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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]

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]