Resorcinol–formaldehyde xerogel as a micro‐solid‐phase extraction sorbent for the determination of herbicides in aquatic environmental samples

In this study, organic aerogels were synthesized by the sol–gel polycondensation of mixed cresol with formaldehyde in a slightly basic aqueous solution. Carbon aerogels and xerogels are generated by pyrolysis of organic aerogels. The novel sol–gel‐based micro‐solid‐phase extraction sorbent, resorcinol–formaldehyde xerogel, was employed for preconcentration of some selected herbicides. Three herbicides of the aryloxyphenoxypropionate group, clodinafop‐propargyl, haloxyfop‐etotyl, and fenoxaprop‐P‐ethyl, were extracted from aqueous samples by micro‐solid‐phase extraction and subsequently determined by gas chromatography with mass spectrometry. The effect of different parameters influencing the extraction efficiency of these herbicides including sample flow rate, sample volume, and extraction time were investigated and optimized. Under optimum conditions, linear calibration curves in the range of 0.10–500 ng/L with R² > 0.99 were obtained. The relative standard deviation at 50 μg/L concentration level was lower than 10% (n = 5) and detection limits were between 0.05 and 0.20 μg/L. The proposed method was successfully applied to the sampling and extraction of herbicides from Zayanderood and paddy water samples.     

Dicationic polymeric ionic‐liquid‐based magnetic material as an adsorbent for the magnetic solid‐phase extraction of organophosphate pesticides and polycyclic aromatic hydrocarbons

Magnetic particles modified with a dicationic polymeric ionic liquid are described as a new adsorbent in magnetic solid‐phase extraction. They were obtained through the copolymerization of a 1,8‐di(3‐vinylimidazolium)octane‐based ionic liquid with vinyl‐modified SiO₂@Fe₃O₄, and were characterized by FTIR spectroscopy, X‐ray diffraction, and vibrating sample magnetometry. The modified magnetic particles are effective in the extraction of organophosphate pesticides and polycyclic aromatic hydrocarbons. Also, they can provide different extraction performance for the selected analytes including fenitrothion, parathion, fenthion, phoxim, phenanthrene, and fluoranthene, where the extraction efficiency is found to be in agreement with the hydrophobicity of analytes. Various factors influencing the extraction efficiency, such as, the amount of adsorbent, extraction, and desorption time, and type and volume of the desorption solvent, were optimized. Under the optimized conditions, a good linearity ranging from 1–100 μg/L is obtained for all analytes, except for parathion (2–200 μg/L), where the correlation coefficients varied from 0.9960 to 0.9998. The limits of detection are 0.2–0.8 μg/L, and intraday and interday relative standard deviations are 1.7–7.4% (n = 5) and 3.8–8.0% (n = 3), respectively. The magnetic solid‐phase extraction combined with high‐performance liquid chromatography can be applied for the detection of trace targets in real water samples with satisfactory relative recoveries and relative standard deviations.     

Developing an alcoholic‐assisted dispersive liquid–liquid microextraction for extraction of pentachlorophenol in water

Optimization of alcoholic‐assisted dispersive liquid–liquid microextraction of pentachlorophenol (PCP) and determination of it with high‐performance liquid chromatography (UV‐Vis detection) was investigated. A Plackett‐Burman design and a central composite design were applied to evaluate the alcoholic‐assisted dispersive liquid–liquid microextraction procedure. The effect of seven parameters on extraction efficiency was investigated. The factor studied were type and volume of extraction and dispersive solvents, amount of salt, and agitation time. According to Plackett‐Burman design results, the effective parameters were type and volume of extraction solvent and agitation time. Next, a central composite design was applied to obtain optimal condition. The optimized conditions were obtained at 170‐μL 1‐octanol and 5‐min agitation time. The enrichment factor of PCP was 242 with limits of detection of 0.04 μg L^?1. The linearity was 0.1–100 μg L^?1 and the extraction recovery was 92.7%. RSD for intra and inter day of extraction of PCP were 4.2% and 7.8%, respectively for five measurements. The developed method was successfully applied for the determination of PCP in environmental water samples.     

Extraction of phenolic compounds from water samples by dispersive micro‐solid‐phase extraction

In this article, the use of magnetically separable sorbent polyaniline/silica‐coated nickel nanoparticles is evaluated under a dispersive micro‐solid‐phase extraction approach for the extraction of phenolic compounds from water samples. The sorbent was prepared by in situ chemical polymerization of aniline on the surface of silica‐modified nickel nanoparticles and was characterized by Fourier transform infrared spectroscopy, transmission electron microscopy, X‐ray powder diffraction, scanning electron microscopy, energy‐dispersive X‐ray spectrometry, and vibrating sample magnetometry. Effective variables such as amount of sorbent (milligrams), pH and ionic strength of sample solution, volume of eluent solvent (microliters), vortex, and ultrasonic times (minutes) were investigated by fractional factorial design. The significant variables optimized by a Box–Behnken design were combined by a desirability function. Under the optimized conditions, the calibration graphs of analytes were linear in a concentration range of 0.02–100 μg/mL, and with correlation coefficients more than 0.999. The limits of detection and quantification were in the ranges of 10–23 and 33–77 μg/L, respectively. This procedure was successfully employed in the determination of target analytes in spiked water samples; the relative mean recoveries ranged from 96 to 105%.     

Ultrasound‐assisted dispersive micro‐solid‐phase extraction based on N‐doped mesoporous carbon and high‐performance liquid chromatographic determination of 1‐hydroxypyrene in urine samples

In this research, a new ultrasound‐assisted dispersive micro‐solid‐phase extraction method based on N‐doped mesoporous carbon sorbent followed by high‐performance liquid chromatography equipped with diode array detector for trace measurement of 1‐hydroxypyrene as a metabolite of exposure to polycyclic aromatic hydrocarbons was optimized. Herein, the hard template method was used for the preparation of N‐doped mesoporous carbon sorbent. The prepared sorbent was characterized using the Brunauer–Emmett–Teller method, transmission electron microscopy, and elemental analysis. Parameters affecting the extraction of the target metabolite were investigated using the Box–Behnken design method. Considering optimum parameters, the plotted calibration curve for 1‐hydroxypyrene was linearly correlated with the concentration span of 0.1–50 μg/L for urine media. The accuracy of the optimized procedure was examined through the relative recovery tests on the fortified urine specimens. The relative recoveries fell between 95 and 101%. The method detection limit of the proposed procedure was also calculated to be 0.03 μg/L.     

Molecularly imprinted polymer on a SiO2‐coated graphene oxide surface for the fast and selective dispersive solid‐phase extraction of Carbamazepine from biological samples

A surface carbamazepine‐imprinted polymer was grafted and synthesized on the SiO₂/graphene oxide surface. Firstly SiO₂ was coated on synthesized graphene oxide sheet using the sol–gel technique. Prior to polymerization, the vinyl group was incorporated on to the surface of SiO₂/graphene oxide to direct selective polymerization on the surface. Methacrylic acid, ethylene glycol dimethacrylate and ethanol were used as monomer, cross‐linker and porogen, respectively. Nonimprinted polymer was also prepared for comparison. The properties of the molecularly imprinted polymer were characterized using field‐emission scanning electron microscopy and Fourier‐transform infrared spectroscopy. The surface molecularly imprinted polymer was utilized as an adsorbent of dispersive solid‐phase extraction for separation and preconcentration of carbamazepine. The effects of the different parameters influencing the extraction efficiency, such as sample pH were investigated and optimized. The specificity of the molecular imprinted polymer over the nonimprinted polymer was examined in absence and presence of competitive drugs. The carbamazepine calibration curve showed linearity in the ranges 0.5–500 μg/L. The limits of detection and quantification under the optimized conditions were 0.1 and 0.3 μg/L, respectively. The within‐day and between‐day relative standard deviations (n = 3) were 3.6 and 4.3%, respectively. Furthermore, the relative recoveries for spiked biological samples were above 85%.     

Application of magnetized MOF‐74 to phthalate esters extraction from Chinese liquor

In this study, magnetized MOF‐74 (Ni) was prepared using an ultrasound‐assisted synthesis method. This novel functional magnetic adsorbent was characterized using various techniques. Using the prepared material as adsorbents, a magnetic solid‐phase extraction method coupled with high‐performance liquid chromatography was proposed for determining four phthalate esters in Chinese liquor samples. The extraction parameters, including solution pH, adsorbent amount, extraction time, and eluent type and volume, were optimized. Under the optimized conditions, proposed method showed good linearity within the range of 1.53–200 μg/L for diphenyl phthalate, 2.03–200 μg/L for butyl benzyl phthalate, 7.02–200 μg/L for diamyl phthalate, and 6.03–200 μg/L for dicyclohexyl phthalate, with correlation coefficients > 0.9944, low limits of detection (0.46–2.10 μg/L, S/N = 3), and good extraction repeatability (relative standard deviations of 3.7%, n = 6). This method was successfully used to analyze phthalate esters in Chinese liquor samples with recoveries of 74.4–104.8%. Two phthalate esters were detected in two samples, both at concentrations that satisfied the Chinese national standard, indicating this method has practical application prospects. The extraction efficiency of this method was also compared with conventional solid‐phase extraction using commercial C₁₈ cartridges. The results demonstrated that the proposed magnetic solid‐phase extraction is a simple, time‐saving, efficient, and low‐cost method.     

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 of novel ionic‐liquid‐modified magnetic nanoparticles by a microwave‐assisted method for sulfonylurea herbicides extraction

Ionic liquids immobilized on magnetic nanoparticles were prepared by an efficient microwave‐assisted synthesis method, and the properties of the ionic liquids were tuned based on the aromatic functional modification of its anion through a simple metathesis reaction. The novel as‐synthesized magnetic materials were characterized by various instrumental techniques. The magnetic nanoparticles have been utilized as adsorbents for the extraction of four sulfonylurea herbicides in tea samples, in combination with high‐performance liquid chromatography analysis. Significant extraction parameters, including type and volume of desorption solvent, extraction time, amount of adsorbent, and ionic strength were investigated. Under the optimum conditions, good linearity was obtained in the concentration range of 1–150 μg/L for metsulfuron‐methyl and bensulfuron‐methyl, and 3–150 μg/L for sulfometuron‐methyl and chlorimuron‐ethyl, with correlation coefficients R² > 0.9987. Low limits of detection were obtained ranging from 0.13 to 0.81 μg/L. The relative standard deviations were 1.8–3.9%. Comparisons of extraction efficiency with conventional solid‐phase extraction equipped with a commercial C₁₈ cartridge were performed. Results indicated that magnetic solid‐phase extraction is simple, time‐saving, efficient and inexpensive with the reusability of adsorbents. The proposed method has been successfully used to determine sulfonylurea herbicides from tea samples with satisfactory recoveries of 80.5–104.2%.     

Microwave‐assisted preparation of poly(ionic liquids)‐modified magnetic nanoparticles for pesticide extraction

Novel poly(ionic liquids) were synthesized and immobilized on prepared magnetic nanoparticles, which were used to extract pesticides from fruit and vegetable samples by dispersive solid‐phase extraction prior to high‐performance liquid chromatography analysis. Compared with monomeric ionic liquids, poly(ionic liquids) have a larger effective contact area and higher viscosity, so they can achieve higher extraction efficiency and be used repeatedly without a decrease in analyte recovery. The immobilized poly(ionic liquids) were rapidly separated from the sample matrix, providing a simple approach for sample pretreatment. The nature and volume of the desorption solvent and amount of poly(ionic liquid)‐modified magnetic material were optimized for the extraction process. Under optimum conditions, calibration curves were linear (R² > 0.9988) for pesticide concentrations in the range of 0.100–10.000 μg/L. The relative standard deviations for repeated determinations of the four analytes were 2.29–3.31%. The limits of detection and quantification were 0.29–0.88 and 0.97–2.93 μg/L, respectively. Our results demonstrate that the developed poly(ionic liquid)‐modified material is an effective absorbent to extract pesticides from fruit and vegetable samples.     

Simultaneous preconcentration and determination of 2,4‐D,alachlor and atrazine in aqueous samples using dispersive liquid–liquid microextraction followed by high‐performance liquid chromatography ultraviolet detection

Dispersive liquid–liquid microextraction coupled with high‐performance liquid chromatography‐ultraviolet detection as a fast and inexpensive technique was applied to the simultaneous extraction and determination of traces of three common herbicides, 2,4‐D, alachlor and atrazine, in aqueous samples. The critical experimental parameters, including type of the extraction and disperser solvents as well as their volumes, sample pH, salt addition, extraction time and centrifuging time, and speed were investigated and optimized. Under the optimum conditions, the calibration graphs found to be linear in the range of 0.3–200 μg/L with limits of detection in the range of 0.05–0.1 μg/L. The relative standard deviations were in the range of 4.5–6.2% (n = 7). The relative recoveries of well, tap, and river water samples which have been spiked with different levels of herbicides were 92.0–107.0, 82.0–104.0, and 82.0–86.0%, respectively.     

Ultrasound/microwave‐assisted solid–liquid–solid dispersive extraction with high‐performance liquid chromatography coupled to tandem mass spectrometry for the determination of neonicotinoid insecticides in Dendrobium officinale

A one‐step ultrasound/microwave‐assisted solid–liquid–solid dispersive extraction procedure was used for the simultaneous determination of eight neonicotinoids (dinotefuran, nitenpyram, thiamethoxam, clothianidin, imidacloprid, acetamiprid, thiacloprid, imidaclothiz) in dried Dendrobium officinale by liquid chromatography combined with electrospray ionization triple quadrupole tandem mass spectrometry in multiple reaction monitoring mode. The samples were quickly extracted by acetonitrile and cleaned up by the mixed dispersing sorbents including primary secondary amine, C₁₈, and carbon‐GCB. Parameters that could influence the ultrasound/microwave‐assisted extraction efficiency such as microwave irradiation power, ultrasound irradiation power, temperature, and solvent were investigated. Recovery studies were performing well (70.4–113.7%) at three examined spiking levels (10, 50, and 100 μg/kg). Meanwhile, the limits of quantification for the neonicotinoids ranged from 0.87 to 1.92 μg/kg. The method showed good linearity in the concentration range of 1–100 μg/L with correlation coefficients >0.99. This quick and useful analytical method could provide a basis for monitoring neonicotinoid insecticide residues in herbs.     

Extraction and determination of flavonoids in fruit juices and vegetables using Fe3O4/SiO2 magnetic nanoparticles modified with mixed hemi/ad‐micelle cetyltrimethylammonium bromide and high performance liquid chromatography

Extraction and determination of three flavonoids (morin, quercetin, and kaempferol) were performed by dispersive magnetic solid phase extraction based on mixed hemi/ad‐micelles and high‐performance liquid chromatography with UV detection. The Fe₃O₄/SiO₂ nanoparticles were synthesized and characterized by X‐ray diffraction, FTIR, scanning electron microscopy, and thermogravimetric analysis. Fe₃O₄/SiO₂ nanoparticles coated with mixed hemi/ad‐micelles cetyltrimethyl ammonium bromide was applied as a sorbent and used for extraction of flavonoids. Effective parameters on the extraction recovery such as amount of magnetic nano particles, volume of cetyltrimethyl ammonium bromide solution with specific concentration, pH of sample solution, adsorption equilibrium time, volume of desorption solvent, and desorption times were evaluated and optimized using fractional factorial design and central composite design. Under the optimum condition limit of detection and linearity were 0.83, 2.7–500.0 for morin, 0.18, 0.7–500.0 for quercetin and, 0.37, 1.3–500.0 µg/L for kaempferol. The extraction recovery with relative standard deviation were 97.88, 1.94 for morin, 95.77, 0.80 for quercetin, and 93.35, 1.45 for kaempferol. The proposed method was applied for simultaneous extraction and determination of flavonoids in several fruit juices and vegetable samples.     

Determination of phthalate esters from environmental water samples by micro‐solid‐phase extraction using TiO2 nanotube arrays before high‐performance liquid chromatography

We describe a highly sensitive micro‐solid‐phase extraction method for the pre‐concentration of six phthalate esters utilizing a TiO₂ nanotube array coupled to high‐performance liquid chromatography with a variable‐wavelength ultraviolet visible detector. The selected phthalate esters included dimethyl phthalate, diethyl phthalate, dibutyl phthalate, butyl benzyl phthalate, bis(2‐ethylhexyl)phthalate and dioctyl phthalate. The factors that would affect the enrichment, such as desorption solvent, sample pH, salting‐out effect, extraction time and desorption time, were optimized. Under the optimum conditions, the linear range of the proposed method was 0.3–200 μg/L. The limits of detection were 0.04–0.2 μg/L (S/N = 3). The proposed method was successfully applied to the determination of six phthalate esters in water samples and satisfied spiked recoveries were achieved. These results indicated that the proposed method was appropriate for the determination of trace phthalate esters in environmental water samples.     

Phenyl‐functionalized silica‐coated magnetic nanoparticles for the extraction of chlorobenzenes,and their determination by GC‐electron capture detection

We have prepared a solid phase for the extraction of chlorobenzenes (CBs) by coating magnetic (Fe₃O₄) nanoparticles with silica via a sol‐gel process using a mixture of tetraethoxysilane and triethoxyphenylsilane. The nanoparticles were characterized by SEM, energy‐dispersive spectroscopy, and X‐ray diffractometry. The nanoparticles were used for the extraction of 1,4‐dichlorobenzene (1,4‐DCB), 1,2,3‐trichlorobenzene (1,2,3‐TCB), 1,2,4‐trichlorobenzene (1,2,4‐TCB), and 1,2,3,4‐tetrachlorobenzene (1,2,3,4‐TeCB) from water, followed by their determination by GC‐electron capture detection. Under optimal conditions, enrichment factors ranging from 220 to 360 were obtained. All determination coefficients (r²) are >0.99, and linear response is found in range 0.025–1.5 μg/L (at the lower end), and 6–120 μg/L (at the higher end). Detection limits are 6, 10, 11, and 500 ng/L for 1,2,3,4‐TeCB, 1,2,4‐TCB, 1,2,3‐TCB, and 1,4‐DCB, respectively. All RSDs are <6% (for n = 5). The method was successfully applied to the determination of CBs in environmental water samples.     

Selective and sensitive determination of silver ions at trace levels based on ultrasonic‐assisted dispersive solid‐phase extraction using ion‐imprinted polymer nanoparticles

We describe ultrasonic‐assisted dispersive solid‐phase extraction based on ion‐imprinted polymer (UA‐DSPE‐IIP) nanoparticles for the selective extraction of silver ions. Ultrasound is a good and robust method to facilitate the extraction of target ions in the sorption step and elution of the target ions in the desorption step. The IIP nanoparticles used in the UA‐DSPE‐IIP were prepared by precipitation polymerization. To prepare the IIP nanoparticles, 2‐vinylpyridine, ethylene glycol dimethacrylate, 2,2′‐azobisisobutyronitrile, 2‐picolinic acid, silver and chloroform–methanol (50:50) solution were used as functional monomer, cross‐linker, initiator, silver‐binding ligand, template ion and porogen, respectively. The IIP nanoparticles were characterized using Fourier transformed infrared spectroscopy, thermogravimetric and differential thermal analysis, X‐ray diffraction and scanning electron microscopy. A Box–Behnken design was used for optimization of sorption and desorption steps in UA‐DSPE‐IIP. In the sorption step: pH of solution, IIP amount (mg), sonication time for sorption (min); in the desorption step: concentration of eluent (mol l⁻¹), volume of eluent (ml), sonication time (min) for desorption were investigated and optimized by Box–Behnken design. The optimum conditions for the method were: pH of solution, 7; sonication time for sorption, 7 min; IIP amount, 17 mg; type and concentration of eluent, HCl 1.5 mol l⁻¹; volume of eluent, 2 ml; sonication time for desorption, 140 s. Under the optimized conditions the limit of detection and relative standard deviation for the detection of silver ions using UA‐DSPE‐IIP were found to be 0.09 μg l⁻¹ and <3%, respectively.     

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.     

Magnetic nanocomposite of self‐doped polyaniline–graphene as a novel sorbent for solid‐phase extraction

This work is the first study on the extraction efficiency of self‐doped polyaniline that is immobilized on the graphene‐modified magnetic nanoparticles. The new material was used as a sorbent for the magnetic solid‐phase extraction of methyl‐, propyl‐, and butylparabens. The use of graphene provides a high surface area and prevents aggregation of the nanoparticles. The self‐doped polyaniline also provides multifunctionality, high extraction capacity, and chemical stability even in the basic medium. The parabens were acetylated for determination by gas chromatography with flame ionization detection. The effects of monomer ratio, extraction solvent, sorbent amount, sample volume, desorption solvent volume, adsorption and desorption times, and sample ionic strength were optimized. Preconcentration factors obtained were from 190 to 310. The detection limits of the method were <2.8 μg/L. Linear ranges of the method were 5–2000 μg/L for propyl and butyl parabens, and 10–2000 μg/L for methyl paraben. The method was applied for the determination of the parabens in cosmetic products and extraction recoveries were 89–101% with RSDs ≤7.9%.     

Chemically functionalized silica nanoparticles‐based solid‐phase extraction for effective pre‐concentration of highly toxic metal ions from food and water samples

In this research study, an efficient solid‐phase extraction procedure based on a new organometallic, effective, eco‐friendly and bio‐degradable nanoadsorbent was firstly introduced for influential pre‐concentration of Cu(II), Zn(II), Pb(II), Cd(II) and Mn(II) ions from food and water samples followed by flame atomic absorption spectrophotometric determination. This safe adsorbent consisted of silica nanoparticles chemically functionalized with di‐ethylen tri‐amine (SiO₂@NH₂NPs); easily prepared via an effective and simple approach. Characterization of SiO₂@NH₂NPs was subsequently implemented via SEM, FT‐IR and XRD; certifying high quality of the modified nanoadsorbent in terms of size, shape and surface functional groups. The effects of the main factors on the extraction efficiency were then optimized. Efficient extraction of the analytes of interest at neutral media accompanied with the aid of a bio‐compatible organometallic nanoadsorbent can be considered as valuable advantages of the proposed approach. In the optimum conditions, calibration graphs were linear in the range of 4–700 μg l^?1, with higher correlation coefficients than 0.997 and limits of detection of 1.45–4.10 ng ml^?1. The enrichment factor values were found to be in the span of 120–400. The resultant extraction recovery values were satisfactory; possessing the proper relative standard deviation (%, n  =  5) values of 2.05–4.28%.     

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.