Covalent Organic Framework as Fiber Coating for Solid-Phase Microextraction of Chlorophenols Followed by Quantification with Gas Chromatography-Mass Spectrometry

Structural and functional optimization of COF-coated stirring bars for environmental monitoring and biological sample analysis

In this study, a series of covalent organic framework (COF)-coated stirring bars-COF-a, COF-b, and COF-c-were innovatively designed and evaluated for the efficient extraction of estrogens from complex environmental and biological samples. The most notable advancement lies in the successful application of COF-c, which exhibited exceptional adsorption capacity, thermal stability, and reusability. Unlike conventional PDMS coatings, COF-c demonstrated enhanced performance in capturing estrogens from actual meat samples, achieving high recovery rates (78.6-119.3%) and maintaining consistent extraction efficiency over multiple cycles. These findings highlight the structural advantages of COF-c, such as its larger pore volume and strong π-π and hydrogen bonding interactions with target molecules. This work underscores the potential of COF-c as a next-generation SBSE coating material, offering a highly selective, thermally stable, and reusable platform for trace hormone analysis in complex matrices.

Preparation of boric acid functionalized hyper-crosslinked polymer for efficient extraction of phenylurea herbicides from lake water, green tea drink and tomato samples

A boric acid functionalized hyper-crosslinked polymer (HCP), designated as NPCBA/TBM-HCP, was successfully synthesized via Friedel-Crafts reaction by copolymerizing N-phenylcarbazole-2-boronic acid (NPCBA) and 2,4,6-Tris(bromomethyl)mesitylene (TBM). The NPCBA/TBM-HCP showed a large surface area and a good adsorption property for phenylurea herbicides (PUHs). A method with NPCBA/TBM-HCP based solid phase extraction and high-performance liquid chromatographic detection was developed for the simultaneous analysis of PUHs in lake water, green tea drink and tomato samples. Under the optimized experimental conditions that the amount of the NPCBA/TBM-HCP was 30 mg, sample solution was 100 mL, sample loading rate was 4 mL min-1, and eluent was 0.3 mL acetonitrile, the linear response for the PUHs was in the range of 0.06-80.0 ng mL-1, 0.6-80.0 ng mL-1 and 0.9-200 ng g-1 for lake water, green tea drink and tomato samples, respectively, with a good linearity (the coefficients of determination (r2) ≥ 0.9916). The detection limits (S/N = 3) for lake water, green tea drink and tomato samples were 0.02-0.03 ng mL-1, 0.2 ng mL-1 and 0.3-0.5 ng g-1, respectively. The method recoveries for spiked samples were 80.0 %-119.1 % and RSDs were lower than 9.9 % for the determination. The method provides a new and feasible approach for the determination of phenylurea herbicide in real samples.

In situ growth of hierarchical porous covalent organic framework coating for enhanced solid-phase microextraction of phenolic compounds

Covalent organic frameworks (COFs), when utilized as solid-phase microextraction (SPME) coating materials, exhibit remarkable abilities to concentrate phenols by thousands-fold owing to their vast surface area and exceptional stability. However, the prevalent micropores inherent in COFs can impede rapid mass transfer of target molecules, prolonging SPME extraction times. To addresses this limitation, this work introduces a novel approach by integrating hierarchical porous structures into COFs, leveraging polystyrene microspheres as hard templates during the in situ growth process of the SPME coating. Due to the presence of a hierarchical porous structure derived from the template, the resulting hierarchical porous TpBD coating, termed HP-TpBD, demonstrated enhanced extraction efficiency, accelerated extraction kinetics, and notably shortened extraction times for phenolic compounds. Coupled with gas chromatography-mass spectrometry, a highly sensitive method featuring a low limit of detection (0.20-0.28 ng L-1), a broad linear range (1.0∼1.0 × 104 ng L-1), and excellent precision (RSD < 8.5 %) was established. This methodology enables accurate quantitative analysis of phenols in water and soil samples. This work provides valuable insights into developing COF-based SPME coatings for the efficient extraction of volatile contaminants, paving the way for more efficient and sensitive analytical procedures.

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.

Development of amphiphilic hypercrosslinked porous polymers for magnetic extraction of multiple environmental pollutants in water

Under the principle of similar compatibility, researchers have developed various polarity extractants corresponding to a class of chemicals. Separating different polarities chemicals with one extractant effectively has become a novel research trend in separation science. Given the complexity of environmental sample matrices and the significant differences in polarity and solubility of various compounds, the introduction of hydrophilic groups to hydrophobic material skeletons can lead to sorbents with hydrophilic-lipophilic balance (HLB) property and thus improve their extraction performance for substances with different polarities. In this work, a hypercrosslinked polymer (HCPPz-TPB), designated as HLB, was synthesized by incorporating polar pyrazine and nonpolar triphenylbenzene molecules within each other. Subsequently, a core-shell magnetic composite material was obtained by encapsulating magnetic Fe3O4 nanoparticles in HCPPz-TPB. The material was applied as an adsorbent for magnetic solid phase extraction (MSPE) and combined with a high-performance liquid chromatography-photodiode array detector (HPLC-PDA) to enrich, separate, and detect seven polar contaminants in environmental water samples. The proposed approach, Fe3O4@SiO2@HCPPz-TPB-MSPE-HPLC-PDA, is characterized by its outstanding high sensitivity, low detection limits, wide linear range, and good reproducibility. The method demonstrated satisfactory linearity in the range of 0.05-2 μg mL-1 with R2 values between 0.9969 and 0.9997; the limits of detection (LOD) were observed to be within the range of 0.0019-0.016 μg L-1, and limits of quantification (LOQ) was observed to be within the range of 0.0064-0.054 μg L-1 range with good precision. The recoveries of the different contaminants in the environmental samples ranged from 83.61 to 116.46% (RSD≤10.56, n = 5). The new hydrophilic-lipophilic balance extractant is highly efficient, sensitive, and precise for extracting different polar pollutants. The findings demonstrate that the Fe3O4@SiO2@HCPPz-TPB display a remarkable affinity for multiple targets, driven by complex interactions including multi-stackings and hydrogen bonding as a sorbent. The synthesized Fe3O4@SiO2@HCPPz-TPB may be employed in diverse applications, including extraction, removal, and determination of diverse trace multi-target analytes in complex media.

Regarding Bioanalysis Lasting a Few Minutes: Automated Cooling-SPME and Fast-GC for Urinary 2-Phenyl-2-Propanol Monitoring

An innovative SPME head space GC-MS method, in cooling mode, using a fully automated routine, was developed to detect 2-phenyl-2-propanol, a representative urinary metabolite of cumene. Following an acid hydrolysis and derivatization step with lowered quantities of reagents, acetic anhydride and pyridine, a 30 μm polydimethylsiloxane SPME fiber was used to sample derivatized 2-phenyl-2-propanol, such as benzenemethanol,α,α-dimethyl-acetate, from the headspace. Performances of the method, optimized through experimental design, provide an LOD of 0.034 mg/L and an LOQ 0.10 mg/L, with a short sampling time necessary per sample. The method, developed on standard solutions, will be applied to both occupationally exposed and non-exposed populations.

Fluorine-functionalized covalent organic framework coated solid-phase microextraction probe coupled with electrospray ionization mass spectrometry for monitoring triclosan, triclocarban, and chlorophenols in mice

Triclosan (TCS), triclocarban (TCC), and chlorophenols (CPs) are broad-spectrum antibacterials widely used in dermatological and oral hygiene products, which could induce severe liver and intestine injuries. Hence, it is essential to establish a rapid and sensitive method to monitor TCS, TCC, and CPs in various organisms. In this work, fluorine-functionalized covalent organic framework (COF-F) was prepared by using 4,4',4''-(1,3,5-triazine-2,4,6-triyl)tri-aniline and 2,3,5,6-tetrafluoroterephthalaldehyde as two building units and employed as a solid phase microextraction (SPME) probe for the extraction of TCS, TCC and CPs. The COF-F possessed excellent hydrophobicity, a large specific surface area (1354.3 m2 g-1) and high uniform porosity (3.2 nm), which facilitated high selectivity and adsorption properties towards TCS, TCC, and CPs. Therefore, the as-prepared COF-F-SPME in combination with electrospray ionization mass spectrometry has been developed to provide fast and ultrasensitive detection of TCS, TCC, and CPs in biological samples. The established method demonstrated satisfactory linear ranges (0.01-100.00 μg L-1) and low limits of detection (0.003-0.040 μg L-1) for TCS, TCC and CPs. The developed method could be successfully applied to detect TCS, TCC and CPs in the liver and kidney tissues of mice, demonstrating the potential for the detection of chlorinated aromatic pollutants in the biological samples.

A novel top-down strategy for in situ construction of vertically oriented hexagonal NiCr LDHs nanosheet arrays with intercalated sulfate ions on Nichrome fiber for selective solid-phase microextraction of phenolic compounds in water samples

BACKGROUND

Phenolic compounds (PCs) are a class of polar aromatic pollutants with high toxicity in environmental water. Generally the efficient sample preparation is essential for the quantification of ultra-trace target PCs in real water sample before appropriative instrumental analysis. SPME is a convenient, solvent-free and time-saving miniaturized technique and has been recognized as a green alternative to conventional extraction techniques. In SPME, however, commercial fused-silica fibers are limited to the fragility, operation temperature, extraction capacity and selectivity as well as lifetime. Therefore, the development of new SPME fibers is always needed to overcome such limitations.

RESULTS

We presented a novel top-down strategy for in situ construction of vertically oriented hexagonal sulfate intercalated NiCr layered double hydroxide nanosheet arrays (NiCr LDHs-SO4 NSAs) on the Nichrome (NiCr) substrate by hydrothermal treatment in NaOH solution containing (NH4)2S2O8. The results showed that much shorter hydrothermal time was needed for the construction of NiCr@NiCr LDHs-SO4 NSAs fiber in the presence of (NH4)2S2O8. Moreover, the unique NiCr LDHs-SO4 NSAs coating offered open access structure, and thereby more available surface area for adsorption. The resulting fiber exhibited better extraction efficiency for phenolic compounds (PCs), faster mass transfer rate, higher mechanical stability, and longer service life than original NiCr@NiCr LDHs NSs fiber and typical commercially fused-silica fibers. After optimizing conditions, the SPME-HPLC-UV method demonstrated a linear range from 0.05 μg L-1 to 200 μg L-1 with LODs of 0.015-0.156 μg L-1 (S/N = 3) and LOQs of 0.048-0.498 μg L-1 (S/N = 10), as well as good repeatability (3.06%-5.22%) and fiber-to-fiber reproducibility (4.32%-6.49%).

SIGNIFICANCE

The developed SPME-HPLC-UV method with the constructed fiber was applied to the preconcentration and detection of different types of PCs in real water samples, showing satisfactory recoveries ranging from 86.20% to 107.8% with RSDs of 3.18%-6.69%. This study provides a new strategy for in situ construction of bimetallic hydroxides and their derived nanocomposite coatings on the NiCr fiber substrate in practical SPME application.

Facile synthesis of hydroxylated triazine-based magnetic microporous organic network for ultrahigh adsorption of phenylurea herbicides: An experimental and density-functional theory study

Microporous organic networks (MONs) are highly porous materials that are particularly useful in analytical chemistry. However, the use of these materials is often limited by the functional groups available on their surface. Here, we described the polymerization of a sea urchin-like structure material at ambient temperature, that was functionalized with hydroxyl, carboxyl, and triazine groups and denoted as OH-COOH-MON-TEPT. A substantial proportion of OH-COOH-MON-TEPT was intricately decorated EDA-Fe3O4, creating a well-designed configuration (EDA-Fe3O4 @OH-COOH-MON-TEPT-EDC) for superior adsorption of the target analytes phenylurea herbicides (PUHs) via magnetic solid-phase extraction (MSPE). The proposed method showed remarkably low limits of detection ranging from 0.03 to 0.22 ng·L-1. Experimental investigations and theoretical analyses unveiled the adsorption mode between EDA-Fe3O4 @OH-COOH-MON-TEPT-EDC and PUHs. These findings establish a robust foundation for potential applications of EDA-Fe3O4 @OH-COOH-MON-TEPT-EDC in the analysis of various polar contaminants.

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.

Headspace Microextraction. A Comprehensive Review on Method Application to the Analysis of Real Samples (from 2018 till Present)

This work describes current trends in the development of headspace microextraction methods. The main trends in the selection of detection techniques used in combination with microextraction and preferences in the selection of headspace liquid-phase microextraction (HS-LPME) or headspace solid-phase microextraction (HS-SPME) methods, depending on the analytes and their quantity, are also briefly presented. In the main part of the work, on the basis of current journal literature, headspace microextraction analytical methods used for the determination of various inorganic and organic analytes are classified and compared over the last five years. The work also reflects the current modifications of techniques and approaches proposed for these microextraction methods.

Keggin type phosphotungstic acid intercalated copper-chromium-layered double hydroxide reinforced porous hollow fiber as a sorbent for hollow fiber solid phase microextraction of selected chlorophenols besides their quantification via high performance liquid chromatography

Herein, a copper-chromium-layered double hydroxide (Cu/Cr-LDH) was synthesized by the co-precipitation method. The Cu/Cr-LDH was intercalated to the Keggin-type polyoxometalate (H₃PW₁₂O₄₀). The modified LDH accommodated in the pores of hollow fiber (HF), to prepare the extracting device for the HF-solid phase microextraction method (HF-SPME). The method was used for the extraction of 4-chlorophenol, 2,4-dichlorophenol, and 2,4,6- trichlorophenol from tap water, river water, and tea sample. The extracted target analytes were quantified via high-performance liquid chromatography-UV detection. The figures of merit of the method such as, linear dynamic ranges (LDRs), limit of detections (LODs) and, limit of quantifications (LOQs), were determined based on the obtained optimum condition. Based on the results, the LDR was between 1 and 500 μg L ^- 1 and r² higher than 0.9960. The LODs and LOQs were obtained in the ranges of 0.28-0.36 µg L ^- 1 and 0.92-1.1 µg L ^- 1, respectively. The relative standard deviations ((RSDs% for inter-and intra-day) of the method for the extraction of target analytes were calculated in two different concentrations of (2 and 10 μg L ^- 1) and (5 and 10 μg L ^- 1) between 3.70% - 5.30% and 3.50% - 5.70%-respectively. The enrichment factors were obtained between 57 and 61. In order to investigate the accuracy of the method, also the relative recovery was obtained, between 93 and 105%. Finally, the proposed method was used for the extraction of the selected analytes in different water and tea samples.

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.

N, N'-methylene bisacrylamide/divinyl benzene based-highly cross-linked hybrid monolithic column: Production and its applications for powerful capture of four chlorophenols

In this paper, the role of the halogen bond in capillary monolithic column microextraction was explored for the first time. Benzene-1,3,5-tricarbohydrazide (BTH) was synthesized as a functional monomer, N, N'-methylene bisacrylamide (MBA) and divinyl benzene (DVB) were used as cross-linking agents, the hybrid monolithic column of poly (BTH-co-DVB-co-MBA) was prepared using methanol and polyethylene glycol as pore-forming agents and azodiisobutyronitrile as the initiator. Due to the existence of BTH, a large number of nitrogen atoms (Lewis base) were introduced into the monolithic column, which could form a halogen bond with chlorine-containing organic pollutants and enhance its adsorption performance. Based on the monolithic column, a sensitive and environment-friendly solid-phase microextraction technology was studied. The monolithic column was integrated with high-performance liquid chromatography (HPLC) to extract and detect four kinds of chlorophenol in real water samples. Under best conditions, the method showed excellent extraction ability and linearity, with a linear correlation coefficient of 0.9958-0.9987, a low detection limit (LOD) of 0.04-0.23 μg L^-1 (S/N = 3), and relative standard deviation (RSD) less than 3.09%. The recovery rate was kept between 87.30% and 123.00%, and the RSD was less than 3.83%, which indicated that the column had powerful capture performance, high precision, and strong anti-matrix interference ability in the real sample, and had potential application value in practical work.

Review of extraction and detection techniques for the analysis of pesticide residues in fruits to evaluate food safety and make legislative decisions: Challenges and anticipations

Fruits are vital parts of the human diet because they include necessary nutrients that the body needs. Pesticide use has increased dramatically in recent years to combat fruit pests across the world. Pesticide usage during production, on the other hand, frequently results in undesirable residues in fruits after harvest. Consumers are concerned about pesticide residues since most of the fruits are directly consumed and even recommended for the patients as dietary supplements. As a result of this worry, pesticide residues in fruits are being randomly monitored to re-assess the food safety situation and make informed legislative decisions. To assess the degree of pesticide residues in fruits, a simple and quick analytical procedure is usually required. As a result, pesticide residue detection (using various analytical techniques: GC, LC and Biosensors) becomes critical, and regulatory directives are formed to regulate their amounts via the Maximum Residue Limit (MRL). Over the previous two decades, a variety of extraction techniques and analytical methodologies for xenobiotic's efficient extraction, identification, confirmation and quantification have been developed, ranging from traditional to advanced. The goal of this review is to give readers an overview of the evolution of numerous extraction and detection methods for pesticide residue analysis in fruits. The objective is to assist analysts in better understanding how the ever-changing regulatory landscape might drive the need for new analytical methodologies to be developed in order to comply with current standards and safeguard consumers.

Novel N-riched covalent organic framework for solid-phase microextraction of organochlorine pesticides in vegetable and fruit samples

A covalent organic framework named N-COF was successfully constructed by the aldehyde-amine condensation reaction between 2,4,6-tris (4-formyl phenoxy)-1,3,5-triazine and 1,3-bis(4-aminophenyl) urea for the first time. The prepared N-COF exhibited good stability and high affinity to organochlorine pesticides (OCPs). Thus, the N-COF was served as solid phase microextraction fiber coating for extraction of six OCPs from vegetables and fruits including romaine lettuce, cabbage, Chinese cabbage, apple, pear and peach, followed by quantitation with gas chromatography-electron capture detector (GC-ECD). Under the optimal conditions, good linearities for the OCPs existed in the ranges from 0.1 to 1.0 ng g^-1 to 100.0 ng g^-1 for the samples. The low limits of detection for analytes were obtained in the range of 0.03-0.3 ng g^-1. The present work can offer new alternative for sensitive analysis of trace level of OCPs in vegetables and fruits.

A novel porphyrin-based conjugated microporous nanomaterial for solid-phase microextraction of phthalate esters residues in children's food

A novel porphyrin-based conjugated microporous polymer (PCMP) with microporous structure and nitrogen-rich pyrrole building blocks was synthesized. The PCMP was used as a coating material to prepare solid-phase microextraction (SPME) fibers by sol-gel technique. Due to the toxicity of the phthalate esters (PAEs) and the necessity for their sensitive determinations in some food samples, the SPME fiber was investigated for the extraction of eleven PAEs from six different children's milk beverages prior to their detection by gas chromatography-mass spectrometry. Under the optimal conditions, the linear response range for the PAEs was in the range from 0.03 to 200 µg L^-1 and the limits of detection (S/N = 3) for the analytes were 0.01-3.00 μg L^-1. The method recoveries for the PAEs were between 80% and 120%, with the relative standard deviations varying from 1.3% to 9.8%. The method was successfully applied for the determination of PAEs in children's milk beverages.

Facile fabrication of hydroxyl-functionalized hypercrosslinked polymer for sensitive determination of chlorophenols

Three hydroxyl-functionalized hypercrosslinked polymers (HCP-POL, HCP-HQ and HCP-PG) were synthesized by Friedel-Crafts reaction. The HCP-HQ displayed the largest surface area and highest adsorption capacity for chlorophenols (CPs). Thus, the HCP-HQ was further modified with magnetism to obtain M-HCP-HQ. An efficient magnetic solid-phase extraction method with M-HCP-HQ as adsorbent was developed for the first time to simultaneously extract four CPs from water and honey samples before analysis by high performance liquid chromatography-diode array detection. Under optimized conditions, the low detection limits (S/N = 3) were obtained to be 0.06-0.10 ng mL^-1 for water and 0.80-1.75 ng g^-1 for honey. The method recovery was 80.7%-119%, with relative standard deviations below 9.5%. The enrichment factors of the CPs were in the range of 57-220. The extraction mechanism could be attributed to the strong polar interaction, hydrogen bonding and π-π interactions between the M-HCP-HQ and CPs. The M-HCP-HQ based method can be served as a reliable and sensitive tool for detection CPs in water and honey samples.

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.

Synthesis of the Magnetically Nanoporous Organic Polymer Fe3O4@SiO2-NH2-COP and Its Application in the Determination of Sulfonamide Residues in Surface Water Surrounding a Cattle Farm

Efficient extractions of trace antibiotic residues in the environment are a key factor for accurate quantification of the residues. A new nanoporous material, namely, magnetically covalent organic polymer (MCOP, Fe₃O₄@SiO₂-NH₂-COP) was synthesized in this work and was used for magnetic solid-phase extraction (MSPE). The combination of MSPE with high-performance liquid chromatography separation together with ultraviolet detection (HPLC-UV) was established as an effective method for the determination of four sulfonamide (SA) residues in surface water surrounding a cattle farm. The synthesized magnetic material was characterized by SEM, TEM, FT-IR, magnetic properties measurement system (MPMS), and nitrogen gas porosimetry. The material possessed many attractive features, such as a unique microporous structure, a larger specific surface area (137.93 m²·g⁻¹) than bare Fe₃O₄ (24.84 m²·g⁻¹), high saturation magnetization (50.5 emu·g⁻¹), open adsorption sites, and high stability. The influencing parameters, including pH, the used amount of MCOPs, the type of eluent, adsorption solution, and desorption time, were optimized. Under the optimized conditions, the method conferred good linearity ranges (R² ≥ 0.9990), low detection limits (S/N = 3, LOD, 0.10–0.25 μg·L⁻¹), and satisfactory recoveries (79.7% to 92.2%). The enrichment factor (EF) for the four SAs was 34.13–38.86. The relative standard deviations of intraday (n = 5) and of interday (n = 3) were less than 4.8% and 8.9%, respectively. The equilibria between extraction and desorption for SAs could be reached within 150 s. The proposed method was sensitive and convenient for detecting SA residues in complex environmental matrices, and the successful application of the new MCOPs as an adsorbent was demonstrated.

Covalent organic frameworks as multifunctional materials for chemical detection

Sensitive and selective detection of chemical and biological analytes is critical in various scientific and technological fields. As an emerging class of multifunctional materials, covalent organic frameworks (COFs) with their unique properties of chemical modularity, large surface area, high stability, low density, and tunable pore sizes and functionalities, which together define their programmable properties, show promise in advancing chemical detection. This review demonstrates the recent progress in chemical detection where COFs constitute an integral component of the achieved function. This review highlights how the unique properties of COFs can be harnessed to develop different types of chemical detection systems based on the principles of chromism, luminescence, electrical transduction, chromatography, spectrometry, and others to achieve highly sensitive and selective detection of various analytes, ranging from gases, volatiles, ions, to biomolecules. The key parameters of detection performance for target analytes are summarized, compared, and analyzed from the perspective of the detection mechanism and structure-property-performance correlations of COFs. Conclusions summarize the current accomplishments and analyze the challenges and limitations that exist for chemical detection under different mechanisms. Perspectives on how future directions of research can advance the COF-based chemical detection through innovation in novel COF design and synthesis, progress in device fabrication, and exploration of novel modes of detection are also discussed.

Fabrication of carbonyl-functional hypercrosslinked polymers as solid-phase extraction sorbent for enrichment of chlorophenols from water, honey and beverage samples

Three carbonyl-functional novel hypercrosslinked polymers (HCP-TPS, HCP-TPA, and HCP-TPP) were successfully fabricated through an one-step Friedel-Crafts acylation reaction by copolymerizing paraphthaloyl chloride with triphenylsilane, triphenylamine, and triphenylphosphine, respectively. The resultant HCPs contained plenty of carbonyl-functional groups. Among the series of such HCPs, HCP-TPS displayed the best adsorption capability to chlorophenols (CPs), and thus it was employed as solid-phase extraction (SPE) adsorbent for enrichment of chlorophenols from water, honey, and white peach beverage prior to determination by high-performance liquid chromatography. Under the optimal conditions, the detection limits of the method (S/N = 3) were 0.15-0.3 ng mL^-1 for tap water and leak water, 2.5-6.0 ng g^-1 for honey sample and 0.4-0.6 ng mL^-1 for white peach beverage sample. The recoveries of CPs in the spiked water, honey samples, and white peach beverage were in the range of 89.0-108.4%, 81.4-118.2%, and 85.0-113.5%, respectively. This work provides a new strategy for constructing functionalized HCPs as efficient SPE adsorbents. In this work, three novel hypercrosslinked polymers (HCPs) were synthesized by the Friedel-Crafts alkylation reaction (paraphthaloyl chloride as the alkylating agent, triphenylsilane, triphenylamine, and triphenylphosphine as the aromatic units). Then, HCP-TPS was applied to soild-phase extraction sorbent for enrichment CPs from water, honey, and white peach beverage samples.

Plugged bifunctional periodic mesoporous organosilica as a high-performance solid phase microextraction coating for improving extraction efficiency of chlorophenols in different matrices

In this study, a sensitive solid phase microextraction (SPME) coating was developed based on two kinds of plugged and non-plugged bifunctional periodic mesoporous organosilicas (BFPMO) with ionic liquid and ethyl units. The extraction efficiency of all plugged and unplugged sorbents was investigated for the extraction of chlorophenols (CPs) in water and honey samples by emphasizing the effect of different physicochemical properties. The separation and determination of the CPs was performed by gas chromatography-mass spectrometry (GC-MS). The extraction results showed that plugged BFPMO coating exhibited outstanding enrichment ability for the extraction of CPs as model analytes with different polarities. This can be attributed to a valuable hydrophobic-hydrophilic balance in the mesochanels of the plugged BFPMO, which is the result of the combination of plug technology and bridged organic groups. Low limits of detection in the range of 5-70 ng L^-1, wide linearity, and good reproducibility (RSD = 8.1-10.1 % for n = 6) under the optimized extraction conditions were achieved. Finally, the BFPMOs coated fiber was successfully used for determination of CPs in real water samples. The relative recoveries for the five CPs were in the range of 92.3-104.0 %, which proved the applicability of the method.

Capillary coated with three-dimensional covalent organic frameworks for separation of fluoroquinolones by open-tubular capillary electrochromatography

The Schiff-base reaction of 1,3,5-triformylphloroglucinol (Tp) and tetra(4-aminophenyl)methane (TAM) was performed for the synthesis of a three-dimensional covalent organic framework named 3D TpTAM, which was obtained by an ultrasound-assisted method for the first time. The morphology and structure of the synthesized TpTAM were characterized through various methods. Then, TpTAM-coated capillary columns were subsequently prepared by a covalent bonding method within a short time and applied for the separation of fluoroquinolones by capillary electrochromatography (CEC) with good resolution and reproducibility. The intraday relative standard deviations (RSDs) of the retention time and peak areas were 0.88%-0.95% and 2.27%-3.81%, respectively. The interday RSDs of retention time and peak areas were 0.71%-0.89% and 0.88%-3.60%, respectively. The column-to-column RSDs of retention time and peak areas were less than 1.90% and 13.56%, respectively. The interbatch RSDs of retention time and peak areas were less than 3.48% and 3.89%, respectively. The TpTAM-coated capillary columns could be used for no less than 100 runs with no observable changes in the separation efficiency. The separation mechanism was also studied, which indicated that π-π stacking effects, hydrophobic interactions and hydrogen bonding were the main factors. The results revealed that 3D TpTAM should have superior potential as the stationary phase in CEC for chromatographic separation.

Applications of covalent organic frameworks and their composites in the extraction of pesticides from different samples

Pesticides are used extensively in a wide range of applications and due to their high rate of consumption, they are ubiquitous in the different media and samples like environment, water sources, air, soil, biological materials, wastes (liquids, solids or sludges), vegetables and fruits, where they can persist for long periods. Pesticides often have hazardous side effects and can cause a range of harmful diseases like Parkinson, Alzheimer, asthma, depression and anxiety, cancer, etc, even at low concentrations. To this end, extraction, pre-concentration and determination of pesticides from various samples presents significant challenges caused by sample complexity and the low concentrations of them in many samples. Often, direct extraction and determination of pesticides are impossible due to their low concentrations and the complexity of samples. The main goals of sample preparation are removing interfering species, pre-concentrating target analyte/s and converting the analytes into more stable forms (when needed). The most popular approach is solid-phase extraction due to its simplicity, efficiency, ease of operation and low cost. This method is based on using a wide variety of materials, among which covalent organic frameworks (COFs) can be identified as an emerging class of highly versatile materials exhibiting advantageous properties, such as a porous and crystalline structure, pre-designable structure, high physical and chemical stability, ease of modification, high surface area and high adsorption capacity. The present review will cover recent developments in synthesis and applications of COFs and their composites for extraction of pesticides, different synthesis approaches of COFs, possible mechanisms for interaction of COFs-based adsorbents with pesticides and finally, future prospects and challenges in the fabrication and utilization of COFs and their composites for extraction of pesticides.

A solid-phase microextraction fiber coating based on magnetic covalent organic framework for highly efficient extraction of triclosan and methyltriclosan in environmental water and human urine samples

Herein, we synthesized a kind of magnetic covalent organic framework nanohybrids (NiFe₂O₄@COF), and integrated it with polydimethyl siloxane and silicone rubber curing agent for solid phase microextraction (SPME) fiber coating. The fiber coating demonstrated a porous and uniform surface with the BET specific surface of 169.7 m² g^-1. As for seven environmental analytes, the NiFe₂O₄@COF-based SPME fiber coating gave the higher extraction recoveries for triclosan (TCS) and methyltriclosn (MTCS) than those of fenpropathrin, bifenthrin, permethrin, fenvalerate and deltamethrin. Several operational parameters were rigorously optimized, such as extraction temperature, extraction time, thermal desorption time, solution pH and salt effect. Combined with the GC-ECD detection, the newly developed microextraction method supplied the wide linear range of 0.1-1000 µg L^-1 with the correlation coefficients of > 0.9995. The limits of detection (LODs) and limits of quantitation (LOQs) reached as low as 1-7 ng L^-1 and 3.3-23 ng L^-1, respectively. The intra-day and inter-day precisions in six replicates (n = 6 ) were < 3.55% and < 5.06%, respectively, and the fiber-to-fiber reproducibility (n = 3) was < 7.64%. To evaluate its feasibility in real samples, the fortified recoveries for TCS and MTCS, at low (0.2 µg L^-1), middle (2.0 µg L^-1) and high (20.0 µg L^-1) levels, varied between 81.9% and 119.1% in tap, river and barreled waters as well as male, female and children urine samples. Especially, it is worth mentioning that the NiFe₂O₄@COF-based SPME coating fiber can be recycled for at least 150 times with nearly unchanged extraction efficiency. Moreover, the extraction recoveries by the as-fabricated fiber coating were much higher than those by three commercial fibers (PDMS, PDMS/DVB and PDMS/DVB/CAR). Overall, the NiFe₂O₄@COF-based SPME is a convenient, sensitive, efficient and "green" pretreatment method, thereby possessing important application prospects in trace monitoring of TCS-like pollutants in complex liquid matrices.

Ketoenamine Covalent Organic Framework Coating for Efficient Solid-Phase Microextraction of Trace Organochlorine Pesticides

Fiber coating is a key part of solid-phase microextraction (SPME) technology, and it determines the selectivity, sensitivity, and reproducibility of the analytical method. A ketoenamine covalent organic framework called Tp-Azo-COF with rich electronegative N atoms was prepared as an SPME coating in this work. The Tp-Azo-COF coating had a large surface area of 1218 m² g^-1 and good thermal and chemical stability, and it was applied for the extraction of organochlorine pesticides (OCPs). According to quantum chemistry calculations, the adsorption affinity of the Tp-Azo-COF coating for five OCPs was primarily affected by the halogen bond and hydrophobicity interaction. The extraction efficiencies of the Tp-Azo-COF coating for five OCPs were higher than those of three commercial SPME fiber coatings, and the enrichment factors ranged from 1061 to 3693. When combined with gas chromatography-tandem mass spectrometry, a wide linear range (0.1-1000 ng L^-1), low limits of detection (0.002-0.08 ng L^-1), and good fiber-to-fiber accuracy (4.3-10.9%) were achieved under optimal conditions. Moreover, the applicability of the developed method was evaluated by analyzing four samples (milk, green tea, tap water, and well water), and the recoveries were in the range of 83.4-101.6%, with relative standard deviations <8.6%. This research extends the application of the stabilized ketoenamine COF as a sample enrichment probe for OCP analysis.

Facile synthesis of uniform spherical covalent organic frameworks for determination of neonicotinoid insecticides

A uniform spherical structure covalent organic framework (TAPA-BPDA-COF) was prepared by a facile method at room temperature with tris(4-aminophenyl)amine (TAPA) and 4,4'-biphenyldicarboxaldehyde (BPDA) as building blocks. Based on the solid phase extraction with the TAPA-BPDA-COF as the sorbent and high performance liquid chromatography-diode array detection, a sensitive analytical method was established for the determination of four neonicotinoid insecticides from water and honey samples. Under the optimum conditions, good linear response for the quantification of the analytes was achieved in the range of 0.3-50.0 ng mL^-1 for water samples and in the range of 8.0-500.0 ng g^-1 for honey samples. The method recoveries fell in the range of 80.0-121.9% with RSDs less than 7.6%. The limits of detection at the signal to noise ratio of 3 were measured to be in the range of 0.08-0.12 ng mL^-1 for water samples and 2.6-3.3 ng g^-1 for honey samples, depending on compounds.

Benzoxazine Porous Organic Polymer as an Efficient Solid-Phase Extraction Adsorbent for the Enrichment of Chlorophenols from Water and Honey Samples

Porous organic polymers have gained great research interest in the field of adsorption. A benzoxazine porous organic polymer (BoxPOP) constructed from p-phenylenediamine, 1,3,5-trihydroxybenzene and paraformaldehyde was fabricated and explored as an adsorbent for solid-phase extraction (SPE) of four chlorophenols from water and honey samples. Under the optimized SPE conditions, the response linearity for the analysis of the SPE extract of the chlorophenols by high performance liquid chromatography-diode array detector was observed in the range of 0.2-40.0 ng mL-1 for water samples and 5.0-400.0 ng g-1 for honey samples. The method detection limits of the analytes were 0.06-0.08 ng mL-1 for water samples and 1.5-2.0 ng g-1 for honey samples. The recoveries of the analytes from fortified water and honey samples ranged from 84.8 to 119.0% with the relative standard deviations below 8.4%. The results indicate that the prepared BoxPOP is an effective adsorbent for the chlorophenols. The established method provides an alternative approach for the determination of chlorophenols in real samples.

Solid-phase microextraction of eleven organochlorine pesticides from fruit and vegetable samples by a coated fiber with boron nitride modified multiwalled carbon nanotubes

A boron nitride modified multiwalled carbon nanotube material (BN@MWCNTs) was synthesized, and the synthesis conditions were optimized. The BN@MWCNTs was then used as the SPME fiber coating adsorbent for the extraction of eleven organochlorine pesticides (OCPs) from fruit and vegetable samples. Under the optimal conditions, the SPME coupled with the detection by GC-ECD had a linear response for the determination of the target analytes in the range of 0.03 to 200 ng g^-1 with the coefficients of determination (r²) ≥ 0.9977. Based on the signal-to-noise ratios of 3 and 10, the limits of detection and the limits of quantification were measured to be 0.01-0.20 ng g^-1 and 0.03-0.67 ng g^-1, respectively. The relative recoveries of the analytes for spiked samples under three concentration levels (1.0, 10.0 and 100 ng g^-1) were between 83.7% and 124% with the relative standard deviations ≤ 10.9%. The established method was successfully applied to the determination of OCPs in real fruit and vegetable samples.

Membrane-protected covalent organic framework fiber for direct immersion solid-phase microextraction of 17beta-estradiol in milk

17beta-estradiol (E2) could accumulate in human body through milk and cause various diseases by interfering with the endocrine system. Herein, we coated stainless steel wire with covalent organic framework LZU1 (COF-LZU1) and Nafion protected by dialysis membrane for direct immersion solid phase microextraction (DI-SPME) and coupled with gas chromatography-flame ionization detection (GC-FID) for the detection of trace E2 in milk samples. With dialysis membrane protection, the stability of SPME fiber was improved and the extraction efficiency was only reduced by 7% after repeated use of 160 times. The extraction efficiency of E2 with the home-made fiber COF-LZU1 was 22.1, 8.4, 3.6 times higher than that of bare stainless steel wire, PDMS/DVB and PDMS, respectively. The method had been successfully applied to milk samples, and the relative recoveries were between 77.27% and 108.26%. It can provide an effective and general method for the pretreatment of complex matrix samples.

Preparation of Polyacrylonitrile/Ni-MOF electrospun nanofiber as an efficient fiber coating material for headspace solid-phase microextraction of diazinon and chlorpyrifos followed by CD-IMS analysis

Herein, an electrospun polyacrylonitrile/nickel-based metal-organic framework nanocomposite (PAN/Ni-MOF) coating on a stainless steel wire was synthesized and employed as a novel nanosorbent for headspace solid-phase microextraction (HS-SPME) of organophosphorus pesticides (OPPs), diazinon (DIZ), and chlorpyrifos (CPS) from the diverse aqueous media followed by corona discharge ion mobility spectrometry (CD-IMS). Under the optimum experimental conditions, the calibration plots were linear in the range of 1.0-250.0 ng mL^-1 for DIZ and 0.5-300.0 ng mL^-1 for CPS with r² > 0.999. The detection limits (S/N = 3) were 0.3 and 0.2 ng mL^-1 for DIZ and CPS, respectively. The intra-day relative standard deviations (RSDs%) (n = 5) at the concentration levels of 20.0, 40.0, and 100.0 ng mL^-1 were ≤ 5.2%. To investigate the extraction efficiency, PAN/Ni-MOF was employed to analyze various juice samples, including orange, apple, and grape juices, and in three water samples where it led to good recoveries ranged between 87% and 98%.

[Synthesis and application progress of covalent organic polymers in sample preparation for food safety analysis]

Food safety is closely related to human health and life. Contaminated foods may result in illness or poisoning. For example, perfluorinated compounds can concentrate in the human body, or they can be transferred to the baby during breastfeeding, thus leading to serious health risks. Phthalate esters may cause damage to the liver, lungs, and kidneys. Therefore, food safety has become a hot topic at a global level. Poisonous and harmful substances in foods are derived from the environment, planting or breeding, food contacting materials, and food processing, or due to unsuitable storage conditions. Residues of pesticides and veterinary drugs, organic pollutants, additives, heavy metals, and biotoxins often hamper food safety, causing diseases or even death. The diversity of available food species, complexity of the sample matrix, and lack of information about the source of pollutants render the direct determination of food contaminants difficult. Pretreatment is vital for the accurate analysis of trace toxins in foods. Optimal pretreatment can not only improve the extract efficiency and determination sensitivity, but also prevent instrument contamination. Pretreatment techniques have played an important role in trace determination for complex matrices. Pretreatment methods can be classified as solvent-based and adsorption-based methods. Adsorption-based techniques such as solid-phase extraction, magnetic solid-phase extraction, and solid-phase microextraction are simple and efficient, and hence, are widely used. In these pretreatment techniques, adsorbents play a key role in the extraction effect. In the last few years, metal organic frameworks, metal oxide materials, carbon nanotubes, graphene, and magnetic nanoparticles, as well as a combination of these materials, have been used as adsorbents. These materials are porous and have a large surface area; they are used to enrich trace targets and eliminate interferents. Covalent organic polymers (COPs) are a class of organic porous materials constructed from organic monomers via covalent bonding. Given their excellent characteristics such as light density, good stability, high surface area, structural controllability, and ease of modification, COPs are potential adsorbents. COPs are often synthesized by solvent thermal methods. However, these methods are time-consuming and require toxic solvents and harsh reaction conditions. As alternatives, room-temperature methods, mechanical chemical methods, microwave-assisted methods, and UV-assisted methods have been developed. This has facilitated the synthesis of a wide range of COPs. In this article, the recent applications of COPs in sample pretreatment for food safety analysis are reviewed. COPs can be used in solid-phase extraction by simple packing into columns, polymerization, or chemical bonding in the capillary. Magnetic compounds have been prepared by one-pot synthesis, in situ growth, in situ reduction, or coprecipitation methods and used in magnetic solid-phase extraction. Coatings of solid-phase microextraction fibers are fabricated by physical methods, chemical bonding, sol-gel methods, or in situ growth. Toxic and harmful substances in foods and foodstuffs are efficiently extracted by exploiting the high adsorbent capacities and specificity of COPs. Future development prospects and challenges in sample pretreatment are also discussed herein. There is increased focus on the development of simple, efficient, and environment-friendly methods to synthesize COPs with specific functions; further, high-throughput, sensitive analytical methods may be established. In the future, more specific COPs will be prepared in a cost-effective manner for widespread use in sample pretreatment.

Covalent organic framework Schiff base network-1-based pipette tip solid phase extraction of sulfonamides from milk and honey

In this work, a covalent organic framework Schiff base network-1 (SNW-1), was synthesized based on the Schiff base reaction between terephthalaldehyde and melamine and characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction and nitrogen adsorption-desorption isotherm analyses. The prepared SNW-1 was employed as pipette tip solid phase extraction adsorbent for the extraction of sulfonamides (SAs) prior to high performance liquid chromatography analysis. The parameters affecting the extraction efficiency, including the salt concentration, sample pH, amount of adsorbent, and types and volume of eluent were investigated in detail. Good linearities were obtained between the peak area and SAs concentration ranging from 5 to 500 ng mL^-1 with correlation coefficients (R²) higher than 0.9998. The limits of detection and RSDs were lower than 0.25 ng mL^-1 and 1.9 %, respectively. The developed method was further applied for the determination of SAs in milk and honey samples with recoveries in the range of 85.8 % - 118.0 % and RSDs less than 9.5 %. The results demonstrate that the SNW-1 shows great potential for the enrichment of trace SAs in complex matrices.

Introducing reticular chemistry into agrochemistry

For survival and quality of life, human society has sought more productive, precise, and sustainable agriculture. Agrochemistry, which solves farming issues in a chemical manner, is the core engine that drives the evolution of modern agriculture. To date, agrochemistry has utilized chemical technologies in the form of pesticides, fertilizers, veterinary drugs and various functional materials to meet fundamental demands from human society, while increasing the socio-ecological consequences due to inefficient use. Thus, more useful, precise, and designable scaffolding materials are required to support sustainable agrochemistry. Reticular chemistry, which weaves molecular units into frameworks, has been applied in many fields based on two cutting-edge porous framework materials, namely metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs). With flexibility in composition, structure, and pore chemistry, MOFs and COFs have shown increasing functionalities associated with agrochemistry in the last decade, potentially introducing reticular chemistry as a highly accessible chemical toolbox into agrochemical technologies. In this critical review, we will demonstrate how reticular chemistry shapes the future of agrochemistry in the fields of farm sensing, agro-ecological preservation and reutilization, agrochemical formulations, smart indoor farming, agrobiotechnology, and beyond.

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.

Zr-MOF modified cotton fiber for pipette tip solid-phase extraction of four phenoxy herbicides in complex samples

Phenoxy herbicides are widely applied in agricultural weeding. The determination of herbicides is important in environmental protection, agricultural production, food safety, and public health. In this study, a facile and efficient analytical method was proposed for the trace detection of phenoxy herbicides in soil, cucumber, and tap water samples by coupling pipette tip solid phase extraction (PT-SPE) with high performance liquid chromatography. UiO-66-funtionalized cotton (Cotton@UiO-66) was packed into pipette-tip as sorbent to fabricate extraction device. The modification of UiO-66 on cotton fiber was confirmed using scanning electron microscope, Fourier transform infrared spectroscopy, and X-ray diffraction. The main factors affecting the adsorption of Cotton@UiO-66 for four phenoxy herbicides were evaluated by response surface methodology in detail. Under optimized conditions, Cotton@UiO-66 displayed excellent properties in the extraction of phenoxy herbicides with good peak shape. Linear ranges of 4-chlorophenoxyacetic acid, dicamba, 2,4-dichlorophenoxyacetic acid, and 2-(2,4-dichlorophenoxy) propionic acid were 1.4-72 μg/L, 5.6-280 μg/L, 2.8-140 μg/L and 3.2-160 μg/L (RSDs < 6.3%), respectively. The recoveries were between 83.3 and 106.8% with RSDs <6.7%, with detection limits ranging from 0.1 μg/L to 0.3 μg/L. The results show that Cotton@UiO-66 in PT-SPE is an effective method for monitoring phenoxy herbicides in complex samples.

Covalent Organic Frameworks in Sample Preparation

Covalent organic frameworks (COFs) can be classified as emerging porous crystalline polymers with extremely high porosity and surface area size, and good thermal stability. These properties have awakened the interests of many areas, opening new horizons of research and applications. In the Analytical Chemistry field, COFs have found an important application in sample preparation approaches since their inherent properties clearly match, in a good number of cases, with the ideal characteristics of any extraction or clean-up sorbent. The review article is meant to provide a detailed overview of the different COFs that have been used up to now for sample preparation (i.e., solid-phase extraction in its most relevant operational modes-conventional, dispersive, magnetic/solid-phase microextraction and stir-bar sorptive extraction); the extraction devices/formats in which they have been applied; and their performances and suitability for this task.