Magnetic Solid-phase Extraction Adsorbent Research Articles

Progress in preparation of plant biomass-derived biochar and application in pesticide residues field

随着农药的广泛使用,其已普遍存在于环境中,对人们的身体健康产生巨大影响。因此,环境中农药残留的去除和分析检测对保护人体安全健康至关重要。同时,农药在环境中残留浓度低,需要一种对目标物有较强选择性和富集作用,并对环境影响小的前处理吸附剂。植物源生物炭是由植物源生物质作为碳源衍生得到的材料,其比表面积大、孔容量高、表面官能团可调节,且环境相容性好,其原料植物源生物质的价格低廉、来源广泛并可再生,是一种廉价高效的吸附剂。该文主要综述了近10年来植物源生物炭用于环境中农药残留去除和分析检测前处理的应用进展。其中在农药残留去除方面的应用主要包括降低农药在土壤中的移动性,修复手性农药造成的污染,负载降解农药的细菌及作为化肥的缓释载体。在农药残留分析检测前处理方面,植物源生物炭可用作分散固相萃取、固相微萃取和磁性固相萃取的吸附剂来选择性吸附水果和蔬菜中的有机磷类和三唑类农药,以及水环境中的有机氯类农药。另外,还介绍了植物源生物炭的吸附机理,详细阐述了基于计算模拟如密度泛函理论、分子动力学模拟和巨正则蒙特卡洛模拟的吸附机理研究并讨论了其优势。最后,总结了植物源生物炭在农药去除和农药残留分析检测前处理方面应用的优势,指出了其在农药残留领域应用待解决的问题。

Synthesis of polydopamine coated magnetic halloysite nanotubes for fast enrichment and extraction of anthraquinones in brewed slimming tea

In this work, a magnetic halloysite nanotubes composite material modified with polydopamine (MHNTs@PDA) was synthesized through a facile and green synthesis strategy, and employed as an efficient adsorbent for magnetic solid-phase extraction (MSPE) of three anthraquinones. The material showed very fast adsorption ability (adsorption time of 3 min), good reusability and strong magnetic response. The main parameters affecting the extraction efficiency of MSPE, including adsorption time, amounts of adsorbent, sample pH, salt concentration and desorption conditions, were investigated and optimized. By coupling MHNTs@PDA-based MSPE with HPLC-UV, the method exhibited good linearity (R2 ≥ 0.9944) in the concentration range of 5–1000 μg L-1 and low limits of detection (1.0–1.5 μg L-1) for anthraquinones. Finally, the developed method was successfully applied to determine anthraquinones in brewed slimming tea, and the obtained recoveries were in the range of 73.5–119.1%, with RSD less than 9.7%.

Design and synthesis of amphiphilic carboxyl-functionalized magnetic polymer microspheres for fast determination of paraquat and its four metabolites in human urine samples prior to ultra-high performance liquid chromatography-high resolution mass spectrometry

In cases of low concentration paraquat (PQ) poisoning, as the disease progresses over a long period of time, the prototype PQ may not be detected in the urine, which has a significant negative impact on the precise treatment of the poisoning. But PQ poisoning can also be confirmed by the detection of specific metabolites of PQ in the urine samples. In the present study, core-shell amphiphilic carboxyl-functionalized magnetic polymer microsphere (Amphiphilic-MPs-COOH) was prepared, and the as-prepared Amphiphilic-MPs-COOH was characterized by transmission electron microscope (TEM), scanning electron microscope (SEM), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and thermogravimetry and differential thermogravimetry analyses (TG-DTG). Then, the Amphiphilic-MPs-COOH was employed as a magnetic solid-phase extraction (MSPE) adsorbent for pretreatment and rapid determination of PQ and its four metabolites from urine samples prior to ultra-high performance liquid chromatography-high resolution mass spectrometry (UPLC-HRMS). The extraction-elution conditions of Amphiphilic-MPs-COOH towards PQ and its metabolites were optimized in spiking urine samples to obtain the best MSPE efficiency. The adsorption mechanism of PQ and its metabolites by Amphiphilic-MPs-COOH involves electrostatic attraction and π-π stacking interactions. Moreover, the effect of different ratios of hydrophilic monomer NVP and functional monomer 4-VBA on the extraction and purification performance of PQ and its metabolites in urine samples. And the results revealed that both hydrophilic monomer and functional monomer were important for the adsorption of PQ and its metabolites, and the addition of the appropriate amount of the hydrophilic monomer NVP can improve the compatibility of the adsorbent with the urine substrate. In addition, this study compared the matrix effect of the Amphiphilic-MPs-COOH based MSPE method and the commercial Waters Oasis WCX SPE method. The results showed that the Amphiphilic-MPs-COOH based MSPE method developed in this paper had better resistance to matrix interference. Under optimal conditions, the recoveries of PQ and its metabolites were ranging from 84.5 to 103%, with relative standard deviations (RSDs) of 1.1–6.3%. While the limits of detection (LODs, S/N ≥ 3) and limits of quantification (LOQs, S/N ≥ 9) of the method were in range of 0.1–1.6 μg/L and 0.3–4.8 μg/L, respectively. Finally, the established MSPE-UPLC-HRMS method in this study was used to confirm PQ poisoning not only based on detecting PQ prototype, but also on its four metabolites, providing strong technical support for clinical precision treatment.

One-pot synthesis of nickel oxide/nickel ferrite nanocomposite and application to dispersive magnetic solid-phase extraction of zinc(II) ions in water and milk samples

An inorganic magnetic nanocomposite named nickel oxide/nickel ferrite (NiO/NiFe2O4) was synthesized using a one-pot hydrothermal method. After successful synthesis and characterization of the nanocomposite, it was applied as a novel adsorbent for dispersive magnetic solid-phase extraction and pre-concentration of zinc(II) ions followed by flame atomic absorption spectrometric detection. The developed method was validated by exploring the affecting parameters, including the amount of the adsorbent (100 mg), sample volume (150.0 mL), sample pH (6.0), adsorption time (15 min), type and eluent concentration (acetic acid 2.0 M), and desorption time (15 min). In the optimal condition, the calibration graph is linear in the concentration range of 0.3–20.0 ng mL1 with a satisfactory determination coefficient of 0.9996. The limit of detection and limit of quantification of the method are 0.04 and 0.13 ng mL1, respectively. The precision of the method in the term of intra-day and inter-day relative standard deviation with six replicates are 1.5% and 3.5%, respectively. A certified reference sample was analyzed applying the developed method and the results confirmed its high accuracy. The applicability of the method was also assayed by determination of Zn(II) ions in various water and milk samples, and the acceptable relative recovery values (96.0–102.0%) were obtained for the spiked samples.

Efficient adsorption removal of organic nitrogen pesticides: Insight into a new hollow NiO/Co@C magnetic nanocomposites derived from metal-organic framework

The removal of pesticides is a prerequisite for reducing potential threat to environmental safety. It is significant to exploit some adsorbents with excellent adsorption performance, facile separation and recovery. Metal-organic framework (MOF)-based magnetic nanocomposites have received extensive attention in terms of pollutant adsorption. Thus, a new hollow NiO/Co@C magnetic nanocomposites derived from MOF was successfully assembled via simple solvothermal reaction, in which cobalt (Co) ions as inducers to conduct the formation of hollow MOFs by regulating the chemical transformation process, and benefiting from its coordination effect, the carbonized bimetallic Ni-Co-MOF were transformed into magnetic-carbon composites by maintaining its initial skeleton without the tedious preparation of Fe3O4. The hollow structure can accelerate the mass transfer efficiency and the magnetism is conducive to rapid and convenient separation. The composite was used as magnetic solid-phase extraction (MSPE) adsorbent and the adsorption removal of organic nitrogen pesticides (ONPs) for the first time. NiO/Co@C contained hollow porous structure, resulting in high pesticides adsorption performance, as high as 62.2 mg g−1. Furthermore, the adsorption properties and mechanisms of ONPs had been discussed in detail including adsorption dynamics and thermodynamics. More importantly, NiO/Co@C could not only realize easy solid–liquid separation, but also demonstrate excellent reusability and stability. After nine cycles and the extraction recovery still retained higher than 90%. Therefore, NiO/Co@C has great promise as an effective adsorbent for pretreatment of aqueous samples and removal of hazardous pollutants.

Biomass magnetic porous carbon prepared from mangosteen shell for the preconcentration of three bisphenols from beverages followed by liquid chromatography with quadrupole-Orbitrap high-resolution mass spectrometry determination.

Natural biomass magnetic porous carbon was successfully prepared via a cost-effective and green route using mangosteen shells as raw material. The prepared magnetic porous carbon was used as a magnetic solid-phase extraction adsorbent for bisphenols enrichment from beverages followed by high-performance liquid chromatography-quadrupole-Orbitrap high-resolution mass spectrometry. Parameters affecting extraction efficiency including sample solution pH, adsorbent amount, extraction time, eluent type, and volume were optimized. Results showed that biomass magnetic porous carbon had excellent adsorption properties for bisphenols due to its large specific surface area and abundant functional groups, which could form hydrogen bonding and π-π stacking with bisphenols. The enrichment factor of 3 bisphenols was in the range of 15-19. Under optimum conditions, favorable linearity for all analytes was obtained with correlation coefficients higher than 0.998. Recoveries of spiked samples were in the range of 88.5-105.1% with a relative standard deviation of 3.4-5.5%. These results demonstrated that magnetic porous carbon may be a promising adsorbent for the enrichment of aromatic compounds.

Waste toner-derived micro-materials as low-cost magnetic solid-phase extraction adsorbent for the analysis of trace Pb in environmental and biological samples.

Lead (Pb) is a toxic heavy metal and is commonly used in industrial applications. Thus, Pb poisoning is a concerning public health issue worldwide. The amounts of lead in natural water, urine, and blood can serve as significant indicators for monitoring the exposure of Pb poisoning. Waste toner has the characteristics of both "waste" and "resource," as it is a "resource in the wrong place." Here, a low-cost carboxylate-functionalized magnetic adsorbent was first synthesized from waste toner by a simple thermal treatment and served as a novel adsorbent with a flexible multidentate O-donor for pre-concentration of trace Pb. The characterization, adsorption behavior, and various factors of adsorption and desorption were adequately optimized, and prior to graphite furnace atomic absorption spectrometry (GFAAS) detection, a new magnetic solid-phase extraction method was proposed for the analysis of Pb in real environmental water and biological samples. The developed method exhibited a low detection limit (0.003μgL-1), high enrichment factor (88.6-fold), good linearity (0.01-0.3μgL-1), satisfactory precision with relative standard deviations of 7.9% (n = 7, CPb = 0.02μgL-1), fast adsorption kinetics (5min), and strong ability to overcome matrix interference. Validation was also performed by analyzing a certified standard reference material, and the method was successfully applied to real tap water, lake water, human urine, and human blood serum with satisfactory recoveries of 92.6-109%.

Determination of sunset yellow, allura red, and fast green using a novel magnetic nanoadsorbent modified with Elaeagnus angustifolia based on magnetic solid-phase extraction by HPLC

Sunset yellow (SY), allura red (AR) and fast green (FG) are frequently used in commercial food products, although they are considered to be hazardous to public health due to their toxic efficacy and high exposure risk potency. In this study, a new, rapid, and reliable method based on a magnetic solid-phase extraction (MSPE) was developed for the simultaneous determination of SY, AR, and FG. Fe3O4 modified with Elaeagnus angustifolia was used for the first time as an adsorbent (Fe3O4-EA) in MSPE. It was characterized with scanning electron microscopy, Brunauer Emmet Teller surface area analysis and X-ray diffraction. MSPE parameters were optimized in terms of pH, adsorption, and elution time and elution volume. High-performance liquid chromatography was used for dye quantitation. Analytical separation was performed by applying ammonium acetate buffer, acetonitrile, and methanol as the mobile phase to a C18 reverse-phase analytical column. Intraday and inter-day repeatability of the method performed at the concentration of 0.2, 1.0 and 2.0 µg/mL exhibited <8.1% RSD (n=3). The limit of detection values was between 0.05-0.1 µg/mL. The adsorption data of SY, AR and FG on Fe3O4-EA were fitted with the Langmuir model with qmax values of 45.0, 70.4 and 73.0 mg/g, respectively.

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@Fe3 O4 ) 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@Fe3 O4 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 (20mg) and reduced extraction time (3min) 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.

Rapid and sensitive analysis of trace β-blockers by magnetic solid-phase extraction coupled with Fourier transform ion cyclotron resonance mass spectrometry

A rapid and sensitive method for analyzing trace β-blockers in complex biological samples, which involved magnetic solid-phase extraction (MSPE) coupled with Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS), was developed. Novel nanosilver-functionalized magnetic nanoparticles with an interlayer of poly(3,4-dihydroxyphenylalanine) (polyDOPA@Ag-MNPs) were synthesized and used as MSPE adsorbents to extract trace β-blockers from biological samples. After extraction, the analytes loaded on the polyDOPA@Ag-MNPs were desorbed using an organic solvent and analyzed by FTICR-MS. The method was rapid and sensitive, with a total detection procedure of less than 10 min as well as limits of detection and quantification in the ranges of 3.5–6.8 pg/mL and 11.7–22.8 pg/mL, respectively. The accuracy of the method was also desirable, with recoveries ranging from 80.9% to 91.0% following the detection of analytes in human blood samples. All the experimental results demonstrated that the developed MSPE-FTICR-MS method was suitable for the rapid and sensitive analysis of trace β-blockers in complex biological samples.

Thiol-ene click synthesis of β-cyclodextrin-functionalized covalent organic framework-based magnetic nanocomposites (Fe3O4@COF@β-CD) for solid-phase extraction and determination of estrogens and estrogen mimics

Estrogens and estrogen mimics have been proved to be possible carcinogenic risks to human health and have drawn extensive attention in the fields of food safety. In this work, a thiol-ene click strategy was proposed for synthesis of a novel β-cyclodextrin-functionalized covalent organic framework-based magnetic nanocomposites (Fe3O4@COF@β-CD) and then employed as adsorbents for magnetic solid-phase extraction (MSPE) of estrogens and estrogen mimics. The Fe3O4@COF@β-CD possess the merits of superparamagnetism, large surface area, and excellent adsorption performance to estrogens and estrogen mimics. By combining with high-performance liquid chromatography-fluorescence detector (HPLC-FLD), the developed method gave a good linearity (R2 ≥ 0.9989) and low limits of detection (0.9–3.4 μg kg−1) under the optimized conditions. The applicability of the presented MSPE-HPLC-FLD method was demonstrated by real milk and meat samples analysis, with the satisfactory recoveries ranging from 89.0 to 105.4% and the relative standard deviations (RSDs) ≤ 5.7%.

Facile preparation of core-shell magnetic organic covalent framework via self-polymerization of two-in-one strategy as a magnetic solid-phase extraction adsorbent for determination of Rhodamine B in food samples

The monomer of two-in-one molecular design strategy (i.e., A2B2 type monomer) 1,6-bis(4-formylphenyl)-3,8-bis((4-aminophenyl) ethynyl)) pyrene (BFBAEPy) was self-polymerized and coated on the modified Fe3O4 surface to synthesize a magnetic covalent organic framework (Fe3O4@COF) nanocomposite with a core-shell structure. Before high-performance liquid chromatography with ultraviolet detection (HPLC-UV) determination, Fe3O4@COF was used as a magnetic solid-phase extraction (MSPE) adsorbent to enrich Rhodamine B (RhB) illegally added to Chili powder and Chinese prickly ash. It had a large specific surface area and suitable pore size, which promoted the efficient adsorption of RhB dye and eliminated the interference of the matrix. Several key parameters affecting the extraction recovery rate were investigated, including adsorption capacity, adsorption time, pH, ionic strength, elution solvent, elution volume and elution time. Under the best optimized conditions, within the linear detection range of 0.05–5 µg/mL for RhB with the limit of detection (LOD) was 0.0038 µg/mL, excellent linearity (correlation coefficient R2=0.9997), and good repeatability (relative standard deviations RSD%< 3.8%), satisfactory extraction recovery rate (91.7%-97.5%). Therefore, the application of the established method to the detection of RhB in food samples has bright prospects.

Simultaneous determination of 11 quinolone residues in freshwater fish samples by magnetic solid‐extraction coupled to liquid chromatography‐tandem mass spectrometry

In this study, well-defined core-shell ethylenediamine-functional magnetic ferroferric oxide polymers were prepared and were fully characterized by transmission electron microscopy, scanning electron microscopy, FTIR spectroscopy, and vibrating sample magnetometry. Then, it was used as a magnetic solid-phase extraction adsorbent for simultaneous determination of 11 trace quinolone residues in freshwater fish samples coupled to liquid chromatography-tandem mass spectrometry. The obtained results revealed that the adsorbent showed good extraction efficiency and the adsorption mechanisms referred to hydrogen bond and π-π stacking interaction. Moreover, the magnetic solid-phase extraction conditions were also carefully optimized. The limits of quantitation of 11 quinolones were in the range of 0.15-0.36 μg/kg, while spiking recoveries were in the range of 80.2-99.5% for the 11 quinolones in freshwater fish samples at four spiked levels including limits of quantitation, 1.0, 40.0, and 80.0 μg/kg with the relative standard deviations ranging from 0.8 to 9.1%. The proposed method was applied to analyze 45 freshwater fish samples, and enrofloxacin was detected in 91.1% samples with concentrations ranging from 0.659 to 333 μg/kg. It could be concluded that the proposed method is fast, simple, sensitive, and accurate for the routine monitor of freshwater fish.

Magnetic solid-phase extraction based on multi-walled carbon nanotubes combined ferroferric oxide nanoparticles for the determination of five heavy metal ions in water samples by inductively coupled plasma mass spectrometry

Abstract An excellent magnetic multi-walled carbon nanotubes (MMWCNT) containing carboxyl material modified with ferroferric oxide (Fe3O4) nanoparticles was synthesized as the adsorbent for magnetic solid-phase extraction (MSPE) of five heavy metal ions (Pb2+, Cu2+, Co2+, Cd2+, Cr4+) in water samples followed by on-line inductively coupled plasma mass spectrometry (ICP-MS) detection. The characteristics of the adsorbent were analyzed using Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), and vibrating sample magnetometer (VSM). Some factors affecting extraction efficiency including pH of sample solution, the amount of adsorbent, extraction method and time, concentration and volume of desorption solvent, desorption time and evaluation of coexisting ions were optimized. Under the optimum conditions, good linearity (r ≥ 0.9951) was obtained within the range of 0.1–50.0 ng·mL−1. The limits of detection (LODs) and limits of quantification (LOQs) were 4.0–25.0 ng·L−1 and 15.0–80.0 ng·L−1, respectively. And satisfactory recoveries of five heavy metal ions ranged from 81.11% to 105.53% were acquired, and the relative standard deviations (RSDs) were no more than 6.05%. The MMWCNT synthesized had strong adsorption force for the five investigated heavy metal ions, respectively. Hence, the proposed method was so suitable and sensitive that it can be applied to the determination of trace analysis of heavy metals in water samples.

Thiol-Yne Click Postsynthesis of a Sulfonate Group-Enriched Magnetic Microporous Organic Network for Efficient Extraction of Benzimidazole Fungicides.

The lack of functional groups or binding sites largely hindered the broad application of microporous organic networks (MONs). Herein, we report the fabrication of the sulfonate group-enriched magnetic MON composite (MMON-SO3H@SO3Na) via the combination of the sulfonic acid group containing the monomer and thiol-yne click postmodification for efficient magnetic solid-phase extraction (MSPE) of benzimidazole fungicides (BZDs) from complex sample matrices. The well-defined core-shell-structured MMON-SO3H@SO3Na was obtained and served as an advanced adsorbent for MSPE for concentrating and monitoring trace BZDs. The MMON-SO3H@SO3Na with numerous sulfonate groups provides plenty of ion-exchange, hydrogen-bonding, and π-π sites, leading to the favorable affinity to BZDs via multiple interaction mechanisms. The MMON-SO3H@SO3Na-based MSPE-high-performance liquid chromatography method afforded a wide linear range, low limits of detection, large enrichment factors, good precisions, and reusability for BZDs. Trace BZDs in complex vegetables and fruit samples were successfully detected by the established method. The MMON-SO3H@SO3Na also exhibited good selectivity toward multiple types of polar contaminants containing hydrogen-bonding sites and aromatic structures. This work provided a new postsynthesis strategy for constructing novel and multifunctioned magnetic MONs for preconcentration of trace analytes in a complex matrix.

One-Pot Strategy as a Green and Rapid Method to Fabricate Magnetic Molecularly Imprinted Nanoparticles for Selective Capture of Sulfonylurea Herbicides.

Magnetic solid-phase extraction (MSPE) based on molecularly imprinted nanoparticles (MINs) has attracted wide attention in sample pretreatment because it combines the merits of high selectivity and quick extraction procedures. However, laborious, time and solvent-consuming steps were involved in the synthesis of magnetic imprinted particles in existing approaches. To circumvent this dilemma, a green and rapid "one-pot" strategy was proposed to prepare MINs. Halosulfuron-methyl (HSM) was selected as a template molecule, and Gaussian 09 simulation software was employed to screen the 2,4,6-trivinylboroxin pyridine complex (TBP) as a functional monomer. Subsequently, the fabrication was simply conducted using a hydrothermal approach by mixing self-assembly solution of TBP-HSM, Fe3+, Fe2+, dimethyl sulfoxide, and azobisisobutyronitrile in one-pot with a total reaction time of 3.0 h. Various characterized results well evidenced the successful imprint of HSM and the resultant HSM-MINs presented satisfying superparamagnetism and saturation magnetism. Under the optimized parameters, the obtained HSM-MINs displayed good recognition capability and selectivity toward HSM (recognition coefficient was 2.60), as well as a satisfactory saturation adsorption capacity (1781 μg/g). The quantification of sulfonylurea herbicides at trace levels in environmental water and soil samples was selected as a paradigm to demonstrate the practicality and reliability of HSM-MINs/MSPE. The present study provides a convenient, reliable, and green approach for fabricating a magnetic molecular-imprinting adsorbent for MSPE.

An in vitro assessment for human skin exposure to parabens using magnetic solid phase extraction coupled with HPLC

Skin contact was a significant source of human exposure to parabens during the use of personal care products. In this study, a novel and simple in vitro evaluation method for human skin exposure to parabens was established for the first time. Firstly, magnetic porous carbon (MPC) derived from discarded cigarette butts was prepared as an adsorbent of magnetic solid-phase extraction (MSPE), which provided a fast and efficient sample preparation method with satisfactory extraction performance for parabens in cosmetics and was easy to couple with high performance liquid chromatography. Secondly, the extraction conditions were optimized including the etching ratio of KOH, amount of MPC, extraction time, pH, salt concentration, desorption solvent volume and desorption time. Under the optimized conditions, the limits of detection were between 0.25 and 0.34 ng mL−1 and the spiked recoveries were in the range of 85.8–112.6%. Thirdly, the developed method was successfully employed to determine five typical parabens in real unspiked cosmetic samples, and two parabens were detected at a relatively high level. Then, the developed method was applied to in vitro assays. The absorbable dose of parabens in cream was investigated and in vitro experiments were further designed with agarose-simulated skin to demonstrate the penetration ability of parabens. In conclusion, these results indicated that parabens did have the risk of entering the body through the skin and the exposure was preferably no more than 3 h with skin contact.

Preparation of Cysteine‐Functionalized Fe3O4 Magnetic Nanoparticles for Determination of Cu2+

AbstractCysteine‐functionalized Fe3O4 magnetic nanoparticles were synthesized by thiol‐ene click reaction and characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier‐transform infrared spectroscopy (FT‐IR), X‐ray diffraction spectrometry (XRD), thermal gravimetric analysis (TGA), vibrating sample magnetometer (VSM), X‐ray photoelectron spectroscopy (XPS), specific surface area (BET) analysis and pore size distribution analysis. The obtained magnetic materials were employed as a magnetic solid phase extraction adsorbent combined with inductively coupled plasma‐atomic emission spectrometry (ICP‐AES) for determination of Cu2+. Several parameters affecting extraction efficiency, including eluent concentration, adsorption time, adsorbent amounts, and sample pH were investigated. Under the optimized conditions, the method was validated. Within the concentration range of 0.01–20 μg mL−1, The limit of detection (LOD) and the limit of quantification (LOQ) were determined to be 0.002 μg mL−1 and 0.007 μg mL−1, respectively. The adsorption percentage of Cu2+ ions remained above 87.0 % when the adsorption‐desorption data of Cu2+ ions through three cycles of the successive adsorption and desorption process. The results show that a reliable and rapid method was established for determination of Cu2+ ions.

Determination of fipronil and its metabolites in egg samples by UHPLC coupled with Q-Exactive high resolution mass spectrometry after magnetic solid-phase extraction

A novel, rapid and simple magnetic solid-phase extraction (MSPE) method combined with ultra-high performance liquid chromatography coupled with Q-Exactive high resolution mass spectrometry (UHPLC-Q-Exactive HRMS) was proposed for determination of fipronil and its metabolites in egg samples. In this study, novel polydopamine functionalized magnetic core-shell mesoporous silica nanoparticles (Fe3O4@nSiO2@mSiO2-PDA) were used as MSPE adsorbent for purification and enrichment of fipronil and its metabolites for the first time. The proposed method showed a good linearity (R2 ≥ 0.997), high sensitivity (limit of detection in the range of 0.002–0.004 μg/kg and limit of quantification in the range of 0.006–0.010 μg/kg), adequate recovery (80.6–95.3%) and repeatability (intra-day precision in the range of 2.2–6.7% and inter-day precision in the range of 4.4–10.7%). Finally, the developed MSPE-UHPLC-Q-Exactive HRMS method was successfully applied for determination of fipronil and its metabolites in egg samples.

A core-shell structured magnetic covalent organic framework as a magnetic solid-phase extraction adsorbent for phenylurea herbicides

In this work, a core-shell structured magnetic covalent organic framework named as M-TpDAB was constructed with 3,3'-diaminobenzidine (DAB) and 1,3,5-triformylphloroglucinol (Tp) as building units. M-TpDAB was characterized by infrared spectroscopy, nitrogen adsorption-desorption isotherms, powder X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Using the M-TpDAB as adsorbent, a simple and highly effective method was proposed for preconcentrating phenylurea herbicides before high performance liquid-phase chromatography analysis. In the optimized conditions, a good linearity was achieved within the range of 0.15-100 ng mL-1 for water sample, 1.0-100.0 ng mL-1 for tea drink samples. The limits of detection for the analytes were 0.05-0.15 ng mL-1 for water sample and 0.30-0.50 ng mL-1 for drink samples. Satisfactory recoveries of spiked target compounds were in the range of 84.6%-105% for water sample and 80.3%-102% for tea drink samples. Finally, the M-TpDAB based method was successfully used to determine phenylurea herbicides in tea drinks and water samples, demonstrating a good alternative for analyzing trace level of phenylurea herbicides in water samples.