Magnetic solid-phase extraction based on Fe3O4/graphene oxide nanoparticles for the determination of malachite green and crystal violet in environmental water samples by HPLC

This work describes a magnetic Fe₃O₄/graphene oxide (GO)-based solid-phase extraction (MSPE) technique for high performance liquid chromatography (HPLC) detection of malachite green (MG) and crystal violet (CV) in environmental water samples. Fe₃O₄/ GO magnetic nanoparticles were synthesised by a chemical co-precipitation method and characterised by scanning electron micrograph, transmission electron microscope, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and surface area analyser. The prepared Fe₃O₄/GO magnetic nanoparticles were used as the adsorbents of MSPE for MG and CV. By coupling with HPLC, a sensitive and cost-effective method for simultaneous determination of MG and CV was developed. The important parameters including the amount of Fe₃O₄/GO, pH of the sample solution, extraction time, salt effect, the type and volume of desorption solvent were investigated in detail. Under optimised conditions, the calibration curves were linear in the concentration range of 0.5–200 μg L^?1, and the limits of detection were 0.091 and 0.12 μg L^?1 for MG and CV, respectively. Finally, the established MSPE-HPLC method was successfully applied to determine MG and CV in environmental water samples with the recoveries ranging from 91.5% to116.7%.     

Simultaneous preconcentration and determination of malachite green and fuchsine dyes in seafood and environmental water samples using nano-alumina-based molecular imprinted polymer solid-phase extraction

Molecular imprinted polymer for determination of malachite green (MG) and fuchsine basic (FU) dyes by spectrophotometry has been used, to develop a novel simultaneous extraction and preconcentration method. Molecularly imprinted layer-coated nano-alumina (MIP@Nano-Al₂O₃) as adsorbent was prepared by surface molecular imprinting technique, and characterised by FTIR spectroscopy, scanning electron microscopy, energy dispersive X-ray analysis (EDAX) and thermogravimetric analysis (TGA). The method is based on simultaneous extraction of MG and FU dyes from aqueous solution by using molecularly imprinted polymer and measuring the absorbance at 617 and 546 nm for MG and FU, respectively. Parameters which affect the extraction efficiency such as pH, volume of eluent and amount of adsorbent were investigated and optimised. Linear calibration curves were obtained in the range of 2–750 ng mL^?1 for MG and 1–240 ng mL^?1 for FU under optimum conditions. Detection limit based on three times the standard deviation of the blank (3S_b) was 0.655 and 0.245 ng mL^?1 (n = 10) for MG and FU, respectively. The relative standard deviation (RSD) for 100 ng mL^?1 of MG and FU was 2.35 and 3.06% (n = 7), respectively. The method was applied to the simultaneous determination of the dyes in different seafood and environmental water samples.     

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.     

Development of graphene-carbon nanotube-coated magnetic nanocomposite as an efficient sorbent for HPLC determination of organophosphorus pesticides in environmental water samples

A magnetic solid-phase extraction (MSPE) method coupled to high performance liquid chromatography with UV (HPLC-UV) was proposed for the determination of organophosphorus pesticides (OPPs) at trace levels in environmental water samples. The ternary nanocomposite of graphene-carbon nanotube-Fe₃O₄ (G-CNT-Fe₃O₄) has been synthesised via a simple solvothermal process and the resultant material was characterised by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. Significant factors that affect the extraction efficiency, such as amount of magnetic nanocomposite, extraction time, ionic strength, solution pH and desorption conditions were carefully investigated. The results demonstrated that the proposed method had a wide dynamic linear range (0.005–200 ng mL^?1), good linearity (R² = 0.9955–0.9996) and low detection limits (1.4–11 pg mL^?1). High enrichment factors were achieved ranging from 930 to 1510. The results show that the developed method is suitable for trace level monitoring of OPPs in environmental water samples.     

A highly sensitive method for detection of bisphenol A in water samples based on functionalised Fe3O4@SiO2@nylon66

A simple and sensitive method was developed for preconcentration and determination of bisphenol A (BPA) in environmental samples by high performance liquid chromatography (HPLC). The hydrophilic silicon-dioxide- and nylon66-functionalised magnetic material (Fe₃O₄@SiO₂@nylon66) was used as a sorbent for magnetic solid-phase extraction (MSPE). With the anhydrous microemulsion reaction, the Fe₃O₄@SiO₂@nylon66 had shown great characteristics such as good magnetic responsivity, water dispersibility and stability. Based on the materials, various extraction parameters including pH, extraction time, elution time, the number of sorbents, sample volume and elution times were optimised. The whole extraction procedure could be accomplished within 20 min and the materials could be used more than 10 times after regeneration. Under the optimised conditions, different types of water samples (Tap water, river water, sea water and underground water) were successfully analysed to verify the applicability of the proposed method. The recoveries of different samples ranged from 88.54% to 104.46%. An enrichment factor of 250 was achieved with 0.05 μg/L detection limit. Thus, the developed MSPE is a potential technique that can be used for water samples preconcentration or combined with other analytical methods for determination of BPA.     

Development of novel magnetic solid-phase extraction sorbent based on Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/carbon nanosphere/polypyrrole composite and their application to the enrichment of polycyclic aromatic hydrocarbons from water samples prior to GC–FID analysis

We describe a magnetic nanocomposite that consists of Fe₃O₄/carbon nanosphere/polypyrrole (Fe₃O₄/CNS/PPy). The synthesized nanocomposites were characterized by scanning electron microscopy, transmission electron microscopy, and Fourier transform infrared spectroscopy. The nanocomposite was successfully applied to extract of the polycyclic aromatic hydrocarbons (PAHs) from water samples. Compared to Fe₃O₄/PPy, the Fe₃O₄/CNS/PPy nanocomposite exhibits improved properties in terms of extraction. The amount of adsorbent, salt effect, extraction time, desorption time, type, and the volume of desorption solvent were optimized. Following the desorption of the extracted analytes, the PAHs (i.e., naphthalene, 2-methylnaphthalene, 2-bromonaphthalene, fluorene, and anthracene) were quantified by gas chromatography–flame ionization detector. The PAHs can be determined in 0.05–100.00 ng mL^?1 concentration range, with limits of detection (at an S/N ratio of 3) ranging from 0.01 to 0.05 ng mL^?1. The repeatability of the method was investigated with relative standard deviations of lower than 9.9% (n = 5). Also, the recoveries from spiked real water samples were in the range of 88.9–99.0%. The results indicate that the novel material can be successfully applied for the extraction and analysis of PAHs from water samples.     

A nanocomposite consisting of graphene oxide and Fe3O4 magnetic nanoparticles for the extraction of flavonoids from tea,wine and urine samples

We describe a single-step solvothermal method for the preparation of nanocomposites consisting of graphene oxide and Fe₃O₄ nanoparticles (GO/Fe₃O₄). This material is shown to be useful as a magnetic sorbent for the extraction of flavonoids from green tea, red wine, and urine samples. The nanocomposite is taking advantage of the high surface area of GO and the magnetic phase separation feature of the magnetic sorbent. The nanocomposite is recyclable and was applied to the extraction of flavonoids prior to their determination by HPLC. The effects of amount of surfactant, pH value of the sample solution, extraction time, and desorption condition on the extraction efficiency, and the regeneration conditions were optimized. The limits of detection for luteolin, quercetin and kaempferol range from 0.2 to 0.5 ng∙ mL⁻¹ in urine, from 3.0 to 6.0 ng∙mL⁻¹ in green tea, and from 1.0 to 2.5 ng∙mL⁻¹ in red wine. The recoveries are between 82.0 and 101.4 %, with relative standard deviations of <9.3 %.

The article describes a method for magnetic solid-phase extraction (MSPE) of trace amounts of natural substances in complex samples by using graphene oxide (GO)-Fe₃O₄nanoparticles as the sorbent.

     

Magnetic solid-phase extraction of imatinib and doxorubicin as cytostatic drugs by Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/graphene oxide nanocomposite

Magnetic solid-phase extraction based on Fe₃O₄/graphene oxide nanocomposites was investigated for the separation, preconcentration and determination of imatinib and doxorubicin in aqueous solutions. Synthesis of Fe₃O₄/graphene oxide was characterized by transmission electron microscopy, energy-dispersive X-ray analyzer and vibrating sample magnetometer. After optimizing the conditions, optimal experimental conditions including sample pH, the amount of the magnetic nanoparticles, the effect of salt concentration and other chemotherapy medications, eluent type and extraction time were studied and established. The method showed good linearity for the determination of doxorubicin and imatinib in the concentration range of 0.01–100 μg mL^?1 in aqueous solutions with limit of detection 1.8 ng mL^?1 for doxorubicin and 1.9 ng mL^?1 for imatinib. The relative recoveries of doxorubicin and imatinib levels were 96.7 and 88.4%, respectively. The results indicate that the present procedure is a suitable method for extraction of imatinib and doxorubicin from environmental water samples.     

Magnetic Solid-Phase Extraction and Ionic Liquid Dispersive Liquid–Liquid Microextraction Coupled with High-Performance Liquid Chromatography for the Determination of Hexachlorophene in Cosmetics

An efficient, simple, and fast method based on ionic liquid dispersive liquid–liquid microextraction (IL-DLLME) followed by magnetic solid-phase extraction (MSPE) was developed as a new technique for extracting and purifying hexachlorophene (HCP) in cosmetics prior to high-performance liquid chromatography (HPLC) determination. In this method based on IL-DLLME and MSPE, 1-hexyl-3-methylimidazolium hexafluorophosphate ([C₆MIM][PF₆]) is used as the extraction solvent and Fe₃O₄ nanoparticles are used to remove hydrophobic additives in the cosmetics by physical adsorption. The main parameters affecting the efficiency of the IL-DLLME and MSPE of HCP were investigated and optimized. Under the optimum conditions, the method was linear in the range 0.5–40 µg mL^?1 with a correlation coefficient (R ²) of 0.9976 and had a detection limit of 0.14 µg mL^?1 at a signal-to-noise ratio (S/N) of 3. The recoveries of HCP in three cosmetic samples using the proposed method were in the range 74.5–97.7%, and the relative standard deviations (RSD, n = 5) were in the range 3.8–6.7%. The developed method was successfully applied to the determination of HCP in cosmetics.     

Synthesis of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@PPy–MWCNT nanocomposite and its application for extraction of ultra-trace amounts of PAHs from various samples

In the present study, multi-walled carbon nanotube oxide was immobilized on the pyrrole magnetic nanoparticles. Application of the synthesized material was investigated for the magnetic solid-phase extraction (MSPE) of polycyclic aromatic hydrocarbons (PAHs), from the environmental samples. Determinations of the analytes were performed with gas chromatography–mass spectrometry. The structure and morphology of Fe₃O₄@PPy–MWCNT were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, thermal gravimetric analysis, and vibrating sample magnetometer. Performance of MSPE is mainly affected by extraction time, sorbent amount, sample solution volume, and eluent type and volume. In this study, the best possible performance of MSPE has been achieved using a combination of central composite design and Bayesian regularized artificial neural network technique. Under the optimum extraction conditions, linear range between 0.5 and 250 µg L^?1 (R ² > 0.994), preconcentration factors from 232 to 403 and limits of detection ranging from 0.1 to 0.3 µg L^?1 were obtained. Relative standard deviations for intra-day and inter-day precision were 3.3–5.1% and 3.7–5.6%, respectively. In addition, feasibility of the method was demonstrated by extraction and determination of PAHs from some real samples containing tap water, hookah water as well as soil samples, and relative recovery in the range of 85.4–106.8% was obtained. This MSPE method provides several advantages, such as high extraction efficiency, minimum sorbent for extraction of the analytes from high sample volumes, convenient extraction procedure, and short analysis times.     

Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@ionic liquid-β-cyclodextrin polymer magnetic solid phase extraction coupled with HPLC for the separation/analysis of congo red

Fe₃O₄@ionic liquids β-cyclodextrin polymer(Fe₃O₄@mono-6-deoxy-6-(1-ethyl-imidazolium)-β-cyclodextrin iodide polymer, Fe₃O₄@ILs-β-CDCP) was prepared. Magnetic solid phase extraction coupled with high-performance liquid chromatography for the separation/analysis of congo red (CR) in water and drysaltery was established. Fe₃O₄@ILs-β-CDCP showed a higher adsorption capacity toward CR. CR was adsorbed rapidly by Fe₃O₄@ILs-β-CDCP (adsorption efficiency: 95%) and eluted by ethanol (elution efficiency: 96%) at room temperature. Under the optimal conditions, preconcentration factor of the proposed method was 20-fold. The linear range, correlation coefficient (R ²), detection limit (DL) and relative standard deviation were found to be 0.005–100.00 µg mL^?1, 0.9910, 1.8 g L^?1 and 0.61% (n = 3, c = 5.00 µg mL^?1), respectively. The adsorption mechanism of CR on Fe₃O₄@ILs-β-CDCP was studied through the FTIR analysis. The accuracy of the developed method was confirmed by spiking city water, lake water, pond water and drysaltery. Fe₃O₄@ILs-β-CDCP can be used repeatedly for 10 times. This proposed method had been successfully applied to the determination of CR in real samples.     

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.     

A magnetic knitting aromatic polymer as a new sorbent for use in solid-phase extraction of organics

Magnetic knitting aromatic polymers (Fe₃O₄/KAPs) are introduced here as a new kind of sorbents. KAPs are hyper-cross-linked-polymers that were prepared via a Friedl-Crafts reaction from triphenylphosphine and benzene as building blocks. The Fe₃O₄/KAP composite was obtained by coprecipitation of KAP with magnetite nanoparticles. The resulting Fe₃O₄/KAP is shown to be a viable magnetic sorbent for various organic materials such as the phenylurea herbicides (PUHs), including metoxuron, monuron, chlortoluron, monolinuron and buturon, and also for various phthalates, polycyclic aromatic hydrocarbons and chlorophenols. The Fe₃O₄/KAP was characterized by means of Brunauer-Emmett-Teller surface area measurements, Fourier-transform infrared spectroscopy, thermogravimetry, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Following desorption with acetonitrile, the analytes were quantified by using HPLC with UV detection. The effects of adsorbent dosage, extraction time, sample pH, ionic strength, desorption solvent and desorption time were optimized for the PUHs. Under optimal conditions, response is linear from 0.5–1.0 up to 50 ng·mL^?1 for the five PUHs. Lower limits of detection range between 0.05 and 0.30 ng·mL^?1. Other figures of merit include (a) high enrichment factors (60–297), (b) good recoveries (91.8–106.5%), and (c) relative standard deviations of <8.4%. The method was successfully applied to analysis of the PUHs in real samples (bottled mixed juice, milk and soymilk). The results indicate that such Fe₃O₄/KAPs have a wide application scope as an adsorbent for use in magnetic solid phase extraction.

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Graphical abstract A magnetic knitting aromatic polymer based nanocomposite (Fe₃O₄/KAP) was prepared by a one-pot method and explored as an absorbent for magnetic solid-phase extraction (MSPE) of phenylurea herbicides (PUHs) from bottled mixed juice, milk and soymilk samples before quantitation by HPLC with UV detection.

     

Trace analysis of Pt (IV) metal ions in roadside soil and water samples by Fe3O4/graphene/polypyrrole nanocomposite as a solid-phase extraction sorbent followed by atomic absorption spectrometry

A novel Fe₃O₄/graphene/polypyrrole nanocomposite has been successfully synthesised via a simple chemical method and applied as a new magnetic solid-phase extraction (MSPE) sorbent for the separation and pre-concentration of trace amounts of Pt (IV) in environmental samples followed by flame atomic absorption spectrometric (FAAS) detection. The nanocomposite has been characterised by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) spectroscopy. Seven important parameters, affecting the extraction efficiency of Pt (IV), including pH, adsorption time, desorption solvent type and concentration, desorption time, elution volume and sample volume, were investigated. Under the optimised conditions, the calibration graph was linear in the range of 50–1500 μg L^?1 (R = 0.993). The detection limit and pre-concentration factor (PF) for Pt (IV) were found to be 16 μg L^?1 and 112.5, respectively. Under the optimised solid-phase extraction (SPE) conditions, the adsorption isotherm and the adsorption capacity of the nanocomposite for Pt (IV) were studied. Pt (IV) adsorption equilibrium data were fitted well to the Langmuir isotherm and the maximum adsorption capacity of the magnetic sorbent was calculated from the Langmuir isotherm model as 416.7 mg g^?1. The precision of the method was studied as intraday and interday variations. A relative standard deviation percentage (RSD%) value less than 3.0 indicates that the method is precise. Also, the accuracy of the method was tested by the analysis of the standard reference material (NIST SRM 2556) and by recovery measurements on spiked real samples. It was also shown that the optimised method was suitable for the analysis of trace amounts of Pt (IV) in roadside soil, tap water and wastewater samples.     

Rapid magnetic solid-phase extraction based on magnetite/silica/poly(methacrylic acid–co–ethylene glycol dimethacrylate) composite microspheres for the determination of sulfonamide in milk samples

A novel magnetic solid-phase extraction (MSPE) sorbent, magnetite/silica/poly (methacrylic acid–co-ethylene glycol dimethacrylate) (Fe₃O₄/SiO₂/P(MAA-co-EGDMA)), was developed. This MSPE material was prepared by distillation–precipitation polymerization of MAA and EGDMA in the presence of Fe₃O₄/SiO₂ microspheres with the surface containing abundant reactive double bonds. The resultant sorbent material was characterized by elemental analysis, electron microscopy, X-ray diffraction and Fourier-transformed infrared spectroscopy. In this work, eleven sulfonamides (SAs) were selected as model analytes to validate the extraction performance of this new MSPE sorbent. Noticeably, the extraction can be carried out quickly, the extraction time for the SAs onto Fe₃O₄/SiO₂/P(MAA-co-EGDMA) sorbent can be clearly shortened to 0.5 min. The desorption solution of SAs was analyzed by LC–MS/MS, and the results showed that the recoveries of these compounds were in the range of 87.6–115.6%, with relative standard deviations ranging between 0.9% and 10.8%; the limit of detection were in the range of 0.5–49.5 ng/L.     

Simultaneous Analysis of Organophosphorus Pesticides in Water by Magnetic Solid-Phase Extraction Coupled with GC–MS

Magnetic solid-phase extraction (MSPE) coupled with gas chromatography–mass spectrometry was applied for the analysis of organophosphorus pesticides (OPPs) in water samples. We chose C18-functionalized Fe₃O₄@mSiO₂ microspheres as the magnetic sorbents to extract and enrich OPPs from water samples with the advantages of good solubility in water, large surface area and fast separation ability. In this study, six kinds of OPPs were analyzed and various parameters of MSPE procedure, including eluting solvent, the amount of magnetic absorbents and extraction time were optimized. Validation experiments showed that the optimized method had good linearity with correlation coefficients r ² > 0.98 and satisfactory precision with the relative standard deviation ≤10.7 %. The limits of detection were 1.8–5.0 μg L^?1 and the limits of quantification ranged from 6.1 to 16.7 μg L^?1. We concluded that the proposed method was successfully applied to analyze OPPs in real water samples and the results indicated that it had the advantages of simplicity, convenience and efficiency.     

Evaluation of a magnetic polysulfone microcapsule containing organic modified montmorillonite as a novel solid-phase extraction sorbent with chlorophenols as model compounds

A porous polysulfone microcapsule containing organic modified montmorillonite and magnetic nanoparticles (OMMT-Fe₃O₄@PSF) has been successfully prepared by a phase-inversion method and evaluated as a magnetic solid-phase extraction (MSPE) sorbent for clean-up and enrichment of 4-chlorophenol (4-CP) and 2-chlorophenol (2-CP) in aqueous samples. Compared with a microcapsule containing the conventional extraction sorbent C18 (C18-Fe₃O₄@PSF), OMMT-Fe₃O₄@PSF had much lower cost, a faster adsorption rate, and superior uptake amounts for the investigated analytes. The proposed microcapsule has been developed for the extraction of 4-CP and 2-CP from environmental water samples and their analysis by high-performance liquid chromatography with UV detection (HPLC-UV). Various parameters, such as pH, extraction time, the mass of sorbent, and the desorption conditions, have been evaluated and the calibration curves of the chlorophenols were linear (R² ≥ 0.9985) in the range from 1.01 to 104.5 ng mL⁻¹. The limits of detection at a signal-to-noise (S/N) ratio of 3 were 0.22 and 0.17 ng mL⁻¹ and the limits of quantification calculated at S/N = 10 were 1.52 and 1.07 ng mL⁻¹ for 2-CP and 4-CP, respectively. The recoveries of 2-CP and 4-CP from natural water and the treated wastewater samples were in the range of 84.4-115% with relative standard deviations (RSDs) lower than 7.0%. The results have demonstrated the suitability of the MSPE approach for the analysis of trace chlorophenols in aqueous samples.     

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 Zineb by C18-functionalised paramagnetic nanoparticles and determination by first-derivative spectrophotometry

Fe₃O₄-SiO₂-C₁₈ paramagnetic nanoparticles have been synthesised and used as magnetic solid-phase extraction (MSPE) sorbent for the extraction of Zineb from agricultural aqueous samples under ultrasonic condition and quantified through a first-derivative spectrophotometric method. The produced magnetic nanoparticles were characterised by using scanning electron microscopy, X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy and zeta potential reader. The Fe₃O₄-SiO₂-C₁₈ paramagnetic nanoparticles had spherical structures with diameters in the range of 198–201 nm. Further, MSPE was performed by dispersion of Fe₃O₄-SiO₂-C₁₈ paramagnetic nanoparticles in a buffered aqueous solution accompanied by sonication. Next, the sorbents were accumulated by applying an external magnetic field and were washed with 4-(2-pyridylazo) resorcinol-dimethyl sulfoxide solution, for the purpose of desorbing the analyte. The extraction conditions (sample pH, washing and elution solutions, amount of sorbents, time of extraction, sample volume and effect of diverse ions), as well as Zineb-PAR first-order derivative spectra, were also evaluated. The calibration curve of the method was linear in the concentration range of 0.055–24.3 mg L^?1 with a correlation coefficient of 0.991. The limit of detection and limit of quantification values were 0.022 and 0.055 mg L^?1, respectively. The precision of the method for 0.27 mg L^?1 solution of the analyte was found to be less than 3.2%. The recoveries of three different concentrations (0.27, 1.37 and 13.7 mg L^?1) obtained 98.3%, 98.5% and 96.0%, respectively. The proposed Fe₃O₄-SiO₂-C₁₈ paramagnetic nanoparticles were found to have the capability of reusing for 7.0 times.     

Magnetic solid-phase extraction using Schiff base ligand supported on magnetic nanoparticles as sorbent combined with dispersive liquid-liquid microextraction for the extraction of phenols from water samples

ABSTRACT

In this work, the magnetic sorbent was developed by covalent binding of a Schiff base ligand, N,N’-bis(3-salicyliden aminopropyl)amine (salpr), on the surface of silica coated magnetic nanoparticles (Salpr@SCMNPs). The core-shell nanoparticle was applied for the magnetic solid-phase extraction (MSPE) combined with dispersive liquid-liquid microextraction (DLLME) of phenolic compounds from water samples prior to gas chromatography-flame ionisation detector (GC?FID). Characterisation of the Salpr@SCMNPs was performed with different physicochemical methods such as Fourier transform infrared (FT-IR), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM). Variables affecting the performance of both extraction steps such as pH of the water sample, the sorbent amount, the desorption conditions, the extraction time; and extraction solvent were studied. Under the optimised conditions, the analytical performances were determined with a linear range of 0.01–100 ng mL^?1 and a limit of detection at 0.003–0.02 ng mL^?1 for all of the analytes studied. The intra-day (n = 5) and inter-day (n = 3) relative standard deviations (RSD%) of three replicates were each demonstrated in the range of 6.9–8.9% and 7.3–10.1%, respectively. The proposed method was executed for the analysis of real water samples, whereby recoveries in the range of 92.9–99.0% and RSD% lower than 6.1% were attained.