Fe3O4/reduced graphene oxide‐carbon nanotubes composite for the magnetic solid‐phase extraction and HPLC determination of sulfonamides in milk

A novel magnetic adsorbent Fe₃O₄/reduced graphene oxide‐carbon nanotubes, was prepared by one‐pot solvothermal synthesis method. It was characterized by scanning electron microscopy, X‐ray powder diffraction and vibrating sample magnetometry. The diameter of Fe₃O₄ microparticles was about 350 nm, which were covered by carbon nanotubes and reduced graphene oxide sheets, while carbon nanotubes inserted between the reduced graphene oxide sheets effectively prevented their aggregation. The composite had large surface area and good magnetic property, suiting for magnetic solid‐phase extraction and the determination of sulfonamides, by coupling with high‐performance liquid chromatography. Under the optimized conditions (including extraction time, amount of adsorbent, solution pH, ionic strength and desorption conditions), a good linear was achieved in the concentration range of 5–500 μg/L and the low limits of detection and low limits of quantification were 0.35–1.32 and 1.16–4.40 μg/L, respectively. The enrichment factors were estimated to be 24.72 to 30.15 fold. The proposed method was applied for the detection of sulfonamides in milk sample and the recoveries were 88.4–105.9%, with relative standard deviations of 0.74–5.38%.     

One‐pot synthesis of magnetic zeolitic imidazolate framework/grapheme oxide composites for the extraction of neonicotinoid insecticides from environmental water samples

Magnetic zeolitic imidazolate framework 67/graphene oxide composites were synthesized by one‐pot method at room temperature for the first time. Electrostatic interactions between positively charged metal ions and both negatively charged graphene oxide and Fe₃O₄ nanoparticles were expected to chemically stabilize magnetic composites to generate homogeneous magnetic products. The additional amount of graphene oxide and stirring time of graphene oxide, Co²⁺, and Fe₃O₄ solution were investigated. The zeolitic imidazolate framework 67 and Fe₃O₄ nanoparticles were uniformly attached on the surface of graphene oxide. The composites were applied to magnetic solid‐phase extraction of five neonicotinoid insecticides in environmental water samples. The main experimental parameters such as amount of added magnetic composites, extraction pH, ionic strength, and desorption solvent were optimized to increase the capacity of adsorbing neonicotinoid insecticides. The results show limits of detection at signal‐to‐noise ratio of 3 were 0.06–1.0 ng/mL under optimal conditions. All analytes exhibited good linearity with correlation coefficients of higher than 0.9915. The relative standard deviations for five neonicotinoid insecticides in environmental samples ranged from 1.8 to 16.5%, and good recoveries from 83.5 to 117.0% were obtained, indicating that magnetic zeolitic imidazolate framework 67/graphene oxide composites were feasible for analysis of trace analytes in environmental water samples.     

Magnetic solid‐phase extraction based on a polydopamine‐coated Fe3O4 nanoparticles absorbent for the determination of bisphenol A,tetrabromobisphenol A, 2,4,6‐tribromophenol,and (S)‐1,1’‐bi‐2‐naphthol in environmental waters by HPLC

Polydopamine‐coated Fe₃O₄ magnetic nanoparticles synthesized through a facile solvothermal reaction and the self‐polymerization of dopamine have been employed as a magnetic solid‐phase extraction sorbent to enrich four phenolic compounds, bisphenol A, tetrabromobisphenol A, (S)‐1,1′‐bi‐2‐naphthol and 2,4,6‐tribromophenol, from environmental waters followed by high‐performance liquid chromatographic detection. Various parameters of the extraction were optimized, including the pH of the sample matrix, the amount of polydopamine‐coated Fe₃O₄ sorbent, the adsorption time, the enrichment factor of analytes, the elution solvent, and the reusability of the nanoparticles sorbent. The recoveries of these phenols in spiked water samples were 62.0–112.0% with relative standard deviations of 0.8–7.7%, indicating the good reliability of the magnetic solid‐phase extraction with high‐performance liquid chromatography method. In addition, the extraction characteristics of the magnetic polydopamine‐coated Fe₃O₄ nanoparticles were elucidated comprehensively. It is found that there are hydrophobic, π–π stacking and hydrogen bonding interactions between phenols and more dispersible polydopamine‐coated Fe₃O₄ in water, among which hydrophobic interaction dominates the magnetic solid‐phase extraction performance.     

Dispersive admicelle solid‐phase extraction based on sodium dodecyl sulfate coated Fe3O4 nanoparticles for the selective adsorption of three alkaloids in Gegen‐Qinlian oral liquid before high‐performance liquid chromatography

A novel dispersive admicelle solid‐phase extraction method based on sodium dodecyl sulfate‐coated Fe₃O₄ nanoparticles was developed for the selective adsorption of berberine, coptisine, and palmatine in Gegen‐Qinlian oral liquid before high‐performance liquid chromatography. Fe₃O₄ nanoparticles were synthesized by a chemical coprecipitation method and characterized by using transmission electron microscopy. Under acidic conditions, the surface of Fe₃O₄ nanoparticles was coated with sodium dodecyl sulfate to form a nano‐sized admicelle magnetic sorbent. Owing to electrostatic interaction, the alkaloids were adsorbed onto the oppositely charged admicelle magnetic nanoparticles. The quick separation of the analyte‐adsorbed nanoparticles from the sample solution was performed by using Nd‐Fe‐B magnet. Best extraction efficiency was achieved under the following conditions: 800 μL Fe₃O₄ nanoparticles suspension (20 mg/mL), 150 μL sodium dodecyl sulfate solution (10 mg/mL), pH 2, and vortexing time 2 min for the extraction of alkaloids from 10 mL of diluted sample. Four hundred microliters of methanol was used to desorb the alkaloids by vortexing for 1 min. Satisfactory extraction recoveries were obtained in the range of 85.9–120.3%, relative standard deviations for intra‐ and interday precisions were less than 6.3 and 10.0%, respectively. Finally, the established method was successfully applied to analyze the alkaloids in two batches of Gegen‐Qinlian oral liquids.     

Specific recognition of ribavirin in animal‐derived foods by high performance liquid chromatography combined with magnetic solid‐phase extraction based on highly selective Zr‐Fe3O4

For the first time, a magnetic solid‐phase extraction with high‐performance liquid chromatography detection method using Zr functionalized Fe₃O₄ magnetic material to enrich ribavirin was successfully established. Zr components that modified in Fe₃O₄ nanoparticles via a simple one‐step hydrothermal method was selected in this work to specifically capture ribavirin by the strong chemical bonding between Zr components of Zr functionalized Fe₃O₄ magnetic material and cis‐hydroxyl of ribavirin, which was confirmed by pseudo‐second‐order kinetic model. And Fe₃O₄ components were selected in this work to achieve simple operation. Under the optimal experimental conditions, proposed magnetic solid‐phase extraction with high‐performance liquid chromatography detection method along with Zr functionalized Fe₃O₄ magnetic material offered a wide range linearity at 10–200 µg/L with correlation coefficient of 0.9978 with low detection limit of 2.68 µg/L for ribavirin. The relative standard deviations obtained from nine parallel extractions of 100 µg/L ribavirin were 4.41% and revealed good repeatability. This established method was successfully applied to detect real samples including chicken liver, egg, and shrimp with satisfactory recoveries of 74.13–92.9%.     

Determination of sulfadimethoxine in milk with aptamer‐functionalized Fe3O4/graphene oxide as magnetic solid‐phase extraction adsorbent prior to HPLC

An aptamer (Apt) functionalized magnetic material was prepared by covalently link Apt to Fe₃O₄/graphene oxide (Fe₃O₄/GO) composite by 1‐ethyl‐3‐(3‐dimethylaminopropyl) carbodiimide hydrochloride and N‐hydroxysuccinimide, and then characterized by FTIR spectroscopy, X‐ray diffraction, and vibration sample magnetometry. The obtained composite of Fe₃O₄/GO/Apt was employed as magnetic solid‐phase extraction adsorbent for the selective preconcentration of sulfadimethoxine prior to analysis by high‐performance liquid chromatography. Under the optimal conditions (sample pH of 4.0, sorbent dosage of 20 mg, extraction time of 3 h, and methanol‐5% acetic acid solution as eluent), a good linear relationship was obtained between the peak area and concentration of sulfadimethoxine in the range of 5.0 to 1500.0 µg/L with correlation coefficient of 0.9997. The limit of detection (S/N = 3) was 3.3 µg/L. The developed method was successfully applied to the analysis of sulfadimethoxine in milk with recoveries in the range of 75.9‐92.3% and relative standard deviations less than 8.1%. The adsorption mechanism of Fe₃O₄/GO/Apt toward sulfadimethoxine was studied through the adsorption kinetics and adsorption isotherms, and the results show that the adsorption process fits well with the pseudo‐second‐order kinetic model and the adsorbate on Fe₃O₄/GO/Apt is multilayer and heterogeneous.     

3‐D graphene‐supported mesoporous SiO2@Fe3O4 composites for the analysis of pesticides in aqueous samples by magnetic solid‐phase extraction with high‐performance liquid chromatography

Three‐dimensional graphene‐supported mesoporous silica@Fe₃O₄ composites (mSiO₂@Fe₃O₄‐G) were prepared by modifying mesoporous SiO₂‐coated Fe₃O₄ onto hydrophobic graphene nanosheets through a simple adsorption co‐condensation method. The obtained composites possess unique properties of large surface area (332.9 m²/g), pore volume (0.68 cm³/g), highly open pore structure with uniform pore size (31.1 nm), as well as good magnetic separation properties. The adsorbent (mSiO₂@Fe₃O₄‐G) was used for the magnetic solid‐phase extraction of seven pesticides with benzene rings in different aqueous samples before high‐performance liquid chromatography. The main parameters affecting the extraction such as adsorbent amount, volume of elution solvent, time of extraction and desorption, salt effect, oscillation rate were investigated. Under the optimal conditions, this method provided low limits of detection (S/N = 3, 0.525–3.30 μg/L) and good linearity (5.0–1000 μg/L, R² > 0.9954). Method validation proved the feasibility of the developed adsorbent, which has a high extraction efficiency and excellent enhancement performance for pesticides in this study. The proposed method was successfully applied to real aqueous samples, and satisfactory recoveries ranging from 77.5 to 113.6% with relative standard deviations within 9.7% were obtained.     

Preparation of ionic liquid‐modified magnetic nanoparticles based on thiol‐ene click chemistry for the analysis of polycyclic aromatic hydrocarbons in water and smoked meat samples

In the present study, ionic liquid (IL)‐modified Fe₃O₄ magnetic nanoparticles (Fe₃O₄) were synthesized by the thiol‐ene click reaction for magnetic solid‐phase extraction (MSPE) of polycyclic aromatic hydrocarbons (PAHs) in water and smoked meat samples. An IL 1‐vinyl‐3‐butylimidazolium bromide was firstly synthesized, and then immobilized on the surface of thiol group‐functionalized Fe₃O₄ via a thiol‐ene click reaction. The as‐synthesized Fe₃O₄@ILs were characterized using Fourier transform infrared spectroscopy, X‐ray diffraction, and transmission electron microscopy. Various parameters (including the amount of adsorbent, extraction time, sample volume, and desorption conditions) affecting MSPE were optimized. Under the optimum conditions, the limits of detection of four PAHs in the range of 0.6–7.2 ng/L were obtained using high‐performance liquid chromatography–ultraviolet detection. The accuracy of the method was assessed by recovery measurements on spiked real samples and good recovery of 80–108% with relative standard deviations lower than 8.16% was achieved. The enrichment factors ranging from 699 to 858 were obtained for the analytes. This result indicated that the proposed method had great potential for sample preparation.     

Ionic‐liquid‐modified magnetic nanoparticles as a solid‐phase extraction adsorbent coupled with high‐performance liquid chromatography for the determination of linear alkylbenzene sulfonates in water samples

Novel ionic‐liquid‐functionalized Fe₃O₄ magnetic nanoparticles were synthesized by the thiol‐ene click reaction. The prepared functionalized Fe₃O₄ nanoparticles possessed multiple interactions, such as electrostatic, hydrophobic, and π–π interactions. The functionalized Fe₃O₄ nanoparticles were characterized by using Fourier transform infrared spectroscopy, X‐ray diffraction, vibrating sample magnetometry, and transmission electron microscopy. Four kinds of linear alkylbenzene sulfonates, namely, sodium decylbenzenesulfonate, sodium undecylbenzene sulfonate, sodium dodecylbenzenesulfonate, and sodium tridecylbenzenesulfonate, were selected as model compounds to evaluate the applicability of adsorbents for extraction and subjected to high‐performance liquid chromatography analysis. In addition, the effects of various parameters, such as sorbent amount, pH value, ionic strength, sample volume, extraction time, and elution conditions on extraction efficiency were studied in detail. Under the optimum conditions, good linearities were attained, with correlation coefficients between 0.9912 and 0.9968. The proposed method exhibited limits of detection ranging from 0.061 to 0.099 μg/L for all the target analytes. The spiked recoveries of the target analytes in real water samples ranged from 86.3 to 107.5%, with relative standard deviations lower than 7.96%. The enrichment factors of the analytes ranged from 364 to 391, indicating that the obtained functionalized Fe₃O₄ nanoparticles can effectively extract trace target analytes from environmental water samples.     

Dispersive liquid–liquid microextraction based on amine‐functionalized Fe3O4 nanoparticles for the determination of phenolic acids in vegetable oils by high‐performance liquid chromatography with UV detection

A novel dispersive liquid–liquid microextraction method based on amine‐functionalized Fe₃O₄ magnetic nanoparticles was developed for the determination of six phenolic acids in vegetable oils by high‐performance liquid chromatography. Amine‐functionalized Fe₃O₄ was synthesized by a one‐pot solvothermal reaction between Fe₃O₄ and 1,6‐hexanediamine and characterized by transmission electron microscopy and Fourier transform infrared spectrophotometry. A trace amount of phosphate buffer solution (extractant) was adsorbed on bare Fe₃O₄‐NH₂ nanoparticles by hydrophilic interaction to form the “magnetic extractant”. Rapid extraction could be achieved while the “magnetic extractant” on amine‐functionalized Fe₃O₄ nanoparticles was dispersed in the sample solution by vortexing. After extraction, the “magnetic extractant” was collected by application of an external magnet. Some important parameters, such as pH and volume of extraction and desorption solvents, the extraction and desorption time needed were carefully investigated and optimized to achieve the best extraction efficiency. Under the optimal conditions, satisfactory extraction recoveries were obtained for the six phenolic acids in the range of 84.2–106.3%. Relative standard deviations for intra‐ and inter‐day precisions were less than 6.3 and 10.0%, respectively. Finally, the established method was successfully applied for the determination of six phenolic acids in eight kinds of vegetable oils.     

Dispersive micro‐solid‐phase extraction using carbon‐based adsorbents for the sensitive determination of verapamil in plasma samples coupled with capillary electrophoresis

A dispersive micro‐solid‐phase extraction procedure coupled with capillary electrophoresis ultraviolet detection was developed for determination of verapamil in plasma samples. Graphene oxide/polydopamin was synthesized by a one‐step polymerization method, and graphene oxide/Fe₃O₄ (magnetic graphene oxide) nanocomposite was prepared by coprecipitation method. Moreover, they were fully characterized. The use of hazardous and water‐immiscible solvents was scaled down, and only 500 μL of acetone was required as the desorption solvent. The detector response concentration plots were linear in the range of 5–500 ng/mL, and the proposed method was validated according to guidelines. The precision and accuracy were less than 15%. Dispersive micro‐solid‐phase extraction method provides a rapid, environmentally friendly, and sensitive analysis for the verapamil in patient plasma samples, which is adequate for therapeutic drug monitoring and pharmacokinetic studies.     

Magnetic solid‐phase extraction of brominated flame retardants from environmental waters with graphene‐doped Fe3O4 nanocomposites

Graphene‐doped Fe₃O₄ nanocomposites were prepared by a solvothermal reaction of an iron source with graphene. The nanocomposites were characterized by transmission electron microscopy, atomic force microscopy, X‐ray diffraction, superconducting quantum interference, Raman spectroscopy, Fourier transform infrared spectroscopy, and X‐ray photoelectron spectroscopy. This nanomaterial has been used as a magnetic solid‐phase extraction sorbent to extract trace brominated flame retardants from environmental waters. Various extraction parameters were optimized including dosage and reusability of the nanocomposites, and pH of sample matrix. The reliability of the magnetic solid‐phase extraction protocol based on graphene‐doped Fe₃O₄ nanocomposites was evaluated by investigating the recoveries of 2,4,6‐tribromophenol, tetrabromobisphenol A, 4‐bromodiphenyl ether, and 4,4?‐dibromodiphenyl ether in water samples. Good recoveries (85.0–105.0%) were achieved with the relative standard deviation ranging from 1.1–7.1%. Moreover, it is speculated from characterization and magnetic solid‐phase extraction experiment that there is not only π–π stacking but also possible hydrophobic interaction between the graphene‐doped Fe₃O₄ nanocomposites and analytes.     

A bioinspired polydopamine approach toward the preparation of gold‐modified magnetic nanoparticles for the magnetic solid‐phase extraction of steroids in multiple samples

In this work, a simple, facile, and sensitive magnetic solid‐phase extraction method was developed for the extraction and enrichment of three representative steroid hormones before high‐performance liquid chromatography analysis. Gold‐modified Fe₃O₄ nanoparticles, as novel magnetic adsorbents, were prepared by a rapid and environmentally friendly procedure in which polydopamine served as the reductant as well as the stabilizer for the gold nanoparticles, thus successfully avoiding the use of some toxic reagents. To obtain maximum extraction efficiency, several significant factors affecting the preconcentration steps, including the amount of adsorbent, extraction time, pH of the sample solution, and the desorption conditions, were optimized, and the enrichment factors for three steroids were all higher than 90. The validity of the established method was evaluated and good analytical characteristics were obtained. A wide linearity range (0.8–500 μg/L for all the analytes) was attained with good correlation (R² ≥ 0.991). The low limits of detection were 0.20–0.25 μg/L, and the relative standard deviations ranged from 0.83 to 4.63%, demonstrating a good precision. The proposed method was also successfully applied to the extraction and analysis of steroids in urine, milk, and water samples with satisfactory results, which showed its reliability and feasibility in real sample analysis.     

One‐step synthesized magnetic MIL‐101(Cr) for effective extraction of triazine herbicides from rice prior to determination by liquid chromatography‐tandem mass spectrometry

The magnetic metal‐organic framework MIL‐101(Cr) material‐based solid‐phase extraction method coupled with high‐performance liquid chromatography and tandem mass spectrometry was applied to extract seven triazine herbicides in rices. Fe₃O₄/MIL‐101(Cr) was synthesized using reduction‐precipitation method, in which steps including pre‐synthesis and modification of Fe₃O₄ nanoparticles were by‐passed. Various parameters including extraction solvent type and volume, ultrasonic extraction time, amount of Fe₃O₄/MIL‐101(Cr) microspheres, adsorption time, desorption volume and time were investigated. Under optimal conditions, the proposed method had the limit of detection (S/N = 3) and the limit of quantification (S/N = 10) of 1.08–18.10 and 3.60–60.20 pg/g, respectively. Relative standard deviations calculated for all herbicides with concentrations of 2 and 20 ng/g were in the range of 0.5 to 13% (n = 3). In addition, at the two above‐mentioned concentrations, the method achieved relative recoveries percentages of 79.3 to 116.7% when applied to determine the triazine herbicides in real samples spiked. This rapid, green, non‐polluting, pre‐concentrated extraction method was successfully developed and applied to analyze herbicides in rice samples.     

Superparamagnetic Fe3O4@SiO2 core–shell composite nanoparticles for the mixed hemimicelle solid‐phase extraction of benzodiazepines from hair and wastewater samples before high‐performance liquid chromatography analysis

Magnetic Fe₃O₄/SiO₂ composite core–shell nanoparticles were synthesized, characterized, and applied for the surfactant‐assisted solid‐phase extraction of five benzodiazepines diazepam, oxazepam, clonazepam, alprazolam, and midazolam, from human hair and wastewater samples before high‐performance liquid chromatography with diode array detection. The nanocomposite was synthesized in two steps. First, Fe₃O₄ nanoparticles were prepared by the chemical co‐precipitation method of Fe(III) and Fe(II) as reaction substrates and NH₃/H₂O as precipitant. Second, the surface of Fe₃O₄ nanoparticles was modified with shell silica by Stober method using tetraethylorthosilicate. The Fe₃O₄/SiO₂ composite were characterized by X‐ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and vibrating sample magnetometry. To enhance their adsorptive tendency toward benzodiazepines, cetyltrimethylammonium bromide was added, which was adsorbed on the surface of the Fe₃O₄/SiO₂ nanoparticles and formed mixed hemimicelles. The main parameters affecting the efficiency of the method were thoroughly investigated. Under optimum conditions, the calibration curves were linear in the range of 0.10–15 μgmL^?1. The relative standard deviations ranged from 2.73 to 7.07%. The correlation coefficients varied from 0.9930 to 0.9996.     

Fe3O4 nanoparticles coated with polyhedral oligomeric silsesquioxanes and β‐cyclodextrin for magnetic solid‐phase extraction of carbaryl and carbofuran

In this study, porous sandwich structure Fe₃O₄ nanoparticles coated by polyhedral oligomeric silsesquioxanes and β‐cyclodextrin were prepared by surface polymerization and were used as the magnetic solid phase extraction adsorbent for the extraction and determination of carbaryl and carbofuran. The Fe₃O₄ nanoparticles coated with polyhedral oligomeric silsesquioxanes and β‐cyclodextrin were characterized by Fourier transform infrared spectroscopy, X‐ray diffraction, thermogravimetric analysis, vibrating sample magnetometry, and scanning electron microscopy. After optimizing the extraction conditions, a method that combined magnetic solid phase extraction with high‐performance liquid chromatography was developed for the determination of carbaryl and carbofuran in apple. The method exhibited a good linearity in the range of 2–400 μg/kg for carbaryl and carbofuran (R² = 0.9995), respectively. The limits of detection were 0.5 μg/kg of carbaryl and 0.7 μg/kg for carbofuran in apple, respectively. Extraction recoveries ranged from 94.2 to 103.1% with the preconcentration factor of 300 and the relative standard deviations were less than 5.9%. These results indicated that the method combined magnetic solid phase extraction with high‐performance liquid chromatography and was promising for the determination of carbaryl and carbofuran at trace amounts.     

Aptamer‐functionalized Fe3O4 magnetic nanoparticles as a solid‐phase extraction adsorbent for the selective extraction of berberine from Cortex phellodendri

The extraction adsorbent was fabricated by immobilizing the highly specific recognition and binding of aptamer onto the surface of Fe₃O₄ magnetic nanoparticles, which not only acted as recognition elements to recognize and capture the target molecule berberine from the extract of Cortex phellodendri , but also could favor the rapid separation and purification of the bound berberine by using an external magnet. The developed solid‐phase extraction method in this work was useful for the selective extraction and determination of berberine in Cortex phellodendri extracts. Various conditions such as the amount of aptamer‐functionalized Fe₃O₄ magnetic nanoparticles, extraction time, temperature, pH value, Mg²⁺ concentration, elution time and solvent were optimized for the solid‐phase extraction of berberine. Under optimal conditions, the purity of berberine extracted from Cortex phellodendri was as high as 98.7% compared with that of 4.85% in the extract, indicating that aptamer‐functionalized Fe₃O₄ magnetic nanoparticles‐based solid‐phase extraction method was very effective for berberine enrichment and separation from a complex herb extract. The applicability and reliability of the developed solid‐phase extraction method were demonstrated by separating berberine from nine different concentrations of one Cortex phellodendri extract. The relative recoveries of the spiked solutions of all the samples were between 95.4 and 111.3%, with relative standard deviations ranging between 0.57 and 1.85%.     

Nickel‐substituted cobalt ferrite nanoparticles supported on arginine‐modified graphene oxide nanosheets: Synthesis and catalytic activity

The amino acid arginine was used to modify the surface of graphene oxide nanosheets and then nickel‐substituted cobalt ferrite nanoparticles were supported on those arginine‐grafted graphene oxide nanosheets (Ni_0.5Co_0.5Fe₂O₄@Arg–GO). The prepared Ni_0.5Co_0.5Fe₂O₄@Arg–GO was characterized using flame atomic absorption spectroscopy, inductively coupled plasma optical emission spectrometry, energy‐dispersive spectroscopy, Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy, Raman spectroscopy, X‐ray diffraction, thermogravimetric analysis, scanning electron microscopy and transmission electron microscopy. The application of Ni_0.5Co_0.5Fe₂O₄@Arg–GO as a catalyst was examined in a one‐pot tandem oxidative cyclization of primary alcohols with o ‐phenylenediamine to benzimidazoles under aerobic oxidation conditions. The results showed that 2‐phenylbenzimidazole derivatives were successfully achieved using Ni_0.5Co_0.5Fe₂O₄@Arg–GO nanocomposite catalyst via the one‐pot tandem oxidative cyclization strategy.     

Facile fabrication of magnetic MoO2–Salen‐modified graphene‐based catalyst for epoxidation of alkenes

A facile, green and efficient method for the immobilization of MoO₂–Salen onto graphene hybridized with glucose‐coated magnetic Fe₃O₄ nanoparticles is proposed to fabricate a magnetic organic–inorganic hybrid heterogeneous RGO/Fe₃O₄@C‐Salen‐MoO₂ catalyst for the epoxidation of cyclooctene and geraniol using tert ‐butyl hydroperoxide or H₂O₂ as oxidant. Carbon‐coated Fe₃O₄ can improve the stability and add functional ─OH groups on the surface of Fe₃O₄. The fabricated composite exhibited good performance due to good dispersion of MoO₂–Salen active sites. The catalyst can be easily separated from the reaction system using a permanent magnet and used three times without significantly losing its catalytic activity and selectivity.     

Facile preparation of boronic acid‐functionalized magnetic nanoparticles with a high capacity and their use in the enrichment of cis‐diol‐containing compounds from plasma

The use of bronate affinity adsorbents is a new separation method that appeared recently with great potential for specific extraction of cis‐diol‐containing compounds. In this work,a new strategy for the facile construction of boronic acid‐functionalized Fe₃O₄ magnetic nanoparticles (Fe₃O₄@FPBA MNPs) with a high capacity was described. The extraction capacity of the Fe₃O₄@FPBA MNPs was determined to be 66.0 ± 2.7 µmol/g for catechol and 80.6 ± 2.0 µmol/g for dopamine, being higher than that for the reported methods. The Fe₃O₄@FPBA MNPs were used to extract four cis‐diol drugs: caffeic acid isopropyl ester, caffic acid bornyl ester, isopropyl 3‐(3,4‐dihydroxyphenyl)‐2‐hydroxypropanoate and 3‐(3, 4‐dihydroxyphenyl)‐2‐hydroxylpropionic acid – from the spiked rabbit plasma, and the recoveries of four drugs were between 87.29 and104.37% with relative standard deviations ranging from 1.34 to 8.81%. Under the most favorable conditions, the solid‐phase extraction combined with HPLC‐UV for the analysis of four drugs in plasma could eliminate interferences from endogenous components of the biological fluids and exhibited sufficient precision and accuracy. These results showed that the prepared Fe₃O₄@FPBA MNPs were qualified for efficiently enriching and determining the trace cis‐diol substances from biological samples. Copyright © 2014 John Wiley & Sons, Ltd.