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

Practicality evaluation of novel microextraction techniques for the determination of PFAS in food and water samples using the Blue Applicability Grade Index

BACKGROUND

Due to their high stability, persistence, and non-degradability, per- and polyfluoroalkyl substances (PFAS) are considered to be "forever chemicals" that can be present in a wide range of samples. Towards the development of novel analytical strategies for the reduction of the environmental impact of the analytical scheme, a plethora of novel solid-phase microextraction and miniaturized extraction techniques have been proposed for the determination of PFAS. However, the evaluation of the applicability of these protocols in terms of their practicality is still scarce.

RESULTS

In this article, the Blue Analytical Grade Index (BAGI) was used to evaluate the practicality of the sorbent-based microextraction techniques that were developed during the last decade for PFAS. In total thirty-four protocols were evaluated, resulting in a minimum score of 50.0 and a maximum score of 77.5.

SIGNIFICANCE

These findings clearly indicate that there is significant room for improvement and there is still a need for the development of microextraction approaches with higher practicality. Moreover, with regards to the best-performing protocols, their greenness was also assessed using the AGREEprep metric to enable a more comprehensive comparison.

Highly hydrophobic calixarene polymers for efficient enrichment of polar nitrobenzene compounds

Macrocyclic polymer materials exhibit excellent selectivity and adsorption performance in pollutant adsorption due to unique host-guest recognition. Herein, three kinds of calixarene polymers (C4P, C6P and C8P) were synthesized through Sonogashira reaction, and were characterized through 1H NMR, FT-IR, SEM, and TEM. The water contact angle experiments revealed that three kinds of calixarene polymers were highly hydrophobic, and they all exhibited high enrichment efficiency for weak polar chloro-substituted benzene compounds (chlorobenzene, o-chlorotoluene, p-dichlorobenzene and o-dichlorobenzene) and BTEX (benzene, toluene, ethylbenzene and xylenes). Surprisingly, three types of calixarene polymers also showed satisfactory enrichment performance for polar nitrobenzene compounds (NBCs). Among them, C8P showed the most outstanding enrichment factors for NBCs (825-1913), which was about 2-7 times better than those of the commercial fibers. Using C8P as coating fiber, a sensitive analytical method was further developed based on solid phase microextraction (SPME), coupled with gas chromatography-mass spectrometry (GC-MS). The established analytical method demonstrated low detection limits (0.06-5.08 ng L-1), a wide linear range (0.5-1000 ng L-1), and good repeatability. The established method was further applied to the quantification of NBCs in environmental water samples, verifying its feasibility.

High-Throughput Screening of Polyfluoroalkyl Substances Using Solid-Phase Microextraction Coupled to Microfluidic Open Interface-Mass Spectrometry

Efficient and sustainable methods for large-scale PFAS monitoring are critical for addressing environmental and public health challenges. This work presents a high-throughput sample preparation system capable of processing up to 48 samples simultaneously using solid-phase microextraction (SPME) and was directly coupled with mass spectrometry (MS) via an automated microfluidic open interface (MOI), bypassing the need for chromatographic separation. The SPME-MOI-MS approach achieves sensitive detection of 18 PFAS in drinking water, with limits of detection (LODs) between 1 and 10 pg/mL, using just 1.5 mL of sample and an average analysis time of 2.8 min per sample. The SPME blades, employed to enhance sensitivity in place of standard SPME fibers, incorporate a matrix-compatible coating material that enables effective PFAS screening in water as well as complex matrices including blood, beer, and beef. In addition, significantly low recovery and reproducibility of nonpolar PFAS in water analysis have been found and studied, indicating that using a glass container and adding a small percentage of acetonitrile can address this issue.

Unlocking Enhanced Detection of Perfluoroalkanesulfonic Acids via Fluorinated Nonpolar 3D Covalent Organic Frameworks-Based Ambient Probe Nanoelectrospray Ionization Mass Spectrometry

The trace levels and severe matrix interferences greatly limited the determination of stable, persistent, and long-range-transported perfluoroalkanesulfonic acids (PFSAs) in complex environments. Here, we design and prepare the first fluorinated nonpolar 3D COF (TFPM-Pa-CF3) as an adsorbent, consisting of tetrakis(4-formylphenyl)methane (TFPM) and 2,5-diaminobenzo-trifluoride (Pa-CF3) for adsorption and extraction of PFSAs. The proposed TFPM-Pa-CF3 demonstrates excellent adsorption capacity (509.1 mg g-1) and rapid adsorption kinetics (5 min) for PFSAs attributed to the synergistic effects of F-F, hydrophobic, and electrostatic interactions. Furthermore, TFPM-Pa-CF3 is grown in situ on a stainless needle and coupled with ambient probe nanoelectrospray ionization mass spectrometry (PESI-MS) to develop a rapid and direct determination method with a low limit of detection (0.05-0.86 ng L-1) and wide linear range (1-10,000 ng L-1) for trace perfluorooctanesulfonate and its alternatives in environmental soil, algae and water. This work unlocks the efficient determination or removal of PFSAs in a complex environment, facilitating the solution of critical environmental PFSAs problems.

Catalyst-derived hierarchy in 2D imine-based covalent organic frameworks

Identifying facile strategies for hierarchically structuring crystalline porous materials is critical for realizing diffusion length scales suitable for broad applications. Here, we elucidate synthesis-structure-function relations governing how room temperature catalytic conditions can be exploited to tune covalent organic framework (COF) growth and thereby access unique hierarchical morphologies without the need to introduce secondary templates or structure directing molecules. Specifically, we demonstrate how scandium triflate, an efficient catalyst involved in the synthesis of imine-based COFs, can be exploited as an effective growth modifier capable of selectively titrating terminal amines on 2D COF layers to facilitate anisotropic crystal growth. We systematically map a compositional pseudo-phase space and uncover key mechanistic insights governing the catalyst-derived evolution of globular COFs with sub-micron diffusion length scales into unique rosette structures. Comprised of interconnected, high-aspect-ratio crystalline porous sheets of only several unit cells in thickness, the resulting COFs offer orders of magnitude reduction in diffusion length scales and several-fold increase in external surface area, enabling rapid uptake of bulky dyes. Generally, the resulting synthesis-structure-function relations hold promise for realizing unique control over COF mesostructure, morphology, and function.

Room-temperature synthesis of fluorinated covalent organic framework coupled with liquid chromatography-mass spectrometry for determination of per- and polyfluoroalkyl substances in drinking water

The routine monitoring of per- and polyfluoroalkyl substances (PFASs) in drinking water has become an important task in the field of public health. In this study, a fluorinated covalent organic framework (COF) was synthesized at room temperature using tetra-(4-aminophenyl) methane (TAM) and 2,3,5, 6-tetrafluoro-terephthalal (TFTA) as building blocks and named as TAM-TFTA-COF. The adsorption characteristics of PFASs on the TAM-TFTA-COF were investigated through adsorption model-fitting and molecular calculation. The TAM-TFTA-COF was served as the solid phase extraction (SPE) cartridge packing for the enrichment of PFASs. Combined with liquid chromatography-tandem mass spectrometry, the proposed method showed good linearity in the range of 1.25-375 ng·L-1, low limits of detection (0.03-0.24 ng·L-1), and excellent intraday and interday precisions with RSD <10.3 %. Furthermore, this analytical method can be utilized for the determination of PFASs in tap water, spring water, and lake water with satisfactory accuracy.

Opportunity and Challenge of Advanced Porous Sorbents for PFAS Removal

Per- and polyfluoroalkyl substances (PFASs), comprising over 9,000 persistent synthetic organic contaminants, are extensively found in the environment and pose significant risks to both human and ecological health. Among the strategies for addressing PFAS contamination, adsorption processes have proven to be cost-effective. Traditional sorbents such as ion-exchange resins and activated carbon have been found to exhibit low adsorption capacities and slow equilibration times. Recent innovations in porous materials, including metal-organic frameworks (MOFs), covalent organic frameworks (COFs), and porous organic polymers (POPs), however, offer significant improvements in the efficiency of PFAS adsorption. This review thoroughly examines the latest advancements in these materials, analyzing their mechanisms of adsorption, and concludes by suggesting directions for future research that could further enhance their effectiveness in PFAS management.

A critical review of bioanalytical and clinical applications of solid phase microextraction

Studying the functions, mechanisms, and effects of drugs and other exogenous compounds on biological systems, together with investigations performed to understand biosystems better, comprises one of the most fascinating areas of research. Although classical sample preparation techniques are dominantly used to infer the relevant information from the investigated system, they fail to meet various imperative requirements, such as being environmentally friendly, applicable in-vivo, and compatible with online analysis. As a chameleon in the analytical toolbox, solid phase microextraction (SPME) is one of the best tools available for studying biological systems in unconventional ways. In this review, SPME is spotlighted, and its capability for bioanalytical applications, including drug analysis, untargeted and targeted metabolomics, in-vivo and clinical studies, is scrutinized based on studies reported in the past five years. In addition, novel extractive phases and instrumental coupling strategies developed to serve bioanalytical research are discussed to give the perspective for state-of-the-art and future developments. The literature assessment showed that SPME could act as a critical tool to investigate in-vivo biological systems and provide information about the elusive portion of the metabolome. Moreover, recently introduced miniaturized SPME probes further improved the low-invasive nature of the sampling and enabled sampling even from a single cell. The coupling of SPME directly to mass spectrometry significantly reduced the total analytical workflow and became one of the promising tools suitable for fast diagnostic purposes and drug analysis. The numerous applications and advancements reported in bioanalysis using SPME show that it will continue to be an indispensable technique in the future.

Ionic liquid-reinforced Hydroxyapatite@nano-TiO2 as a green platform for Immuno-electrochemical sensing applications

In contemporary society, developing dependable point-of-care (POC) biosensors for the timely detection of cancer markers is crucial. Among various sensor types, screen-printed electrode (SPE)-based sensors, particularly electrochemical ones, stand out as promising candidates for POC applications. Despite ongoing efforts to create numerous SPE-based sensors, there is a continuous pursuit to enhance their sensitivity and analytical capabilities. This study presents an advanced electrochemical sensor designed to sensitively detect the hepatocellular carcinoma (HCC) marker Alpha-fetoprotein (AFP) in saliva. The sensor employs a gold SPE modified with hydroxyapatite, TiO2 nanoparticles, 1-butyl-3-methylimidazolium bis(trifluoromethyl sulfonyl)imide ionic liquid (IL), and AFP monoclonal antibodies. After thorough characterization and optimization using cyclic voltammetry (CV) and differential pulse voltammetry (DPV), the biosensor exhibited a broad detection range (0.01-400 ng/mL), a low limit of detection (LOD) at 0.058 ng/mL, and demonstrated high selectivity, repeatability, reproducibility, and stability. Furthermore, when tested with spiked human saliva samples, the biosensor displayed excellent recovery and robustness, showcasing its potential for noninvasive and POC diagnosis of HCC. In an environmentally conscious evaluation, the biosensor's greenness was assessed using the AGREE metric, yielding a high score of 0.85. This score indicates the biosensor's alignment with the principles of green analytical chemistry, underlining its eco-friendly attributes. This innovative electrochemical sensor contributes to the ongoing efforts for efficient and reliable POC diagnostic tools and aligns with a broader commitment to developing environmentally friendly solutions.

Fabrication of fluorinated magnetic microporous organic network for selective and efficient extraction of benzoylurea insecticides in tea beverages

In this work, a novel fluorinated magnetic microporous organic network (Fe3O4@FMON) was exquisitely designed and synthesized for highly efficient and selective magnetic solid phase extraction (MSPE) of fluorinated benzoylurea insecticides (BUs) from complex tea beverage samples. The Fe3O4@FMON exhibited good extraction for BUs via the pre-designed hydrophobic, π-π stacking, hydrogen bonding and specific FF interactions. A sensitive Fe3O4@FMON-based MSPE-HPLC-UV method with wide linear range (0.10-1000 μg L-1, R2 ≥ 0.996), low limits of detection (0.01-0.02 μg L-1), and large enrichment factors (85.6-98.0) for BUs from tea beverage samples was developed. By decorating F elements within MON's networks, the Fe3O4@FMON characterized good hydrophobicity and chemical stability, which could be reused at least 8 times without decrease of recoveries. This work demonstrated the great prospects of Fe3O4@FMON for enriching trace BUs from complex substrates and triggered the potential of FMON for sample pretreatment of fluorinated analytes.

A fast solid-phase microextraction scheme for in vivo monitoring of bio-accumulation and bio-transformation of arbidol in living plants

Large quantity of the antiviral drug arbidol is used for resisting virus infection like the Corona Virus Disease 2019 and influenza, resulting in unanticipated environmental pollution. Herein, to investigate the environmental risks of the unanticipated arbidol contamination, a novel in vivo sampling probe was developed based on a bromo-substituted porous organic polymer (Br-POP) and then adopted for tracking the bio-accumulation and bio-transformation of arbidol in living plants by coupling with a nano-electrospray ionization fourier-transform ion cyclotron resonance mass spectrometry (Nano-ESI-FT-ICR-MS) method. The established method showed good extraction performance towards arbidol with limit of detection (LOD) of 0.48 ng g-1, and relative standard deviation (RSD) of single-and multiple- probe of 2.2 and 14 %. Owing to the interactions between the Br-POP and the target analytes, as well as the fast analysis process of Nano-ESI-FT-ICR-MS, <6 min was cost for total sampling and analysis duration, achieving hourly tracking of arbidol and its metabolites in this work. During 21-d in vivo tracking, the concentration of arbidol in living plant stems increased rapidly within 6 h and peaked at 413.93 ± 47.09 ng g-1. Meanwhile, it was found that dissolved organic matters (DOM) had significant effect on arbidol behaviors in living plants, resulting in a decrease of the maximum concentration of arbidol in plant stems (152.70 ± 42.44 ng g-1) and the change of dominant metabolite of arbidol that the S-oxidation rather than N-demethylation product of arbidol was dominant with DOM participation. Additionally, the plant root secretion was found to be significantly altered by arbidol exposure. To summarized, the combination of in vivo SPME and the FT-ICR-MS analysis provide new and important information regarding arbidol contamination and related alternation of plant root metabolism.

Design and Synthesis of Fluorine-Containing Embedded Carbon Dots Stationary Phase for Separation of Versatile Analytes

Thus far, numerous new stationary phases have been developed. A fluorine-containing embedded carbon dots (F3-CDs-SiO2) stationary phase was first designed and synthesized. The resulting F3-CDs-SiO2 stationary phase was characterized carefully by scanning electron microscopy, transmission electron microscopy, elemental analysis, X-ray photoelectron spectroscopy, and Brunauer-Emmett-Teller experiment. The F3-CDs-SiO2 stationary phase was slurry packed into the HPLC column (150 × 2.1 mm) for evaluation. Furthermore, the F3-CDs-SiO2 column was successfully used for separation of pesticides, nucleosides, sulfonamides, alkaloids, and alkylbenzenes. The retention mechanism (including hydrophobic interaction, F-F, hydrogen bond interaction, ion-exchange, dipole-dipole interaction, electrostatic interaction, etc.) was investigated carefully. Meanwhile, the F3-SiO2 stationary phase was synthesized and used to evaluate the role of CDs. Furthermore, various commercial stationary phases (including amino-SiO2, diol-SiO2, C18-SiO2, and PFP-SiO2) were used for comparison. Moreover, the F3-CDs-SiO2 column possessed good repeatability, reproducibility, and stability in separation of versatile analytes.

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.

Novel pillar[n]arenes magnetic nanoparticles: Preparation and application in quantitative analysis of trace perfluorinated compounds from aqueous samples

BACKGROUND

Perfluorinated compounds (PFCs) are a class of widely manufactured and used emerging persistent pollutants. The recent discovered new class of macrocycles pillararenes have garnered significant attention for the applications in environmental pollutant adsorption, with abundant π electron cavities, a symmetrical rigid structure, and host-guest recognition capabilities.

RESULTS

In this work, we designed and synthesized novel cationic pillar [n]arenes magnetic nanoparticles (CWPA5@MNPs), and investigated its adsorption performance and mechanism as a type of new adsorbent for the enrichment of PFCs. The results indicate that CWPA5@MNPs exhibits selectively strong affinity for perfluorooctane sulfonate (PFOS) and long-chain (C9-C14) perfluorocarboxylic acids (PFCAs), with the adsorption efficiency exceeding 80 % within 12 min. The maximum adsorption capacity of CWPA5@MNPs for PFOS was measured to be 29.02 mg/g. CWPA5@MNPs can be rapidly isolated from the solution using external magnets, offering a quick and easy separation. Consequently, this study established a CWPA5@MNPs-assisted magnetic solid-phase extraction (MSPE) coupled with high-performance liquid chromatography-tandem mass spectrometry (CWPA5@MNPs-MSPE-HPLC-MS/MS) method for the rapid detection of trace levels of PFCs in environmental water samples. The analysis of 7 PFCs yielded recovery rates ranging from 86.1 % to 107.5 %, with intraday and interday relative standard deviations (RSD) of 3.6-6.4 % and 1.3-7.0 %, respectively.

SIGNIFICANCE AND NOVELTY

The study reveals the synthesis and application of novel cationic pillar [n]arenes magnetic nanoparticles (CWPA5@MNPs) as highly efficient adsorbents for selective perfluorinated compounds (PFCs) in water samples. It demonstrates the potential of the newly developed CWPA5@MNPs-MSPE-HPLC-MS/MS method for the quantitative analysis of PFCs in environment, with high sensitivity, accuracy and stability.

Rapid and sensitive determination of legacy and emerging per- and poly-fluoroalkyl substances with solid-phase microextraction probe coupled with mass spectrometry

This study was designed to develop a rapid and sensitive method for quantifying legacy and emerging per- and polyfluoroalkyl substances (PFASs) in environmental samples with solid-phase microextraction (SPME) coupled with mass spectrometry (MS). An innovative SPME probe was fabricated via in situ polymerization, and the probe coating was optimized with response surface methodology to maximize the fluorine-fluorine interactions and electrostatic properties and ensure high selectivity for the target PFASs with enrichment factors of 48-491. The coupled SPME and MS provided a rapid and sensitive method for analyses of PFASs, with excellent linearity (r ≥ 0.9962) over the concentration range 0.001-1 μg/L and remarkably low detection limits of 0.1-13.0 ng/L. This method was used to analyze trace PFASs in tap water, river water, and wastewater samples and proved to be a simple and efficient analytical method for selective enrichment and detection of contaminants in the environment.

Supramolecular Materials as Solid-Phase Microextraction Coatings in Environmental Analysis

Solid-phase microextraction (SPME) has been widely proposed for the extraction, clean-up, and preconcentration of analytes of environmental concern. Enrichment capabilities, preconcentration efficiency, sample throughput, and selectivity in extracting target compounds greatly depend on the materials used as SPME coatings. Supramolecular materials have emerged as promising porous coatings to be used for the extraction of target compounds due to their unique selectivity, three-dimensional framework, flexible design, and possibility to promote the interaction between the analytes and the coating by means of multiple oriented functional groups. The present review will cover the state of the art of the last 5 years related to SPME coatings based on metal organic frameworks (MOFs), covalent organic frameworks (COFs), and supramolecular macrocycles used for environmental applications.

A Novel Multiarmed Bifunctional PEG Derivative for the Preparation of Mass Spectrometry Ion Sources with Antifouling Property and High Selectivity

It is challenging to prepare a highly selective mass spectrometry (MS) ion source for the rapid and highly sensitive detection of analytes, especially mycotoxins. In this study, an amino and tetrazine bifunctionalized multiarm PEG derivative (NH2HCl-4armPEG10K-(MTz)3), which can be easily immobilized on the substrate by the addition reaction between amino and polydopamine, was used for the preparation of MS ionization substrate. NH2HCl-4armPEG10K-(MTz)3 can also be used as a linker to immobilize sufficient streptavidin (SA) on the surface of the substrate by a click reaction. The process further promotes the immobilization of broad-spectrum antibodies (3D4), which were used as the recognition element for ZEN and its metabolites. The prepared SSS-Au-PDA-4armPEG10K-SA-3D4 not only can rapidly enrich ZEN and its metabolites with high selectivity but also shows good antifouling properties in the matrix. After simple sample preparation, the prepared SSS-Au-PDA-4armPEG10K-SA-3D4 can be directly coupled with MS to achieve high sensitivity (LODs: 0.18-0.66 ng/mL, LOQs: 0.5-1.0 ng/mL) and selective detection of ZEN and its metabolites in the matrix. At the same time, satisfactory recoveries (83.60-97.80%) and precision (RSD: 2.80-9.10%) can also be obtained. The prepared SSS-Au-PDA-4armPEG10K-SA-3D4 is expected to provide a powerful tool for the rapid and highly sensitive determination of multiple targets by MS.

Recent advance on microextraction sampling technologies for bioanalysis

The contents of target substances in biological samples are usually at low concentration levels, and the matrix of biological samples is usually complex. Sample preparation is considered a very critical step in bioanalysis. At present, the utilization of microextraction sampling technology has gained considerable prevalence in the realm of biological analysis. The key developments in this field focus on the efficient microextraction media and the miniaturization and automation of adaptable sample preparation methods currently. In this review, the recent progress on the microextraction sampling technologies for bioanalysis has been introduced from point of view of the preparation of microextraction media and the microextraction sampling strategies. The advance on the microextraction media was reviewed in detail, mainly including the aptamer-functionalized materials, molecularly imprinted polymers, carbon-based materials, metal-organic frameworks, covalent organic frameworks, etc. The advance on the microextraction sampling technologies was summarized mainly based on in-vivo sampling, in-vitro sampling and microdialysis technologies. Moreover, the current challenges and perspective on the future trends of microextraction sampling technologies for bioanalysis were briefly discussed.

Efficient dispersive solid phase extraction of trace nitrophenol pollutants in water with triazine porous organic polymer modified nanofiber membrane

Detecting trace endocrine disruptors in water is crucial for evaluating the water quality. In this work, a innovative modified polyacrylonitrile@cyanuric chloride-triphenylphosphine nanofiber membrane (PAN@CC-TPS) was prepared by in situ growing triazine porous organic polymers on the polyacrylonitrile (PAN) nanofibers, and used in the dispersive solid phase extraction (DSPE) to enrich trace nitrobenzene phenols (NPs) in water. The resluted PAN@CC-TPS nanofiber membrane consisted of numerous PAN nanofibers cover with CC-TPS solid spheres (∼2.50 μm) and owned abundant functional groups, excellent enrichment performance and good stability. In addition, the method based on PAN@CC-TPS displayed outstanding capacity in detecting the trace nitrobenzene phenols, with 0.50-1.00 μg/L of the quantification, 0.10-0.80 μg/L of the detection limit, 85.35-113.55 % of the recovery efficiency, and 98.08-103.02 of the enrichment factor, which was comparable to most materials. Meanwhile, when PAN@CC-TPS was adopted in the real water samples (sea water and river water), the high enrichment factors and recovery percentages strongly confirmed the feasibility of PAN@CC-TPS for enriching and detecting the trace NPs. Besides, the related mechanism of extracting NPs on PAN@CC-TPS mainly involved the synergistic effect of hydrogen bonding, π-π stacking and hydrophobic effect.

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.

A heteropore covalent organic framework for highly selective enrichment of aryl-organophosphate esters in environmental water coupled with UHPLC-MS/MS determination

The identification of an increasing number of aryl organophosphate esters (aryl-OPEs) in environmental samples has led to growing attention recently. Due to the potential adverse effects on human health and environment, development of new analytical methods for sensitive and selective determination of aryl-OPEs in complex matrices is urgently needed. Here, a novel analytical method for the identification and determination of trace amounts of aryl-OPEs in water samples is developed by using melamine sponge@heteropore covalent organic framework (MS@HCOF) based on vortex-assisted extraction (VAE) prior to UHPLC-MS/MS analysis. The MS@HCOF was rationally designed and synthesized through an in-situ growth strategy and exhibited superior selectivity toward aryl-OPEs compared with that of MS@single-pore COF (MS@SCOF) due to steric effect. A systematic optimization was conducted on important parameters of VAE, resulting in the successful extraction of nine aryl-OPEs in just 6 min. Under optimized conditions, the limits of detection (S/N = 3) and quantification (S/N = 10) were within the ranges of 0.001-0.027 and 0.005-0.091 ng/L for nine aryl-OPEs, respectively. The validated method was proven applicable to real water samples, i.e., the recoveries were 65.3-119.5 % for seawater, 59.4-112.9 % for effluent, and 76.0-117.4 % for tap water. Furthermore, the adsorption mechanisms were explored through density functional theory (DFT) calculations. DFT results revealed that a notable selective enrichment capacity of MS@HCOF towards aryl-OPEs stems from π-π conjugation and hydrogen bonding. The established method benefits from the advantages of high selectivity and sensitivity for the ultra-trace determination of aryl-OPEs.

Linkage Transformations in a Three-Dimensional Covalent Organic Framework for High-Capacity Adsorption of Perfluoroalkyl Substances

Despite their many advantages, covalent organic frameworks (COFs) built from three-dimensional monomers are synthetically difficult to functionalize. Herein, we provide a new synthetic approach to the functionalization of a three-dimensional covalent organic framework (COF-300) by using a series of solid-state linkage transformations. By reducing the imine linkages of the framework to amine linkages, we produced a more hydrolytically stable material and liberated a nucleophilic amino group, poised for further functionalization. We then treated the amine-linked COF with diverse electrophiles to generate a library of functionalized materials, which we tested for their ability to adsorb perfluoroalkyl substances (PFAS) from water. The framework functionalized with dimethylammonium groups, COF-300-dimethyl, adsorbed more than 250 mg of perfluorooctanoic acid (PFOA) per 1 g of COF, which represents an approximately 14,500-fold improvement over that of COF-300 and underscores the importance of electrostatic interactions to PFAS adsorption performance. This work provides a conceptually new approach to the design and synthesis of functional three-dimensional COFs.

Ionic liquid-modified UiO-66-NH2 as sorbent of dispersive solid-phase extraction for rapid adsorption and enrichment of benzoylurea insecticides

Ionic liquid (IL)-modified UiO-66-NH2 composite was prepared and used as sorbent of dispersed solid-phase extraction (dSPE) for extracting trace benzoylurea insecticides (BUs) from complex environmental matrices. The IL in framework endowed the prepared material had electropositive characteristics, which can produce interaction with electron rich guest molecules, such as BUs. The high thermal and chemical stability of UiO-66-NH2/IL enabled it to be reused for 16 times without significant reduction in adsorption performance. Due to the multiple forces including π-π, hydrogen bonding, and fluorine-fluorine interaction, UiO-66-NH2/IL showed good adsorption performance, short adsorption time (20 s) and rapid desorption ability (60 s) for BUs. Under the optimal conditions, the method exhibited wide linear range (0.02-500 ng mL-1) with correlation coefficient (R2) not worse than 0.9928, high enrichment factor (252-300), and low detection limit (0.005-0.4 ng mL-1). The dispersed solid phase extraction coupling with high-performance liquid chromatography-diode array detector (dSPE-HPLC-DAD) was successfully used to detection of BUs in real environmental samples and satisfactory recoveries were obtained (80.5%±2.4-118%±3.2). The results indicated that UiO-66-NH2/IL composite can be a potential sorbent for the preconcentration of trace insecticides in environmental samples.

Exploring the Accumulation Behavior and Heterogeneity of Perfluorooctanesulfonic Acid in Zebrafish Primary Organ Cells by Single-Cell Mass Cytometry

Perfluorooctanesulfonic acid (PFOS) is a commonly found environmental pollutant with potential toxicity and health risks to biosystems and ecosystems. Study of the accumulation behavior and heterogeneity of PFOS in biological primary organ cells provides us significant insights to explore its cytotoxicity, carcinogenicity, and mutagenicity. Here a single-cell mass cytometry system was established for the high-throughput analysis of trace PFOS and the exploration of its accumulation behavior and heterogeneity in zebrafish primary organ cells. The single-cell mass cytometry system applied a ∼25 μm constant-inner-diameter capillary as the single-cell generation and transportation channel with an etched tip-end of 40 μm as the nanoelectrospray emitter for mass spectrometric analysis. The single-cell mass cytometry system showed satisfactory semiquantitative performance and sensitivity for analysis of PFOS in single cells, with a high detection throughput of ∼35 cells/min. Subsequently, the liver, intestine, heart, and brain from PFOS-exposed zebrafish (100 pg/μL, 28 days) were dissociated and prepared as cell suspensions, and the cell suspensions were introduced into the single-cell mass cytometry system for high-throughput analysis of PFOS in individual primary organ cells. Significant cellular accumulation heterogeneities were observed, with the highest content in liver cells, followed by intestine cells, then heart cells, and the lowest in brain cells. In addition, the dynamics of PFOS in the zebrafish liver, intestine, heart, and brain cells showed typical violin plot distributions and were well-described using a gamma (γ) function.

Ultra-low current electrospray ionization of chloroform solution for the analysis of perfluorinated sulfonic acids

RATIONALE

Femtoamp and picoamp electrospray ionization (ESI) characteristics of a nonpolar solvent were explored. The direct ESI mass spectrometry analysis of chloroform extract solution enabled rapid analysis of perfluorinated sulfonic acid analytes in drinking water.

METHODS

Neat chloroform solvent and extracts were directly used in a typical wire-in ESI setup using micrometer emitter tips. Ionization currents were measured with femtoamp sensitivity while ramping the spray voltage from 0 to -5000 V. Methanol was used as a comparison to illustrate the characteristics of electrospraying chloroform. The effects of spray voltage and inlet temperature were studied. A liquid-liquid extraction workflow was developed to analyze perfluorooctanoate sulfonate (PFOS) in drinking water using an ion-trap mass spectrometer.

RESULTS

The ionization onset of chloroform solution was 41 ± 17 fA at 300 V. The ionization current gradually increased with voltage while remaining below 100 pA when using voltages up to -5000 V. The ion signal of PFOS was significantly enhanced to improve the limit of detection (LoD) to 25 ppt in chloroform. Coupled with a liquid-liquid extraction workflow, LoD of 0.38-5.1 ppt and a quantitation range of 5-400 ppt were achieved for perfluorinated sulfonic compounds in 1-ml water samples.

CONCLUSIONS

Femtoamp and picoamp modes expand the solvent compatibility range of ESI and can enable quantitative analysis in parts per trillion (ppt) concentrations.

A Data-Driven Search of Two-Dimensional Covalent Organic Frameworks for Visible-Light-Driven Overall Water Splitting

Two-dimensional (2D) covalent organic frameworks (COFs) with versatile structural and optoelectronic properties that can be tuned with building blocks and topological structures have received widespread attention for photocatalytic water splitting in recent years. However, few of these have been reported for overall water splitting under visible light. Here, we present a data-driven search of 2D COFs capable of visible-light-driven overall water splitting by combining high-throughput first-principles computations and experimental validations. Seven 2D COFs were identified to be capable of overall water splitting from the CoRE COF database, and their photocatalytic activities were further verified and optimized by our preliminary experiments. The production rates of H2 and O2 reached 80 and 32 μmol g-1 h-1, respectively, without using sacrificial agents. This work represents an attempt to explore 2D COFs for visible-light-driven overall water splitting with a data-driven approach that could accelerate the discovery and design of COFs toward photocatalytic overall water splitting.

Fluorinated covalent-organic polymers as stationary phase for analysis of organic fluorides by open-tubular capillary electrochromatography

Fluorinated porous materials, which can provide specific fluorine-fluorine interaction, hold great promise for fluoride analysis. Here, a novel fluorinated covalent-organic polymer was prepared by using 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and 2,3,5,6-tetrafluorotelephtal aldehyde as the precursors and introduced as stationary phase for open-tubular capillary electrochromatography. The as-synthesized fluorinated covalent-organic polymer and the modified capillary column were characterized by infrared spectroscopy, scanning electron microscopy, and energy dispersive X-ray spectrometry. Based on strong hydrophobic interaction and fluorine-fluorine interaction provided by fluorinated covalent-organic polymer coating layer, the modified column showed powerful separation selectivity toward hydrophobic compounds, organic fluorides, and fluorinated pesticides. Additionally, the fluorinated covalent-organic polymer with good porosity and regular shape was uniformly and tightly coated on the capillary inner wall. The obtained highest column efficiency could reach up to 1.2 × 105 plates⋅m-1 for fluorophenol. The loading capacity of the modified column can reach 141 pmol for trifluorotoluene. Besides, the relative standard deviations of retention times for intraday run (n = 5), interday run (n = 3), and between columns (n = 3) were all less than 2.55%. Significantly, this novel fluorinated material-based stationary phase shows great application potential in fluorides analysis.

Construction of a Highly Selective Enrichment, Ionization, and Detection Platform Based on a Broad-Spectrum Antibody

Ambient mass spectrometry (AMS) allows direct analysis of various raw food samples with minimal or no sample pretreatment, but the trace analytes in complex food samples still have problems with limitations. In this work, we developed a platform based on coated stainless steel sheet spray mass spectrometry for fast, in situ, high-throughput, and high selectivity multiresidue analysis of fluoroquinolone drugs (FQs). The sensitivity of the platform was enhanced via coupling broad-spectrum antibodies against FQs to graphene oxide coated blade spray (CBS)-MS through a streptavidin-biotin (SA-biotin) interaction. The prepared platform had sufficient loading capacity for SA (1.37 mg/piece) and the antibody (84.8 μg/piece), which is greater than that of physical mixing and the EDC/NHS covalent coupling strategy. With simplified sample pretreatment, this platform demonstrated comparable sensitivity to high performance liquid chromatography-mass spectrometry (HPLC-MS/MS) (0.08-0.16 ng/mL in phosphate-buffered saline and 0.21-0.32 ng/mL in diluted milk). Meanwhile, compared with HPLC-MS/MS, the method is rapid (enrichment: 10 min, detection: <1 min) and acceptable recoveries (81.94-102.08%) can be obtained. The presence of analytes can be monitored by MS/MS spectra, and multiple analytes can be measured simultaneously in a single assay. This study is expected to provide a powerful and portable tool for rapid laboratory analysis and reliable screening in the field.

The covalent organic framework based nylon membrane extraction coupled with UHPLC-MS/MS for highly efficiency determination of hexabromocyclododecanes in environmental water

Hexabromocyclododecanes (HBCDs) have given their adverse effects on environment and human health, and highly sensitive analysis of HBCDs in water is urgent. In this study, a new method for the determination of trace HBCDs in water was established by covalent organic framework (COF) based nylon membrane extraction (ME) coupled with ultrahigh-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). The COF had been self-assembled onto the nylon membrane in a gentle strategy to fabricate COF nylon membrane. Several important ME parameters including the dosage of COF, pH, eluent condition and salinity were systematically investigated. The limits of detection and quantification were 0.011-0.014 and 0.038-0.047 ng/L for three HBCDs, respectively. The linear ranges were from 0.04 to 20 ng/L, and the relative standard deviations were 5.7-17.8 % (intra-day) and 5.2-14.1 % (inter-day). In addition, density functional theory (DFT) calculations on adsorption energy proved that the introduction of halogen bond (XB) made a key contribution to high extraction efficiency and excellent selectivity of COF nylon membrane for HBCDs. The 500 mL of samples, including tap water and reservoir water, could be extracted only in 23 min. The established method presented highly sensitive for ultra-trace analysis of HBCDs in environmental water.

Multifunctionalized Covalent Organic Frameworks for Broad-Spectrum Extraction and Ultrasensitive Analysis of Per- and Polyfluoroalkyl Substances

The contamination of surface and ground water by per- and polyfluoroalkyl substances (PFASs) has become a growing concern, and the structural diversity of PFASs is the major challenge for their ubiquitous applications. Strategies for monitoring coexistent anionic, cationic, and zwitterionic PFASs even at trace levels in aquatic environments are urgently demanded for effective pollution control. Herein, novel amide group and perfluoroalkyl chain-functionalized covalent organic frameworks (COFs) named COF-NH-CO-F9 are successfully synthesized and used for highly efficient extraction of broad-spectrum PFASs, attributing to their unique structure and the multifunctional groups. Under the optimal conditions, a simple and high-sensitivity method is established to quantify 14 PFASs including anionic, cationic, and zwitterionic species by coupling solid-phase microextraction (SPME) with ultrahigh-performance liquid chromatography-triple quadrupole mass spectrometry (UHPLC-MS/MS) for the first time. The established method displays high enrichment factors (EFs) of 66-160, ultrahigh sensitivity with low limits of detection (LODs) of 0.0035-0.18 ng L^-1, a wide linearity of 0.1-2000 ng L^-1 with correlation coefficient (R²) ≥0.9925, and satisfactory precision with relative standard deviations (RSDs) ≤11.2%. The excellent performance is validated in real water samples with recoveries of 77.1-108% and RSDs ≤11.4%. This work highlights the potential of rational design of COFs with the desired structure and functionality for the broad-spectrum enrichment and ultrasensitive determination of PFASs in real applications.

Irreversible fluorine covalent organic framework based probe nanoelectrospray ionization mass spectrometry for direct and rapid determination of perfluoroalkyl carboxylic acids

Probe nanoelectrospray ionization mass spectrometry (PESI-MS) is practically desirable for rapid and ultra-sensitive analysis of trace contaminants in environment, but limited with the stable and selective probe coating. Herein, we show the design and preparation of irreversible fluorine-based covalent organic framework (TFPPA-F₄) covalently bonded probe to couple with ESI-MS (TFPPA-F₄-PESI-MS) for direct and rapid determination of perfluoroalkyl carboxylic acids (PFCAs) in environmental water. Chemical bonding coating of irreversible crystalline TFPPA-F₄ not only improved stability of the probe, but also offered accessible multiple interactions including hydrophobic, hydrogen bonding and F-F interactions to promote the kinetics and selectivity for PFCAs. The proposed TFPPA-F₄-PESI-MS realized rapid determination of PFCAs (about 4 min) with low limits of detection of 0.06-0.88 ng L^-1 and wide linear range of 1-5000 ng L^-1 (R² of 0.9982-0.9998). Recoveries for the spiked lake and pond water were 85.9-111.1 %. TFPPA-F₄ based probe can maintain the extraction performance after 100 times of extraction. This work shows the great potential of the irreversible covalent organic framework based PESI-MS in rapid and ultra-sensitive determination of contaminants in environmental samples.

Direct Coupling of SPME to Mass Spectrometry

Solid-phase microextraction devices are normally analyzed by gas or liquid chromatography. Their use has become increasingly widespread since their introduction in 1990, and nowadays most analytical laboratories use or have used SPME as an efficient and green method to perform analyte extraction and sample clean-up in one step. The SPME technique is intrinsically flexible, and allows for a high degree of optimization with regard to the extracting phase, as well as the way sample is analyzed. Since its introduction, researchers have been trying different ways to transfer analytes extracted from the solid phase to a mass spectrometer, with the aim to increase throughput and reduce solvent, gas usage and costs associated with conventional chromatographic techniques. Furthermore, but not less important, for pure fun of developing new, more efficient and sensitive analytical strategies! This chapter aims at providing a comprehensive overview of the most relevant non-chromatographic mass spectrometric approaches developed for SPME. Technical aspects of each SPME-MS approach will be discussed, highlighting their advantages, disadvantages and future potential developments. Particular emphasis will be given on the most recent direct coupling approaches using novel ionization approaches, and a concise overview of the existing applications will also be provided.

Rapid screening of polybrominated diphenyl ethers in water by solid-phase microextraction coupled with ultrahigh-resolution mass spectrometry

Polybrominated diphenyl ethers (PBDEs) are considered emerging organic contaminants that attract more attention in the environment. Herein, online coupling of solid-phase microextraction and ultrahigh-resolution mass spectrometry was developed for rapid screening of eight PBDEs in water samples. This procedure was completed in 22 min, about 6 times faster than the routine workflow such as solid-phase extraction coupled with gas chromatography-mass spectrometry. Thermal desorption and solvent-assisted atmospheric pressure chemical ionization were developed for the effective coupling of solid-phase microextraction (SPME) with ultrahigh-resolution mass spectrometry (UHRMS), which contributed to the signal enhancement and made the methodology feasible for environmental screening. The limits of detection and quantification were 0.01-0.50 ng/mL and 0.05-4.00 ng/mL, respectively. The recoveries were 57.2-75.2% for quality control samples at spiking levels of 0.8-10 ng/mL (4-50 ng/mL for BDE209), with relative standard deviation less than 19.0%. Twelve water samples from different river sites near industrial areas were screened using the developed method. The results showed that BDE-209 was the dominant PBDE (1.02-1.28 ng/mL in positive samples), but its amount was lower than the human health ambient water quality criteria. Consequently, the developed method provides a rapid and reliable way of evaluating contamination status and risks of PBDEs in aqueous environment.

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.

Two-Dimensional Nitrogen-Doped Carbon Nanosheets Derived from g-C3N4 /ZIF-8 for Solid-Phase Microextraction in Exhalation of Esophageal Cancer Patients

Here, two-dimensional (2D) nitrogen-doped carbon nanosheets (CNSs) were prepared through carbonizing MOFs (ZIF-8) in-situ grown using graphitic carbon nitride (g-C₃N₄) as a template. The developed ZIF-8 CNS was then used as solid-phase microextraction (SPME) fiber coating for beneficiation of five biomarkers in exhalation of patients with esophageal cancer and in gas chromatography-mass spectrometry (GC-MS) for determination. The ZIF-8 CNS fiber exhibits satisfactory enrichment factors (3490-5631), wide linearity (5-1000 μg L^-1), and low detection limits (0.26-0.96 μg L^-1). The relative standard deviations (RSDs) for six replicate extractions of the same ZIF-8 CNS fiber were between 2.0-3.9% (intra-day) and 2.8-5.2% (inter-day). The reproducibility of three fibers prepared by the same approach was in the range 6.8-12.3% (RSD). The developed ZIF-8 CNS fiber can persist in 120 SPME cycles with no prominent loss of extraction efficiency and precision. The high enrichment factors of the 2D ZIF-8 CNS coatings are attributed to the high specific surface area, ultrathin thickness, and nano-pore or interlayer channels; moreover, nitrogen doping also endows the π system with a strong electron absorption ability, which will enhance the π-π interaction between the ZIF-8 CNS and the aromatic ring. Ultimately, the self-made ZIF-8 CNS-coated SPME fiber was applied to the analysis of exhaled breath samples. The recoveries of spiked analytes are between 84 and 105%.

Primary amide-functionalized cyclotricatechylene covalent organic frameworks membrane for efficient enrichment of melamine and its derivatives in migration solution of food contact materials

A highly chemically stable primary amide-functionalized cyclotricatechylene covalent organic framework was synthesized by an irreversible reaction and a post-synthetic modification. It possessed a rod-like morphology and exhibited strong solvent stability owing to the polyether bonds. The material showed good adsorption performance for melamine and its derivatives and adsorption mechanism was investigated by molecular simulations. The adsorbent was coated on the nylon-66 membrane to prepare the enrichment membrane. Under optimized conditions, an in-syringe membrane-based extraction method, combined with ultra-high performance liquid chromatography-tandem mass spectrometry was developed for the analysis of melamine and six melamine derivatives in the migration solution. A good linearity was obtained with correlation coefficients ranging from 0.9924 to 0.9995. The limits of detection were 1-200 ng/L and the limits of quantification were 3-500 ng/L. This method was successfully applied to the migration solution of sushi bamboo rolling mats with spiked recoveries of 73.2%-115% and relative standard deviations of 0.9%-9.9%. This work shows a practical and perspective approach for the efficient enrichment of food contact material hazards.

Selective cationic covalent organic framework for high throughput rapid extraction of novel polyfluoroalkyl substances

Novel per- and polyfluoroalkyl substances (PFASs) raise global concerns due to their toxic effects on environment and human health. However, researches on analytical methods of novel PFASs are lacking. Here, a kind of selective cationic covalent organic framework (iCOF) was designed and loaded on the surface of cotton as an adsorbent. Then, a simple solid-phase extraction (SPE) method based on the cotton@iCOF was developed for high throughput rapid extraction of six novel PFASs in water samples, coupled with ultrahigh-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) determination. Several important SPE parameters, such as the amount of iCOF, sample pH, desorption conditions and salinity were systematically investigated. Under optimal conditions, the limits of detection and quantification of this SPE-UHPLC-MS/MS method were as low as 0.08-2.14 ng/L and 0.28-7.15 ng/L, respectively. The recoveries were 77.9-117.6 % for the tap water and surface water, and F-53 B in surface water were detected. Notably, this SPE process was rapid (1 h for 500 mL water sample) compared with commercial SPE (normal 2-3 h), owing to little resistance of cotton@iCOF and omission of nitrogen blowing process, and high throughput with 12 samples concurrently extracted. Additionally, various characterization means and density functional theory (DFT) calculations showed that ion-exchange effect, hydrophobic interaction, hydrogen bonding and ordered channel structure synergistically contributed to the PFASs adsorption on cotton@iCOF. The cotton@iCOF-based SPE method with simplicity, rapidity, selectivity and efficiency provided new research ideas for the analysis and control of ionic emerging pollutants in water.

Fluoro-Functionalized Spherical Covalent Organic Frameworks as a Liquid Chromatographic Stationary Phase for the High-Resolution Separation of Organic Halides

The development of novel stationary phases with specific functionality is of great importance in chromatographic separation. Herein, we fabricated fluoro-functionalized spherical covalent organic frameworks (S_F-COFs) via a bottom-up strategy as stationary phases for high-performance liquid chromatography (HPLC). Benefiting from the significant monodispersity, narrow size distribution, and high fluorine content, the S_F-COFs packed column showed high column efficiency and excellent resolution for the separation of the organic fluorides involving polyfluorobenzenes, polychlorobenzenes, polybromobenzenes, perfluoroalkyl methacrylates, and halogenated trifluorotoluenes, which cannot be separated on the fluorine-free spherical covalent organic frameworks packed column. Especially, the column efficiency of 20 100-38 500 plates/m was obtained for polyfluorobenzenes, and the relative standard deviations of the retention time for continuous 10 separations of polychlorobenzenes and polybromobenzenes were less than 0.98%. Furthermore, the prepared S_F-COFs packed column showed overwhelming superiority in the separation of organic halides compared with commercial C18 and pentafluorophenyl (PFP) packed columns. In addition, the compounds with different hydrophobicity or aromatic ring structure were also successfully separated on the S_F-COFs packed column. This work extended the application of spherical COFs and provided a new way to introduce specific functional groups into the COF-based stationary phase for HPLC.

Fluorine-Functionalized Covalent-Organic-Framework-Coated Stir Bar for the Extraction of Benzoylurea Insecticides in Pear Juice and Beverage Followed by High-Performance Liquid Chromatography-Ultraviolet Detection

A fluorinated covalent organic framework (COF), named F-COF, was fabricated via simple room-temperature synthesis. With the characteristics of rich fluorine atoms, hydrophobicity, and large conjugated structure, F-COF was evaluated for the extraction of five benzoylurea insecticides (BUs) containing fluorine atoms, benzene ring, and urea bridge. Specifically, F-COF-coated stir bars were prepared by physical adhesion and exhibited higher extraction recovery (73-93 versus 40-85%) toward BUs than commercial stir bars in a shorter extraction time (50 min versus 24 h). The adsorption behavior of BUs on F-COF was explored, and it was assumed that the halogen bond (O-F), hydrophobic interaction, electrostatic interaction, and π-π stacking contributed to the adsorption. On the basis of it, a method combining stir bar sorptive extraction with liquid chromatography-ultraviolet detector was developed for trace analysis of five BUs. Under the optimal conditions, the limits of detection for BUs were found to be 0.301-0.672 μg/L, with the linear range of 1.0/2.0-500 μg/L and relative standard deviations of <8.0% (c = 5 μg/L and n = 7). The accuracy of the proposed method was validated by the recovery test, and the recoveries of target BUs in spiked pear juice and pear beverage were 82.0-113 and 84.0-112%, respectively.

Recent applications of organic molecule-based framework porous materials in solid-phase microextraction for pharmaceutical analysis

Sample preparation is an indispensable part of detection of complex samples in pharmaceutical analysis. Solid-phase microextraction (SPME) has obtained a lot of attention due to its advantages of time saving, less solvent and easily automation. A variety of functional materials are used as sorbents in SPME to carry out selective and high extraction. This review centers around the recent applications of organic molecule-based framework porous materials, such as metal organic frameworks (MOFs) and covalent organic frameworks (COFs), as SPME coating materials mainly focus on pharmaceutical analysis in food, environment, and biological samples. Four representative extraction devices are introduced, including on-fiber SPME, in-tube SPME, thin film SPME, stir bar SPME. The application prospect of other organic porous materials as sorbents for pharmaceutical analysis are also discussed, such as hyper crosslinked polymers (HCPs) and conjugated microporous polymers (CMPs). The progresses and discusses are provided to offer references for further research focusing on application and development of organic molecule-based framework porous materials in the field of SPME.

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.

Preparation of cationic hierarchical porous covalent organic frameworks for rapid and effective enrichment of perfluorinated substances in dairy products

Perfluorinated substances (PFASs) are harmful pollutants that have environmental persistence and high bioaccumulation. Effective sample pretreatment must be performed to detect trace or even ultra-trace PFASs in actual samples because of their extremely low contents in complex samples. In this study, a cationic hierarchical porous covalent organic frameworks (C-H-COF) were customized via a template-assisted strategy using polystyrene spheres (PS) as sacrificial materials and a post-synthetic modification method. C-H-COF showed good adsorption selectivity for PFASs owing to the dual effects of the full utilization of the internal adsorption sites and electrostatic interaction. The key role of electrostatic attraction in the extraction of PFASs using C-H-COF was further proven by density functional theory (DFT) calculations. The maximum adsorption capacity of the C-H-COF for perfluorooctanoic acid (PFOA) was 400 mg·g⁻¹, which was superior to that of microporous COFs (M-COF) and hierarchical porous COFs without cationic functionalization (H-COF). Accordingly, an analytical method for sensitively detecting five PFASs was established by employing C-H-COF as a dispersive solid phase extraction (DSPE) adsorbent combined with ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS), and the limits of detection were 0.011‒0.29 ng·L⁻¹. Moreover, the hierarchical porous structure of the C-H-COF accelerated the mass transfer of analytes so that the extraction process could be completed within 10 min. This method was employed to analyze PFASs in dairy products, in which the ultra-trace levels of analytes were quickly determined with spiked recoveries of 80.1‒112.6%. This work not only provides a rational synthetic strategy for novel ionic hierarchical porous COFs but also helps to expand the application of COFs in sample pretreatment.