Solid‐phase extraction disk based on multiwalled carbon nanotubes for the enrichment of targeted pesticides from aqueous samples

A sensitive method for the determination of six varying polarity pesticides (imidacloprid, acetamiprid, carbendazim, simazine, linuron, and tebufenozide) based on a solid‐phase extraction disk with multiwalled nanotubes is proposed.A dispersion of multiwalled nanotubes in a surfactant aqueous solution (Triton X‐100) was used for the preparation of the solid‐phase extraction disk. The effect of surfactant on the functional groups of multiwalled nanotubes was examined by applying temperature‐programmed desorption. It was found that this treatment increased the amount of oxygen groups of treated multiwalled nanotubes comparing with untreated ones. The factors that may influence the adsorption and recovery such as the kind and volume of eluent, volume, flow rate and pH of sample were investigated and optimized. Under the optimized conditions, the maximal enrichment factors for low polar pesticides are ranging from 4000 to 4985 and for more polar are 2250 and 2750. The linear range of calibration curves was 10–500 ng/L with correlation coefficient higher than 0.9960, and the detection limit was 6.2–23.7 ng/L. Finally optimized method was applied for determination trace level of five out of six pesticides in tap and river water samples with good recovery.     

Core–shell SiO2‐coated Fe3O4 with a surface molecularly imprinted polymer coating of folic acid and its applicable magnetic solid‐phase extraction prior to determination of folates in tomatoes

A novel core–shell magnetic surface molecularly imprinted polymer with folic acid as a template was successfully synthesized by the sol–gel method. To generate Lewis acid sites in the silica matrix for the interaction of the metal coordinate with the template, 3‐aminopropyltriethoxysilane was used as a functional monomer, tetraethyl orthosilicate as a cross‐linker, and aluminum ions as a dopant. The magnetite encapsulated by the silica shell plays an important role as a magnetic‐coated polymer. The synthesized product was characterized by powder X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, and FTIR and UV/Vis spectroscopy. The powder X‐ray diffraction patterns, FTIR and UV/Vis spectra confirmed the characteristics of the as‐prepared silica coated magnetite and folic acid molecularly imprinted polymer. It was successfully applied for magnetic solid‐phase extraction prior to the determination of folates in tomato samples using high‐performance liquid chromatography with photodiode array detection. The detection limit of the proposed method was 1.67 μg/L, and results were satisfactory, with a relative standard deviation of < 3.94%.     

Magnetic porous carbon derived from Co‐doped metal–organic frameworks for the magnetic solid‐phase extraction of endocrine disrupting chemicals

Metal–organic frameworks‐5 (MOF‐5) was explored as a template to prepare porous carbon due to its high surface area, large pore volume, and permanent nanoscale porosity. Magnetic porous carbon, Co@MOF‐5‐C, was fabricated by the one‐step direct carbonization of Co‐doped MOF‐5. After carbonization, the magnetic cobalt nanoparticles are well dispersed in the porous carbon matrix, and Co@MOF‐5‐C displays strong magnetism (with the saturation magnetization intensity of 70.17emu/g), high‐specific surface area, and large pore volume. To evaluate its extraction performance, the Co@MOF‐5‐C was applied as an adsorbent for the magnetic solid‐phase extraction of endocrine disrupting chemicals, followed by their analysis with high‐performance liquid chromatography. The developed method exhibits a good linear response in the range of 0.5–100 ng/mL for pond water and 1.0–100 ng/mL for juice samples. The limits of detection (S/N  = 3) for the analytes were in the range of 0.1–0.2 ng/mL.     

Cost‐efficient magnetic nanoporous carbon derived from citrus peel for the selective adsorption of seven insecticides

A magnetic solid‐phase extraction adsorbent that consisted of citrus peel‐derived nanoporous carbon and silica‐coated Fe₃O₄ microspheres (C/SiO₂@Fe₃O₄) was successfully fabricated by co‐precipitation. As a modifier for magnetic microspheres, citrus peel‐derived nanoporous carbon was not only economical and renewable for its raw material, but exerted enormous nanosized pore structure, which could directly influence the type of adsorbed analytes. The C/SiO₂@Fe₃O₄ also possessed the advantages of Fe₃O₄ microspheres like superparamagnetism, which could be easily separated magnetically after adsorption. Integrating the superior of biomass‐derived nanoporous carbon and Fe₃O₄ microspheres, the as‐prepared C/SiO₂@Fe₃O₄ showed high extraction efficiency for target analytes. The obtained material was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, and the Brunauer–Emmett–Teller method, which demonstrated that C/SiO₂@Fe₃O₄ was successfully synthesized. Under the optimal conditions, the adsorbent was selected for the selective adsorption of seven insecticides before gas chromatography with mass spectrometry detection, and good linearity was obtained in the concentration range of 2–200 μg/kg with the correlation coefficient ranging from 0.9952 to 0.9997. The limits of detection were in the range of 0.03–0.39 μg/kg. The proposed method has been successfully applied to the enrichment and detection of seven insecticides in real vegetable samples.     

Facile synthesis of magnetic zinc metal‐organic framework for extraction of nitrogen‐containing heterocyclic fungicides from lettuce vegetable samples

We present a simple method for the fabrication of a magnetic amino‐functionalized zinc metal‐organic framework based on a magnetic graphene oxide composite. The resultant framework exhibited a porous 3D structure, high surface area and good adsorption properties for nitrogen‐containing heterocyclic fungicides. The adsorption process and capacity indicated that the primary adsorption mechanism might be hydrogen bonding and π‐π conjugation. In addition, an optimized protocol for magnetic solid phase extraction was developed (such as adsorbent content, pH, and desorption solvent), and utilized for the extraction of nitrogen‐containing heterocyclic fungicides from vegetable samples. Quantitation by high performance liquid chromatography coupled with tandem mass spectrometry offered a detection limit of 0.21–1.0 μg/L (S/N = 3) with correlation coefficients larger than 0.9975. These results demonstrate that magnetic amino‐functionalized zinc metal‐organic framewor is a promising adsorbent for the extraction and quantitation of nitrogen‐containing heterocyclic fungicides.     

Extraction of ochratoxin A in red wine with dopamine‐coated magnetic multi‐walled carbon nanotubes

A new, rapid, green, and cost‐effective magnetic solid‐phase extraction of ochratoxin A from red wine samples was developed using polydopamine‐coated magnetic multi‐walled carbon nanotubes as the absorbent. The polydopamine‐coated magnetic multi‐walled carbon nanotubes were fabricated with magnetic multi‐walled carbon nanotubes and dopamine by an in situ oxidative self‐polymerization approach. Transmission electron microscopy, dynamic light scattering, X‐ray photoelectron spectroscopy and vibrating sample magnetometry were used to characterize the absorbents. Ochratoxin A was quantified with high‐performance liquid chromatography coupled with fluorescence detection, with excitation and emission wavelengths of 338 and 455 nm, respectively. The conditions affecting the magnetic solid‐phase extraction procedure, such as pH, extraction solution, extraction time, absorbent amount, desorption solution and desorption time were investigated to obtain the optimal extraction conditions. Under the optimized conditions, the extraction recovery was 91.8–104.5% for ochratoxin A. A linear calibration curve was obtained in the range of 0.1–2.0 ng/mL. The limit of detection was 0.07 ng/mL, and the limit of quantitation was 0.21 ng/mL. The recoveries of ochratoxin A for spiked red wine sample ranged from 95.65 to 100.65% with relative standard deviation less than 8%. The polydopamine‐coated magnetic multi‐walled carbon nanotubes showed a high affinity toward ochratoxin A, allowing selective extraction and quantification of ochratoxin A from complex sample matrixes.     

Aminosilanized magnetic carbon microspheres for the magnetic solid‐phase extraction of bisphenol A,bisphenol AF,and tetrabromobisphenol A from environmental water samples

Aminosilanized magnetic carbon microspheres as a novel adsorbent were designed and fabricated. The adsorbent was used for the magnetic solid‐phase extraction of bisphenols at trace levels from environmental water samples before liquid chromatography with tandem mass spectrometry analysis. The structure, surface, and magnetic behavior of the as‐prepared aminosilanized magnetic carbon microspheres were characterized by elemental analysis, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, powder X‐ray diffraction, and vibrating sample magnetometry. The effects of the experimental parameters were investigated by the Plackett–Burman design, and then the parameters that were significant to the extraction efficiencies were optimized through a response surface methodology. The aminosilanized magnetic carbon microspheres exhibited high adsorption efficiency and selectivity for bisphenols. Under optimal conditions, low limits of detection (0.011–2.22 ng/L), and a wide linear range (2–3 orders of magnitude), good repeatability (4.7–7.8%, n = 5), and reproducibility (6.0–8.3%, n = 3) were achieved. The results demonstrate that the novel adsorbent possesses great potentials in the determination of trace levels of bisphenols in environmental water samples.     

Magnetic solid‐phase extraction of pyrethroid pesticides in environmental water samples with CoFe2O4‐embedded porous graphitic carbon nanocomposites

Magnetic CoFe₂O₄‐embedded porous graphitic carbon nanocomposites were prepared through a facile solid‐phase thermal reaction with NaCl as a template. The material was applied in the magnetic solid‐phase extraction process coupled with high performance liquid chromatography with a diode array detector to detect the trace fenpropathrin, cyhalothrin, S‐fenvalerate, and bifenthrin in different water samples. The synthesis conditions of nanomaterial including glucose concentration and calcination time on extraction performance for pyrethroid pesticides have been investigated. Different magnetic solid‐phase extraction parameters have been studied, such as the nanomaterial amount, solution pH, eluent types, adsorption time, and the reusability. Under the optimum conditions, good recoveries (80.2–110.9%) were achieved with relative standard deviations of 0.2–5.8%. There are probably hydrophobic interactions and dipole–dipole attractions between nanocomposites and the analytes.     

Covalently bonded aptamer‐functionalised magnetic mesoporous carbon for high‐efficiency chloramphenicol detection

A novel aptamer‐modified magnetic mesoporous carbon was prepared to develop a specific and sensitive magnetic solid‐phase extraction method through combination with ultra‐high performance liquid chromatography‐tandem mass spectrometry for the analysis chloramphenicol in complex samples. More specifically, the chloramphenicol aptamer‐modified Mg/Al layered double hydroxide magnetic mesoporous carbon was employed as a novel magnetic solid‐phase extraction sorbent for analyte enrichment and sample clean‐up. The extraction solvent, extraction time, desorption solvent, and desorption time were investigated. It was found that the mesoporous structure and aptamer‐based affinity interactions resulted in acceptable selective recognition and a good chemical stability toward trace amounts of chloramphenicol. Upon combination with the ultra‐high performance liquid chromatography‐tandem mass spectrometry technique, a specific and sensitive recognition method was developed with a low limit of detection (0.94 pmol/L, S/N = 3) for chloramphenicol analysis. The developed method was successfully employed for the determination of chloramphenicol in complex serum, milk powders, fish and chicken samples, giving recoveries of 87.0‐107% with relative standard deviations of 3.1‐9.7%.     

Fabrication of glucose‐derived carbon‐decorated magnetic microspheres for extraction of bisphenols from water and tea drinks

Glucose‐derived carbon‐decorated magnetic microspheres were synthesized by an easy hydrothermal carbonization method and used as a high‐efficiency adsorbent to extract bisphenols in water and tea drinks. The as‐prepared carbon‐decorated magnetic microspheres had a well‐defined core–shell structure with a shell thickness of about 5 nm. The microspheres possessed high saturation magnetization at 60.8 emu/g and excellent chemical stability in aqueous solution. The experimental parameters affecting the extraction efficiency, including extraction time, pH, adsorbent dosage, desorption solvents, desorption time, and solution volume were evaluated. Electrostatic and π–π interactions were the major driving forces during extraction. Overall, a new magnetic solid‐phase extraction method of determining bisphenols was developed on the basis of as‐prepared magnetic microspheres. The method had a wide linear range, low limits of detection (0.03–0.10 µg/L), and high recoveries (85.4–104.6%).     

Magnetic porous carbon derived from a metal–organic framework as a magnetic solid‐phase extraction adsorbent for the extraction of sex hormones from water and human urine

An iron‐embedded porous carbon material (MIL‐53‐C) was fabricated by the direct carbonization of MIL‐53. The MIL‐53‐C possesses a high surface area and good magnetic behavior. The structure, morphology, magnetic property, and porosity of the MIL‐53‐C were studied by scanning electron microscopy, transmission electron microscopy, vibrating sample magnetometry, and N₂ adsorption. With the use of MIL‐53‐C as the magnetic solid‐phase extraction adsorbent, a simple and efficient method was developed for the magnetic solid‐phase extraction of three hormones from water and human urine samples before high‐performance liquid chromatography with UV detection. The developed method exhibits a good linear response in the range of 0.02–100 ng/mL for water and 0.5–100 ng/mL for human urine samples , respectively. The limit of detection (S/N = 3) for the analytes was 0.005–0.01 ng/mL for water sample and 0.1–0.3 ng/mL for human urine sample. The limit of quantification (S/N = 10) of the analytes were in the range of 0.015–0.030 and 0.3–0.9 ng/mL, respectively.     

Magnetic N‐doped mesoporous carbon as an adsorbent for the magnetic solid‐phase extraction of phthalate esters from soft drinks

A new kind of magnetic N‐doped mesoporous carbon was prepared by the one‐step carbonization of a hybrid precursor (glucose, melamine, and iron chloride) in a N₂ atmosphere with a eutectic salt (KCl/ZnCl₂) as the porogen. The obtained magnetic N‐doped mesoporous carbon showed excellent characteristics, such as strong magnetic response, high surface area, large pore volume, and abundant π‐electron system, which endow it with a great potential as a magnetic solid‐phase extraction adsorbent. To evaluate its adsorption performance, the magnetic N‐doped mesoporous carbon was used for the extraction of three phthalate esters from soft drink samples followed by high‐performance liquid chromatographic analysis. Under the optimum conditions, the developed method showed a good linearity (1.0–120.0 ng/mL), low limit of detection (0.1–0.3 ng/mL, S/N = 3), and good recoveries (83.2–119.0%) in soft drink samples. The results indicated that the magnetic N‐doped mesoporous carbon has an excellent adsorption capacity for phthalate esters and the present method is simple, accurate, and highly efficient for the extraction and determination of phthalate esters in complex matrix samples.     

Fe3O4磁性纳米材料萃取光度法测定苯磺酸倍他司汀

提出了基于表面活性剂磁性固相萃取光度法测定药片及血清中苯磺酸倍他司汀含量的方法。在表面活性剂十二烷基磺酸钠(SDS)的辅助下,磁性材料四氧化三铁可以高效的定量萃取苯磺酸倍他司汀。对实验条件如缓冲溶液pH及用量、磁性材料用量、表面活性剂用量、萃取时间、洗脱剂种类及用量、材料重复利用率等进行优化。在优化条件下,吸附率与洗脱率均>90%,磁性纳米材料可重复使用5次,方法的回收率为95.2%~105.9%。方法可用于测定人血清及药物中苯磺酸倍他司汀含量。     

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.     

Zeolite/Fe3O4 as a new sorbent in magnetic solid‐phase extraction followed by gas chromatography for determining phthalates in aqueous samples

In the present study, for the first time, we successfully employed zeolite/Fe₃O₄ as a new magnetic nanoparticle sorbent in magnetic solid‐phase extraction for determining phthalates in aqueous samples. Gas chromatography with flame ionization detection was used to detect the target analytes as a powerful instrumental analysis. Affecting parameters in the extraction process, including the amount of adsorbent, adsorption and desorption time, and volume of desorption solvent, were optimized using a response surface methodology based on central composite design. Under the optimum conditions, the linear range for dibutyl phthalate and bis(2‐ethylhexyl phthalate) was varied in the interval of 10–1700 and 10–1200 μg/L, respectively. Limits of detection were 2.80 μg/L for dibutyl phthalate and 3.20 μg/L for bis(2‐ethylhexyl phthalate). The recovery value for the extraction of target analytes was between 97 and 111%. The repeatability and reproducibility of the new proposed method were obtained: 10–13% and 13–13.5%, respectively. The increased sensitivity in using the proposed method has been demonstrated. Compared with previous methods, the new proposed method is an accurate, rapid, and reliable sample‐pretreatment method.     

Self‐assembly of poly(ionic liquid) functionalized mesoporous magnetic microspheres for the solid‐phase extraction of preservatives from milk samples

In this work, a novel, rapid, and simple analytical method was proposed for the detection of parabens in milk sample by gas chromatography coupled with mass spectrometry. At the same time, milk sample was pretreated by magnetic solid phase extraction, which detected up to five parabens. A series of important parameters of magnetic solid phase extraction were investigated and optimized, such as pH value of loading buffer, amount of material, adsorption time, ionic strength, eluting solvents, and eluting time. Under the optimized conditions, the corresponding values were more than 0.9991, limits of detection and the limit of quantification were 0.1 and 0.5 ng/mL, respectively. In addition, the recoveries were achieved in range of 95–105%, the liner range were within 0.1–600 ng/mL, and the relative standard deviations were even lower than 5%.     

Simple magnetization of Fe3O4/MIL‐53(Al)‐NH2 for a rapid vortex‐assisted dispersive magnetic solid‐phase extraction of phenol residues in water samples

The present work describes a simple route to magnetize MIL‐53(Al)‐NH₂ sorbent for rapid extraction of phenol residues from environmental samples. To extend the applications and performances of the metal‐organic frameworks in the field of adsorption materials, we combined the properties of metal‐organic frameworks and magnetite to decrease the extraction time and simplify the extraction process as well. In this study, a simple and quick vortex‐assisted dispersive magnetic solid phase extraction method for the extraction of ten United States Environmental Protection Agency's priority phenols from water samples prior to analysis by high‐performance liquid chromatography with photodiode array detection was proposed. The developed method exhibits a rapid enrichment of the target analytes within 10 s for extraction and 10 s for desorption. Low detection limits of 1.8‐41.7 µg/L and quantitation limits of 6.0‐139.0 µg/L with the relative standard deviations for intra‐ and interday analyses less than 12% were achieved. Satisfactory recoveries in the range of 80‐111% with the relative standard deviations less than 11% demonstrated that Fe₃O₄/MIL‐53(Al)‐NH₂ is promising sorbent in the field of magnetic solid‐phase extraction for environmental samples.     

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%.     

Magnetic spherical carbon as an efficient adsorbent for the magnetic extraction of phthalate esters from lake water and milk samples

Magnetic spherical carbon was synthesized by a facile hydrothermal carbonization procedure with biomass glucose as the carbon precursor and nanoclusters iron colloid as magnetic precursor. The textures of the as‐prepared magnetic spherical carbon were characterized by nitrogen adsorption–desorption isotherms, X‐ray diffraction, transmission electron microscopy, scanning electron microscopy and vibration sample magnetometry. Results indicated that the magnetic spherical carbon possessed high surface area as well as strong magnetism, which endows the material with good adsorption capability and easy separation properties. To assess its absorption performance, the magnetic spherical carbon was employed as adsorbent for the extraction and preconcentration of phthalate esters from lake water and milk samples before high‐performance liquid chromatographic analysis. Some key parameters that could influence the enrichment efficiency were investigated. Under the optimum conditions, a good linearity was achieved with the linear correlation coefficients higher than 0.9973. The limits of detection (S/N = 3) were 0.05–0.08 ng/mL for lake water and 0.1–0.2 ng/mL for milk samples. The recoveries of the analytes for the method were in the range 80.1–112.6%.     

Magnetic solid‐phase extraction of polycyclic aromatic hydrocarbons in water samples by Fe3O4@polypyrrole/carbon nanotubes

A magnetic solid‐phase extraction method coupled with gas chromatography was proposed for the determination of polycyclic aromatic hydrocarbons in the environmental water samples. The magnetic adsorbent was prepared by incorporating Fe₃O₄ nanoparticles, multi‐walled carbon nanotubes, and polypyrrole. The main factors affecting the extraction efficiency including the amount of the sorbents, desorption conditions, extraction time, salt concentration, and sample solution pH were investigated and optimized. Under the optimum conditions, good linearity was obtained within the range of 0.03?100 ng/mL for all analytes, with correlation coefficients ranging from 0.9942 to 0.9973. The method detection limits (S/N = 3) were in the range of 0.01–0.04 ng/mL and the limits of quantification (S/N = 10) were 0.03–0.1 ng/mL. Repeatability of the method was assessed through five consecutive extractions of independently prepared solutions at concentrations of 0.1, 10, and 100 ng/mL of the compounds. The observed repeatability ranged 3.4–10.9% depending of the compound considered. The proposed method was successfully applied in the analysis of PAHs in environmental samples (tap, well, river, and wastewater). The recoveries of the method ranged between 93.4 and 99.0%. The procedure proved to be efficient and environmentally friendly.