Determination of trace bisphenols in milk based on Fe3O4@NH2-MIL-88(Fe)@TpPa magnetic solid-phase extraction coupled with HPLC.

Herein, a covalent organic framework (COF) was grown on a magnetic metal-organic framework (MOF) by a solvothermal method for the efficient extraction of bisphenols (BPs). The magnetic solid-phase extraction (MSPE) of four bisphenols (bisphenol A, bisphenol B, bisphenol AF and bisphenol C) was carried out without adjusting the pH and salt concentration. When 30 mg Fe3O4@NH2-MIL-88(Fe)@TpPa was used to adsorb for 25 min, 6 mL methanol was used to elute for 20 min, and the extract was detected by high-performance liquid chromatography (HPLC). The proposed method has a low detection limit of 0.011-0.036 ng mL-1, a wide linear range of 0.05-100 ng mL-1, and a correlation coefficient (R2) of 0.9980-0.9998. The intra-day and inter-day precisions are 0.74-2.54% and 1.68-3.72%, respectively. Bisphenol A was determined by applying the proposed method to the determination of actual milk samples. The standard addition experiment showed that the relative recovery of the four bisphenols was 85.70-119.7%. Pseudosecond-order, first-order, Langmuir and Freundlich models were applied to explore the adsorption characteristics of Fe3O4@NH2-MIL-88(Fe)@TpPa. In general, the established Fe3O4@NH2-MIL-88(Fe)@TpPa-MSPE-HPLC-UV method exhibits attractive sensitivity, simple manipulation, and excellent reusability, and it has excellent prospects for the detection of trace BPs in complex milk matrices.

Fabrication of Two Luminescent Imidazolyl Cadmium-Organic Frameworks and Their Sensing Mechanism for 2,6-Dichloro-4-nitroaniline.

2,6-Dichloro-4-nitroaniline, alias dicloran (DCN), is a broad-spectrum pesticide that can cause irreversible damage to the human body. Therefore, it is of great significance to develop a technology for the rapid and convenient detection of DCN. Luminescent metal organic frameworks have attracted extensive attention in the field of sensing and detection due to their excellent optical properties. In this study, two kinds of 2D Cd-MOFs (CdMOF-1 and CdMOF-2) were developed for the detection of residual DCN in the environment. Both CdMOFs exhibit excellent solvent and acid-base stability and can respond to DCN quickly and sensitively in a short time (30 s). CdMOFs not only have good selectivity and anti-interference toward DCN but also have good reusability. Under the conditions of DCN concentrations of 1-15 and 0.3-30 µM, the change in fluorescence intensity of CdMOF-1 and CdMOF-2 showed a good linear relationship with DCN concentration (R2 = 0.999/0.991), and the detection limits were 0.36 and 0.12 µM, respectively. Through ultraviolet-visible absorption spectroscopy (UV-Vis), X-ray photoelectron spectroscopy, fluorescence lifetime, and density functional theory calculations, it is revealed that the fluorescence quenching mechanisms of DCN for two kinds of Cd-MOFs are competitive absorption and photoinduced electron transfer, and there may be a weak π-π interaction. Finally, it is demonstrated that by using two types of fluorescent CdMOFs to make the fluorescent test paper and detect actual soil, these can be applied to the actual scene and achieve onsite real-time detection.

A gold-silver bimetallic nanocluster-based fluorescent probe for cysteine detection in milk and apple.

Noble metal nanoclusters have attracted much attention due to their excellent optical properties. In the present work, a silver-doped gold-based bimetallic nanoclusters (Au/Ag NCs) were reasonably designed and prepared through a one-pot method by using 5-mercapto-1-tetrazolea-acetic acid sodium salt (MTAS) as a protector and capping agent. In comparison with the monometallic nanoclusters, Ag-doped metallic nanoclusters show better performance. The particle size of the MTAS-Au/Ag NCs is slightly larger than that of the undoped Au NCs by about 1.86 ± 0.5 nm, and the MTAS-Au/Ag NCs exhibit an emission peak at 635 nm with a quantum yield (QY) of 3.05%. The presence of cysteine (Cys) induces efficient quenching of the photoluminescence of the obtained Au/Ag NCs, achieving the sensitive detection of Cys with a detection limit of 16 nM. The fluorescence quenching rate of the nano fluorescent probe has a linear relationship with the cysteine concentration. Under the best detection conditions, the linear range for Cys detection with MTAS-Au/Ag NCs as a probe is 0.05-25.0 µM. Moreover, this probe has been successfully applied to the analysis of Cys in milk and apples, and a satisfactory recovery rate has been obtained, indicating the effectiveness and reliability of the sensor system for the detection of actual samples.

Improving permeability and chromatographic performance of poly(pentaerythritol diacrylate monostearate) monolithic column via photo-induced thiol-acrylate polymerization.

A simple approach was developed for rapid preparation of polymeric monolithic columns in UV-transparent fused-silica capillaries via photoinitiated thiol-acrylate polymerization of pentaerythritol diacrylate monostearate (PEDAS) and trimethylolpropane tris(3-mercaptopropionate) (TPTM) within 10min, in which the acrylate homopolymerized and copolymerized with the thiol simultaneously. The morphology, permeability and chromatographic performance of the resulting poly(PEDAS-co-TPTM) monoliths were studied. It could be observed from SEM that the morphology of poly(PEDAS-co-TPTM) monolith was rather different from that of poly(PEDAS) monolith, which was fabricated via photo-induced free radical polymerization using PEDAS as the sole monomer. Compared with poly(PEDAS) monolith, poly(PEDAS-co-TPTM) monolith possessed better permeability when they were fabricated under the same preparation conditions. By adjusting the composition of porogenic solvents, poly(PEDAS-co-TPTM) monolith exhibited lower plate heights (15.7-17.7µm) than poly(PEDAS) monolith (19.1-37.9µm) in µLC. In addition, 66 unique peptides were positively identified on poly(PEDAS-co-TPTM) monolith when tryptic digest of four proteins was separated by µLC-MS/MS, demonstrating its potential in proteome analysis.