Magnetic Covalent Organic Framework Research Articles

COF-SiO2@Fe3O4 Composite for Magnetic Solid-Phase Extraction of Pyrethroid Pesticides in Vegetables.

Pyrethroid pesticides (PYRs) have found widespread application in agriculture for the protection of fruit and vegetable crops. Nonetheless, excessive usage or improper application may allow the residues to exceed the safe limits and pose a threat to consumer safety. Thus, there is an urgent need to develop efficient technologies for the elimination or trace detection of PYRs from vegetables. Here, a simple and efficient magnetic solid-phase extraction (MSPE) strategy was developed for the simultaneous purification and enrichment of five PYRs in vegetables, employing the magnetic covalent organic framework nanomaterial COF-SiO2@Fe3O4 as an adsorbent. COF-SiO2@Fe3O4 was prepared by a straightforward solvothermal method, using Fe3O4 as a magnetic core and benzidine and 3,3,5,5-tetraaldehyde biphenyl as the two building units. COF-SiO2@Fe3O4 could effectively capture the targeted PYRs by virtue of its abundant π-electron system and hydroxyl groups. The impact of various experimental parameters on the extraction efficiency was investigated to optimize the MSPE conditions, including the adsorbent amount, extraction time, elution solvent type and elution time. Subsequently, method validation was conducted under the optimal conditions in conjunction with gas chromatography-mass spectrometry (GC-MS). Within the range of 5.00-100 μg·kg-1 (1.00-100 μg·kg-1 for bifenthrin and 2.5-100 μg·kg-1 for fenpropathrin), the five PYRs exhibited a strong linear relationship, with determination coefficients ranging from 0.9990 to 0.9997. The limits of detection (LODs) were 0.3-1.5 μg·kg-1, and the limits of quantification (LOQs) were 0.9-4.5 μg·kg-1. The recoveries were 80.2-116.7% with relative standard deviations (RSDs) below 7.0%. Finally, COF-SiO2@Fe3O4, NH2-SiO2@Fe3O4 and Fe3O4 were compared as MSPE adsorbents for PYRs. The results indicated that COF-SiO2@Fe3O4 was an efficient and rapid selective adsorbent for PYRs. This method holds promise for the determination of PYRs in real samples.

Magnetic covalent organic frameworks combined with HPLC for determination of alkylphenols

Alkylphenols are widely applied in the field of industry and agriculture, but their endocrine disrupting properties harm to human health. Moreover, alkylphenols often exhibit the low content in complex samples. Thus, we proposed magnetic covalent organic framework composites (Fe3O4@TatTpa) for efficient magnetic solid phase extraction (MSPE) of alkylphenols via hydrogen bonding, π-π and hydrophobic interactions. In combination with HPLC detection, good linearity (0.006–10 µg mL−1) with R2 (≥0.997) and low limit of detections (1.8–6 × 10−3 µg mL−1) were realized for alkylphenols. The proposed method was successfully employed to determine alkylphenols in soft drink, black oolong tea, and watermelon samples with satisfactory recoveries (86.1–118.5 %) and relative standard deviations (6.3–14.8 %).

Determination of bisphenols in food and its contact materials migration by magnetic solid-phase extraction coupled with LC-MS/MS

Bisphenols (BPs) pose a pervasive threat to human health due to their potential to leach from plastic packaging into food, thereby endangering the endocrine system. Given their low concentrations in complex samples, the development of a swift, efficient pretreatment method is imperative. In this study, a magnetic covalent organic framework (Fe3O4@TzDa) was synthesized via a layer-by-layer growth approach, utilized in rapid magnetic solid-phase extraction (MSPE) combined with liquid chromatography-tandem mass spectrometry (LC-MS/MS) for the determination BPs. This method exhibited remarkable sensitivity, detecting five BPs (BPS, BPF, BPA, BPB, and BPAF) at levels between 0.68 and 0.77 μg L−1. Fe3O4@TzDa nanocomposites maintained an extraction efficiency of approximately 98.0% over five cycles, ensuring robust and repeatable performance. Sample analysis, encompassing plastic bottled water, pear juice, mix juices, pop-top canned curry beef, and box-packed milk, yielded recoveries of 72.0%–114.0% (RSDs <7.5%, n = 5). Furthermore, BPs migration in sports cups and portable bottles was evaluated, revealing migration levels ranging from 0.0014 to 0.0058 mg kg−1. This study advances BP analysis by introducing a reliable method for their efficient determination in beverage samples from plastic food packages. The utilization of Fe3O4@TzDa underscores a pivotal advancement in sample preparation, enhancing both sensitivity and efficiency for the extraction and determination of BPs in food samples.

Application of continuous magnetic solid phase extraction in the extraction of tetracycline antibiotics from honey samples

This study aimed to develop a continuous magnetic solid phase extraction method in a narrow bore tube for the extraction of tetracycline antibiotics from honey samples before their determination with high performance liquid chromatography–diode array detector. In this work, a magnetic covalent organic framework is used as the sorbent. The extraction method is performed in a narrow bore tube by adding 25 mg of a magnetic sorbent prepared from melamine, barbituric acid, and Fe3O4 into the diluted honey sample solution. By using a magnet, the sorbent is moved up and down through the narrow bore tube for five times to improve extraction efficiency. After adsorption the analytes, they are eluted from the sorbent surface using 2,2–dimethoxypropane under vortexing. Then, by using a magnet, the eluent containing the extracted analytes are taken and evaporated with continuous flow of nitrogen. Finally, the residue containing the enriched analytes is reconstituted in microliter–level of mobile phase and injected into chromatographic system for quantitative analysis. Based on the outcomes, the method demonstrated good linearity (0.37–1000 ng g−1), high enrichment factors (175–203), good extraction recoveries (70–81 %), low LODs (0.11–0.18 ng g−1) and LOQs (0.37–0.60 ng g−1). The proposed method is effectively applied for quantification of tetracyclines in twenty–four honey samples. Considering the results, none of the honey samples was contaminated with the studied antibiotics. Regarding to the above–mentioned analytical advantages of the proposed method, its simplicity and rapidity, and green synthesis of the magnetic sorbent particles, the suggested method can be used as a routine method for the extraction of tetracyclines from honey samples.

Specific and Magnetic Covalent Organic Framework Confined Os Nanoclusterzyme for Interference‐Free and Ultrasensitive Biosensing

AbstractThe peroxidase (POD)‐mimic nanozymes can be a potential tool for point‐of‐care (POC) diseases diagnosis. However, the complex sample matrix and unspecific multiple‐enzyme activities of nanozyme can generate false background signal and decrease the diagnostic accuracy. Here, a magnetic and POD‐specific covalent organic framework (COF) confined osmium (Os) nanoclusterzyme Fe3O4@COF@Os is developed for biomarkers biosensing. First, found that the catalytic activity and specificity of Fe3O4@COF@Os can be regulated by the deoxidizers and the functional groups of COF ligands. By using ascorbic acid as deoxidizer and F functional COF ligands, Fe3O4@COF@Os displayed superior POD‐specific activity and negligible oxidase (OXD) and catalase (CAT) mimic activity. Therefore, Fe3O4@COF@Os can separate and analyze of targets in bio‐matrix without background interference. For application, Fe3O4@COF@Os based lateral flow assay is established for serum cancer biomarker prostate‐specific antigen, the detection limit is 3.83 pg mL−1. For clinical prostatic cancer samples, the accuracy is 100% with a correlation coefficient of 0.998 with commercial ELISA kit. For chronic disease biomarker sensing, salivary glucose can be quantified as low as 0.1 µm, with negligible background interference and favorable recyclability. This specific magnetic nanozymes can offer a promising pretreatment‐free and POC strategy for rapid and accurate diseases diagnosis.

Portable mass spectrometer with solid phase extraction using a novel amide-functionalized magnetic covalent organic framework adsorbent for on-site detection of two triphenylmethane dyes in aquatic products

Triphenylmethane dyes have been employed as fish drugs to prevent fish diseases for aquatic products in some developing countries. Their residues in aquatic products can bring significant impact on human health. In this study, an amide-functionalized magnetic covalent organic framework assisted magnetic solid phase extraction-portable mass spectrometry (MSPE-PMS) strategy was employed for on-site simultaneous detection of cationic triphenylmethane dyes, crystalline violet (CV) and brilliant green (BG). At the optimum MSPE conditions, the adsorbent was used to efficiently enrich CV and BG through magnetic solid phase extraction within 20 min with satisfied high concentration rate (10 folds). Then, the portable mass spectrometer was employed for simultaneous detection CV and BG within 0.2 min, with good linearity (R2 ≥ 0.9973) and low detection limit (0.135–0.694 μg kg−1). The results demonstrated the method is fast and simple and has the potential to detect triphenylmethane dyes residues in aquatic products quickly and on site.

Facile synthesis of magnetic covalent organic framework nanocomposites for the enrichment and quantification of trace organophosphorus pesticides in fruit juice

Facile synthesis of magnetic covalent organic framework nanocomposites for the enrichment and quantification of trace organophosphorus pesticides in fruit juice

Amino-functional magnetic covalent organic framework as an effective adsorbent for the determination of neonicotinoids in food samples.

Recently, covalent organic frameworks have gained popularity in sample pretreatment. However, the application of covalent organic frameworks in the enrichment of hydrophilic compounds remains a challenge. Thus, a functionalized magnetic covalent organic framework equipped with amino groups was constructed using a bottom-up functionalization strategy. Considering the advantages of this novel adsorbent such as high porosity, large adsorption capacity, and hydrophilic surface, a sensitive magnetic solid-phase extraction coupled with high-performance liquid chromatography-tandem mass spectrometry method was established for the effective determination of neonicotinoids. This method exhibited good linearities with correlation coefficients ranging from 0.9983 to 0.9995, low detection limits in the range 0.003-0.009 ng g-1 and 0.001-0.013 ng mL-1, and limits of quantification in the range 0.010-0.031 ng g-1 and 0.004-0.044 ng mL-1. Furthermore, satisfactory repeatability with relative standard deviations ≤ 6.7% and spiked recoveries between 82.3 and 99.8% were obtained. This work not only provided a promising adsorbent for the sensitive determination of trace-level neonicotinoids but also represented a unique insight for effective enrichment of super hydrophilic hazards.

Determination of abamectin in food based on magnetic covalent organic frameworks and HPLC-FLD

Abamectin is widely applied in agriculture and aquaculture, easily accumulates through the food chain and endangers human health. Sample pretreatment is the crucial and fundamental procedure prior to the precise analysis of trace abamectin. Herein, 4,4',4''-(1,3,5-triazine-2,4,6-triyl) trianiline (Tz) and 2,5-dihydroxy-1,4-benzenedicarboxaldehyde (Da) were modified on the surface of Fe3O4 nanoparticles to prepare magnetic covalent organic frameworks (Fe3O4@TzDa) adsorbent for abamectin. Depending on the large specific surface of TzDa and hydrogen bonding, π-π and hydrophobic interactions between TzDa and abamectin, the efficient magnetic solid-phase extraction (MSPE) of abamectin residue was achieved. Under the optimal MSPE conditions, the developed MSPE-HPLC-FLD based on Fe3O4@TzDa method for abamectin residue afforded good linearity (0.05–500 μg L−1) with high R2 (0.998) and low limit of detection (0.015 μg L−1). The developed MSPE-HPLC method was evaluated and successfully applied to determine abamectin residue in lake water, milk and peach juice samples with satisfactory recoveries (87.1–119.1%) and relative standard deviations (1.9–4.9%).

Ionic double-shell magnetic covalent organic framework for sharp and fast adsorption of critical metals

The recovery of critical metals (CMs) from waste streams has garnered increasing attention in recent years due to their increased demand, engineering applications, and vulnerability to supply disruptions. Herein, we synthesize two novel ionic materials, namely GIEC704a (magnetic covalent organic framework consisting of Fe3O4/TAGH-Dha) and GIEC704b (double-shell magnetic material formed of Fe3O4/TAGH-Dha/TpPa) using the solvothermal method for the recovery of CMs. The experimental data supported Langmuir's isotherm model, and the results showed that both GIEC704a and GIEC704b exhibited remarkable adsorption capacities (qmax). GIEC704a exhibited adsorption capacities of 1531.8, 884.9, and 729.9 mg/g, while GIEC704b had 1681.5, 854.7, and 800 mg/g (Al3+, Fe3+ and Cu2+) capacities, respectively. Furthermore, GIEC704a and GIEC704b demonstrated approximately 80 % adsorption of REEs with high adsorption capacities of 53.6, 52.3, 41.2 mg/g and 55.3, 55.4, and 43.4 mg/g (Lanthanum, Yttrium, and Neodymium), respectively with excellent selectivity. The large surface areas of GIEC704a and GIEC704b—147.9 m2/g and 2143.1 m2/g, respectively—explain their excellent performance. The results of the kinetic study support the pseudo-second-order model with a high coefficient of (R2 = 0.9999), and an efficiency of over 90 % was achieved within 5 min. The findings of the thermodynamic analysis indicated that the adsorption process was spontaneous and endothermic. Furthermore, the outstanding reusability of GIEC704a and GIEC704b confirmed their suitability for environmental chemical engineering and industrial applications.

Fabrication of molecularly imprinted polymers based on magnetic covalent organic framework for highly selective and sensitive analysis of genistein in F. Philippinensis

Flemingia philippinensisMerr.et Rolfe (F. philippinensis) is an important food ingredient as well as a traditional Chinese medicine with numerous pharmacological actions. Unfortunately, there was no defined method for monitoring the quality of F. philippinensis in the Chinese Pharmacopoeia. In this study, a magnetic covalent organic framework molecularly imprinted polymers (MCOFs-MIPs) was prepared using MCOFs as a support material, genistein (Gen), which was abundant in F. philippinensis, as a template molecule, and acrylamide as a functional monomer. The preparation process of MCOFs-MIPs was optimized and their structures and adsorption characteristics were characterized. In the selectivity test, the imprinting factor of Gen was 1.93, demonstrating that the imprinting effect of MCOFs-MIPs could selectively enrich Gen in complex samples. Following that, a new and effective quality control method (Gen-MCOFs-MIPs-HPLC) was established to determine Gen content in F. philippinensis roots. The method showed good linearity (R2 = 0.9936) in the range of 0.12–80 µg mL−1. The recoveries of Gen in F. philippinensis high, medium and low samples were 90.5–91.0 %, 92.1–100.1 and 92.8–100.8, respectively. Stability and reproducibility tests revealed that this method was stable (RSD of 1.20 %) and reproducible (RSD of 0.70 %). Moreover, the calculation showed that the amount of Gen in the F. philippinensis powder was 0.4489 mg g−1. As a result, the approach was shown to be simple, repeatable, and stable, and it provided a sensitive and reliable method for the extraction and detection of Gen in natural products.

A novel deep eutectic solvent modified magnetic covalent organic framework for the selective separation and determination of trace copper ion in medicinal plants and environmental samples

BackgroundPretreatment techniques should be introduced before metal ion determination because there is very low content of heavy metals in Chinese medicinal plants and environmental samples. Magnetic dispersive micro solid phase extraction (MDMSPE) has been widely used for the separation and adsorption of heavy metal pollutants in medicinal plants and environmental samples. However, the majority of MDMSPE adsorbents have certain drawbacks, including low selectivity, poor anti-interference ability, and small adsorption capacity. Therefore, modifying currently available adsorption materials has gained attention in research. ResultsIn this study, a novel adsorbent MCOF-DES based on a magnetic covalent organic framework (MCOF) modified by a new deep eutectic solvent (DES) was synthesized for the first time and used as an adsorbent of MDMSPE. The MDMSPE was combined with inductively coupled plasma optical emission spectrometry (ICP-OES) for selective separation, enrichment, and accurate determination of trace copper ion (Cu2+) in medicinal plants and environmental samples. Various characterization results show the successful preparation of new MCOF-DES. Under the optimal conditions, the enrichment factor (EF) of Cu2+ was 30, the limit of detection (LOD) was 0.16 μg L−1, and the limit of quantitation (LOQ) was 0.54 μg L−1. The results for the determination of Cu2+ were highly consistent with those of inductively coupled plasma mass spectrometry (ICP-MS), which verified the accuracy and reliability of the method. SignificanceThe established method based on a new adsorption material MCOF-DES has achieved the selective separation and determination of trace Cu2+ in medicinal and edible homologous medicinal materials (Phyllanthus emblica Linn.) and environmental samples (soil and water), which provides a promising, selective, and sensitive approach for the determination of trace Cu2+ in other real samples.

A miniaturized stir bar sorptive dispersive microextraction method for the determination of bisphenols in follicular fluid using a magnetic covalent organic framework

BackgroundBisphenols, particularly bisphenol A (BPA), are the primary monomers used as additives in the manufacturing of many consumer products. The exposure to these compounds is related to endocrine-disrupting and reproductive effects, among others. For this reason, the development of analytical methods for their determination in biological matrixes is needed to monitor the population exposure to these compounds. Their quantification at ovarian level (i.e., follicular fluid) is interesting for the assessment of the bisphenol content to draw conclusions about infertility problems. However, the background does not meet all requirements by focusing mainly on BPA. ResultsIn this work, a miniaturized stir bar sorptive dispersive microextraction (mSBSDME) approach has been developed for the determination of BPA and eight analogues in follicular fluid. In the proposed method, the sample is previously cleaned-up using a zirconia-based solid-phase extraction cartridge, removing proteins and phospholipids, and then subjected to the mSBSDME for the preconcentration of the analytes. For this purpose, a magnetic covalent organic framework was used as sorbent. A Plackett-Burman design was applied to select the significant variables affecting the mSBSDME. Afterwards, the only significant variable (i.e., sorbent amount) was optimized. Under the optimized conditions, the proposed method was properly validated, and satisfactory analytical parameters in terms of linearity (up to 50 ng mL−1), enrichment factors (8.5–14.3), limits of detection in the low ng mL−1 range, and precision (relative standard deviations below 11.5 %) were obtained. Finally, the method was successfully applied to five samples, detecting BPA and other two analogues. SignificanceThis method expands the potential applicability of the mSBSDME to other low-availability complex matrixes, which would otherwise be difficult to analyze. Moreover, it offers a valuable tool for monitoring the female population's exposure to bisphenols with the final aim of evaluating if infertility problems of women might be associated to the exposure to these highly endocrine disrupting compounds.

Effective extraction and determination of 24 quinolones in water and egg samples using a novel magnetic covalent organic framework combined with UPLC-MS/MS.

The excessive use of quinolones (QNs) has seriously threatened human health. In this study, a novel functionalized magnetic covalent organic framework Fe3O4@SiO2@Ah-COF was fabricated with biphenyl-3,3',5,5'-tetracarbaldehyde and hydrazine hydrate (85%) as monomers and was used as a magnetic solid-phase extraction (MSPE) absorbent for the determination of 24 QNs in water and egg samples through ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The extraction parameters of MSPE were optimized, including pH, adsorbent dosage, adsorption time, and eluent type. An effective and rapid detection method was then established, which showed good linearity (R2 ≥ 0.9990), low limits of detection (0.003-0.036 μg L-1) and low limits of quantitation (0.008-0.110 μg L-1) for QNs. The good recoveries of 24 QNs in water and egg samples were in the range of 70.3-106.1% and 70.4-119.7%, respectively, with relative standard deviations lower than 10% (n = 5). As a result, Fe3O4@SiO2@Ah-COF is a promising magnetic adsorbent, and the established method was successfully applied for the determination of 24 QNs in water and egg samples.

Ultrasonic synthesis of magnetic covalent organic frameworks and application magnetic solid phase extraction for rapid adsorption of trace bisphenols in food samples

A simple ultrasonic synthesis strategy was developed for a novel magnetic covalent organic framework. Firstly, the Fe3O4 nanoparticles were encapsulated by imine-type COF, which generated by the Schiff reaction of 4,4′,4′'-(1,3,5-Triazine-2,4,6-triyl)-trianiline (TAPT) and tris(4-formylphenyl)-amine (TFPA) using ultrasonic synthesis method within 2 h. The synthesised nanocomposites showed a sizeable specific surface area, and high adsorption capacity. A fast, sensitive MSPE method with Fe3O4@TAPT-TFPA-COF as adsorbent for analysing bisphenol compounds was developed. This method's advantages were simple operation, short extraction time, and avoidance of the use of centrifugal equipment. The method validation indicate that this method exhibited superior linearity, and detection limits range between 0.33 and 0.60 μg L–1. The recoveries of BPs ranged from 74.7 % to 107.0 %, with relative standard deviations of less than 3.8 % in water, milk, vinegar, and soy sauce samples. The proposed method was successfully applied for extracting BPs in food samples.

A CRISPR/Cas12a-assisted bacteria quantification platform combined with magnetic covalent organic frameworks and hybridization chain reaction

The total bacterial count is an important indicator of food contamination in food safety supervision and management. Recently, the CRISPR/Cas12a system integrated with nucleic acid amplification has increasingly shown tremendous potential in microorganism detection. However, a general quantification strategy for total bacteria count based on the CRISPR/Cas12a system has not yet been developed. Herein, we established a sensitive bacterial quantification strategy based on the CRISPR/Cas12a system combined with magnetic covalent organic frameworks (MCOFs) and hybridization chain reaction (HCR). MCOFs acted as a carrier, adsorbing the ssDNA as HCR trigger sequence through π-π stacking. Then, the HCR circuit produces DNA duplexes containing the PAM sequences that activate the trans-cleavage activity of Cas12a for further signal amplification. Under the optimal conditions, the proposed method can quantify total bacteria in 50 min with a minimum detection concentration of 10 CFU/mL. The successful applications in food samples confirmed the feasibility and broad application prospects.

Colorimetry/fluorescence dual-mode detection of Salmonella typhimurium based on self-assembly of MCOF with Au NPs nanozyme coupled AIEgen

Sensitive, accurate, simple and quick monitoring of Salmonella typhimurium (S. typhimurium) in food is significant for preventing food poisoning, but still remains a challenge. Herein, a colorimetry/fluorescence dual-mode sensing strategy was fabricated to detect S. typhimurium by integrating the self-assembly of magnetic covalent organic framework (MCOF) with gold nanoparticles (Au NPs) as the peroxidase-mimicking nanozyme and aggregation-induced emission luminogen (AIEgen). S. typhimurium could competitive bind to aptamer conjugated Au NPs (Au NPs@apt), inhibit the self-assembly of MCOF with Au NPs, and shield the catalytic activity of AuNPs. After adding H2O2 and TPE-4A, the dark green solution changed to light with increasing S. typhimurium concentration, on the contrary, the fluorescent signals were generated. As a result, in colorimetry/fluorescence modes, S. typhimurium could be detected in the linear ranges of 103–108 CFU mL−1 and 101–107 CFU mL−1, with LODs of 1000 and 10 CFU mL−1, respectively. Importantly, different colors consistent with various S. typhimurium concentrations can be accurately classified by smartphone app and linear discriminant analysis (LDA). The smartphone-assisted data interpretation can generate complementary colorimetry and fluorescence signals without any sophisticated equipment and achieve on-site detection. Moreover, the proposed strategy could be explored for S. typhimurium monitoring in milk with satisfactory recoveries (97.6–100.4 %) in colorimetry and fluorescence mode and good classification and prediction performance in smartphone/LDA system, suggesting the feasibility and potential applications of the sensing platform.

Synthesis of a core-shell magnetic covalent organic framework for the enrichment and detection of aflatoxin in food using HPLC-MS/MS.

A porous magnetic covalent organic framework, Fe3O4@TPBD-TPA (terephthalaldehyde (TPA) , N, N, N', N'-tetrakis(p-aminophenyl)-p-phenylenediamine (TPBD)), was synthesized using the Schiff base reaction under mild reactionconditions. This adsorbent exhibited excellent adsorption performance for aflatoxins. The adsorption capacity of Fe3O4@TPBD-TPA for aflatoxins ranged from 64.4 to 84.4 mg/g. A magnetic solid-phase extraction combined with high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method based on Fe3O4@TPBD-TPA was developed for the efficient determination of four types of aflatoxins in food samples (maize, maize oil, peanut, and peanut oil). The determination coefficients (R2) were ≥0.9972. The method exhibited detection limits ranging from 0.01 to 0.06 μg/kg and spiked recoveries of 80.0 to 113.1%. The intra-day and inter-day precision were less than 6.77%, indicating good repeatability. The adsorbent showed promising prospects for the efficient enrichment of trace amounts of aflatoxins in complex food matrices.

Membrane–protected magnetic covalent organic framework for efficient extraction of estrogens in dairy products

The presence of estrogens residues in dairy products is a growing concern due to their potential health risk. Herein, in this study, we have developed a membrane–protected magnetic solid–phase extraction (MP–MSPE) method that utilized a magnetic adsorbent (Fe3O4@COF–LZU1) with in–situ growth for the efficient extraction of estrone (E1), 17β–estradiol (E2), and estriol (E3). When combined with HPLC–FLD, this method allows for the efficient detection of estrogens in dairy products. The stability of the MP–MSPE was improved by the presence of a dialysis membrane, which remained a high extraction efficiency (90 %) even after ten reuse cycles. The hydrogen bonding, π–π interactions and pore size effect contribute to the excellent adsorption of three estrogens onto Fe3O4@COF–LZU1. Under optimal conditions, the method exhibits a low detection limit (0.01–0.15 μg L−1), wide linear range (0.1–800 μg L−1), and favorable recoveries (77.3 %–109.4 %) at three concentration levels (10, 50 and 100 μg L−1). This proposed method is characterized by its simplicity, high efficiency and eco–friendliness, making it a promising approach for extracting estrogens from dairy products.

Magnetic porous carbon material derived from imine-linked covalent organic frameworks for magnetic solid phase extraction of trace chlorine-containing herbicides in soil

Here, imine-linked covalent organic frameworks coated Fe3O4 microspheres were fabricated and employed as the self-template to prepare magnetic porous carbon material. The magnetic solid phase extraction (MSPE) performance of such magnetic covalent organic frameworks derived porous carbons (CMCOFs) were studied for the first time, and the improved MSPE performance was verified. The variations of chemical and material properties in the carbonization processes were studied, and it was found that the CMCOFs carbonated at 400°C exhibited highest adsorption efficiencies for chlorine-containing herbicides due to the formation of nitrile components at this stage. The CMCOFs retained high adsorption efficiencies (above 90 %) to chlorine-containing herbicides at wide pH range (3–12) and high salt concentration. The CMCOFs-based MSPE coupled with HPLC technique was in good potential for analysis of trace chlorine-containing herbicides in soil samples. Under the optimized conditions, this approach displayed short extraction and elution time (5 and 8 min) and low limits of detection (0.35–5.5 ng/mL) for chlorine-containing herbicides. The recoveries of spiked analytes and the relative standard deviations in real soil samples were 81.86 %–110.9 % and less than 5.92 %, respectively. This study provides an efficient method for the analysis of trace chlorine-containing herbicides in complex samples, as well as give some inspiration on material modulation by controlled carbonization to achieve improved sorption performances.