Magnetic metal-organic framework MIL-100 (Fe)/polyethyleneimine composite as an adsorbent for the magnetic solid-phase extraction of fungicides and their determination using HPLC-UV.

Fe3O4@MIL-100 (Fe)/PEI are used for the first time as an adsorbent material for the extraction of pesticide residues (epoxiconazole, flusilazole, tebuconazole, and triadimefon) from food matrices. The adsorbent proposed (Fe3O4@MIL-100(Fe)/PEI) was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), thermogravimetric (TG) analysis, and vibrating sample magnetometer (VSM) techniques to evaluate the properties of the sorbent. Then, the Fe3O4@MIL-100 (Fe)/PEI was employed for the quantification of the four triazole fungicides in fruits and vegetables (apple, orange, tomato, cabbage, and cucumber) using HPLC-UV for separation and detection. During the extraction process, the main parameters such as amount of adsorbent, extraction time, pH value, ionic strength, eluting solvent, and eluting volume were optimized. Under the optimum conditions, good linearity of this method was observed for all analytes, with correlation coefficients (R2) ≥ 0.9908. The limits of detection (LODs) ranged from 0.021-3.04 µg kg-1. The extraction recoveries of the four triazole fungicides varied from 73.9 to 109.4% with relative standard deviations (RSD) in the range 0.5 to 6.2%. Compared with other MOFs, the modification of Fe3O4@MIL-100 (Fe) with PEI shows high efficient adsorption due to the combined benefits of MIL-100 (Fe) and PEI. The material is easily synthesized, has good stability, and is of low cost.  Graphical abstract.

Adsorption behavior of azole fungicides on polystyrene and polyethylene microplastics.

Agricultural plastic films and triazole fungicides are widely used in agricultural production process. Exposure to natural environment, agricultural plastic films will degrade into micron plastic particles, which will adsorb pesticide molecules and may affect their toxicity, biological activity and persistence. The long-term coexistence of microplastics (MPs) and triazole fungicides will bring potential harms to the agricultural ecological environment. Therefore, two kinds of triazole fungicides flusilazole (FLU) and epoxiconazole (EPO) were selected as cases and the adsorption behaviors of them on polystyrene and polyethylene were investigated. A series of factors which could affect the adsorption behavior were evaluated. Specifically, the particle size of MPs could affect its adsorption capacity, and the smaller the particle size, the stronger the adsorption capacity. Moreover, with the increase of pH value from 6.0 to 9.0, the adsorption capacity of MPs to target compounds gradually increased. The effect of ionic strength was evaluated by NaCl, and 0.05% of NaCl was beneficial to the adsorption process, while the continuous increase of NaCl concentration inhibited the adsorption. Oxalic acid and humic acid decreased the adsorption capacity of flusilazole on PE by 15.99-32.00% and PS by 35.02-48.67%, respectively. In addition, compared with the single pesticide system, the adsorption capacity of MPs for flusilazole and epoxiconazole in the binary pesticides system decreased by 36.13-37.93% and 44.36-51.35%, respectively, indicating that competitive adsorption occurred between the two pesticides. Meanwhile, the adsorption process was evaluated by adsorption kinetics and adsorption isotherms and were consistent with pseudo-second-order kinetic model and Freundlich isotherm model, respectively. Finally, several characterization analyses were conducted to investigated the adsorption mechanism, and hydrogen, halogen bonding and hydrophobic interaction proved to play an important role. The study on the adsorption behavior and mechanism of pesticide on MPs was the basis of assessing the risk of joint exposure.

Application of polydopamine functionalized magnetic graphene in triazole fungicides residue analysis.

In this work, a new analytical method based on polydopamine functionalized magnetic graphene (PDA@MG) adsorbent material has been developed to determine three triazole fungicides in water samples. As previous step, a novel polydopamine functionalized PDA@MG adsorbent material has been successfully prepared, which was characterized by fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscope (TEM), and vibrating sample magnetometer (VSM). Based on this novel material, a new magnetic solid phase extraction (MSPE) method coupled with high performance liquid chromatography (HPLC) has been established for the determination of triazole fungicides in water samples. The main factors which could affect the experimental results were optimized. Under the optimal conditions, good linarites has been achieved in the range of 0.2-50 µg L-1, with the correlation coefficients (R2) were between 0.9962 and 0.9996. The limits of detections (LODs) were 0.0048-0.0084 µg L-1, and the relative standard deviations (RSDs) were between 1.7% and 4.8%. In addition, enrichment factors (EFs) were 572-916 times, which showed triazole fungicides residues could be accurately extracted and analyzed in this way. In the final experiment, the established method was applied to the detection of target analyzes in water samples. Satisfied results could be obtained for tebuconazole, propiconazole, and flusilazole. The recoveries of five water samples were between 69.4% and 106.4%, and the RSD were between 1.0% and 6.5%. The development method is more easy, effective, green and environmental-friendly, and has potential for application.