Novel covalent organic frameworks based electrospun composite nanofiber membranes as pipette-tip strong anion exchange sorbent for determination of inorganic arsenic in rice

Detection of arsenate in colored grains using an interference-free dual-signal ratiometric HEC sensor

The design of novel homogeneous electrochemical (HEC) sensors with dual-signal ratiometric response holds great potential for highly sensitive and reliable detection of arsenic in food matrices. Herein, COF-based hybrids were prepared by integrating methylene blue (MB) signals and MnO2 nanozyme coatings, possessing the advantages of high signal loading, oxidase-mimicking activity, and ascorbic acid (AA)-specific recognition to realize ratiometric HEC detection of arsenate. The hydrolysate AA, produced from ALP-catalyzed AAP hydrolysis, could decompose MnO2 coatings into Mn2+, and regulate MB release and o-phenylenediamine oxidation to 2,3-diaminophenazine (DAP). Furthermore, arsenate specifically inhibited ALP, subsequently restraining AA formation and MnO2 decomposition. Consequently, a decreased MB current and an increased DAP current with opposite responses were regulated by arsenate compared with those without arsenate. Thus, this dual-signal ratiometric HEC sensor achieved sensitive detection of arsenate, with a LOD of 0.509 ppb. It was successfully applied to reliable detection of arsenate in complex food matrices.

Interface-assisted synthesized covalent organic framework film for efficient extraction of microcystins in aquatic organisms

Covalent organic framework (COF) film-based solid-phase extraction (F-SPE) has garnered great attention in sample pretreatment. However, harsh synthesis conditions of COF films have severely hindered their potential applications. In this study, a kind of COF (TPB-DMTP) films were fabricated via a liquid-liquid interfacial synthesis method at a mild condition. The obtained films exhibited excellent extraction performance towards microcystins (MCs, an algal toxin) due to their porous structure, high specific surface area and abundant accessible adsorption sites. Coupled TPB-DMTP films-based F-SPE with high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS), a sensitive and environment-friendly analytical method was established for MCs detection. Under the optimal conditions, this method possessed wide linear ranges (2.0-800.0 pg mL-1) with good linearity (R ≥ 0.9991), low limits of detection (0.8-3.0 pg mL-1) and satisfactory precision (RSDs ≤7.1 %), which then successfully applied for MCs detection in actual aquatic organism samples. Trace amounts of MC-RR (42.4 pg mL-1) and MC-YR (14.6 pg mL-1) were detected in the mussels. The results demonstrate the excellent application potential of COF films in sample pretreatment.

Advances in covalent organic frameworks for sample preparation

Sample preparation is crucial in analytical chemistry, impacting result accuracy, sensitivity, and reliability. Solid-phase separation media, especially adsorbents, are vital for preparing of liquid and gas samples, commonly analyzed by most analytical instruments. With the advancements in materials science, covalent organic frameworks (COFs) constructed through strong covalent bonds, have been increasingly employed in sample preparation in recent years. COFs have outstanding selectivity and/or excellent adsorption capacity for a single target or can selectively adsorb multiple targets from complex matrix, due to their large specific surface area, adjustable pore size, easy modification, and stable chemical properties. In this review, we summarize the classification of COFs, such as pristine COFs, COF composite particles, and COFs-based substrates. We aim to provide a comprehensive understanding of the different classifications of COFs in sample preparation within the last three years. The challenges and development trends of COFs in sample preparation are also presented.

Covalent Organic Framework Membranes and Water Treatment

Covalent organic frameworks (COFs) are an emerging class of highly porous crystalline organic polymers comprised entirely of organic linkers connected by strong covalent bonds. Due to their excellent physicochemical properties (e.g., ordered structure, porosity, and stability), COFs are considered ideal materials for developing state-of-the-art separation membranes. In fact, significant advances have been made in the last six years regarding the fabrication and functionalization of COF membranes. In particular, COFs have been utilized to obtain thin-film, composite, and mixed matrix membranes that could achieve effective rejection (mostly above 80%) of organic dyes and model organic foulants (e.g., humic acid). COF-based membranes, especially those prepared by embedding into polyamide thin-films, obtained adequate rejection of salts in desalination applications. However, the claims of ordered structure and separation mechanisms remain unclear and debatable. In this perspective, we analyze critically the design and exploitation of COFs for membrane fabrication and their performance in water treatment applications. In addition, technological challenges associated with COF properties, fabrication methods, and treatment efficacy are highlighted to redirect future research efforts in realizing highly selective separation membranes for scale-up and industrial applications.

Polymeric Materials in Speciation Analysis Based on Solid-Phase Extraction

Speciation analysis is a relevant topic since the (eco)toxicity, bioavailability, bio (geo)chemical cycles, and mobility of a given element depend on its chemical forms (oxidation state, organic ligands, etc.). The reliability of analytical results for chemical species of elements depends mostly on the maintaining of their stability during the sample pretreatment step and on the selectivity of further separation step. Solid-phase extraction (SPE) is a matter of choice as the most suitable and widely used procedure for both enrichment of chemical species of elements and their separation. The features of sorbent material are of great importance to ensure extraction efficiency from one side and selectivity from the other side of the SPE procedure. This review presents an update on the application of polymeric materials in solid-phase extraction used in nonchromatographic methods for speciation analysis.

Fabrication of porous cobalt oxide/carbon nanopolks on electrospun hollow carbon nanofibers for microextraction by packed sorbent of parabens from human blood

In this work, electrospinning and hydrothermal methods were employed to synthesize an innovative 3D Co₃O₄/C@HCNFs nanocomposite as the sorbent. It was then used in a packed sorbent microextraction system for parabens analysis in human blood samples, followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The coaxial electrospun core-shell nanofibers mat was stabilized and carbonized to produce the hollow carbon nanofibers (HCNFs) substrate. A coating of cobalt carbonate hydroxide nanopolks was then grown on the HCNFs through hydrothermal synthesis. Ultimately, some of the nanopolks were converted to ZIF-67 by pouring the mat into a warm solution of 2-methyl imidazole and heat-treated into porous Co₃O₄/C afterward. X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) analyses were used to characterize the produced nanocomposite. The effective parameters of the adsorption and desorption steps were optimized by a central composite design. The figures of merit were evaluated under optimal conditions. The linear range of parabens was obtained between 0.5-500.0 ng ml^-1 with R² ≥ 0.9980. The detection limits of the method were between 0.1 and 0.2 ng ml^-1. The intra-day and inter-day precisions were less than 4.3%. Relative recoveries between 92.0% and 109.3% were achieved. The findings demonstrated the eligible performance of the method.