A hybrid triazine-imine core-shell magnetic covalent organic polymer for analysis of pesticides in fruit samples by ultra high performance liquid chromatography with tandem mass spectrometry

A carboxyl-functionalized covalent organic polymer for the efficient adsorption of saxitoxin

Saxitoxin (STX), the most widely distributed neurotoxin in marine waters and emerging cyanotoxin of concern in freshwaters, causes paralytic shellfish poisoning in humans upon consumption of contaminated shellfish. To allow for the efficient monitoring of this biotoxin, it is of high importance to find high-affinity materials for its adsorption. Herein, we report the design and synthesis of a covalent organic polymer for the efficient adsorption of STX. Two β-keto-enamine-based materials were prepared by self-assembly of 2,4,6-triformylphloroglucinol (Tp) with 2,5-diaminobenzoic acid (Pa-COOH) to give TpPa-COOH and with 2,5-diaminotoluene (Pa-CH₃) to give TpPa-CH₃. The carboxylic acid functionalized TpPa-COOH outperformed the methyl-bearing counterpart TpPa-CH₃ by an order of magnitude despite the higher long-range order and surface area of the latter. The adsorption of STX by TpPa-COOH was fast with equilibrium reached within 1 h, and the Langmuir adsorption model gave a calculated maximum adsorption capacity, Q_m, of 5.69 mg g^-1, making this material the best reported adsorbent for this toxin. More importantly, the prepared TpPa-COOH also showed good reusability and high recovery rates for STX in natural freshwater, thereby highlighting the material as a good candidate for the extraction and pre-concentration of STX from aquatic environments.

Recent advances and applications of magnetic covalent organic frameworks in food analysis

Recently, covalent organic frameworks (COFs) have been widely used to prepare magnetic adsorbents for food analysis due to their highly tunable porosity, large specific surface area, excellent chemical and thermal stability and large delocalised π-electron system. This review summarises the main types and preparation methods of magnetic COFs and their applications in food analysis for the detection of pesticide residues, veterinary drugs, endocrine-disrupting phenols and estrogens, plasticisers and other food contaminants. Furthermore, challenges and future outlook in the development of magnetic COFs for food analysis are discussed.

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.

Covalent organic frameworks as multifunctional materials for chemical detection

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

Recent Advances of Triazine-Based Materials for Adsorbent Based Extraction Techniques

This review mainly focused on the synthesis and properties of triazine-based materials as well as the state-of-the-art development of these materials in adsorption-based extraction techniques in the past 5 years, such as solid-phase extraction, magnetic solid-phase extraction, solid-phase microextraction and stir bar sorptive extraction, and the detection of various pollutants, including metal ions, drugs, estrogens, nitroaromatics, pesticides, phenols, polycyclic aromatic hydrocarbons and parabens. In the triazine-functionalized composites, triazine-based polymers and covalent triazine frameworks have been developed as the adsorbents with potential for environmental pollutants, mainly relying on the large surface area and the affinity of triazinyl groups with the targets. Triazine-based adsorbents have satisfactory sensitivity and selectivity towards different types of analytes, attributed from various mechanisms including π-π, electrostatics, hydrogen bonds, and hydrophobic and hydrophilic effects. The prospects of the materials for adsorption-based extraction were also presented, which can offer an outlook for the further development and applications.

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

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

Analytical methods to analyze pesticides and herbicides

This paper reviews studies published in 2019, in the area of analytical techniques for determination of pesticides and herbicides. It should be noted that some of the reports summarized in this review are not directly related to but could potentially be used for water environment studies. Based on different methods, the literatures are organized into six sections, namely extraction methods, electrochemical techniques, spectrophotometric techniques, chemiluminescence and fluorescence methods, chromatographic and mass spectrometric techniques, and biochemical assays. PRACTITIONER POINTS: Totally 141 research articles have been summarized. The review is divided into six parts. Chromatographic and mass spectrometric techniques are the most widely used methods.

Facile synthesis and immobilization of boroxine polymers containing carbon chains and their application as adsorbents

Novel boroxine-linked covalent organic polymers was synthesized and immobilized by one pot reaction for extraction of anthraquinones.

Fabrication of glucose-derived carbon-decorated magnetic microspheres for extraction of bisphenols from water and tea drinks

Glucose-derived carbon-decorated magnetic microspheres were synthesized by an easy hydrothermal carbonization method and used as a high-efficiency adsorbent to extract bisphenols in water and tea drinks. The as-prepared carbon-decorated magnetic microspheres had a well-defined core-shell structure with a shell thickness of about 5 nm. The microspheres possessed high saturation magnetization at 60.8 emu/g and excellent chemical stability in aqueous solution. The experimental parameters affecting the extraction efficiency, including extraction time, pH, adsorbent dosage, desorption solvents, desorption time, and solution volume were evaluated. Electrostatic and π-π interactions were the major driving forces during extraction. Overall, a new magnetic solid-phase extraction method of determining bisphenols was developed on the basis of as-prepared magnetic microspheres. The method had a wide linear range, low limits of detection (0.03-0.10 µg/L), and high recoveries (85.4-104.6%).