Heterocyclic frameworks as efficient sorbents for solid phase extraction-high performance liquid chromatography analysis of nitroimidazoles in chicken meat

Construction of carboxyl-functionalized hyper-cross-linked porous polymers using waste polystyrene for effective adsorption of phenolic contaminants

The extensive presence of phenolic organic contaminants (POCs) poses a serious threat to humans. Meanwhile, the upcycling/reusing of waste polystyrene to reduce the exponential growth of plastic pollution is a very important environmental issue. Addressing these demands, a series of carboxyl-functional hypercrosslinked polymers (labeled PP-HCPs) were constructed by knitting waste polystyrene with pyromellitic dianhydride at different ratios through a one-step Friedel-Crafts reaction for effective adsorption of POCs. Among the prepared PP-HCPs, PP-HCP2 displayed a large specific surface area with high adsorption capacity (37.3 mg g-1) for POCs. Using PP-HCP2 as solid phase extraction sorbent, six POCs were effectively extracted from water and peach drink samples, then subjected to high-performance liquid chromatography-ultraviolet detection. The method demonstrated good linearity in the range of 0.03-100.0 ng mL-1 for water samples and 0.06-100.0 ng mL-1 for peach drinks under optimum experimental conditions. At a signal-to-noise ratio of 3, low detection limits were found to be 0.01-0.10 ng mL-1 for water samples and 0.02-0.15 ng mL-1 for peach drinks. Good accuracy and repeatability were achieved with recoveries of 85.3-111.8 % and the relative standard deviations below 8.6 %. The PP-HCP2-based approach can be employed as a dependable and sensitive tool to detect POCs in water and peach drink samples. This work delivers a simple and economically viable approach to fabricate carboxyl-functional HCPs by converting waste foam into high-value-added sorbent, with great significance for sustainable development.

Storage stability study of metronidazole and hydroxymetronidazole in chicken eggs by liquid chromatography tandem mass spectrometry

Metronidazole (MNZ) is one of the most commonly used antibiotics in the food industry. High levels in food can lead to the development of antimicrobial resistance in humans, so it is important to monitor its levels in food. In the context of legal proceedings, it is frequently necessary to re-examine samples after an extended period of time. It is therefore crucial to ensure that the analytes in question do not degrade during the storage period. In this study, HPLC-MS/MS approach was validated and used to analyze levels of MNZ and its hydroxy metabolite in chicken eggs during storage in the refrigerator (+4 °C) and in the freezer (-20 °C) for 3 months. An analyte solution was administered to hens to obtain eggs containing MNZ and hydroxymetronidazole (MNZ-OH). The dependence of the analyte content in eggs as a function of time after sampling was also investigated.

Green construction of hydroxyl-functionalized magnetic porous organic framework for effective extraction of triazine herbicides from environmental water and watermelon juice samples

Triazine herbicides have been widely detected in water resources and food, which poses a potential hazard to both ecosystem and human health. Due to their high polarity, conventional adsorbents have limitations for their extractions. Herein, for the effective magnetic extraction of triazine herbicides, a novel and effective magnetic adsorbent was prepared with a satisfactory extraction performance. In the experiments, five porous organic frameworks (POFs) with hydroxyl functional groups were synthesized by diazo-coupling reactions in aqueous solution with β-cyclodextrin (β-CD) as a green monomer. After evaluation of the five POFs, the DDM-CD-POF, which was synthesized with 4'4-diaminodiphenylmethane (DDM) and β-CD, showed the largest specific surface area and the best adsorption capacity for the five triazine herbicides. Then, it was magnetized by introducing Fe₃O₄@SiO₂ into it to prepare a magnetic adsorbent (M-DDM-CD-POF) to facilitate separation and recycling. Finally, the M-DDM-CD-POF-based magnetic solid-phase extraction in combination with high performance liquid chromatographic detection method was established for the quantitative determination of the triazine herbicides in environmental water and watermelon juice samples. The current strategy showed low limits of detection of 0.03-0.11 ng mL^-1 for environmental water and 0.07-0.22 ng mL^-1 for watermelon juice sample. The method recoveries for spiked samples ranged from 84.0% to 113.0% with the relative standard deviations ≤8.8%. This work provides a new approach for the detection of the triazine herbicides with good application prospect.

Porphyrin-based hypercrosslinked polymers as sorbents for efficient extraction of nitroimidazoles from water, honey and chicken breast

In this work, a series of 5,10,15,20-tetraphenylporphyrin (TPP)-based hyper crosslinked polymers were prepared by Friedel-Crafts reaction. Among them, the HCP-TPP-BCMBP, which was prepared by using TPP as the monomer and with 4,4'-Bis(chloromethyl)-1,1'-biphenyl (BCMBP) as the cross-linking agent, had the best adsorption capability for the enrichment of the nitroimidazoles of dimetridazole, ronidazole, secnidazole, metronidazole, and ornidazole. Then, a solid-phase extraction (SPE) method with the HCP-TPP-BCMBP as adsorbent coupled with HPLC-UV detection for the determination of nitroimidazole residues in honey, environmental water, and chicken breast samples was established. The influence of the main factors that affect the SPE, i.e., sample solution volume, sample loading rate, sample pH, and eluent and its volume, were studied. Under the optimal conditions, the limits of detection (S/N = 3) for the nitroimidazoles were measured to be in the range of 0.02-0.04 ng mL^-1, 0.4-1.0 ng g^-1 and 0.5-0.7 ng g^-1 for environmental water, honey, and chicken breast samples, with the determination coefficients being in the range of 0.9933-0.9998. The analytes recoveries by the method in fortified samples fell in the range from 91.1% to 102.7% for environmental water, from 83.2% to 105.0% for honey, and from 85.9% to 103.0% for chicken breast samples, and the relative standard deviations for the determination were less than 10%. It shows that the HCP-TPP-BCMBP has a strong adsorption capability for some polar compounds.

Fluorine-Functionalized Triazine-Based Porous Organic Polymers for the Efficient Adsorption of Aflatoxins

Food safety issue caused by aflatoxins has aroused widespread concern in society. Herein, a novel fluorine-functionalized triazine-based porous organic polymer (F-POP) was developed for the first time by the simple condensation polymerization of 2,2'-bis(trifluoromethyl)benzidine and cyanuric chloride. With in-built fluorine functional group (F) and imine group (-NH-), F-POP displayed significantly superior adsorption ability for aflatoxins, outperforming fluorine-free POP due to the multiple interaction mechanisms of hydrogen bond, F-O interaction, π-π interaction, F-π interaction, and hydrophobic interaction. Thus, magnetic F-POP was prepared by introducing Fe₃O₄ into F-POP and then utilized as a magnetic sorbent for the extraction of trace aflatoxins in peanut and rice samples prior to high-performance liquid chromatography-fluorescence detection. Under the optimal conditions, the proposed method presented high sensitivity with the limit of detections at 0.005-0.15 ng g^-1. F-POP also exhibited outstanding adsorption capability for many other organic pollutants, revealing its great potential for analysis or adsorption applications.

Facile synthesis of hypercrosslinked polymer as high-efficiency adsorbent for the enrichment of nitroimidazoles from water, honey and chicken meat

Design and fabrication of functionalized hypercrosslinked polymers (HCPs) for enhancing their performance by using green renewable monomers has attracted considerable research interest. In this study, hydroxyl‑functional HCP (labeled as OHHCP) was prepared via the knitting method by applying natural naringenin as a monomer for the first time. Due to the good hydrophilicity and strong H-bonding ability, the OHHCP showed high extraction capacity for nitroimidazoles. Thus, it was successfully applied as a potent adsorbent for solid phase extraction of five nitroimidazoles in water, honey and chicken meat, followed by high-performance liquid chromatography-diode array detector analysis. At the optimized conditions, the limit of detections (S/N = 3) of the proposed method for water, honey and chicken samples were 0.02 - 0.06 ng mL^-1, 0.5 - 1.0 ng g^-1 and 0.8 - 1.0 ng g^-1, respectively. The recoveries were 80.0 - 110%, and the relative standard deviations were below 10.0%. The OHHCP also displayed good application prospects for other organic compounds with H-bonding capability. This study highlights the facile preparation of OH-functionalized HCPs from renewable and natural resources as potent adsorbents for polar compounds.

Ligand-variable metal clusters charge transfer in Ce-Por-MOF/AgNWs and their application in photoelectrochemical sensing of ronidazole

A photoelectrochemical sensing platform based on ligand-variable metal clusters charge transfer was established for the quantitative assay of ronidazole (RNZ) using Ce-porphyrin-metal-organic frameworks/silver nanowires (Ce-Por-MOFs/AgNWs). Rod-like Ce-Por-MOFs and well-dispersed sub-50 nm AgNWs were prepared using a hydrothermal method and polyol strategy, and then through simple drop coating to yield Ce-Por-MOFs/AgNWs nanocomposites. We investigated the intrinsic semiconducting properties of the composites. More importantly, it was found that the variable-valence metal node can provide electronic defect states similar to those caused by multi-metal doping, synergizing with the surface plasmon effect of AgNWs, which significantly improved the photoelectric conversion efficiency, thereby resulting in excellent optoelectronic properties. In combination with molecular imprinting, a competitive type trace photoelectrochemical sensor for RNZ was constructed using Fe2+ as the electron donor and probe. Under optimal conditions, the sensor response is proportional to the logarithm of RNZ concentration in the range 0.1-104 nM with a detected limit of 0.038 nM. The recoveries ranged from 87.2 to 116% with relative standard deviations (RSDs) < 6.5% (n = 3) in milk sample. This work reveals the charge-transfer process of variable-valence metal nodes in MOFs during photoelectrochemical processes, which will provide new insights for the sensing application of variable-valence metal MOFs.

Sensitive determination of auxins in environmental water and peach beverage by hyper crosslinked polymer-based solid-phase extraction with high performance liquid chromatography-fluorescence detection

As plant regulators, auxins can promote plant growth. However, they have toxicity and may cause harm to humans. Due to their low concentrations in food sample matrices, the enrichment and analysis of trace auxins in food samples is a challenging work. In this work, a series of hyper crosslinked polymers (HCPs) were synthesized by Friedel-Crafts acylation to extract four auxins (indole-3-acetic acid, indole-3-propionic acid, indole-3-butyric acid and 1-naphthylacetic acid). Among these HCPs, the QP-TC-HCP, synthesized from p-quaterphenyl (QP) and terephthaloyl chloride (TC), showed the best adsorption performance for the auxins. It was then applied as the adsorbent for the solid-phase extraction of the auxins from environmental water and peach beverage samples, followed by high performance liquid chromatography-fluorescence detection. Under the optimized conditions, the limits of detection were 3.0-12.0 pg mL^-1 for environmental water and 18.0-36.0 pg mL^-1 for peach beverage sample. The method recoveries of the auxins for the spiked samples were in the range of 85.0-110.0%. The established method provided an alternative approach for the determination of auxins in food samples. In addition, different types of organic compounds were tested for the extraction by the QP-TC-HCP to assess its application potential and adsorption mechanism. It was concluded that the QP-TC-HCP had better extraction performance for the compounds with certain hydrophilicity and more hydrogen bonding sites.

In-situ preparation of CuO nanoparticles decorated In2O3 pn heterojunction composite for the photoelectrochemical detection of ornidazole

The eco-friendly synthesis of metal oxides pn junction composite with high visible light absorption and its photoelectrochemical monitoring on antibiotics is reported. The In2O3-CuO pn heterojunction composite was successfully prepared by in-situ hydrothermal decoration of CuO on the prepared In2O3 using a simple reflux method. The obtained nanorods like In2O3-CuO pn heterojunction exhibited high conductivity with excellent stability for the facilitated photoelectrochemical detection of ornidazole (ONZ) that plays a role in aquatic toxicology. The photo-stability and optical characteristics of the In2O3-CuO heterojunction composite were analyzed through photocurrent and UV-visible studies. Mechanism of ONZ signaling has been proposed with appropriate band levels derived by Mott-Schottky analysis. An optimized In2O3-CuO heterojunction detects ONZ in the range 0.05-65.3 nM with 0.0092 nM as the limit of detection at - 0.45 V (vs. Ag/AgCl) working potential. The practical applicability of the sensor device was tested in chicken meat, human urine, and lake water samples containing ONZ. The recoveries of real samples were above 95% and results obtained were compared with electrochemical methods.