Application of a highly sensitive magnetic solid phase extraction for phytochemical compounds in medicinal plant and biological fluids by ultra‐high performance liquid chromatography coupled with quadrupole time‐of‐flight tandem mass spectrometry

A highly sensitive method using reduced graphene oxide with iron oxide (rGO/Fe₃O₄) as the sorbent in magnetic SPE has been developed for the purification of five anthraquinones (emodin, rhein, aloeemodin, physcion, and chrysophanol) in rhubarb and rat urine by ultra‐HPLC coupled with quadrupole TOF/MS. The extraction was accomplished by adding trace amount rGO/Fe₃O₄ suspension to 200 mL of aqueous mixture, and the excellent adsorption capacity of the nanoparticles was fully demonstrated in this procedure. Under the optimized conditions, the calibration curves were linear in the concentration range of 0.05–27.77 ng/mL with correlation coefficients varying from 0.9902 to 0.9978. The LODs ranged from 0.28 to 58.99 pg/mL. The experimental results indicated that the proposed method was feasible for the analysis of anthraquinones in rhubarb and urine samples.     

Determination of Tetracycline in Water and Honey by Iron(II,III)/Aptamer-Based Magnetic Solid-Phase Extraction with High-Performance Liquid Chromatography Analysis

A novel aptamer-based adsorbent was prepared for the magnetic solid-phase extraction of tetracycline. The Fe₃O₄/aptamer adsorbent was fabricated by immobilizing an aptamer on the surface of Fe₃O₄ magnetic nanoparticles by the reaction between avidin and biotin. The parameters affecting the isolation efficiency such as the pH, extraction time, extraction temperature, eluent, and elution time were investigated in detail. Under the optimal conditions, a linear relationship between the peak area and the concentration of tetracycline was observed in the range from 10.0 to 3000.0?µg L^?1 with a correlation coefficient of 0.9985 and a limit of detection of 2.5?µg L^?1. The developed method was successfully employed for the determination of tetracycline in honey and water samples with recovery values from 82.9 to 107.3% and relative standard deviations less than 7.6%. Compared with previously reported methods for the determination of tetracycline, the proposed protocol provides improvements in the limit of detection and specificity with reduced consumption of adsorbent and organic solvents.     

Determination of Anagliptin in Serum by Mixed-Hemimicelle Magnetic Solid-Phase Extraction with Surfactant-Coated Iron(II,III) Nanocomposites and High-Performance Liquid Chromatography

Magnetic solid-phase extraction based on the adsorption of sodium dodecyl sulfate on the surface of Fe₃O₄ nanoparticles was used to isolate the new hypoglycemic drug anagliptin in human and mouse serum before determination by high-performance liquid chromatography. The magnetic adsorbent was characterized by transmission electron microscopy, Fourier transform infrared spectroscopy, and the zeta potential. The factors affecting the extraction performance such as the type of surfactant, the amount of adsorbent and sodium dodecyl sulfate, pH of solution, time and temperature of adsorption and elution, and eluent type were examined. Under the optimized conditions, the adsorbent could be reused for six times and the efficiency of extraction or elution was over 95.0%. The calibration curve was linear in the range of 0.050–4.00?µg?mL^?1, with detection limits of 0.021 and 0.023?µg?mL^?1 for human and mouse serum, respectively. The recovery values of 92.0–99.1% (human serum) or 94.8–105.7% (mouse serum) illustrated the accuracy of the proposed method. Moreover, it may be the first time that this extraction method has been used to determine anagliptin in biological liquids.     

Extraction of Anthraquinones from Rhubarb by a Molecularly Imprinted–Matrix Solid-Phase Dispersion Method with HPLC Detection

A simple method based on matrix solid-phase dispersion for selective extraction of anthraquinones from rhubarb samples was developed using a molecularly imprinted polymer as sorbent. The molecularly imprinted polymer was prepared using emodin as the template molecule, methacrylic acid as the functional monomer, and ethylene glycol dimethacrylate as the cross-linking agent. The polymer was characterized by scanning electron microscopy and Fourier-transform infrared spectrometry. Isothermal adsorption and dynamic adsorption experiments were performed. The best extraction conditions for anthraquinones were obtained at a ratio of molecularly imprinted polymer to sample of 1:1, a dispersion time of 5 minutes, with 5% aqueous methanol as the washing solvent, and an elution solvent of methanol-acetic acid (99:1, v/v). Once the matrix solid-phase dispersion process was optimized, the extract was reacted with 8% hydrochloric acid for hydrolysis. The anthraquinones extracted from rhubarb were determined by liquid chromatography. The detection limits of chrysophanol, emodin, physcion, and aloe-emodin were 0.23, 0.24, 0.28, and 0.27 µg mL^?1, respectively. The proposed method was compared with the method in Chinese pharmacopoeia, and the results show that the extraction yield of anthraquinones obtained by molecularly imprinted polymer–matrix solid-phase dispersion method was higher. Moreover, the proposed method is faster and simpler and can achieve extraction and purification in the same system.     

Ultrasound‐assisted magnetic SPE based on Fe3O4‐grafted graphene for the determination of polychlorinated biphenyls in water samples

An ultrasound‐assisted magnetic SPE procedure with an Fe₃O₄‐grafted graphene nanocomposite as the magnetic adsorbent has been developed to determine seven polychlorinated biphenyls (PCBs; PCB28, PCB52, PCB101, PCB118, PCB138, PCB153, and PCB180) simultaneously in 200 mL environmental water samples, in combination with GC–MS/MS. Several factors related to magnetic SPE efficiencies, such as the superparamagnetic intensity and amount of adsorbent, extraction time, sample pH, and desorption conditions were investigated. With the assistance of ultrasound, the extraction achieved the maximum within only 20 s, attributed to the powerful adsorptive ability of the magnetic adsorbent toward the PCBs. Under the optimized conditions, an excellent linearity was observed in the range of 0.1–100 ng/L for PCB28, 0.2–100 ng/L for PCB52, and 0.5–100 ng/L for the other five PCBs with the correlation coefficients ranging from 0.9988 to 0.9996. The mean recoveries at spiked levels of 5.0 and 10.0 ng/L were 84.9–108.5%, the coefficients of variations were <6.5%. With convenient magnetic separation, the synthesized magnetic adsorbent could be recycled more than ten times. The proposed method was demonstrated to be feasible, simple, rapid, and easy to operate for the trace analysis of the PCBs in environmental water samples.     

Application of modified magnetic nanoparticles with amine groups as an efficient solid sorbent for simultaneous removal of 2,4-Dichlorophenoxyacetic acid and 2-methyl-4-chlorophenoxyacetic acid from aqueous solution: optimization and modeling

In the present work, functionalized magnetic nano-adsorbent with amine groups (Fe₃O₄@SiO₂@NH₂) was prepared for the simultaneous removal of 2,4-Dichlorophenoxyacetic acid (2,4-D) and 2-methyl-4-chlorophenoxyacetic acid (MCPA) from aqueous solution. Characterization such as Fourier transform infrared spectroscopy, vibrating sample magnetometry, and scanning electron microscope confirmed that the magnetic nanoparticles structure of Fe₃O₄@SiO₂ nano-adsorbent was successfully functionalized by amine groups. The impact of some influencing parameters such as contact time, pH, adsorbent dosage, 2,4-D and MCPA initials concentration and solution temperature were studied. The equilibrium data were analyzed by Langmuir and Freundlich adsorption isotherms and also two models kinetically of pseudo-first-order and pseudo-second-order. Findings of the present study showed that the synthesized amino-functionalized MNPs will be helpful in use as an effective recyclable adsorbent for the removal of phenoxy acid herbicides from aqueous solution due to its advantages such as facile and rapid separation of target molecules from solution.     

Metal-organic framework functionalized with deep eutectic solvent for solid-phase extraction of Rhodamine 6G in water and cosmetic products

An NH₂-MIL-53(Al)-DES(ChCl-Urea) nanocomposite was synthesized for extraction and determination of Rhodamine (Rh) 6G from environmental and cosmetic samples. The deep eutectic solvent (DES) was prepared by mixing choline chloride and urea in a mole ratio of 1:2. NH₂-MIL-53(Al)-DES(ChCl-Urea) nanocomposite was synthesized using the impregnation method at a ratio of 60:40 (w/w). The optimum conditions were determined after NH₂-MIL-53(Al)-DES(ChCl-Urea) characterization was performed. The optimum conditions were determined as pH 8, adsorbent amount of 15 mg, total adsorption-desorption time of 6 min, and enrichment factor of 20. The recovery values of the solid-phase extraction method for water and cosmetic samples under optimum conditions were between 95% and 106%. NH₂-MIL-53(Al)-DES(ChCl-Urea) nanocomposite was an economically advantageous adsorbent because of its reusability of 15 times. All analyses were performed using the ultraviolet-visible spectrophotometer. The linear range, limit of detection, and limit of quantification of the method were 100–1000, 9.80, and 32.68 μg/L, respectively. The obtained results showed that the synthesized nanocomposite is a suitable adsorbent for the determination of Rh 6G in water and cosmetic samples. The real sample applications were verified with the high-performance liquid chromatography system.     

Preparation of iron‐based MIL‐101 functionalized polydopamine@Fe3O4 magnetic composites for extracting sulfonylurea herbicides from environmental water and vegetable samples

Here, we describe a simple one‐pot solvothermal method for synthesizing MIL‐101(Fe)@polydopamine@Fe₃O₄ composites from polydopamine‐modified Fe₃O₄ particles. The composite was used as a magnetic adsorbent to rapidly extract sulfonylurea herbicides. The herbicides were then analyzed by high‐performance liquid chromatography. The best possible extraction efficiencies were achieved by optimizing the most important extraction parameters, including desorption conditions, extraction time, adsorbent dose, salt concentration, and the pH of the solution. Good linearity was found (correlation coefficients >0.9991) over the herbicide concentration range 1–150 μg/L using the optimal conditions. The limits of detection (the concentrations giving signal/noise ratios of 3) were low, at 0.12–0.34 μg/L, and repeatability was good (the relative standard deviations were <4.8%, n = 6). The method was used successfully to determine four sulfonylurea herbicides in environmental water and vegetable samples, giving satisfactory recoveries of 87.1–108.9%. The extraction efficiency achieved using MIL‐101(Fe)@polydopamine@Fe₃O₄ was compared with the extraction efficiencies achieved using other magnetic composites (polydopamine@Fe₃O₄, Hong Kong University of Science and Technology (HKUST)‐1@polydopamine@Fe₃O₄, and MIL‐100(Fe)@polydopamine@Fe₃O₄). The results showed that the magnetic MIL‐101(Fe)@polydopamine@Fe₃O₄ composites have great potential for the extraction of trace sulfonylurea herbicides from various sample types.     

Magnetic nanofibrous polyaniline nanocomposite for solid-phase extraction of naproxen from biological samples prior to its spectrofluorimetric determination

Nanofibrous polyaniline–magnetite (PANI/Fe₃O₄) nanocomposite was in situ prepared through adsorption of magnetite nanoparticles onto PANI nanofibers surface and utilized as an efficient sorbent for magnetic solid-phase extraction of naproxen from water and biological samples, followed a desorption step and spectrofluorimetric determination. Field-emission scanning electron microscopy, transmission electron microscopy, Fourier-transform infrared spectroscopy, thermal gravimetric analysis and X-ray diffraction techniques were employed for characterization of the prepared nanocomposite. The important parameters influencing the extraction efficiency including PANI/Fe₃O₄ mass ratio, adsorbent dose, extraction time, sample solution pH, ionic strength, type and volume of desorption solvent and the elution time were studied and optimized. The investigated nanocomposite was successfully applied to the extraction of naproxen in spiked tap water, urine and plasma samples, with a relative recovery in the range of 90–98%. The reusability of PANI/Fe₃O₄ was examined for ten successive cycles, and the results confirm that the efficiency did not change significantly. A linear calibration plot was obtained in the range of 40–1000 ng mL^?1 with a limit of detection about 17 ng mL^?1 under the optimum conditions. The relative standard deviation (RSD) was found to be 2.34% (n = 8, concentration level of 100 ng mL^?1). The kinetics and thermodynamics of the extraction process were also studied.     

Phenylboronic acid-functionalized cross-linked chitosan magnetic adsorbents for the magnetic solid-phase extraction of benzoylurea pesticides

In this study, a 4-formylphenylboronic acid-modified cross-linked chitosan magnetic nanoparticle (FPBA@CCHS@Fe₃O₄) was fabricated. The synthesized material was utilized as the magnetic solid-phase extraction adsorbent for the enrichment of six benzoylurea pesticides. In addition to B-N coordination, FPBA@CCHS@Fe₃O₄ interacts with benzoylureas through hydrogen bonds and π-π stacking interaction on account of rich active groups (amino and hydroxyl) and aromatic rings in structure. Compared to traditional extraction methods, less adsorbent (20 mg) and reduced extraction time (3 min) were achieved. The adsorbent also exhibited good reusability (no less than 10 times). Coupled with a high-performance liquid chromatography–diode array detector, satisfactory recoveries (89.1–103.9%) and an acceptable limit of detection (0.2–0.7 μg/L) were obtained. Under optimized conditions, the established method was successfully applied to the tea infusion samples from six major tea categories with acceptable recoveries ranging from 76.8 to 110%, indicating its application potential for the quantitative detection of pesticides in complex matrices.     

Determination of diuretics in human urine using HPLC coupled with magnetic solid-phase extraction based on a metal–organic framework

Magnetic solid-phase extraction (MSPE) employing a metal–organic framework (Fe₃O₄@UiO-66-OH) combined with high-performance liquid chromatography was developed for the determination of trace diuretics in urine. The structure and properties of Fe₃O₄@UiO-66-OH were investigated using X-ray diffraction, infrared spectroscopy, scanning electron microscopy and vibrating sample magnetometry. Magnetic solid-phase extraction conditions, such as adsorbent amount and solution pH, were optimized using response surface methodology. Under the optimal conditions, the method resulted in excellent linearity with a high correlation coefficient (r > 0.99), satisfactory intraday repeatability (1.78–2.99%), low limits of detection (0.08–0.23 ng/ml), and good recoveries in urine samples (between 93.5 and 103%). Fe₃O₄@UiO-66-OH based on MSPE is a novel pretreatment technique for the detection of trace diuretics in urine.     

Magnetic solid-phase extraction of malachite green using soluble eggshell membrane protein doped with magnetic graphene oxide nanocomposite

ABSTRACT

This study describes a new magnetic solid-phase extraction (MSPE) technique based on Fe₃O₄/graphene oxide-soluble eggshell membrane protein (Fe₃O₄/GO-SEP) for accurate measurement of malachite green (MG) residue in various water samples residues by UV-Vis spectroscopy. The morphology of the prepared adsorbent has been studied by scanning electron microscopy and atomic force microscopy in details. Parameters affecting the MSPE were optimised and determined with UV-Vis spectrophotometry thoroughly. Under the optimised extraction circumstances, the introduced method represented a wide linearity over the concentration of 0.5–250 ng mL^?1, a high enrichment factor of 83.3 and low detection limit of 0.2 ng mL^?1. The prepared Fe₃O₄/GO-SEP was successfully used for preconcentration and determination of MG in river and fish farming water samples with suitable precision and accuracy.     

Accelerated FeIII/FeII redox cycle of Fenton reaction system using Pd/NH2-MIL-101(Cr) and hydrogen

In this paper, a novel improvement in the catalytic Fenton reaction system named MHACF-NH₂-MIL-101(Cr) was constructed based on H₂ and Pd/NH₂-MIL-101(Cr). The improved system would result in an accelerated reduction in Fe^III, and provide a continuous and fast degradation efficiency of the 10 mg L^-1 4-chlorophenol which was the model contaminant by using only trace level Fe^II. The activity of Pd/NH₂-MIL-101(Cr) decreased from 100% to about 35% gradually during the six consecutive reaction cycles of 18 h. That could be attributed to the irreversible structural damage of NH₂-MIL-101(Cr).     

Polythiophene-coated Fe3O4 nanoparticles as a selective adsorbent for magnetic solid-phase extraction of silver(I), gold(III), copper(II) and palladium(II)

We have developed a fast method for sensitive extraction and determination of the metal ions silver(I), gold(III), copper(II) and palladium(II). Fe₃O₄ magnetic nanoparticles were modified with polythiophene and used for extraction the metal ions without a chelating agent. Following extraction, the ions were determined by flow injection inductively coupled plasma optical emission spectrometry. The influence of sample pH, type and volume of eluent, amount of adsorbent, sample volume and time of adsorption and desorption were optimized. Under the optimum conditions, the calibration plots are linear in the 0.75 to 100 μg L^?1 concentration range (R²?>?0.998), limits of detection in the range from 0.2 to 2.0 μg L^?1, and enhancement factors in the range from 70 to 129. Precisions, expressed as relative standard deviations, are lower than 4.2 %. The applicability of the method was demonstrated by the successful analysis of tap water, mineral water, and river water.

Determination of Melamine Using Magnetic Molecular Imprinted Polymers and High Performance Liquid Chromatography

A novel method using magnetic molecular imprinting polymers (MMIP) specific for recognizing, separating, and extracting melamine in bovine milk was developed with an external additive magnetic shelf in this paper. The MMIP was synthesized with Fe₃O₄ nanoparticles and molecular imprinted polymer synthesis technology. With the help of an elution step using methanol/acetic acid mixture elution, the melamine could be collected and concentrated. By using high performance liquid chromatography combined with this pretreatment technique, the analytes eluted from the magnetic polymers can be determined. This extraction method was validated by analysis of incurred bovine milk matrix. The proposed method simplified the procedures of classical solid-phase extraction method and improved the reliability of method. The obtained recoveries of this method were in the range of 85.04–105.2% in spiked milk samples. The limit of detection (LOD) was below 29.2 ng g^?1.     

Fe3O4 nanoparticles as the adsorbent of magnetic solid-phase extraction for clean and preconcentration of maltol and ethyl maltol in food samples followed by HPLC analysis

In this work, a magnetic solid-phase extraction protocol followed with high-performance liquid chromatography analysis was developed for the determination of maltol and ethyl maltol in food samples. The Fe₃O₄ nanoparticles were prepared by one-step hydrothermal method and was used as adsorbent for clean and preconcentrated maltol and ethyl maltol in food samples. The as-prepared Fe₃O₄ nanoparticle was characterized by transmission electron microscope, Fourier transform infrared spectroscopy, X-ray diffraction, and vibrating sample magnetometer. The extraction conditions including the amount of material, extraction time, pH, temperature, and desorption solvents were investigated, respectively. Under the optimized conditions, the detection limits of 0.04 and 0.05?µg?mL^?1 could be achieved for maltol and ethyl maltol. The recoveries between 84.2 and 103.4% with RSDs lower than 2.30% were obtained for the analysis of spiked plum candy sample. The developed method was successfully applied to the analysis of real samples, such as juice, chocolate, and plum candy.     

Novel I–V Disposable Urea Biosensor Based on a Dip‐coated Hierarchical Magnetic Nanocomposite (Fe3O4@SiO2@NH2) on SnO2:F Layer

Silicon oxide was initially loaded on a Fe₃O₄ magnetic nanoparticle substrate (Fe₃O₄@SiO₂) and then functionalized with ─NH₂ group (Fe₃O₄@SiO₂@NH₂) to construct a novel hierarchical magnetic nanocomposite. A sensitive urea biosensor medium involving a dip‐coated hierarchical magnetic nanocomposite on F‐doped SnO₂ conducting glass was designed (Fe₃O₄@SiO₂@NH₂/SnO₂:F) to achieve an excellent platform for urease (Urs) enzyme immobilization via covalent linking to the exposed NH₂ groups through glutaraldehyde (Urs/Fe₃O₄@SiO₂@NH₂/SnO₂:F). The hierarchical magnetic nanocomposite selection criteria were based on enhancement of urea biosensing by Urs immobilization via covalent linking to the exposed NH₂ groups, while the SnO₂:F selection as substrate was based on its ability to afford high electronic density to the biosensor surface as an electrostatic repulsion layer for the anionic interferents in the biological environment. FE‐SEM, TEM, FTIR, CV, EIS, and I–V techniques established the morphology of the modified electrode's surface and electrochemical behavior of urea on the fabricated Urs/Fe₃O₄@SiO₂@NH₂/SnO₂:F biosensor. The sensing mechanism can be clarified on the basis of the two reactions, namely (1) catalytic reaction and (2) oxidation or reduction of metal oxides, same as in the case of solid‐state gas sensors. The I–V results display high sensitivity for urea detection of within 5–210 mg/dL and a limit of detection of 3 mg/dL.     

Dispersive magnetic solid‐phase extraction of phthalate esters from water samples and human plasma based on a nanosorbent composed of MIL‐101(Cr) metal–organic framework and magnetite nanoparticles before their determination by GC–MS

In this study, a magnetic metal–organic framework was synthesized simply and utilized in the dispersive magnetic solid‐phase extraction of five phthalate esters followed by their determination by gas chromatography with mass spectrometry. First, MIL‐101(Cr) was prepared hydrothermally in water medium without using highly corrosive hydrofluoric acid, utilizing an autoclave oven heat supply. Afterward, Fe₃O₄ nanoparticles were decorated into the matrix of MIL‐101(Cr) to fabricate magnetic MIL‐101 nanocomposite. The nanocomposite was characterized by various techniques. The parameters affecting dispersive magnetic solid‐phase extraction efficiency were optimized and obtained as: a sorbent amount of 15 mg; a sorption time of 20 min; an elution time of 5 min; NaCl concentration, 10% w/v; type and volume of the eluent 1 mL n‐hexane/acetone (1:1 v/v). Under the optimum conditions detection limits and linear dynamic ranges were achieved in the range of 0.08–0.15 and 0.5–200 μg/L, respectively. The intra‐ and interday RSD% values were obtained in the range of 2.5–9.5 and 4.6–10.4, respectively. Ultimately, the applicability of the method was successfully confirmed by the extraction and determination of the model analytes in water samples, and human plasma in the range of microgram per liter and satisfactory results were obtained.     

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%.     

Preparation and adsorption properties of glucose molecularly imprinted polymers in hydrous solution for effective determination of glucose in fruits by MISPE–HPLC

In this paper, a kind of surface molecular imprinting polymers in hydrous solution, with glucose selectively recognition, was successfully synthesized by surface molecular imprinting method, using glucose (Glu) as template molecule, acrylamide as functional monomers, N,N′-methylenebisacrylamide as the cross-linking agent, ammonium peroxydisulfate as the initiator, activated silica gel (SiO₂@NH₂) as support particles. The influences of cross-linker, initiator as well as support particles amount on the adsorption capacity of Glu-MIPs were performed by single-factor experiments. The optimum conditions were 100 mg of cross-linker, 25 mg of initiator and 1 g of SiO₂@NH₂. The adsorption and thermodynamics research revealed that the adsorption of MIPs was fitted to Langmuir, maximum imprinting factor of 2.49 and maximum absorption capacity of 50.06 mg/g. Furthermore, a procedure of extraction of glucose from real fruits samples using the Glu-MIPs as solid-phase extraction adsorbent was developed to apply in analytical techniques.