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

Construction of a natural puerarin-based green hypercrosslinked polymer fiber coating for the effective SPME of nitrobenzenes from environmental samples

Due to the potential hazardous effect caused by the possible nitrobenzenes (NBs) residues in environmental samples, the development of effective analytical methods for the quantification of NBs in some environmental samples becomes necessary in monitoring the environmental quality and protecting the public health. Herein, we developed a natural product-derived solid-phase microextraction (SPME) coating through a green synthesis of a natural puerarin-based hypercrosslinked polymer (Pue-HCP1) via Friedel-Crafts alkylation. Featuring abundant adsorption sites and suitable hydrophobicity, the Pue-HCP1-based fiber coating achieved the enrichment factors as high as 1112-6483 for the NBs. The coating also exhibited a good stability and durability. By integrating the SPME with gas chromatography-flame ionization detection, we developed a sensitive and reliable method for detecting NBs from environmental water and soil samples, with high sensitivity (limits of detection: 0.01-0.2 ng mL-1 for water; 0.4-1.0 ng g-1 for soil) and good accuracy (recoveries: 83.8%-115%).

A vertical/horizontal graphene-based microneedle plant sensor for on-site detection of indole-3-acetic acid in vegetables

Plant hormones are important regulators of crop growth and production. In this study, an in situ electrochemical sensor was successfully built using flat microelectrodes with horizontally and vertically grown graphene to detect the plant regulator indole-3-acetic acid (IAA) in plants. Vertical and horizontal graphene layers were prepared by electron-assisted hot-filament chemical vapor deposition. Vertical graphene nanosheets were grown on a horizontal graphene layer as sensing electrodes, and a microneedle sensor was assembled by combining Pt and Ti microelectrodes. The vertical/horizontal graphene (VHG) microneedle sensor can rapidly detect IAA levels in various plants in situ over a wide pH range of 4.0-9.0 and concentration range of 1-100 μM, with a minimum detection limit of 0.21 μM (3σ/S). Subsequently, this microneedle sensor was used to determine the IAA content in different tissues of cucumber and cauliflower stems with satisfactory results. The combination of VHG microelectrode arrays and small electrochemical workstations is useful for constructing portable, low-cost, on-site, and fast electrochemical sensing platforms for plant growth monitoring.

Fabrication and evaluation of a molecular-imprinted-polymer functionalized electrode for selective electric field-assisted solid-phase microextraction of phytohormones

Specific extraction and separation plays a pivotal role in the accurate quantification of trace phytohormones (PHs). However, due to their high polarity, specific capture of PHs is challenging. In this study, under the assistance of electric field, a molecular-imprinted-polymer functionalized electrode (MIP@ED) was in-situ prepared using 3-indoleacetic acid (IAA) as template and employed as the adsorbent of electric field-assisted solid-phase microextraction (EA-SPME) for specific capture of PHs. Results showed that the implementation of electric field during the preparation of MIP@ED and EA-SPME procedures improved the extraction selectivity, the selective factors towards IAA and its structural analogues increased from 2.09 to 2.45 to 2.88-3.51. Under the optimum conditions, the proposed MIP@ED/EA-SPME was combined with HPLC technique to monitor trace PHs in water and agricultural products. The achieved limits of detection were in the ranges of 0.0053-0.011 μg/L and 0.048-0.12 μg/kg for water and agricultural product, respectively. The established approach was successfully applied to quantify trace PHs in real samples, and the spiked recoveries varied from 84.0 % to 118 % with good repeatability (RSDs blow 10 %). The obtained results provided clear evidence that the developed approach employing the MIP@ED/EA-SPME technique demonstrated high sensitivity, good selectivity, satisfactory reproducibility and environmental friendliness in the quantification of trace PHs in complex samples. In addition, the current study supplied a new strategy to enhance the specific recognition performance of MIP-based SPME.

One-pot fabrication of magnetic adsorbent based on polymeric ionic liquid/aminated carbon nanotubes composite for efficient capture of synthetic auxins in complex samples prior to chromatographic analysis

Efficient enrichment is a challenging and indispensable step in the quantification of polar synthetic auxins in complex samples. In the current study, a new magnetic adsorbent based on polymeric ionic liquid/aminated carbon nanotube composite was fabricated with a one-pot precipitation copolymerization strategy and employed as the extraction phase of magnetic solid phase extraction of synthetic auxins. Various characterization techniques were utilized to inspect the morphology, structure, magnetic property, and functional groups of the prepared adsorbent. Under the optimal conditions, the obtained adsorbent displayed satisfactory capture performance towards studied auxins through multiple interactions. Adsorption studies evidenced that the adsorption procedure of the developed method towards analytes was fit for the Freundlich adsorption model and pseudo-second-order kinetics. Combining with high-performance liquid chromatography, sensitive and reliable method for the identification and quantification of trace synthetic auxins in environmental water and fruit juice samples was developed. The obtained limits of detection for water and fruit juice samples located in the ranges of 0.0059-0.013 and 0.018-0.031 μg/L, respectively. Recoveries in actual samples with different fortified contents varied from 82.2% to 117%, with satisfactory reproducibility. The results will evidence that the introduced extraction technique is a useful alternative for the entrapment of trace synthetic auxins from complex samples.

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.