Efficient Extraction and Determination of Carbamate Pesticides in Vegetables Based on a Covalent Organic Frameworks with Acylamide Sites

Large-size porous spherical 3D covalent organic framework for preconcentration of bisphenol F in water samples and orange juice

Large-size spherical sorbents with particle size of 10-50 μm are widely applied in separation fields, however it is still a great challenge to synthesize such large-size spherical covalent organic framework (COF). In this work, a type of large-size porous 3D COF was size-controablly synthesized via a two-step strategy, in which a large-size porous 3D spherical polymer was prepared first through a Pickering emulsion polymerization using nano silica as the stabilizer, and subsequently it was converted into porous spherical 3D COF by a solvothermal method. The as-prepared porous spherical COF (COF-320 as a model) showed size-controllable uniform spherical morphology within 15-45 μm, large specific surface area, fine crystalline structure, and good chemical stability. When used as the sorbent for dispersive solid-phase extraction (d-SPE) of bisphenol F (BPF), the porous spherical COF-320 (15 μm) displayed high adsorption capacity (Qmax = 335.6 mg/g), high enrichment factor (80 folds), and good reusability (at least five cycles). By coupling the d-SPE method to HPLC, a new analytical approach was developed and successfully applied to the determination of trace BPF in two water samples, an orange juice and a standard sample with recoveries of 96.0-102.2 % (RSD = 1.1-1.5 %), 95.7-97.4 % (RSD = 1.4-4.4 %) and 98.7 % (RSD = 2.3 %), respectively. The limit of detection (S/N = 3) and limit of quantification (S/N = 10) were 0.1 and 0.3 ng/mL, respectively. The new synthesis strategy opens a viable way to prepare large-size porous spherical COFs, and the developed analytical method can be potentially applied to sensitively detect the trace BPF in water samples and beverages.

Size-controllable synthesis of large-size spherical 3D covalent organic frameworks as efficient on-line solid-phase extraction sorbents coupled to HPLC

BACKGROUND

Covalent organic frameworks (COFs) have found promising applications in separation fields due to their large surface area and high adsorption capacity, but the exiting COFs can not be directly used as the packing materials of on-line solid-phase extraction (SPE) coupled to HPLC and HPLC because their nano/submicron size or irregular shapes might cause ultrahigh column back pressure and low column efficiency. To synthesize the large-size spherical COFs larger than 3 μm as sorbents might be able to address these problems, however it is still a great challenge till now.

RESULTS

In this work, two large-size spherical 3D COFs (COF-320 and COF-300) were size-controllably synthesized within 10-90 μm via a two-step strategy. These two spherical COFs showed large surface area, fine crystallinity, good chemical/mechanical stability, and good reproducibility. As an application case, when used as the on-line SPE sorbents coupled to HPLC, the large-size spherical COF-320 displayed high binding capacity for bisphenol F (Qmax of 452.49 mg/g), low column back pressure (6-8 psi at flow rate of 1 mL/min), and good reusability (at least 30 cycles). The developed on-line-SPE-HPLC-UV method presented good analytical performance with enrichment factor of 667 folds, linear range of 1.0-400 ng/mL, limit of detection (LOD, S/N = 3) of 0.3 ng/mL, limit of quantification (LOQ, S/N = 10) of 1.0 ng/mL, and recoveries of 100.3-103.2 % (RSDs of 2.0-3.5 %) and 95.2-97.0 % (RSDs of 4.3-5.6 %) for tap water and lake water samples, respectively.

SIGNIFICANCE

This is the first case to synthesize the large-size spherical COFs within 10-90 μm, and this work made it possible to directly use COFs as the filling materials of on-line SPE coupled to HPLC and HPLC. The developed analytical method can be potentially applied to the rapid and sensitive detection of trace bisphenol F in environmental water samples.

Research progress of the combination of COFs materials with food safety detection

Covalent organic frameworks (COFs) have received lots of attention due to their multiple advantages such as high specific surface area, controlled pore size, and excellent stability. When detecting food contaminants, the matrix effect brought by complex food samples can significantly affect the accuracy of the results. How to attenuate matrix effect has always been a major challenge. Utilizing the advantages of COFs and applying them to detect food contaminants is currently a key research direction. The aim of this work is to provide a systematic summary of sample pretreatment techniques and detection techniques combined with COFs, which include almost all current techniques combined with COFs. In addition, the principles of combining COFs with different techniques are explained. Finally, the research foci and development direction of COFs in food contaminant detection are discussed. This is an important reference for the future development of food safety and the design of COFs.

Assessing the greenification potential of cyclodextrin-based molecularly imprinted polymers for pesticides detection

Cyclodextrins, with their unparalleled attributes of eco-friendliness, natural abundance, versatile utility, and facile functionalization, make a paramount contribution to the field of molecular imprinting. Leveraging the unique properties of cyclodextrins in molecularly imprinted polymers synthesis has revolutionized the performance of molecularly imprinted polymers, resulting in enhanced adsorption selectivity, capacity, and rapid extraction of pesticides, while also circumventing conventional limitations. As the concern for food quality and safety continues to grow, the need for standard analytical methods to detect pesticides in food and environmental samples has become paramount. Cyclodextrins, being non-toxic and biodegradable, present an attractive option for greener reagents in imprinting polymers that can also ensure environmental safety post-application. This review provides a comprehensive summary of the significance of cyclodextrins in molecular imprinting for pesticide detection in food and environmental samples. The recent advancements in the synthesis and application of molecularly imprinted polymers using cyclodextrins have been critically analyzed. Furthermore, the current limitations have been meticulously examined, and potential opportunities for greenification with cyclodextrin applications in this field have been discussed. By harnessing the advantages of cyclodextrins in molecular imprinting, it is possible to develop highly selective and efficient methods for detecting pesticides in food and environmental samples while also addressing the challenges of sustainability and environmental impact.

A stable core-shell metal-organic framework@covalent organic framework composite as solid-phase extraction adsorbent for selective enrichment and determination of flavonoids

Hydrophobization and stability is crucial for the practical application of most metal-organic frameworks (MOFs) in extraction technique. In this study, a stable core-shell MOF@COF composite (NH2-MIL-101(Fe)@TAPB-FPBA-COF) was successfully prepared by Schiff base reaction and applied to solid-phase extraction (SPE) of hydrophobic flavonoids. Notably, the TAPB-FPBA-COF shell acts as a hydrophobic "shield", which not only improves the hydrophobicity and stability of hydrophilic NH2-MIL-101(Fe), but also makes the extraction efficiency of flavonoids from MOF@COF composite significantly higher than that of pure NH2-MIL-101(Fe) and TAPB-FPBA-COF. In addition, a sensitive analytical method with excellent linearities (0.1-500 ng mL-1, R2 ≥ 0.9967), low limits of detection (0.02-0.04 ng mL-1 for water; 0.04-0.07 ng mL-1 for grape juice; 0.06-0.08 ng mL-1 for honey), good repeatability (intra-day/inter-day precision are 1.86-5.37%/1.82-7.79%, respectively) and only 5 mg of adsorbent per cartridge was established by optimizing the SPE process combined with high performance liquid chromatography with ultraviolet-visible detector (HPLC-UV). Meanwhile, selectivity study and comparative experiments with the commercial C18 adsorbent showed that the MOF@COF adsorbent exhibited satisfactory extraction efficiency for flavonoids due to multiple interactions such as hydrogen bonding, hydrophobic, and π-π interactions. Finally, the good recoveries in grape juice (84.5-102.5%) and honey (87.5-104.6%) samples further validated the applicability of the proposed method in complex samples.

Emerging Insights into the Use of Advanced Nanomaterials for the Electrochemiluminescence Biosensor of Pesticide Residues in Plant-Derived Foodstuff

Pesticides have an important role in rising the overall productivity and yield of agricultural foods by eliminating and controlling insects, pests, fungi, and various plant-related illnesses. However, the overuse of pesticides has caused pesticide pollution of water bodies and food products, along with disruption of environmental and ecological systems. In this regard, developing low-cost, simple, and rapid-detecting approaches for the accurate, rapid, efficient, and on-site screening of pesticide residues is an ongoing challenge. Electrochemiluminescence (ECL) possesses the benefits of great sensitivity, the capability to resolve several analytes using different emission wavelengths or redox potentials, and excellent control over the light radiation in time and space, making it a powerful strategy for sensing various pesticides. Cost-effective and simple ECL systems allow sensitive, selective, and accurate quantification of pesticides in agricultural fields. Particularly, the development and progress of nanomaterials, aptamer/antibody recognition, electric/photo-sensing, and their integration with electrochemiluminescence sensing technology has presented the hopeful potential in reporting the residual amounts of pesticides. Current trends in the application of nanoparticles are debated, with an emphasis on sensor substrates using aptamer, antibodies, enzymes, and molecularly imprinted polymers (MIPs). Different strategies are enclosed in labeled and label-free sensing along with luminescence determination approaches (signal-off, signal-on, and signal-switch modes). Finally, the recent challenges and upcoming prospects in this ground are also put forward.

Facile synthesis of triazine-based porous organic polymer for the extraction and determination of nitrofuran metabolites residues from meat samples with ultra-high performance liquid chromatography-quadrupole time of flight mass spectrometry

In this work, a novel triazine-based porous organic polymers, TAPT-BPDD, was firstly synthesized by a facile method at room temperature. After characterized by FT-IR, FE-SEM, XRPD, TGA, and nitrogen-sorption experiments, TAPT-BPDD was applied as solid-phase extraction (SPE) adsorbent for the extraction of four trace nitrofuran metabolites (NFMs) from meat samples. The key parameters including the adsorbent dosage, sample pH, type and volume of eluents, type of washing solvents were evaluated in the extraction process. Combined with ultra-high performance liquid chromatography-quadrupole time of flight mass spectrometry (UHPLC-QTOF-MS/MS) analysis, good linear relationship (1-50 µg·kg^-1, R²>0.9925) and low limits of detection (LODs, 0.05-0.56 µg·kg^-1) were obtained under the optimal conditions. When spiked at different level, the recoveries were in the range of 72.7-111.6%. The adsorption isothermal model and extraction selectivity of TAPT-BPDD were also studied in detail. The results showed that TAPT-BPDD was a kind of promising SPE adsorbent for the enrichment of organics in food samples.

Current electroanalytical approaches in the carbamates and dithiocarbamates determination

Pesticides are a suitable tool for controlling plagues and disease vectors. However, their inappropriate use allows for contamination of the environment, soil, water, and foods. Carbamates and dithiocarbamates pesticides present accumulative effects in the human body resulting in hormonal, neurological and reproductive disorders, and some are still suspected or proven to give carcinogenic or mutagenic effects. This review provides a current electroanalytical approach in the carbamates and dithiocarbamates determination, showing the use of voltammetric techniques such as amperometry, cyclic and linear scan, differential pulse, and square wave voltammetry, indicating their advantages, disadvantages, and perspectives in electroanalytical detection of carbamates and dithiocarbamates in natural water and foods. Also are reported the different materials used in the preparation of working electrodes since their choice has an important impact on the success of the analytical applications, resulting in suitable sensitivity, selectivity, stability, and robustness.

Post-synthetic modification of a magnetic covalent organic framework with alkyne linkages for efficient magnetic solid-phase extraction and determination of trace basic orange II in food samples

Efficient magnetic solid phase extraction using covalent organic frameworks (COFs) can find important applications in food safety. In this work, a sulfonate-functionalized magnetic COF (Fe₃O₄@COF-SO₃Na) was synthesized by self-polycondensation of two-in-one monomer 1,6-bis(4-formylphenyl)-3,8-bis((4-aminophenyl) ethynyl)) pyrene (BFBAEPy) on the surface of aminated Fe₃O₄ and a thiol-yne click reaction. It was further adopted as an adsorbent for the efficient magnetic solid-phase extraction (MSPE) of basic orange II. The selective adsorption experiment indicated that it displayed selective adsorption ability to basic orange II due to the ion exchange, hydrogen bonds, and π-π interactions. Under the optimized conditions, the proposed MSPE method coupled with HPLC-DAD showed excellent linearity in the range of 0.05-0.5 µg/mL (R² = 0.9997) for basic orange II. The lower limits of detection (LODs) for basic orange II were 1.0-1.4 µg/L for three food samples: yellow croaker, paprika and dried bean curd. The recoveries were 90.1-98.8% with relative standard deviations (RSDs) below 4.2%. Therefore, this work provides an effective strategy to modify magnetic COFs as absorbents in MSPE. Due to the tunability of functional groups in thiol‑yne click reactions, the functional groups of magnetic COFs can be readily designed to enrich their multifunctional applications. Meanwhile, this work proposed a new method to detect trace amounts of basic orange II in food samples.

Facile synthesis of Cu2+-immobilized magnetic covalent organic frameworks for highly efficient enrichment and sensitive determination of five phthalate monoesters from mouse plasma with HPLC-MS/MS

Development of a simple, highly selective, and sensitive analytical method for phthalate monoesters (mPAEs) remains a challenge due to the complexity of biological samples. To address this issue, Cu²⁺ immobilized magnetic covalent organic frameworks (Fe₃O₄@TtDt@Cu²⁺ composites) with core-shell structures were prepared to enhance the enrichment efficiency of mPAEs by a facile approach synthesis of COFs shells with inherent bifunctional groups on Fe₃O₄ NPs and further Cu²⁺ immobilization. The composites exhibit high specific surface area (348.1 m² g^-1), outstanding saturation magnetization (34.94 emu g^-1), ordered mesoporous structure, Cu²⁺ immobilization, and excellent thermal stability. Accordingly, a magnetic solid-phase extraction (MSPE) pretreatment technique based on Cu²⁺ immobilized COF composites combined with high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) was established, and key parameters including the adsorbent amount, adsorption time, elution solvent, etc. were examined in detail. The developed analytical method showed wide linear ranges (10-8000 ng L^-1), low limit of detections (LODs, 2-10 ng L^-1), and good correlation coefficients (R² ≥ 0.9904) for the five mPAEs. Furthermore, the analytical method was also successfully applied to the highly sensitive detection of metabolite mPAEs in mouse plasma samples, indicating the promising application of the Fe₃O₄@TtDt@Cu²⁺ composites as a quick and efficient adsorbent in the sample pretreatment.

Porous organic framework as coating for stir bar sorptive extraction of carbamate pesticides from corn and potato samples

Three porous organic frameworks (POFs) were synthesized by the reaction between phloroglucinol and 1,4-phthalaldehyde, 4,4'-biphenyldialdehyde or tris-(4-formylphenyl) amine; the products are named as POF-a, POF-b and POF-c, respectively. They were used to prepare POFs coated stir bars respectively for the extraction of four carbamate pesticides (CMPs). POF-c coated stir bar exhibited better adsorption performance than POF-a/b coated stir bar and commercial stir bars, probably due to the stronger conjugated structure and hydrophobicity of POF-c, and resultant hydrophobic, π-π and hydrogen bonding interactions between them. The adsorption mechanism for target CMPs was verified by characterization techniques and molecular dynamics simulation. A method of POF-c coated stir bar sorptive extraction-high performance liquid chromatography-variable wavelength ultraviolet detector was developed for the analysis of four CMPs in corn and potato samples. Under the optimal conditions, LODs of the method were between 0.017 and 0.048 μg/L, and the linear range for four CMPs was 0.1/0.2-200 μg/L.

Urea-linked covalent organic framework functionalized polytetrafluoroethylene film for selective and rapid thin film microextraction of rhodamine B

Incorporation of highly selective and stable adsorbent with facile extraction technology is desired in practical analysis. Here we show the rational preparation of a urea-linked covalent organic framework functionalized polytetrafluoroethylene film (COF-117-PTFE) with ordered porous structure, rich functional groups, and large surface area-to-volume ratio as the effective adsorbent for convenient, selective and rapid thin film microextraction (TFME) of rhodamine B (RB). The COF-117-PTFE based TFME coupled with high performance liquid chromatography-fluorescence detector (HPLC-FLD) successfully realized the determination of RB with the limit of detection of 0.007 μg L^-1, the linear range of 0.1 - 100 μg L^-1. The relative standard deviation (RSD) of intraday (n = 5) and interday (n = 5) for the determination of 10 μg L^-1 RB were 2.3% and 6.8%, respectively. The absolute recoveries were 80.3%, 71.2% and 67.9% in river water, chili powder and Sichuan pepper powder, respectively. The recoveries for RB spiking in complicated real samples (dry chili, chili powder, dry Sichuan pepper, Sichuan pepper powder and river water) ranged from 90.4% to 107.5%. The developed COF-117-PTFE based TFME-HPLC-FLD method is promising in practical application. This work reveals the high potential of functionalized COF film as the adsorbent for effective extraction of trace contaminants in complicated samples.