Facile synthesis of magnetic hypercrosslinked polystyrene and its application in the magnetic solid-phase extraction of sulfonamides from water and milk samples before their HPLC determination

Recent advances in synthesis and applications of hyper-crosslinked porous organic polymers for sample pretreatment: A review

Hyper-crosslinked porous organic polymers (HCPs) are nanoporous materials synthesized through Friedel-Crafts reactions, which covalently crosslink monomeric units to integrate the high porosity, large surface area, and tunable pore architecture of porous networks with the structural diversity, lightweight nature, and compositional flexibility inherent to polymeric systems. These materials exhibit excellent thermal/chemical stability, facile surface functionalization, and scalable synthesis protocols, enabling versatile applications in drug delivery, chromatography, catalysis, and gas storage. In recent years, HCPs have gained prominence as advanced sorbents in sample pretreatment, owing to their inherent physicochemical characteristics that align closely with the critical requirements for high-performance extraction or purification adsorbents. This review aims to present recent advancements in HCPs preparation, with a primary focus on their applications in analytical sample preparation. A systematic investigation of HCP-based adsorption mechanisms, structural design principles, and fabrication methodologies was conducted to establish robust structure-function correlations through performance evaluation across diverse extraction techniques, including column solid-phase extraction (SPE), magnetic SPE (MSPE), solid-phase microextraction (SPME), and other miniaturized SPE formats, for the pre-concentration of target analytes in food, environmental, and biological samples. Finally, we delineate current challenges and future research directions, proposing innovative engineering strategies to advance HCPs for addressing complex analytical matrix challenges.

Fe3O4@SiO2-BD-DADB-COF is proposed as a novel magnetic covalent organic framework for the determination and extraction of 15 macrolide antibiotics in water and honey

In our research, an emerging magnetic covalent organic framework (Fe3O4@SiO2-BD-DADB-COF) was formulated through Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), etc. Several parameters affecting the extraction process were refined. Accordingly, a novel method of determining 15 macrolides (MALs) in honey and water was established through the Fe3O4@SiO2-BD-DADB-COF as a magnetic solid-phase extraction (MSPE) adsorbent and ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). In consequence, the standard curves for the 15 MALs exhibited an exceptional linearity from 0.1 to 200 μg L-1, and the correlation coefficients (R 2) varied from 0.9990 to 0.9999. The recoveries fell between 70.01% and 115.56%, with the relative standard deviations (RSDs) being below 9.93% (n = 5). The detection limits reached 0.001-0.075 μg L-1 with the quantification limits being 0.004-0.228 μg L-1. Ultimately, the method was excellently applied to the analysis of MALs in honey and water.

Molecularly imprinted polymers-coated magnetic covalent organic frameworks for efficient solid-phase extraction of sulfonamides in fish

In this study, covalent organic frameworks (COFs) were grown in situ on magnetic nitrogen-doped graphene foam (MNGF), and the resulting composite of COFs-modified MNGF (MNC) was wrapped by molecularly imprinted polymers (MNC@MIPs) for specifically capturing SAs. A magnetic solid phase extraction (MSPE) method for SAs was established using MNC@MIPs with good magnetic responsiveness. The adsorption performance of MNC@MIPs was superior to that of non-molecularly imprinted polymers (MNC@NIPs), with shorter adsorption/desorption time and higher imprinting factors. A high-efficiency SAs analytical method was developed by fusing HPLC and MNC@MIPs-based MSPE. This approach provides excellent precision, a low detection limit, and wide linearity. By analyzing fish samples, the feasibility of the approach was confirmed, with SAs recoveries and relative standard deviations in spiked samples in the ranges of 77.2-112.7 % and 2.0-7.2 %, respectively. This study demonstrated the potential use of MNC@MIPs-based MSPE for efficient extraction and quantitation of trace hazards in food.

Construction of Cu2Y2O5/g-C3N4 Novel Composite for the Sensitive and Selective Trace-Level Electrochemical Detection of Sulfamethazine in Food and Water Samples

The most frequently used sulfonamide is sulfamethazine (SMZ) because it is often found in foods made from livestock, which is hazardous for individuals. Here, we have developed an easy, quick, selective, and sensitive analytical technique to efficiently detect SMZ. Recently, transition metal oxides have attracted many researchers for their excellent performance as a promising sensor for SMZ analysis because of their superior redox activity, electrocatalytic activity, electroactive sites, and electron transfer properties. Further, Cu-based oxides have a resilient electrical conductivity; however, to boost it to an extreme extent, a composite including two-dimensional (2D) graphitic carbon nitride (g-C3N4) nanosheets needs to be constructed and ready as a composite (denoted as g-C3N4/Cu2Y2O5). Moreover, several techniques, including X-ray diffraction analysis, scanning electron microscopy analysis, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy were employed to analyze the composites. The electrochemical measurements have revealed that the constructed g-C3N4/Cu2Y2O5 composites exhibit great electrochemical activity. Nevertheless, the sensor achieved outstanding repeatability and reproducibility alongside a low limit of detection (LOD) of 0.23 µM, a long linear range of 2 to 276 µM, and an electrode sensitivity of 8.86 µA µM-1 cm-2. Finally, the proposed GCE/g-C3N4/Cu2Y2O5 electrode proved highly effective for detection of SMZ in food samples, with acceptable recoveries. The GCE/g-C3N4/Cu2Y2O5 electrode has been successfully applied to SMZ detection in food and water samples.

Nano-sized magnetic molecularly imprinted polymer solid-phase microextraction for highly selective recognition and enrichment of sulfamethoxazole from spiked water samples

This research, described ultrasound-assisted dispersive magnetic solid-phase microextraction, which is efficient for the enrichment and determination of sulfamethoxazole, based on magnetic molecularly imprinted polymer (USA-DMSPME-MIP). Meanwhile, the initial characterization of Fe3O4-MIP was completed by conventional methods and well-known protocols to obtain recognition and adsorbing performance at pre-specified optimum conditions. Fe3O4-MIP exhibited information regarding its selective recognition pattern towards sulfamethoxazole. The USA-DMSPME-MIP parameters were optimized by response surface methodology, and based on optimum conditions, this efficient method for the extraction and enrichment of sulfamethoxazole from spiked water samples and quantification by HPLC-UV was used. The enhanced technique indicates the limit of detection is 2 ng mL-1 for sulfamethoxazole, along with excellent linear range with coefficients of determination >0.99 and good recoveries for spiked water samples (94.2 and 98.2 %) with RSDs less than 3.5 %.

Determination of sulfonamide antibiotics by magnetic porous carbon solid-phase extraction coupled with capillary electrophoresis

Sulfonamide antibiotics (SAs) have been widely used as antibacterial drugs for the prevention and treatment of livestock and poultry diseases, but they seriously threaten human health because they can accumulate in humans. Therefore, it is highly important to develop methods for monitoring sulfonamide residues in aquaculture and food. In this research, based on the generation of porous carbon (PC) by the pyrolysis of sodium citrate, magnetic porous carbon (PC@Fe3O4) was synthesized by a solvothermal method and used as an adsorbent for the magnetic solid-phase extraction of SAs. The effects of the proportion of PC in PC@Fe3O4, adsorbent dosage, adsorption time, eluent type, extraction pH, salt concentration and eluent dosage on the extraction efficiency were systematically studied. The adsorption performance and behavior of PC@Fe3O4 on SAs were evaluated using adsorption kinetics and adsorption isotherms, and the adsorption mechanism was preliminarily discussed. Under optimal conditions, combined with capillary electrophoresis diode array detection, a sensitive detection method for SAs was developed. The proposed method can be used for the determination of six SAs in fishpond water and milk samples, with a linear range of 0.5-200 ng mL-1, detection limits of 0.24-0.34 ng mL-1, and spiked recoveries of 85.9-109.0 %.

Fabrication and characterization of magnetic mesoporous nanoparticles for efficient determination and magnetic separation of sulfonamides in food samples

A magnetic, mesoporous core/shell structured Fe3O4@SiO2@mSiO2 nanocomposite was synthesized and employed as a magnetic solid phase extraction (MSPE) sorbent for the determination of trace sulfonamides (SAs) in food samples. The synthesized nanocomposite was characterized by transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, X-ray diffraction, N2 sorption analysis and vibrating sample magnetometry. The results showed that Fe3O4@SiO2@mSiO2 possessed a mesoporous structure with a large surface area. Batch experiments were carried out to investigate the adsorption ability for SAs. Fe3O4@SiO2@mSiO2 showed fast kinetics and high adsorption capacity, and the pseudo-second-order model and Langmuir adsorption isotherm are well fitted with the experimental data, indicating that chemical adsorption might be the rate-limiting step. Moreover, the high adsorption capacity can be maintained for at least 8 runs, indicating excellent stability and reusability. The proposed method exhibited good linearity in the range of 0.2-500 μg L-1, the R2 values of all the analytes were greater than 0.99 and the LODs were all lower than 0.2 μg L-1. Furthermore, real food samples were successfully analyzed with Fe3O4@SiO2@mSiO2 and high recoveries varying from 89.7% and 110.6% were obtained with low relative standard deviations ranging from 1.78% to 6.91%. The Fe3O4@SiO2@mSiO2 magnetic nanocomposite is a promising sorbent for the efficient extraction of SAs from complex food samples.

Magnetic phytic acid-modified kapok fiber biochar as a novel sorbent for magnetic solid-phase extraction of antidepressants in biofluids

BACKGROUND

Therapeutic drug monitoring (TDM) of antidepressants is essential for monitoring patient medication to avoid drug toxicity, complications, or nonadherence. Chromatographic techniques with high sensitivity and reproducibility are the main detection method for antidepressants. Effective pretreatment of biological sample processes is necessary prior to instrumental analysis. Magnetic solid-phase extraction (MSPE) has received much attention for its advantages of simple operation, rapidity, cost-effectiveness and low organic solvent consumption. Therefore, the development of a suitable and green magnetic sorbent for the detection of antidepressants in plasma and urine is apparently necessary. (88) RESULTS: A magnetic phytic acid-modified kapok fiber biochar sorbent (Fe3O4/PAKFBC) was successfully synthesized by pyrolytic impregnation and physical milling methods. Fe3O4/PAKFBC exhibited a large specific surface area (214 m2 g-1) and a rich pore structure (5-10 nm). The extraction equilibrium, using 10 mg Fe3O4/PAKFBC, can be completed in about 1 min. The density functional theory (DFT) results showed that the adsorption mechanism of Fe3O4/PAKFBC on the six antidepressants mainly included electrostatic interactions, van der Waals interactions, π-π interactions and weak hydrogen bonding. Examination using the greenness assessment tools showed that the developed method exhibited excellent greenness. By combining with liquid chromatography-ultraviolet (LC-UV), a quantitative method with good linearity (R2 > 0.993) and relative recoveries (92.4-107.7%) and negligible matrix effect (-11.5-6.0%) was developed. The Fe3O4/PAKFBC successfully detected six antidepressants in plasma and urine samples, requiring no pH adjustment with buffer salts. (142) SIGNIFICANCE: The environmental sustainability of the proposed methods was affirmed by six greenness evaluation tools, all indicating exceptional eco-friendliness. The Fe3O4/PAKFBC demonstrated outstanding greenness in both its creation and analytical application, proving highly effective in real sample applications and showcasing potential for broader use. This study contributes to a deeper and broader understanding of the microscopic adsorption mechanism, which can help in the optimization and development of more green sorbents. (69).

Carrageenan derived polyelectrolyte complexes material: An effective bifunctional for electrochemical sensing of sulfamethazine and antibacterial activity

Biopolymer-derived polyelectrolyte complexes (PECs) are a class of materials that have emerged as promising candidates for developing advanced electrochemical sensors due to their tunable properties, biocompatibility, cost-effective production, and high surface area. PECs are formed by combining positively and negatively charged polymers, resulting in a network with intriguing properties that can be tailored for specific sensing applications. The resultant PECs-based nanocomposites were used to modify the glassy carbon electrode (GCE) to detect the sulfamethazine (SFZ) antibiotic drug. In addition, electrochemical studies using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and differential pulse voltammetry (DPV) are used to evaluate the SFZ detection ability. Similarly, various microscopic and spectroscopic studies investigated the nano composite's structural features and morphological behavior. The κ-CGN/P(Am-co-DMDAAc)-GO modified GCE demonstrated excellent detection ability of SFZ with the nano molar range and without interference with similar structural components. Furthermore, the newly fabricated electrode κ-CGN/P(Am-co-DMDAAc)-GO was derived from naturally available materials, water-soluble, low cost, biocompatible, exhibits good conductivity, and excellent catalytic properties. Finally, κ-CGN/P(Am-co-DMDAAc)-GO- modified GCE has versatile, practical applications for detecting SFZ in real-time samples and determining the efficacy of an antibacterial activity.

Green preparation of magnetic pyrene-based hyper-cross-linked polymer using dual-purpose ferric chloride reagent for extraction of polycyclic aromatic hydrocarbons from natural water bodies

A magnetic hyper-cross-linked polymer Fe3O4/HCPPYR was prepared using pyrene as the monomer and formaldehyde dimethyl acetal (FDA) as the cross-linking agent. The objective of green chemistry was achieved by employing FeCl3 during the synthesis, as it played a dual role of a catalyst for the Friedel-Crafts reaction and an iron source for the synthesis of magnetic Fe3O4, thus maximizing efficiency and minimizing waste. Fe3O4/HCPPYR was applied as a sorbent for magnetic solid-phase extraction (MSPE) to extract fifteen polycyclic aromatic hydrocarbons (PAHs) from water. The effects of different parameters such as the quantity of adsorbent, the extraction time, the desorption conditions, the pH value and the effect of the salt concentration on the extraction efficiency were optimized. A simple and efficient method in combination with gas chromatography-mass spectrometry (GC-MS) (Fe3O4/HCPPYR-MSPE/GC-MS) was developed and successfully applied for the detection of PAHs in environmental water samples The analytical method showed LODs in the range of 0.004-0.06 µg L-1, which proved to be adequate for the detection all 15 PAHs at trace concentration. Spiked recoveries of PAHs in actual water samples ranged from 85.2 % to 118.5 % with relative standard deviations (RSDs) below 10.2%. These results indicate that the method has a good potential for reusability and possesses excellent sensitivity. This study showcased the potential of Fe3O4/HCPPYR composites in effectively removing organic pollutants from the aqueous environments, demonstrating their ability for water treatment applications.

MIL-88B(Fe)/cellulose microspheres as sorbent for the fully automated dispersive pipette extraction towards trace sulfonamides in milk samples prior to UPLC-MS/MS analysis

MIL-88B(Fe)/cellulose microspheres (MIL-88B(Fe)/CMs) were characterized by the means of SEM, XRD, TGA and N₂ adsorption-desorption test. The composite was used as the sorbent for fully automated dispersive pipette extraction (DPX), after introducing CMs as the support, the loss of MIL-88B(Fe) in DPX was avoided. Coupled to UPLC-MS/MS, the proposed method was employed for the analysis of trace sulfonamides (SAs) in milk samples. The parameters affecting the extraction efficiency, including pH of sample solution, the rate of aspiration and dispense, amount of the adsorbent, type and volume of elution solvent were optimized. Under the optimal conditions, good linearity (r ≥ 0.9978 for five analytes), high sensitivity (limit of detection: 0.00660-0.0136 μg kg^-1) and satisfactory recovery (69.8%-100.9%) were achieved. Furthermore, the sorbent showed desirable reusability over eight extraction cycles. Compared with other methods for the pretreatment of SAs, the proposed method showed advantages of high sensitivity, less sorbent consumption, environmental friendliness and automation, providing a promising protocol for sample preparation.

In-situ sorbent formation for the extraction of pesticides from honey

An organic polymer was re-precipitated in solution to use as an adsorbent in dispersive solid phase extraction of some pesticides from honey samples prior to their determination by high performance liquid chromatography-tandem mass spectrometry. In this approach, different deep eutectic solvents were prepared using lysine and their ability in elution of the analytes from the adsorbent surface were tested. A diluted honey solution was transferred into a glass test tube and then a solution of polystyrene dissolved in dimethylformamide was injected into the solution. By doing this, polystyrene re-precipitated in the solution and dispersed in whole parts of it as many tiny particles. Then the mixture was centrifuged and the adsorbed analytes on the particles were eluted using a proper hydrophilic deep eutectic solvent. Central composite design approach was used for optimization of effective parameters. The limits of detection and quantification were in the ranges of 0.06-0.20 and 0.22-0.69 ng/g, respectively. The calibration curves obtained by matrix-matched standard solutions were linear in the range of 0.69-500 ng/g with coefficient of determinations ≥0.9962. The method provided high extraction recoveries (70-99%) and enrichment factors (140-198), and an acceptable precision (relative standard deviations ≤7.1%). This article is protected by copyright. All rights reserved.

Synthesis of the Magnetically Nanoporous Organic Polymer Fe3O4@SiO2-NH2-COP and Its Application in the Determination of Sulfonamide Residues in Surface Water Surrounding a Cattle Farm

Efficient extractions of trace antibiotic residues in the environment are a key factor for accurate quantification of the residues. A new nanoporous material, namely, magnetically covalent organic polymer (MCOP, Fe₃O₄@SiO₂-NH₂-COP) was synthesized in this work and was used for magnetic solid-phase extraction (MSPE). The combination of MSPE with high-performance liquid chromatography separation together with ultraviolet detection (HPLC-UV) was established as an effective method for the determination of four sulfonamide (SA) residues in surface water surrounding a cattle farm. The synthesized magnetic material was characterized by SEM, TEM, FT-IR, magnetic properties measurement system (MPMS), and nitrogen gas porosimetry. The material possessed many attractive features, such as a unique microporous structure, a larger specific surface area (137.93 m²·g⁻¹) than bare Fe₃O₄ (24.84 m²·g⁻¹), high saturation magnetization (50.5 emu·g⁻¹), open adsorption sites, and high stability. The influencing parameters, including pH, the used amount of MCOPs, the type of eluent, adsorption solution, and desorption time, were optimized. Under the optimized conditions, the method conferred good linearity ranges (R² ≥ 0.9990), low detection limits (S/N = 3, LOD, 0.10–0.25 μg·L⁻¹), and satisfactory recoveries (79.7% to 92.2%). The enrichment factor (EF) for the four SAs was 34.13–38.86. The relative standard deviations of intraday (n = 5) and of interday (n = 3) were less than 4.8% and 8.9%, respectively. The equilibria between extraction and desorption for SAs could be reached within 150 s. The proposed method was sensitive and convenient for detecting SA residues in complex environmental matrices, and the successful application of the new MCOPs as an adsorbent was demonstrated.

Rapid Determination of Vitamin D3 in Aquatic Products by Polypyrrole-Coated Magnetic Nanoparticles Extraction Coupled with High-Performance Liquid Chromatography Detection

A method using polypyrrole-coated Fe3O4 (Fe3O4@PPy composites) based extraction coupled with high performance liquid chromatography was developed for adsorption and detection of trace vitamin D3 (VD3) in aquatic products. The fabricated Fe3O4@PPy composites were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and thermogravimetric analysis. Fe3O4@PPy composites showed efficient adsorption of VD3 at pH 9.0 and 25 °C with a dose of 25 mg per 10 mL of sample solution and an adsorption time of 11 min. Methanol was selected as the desorption solvent to recover VD3 from Fe3O4@PPy composites after 3 min of static treatment. Fe3O4@PPy composites can be used for VD3 adsorption at least two times. The developed method showed a good linearity for VD3 determination in the range of 0.1-10 μg/mL with a correlation coefficient of 0.9989. The limits of detection and quantification were 10 ng/mL and 33 ng/mL, respectively. The recovery of VD3 in a spiking test was 97.72% with a relative standard deviation value of 1.78%. The content of VD3 in nine aquatic products was determined with this method. Our results show that Fe3O4@PPy composites provide a convenient method for the adsorption and determination of VD3 from the complex matrix of aquatic products.

Molecularly imprinted wax

The development of an elution-free solid-phase extraction (SPE) process is of special interest in sample pretreatment. Due to the phase-change merits at relatively low temperatures and easy dissolution in n-hexane, wax spheres show great potential in this field. However, the conventional wax spheres possess a low affinity towards the target analytes when they are used as SPE adsorbents. In this study, using octadecanoic acid as the functional monomer and wax as the matrix, molecularly imprinted wax (MIW) spheres were successfully prepared. The obtained MIW spheres displayed remarkable molecular recognition ability and high selectivity towards the template. Interestingly, the as-synthesized molecularly imprinted wax (MIW) could be dissolved in n-hexane or melted by heating for subsequent fluorescence and mass spectrum analysis without the target elution process. Moreover, the melted MIW exhibited high repeatability, sensitivity and specificity for solid-state fluorescence detection. We believe that the imprinting method presented in this study will open a new window in analytical chemistry.

Multi-class, multi-residue determination of 132 veterinary drugs in milk by magnetic solid-phase extraction based on magnetic hypercrosslinked polystyrene prior to their determination by high-performance liquid chromatography-tandem mass spectrometry

A quantitative multi-class multi-residue analytical method was developed for the determination of veterinary drugs in milk by high-performance liquid chromatography - tandem mass spectrometry (HPLC-MS/MS). A total of 132 veterinary drugs investigated belonged to almost 15 classes including sulfonamides, β-lactams, tetracyclines, quinolones, macrolides, nitrofurans, nitroimidazoles, phenicols, lincosamides, pleuromutilins, macrocyclic lactones, quinoxaline antibiotics, benzimidazoles, anthelmintics, coccidiostats and some others. A magnetic solid-phase extraction procedure was developed using magnetic hypercrosslinked polystyrene (HCP/Fe₃O₄) for the sample preparation prior to HPLC-MS/MS without deproteinization step. The results indicated recoveries of 85-107% for 14 sulfonamides, 85-120% for 13 β-lactams, 89-115% for 4 tetracyclines, 82-119% for 14 quinolones, 82-115% for 8 macrolides, 97-109% for 4 nitrofurans, 84-115% for 10 nitroimidazoles, 89-114% for 3 phenicols, 86-111% for 3 lincosamides, 97-102% for 2 pleuromutilins, 72-88% for 4 macrocyclic lactones, 87-104% for 4 quinoxaline antibiotics, 76-119% for 21 benzimidazoles, 79-115% for 12 anthelmintics, 81-118% for 12 coccidiostats and 75-119 % for 5 unclassified drugs, with relative standard deviations (RSDs) of less than 20%, and the LOQs ranged from 0.05 to 1 μg kg^-1. This methodology was then applied to field-collected real milk samples and trace levels of some veterinary drugs were detected.

Lateral flow immunoassay based on dual spectral-overlapped fluorescence quenching of polydopamine nanospheres for sensitive detection of sulfamethazine

Herein, we propose a lateral flow immunoassay (LFIA) based on the dual spectral-overlapped fluorescence quenching of polydopamine nanospheres (PDANs) caused by the inner filter effect to sensitively detect sulfamethazine (SMZ). The fluorescence quenching LFIA device consists of four parts: absorbent pad, polyvinyl chloride pad, sample pad, and nitrocellulose membrane. Compared with traditional quenchers such as gold nanoparticles (AuNPs) with single spectral-overlapped quenching ability, PDANs can quench the excitation light and emission light of three fluorescence donors (aggregation-induced emission fluorescent microsphere, AIEFM; fluorescent microsphere, FM; and quantum dot bead, QB). The fluorescence intensity changes (ΔF) are numerically larger for PDANs-LFIA (ΔF_AIEFM = 2315, ΔF_FM = 979, ΔF_QB = 910) than those for AuNPs-LFIA (ΔF_AIEFM = 1722, ΔF_FM = 833, ΔF_QB =;520). AIEFM-based PDANs-LFIA exhibits a large ΔF (2315) in response to the changes in the SMZ concentration, and produces a high signal-to-noise ratio. The limit of detection (LOD) and visual LOD of LFIA based on PDANs quenching AIEFM for the detection of SMZ in chicken are 0.043 and 0.5 ng/mL, respectively. The results confirm that the proposed method can be used for the detection of hazardous materials in practical applications.

Functionalized Magnetic Nanomaterials in Agricultural Applications

The development of functional nanomaterials exhibiting cost-effectiveness, biocompatibility and biodegradability in the form of nanoadditives, nanofertilizers, nanosensors, nanopesticides and herbicides, etc., has attracted considerable attention in the field of agriculture. Such nanomaterials have demonstrated the ability to increase crop production, enable the efficient and targeted delivery of agrochemicals and nutrients, enhance plant resistance to various stress factors and act as nanosensors for the detection of various pollutants, plant diseases and insufficient plant nutrition. Among others, functional magnetic nanomaterials based on iron, iron oxide, cobalt, cobalt and nickel ferrite nanoparticles, etc., are currently being investigated in agricultural applications due to their unique and tunable magnetic properties, the existing versatility with regard to their (bio)functionalization, and in some cases, their inherent ability to increase crop yield. This review article provides an up-to-date appraisal of functionalized magnetic nanomaterials being explored in the agricultural sector.

A magnetic solid phase extraction based on UiO-67@GO@Fe3O4 coupled with UPLC-MS/MS for the determination of nitroimidazoles and benzimidazoles in honey

A novel composite material consisting of zirconiumbiphenyldicarboxylate metal-organic framework, graphite oxide and ferroferric oxide was fabricated by a facile one-step method and served as a magnetic solid phase extraction sorbent for the simultaneous determination of nitroimidazoles and benzimidazoles in honey. The amount of graphite oxide for the synthesis of composite material and analysis parameters were optimized. The optimum parameters were: dipotassium hydrogen phosphate buffer solution (pH 6) as diluent solvent, adsorption time 10 min, desorption time 5 min, methanol/acetonitrile (1:1, V/V) as desorption solvent. The targets were detected by ultra-high performance liquid chromatography tandem mass spectrometry. The recoveries of twelve analytes ranged in 70.5%-103.4% with relative standard deviations lower than 12.9% (n = 3). The quantification limits were 0.2-0.6 μg/kg. Using the composite material as sorbent, a simple, rapid and environmental-friendly method based on magnetic solid phase extraction was successfully developed for determination of seven nitroimidazoles and five benzimidazoles in honey.

Determination of sulfonamides in milk and egg samples by HPLC with mesoporous polymelamine-formaldehyde as magnetic solid-phase extraction adsorbent

In this work, magnetic mesoporous polymelamine-formaldehyde composites were synthesized via a facile Schiff base reaction. The magnetic mesoporous polymelamine-formaldehyde composites combined both the properties of mesoporous polymelamine-formaldehyde and the magnetism of NH₂ -SiO₂ @Fe₃ O₄ nanoparticles, possessing high specific surface area (150.66 m² g^-1 ) and good magnetism (24.50 emu g^-1 ). The magnetic mesoporous polymelamine-formaldehyde composites were employed as magnetic adsorbent for the extraction of sulfonamides. Under optimal conditions, good linearities with correlation coefficients higher than 0.9984 were obtained between peak area and sulfonamides concentration (2-200 μg L^-1 ) with limits of detection in the range of 0.33-0.58 μg L^-1 . The established method was successfully applied for the determination of sulfonamides in egg and milk samples. The adsorption mechanisms demonstrated that the adsorption of magnetic mesoporous polymelamine-formaldehyde composites toward sulfonamides was a multilayer process, and adsorption kinetics followed the pseudo-second-order model.

Three-dimensional magnetic stannic disulfide composites for the solid-phase extraction of sulfonamide antibiotics

In the present work, three-dimensional (3D) and flower-like SnS₂ materials were coated on the surface of Fe₃O₄@nSiO₂ through an in-situ growth method. The 3D architecture could avoid the accumulation and reaggregation with better stability and was beneficial for the exposure of more active sites. The prepared magnetic SnS₂ composites were used for the enrichment of sulfonamide antibiotics (SAs), and various experimental parameters affecting the extraction efficiency were investigated. The results showed the equilibrium of extraction and desorption towards target SAs could be reached within 3 min by using the Fe₃O₄@nSiO₂-SnS₂ composites. Under optimized conditions, the proposed approach possessed good linearity in the range of 0.1-200 ng·mL^-1 with correlation coefficients r² above 0.9964 and low limits of detection (LODs) from 0.025 to 0.250 ng·mL^-1 for the five target SAs. Moreover, good repeatability was obtained with the intra-day and inter-day precision in terms of relative standard deviations (RSDs) within 1.1%-10.8% and 7.4%-13.1%, and the recoveries under three spiked concentrations were between 81.8% and 119.7% with adequate accuracy. Different samples including tap water, milk and honey were collected for magnetic solid-phase extraction and determination of target SAs by using the obtained Fe₃O₄@nSiO₂-SnS₂ composites to demonstrate the utility. All the results indicated that the proposed method had great potential for effective preconcentration and determination of SAs in complex samples.

Electrochemical methods for the determination of antibiotic residues in milk: A critical review

Several antibiotics have been applied to veterinary medicine due to their broad-spectrum of antibacterial activity and prophylactic power. Residues of these antibiotics can be accumulated in dairy cattle, in addition to promoting contamination of the environment and, in more serious cases, in milk, causing a public health problem. Different regulatory agencies establish maximum residue limits for these antibiotics in milk, so it becomes important to develop sensitive analytical methods for monitoring these compounds. Electrochemical techniques are important analytical tools in analytical chemistry because they present low cost, simplicity, high sensitivity, and adequate analytical frequency (sample throughput) for routine analyses. In this sense, this review summarizes the state of the art of the main electrochemical sensors and biosensors, instrumental techniques, and sample preparation used for the development of analytical methods, published in the last five years, for the monitoring of different classes of antibiotics: aminoglycosides, amphenicols, beta-lactams, fluoroquinolones, sulfonamides, and tetracyclines, in milk samples. The different strategies to develop electrochemical sensors and biosensors are critically compared considering their analytical features. The mechanisms of electrochemical oxidation/reduction of the antibiotics are revised and discussed considering strategies to improve the selectivity of the method. In addition, current challenges and future prospects are discussed.

Determination of nitrofuran metabolites in honey using a new derivatization reagent, magnetic solid-phase extraction and LC-MS/MS

In this study, 5-nitro-2-furaldehyde (5-NFA) was proposed as a new derivatizing agent for nitrofuran metabolites. It reacts with nitrofuran metabolites producing the parent nitrofurans (furazolidone, furaltadone, nitrofurantoin, and nitrofurazone). Magnetic hypercrosslinked polystyrene (HCP/Fe₃O₄) was first used for magnetic solid phase extraction (MSPE) clean-up before the determination of nitrofuran metabolite derivatives in honey via LC-MS/MS. Main parameters affecting the derivatization and MSPE efficiency were investigated in detail and the optimal conditions were found. The method was validated using honey spiked with the four metabolites at 1, 2 and 200 μg kg^-1. Recoveries of >85% were achieved for the all analytes. The matrix calibration curve was fitted with the correlation coefficient (R²) > 0.99 in the range of 1-200 μg kg^-1. Precision values expressed as relative standard deviation (RSD) were <12% and <15% for intra-day and inter-day precision, respectively. The limits of detection (LODs) for the nitrofuran metabolites were of 0.1-0.3 μg kg^-1 and the limits of quantitation (LOQs) were of 0.3-1.0 μg kg^-1. The proposed LC-MS/MS method was applied to the analysis of real honey samples.

Development of an electrochemical sensor for the determination of antibiotic sulfamethazine in cow milk using graphene oxide decorated with Cu-Ag core-shell nanoparticles

Determination and sensing of antibiotics in dairy products are the biggest challenges in the world. In continuation of our earlier study, a facile and novel determination method for the detection of sulfamethazine (SMZ) in cow milk has been developed using a glassy carbon electrode modified with graphene oxide decorated with Cu-Ag core-shell nanoparticles. The Cu-Ag core-shell nanoparticles and graphene oxide were synthesized and characterized via different techniques such as TEM, SEM, XRD and FTIR. The as-synthesized Cu-Ag core-shell nanoparticles were used for the decoration of the glassy carbon electrode modified with graphene oxide. The electroanalytical measurements including cyclic voltammetry and square wave voltammetry were performed and compared with HPLC, which was utilized for the determination of SMZ in cow milk. The experimental conditions were optimized to obtain a well-defined response signal. The concentration linear range was 10-1000 μM and the limit of detection was 0.46 μM for S/N = 3. The obtained results show good agreement with HPLC reported data.

Construction of hypercrosslinked polymers for high-performance solid phase microextraction of phthalate esters from water samples

Design and synthesis of novel coatings for solid phase microextraction (SPME) is urgently needed for sample pretreatment. In this study, three hypercrosslinked polymers (HCPs) were constructed by the facile Friedel-Crafts alkylation reactions between tetraphenylethylene (TPE) and 1,4-bis(chloromethyl)benzene (BCMB), 4,4'-bis(chloromethyl)-1,1'-biphenyl (BCMBP), and cyanuric chloride (CC), respectively. The newly-synthesized HCPs were employed as SPME coatings for the extraction of phthalate esters (PAEs). Various parameters influencing the SPME efficiencies, including extraction time and temperature, ionic strength, stirring rate, desorption temperature and time were optimized. Under the optimal conditions, low limits of detection (0.003-0.033 μg L ^- 1), wide linearity (0.01-10 μg L ^- 1) and good repeatability (4.1-9.3%) were achieved. The HCPs-based SPME method was successfully applied for the determination of eight PAEs in environmental water and bottled water samples with recoveries from 75.3% to 116%. This method provides a good alternative for monitoring trace level of PAEs in water samples.

Preparation of a ZIF-67-modified magnetic solid phase extraction material and its application in the detection of pyridine ring insecticides

An advanced and reliable m-SPE material of a water-stable ZIF was developed for the determination of trace praziquantel and pymetrozine in spinach and broccoli.

The fabrication of a covalent triazine-based organic framework for the solid-phase extraction of fourteen kinds of sulfonamides from meat samples

A novel covalent triazine-based organic framework (CTF), SCAU-2, was fabricated and used as an adsorbent for the solid-phase extraction of fourteen kinds of sulfonamides (SAs) from meat. Another CTF, SCAU-1, was adopted as a comparison material, as it has a similar motif. A series of structural characterization steps was carried out on the synthesized materials and several parameters were investigated during the extraction process, including the amount of adsorbent, the dilution ratio, the pH of the sample, and the washing and elution solvents. After detection with UHPLC-Q/TOF-MS/MS, the results revealed that SCAU-2 showed high extraction efficiencies towards the selected SAs. The LOD values are from 0.05 to 0.54 ng g-1, and the recoveries are from 84.1% to 91.9%, with RSDs ranging from 3.2% to 4.8% for SCAU-2 when spiked at 50 ng g-1. The results demonstrated that the proposed method has good applicability for the determination of SAs in complicated samples.

Trends in sensitive detection and rapid removal of sulfonamides: A review

Sulfonamides in environmental water, food, and feed are a major concern for both aquatic ecosystems and public health, because they may lead to the health risk of drug resistance. Thus, numerous sensitive detection and rapid removal methodologies have been established. This review summarizes the sample preparation techniques and instrumental methods used for sensitive detection of sulfonamides. Additionally, adsorption and photocatalysis for the rapid removal of sulfonamides are also discussed. This review provides a comprehensive perspective on future sulfonamide analyses that have good performance, and on the basic methods for the rapid removal of sulfonamides.

Synthesis of magnetic nanoparticles to detect Sudan dye adulteration in chilli powders

Magnetic nanoparticles were synthesised to extract Sudan dyes from chilli powders. The adsorbents used were magnetic ferroferric oxide nanoparticles coated with polystyrene. The extraction procedures for Sudan dyes comprised liquid-solid extraction and magnetic solid phase extraction. The conditions were optimised to achieve efficient magnetic solid phase extraction, including extraction and desorption time, type and volume of the desorption solvent, and the mass of the adsorbents. Repeatability tests showed satisfactory recovery rates of 80.2-115.8%, with a relative standard deviation <3.8%. The results suggested that the proposed extraction method was effective and efficient to extract Sudan dyes from chilli powders. The extraction process was simpler compared with traditional approaches because the adsorbents can be rapidly removed from the sample matrix using a permanent magnet. The use of recyclable adsorbents decreased the cost greatly. Chilli powder samples collected from local markets in Singapore were tested using the proposed method under optimum conditions.

Synthesis of Graphene Oxide Based Sponges and Their Study as Sorbents for Sample Preparation of Cow Milk Prior to HPLC Determination of Sulfonamides

In the present study, a novel, simple, and fast sample preparation technique is described for the determination of four sulfonamides (SAs), namely Sulfathiazole (STZ), sulfamethizole (SMT), sulfadiazine (SDZ), and sulfanilamide (SN) in cow milk prior to HPLC. This method takes advantage of a novel material that combines the extractive properties of graphene oxide (GO) and the known properties of common polyurethane sponge (PU) and that makes sample preparation easy, fast, cheap and efficient. The PU-GO sponge was prepared by an easy and fast procedure and was characterized with FTIR spectroscopy. After the preparation of the sorbent material, a specific extraction protocol was optimized and combined with HPLC-UV determination could be applied for the sensitive analysis of trace SAs in milk. The proposed method showed good linearity while the coefficients of determination (R²) were found to be high (0.991-0.998). Accuracy observed was within the range 90.2-112.1% and precision was less than 12.5%. Limit of quantification for all analytes in milk was 50 μg kg^-1. Furthermore, the PU-GO sponge as sorbent material offered a very clean extract, since no matrix effect was observed.