Covalent Organic Frameworks-Based Solid-Phase Microextraction Probe for Rapid and Ultrasensitive Analysis of Trace Per- and Polyfluoroalkyl Substances Using Mass Spectrometry

Determination of anionic perfluorinated compounds in water samples using cationic fluorinated metal organic framework membrane coupled with UHPLC-MS/MS

Global concerns stem from the environmental crisis have compelled researchers to develop selective and sensitive methods for the identification and measurement of emerging pollutants in the environmental matrices. The cationic F-TMU-66⁺Cl^-/polyvinylidene fluoride metal-organic frameworks (MOFs) mixed matrix membrane (F-TMU-66⁺Cl^-/PVDF MMM) was synthesized and used as a versatile adsorbent with multiple binding sites for the simultaneous extraction of twelve anionic perfluorinated compounds (PFCs) from reservoir water samples. The physical and chemical characteristics of the materials, as well as adsorption mechanism were fully surveyed by various instrumental techniques. Important extraction parameters, including amount of MOFs, pH, desorption conditions, and salinity were systematically investigated and optimized. The combination of dispersive membrane solid extraction based on F-TMU-66⁺Cl^-/PVDF MMM with ultra-high performance liquid chromatography-tandem mass spectrometry provided ultra-low limit of detections within the range of 0.03-0.48 ng/L. By virtue of the simplicity and robustness of the extraction procedure, high sensitivity of detection scheme, good stability and selectivity of the F-TMU-66⁺Cl^-/PVDF MMM, the developed method exhibits excellent practicability for ultra-trace analysis of anionic PFCs in water samples.

Superficially capped amino metal-organic framework for efficient solid-phase microextraction of perfluorinated alkyl substances

Perfluorinated alkyl substances (PFASs) were ubiquitously in the surface and groundwater. It is crucial and urgent to develop a rapid and ultrasensitive analysis method for the quantification of trace-level PFASs. Herein, a highly hydrophobic sorbent by capping phenylsilane groups on the surfaces of NH₂-UiO-66(Zr) nanocrystals was used for efficient solid-phase microextraction (SPME) of PFASs in water samples. It was found that the superficially capped nanocrystals (NH₂-UiO-66(Zr)-hp) exhibited both faster extraction kinetics and higher enrichment capacity than the non-capped nanocrystals. The extraction of eleven kinds of PFASs by NH₂-UiO-66(Zr)-hp fiber reached equilibrium in 20 min. The enrichment factors of the NH₂-UiO-66(Zr)-hp fiber ranged from 6.5 to 48, with a preference for long-chain PFASs over short-chain PFASs. It was proposed that superficial capping eliminated competitive moisture adsorption on the surfaces of the non-capped nanocrystals, thus facilitating the adsorption of PFASs through hydrophobic interaction. By using this new sorbent, the limits of detection of the SPME method as low as 0.035 to 0.616 ng·L^-1 were achieved for the target PFASs. The recoveries of PFASs in the environmental water samples were 80.9%-120%. This study presents a new strategy for developing an efficient sorbent for PFASs by surface hydrophobic modification.

Covalent organic framework-based solid phase microextraction coupled with electrospray ionization mass spectrometry for sensitive screening and quantitative evaluation of carbamazepine and its metabolite in mice

Carbamazepine (CBZ) and its metabolite carbamazepine-10,11-epoxide (CBZEP) play vital role in the treatment of epilepsy. It is of great importance to develop a method for rapid and sensitive monitoring of CBZ and CBZEP due to their narrow therapeutic index. Herein, an imine-linked-based covalent organic framework was synthesized by using 1,3,5-tris (4-aminophenyl) benzene (TPB) and 1,3,5-triformylbenzene (TFB) (denoted as TPB-TFB-COF)，and applied as a solid-phase microextraction (SPME) probe for extracting CBZ and CBZEP. The TPB-TFB-COF showed large surface areas (371 m² g^-1), high regular porosity (1.23 nm) and extraordinary stability, which rendered it an ideal adsorbent for highly efficient enrichment of CBZ and CBZEP. Accordingly, an attractive strategy of the combination of the TPB-TFB-COF-based SPME probe and electrospray ionization mass spectrometry system (ESI/MS) was proposed for rapid screening and sensitive monitoring of CBZ and CBZEP. Under the optimized parameters, the developed method exhibited good linearity for CBZ and CBZEP in the range of 4-1000 μg L^-1 with correlation coefficient (r) no less than 0.9953, and the corresponding limits of detection (LODs) were 0.4 and 2.5 μg L^-1, respectively. Moreover, high enrichment factors (EFs, 202-351 folds) and satisfactory relative standard deviations (RSDs) of one probe (3.3-5.1%) and probe-to-probe (4.8-5.6%) were obtained. By using the proposed method, sensitive screening and quantitative evaluation of CBZ and CBZEP in mice whole blood and tissue homogenates were successfully achieved, indicating the promising applicability of the TPB-TFB-COF-SPME-AMIS as a powerful tool for drug monitoring.

Matrix compatibility of typical sol-gel solid-phase microextraction coatings in undiluted plasma and whole blood for the analysis of phthalic acid esters

Sol-gel materials have been widely used for solid-phase microextraction (SPME) coatings due to their outstanding performance; in contrast, sol-gel SPME coatings have seldom been used for in vivo sampling. The main reason is that their matrix compatibility is unclear. In order to promote the application of this type of coating and accelerate the development of in vivo SPME, in this study, the matrix compatibility of several typical sol-gel coatings was assessed in plasma and whole blood using phthalic acid esters as analytes. The service life of five kinds of sol-gel coatings was among 20-35 times in undiluted plasma, while it was 27 times for a homemade commercial polydimethylsiloxane coating, which indicates good matrix compatibility of sol-gel coatings in untreated plasma. The sol-gel hydroxy-terminated silicone oil/methacrylic acid fiber achieved the highest extraction ability among all of the fibers, and it was tested in pig whole blood. It could be continuously used for at least 22 times, demonstrating good potential for in vivo sampling. Subsequently, a direct-immersion SPME/gas chromatography-flame ionization detection method was established for the determination of 5 phthalic acid esters in blood. Compared with other methods reported in the literature, this method is rapid, simple, sensitive, and accurate, and does not need expensive instruments or tedious procedures. A simulation system of animal blood circulation was constructed to verify the practicability of sol-gel SPME coatings in animal vein sampling. The result illustrated the feasibility of that coating for in vivo blood sampling, but a more accurate quantification calibration approach needs to be explored.

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.

Portable paper-in-tip spray ionization for the direct mass spectrometric analysis of target analytes in biofluid samples

Portable sampling of target analytes in complex biofluid samples makes mass spectrometric analysis more efficient. This study reports the development of paper-in-tip spray ionization for solid-phase microextraction and in situ electrospray of therapeutic drugs and proteins in complex biological matrices using a piece of hydrophobic paper substrate. This technique possesses a long (more than 8 min) and stable spray duration with only 20 μL of spray solvent. The entire analytical process for a complex sample can be completed in less than 1.5 min and enables high sensitivity (picogram-per-milliliter level) and high quantitation precision.

Novel solid-phase microextraction fiber coatings: A review

The materials used for the fabrication of solid-phase microextraction fiber coatings in the past five years are summarized in the current review, including carbon, metal-organic frameworks, covalent organic frameworks, aerogel, polymer, ionic liquids/poly (ionic liquids), metal oxides, and natural materials. The preparation approaches of different coatings, such as sol-gel technique, in-situ growth, electrodeposition, and glue methods, are briefly reviewed together with the evolution of the supporting substrates. In addition, the limitations of the current coatings and the future development directions of solid-phase microextraction are presented.

Fabrication of a Magnetic Fluorinated Covalent Organic Framework for the Selective Capture of Benzoylurea Insecticide Residue in Beverages

Efficient capture of benzoylurea insecticide (BU) residue in food is a vital procedure for food safe monitoring. Herein, a core-shell structured magnetic fluorinated covalent organic framework with good magnetic responsiveness and abundant fluorine affinity sites was successfully synthesized, suitable for magnetic solid-phase extraction (MSPE) of BUs. Using a room-temperature synthesis strategy, the magnetic fluorinated covalent organic framework was fabricated by in situ polymerization of 1,3,5-tris(4-aminophenyl) triazine (TAPT) and 2,3,5,6-tetrafluoroterephthaldehyde (TFTA) on the surface of carboxylated Fe₃O₄ nanoparticles. The competitive adsorption experiment and molecular simulation verified that this magnetic fluorinated covalent organic framework possesses favorable adsorption affinity for BUs. This magnetic fluorinated covalent organic framework could be easily regenerated and reused at least eight times with no reduction of enrichment performance. Combining this magnetic fluorinated covalent organic framework-based MSPE with high-performance liquid chromatography-tandem mass spectrometry, a novel sensitive method for the analysis of BUs was developed. In yellow wine and fruit juice samples, good linear correlations were obtained for BUs in the range of 10-2000 and 20-4000 ng·L^-1, respectively. The limit of quantitation of the BUs ranged from 1.4 to 13.3 ng·L^-1 in the two beverage matrices. Desirable precision was achieved, with intraday and interday relative standard deviations lower than 11%.

Determination of sulfonamides in meat by monolithic covalent organic frameworks based solid phase extraction coupled with high-performance liquid chromatography-mass spectrometric

In this work, hierarchical porous covalent organic frameworks (HP-COFs) foam, named as HP-TpBD, was prepared by using 1,3,5-trimethylphloroglucinol (Tp) and benzidine (BD) as building blocks under the assistant of NaCl template. Its potential application as the sorbent for solid phase extraction (SPE) of sulfonamides (SAs) in meat products were explored by coupling with high performance liquid chromatography-mass spectrum (HPLC-MS) analysis. The key factors affecting extraction efficiency were well studied. Under the optimum conditions, the proposed method exhibited high preconcentration factors of 100, low limit of detection (0.10-0.23 μg/kg), and wide linear ranges (0.5-200 μg/kg). In addition, the determination of SAs in real samples were realized with satisfactory recoveries (82.8-119.9%), demonstrating the applicability of the proposed method. The easy operation, superior extraction affinity and good recycle performance demonstrated the resulting HP-COF foam is a promising adsorbent for the preconcentration of trace organic compounds from complex matrix.

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.

Core-shell structured Fe2O3/CeO2@MnO2 microspheres with abundant surface oxygen for sensitive solid-phase microextraction of polycyclic aromatic hydrocarbons from water

Core-shell structured Fe₂O₃/CeO₂@MnO₂ microspheres were fabricated and used as solid-phase microextraction coating for determination of polycyclic aromatic hydrocarbons (PAHs) in water samples. XPS spectra demonstrated the generation of abundant surface oxygen on Fe₂O₃/CeO₂@MnO₂ microspheres, which provided binding sites for enhancement of analyte extraction. Under optimized conditions, the proposed method presented good linearity in the concentration range 0.04-100 ng mL^-1, with low limits of detection varying from 0.38 to 3.57 ng L^-1 for eight PAHs. Relative standard deviations for a single fiber and five batches of fibers were in the ranges of 4.1-8.2% and 7.1-11.4%, respectively. The proposed method was successfully used for determination of PAHs in real river water samples with recoveries ranging from 87.1 to 115.9%. The proposed method using as-prepared Fe₂O₃/CeO₂@MnO₂ microspheres as SPME coating exhibit significant potential for real sample analysis due to its excellent reproducibility, high sensitivity, and good linearity.

Dual-Functionalized MIL-101(Cr) for the Selective Enrichment and Ultrasensitive Analysis of Trace Per- and Poly-fluoroalkyl Substances

The presence of per- and poly-fluoroalkyl substances (PFASs) even at trace levels poses a potential threat to ecological safety and human health. PFASs often require an extraction pretreatment for enrichment before detection and analysis, which is still challenged by the relatively low efficiency because of the limited specific interactions involved. Here, we deliberately introduced multiple interactions into the solid-phase microextraction (SPME) process via a dual-functional modification of MIL-101(Cr), i.e., amination and subsequent fluorination, which is then used as an adsorbent for the efficient enrichment of PFASs. In combination with ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS), ultrasensitive quantitative analysis is available for nine selected PFASs with high linearities above 0.9941 in the ranges of 0.5-1500 ng/L, low limits of detection of 0.004-0.12 ng/L, satisfactory repeatability and reproducibility with a relative standard deviation (RSD) < 11.6%, as well as excellent performance in complicated real water samples (recovery ratio of 76.2-108.6%). This work represents a rational design of a solid extractant with the desired structure and functionality for the selective enrichment and analysis of PFASs at trace concentrations in real applications.

Heteropore covalent organic framework-based composite membrane prepared by in situ growth on non-woven fabric for sample pretreatment of food non-targeted analysis

A heteropore covalent organic framework (COF)-based composite membrane material was prepared and proved to have a satisfactory effect on the pretreatment of vegetable samples. The composite membrane was fabricated by in situ growth of a dual-pore COF on the surface of polydopamine (PDA)-aminated non-woven (NW) fabric. Due to the difference in the strength of the interaction between the phytochromes/COF and the pesticides/COF, the removal of phytochromes and the recovery of pesticides can be achieved by adjusting the composition of the solution. Through a simple immersion or filtration operation, NW@PDA@COF composite membrane can quickly and almost completely remove interfering phytochromes in the samples. The recovery of pesticides was determined by HPLC-MS/MS, and the recovery efficiencies were 72.3~101.7% and 67.3~106.7% for immersion and filtration modes of five different vegetable samples, respectively; the RSD is between 1.1 and 19% (n = 3). The limits of detection and quantification for the 13 pesticides investigated were 0.08 μg·L^-1 and 0.23 μg·L^-1, respectively. A wide linear range of 1~1000 μg·L^-1 was observed with R² values from 0.9774 to 0.9998. The membrane can be repeatedly used for at least 10 times by using a facile elution treatment. Compared to other commonly used sample pretreatment materials, heteropore COF-based composite membrane is superior in terms of sorbent amount, treatment time, operation simplicity, and material reusability.

Sulfonic acid functionalized hierarchical porous covalent organic frameworks as a SALDI-TOF MS matrix for effective extraction and detection of paraquat and diquat

Design and construction of a matrix with specific adsorption on the target compounds can effectively reduce the detection limit of surface-assisted laser desorption/ionization time-of-flight mass spectrometry (SALDI-TOF MS) analysis. Sulfonic acid functionalized hierarchical porous covalent organic frameworks (H-COF-SO₃H) was synthesized by defect-structure and post-modification method, and then used as matrix and adsorbent for the determination of quaternary ammonium herbicides paraquat (PQ) and diquat (DQ). N₂ adsorption-desorption experiments confirmed that H-COF-SO₃H possesses hierarchical porosity with pore widths concentrated at 1.3,1.5, and 2.8 nm. The strong UV absorption at 200-450 nm and good thermal stability made H-COF-SO₃H being a promising matrix without background interference. H-COF-SO₃H can efficiently enrich PQ and DQ via electrostatic attraction, and the key role of -SO₃H group on specific adsorption was confirmed by density functional theory (DFT) calculations. The limits of detection (LODs) for PQ and DQ with H-COF-SO₃H enrichment were 0.5 and 0.1 ng·mL^-1, respectively, which were 20 and 60 times higher than those without H-COF-SO₃H enrichment, respectively. The spiked recoveries of PQ and DQ for the three food samples were 92.0-113.2% and 80.1-102.6% with RSDs of 2.2-9.2% and 2.0-8.7%, respectively. This work provides an analyte-oriented approach for fabricating SALDI-TOF MS matrix.

Online extraction based on ionic covalent organic framework for sensitive determination of trace per- and polyfluorinated alkyl substances in seafoods by UHPLC-MS/MS

The ionic covalent organic framework (TPB-BFBIm-iCOF) was facilely synthetized by the size-controllable confinement method and chosen as the online solid phase extraction (SPE) adsorbent. This adsorbent showed fast adsorption equilibrium (5 min) and high adsorption capacity (87.7-140.8 mg g^-1) for the per- and polyfluorinated alkyl substances (PFASs). The TPB-BFBIm-iCOF microsphere revealed the satisfactory enrichment performance for PFASs by means of the electrostatic interaction, hydrophobic effect and ordered channel structure. After extraction, the loaded TPB-BFBIm-iCOF-online SPE column was eluted and applied to the ultrahigh performance liquid chromatography tandem mass spectrometry analysis. Under the optimum conditions, the method displayed satisfactory linearity (R² ≥ 0.9910) and low limits of detection (≤0.0017 ng g^-1) for five seafoods. The relative recoveries of PFASs were 85.3%-109.4% with the relative standard deviation ≤ 9.9%. The method exhibited potential value in monitoring the toxicokinetics and environmental behaviors of PFASs.

Green bioanalytical sample preparation: fabric phase sorptive extraction

Fabric phase sorptive extraction (FPSE) is a recently introduced sample preparation technique that has attracted substantial interest of the scientific community dealing with bioanalysis. This technique is based on a permeable and flexible substrate made of fabric, coated with a sol-gel organic-inorganic sorbent. Among the benefits of FPSE are its tunable selectivity, adjustable porosity, minimized sample preparation workflow, substantially reduced organic solvent consumption, rapid extraction kinetics and superior extraction efficiency, many of which are well-known criteria for Green Analytical Chemistry. As such, FPSE has established itself as a leading green sample preparation technology of 21st century. In this review, we discuss the principal steps for the development of an FPSE method, the main method optimization strategies, as well as the applications of FPSE in bioanalysis for the extraction of a wide range of analytes (e.g., estrogens, benzodiazepines, androgens and progestogens, penicillins, anti-inflammatory drugs, parabens etc.).

Recent applications of microextraction sample preparation techniques in biological samples analysis

Analysis of biological samples is affected by interfering substances with chemical properties similar to those of the target analytes, such as drugs. Biological samples such as whole blood, plasma, serum, urine and saliva must be properly processed for separation, purification, enrichment and chemical modification to meet the requirements of the analytical instruments. This causes the sample preparation stage to be of undeniable importance in the analysis of such samples through methods such as microextraction techniques. The scope of this review will cover a comprehensive summary of available literature data on microextraction techniques playing a key role for analytical purposes, methods of their implementation in common biological samples, and finally, the most recent examples of application of microextraction techniques in preconcentration of analytes from urine, blood and saliva samples. The objectives and merits of each microextration technique are carefully described in detail with respect to the nature of the biological samples. This review presents the most recent and innovative work published on microextraction application in common biological samples, mostly focused on original studies reported from 2017 to date. The main sections of this review comprise an introduction to the microextraction techniques supported by recent application studies involving quantitative and qualitative results and summaries of the most significant, recently published applications of microextracion methods in biological samples. This article considers recent applications of several microextraction techniques in the field of sample preparation for biological samples including urine, blood and saliva, with consideration for extraction techniques, sample preparation and instrumental detection systems.

[Advances in construction of triazine-based porous organic polymers and their applications in solid phase microextraction]

The large surface area, adjustable pore structure, good thermal and chemical stabilities, and abundant π-electron systems make triazine-based porous organic polymers (TPOPs) as promising porous materials for gas storage, catalysis, energy conversion and adsorption. Recently, TPOPs have aroused ever-increasing interest and are considered as one of the research highlights in solid phase microextraction (SPME) and other sample pretreatment techniques. This minireview summarizes the recent advancements in the synthesis of TPOPs and their applications in SPME. The application prospects of the TPOPs in SPME and other sample pretreatment techniques are also presented.

Synchronous Construction of Hierarchical Porosity and Thiol Functionalization in COFs for Selective Extraction of Cationic Dyes in Water Samples

Pore size and functionalization are two critical factors for covalent organic frameworks (COFs) as effective adsorbents. However, due to the low crystallinity of COFs, it is a grand challenge to accomplish pore diameter adjustment and functionalization at the same time. In this work, we developed a simple and ingenious strategy, cutting off linkage, to synchronously construct hierarchical porosity and modify thiol groups in COFs under mild conditions. The hybrid COFs containing disulfide bonds were designed and synthesized, and then the disulfide bonds were cleaved by glutathione, resulting in the formation of thiol groups as well as the increase in pore size caused by skeleton defects. The pore diameter of thiol-functionalized hierarchical porous COFs (denoted as HP-TpEDA-SH) was concentrated at 2.6 and 3.5 nm. Thanks to the electrostatic attraction of thiol groups to cationic dyes and the higher number of available adsorption sites, the maximum extraction amounts of methylene blue (MB), malachite green (MG), and crystal violet (CV) by HP-TpEDA-SH were 2.6, 2.1, and 3.3 times those of microporous COFs under optimal extraction conditions, respectively. The proposed analytical method (solid-phase extraction-high-performance liquid chromatography/ultraviolet (SPE-HPLC/UV)) with HP-TpEDA-SH as the adsorbent showed low detection limits of 1.3, 0.13, and 0.12 μg·L^-1 for MB, MG, and CV, respectively. The recoveries of three spiked water samples ranged from 81.5 to 113.8%, with relative standard deviations (RSDs) less than 9.7%. This work not only opened a new avenue for the preparation of functionalized hierarchical porous COFs but also established an effective method for detecting trace cationic dyes in fishery water.

Applications of porous frameworks in solid-phase microextraction

Porous frameworks are a term of attracting solid materials assembled by interconnection of molecules and ions. These trendy materials due to high chemical and thermal stability, well-defined pore size and structure, and high effective surface area gained attention to employ as extraction phase in sample pretreatment methods before analytical analysis. Solid-phase microextraction is an important subclass of sample preparation technique that up to now different configurations of this method have been introduced to get adaptable with different environments and analytical instruments. In this review, theoretical aspect and different modes of solid-phase microextraction method are investigated. Different classes of porous frameworks and their applications as extraction phase in the proposed microextraction method are evaluated. Types and features of supporting substrates and coating procedures of porous frameworks on them are reviewed. At the end, the prospective and the challenges ahead in this field are discussed.

Insights into the structure-performance relationships of extraction materials in sample preparation for chromatography

Sample preparation is one of the most crucial steps in analytical processes. Commonly used methods, including solid-phase extraction, dispersive solid-phase extraction, dispersive magnetic solid-phase extraction, and solid-phase microextraction, greatly depend on the extraction materials. In recent decades, a vast number of materials have been studied and used in sample preparation for chromatography. Due to the unique structural properties, extraction materials significantly improve the performance of extraction devices. Endowing extraction materials with suitable structural properties can shorten the pretreatment process and improve the extraction efficiency and selectivity. To understand the structure-performance relationships of extraction materials, this review systematically summarizes the structural properties, including the pore size, pore shape, pore volume, accessibility of active sites, specific surface area, functional groups and physicochemical properties. The mechanisms by which the structural properties influence the extraction performance are also elucidated in detail. Finally, three principles for the design and synthesis of extraction materials are summarized. This review can provide systematic guidelines for synthesizing extraction materials and preparing extraction devices.

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.