalent organic frameworks (COF) were in situ synthesized on steel needles by using 1,3,5-tris(4-aminophenyl)benzene (TAPB) and 2,5-dimethoxybenzene-1,4-dicarboxaldehyde (DMTP) as two organic units and employed for extraction of bile acids. This TAPB-DMTP-COF-SPME possessed an excellent specified surface area (3351 m2 g-1) and a high regular porosity (∼3.6 nm), which was an ideal adsorbent to concentrate bile acids efficiently. The created probe, together with electrospray ionization mass spectrometry (ESI/MS), proved to be a fast and specific assay for the detection of bile acids in bio-samples. The proposed method had a low limitation of detection (0.03 μg L-1), good linearity (R2 ≥ 0.9931), wide linear range (0.10-1000.00 μg L-1) and excellent enrichment factor (63.60-252.00). Based on these excellent properties, it was successful application for the analyzing of bile acids in mice liver and feces, demonstrating the great potential of TAPB-DMTP-COF-SPME-ESI/MS in bile acids detection and liver injury diagnosis.

Electro-assisted solid-phase microextraction of Hg(II) in rice and water samples using NiCo-LDH-MXene fiber

Food and water contamination with heavy metals is still a significant public health issue, necessitating development of simple and rapid analytical methods. Herein, a novel electro-assisted solid-phase microextraction (EA-SPME) method was developed to determine mercury (Hg(II)) in rice and water samples. A novel SPME-fiber coating was prepared through electrosynthesis of NiCo-layered double hydroxide (NiCo-LDH) onto MXene deposited onto the graphenized pencil fiber. This EA-SPME-DPV method demonstrated good linearity (0.01 to 1.5 ng mL-1) and limits of detection and quantification (0.003 and 0.01 ng mL-1, respectively). Analytical performance of the EA-SPME-DPV method indicated that this method is cost-effective, rapid, and green, but also sensitive, selective, accurate, and repeatable, without significant matrix effects, making it suitable to determine Hg(II) in water and rice samples.

Covalent organic frameworks with nitrogen-rich triazine units and suitable pore size for highly efficient adsorption and sensitive detection of bisphenols in water

Herein, using 1,3,5-triformylphloroglucinol (Tp) and 4,4',4″-(1,3,5-triazine-2,4,6-triyl) tris(1,1'-biphenyl) trianiline (Ttba) as ligands, nitrogen-rich triazine unit-based covalent organic frameworks (COFs) with a suitable pore size, named TpTtba-COFs, were synthesized, and they were employed as adsorbents for the extraction and detection of three bisphenols (BPs)-BP A (BPA), BP B (BPB), and BP S (BPS)-in water. Using 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (Tapt) and 1,3,5-tris(4-aminophenyl)benzene (Tapb) ligands as substitutes for Ttba, nitrogen-rich triazine unit-based COFs with a smaller pore size and nitrogen-poor triazine unit-based COFs, named TpTapt-COFs and TpTapb-COFs, respectively, were also prepared for comparison. The adsorption performances of the three COF adsorbents with regard to the three BPs were tested. Owing to nitrogen-rich triazine units and a pore size suitable for BP adsorption, the maximum adsorption capacities of TpTtba-COFs for BPA, BPB, and BPS were 1.13, 1.33, and 1.37 times those of TpTapt-COFs and 2.10, 2.27, and 1.92 times those of TpTapb-COFs, respectively. The adsorption behavior and possible adsorption mechanism of the BPs on the TpTtba-COFs were also investigated. In addition, a TpTtba-COF-based dispersive solid-phase extraction-high-performance liquid chromatography/ultraviolet method exhibited an excellent linear range (1-800 ng/mL) and satisfactory limit of detection values (0.20-0.32 ng/mL) for the three BPs. The spiked recoveries of the three BPs in river and lake water ranged within 81.9%-101.9% and 82.8%-100.8%, respectively. Overall, this study offers valuable insights into the rational design of adsorbents for adsorption and sensitive detection of BPs in environmental water.

Chlorophenols in environment: Recent updates on pretreatment and analysis methods

Chlorophenols (CPs) are widely used in industries such as petrochemicals, insecticides, pharmaceuticals, synthetic dyes and wood preservatives. However, owing to the improper discharge and disposal, they have become major contaminants that are ubiquitously distributed in water, soil, and sewage sediments, posing a significant threat to ecosystems and human health. Consequently, accurate, sensitive and effective pretreatment and analysis methods for CPs are urgently required and have been actively explored in recent years. This review encompasses the pretreatment and detection methods for CPs in environmental samples from 2010 to 2024. The pretreatment methods for CPs primarily include solid-phase extraction, liquid-liquid extraction, solid-phase microextraction, liquid-phase microextraction, and QuEChERS. These methods are evolving towards more effective and environmentally friendly technologies, such as the miniaturization and automation of equipment, the development of innovative materials (including graphene, molecularly imprinted polymers, layered double hydroxides, porous organic polymers, and porous carbon), and the use of green solvents like deep eutectic solvents. Detection methods emphasize liquid chromatography-mass spectrometry, gas chromatography-mass spectrometry, sensors, and capillary electrophoresis. Advances in chromatographic columns, novel ion sources, and high-resolution mass spectrometry have significantly improved detection performance. In addition, the pros and cons of diverse techniques, critical comments and future perspectives are elaborated.

Preparation and evaluation of Fe3O4@C@NiCo-LDH@CDs composites for magnetic solid-phase extraction of trace endocrine disruptors

The widespread use of endocrine disruptors (EDPs) has certain potential hazards to organisms and environments, and it is particularly important to develop effective pretreatment methods before detection of EDPs in complex samples. In this work, a novel magnetic nanocomposite decorated with layered double hydroxides (LDHs) and carbon dots (CDs) was designed and prepared for magnetic solid-phase extraction (MSPE) of EDPs (bisphenol S, bisphenol F, bisphenol A, bisphenol AF, diethylstilbestrol and 4-cumylphenol) combined with high-performance liquid chromatography-ultraviolet (HPLC-UV) detection. The prepared composites were characterized by field emission scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS), and the adsorption mechanism towards these EDPs might be mainly based on hydrogen bonds and π-π conjugation. Under the optimized conditions, the proposed method showed limits of detection within 0.05-0.50 μg L-1 and limits of quantitation within 0.2-2.0 μg L-1, and good linearity (R2 ≥ 0.9975) was presented in the range of 0.2-200 μg L-1. Finally, the Fe3O4@C@NiCo-LDH@CDs composite-based MSPE-HPLC-UV method was applied for enrichment and determination of EDPs in water, milk, and tea beverage samples with recoveries in the range of 81.2-119.8% and relative standard deviations below 9.7%.

In-situ growth of a covalent organic framework-based matrix-compatible microextraction coating for sensitive extraction of multiple pesticides

The potential pesticide hazard to non-target organisms is a global concern. It is critical to develop the sensitive detection methods of multiple pesticides in various complex matrices. Here, benzene-1,3,5-tricarbaldehyde (BTCA) and 1,3,5-Tri (4-aminophenyl) benzene (TAPB) were employed as precursors for the in-situ growth of COFTAPB-BTCA on the surface of amino-functionalized stainless steel wire (SS) via a solvothermal method. The successful COFTAPB-BTCA bonded fiber exhibited significant enrichment capability of pyrethroids insecticides (PYs), organophosphorus (OPPs), and organochlorine (OCPs), with enrichment factors (EFs) ranging from 1133-7762, 1319-7291, and 734.1-2882, respectively. X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations indicated that various interactions contributed to its high enrichment capacity. Automated detection of PYs, OPPs, and OCPs in water, foods, and biological samples was realized by coupling this fiber with gas chromatography-mass spectrometry (GC-MS). The detection limits were as low as 0.0370-0.657 ng/L, 0.0128-0.400 ng/L, and 0.0329-0.202 ng/L for PYs, OPPs, and OCPs, respectively. In addition, the environmental risks of these samples were assessed based on the above data. This work not only provided a straightforward technique for sensitive monitoring of pesticides in complex matrices but also presented a novel approach for the in-situ controlled growth of versatile adsorbents with broad-spectrum properties.

Preparation of ionic porous polymers for extraction of four phenolic endocrine disrupting chemicals from fish and water samples

In this paper, series of ionic polymers were synthesized by crosslinking alkyl quaternary ammonium salts with 1,4-bis(chloromethyl)benzene. Among them, hyper-crosslinked polymer fabricated with dodecyl dimethyl benzyl ammonium chloride (HCP-DD) as monomer delivered superior adsorption performance for endocrine disrupting chemicals (EDCs). The adsorption mechanism mainly includes π-π stacking, hydrophobic and electrostatic interaction. With HCP-DD as solid phase extraction sorbent, a high performance liquid chromatography-diode array detection method was developed for the detection of four phenolic EDCs in water and fish samples. The detection limits of the method were 0.005-0.02 ng mL-1 for water samples and 3-30 ng g-1 for fish samples. The recoveries of EDCs in water samples and fish samples were 80-119% and 81.3-117% (relative standard deviations <4.4%), respectively. The study not only provides a route for preparation ionic porous polymers, but also highlights the applications of ionic polymers as efficient adsorbent to enrich organic pollutants.

Microwave-assisted esterification and electro-enhanced solid-phase microextraction of omega-3 polyunsaturated fatty acids in eggs

Omega-3 polyunsaturated fatty acids (ω-3 PUFAs), a type of fatty acid that has many health benefits, are of increasing concern. Herein, we developed a method for the rapid esterification and enrichment of ω-3 PUFAs in eggs, which includes microwave-assisted esterification (MAE) and electrically enhanced solid-phase microextraction (EE-SPME). Combined with gas chromatographic, efficient detection of ω-3 PUFAs was achieved in eggs. Under microwave radiation, the esterification efficiency exhibited a significant increase ranging from 5.06 to 10.65 times. The EE-SPME method reduced extraction time from 50 to 15 min. In addition, improvements in extractive fiber coating materials were explored, which ensured efficient extraction of ω-3 PUFAs. Under the optimal conditions, the method displayed a low detection limit (1.01-1.54 μg L-1), good recoveries (85.82%-106.01%), and wide linear range (7.5-1000 μg L-1), which was successfully applied to determine ω-3 PUFAs in real egg samples.

Thiocarbamide conversion-based nitrogen-rich covalent organic framework coatings for electro-enhanced solid-phase microextraction of bisphenols

Design and preparation of fiber coatings with excellent electrochemical performance and high polarity is significant for efficient extraction of polar targets in electro-enhanced solid-phase microextraction (EE-SPME). In this work, a combination strategy for structure regulation of covalent organic framework (COF) was proposed to fabricate a nitrogen-rich thiocarbamide linked COF coating (Thiocarbamide-TZ-DHTP) via molecular design and post-synthetic thiocarbamide conversion. The prepared COF coating possesses a large number of O, N, and S functional groups, which not only endow the coating with higher polarity but also significantly enhance its electrochemical performance. The COF coating was used for EE-SPME of polar bisphenols (BPs), demonstrating excellent enrichment efficiency and durability. Subsequently, coupled with gas chromatography-tandem mass spectrometry (GC-MS/MS), a sensitive method was developed for determination of trace BPs. The established method possess wide linear ranges (2.0-800.0 ng L-1), good correlation coefficients (0.9985-0.9994) and low detection limits (0.1-2.0 ng L-1). Moreover, the established method had been successfully applied to detection of trace BPs in tea beverage with satisfactory recoveries (81.6 % to 118.6 %). This research provides a feasible pathway for preparing COF coating with excellent electrochemical performance and high polarity for EE-SPME.

Electrospun nanofibers-based thin film microextraction for enrichment of phthalate esters in biodegradable plastics

In this work, a novel electrospun nanofiber (PAN/TpBD; 2,4,6-triformylphloroglucinol [Tp] and benzidine [BD]; polyacrylonitrile [PAN]) was fabricated via a facile electrospinning method and utilized as adsorbent in thin film microextraction (TFME) of phthalate esters (PAEs) (dimethyl phthalate, diethyl phthalate, diallyl phthalate, dibutyl phthalate, and dioctyl phthalate) in biodegradable plastics. The prepared PAN/TpBD combines the strong stability of nanofibers with increased exposure sites for covalent organic frameworks and enhanced interactions with the target, thus improving the enrichment effect on the target. The extraction efficiency of PAN/TpBD reached above 80%. Based on PAN/TpBD, a TFME-high-performance liquid chromatography method was established, and the experimental parameters were optimized. Under the optimal extraction conditions, the PAEs of this method varied linearly in the range of 10-10 000 µg/L with low detection limits (0.69-2.72 µg/L). The intra-day and inter-day relative standard deviation values of the PAEs were less than 8.04% and 8.73%, respectively. The adsorbent can achieve more than 80% recovery of the five targets after six times reuse. The developed method was successfully applied for the determination of trace PAEs in biodegradable plastics with recoveries ranging from 80.1% to 113.4% and relative standard deviations were less than 9.45%. The as-synthesized PAN/TpBD adsorbent exhibited great potential in PAE analysis.

Chiral-induced synthesis of chiral covalent organic frameworks core-shell microspheres for HPLC enantioseparation

Two chiral covalent organic frameworks (CCOFs) core-shell microspheres based on achiral organic precursors by chiral-induced synthesis strategy for HPLC enantioseparation are reported for the first time. Using n-hexane/isopropanol as mobile phase, various kinds of racemates were selected as analytes and separated on the CCOF-TpPa-1@SiO2 and CCOF-TpBD@SiO2-packed columns with a low column backpressure (3 ~ 9 bar). The fabricated two CCOFs@SiO2 chiral columns exhibited good separation performance towards various racemates with high column efficiency (e.g., 19,500 plates m-1 for (4-fluorophenyl)ethanol and 18,900 plates m-1 for 1-(4-chlorophenyl)ethanol) and good reproducibility. Some effects have been investigated such as the analyte mass and column temperature on the HPLC enantioseparation. Moreover, the chiral separation results of the CCOF-TpPa-1@SiO2 chiral column and the commercialized Chiralpak AD-H column show a good complementarity. This study demonstrates that the usage of chiral-induced synthesis strategy for preparing CCOFs core-shell microspheres as a novel stationary phase has a good application potential in HPLC.

In situ fabrication of covalent organic frameworks on solid-phase microextraction probes coupled with electrospray ionization mass spectrometry for enrichment and determination of androgens in biosamples

Solid-phase microextraction (SPME) coupled with electrospray ionization mass spectrometry (ESI-MS) was developed for rapid and sensitive determination of endogenous androgens. The SPME probe is coated with covalent organic frameworks (COFs) synthesized by reacting 1,3,5-tri(4-aminophenyl)benzene (TPB) with 2,5-dioctyloxybenzaldehyde (C8PDA). This COFs-SPME probe offers several advantages, including enhanced extraction efficiency and stability. The analytical method exhibited wide linearity (0.1-100.0 µg L-1), low limits of detection (0.03-0.07 µg L-1), high enrichment factors (37-154), and satisfactory relative standard deviations (RSDs) for both within one probe (4.0-14.8%) and between different probes (3.4-12.7%). These remarkable performance characteristics highlight the reliability and precision of the COFs-SPME-ESI-MS method. The developed method was successfully applied to detect five kinds of endogenous androgens in female serum samples, indicating that the developed analytical method has great potential for application in preliminary clinical diagnosis.

Recent progress of covalent organic frameworks as attractive materials for solid-phase microextraction: A review

Solid-phase microextraction (SPME) is a green, environmentally friendly, and efficient technique for sample pre-treatment. Covalent organic frameworks (COFs), a class of porous materials formed by covalent bonds, have gained prominence owing to their remarkable attributes, including large specific surface area, tunable pore size, and robust thermal/chemical stability. These characteristics have made COFs highly appealing as potential coatings for SPME fiber over the past decades. In this review, various methods used to prepare SPME coatings based on COFs are presented. These methods encompass physical adhesion, sol-gel processes, in situ growth, and chemical cross-linking strategies. In addition, the applications of COF-based SPME coating fibers for the preconcentration of various targets in environmental, food, and biological samples are summarized. Moreover, not only their advantages but also the challenges they pose in practical applications are highlighted. By shedding light on these aspects, this review aims to contribute to the continued development and utilization of COF materials in the field of sample pretreatment.

Fabrication of magnetic Fe3O4 doped β-cyclodextrin microporous organic network for the efficient extraction of endocrine disrupting chemicals from food takeaway boxes

Endocrine disrupting chemicals (EDCs) are a typical class of natural or man-made endogenous hormone agonists or antagonists that can directly or potentially interfere with human endocrine system. However, it is still difficult to analyze trace EDCs directly from complex environment and food matrices. Therefore, the proper sample pretreatment is highly desired and the preparation of efficient adsorbents is of great challenge and importance. Herein, we report the facile one-pot solvothermal synthesis of Fe3O4 nanoparticle doped magnetic β-cyclodextrin microporous organic network composites (MCD-MONs) for the magnetic solid phase extraction (MSPE) of four phenolic EDCs in water and food takeaway boxes prior to the high-performance liquid chromatography analysis. The sheet-like Fe3O4 doped MCD-MONs offered good magnetic property (16.5 emu g-1) and stability, and provided numerous hydrogen bonding, hydrophobic, π-π, and host-guest interaction sites for EDCs. Under the optimal experimental conditions, the established method was successfully verified with wide linear range (2.0-1000 µg L-1), low limits of detection (0.6-1.0 µg L-1), good precisions (intra-day and inter-day RSDs < 5.2 %, n = 3), large enrichment factors (88-98) and adsorption capacity (90.3-255.8 mg g-1), short extraction time (6 min), less adsorbent consumption (3 mg), and good reusability (at least 8 times) for EDCs. The proposed method was successfully applied to detect the trace EDCs in real samples with the recovery of 84.0-99.7 %. This work demonstrated the great potential of MCD-MONs for the efficient MSPE of trace EDCs from complex food takeaway boxes and water samples and uncovered the prospect of CD-based MONs in sample pretreatment.

Synthesis of cyano and ionic dual-functional hypercrosslinked porous polymer for effective adsorption and detection of endocrine disrupting chemicals in milk matrix

Endocrine disrupting chemicals (EDCs) can interfere with the normal function of endocrine system, posing serious risk to human health. The monitoring of EDCs in foods is of great importance to ensure food security. Herein, a cyano and ionic dual-functionalized hypercrosslinked porous polymer (CN-iHCP) was designed and prepared for the first time through hyper-crosslink of 1-(4-cyanophenyl)imidazole and 1,4-bis(chloromethyl)benzene. The adsorption mechanism mainly involves electrostatic interaction, hydrogen bonding and π-π stacking interaction. A sensitive analytical method for simultaneous detection of the four phenolic EDCs was established by coupled CN-iHCP based solid-phase extraction with high performance liquid chromatography. Under optimal conditions, the target EDCs exhibited good linearity with coefficient r > 0.993 and high enrichment factors of 164-243. The detection limits (S/N = 3) of EDCs were 0.20-0.50 ng mL-1 for milk sample. The extraction recoveries for the spiked milk samples were in the range of 85.5%- 116.0%. This work not only highlights the CN-iHCP as a promising adsorbent to efficiently enrich EDCs and other pollutants, but also provides a new strategy for the functionalization of HCP for wide applications.

Covalent organic frameworks: Pioneering remediation solutions for organic pollutants

Covalent Organic Frameworks (COFs) have emerged as a promising class of crystalline porous materials with customizable structures, high surface areas, and tunable functionalities. Their unique properties make them attractive candidates for addressing environmental contamination caused by pharmaceuticals, pesticides, industrial chemicals, persistent organic pollutants (POPs), and endocrine disruptors (EDCs). This review article provides a comprehensive overview of recent advancements and applications of COFs in removing and remedying various environmental contaminants. We delve into the synthesis, properties, and performance of COFs and their potential limitations and future prospects.

Applications of covalent organic frameworks for the elimination of dyes from wastewater: A state-of-the-arts review

Covalent organic frameworks (COFs) are class of porous coordination polymers made up of organic building blocks joined together by covalent bonding through thermodynamic and controlled reversible polymerization reactions. This review discussed versatile applications of COFs for remediation of wastewater containing dyes, emphasizing the advantages of both pristine and modified materials in adsorption, membrane separation, and advanced oxidations processes. The excellent performance of COFs towards adsorption and membrane filtration has been centered to their higher crystallinity and porosity, exhibiting exceptionally high surface area, pore size and pore volumes. Thus, they provide more active sites for trapping the dye molecules. On one hand, the photocatalytic performance of the COFs was attributed to their semiconducting properties, and when coupled with other functional semiconducting materials, they achieve good mechanical and thermal stabilities, positive light response, and narrow band gap, a typical characteristic of excellent photocatalysts. As such, COFs and their composites have demonstrated excellent potentialities for the elimination of the dyes.

Piperazine-linked metal covalent organic framework-coated fibers for efficient electro-enhanced solid-phase microextraction of chlorophenols

Conductive covalent organic frameworks (COFs) have received considerable attention and are critical in various applications such as electro-enhanced solid-phase microextraction (EE-SPME). In this work, a novel piperazine-linked copper-doped phthalocyanine metal covalent organic framework (CuPc-MCOF) was synthesized with good stability and high electrical conductivity. The synthesized CuPc-MCOF was then used as an EE-SPME coating material for extraction of five trace chlorophenols (CPs), including 2,4-dichlorophenol (2,4-DCP), 2,6-dichlorophenol (2,6-DCP), 2,4,6-trichlorophenol (2,4,6-TCP), 2,4,5-trichlorophenol (2,4,5-TCP) and 2,4,5,6-tetrachlorophenol (2,4,5,6-TCP), exhibiting excellent extraction performance because of various synergistic forces between CuPc-MCOF fibers and CPs. By combining EE-SPME with gas chromatography-tandem mass spectrometry (GC-MS/MS), a sensitive method for CPs detection was established with a low limit of detection (0.8-5 ng L^-1) and good reproducibility (RSD≤8.4%, n = 3). This method was then successfully applied to the analysis of trace CPs in real samples of seawater and seafood. Results showed that the developed CuPc-MCOF coating material possessed superior extraction performance and potential application in extraction of trace polar pollutants from complex samples.

In Situ Rapid Electrochemical Fabrication of Porphyrin-Based Covalent Organic Frameworks: Novel Fibers for Electro-Enhanced Solid-Phase Microextraction

Electro-enhanced solid-phase microextraction (EE-SPME) is a bright separation and enrichment technique that integrates solid-phase microextraction with the electric field. It retains the excellent extraction performance of SPME technology while having the advantages of efficient driving of electric field and special interaction between the electric field and electrons in the molecules of material structure. Replacing conventional SPME fibers with highly efficient and highly conductive original EE-SPME fibers is critical for the practical applications of these technologies. Here, a novel fiber preparation strategy was proposed to obtain a highly conductive porphyrin-based covalent organic framework (POR-COF) by one-step electropolymerization. Benefiting from the excellent semiconducting properties of porphyrin groups, the POR-COF can be spontaneously polymerized on the fiber surface under an appropriate voltage within a few hours. Its performance was evaluated by the EE-SPME of phthalate esters (PAEs) from food and environmental samples, followed by gas chromatography-tandem triple quadrupole mass spectrometry (GC-MS/MS) technology. The results showed that the POR-COF fiber has been successfully used for the detection of trace PAEs in beverages, industrial wastewater, lake water, and oyster samples with high adsorption selectivity and satisfactory sensitivity. The remarkable extraction properties are mainly attributed to the synergistic effect from material characteristics and electrical parameters' control in the extraction process. The presented strategy for the controlled design and synthesis of highly conductive porphyrin-based covalent organic framework fibers offers prospects in developing EE-SPME technologies.

In-situ growth of covalent organic framework on stainless steel needles as solid-phase microextraction probe coupled with electrospray ionization mass spectrometry for rapid and sensitive determination of tricyclic antidepressants in biosamples

Tricyclic antidepressants (TCAs) including amitriptyline (AT), doxepin (DOX) and nortriptyline (NT) are the first-line drugs for the clinical treatment of depression; however, monitoring TCA concentrations in biological fluids and tissues is necessary to improve therapeutic effect and determine the cause of death in patients. It is of great significance to develop a rapid and sensitive method for real-time monitoring of TCAs in various biosamples. In this work, we fabricated a novel covalent organic framework (COF) based solid-phase microextraction (SPME) probe by an in-situ step-by-step strategy, which was obtained by sequentially modifying 1,3,5-tri (4-aminophenyl) benzene (TPB) and 2, 5-divinylbenzaldehyde (DVA) on the surface of polydopamine layer. The TPB-DVA-COF-SPME probe possessed high specific surface area (1244 m²·g ^- 1), regular pores (3.23 nm), good hydrophobicity and stability, resulting in efficient enrichment for TCAs. Furthermore, the combination of TPB-DVA-COF-SPME probe and ambient electrospray ionization mass spectrometry system (ESI/MS) was firstly proposed for rapid and sensitive determination of TCAs in biosamples. As a result, the developed method exhibited low limits of detection (LODs) (0.1-0.5 μg∙L ^- 1), high enrichment factors (39-218), and low relative standard deviations (RSDs) for one probe (1.2-3.8%) and probe-to-probe (2.0-3.7%). Benefiting from these outstanding performance, TPB-DVA-COF-SPME probe was further successfully applied to biosamples (i.e., serum, liver, kidney, and brain) with excellent reusability, indicating the promising applicability of the TPB-DVA-COF-SPME-ESI/MS as a powerful tool for drug monitoring.

The Preparation of Covalent Bonding COF-TpBD Coating in Arrayed Nanopores of Stainless Steel Fiber for Solid-Phase Microextraction of Polycyclic Aromatic Hydrocarbons in Water

Covalent organic framework (COF)-TpBD was grafted on the arrayed nanopores of stainless steel fiber (SSF) with (3-aminopropyl) triethoxysilane as the cross-linking agent. The prepared SSF bonded with COF-TpBD showed high thermal and chemical stability and excellent repeatability. The prepared SSF bonded with COF-TpBD was also used for the solid-phase microextraction (SPME) of seven kinds of polycyclic aromatic hydrocarbons (PAHs) in actual water samples, followed by gas chromatography with flame ionization detection (GC-FID) determination, which exhibited low limits of detection (LODs), good relative standard deviation (RSD) and high recoveries.

Three-dimensional flower-like SnS2 materials for dispersive solid-phase extraction of endocrine-disrupting phenols

In this study, three-dimensional flower-like tin disulfide materials were prepared, and a highly efficient dispersive solid-phase extraction method was developed using the obtained three-dimensional tin disulfide adsorbents for the preconcentration and determination of six endocrine-disrupting phenols in combination with high-performance liquid chromatography-ultraviolet detection. Several important experimental parameters influencing extraction efficiency were investigated, including the amount of adsorbent, ultrasound time, sample solution pH, sample volume, type of elution solvent, desorption time, and the number of desorption times. Under the optimized experimental conditions, the developed method showed good linearity with the determination coefficients of 0.993-0.998 in the linear range of 0.5-400 ng/ml and low limits of detection in the range of 0.15-1.0 ng/ml, as well as satisfactory intra-day and inter-day precisions with relative standard deviations of 0.1-9.8%. Finally, the proposed method was successfully applied for the enrichment and determination of trace endocrine-disrupting phenols in milk, tea beverage, and plastic bottled water samples, and acceptable recoveries were obtained from 70.1% to 119.1% under four different spiked concentration levels. The results showed that the three-dimensional tin disulfide materials had great potential for the extraction of endocrine-disrupting phenols contaminants in environmental and food samples.

Highly Efficient Solvothermal Synthesis of Poly(1,5-diaminoanthraquinone) Nanoflowers for Energy and Environmental Applications

Poly(1,5-diaminoanthraquinone) (PDAA) has attracted more interest because of its unique molecular structure. However, the lower polymerization yield limits its practical application. Here, the solvothermal chemically oxidative polymerization of 1,5-diaminoanthraquinone (DAA) was developed, and the well-defined PDAA nanoflowers were obtained with a high yield of 72.6% within 16 h. The PDAA nanoflower-based flexible film electrodes were fabricated with expandable graphene as conductive support, delivering a capacitance of 277 F g-1 and 258 mF cm-2 at 0.5 A g-1 (1 mA cm-2) and superior cycling stability with retention of 99% after 10000 cycles. The flexible symmetric solid-state supercapacitors (SSSCs) possessed a high capacitance of 52.5 F g-1 at 0.25 A g-1 and 96.6 mF cm-2 at 1 mA cm-2 and had only a 14% capacitance loss after 10000 cycles at 0.1 V s-1 as well as excellent flexibility. Besides, the PDAA nanoflowers could be used as self-separable adsorbent for methylene blue (MB) with a capacity of 93.8 mg g-1 at pH 9.

An electrochemical sensor for detection of trace-level endocrine disruptor bisphenol A using Mo2Ti2AlC3 MAX phase/MWCNT composite modified electrode

Bisphenol A (BPA) is an industrially preferred material for the production of plastic and polycarbonate as well as a used material for the interior of food and beverage cans. In this study, synthesis and electrochemical sensor application of Mo₂Ti₂AlC₃/MWCNT (multi-walled carbon nanotube) nanocomposite for BPA sensing was evaluated. Mo₂Ti₂AlC₃ was used as MAX phase material in the design of the sensor, and MWCNT was preferred to increase conductivity and sensitivity. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used to determine Mo₂Ti₂AlC₃/MWCNT nanocomposite's electrochemical sensor performances which had LOD of 2.7 nM and LOQ of 8.91 nM in the linear working range of 0.01-8.50 μM calculated from DPV. The composite showed a single oxidation step against BPA which is diffusion-controlled and irreversible. The sensor was successfully applied for the determination of BPA in milk pack, plastic bottle, and can with recoveries ranging from 95.67% to 100.60%. In addition, sensor performance was examined through selectivity, repeatability, and reusability studies. HPLC as a standard determination method was carried out for accuracy of the voltammetric determination method in the real samples. The developed sensor could be applied to different areas from industry quality control to clinical analysis for the detection of BPA.

Metal-organic framework mixed-matrix membrane-based extraction combined HPLC for determination of bisphenol A in milk and milk packaging

The residues of bisphenol A (BPA) in milk packaging may transfer to milk, adversely affecting the human endocrine system. Consequently, to analyse or monitor BPA, it is imperative to develop rapid and effective approaches to BPA extraction from milk and milk packing as BPA is usually present in trace levels. Herein, we developed a rapid, simple, and low-cost dispersive-membrane-solid-phase-extraction (DME) for BPA with MIL-101(Cr) mixed-matrix-membrane (MMM). The MMM had large surface area (1322.09 m²/g) and pore volume (0.65 cm³/g), possessed great extraction efficiency of BPA, and kept more than 90% extraction efficiency after 20 times of reuse. Using the developed MIL-101(Cr)-MMM-based DME coupled with HPLC-fluorescence detector, we received an adequate linearity in the range of 0.1 ∼ 50 μg/L BPA and a limit of detection as low as 16 ng/L under optimized conditions. The recoveries of BPA in milk and milk bottles were from 74.2% to 110.6%, with RSDs less than 9.4%.

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.

Dynamic SPME-SERS Induced by Electric Field: Toward In Situ Monitoring of Pharmaceuticals and Personal Care Products

The core of the surface-enhanced Raman spectroscopy (SERS)-based techniques for dynamic monitoring is to realize rapid and reversible adsorption. Herein, the integration technology of electro-enhanced adsorption, solid-phase microextraction, and surface-enhanced Raman spectroscopy (EE-SPME-SERS) was developed to obtain sensitive, ultrafast, and reversible SERS response toward in situ monitoring of pharmaceuticals and personal care products (PPCPs). In the EE-SPME-SERS method, a roughened Ag fiber with Au modification (r-Ag/Au fiber) was used as the SERS substrate, SPME sorbent, and working electrode. The r-Ag/Au fiber displayed good SERS sensitivity, ultrahigh photostability, and adsorption properties. The adsorption efficiency of benzidine was 76 times accelerated in EE-SPME-SERS compared to that in static adsorption. The whole process of "sampling and detection" in EE-SPME-SERS can be finished within 1 s. Reversible adsorption and desorption can be achieved in situ by switching the direction of electric field, and the regeneration process takes only a few minutes. Simulated release of benzidine from household wastewater was in situ and dynamically monitored using this strategy. EE-SPME-SERS was proved universal for ionized PPCPs and can detect multicomponents simultaneously. In addition, EE-SPME-SERS showed very good analytical properties. Great potential of EE-SPME-SERS can be expected in environmental monitoring.

[Application of imine covalent organic frameworks in sample pretreatment]

Imine covalent organic frameworks (I-COFs), including imine-linked COFs and hydrazone-linked COFs, are a new type of crystalline porous organic materials constructed by the condensation of organic monomers by the Schiff-base reaction. Because they are composed of lightweight elements linked by strong covalent bonds, I-COF materials possess the advantages of low skeleton density, large surface area, high porosity, abundant monomer species, controllable pore size, functionalized structure, diverse synthetic methods, excellent adsorption performance, outstanding physical and chemical stabilities, etc. In recent years, interest in the field of I-COFs has increased tremendously because of their exceptional performance and broad applications in gas storage, gas separation, catalysis, sensing, photoelectric materials, sample pretreatment, drug delivery, and other fields. To date, imine bonds are one of the most widely used covalent bonds in COFs, and represent one of the most important ways to obtain I-COFs with excellent chemical stabilities. The synthesis methods for I-COFs include solvothermal synthesis, microwave synthesis, mechanochemical grinding synthesis, and room-temperature synthesis methods. Solvothermal synthesis is the most extensively used method for the production of I-COFs with high specific surface areas and good thermal stabilities. The microwave synthesis method is conducive to the rapid synthesis of COFs in industry, providing a more time-saving, simpler, and safer route for large-scale preparation of I-COFs. The mechanochemical grinding synthesis of porous solids has gained importance as an alternative to conventional solvothermal synthesis, because the process is quick, environment-friendly, and potentially scalable. The room-temperature method is characterized by mild reaction conditions and rapid reactions. It is an energy-saving, economic, safe, and green synthesis method, which has emerged as a hot spot in the preparation of I-COFs in recent years. Research progress over the past years on the application of I-COFs in the field of materials science has undoubtedly established the basis of its application in analytical chemistry. Owing to the excellent physical and chemical properties of I-COF materials, they are suitable for use as separation and enrichment media for trace target compounds in complex samples. The high specific surface area and porosity, extended conjugate network skeleton, and π-electron-rich nature of the materials endow it with a high adsorption capacity. These materials are highly enriched in target analytes by π-π interactions, acid-base interactions, donor-acceptor interactions, hydrogen bonding, hydrophobic interactions, and other intermolecular interactions. Precise control of the microporous structure of I-COFs was obtained by controlling the chain length, geometric structure, doping elements, and substituent groups of the organic monomers. Selective enrichment of target trace substances was achieved by modifying the groups of I-COFs based on the principle of host guest adaptation, molecular sieving, or microporous filling effect. At present, research on the synthesis of I-COF materials is in the stage of rapid development, and many I-COFs with excellent properties and great application potential have been synthesized, allowing widespread application of I-COFs in sample pretreatment medium. This review summarizes the current state-of-the-art on the main types and synthetic methods of I-COFs, as well as the applications of I-COFs in solid-phase extraction, magnetic solid-phase extraction, dispersive solid-phase extraction, and solid-phase microextraction. The prospects of I-COFs in sample pretreatment are also presented.

An amine-functionalized olefin-linked covalent organic framework used for the solid-phase microextraction of legacy and emerging per- and polyfluoroalkyl substances in fish

Due to the environmental persistence and various health problems associated with per- and polyfluoroalkyl substances (PFASs), they have come under increased public scrutiny. However, the efficient extraction of PFASs from complex media remains challenging. Herein, an olefin-linked covalent organic framework (COF-CN) has been prepared via a Knoevenagel condensation reaction, followed by reduction using LiAlH₄ to form an amine-functionalized COF (COF-NH₂). The characterization results demonstrated that the crystal structure was maintained during the post-modification step. Isothermal and kinetic adsorption studies showed the higher affinity of COF-NH₂ toward PFASs. Based on density functional theory, the adsorption mechanism of the stable six-member-ring structure formed between COF-NH₂ and PFASs via hydrogen bonding was tentatively revealed. After optimizing the solid-phase microextraction parameters, legacy and emerging PFASs were efficiently extracted from fish using the COF-NH₂ coating, followed by detection using ultra-performance liquid chromatography-tandem mass spectrometry. The method exhibited ideal linearity, low limits of quantification, excellent precision, and high relative recoveries. Finally, the bioconcentration kinetics for goldfish was studied, which can provide a feasible platform for investigating the accumulate ion and toxicity of PFASs.

Covalent organic framework DQTP modified pencil graphite electrode for simultaneous determination of bisphenol A and bisphenol S

The sensitivity and selectivity of electrochemical analysis are challenging due to the materials used for electrode modification as well as electrical conductivity, catalytic activity and recognition ability of the working electrode. In this work, a portable 3D-printed electrochemical electrode clamp was designed and applied in combination with the developed covalent organic framework (COF DQTP)-modified pencil graphite electrode (DQTP/PGE). The β-ketoenamine-linked COF DQTP synthesized by 1,3,5-triformylphloroglucinol (TP) and 2,6-diaminoanthraquinone (DQ) through solvothermal method is a porous crystalline with excellent conductivity and large periodic π-arrays, coupled with commercial available pencil graphite electrode to fabricate a disposable sensor for simultaneous determination of environmental endocrine disruptors bisphenol A and bisphenol S. The DQTP/PGE sensor exhibited high electrical conductivity and catalytic activity, and a good linearity was obtained in a range of 0.5-30 μM for two bisphenols with a detection limit of 0.15 μM (S/N = 3). Moreover, the sensor showed a reproducible and stable response over one month with negligible interference, and an accepted recovery with real food packaging samples.

Electrophoretic deposition of polyaniline nanofibers on a stainless steel wire as an adsorbent for determination of tamoxifen by SPME/GC-FID in urine samples

Polyaniline nanofiber films were fabricated on the surface of stainless steel wire via a controllable and simple electrophoretic deposition route from a nonaqueous colloidal suspension consisting of polyaniline nanofibers. The prepared coating material was then characterized by field emission scanning electron microscopy equipped with energy dispersive spectroscopy and elemental mapping analysis. The fabricated polyaniline film-coated stainless steel wire was then utilized as an effective and novel sorbent phase for solid-phase microextraction of tamoxifen for subsequent gas chromatography/flame ionization detection of this anticancer drug. Parameters consisting of the temperature, extraction time, salt concentration, agitation speed, pH, temperature and time of desorption were studied and optimized using a one-at-a-time strategy. Under the optimum conditions, detection limit (S/N = 3), the limit of quantification (10/3 limit of detection), linear dynamic range, repeatability and reproducibility values of 0.51 μg L^-1 , 1.7 μg L^-1 , 2-1,130 μg L^-1 , 5.7% and 8.6% were attained, respectively. The prepared fiber can preserve 90% of its efficacy after 20 consecutive cycles, demonstrating the suitable thermal stability and cyclability of the proposed solid-phase microextraction coating material for the determination of tamoxifen by gas chromatography/flame ionization detection. The route was effectively utilized to determine tamoxifen in urine samples, with relative recoveries ranging from 89 to 106%.

In-situ fabrication of a chlorine-functionalized covalent organic framework coating for solid-phase microextraction of polychlorinated biphenyls in surface water

The functionalization of covalent organic frameworks (COFs) identifies significant potential for developing selective coating materials for solid-phase microextraction (SPME). Herein, a chlorine-functionalized covalent organic framework (CF-COF) was in-situ synthesized by employing triformylphloroglucinol (Tp) and 2,5-dichloro-1,4-phenylenediamine (2,5-DCA) as monomers on an amino-functionalized stainless steel wire. The obtained CF-COF coated fiber exhibited a higher enrichment capacity for polychlorinated biphenyls (PCBs) than commercial fibers and non-chlorinated COF fiber, owing to a more hydrophobic surface, size-matching effect, a large number of micropores and the π-π stacking interactions between COF coating and analytes. As a practical application, the CF-COF coated fiber was applied to the headspace extraction of 17 PCBs prior to their quantification by GC/MS. The established analytical method offered a good linearity in the range of 0.1-1000 ng L^-1, low detection limits of 0.0015-0.0088 ng L^-1, and satisfactory enhancement factors (EFs) of 699-4281. The repeatability for single fiber and the fiber-to-fiber reproducibility was lower than 9.26% and 9.33%, respectively. The proposed method was verified to be sensitive, selective, and applicable for the analysis of ultra-trace PCBs in environmental surface water samples with the recoveries ranged from 78.7% to 124.0%.

In situ room-temperature rapidly fabricated imine-linked covalent organic framework coated fibers for efficient solid-phase microextraction of pyrethroids

A facile and rapid strategy for preparation of covalent organic framework (COF) coated fibers at ambient temperature is urgently needed for solid-phase microextraction (SPME) technology. In this work, an in situ room-temperature rapid growth strategy was developed to high-efficiently fabricate imine-linked COF (TPB-DVA) coated fibers in as little as 30 min at room temperature, and the thickness of the coating reached 9 μm. The prepared TPB-DVA coated fiber offer high thermal and chemical stability, and outstanding service lifetime. Moreover, we generalize this strategy to other two imine-linked COF (TPB-DMTP and TFPB-TAPB) coated fibers and the fibers were fabricated at room temperature for 3 h and 12 h, respectively, which demonstrate the applicability of this strategy. Subsequently, a SPME-GC-MS/MS analytical method was developed for trace pyrethroids (PYs) detection, which exhibited high enhancement factors (EFs, 2700-13195), wide linear range (0.08-800 ng L^-1), low limits of detection (LODs, 0.02-0.20 ng L^-1), and good repeatability (RSD ≤ 8.5%, n = 6). Furthermore, the developed analytical method was applied to tea samples and trace PYs (1.31-4.32 ng L^-1) were found with satisfactory recovery (80.2-119.8%). The above results demonstrated that the feasibility of the developed strategy for the facile and rapid fabrication of imine-linked COF coated fibers.

Facile separation of enantiomers via covalent organic framework bonded stationary phase

Covalent organic frameworks (COFs), a type of crystalline polymers, have attracted increasing interest because of their controllability of geometry and functionality. Featuring infinitely extended networks and tremendous interaction sites, COFs emerge as a potential platform for separation science. Here, a novel chiral COF (β-CD COF_BPDA) constructed by the imine condensation of 4,4'-biphenyldicarboxaldehyde and heptakis(6-amino-6-deoxy)-β-cyclodextrin was introduced into an electrochromatographic system via a photopolymerization method and applied to the separation of enantiomers. The structure and properties of as-synthesized β-CD COF_BPDA were investigated by powder X-ray diffraction (PXRD) patterns, Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), and N₂adsorption-desorption isotherms. It was proved that β-CD COF_BPDA was provided with larger pore size and BET surface area. The β-CD COF_BPDA coating endowed the chiral stationary phase with superior three-dimensional orientation, and realized satisfactory separation with improved selectivity and column efficiency for a dozen racemic drugs. Under the optimized conditions, homatropine, ondansetron, metoprolol, terbutaline, tulobuterol, and promethazine were all baseline separated with resolution values of 2.24, 2.03, 1.65, 1.62, 1.60, and 1.58, respectively. The results indicate the high perspective of COF modified stationary in enantioseparation.