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A novel ratiometric electrochemical sensor was developed based on a carbon cloth electrodeposited with silver nanoparticles and drop-coated by covalent organic framework (COF-LZU1) for simultaneous determination of bisphenol A (BPA) and bisphenol S (BPS). Carbon cloth exhibited a significantly larger electrochemical active area than common glassy carbon electrodes (27.5 times). Silver nanoparticles not only provided a stable reference signal but also enhanced electroactivity for the oxidation of BPA and BPS. COF-LZU1 with good adsorption performance and large periodic π-arrays promoted the enrichment of BPA and BPS to further increase the current response. Compared with the traditional single-signal electrochemical sensor, the developed ratiometric sensor exhibited better reproducibility and a wider linear range for BPA and BPS from 0.5 to 100 μM with a limit of detection of 0.15 μM. Furthermore, the developed sensor showed excellent stability and superior anti-interference ability. The real sample analysis for BPA and BPS has been successfully carried out in mineral water, electrolyte drink, tea, juice, and beer with recoveries of 88.3–111.7%. The developed ratiometric sensor is expected to be a candidate for the preparation of other electrochemical sensors and the analysis of additional practical samples. [ABSTRACT FROM AUTHOR]

In this work, electro-enhanced solid-phase microextraction (EE-SPME) and covalent organic framework (COF) were adopted to improve the extraction efficiency. A conductive COF synthesized of 2,6-diaminoanthraquinone (DQ) and 1,3,5-triformylphloroglucinol (TP) was in situ bonded to the stainless steel wire via facile solution-phase approach and used as the EE-SPME fiber coating to preconcentrate a typical endocrine disruptor bisphenol A (BPA). Compared with conventional SPME, the DQTP bonded fiber coupled with EE-SPME device exhibited higher extraction efficiency and achieved extraction equilibrium within 10 min. The proposed approach based on EE-SPME and gas chromatography coupled with flame ionization detector gave a linear range of 0.05–10 μ g mL−1 and detection limit of 3 μ g L−1 (S/N = 3) with good precision (<6.7%) and reproducibility (<7.1%) spiked with 0.1, 0.5, 1.0 μ g mL−1 BPA. Quantitative determination of BPA in extracts of food packagings (mineral water bottles, milk boxes and milk tea cups) was achieved with recoveries from 88.6 to 118.0%. A sampling device based on a conductive covalent organic framework (COF, DQTP) and electro-enhanced solid-phase microextraction has been constructed for rapid extraction of bisphenol A. Image 1 • Covalent organic framework DQTP was grown in situ on stainless steel wire via Schiff base reaction. • Extraction efficiency of SPME was enhanced by the external electrical field with shorter extraction time. • The developed EE-SPME coupled with GC-FID method was applied to determine bisphenol A in extracts of food packagings. [ABSTRACT FROM AUTHOR]

• The fiber modified by COFs improved extraction efficiency of bisphenols. • The SPME fiber was protected during extraction from canned meat. • Only 10 min can reach the extraction equilibrium under the electric field. • Bisphenols in canned meats were detected by GC-FID. Bisphenols (BPs), one of the endocrine disrupting chemicals (EDCs), are harmful to health with the potential carcinogenicity, teratogenicity and neurotoxicity. In this paper, we developed an electro-enhanced solid-phase microextraction with membrane protection method to enrich BPs. The extraction time can be shortened to 10 min with the electric field, and the prepared fiber can be repetitively used 100 times with the membrane protection. The factors affecting extraction such potential, pH, extraction temperature and extraction time were optimized. Under optimal conditions, the linear ranges were 2-600 ng mL−1 for BPAF and 2-800 ng mL−1 for the other four BPs (BPB, BPF, BPA, BPZ), and the limits of detection (S/N=3) were from 0.09 (BPAF) to 0.41 (BPA) ng mL−1, with intra-day and inter-day precisions <5.16% and 9.29%, respectively. The developed method has been applied to the determination of trace BPs in canned meat with the recoveries of 73%-117%, showing a promising application for pretreatment in complex samples. [ABSTRACT FROM AUTHOR]

The sensitivity and selectivity of electrochemical analysis are challenging due to the materials used for electrode modification as well as electrical conductivity, catalytic activity and recognition ability of the working electrode. In this work, a portable 3D-printed electrochemical electrode clamp was designed and applied in combination with the developed covalent organic framework (COF DQTP)-modified pencil graphite electrode (DQTP/PGE). The β -ketoenamine-linked COF DQTP synthesized by 1,3,5-triformylphloroglucinol (TP) and 2,6-diaminoanthraquinone (DQ) through solvothermal method is a porous crystalline with excellent conductivity and large periodic π-arrays, coupled with commercial available pencil graphite electrode to fabricate a disposable sensor for simultaneous determination of environmental endocrine disruptors bisphenol A and bisphenol S. The DQTP/PGE sensor exhibited high electrical conductivity and catalytic activity, and a good linearity was obtained in a range of 0.5–30 μ M for two bisphenols with a detection limit of 0.15 μ M (S/N = 3). Moreover, the sensor showed a reproducible and stable response over one month with negligible interference, and an accepted recovery with real food packaging samples. A covalent organic framework (COF, DQTP) modified pencil graphite electrode (DQTP/PGE) equipped with a 3D-printed electrochemical electrode clamp has been fabricated for simultaneous determination of bisphenol A and bisphenol S. [Display omitted] • Covalent organic framework DQTP coated pencil graphite electrode. • 3D-printed electrochemical electrode clamp for pencil graphite electrode. • Simultaneous determination of bisphenol A and bisphenol S in food packagings. [ABSTRACT FROM AUTHOR]

Phthalate esters (PAEs), a category of widely used plasticizers, are tend to migrate from plastic packaging to drinks. In this paper, we develop a simple and rapid coprecipitation method for synthesis of a magnetic covalent organic framework (COF) adsorbent. The fabricated COF-(TpBD)/Fe 3 O 4 was applied to magnetic solid phase extraction (MSPE) of 15 phthalate esters (PAEs) for subsequent GC-MS/MS determination in beverage samples. The as-synthesized magnetic adsorbent exhibited great potential in PAEs analysis with a limit of detection of 15 PAEs ranged from 0.005 to 2.748 μg L−1 (S/N = 3). The intra-day and inter-day relative standard deviations (RSD) value of the PAEs were less than 8.8% and 9.9%, respectively. The adsorbent can be reused after washing with methanol. The developed method was successfully applied for the determination of trace PAEs in eight beverages with recoveries ranging from 79.3% to 121.8% and RSDs were less than 11.9%. This work provides a simple magnetization process, which facilitates the application of COFs for enrichment and separation of PAEs in beverages with different matrices. Image 1 • A simple and rapid coprecipitation method for the preparation of a magnetic covalent organic framework. • COF-based magnetic solid phase extraction efficiently enrich 15 phthalate esters in beverage samples. • Method development for the simultaneous analysis of 15 phthalate esters by GC-MS/MS. [ABSTRACT FROM AUTHOR]

Based on covalent organic framework (COF) 1,3,5-tris-(4-formylphenyl)benzene-benzidine (TFPB-BD) in situ grown on Fe3O4 hollow microspheres and combined with gas chromatography-flame thermionic detector, a rapid and simple stir bar sorptive-dispersive microextraction method was developed for the determination of five triazole pesticides (paclobutrazol, hexaconazole, flusilazole, propiconazole, and tebuconazole). The synthesized TFPB-BD/Fe3O4 microspheres were characterized by transmission electron microscope, vibrating sample magnetometer, and thermogravimetric analysis, which showed that the material has strong magnetism and higher load capacity of COF. Under optimal conditions, the extraction equilibrium could be achieved within 9 min with detection limits of 0.17–1.48 μg L−1 (S/N = 3) and a linear range of 5–1000 μg L−1. The developed method was applied to the determination of trace triazole pesticides in apples, pears, and cabbages with recoveries from 81 to 117%. [ABSTRACT FROM AUTHOR]

[Display omitted] • Synergistic effects of 1-octanol and COF@Tp-NDA improved bisphenols extraction. • Consumption of COF@Tp-NDA and organic solvents was less than existing methods. • HF porous structure avoided pollution of the extractant. • Method was successfully applied to the detection of BPs in three beverages samples. Bisphenols (BPs) can migrate from packaging materials into foods, resulting in potentially harmful residues. For example, accumulation of BPs is associated with endocrine disorders. Owing to matrix effects, development of an effective and eco-friendly sample pretreatment would be helpful for BPs detection in beverages packed in plastic containers. In this work, an extraction bar, composed of hollow fiber (HF) functionalized with covalent organic frameworks (COF@Tp-NDA) and 1-ocanol, was prepared for extraction of five BPs simultaneously. The synergistic effect of COF@Tp-NDA and 1-octanol improved the extraction efficiency of BPs from milk-based beverage, juice, and tea beverage. Under optimal conditions, limits of detection ranged from 0.10 to 2.00 ng mL−1 (R2 ≥ 0.9974) and recoveries ranged from 70.1 % to 106.8 %. This method has the potential to enrich BPs, supporting their accurate determination in complex beverages. [ABSTRACT FROM AUTHOR]

[Display omitted] • The composite beads (CACPs) were prepared facilely at room temperature. • CACPs can be completely separated within 1 min without centrifugation. • A convenient and sensitive method was developed for detecting neonicotinoids. • The developed method was successfully validated in fruit and vegetable samples. Neonicotinoids, the fastest-growing class of insecticides, have posed a multi-media residue problem with adverse effects on environment, biodiversity and human health. Herein, covalent organic framework-sodium alginate-Ca2+-polyacrylic acid composite beads (CACPs), facilely prepared at room temperature, were used in convenient dispersive solid-phase extraction (dSPE) and combined with high-performance liquid chromatography (HPLC) for the detection of five neonicotinoid insecticides (thiamethoxam, acetamiprid, dinotefuran, clothianidin, imidacloprid). CACPs can be completely separated within 1 min without centrifugation. After seven adsorption/desorption cycles, it maintained high extraction efficiencies (>90%). The developed method exhibited a wide linear range (0.01 ∼ 10 μg mL−1), low limits of detection (LODs, 0.0028 ∼ 0.0031 mg kg−1), and good repeatability (RSD ≤ 8.11%, n = 3). Moreover, it was applied to the determination of five neonicotinoids in fruit and vegetables (peach, pear, lettuce, cucumber, tomato), and recoveries ranged from 73.6% to 116.2%. [ABSTRACT FROM AUTHOR]

• Membrane-protected magnetic adsorbent was used for efficient extraction of estrogens. • The extraction efficiency was still above 90% after repeated use 10 times. • This developed method is simple, highly efficient and eco-friendly. The presence of estrogens residues in dairy products is a growing concern due to their potential health risk. Herein, in this study, we have developed a membrane–protected magnetic solid–phase extraction (MP–MSPE) method that utilized a magnetic adsorbent (Fe 3 O 4 @COF–LZU1) with in–situ growth for the efficient extraction of estrone (E1), 17β–estradiol (E2), and estriol (E3). When combined with HPLC–FLD, this method allows for the efficient detection of estrogens in dairy products. The stability of the MP–MSPE was improved by the presence of a dialysis membrane, which remained a high extraction efficiency (90 %) even after ten reuse cycles. The hydrogen bonding, π–π interactions and pore size effect contribute to the excellent adsorption of three estrogens onto Fe 3 O 4 @COF–LZU1. Under optimal conditions, the method exhibits a low detection limit (0.01–0.15 μg L−1), wide linear range (0.1–800 μg L−1), and favorable recoveries (77.3 %–109.4 %) at three concentration levels (10, 50 and 100 μg L−1). This proposed method is characterized by its simplicity, high efficiency and eco–friendliness, making it a promising approach for extracting estrogens from dairy products. [ABSTRACT FROM AUTHOR]

• Covalent organic framework TpBD grows on titanium wire via TiO 2 nanotube arrays. • TpBD-TiO 2 fiber has good thermal stability and long lifetime. • HS-SPME on the fiber exhibits excellent extraction efficiency for trace PAEs. • Coupled with GC-MS/MS, it presents a sensitive methodology for PAEs determination. Vegetables are easily contaminated by phthalate esters (PAEs) from the environment, agricultural films and fertilizers, affecting human health. In this paper, titanium dioxide (TiO 2) nanotube arrays were prepared by electrochemical anodic oxidation on the surface of titanium wire. Covalent organic framework of TpBD was in situ bonded to the titanium wire via TiO 2 nanotube arrays using monomers of 1,3,5-trimethylphloroglucinol (Tp) and benzidine (BD). The fabricated TpBD-TiO 2 coated titanium wire was used as the solid-phase microextraction fiber to extract 11 PAEs in vegetable samples. Coupled with gas chromatography-tandem mass spectrometry (GC–MS/MS), the limits of detection for PAEs were from 0.001 (di- n -butyl phthalate) to 0.430 (butyl benzyl phthalate) μ g/L (S/N = 3) and enrichment factors were between 226 (dimethyl phthalate) and 2154 (di- n -butyl phthalate). Our fabricated TpBD-TiO 2 fiber can be used at least 150 times without significant loss of extraction efficiency (<4.8%). Quantitative determination of PAEs in vegetable samples (tomato, lettuce, cucumber) was achieved by standard addition. [ABSTRACT FROM AUTHOR]