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

Magnetic cationic covalent organic framework for efficient enrichment and detection of phenolic endocrine disruptors in foodstuffs

Endocrine disrupting chemicals (EDCs) have received significant attention in the food field due to their potential health risks. Herein, we proposed a novel core-shell structure magnetic cationic covalent organic framework (EB-DHTA-iCOF@Fe3O4) designed for the efficient enrichment of trace-level EDCs in foodstuffs and analyzed using HPLC-MS/MS. Due to the phenolic EDCs structure possessing hydroxyl functional groups which become protonated under alkaline conditions, resulting in the formation of negatively charged anions. The EB-DHTA-iCOF@Fe3O4 positively charged surface can have a good enrichment effect on EDCs with phenolic structures through electrostatic interactions, π - π interactions, and hydrogen bonding. This unique combination of interactions enhances the iCOF ability to selectively capture and enrich phenolic EDCs from complex matrices, thereby improving the sensitivity and efficiency of their detection in analytical applications. Under optimal magnetic solid-phase extraction (MSPE) conditions, the method showed excellent linearity (5-250 μg kg-1, R2 ≥ 0.9993) and a low detection limit (0.03-1.2 μg kg-1) for phenolic EDCs, with recovery rates between 86.0 % and 106.8 % and a relative standard deviation under 5.8 %. The approach highlights the potential of the ionic covalent organic framework as an adsorbent for MSPE, offering a promising approach for the detection and analysis of trace-level EDCs in foodstuffs.

Casein-Tb-Ti3C2 quantum dots ratiometric fluorescence probe for the detection of ciprofloxacin

A water-stable ratiometric fluorescence probe based on casein-Tb-Ti3C2 quantum dots was developed for the highly sensitive and selective detection of ciprofloxacin. With the increase in ciprofoxacin concentration, the fluorescence intensity at 440 nm remained relatively stable, while the fluorescence emission at 543 nm exhibited progressive enhancement. This may be attributed to ciprofloxacin being able to effectively coordinate with Tb3+ ions while displacing surrounding water molecules, leading to enhanced luminescence. Thus, the I543/I440 ratio was utilized as an indicator for monitoring changes in ciprofloxacin concentration. The ratiometric fluorescence probe demonstrated excellent linearity across a concentration range 0.1-800 µM and exhibited high sensitivity, achieving a detection limit of 0.018 μM for ciprofloxacin. Furthermore, the ratiometric fluorescence probe was successfully employed for the detection of ciprofloxacin in pork, beef, fish, honey, eggs, and milk samples, achieving recoveries that ranged from 76.5 to 123%. Owing to its advantages of high sensitivity and excellent selectivity, the ratiometric fluorescence probe demonstrates significant potential for practical applications in ciprofloxacin detection.

Facile synthesis of magnetic ionic covalent organic framework and dispersive magnetic solid phase extraction of aromatic amino acid oxidation products in thermally processed foods

Aromatic amino acid oxidation products (AAAOPs) are newly discovered risk substances of thermal processes. Due to its significant polarity and trace level in food matrices, there are no efficient pre-treatment methods available to enrich AAAOPs. Herein, we proposed a magnetic cationic covalent organic framework (Fe3O4@EB-iCOF) as an adsorbent for dispersive magnetic solid-phase extraction (DMSPE). Benefiting from the unique charged characteristics of Fe3O4@EB-iCOF, AAAOPs can be enriched through electrostatic interaction and π-π interactions. Under the optimal DMSPE conditions, the combined HPLC-MS/MS method demonstrated good linearity (R2 ≥ 0.990) and a low detection limit (0.11-7.5 μg·kg-1) for AAAOPs. In addition, the method was applied to real sample and obtained satisfactory recoveries (86.8 % ∼ 109.9 %). Especially, we applied this method to the detection of AAAOPs in meat samples and conducted a preliminarily study on its formation rules, which provides a reliable basis for assessing potential dietary risks.

Development and Application of a Robust Imine-Based Covalent Organic Framework for Stir Bar Sorptive Extraction of Estrogens in Environmental Water

A covalent organic framework (COF) based on imine was synthesized using 2,5-dihexoxyterephthalaldehyde (DHT) and 1,3,5-tris(4-aminophenyl) benzene (TAPB) as starting materials. The TAPB-DHT-COF exhibited satisfactory chemical stability, making it a promising adsorbing material for stir bar sorptive extraction (SBSE) of four estrogens, including estrone (E1), β-estradiol (E2), hexestrol (HES), and mestranol (MeEE2), in ambient water samples. The extracted analytes were subsequently analyzed using a high-performance liquid chromatography-diode array detector (HPLC-DAD). A series of parameters affecting the SBSE process, such as solution pH, ionic strength, extraction time, and desorption solvent, were investigated by the controlled variable method. Under optimal conditions, the limit of detection (LODs) for the four targeted estrogens ranged from 0.06 to 0.15 µg/L, with a linear range from 0.2 to 100 µg/L. The observed enrichment factor (EF) ranged from 39 to 49, while the theoretical EF was estimated to be 50-fold. This methodology can be applied to the identification of estrogens in three environmental water samples.

Recent Progress and Applications of Advanced Nanomaterials in Solid-Phase Extraction

Sample preparation maintains a key bottleneck in the whole analytical procedure. Solid-phase sorbents (SPSs) have garnered increasing attention in sample preparation research due to their crucial roles in achieving high clean-up and enrichment efficiency in the analysis of trace targets present in complex matrices. Novel nanoscale materials with improved characteristics have garnered considerable interest across different scientific disciplines due to the limited capabilities of traditional bulk-scale materials. The purpose of this review is to offer a thorough summary of the latest developments and uses of SPSs in preparing samples for chromatographic analysis, focusing on the years 2020-2024. The techniques for preparing SPSs are examined, such as metal-organic frameworks (MOFs), covalent organic frameworks (COFs), carbon nanoparticles (CNPs), molecularly imprinted polymers (MIPs), and metallic nanomaterials (MNs). Examining the pros and cons of different extraction methods, including solid-phase extraction (SPE), magnetic SPE (MSPE), flow-based SPE (FBA-SPE), solid-phase microextraction (SPME), stir-bar sorptive extraction (SBSE), and dispersive SPE (DSPE), is the main focus. Furthermore, this article presents the utilization of SPE technology for isolating common contaminants in various environmental, biological, and food specimens. We highlight the persistent challenges in SPSs and anticipate future advancements and applications of novel SPSs.

The magnetic layered double hydroxide/zeolitic imidazolate framework-8 nanocomposite coupled with HPLC-MS/MS for the detection of heterocyclic aromatic amines in thermally processed meat

In this research, a novel magnetic nanocomposite (Fe3O4@Zn/Al-LABSA-LDH/ZIF-8) was synthesized using Fe3O4 as the magnetic core, layered double hydroxide (LDH) with linear alkylbenzene sulfonic acid (LABSA) intercalation and zeolitic imidazolate framework-8 (ZIF-8) as the shell. Benefiting from the intercalation of LABSA into LDH combined with ZIF-8, the multiple interactions, including π-π stacking, hydrogen bonding, and electrostatic interactions, conferred high selectivity and good extraction capability to the material towards heterocyclic aromatic amines (HAAs). Fe3O4@Zn/Al-LABSA-LDH@ZIF-8 was used as an adsorbent for magnetic solid-phase extraction (MSPE) to enrich HAAs in thermally processed meat samples, followed by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) detection. The method exhibited a low detection limit (0.021-0.221 ng/g), good linearity (R2 ≥ 0.9999), high precision (RSD < 7.2 %), and satisfactory sample recovery (89.7 % -107.5 %). This research provides a promising approach for developing novel adsorbents in sample preparation and improving analytical performance.

Fabrication of imidazoline-linked cationic covalent triazine framework for enrichment of environmental estrogens

Imidazoline-linked cationic covalent triazine framework (IM-iCTF) was facilely prepared through the Debus-Radziszewski reaction, involving 4,4',4''-(1,3,5-triazine-2,4,6-triyl)trianiline, formaldehyde and methylglyoxal. The IM-iCTF was applied as a sorbent for cartridge solid-phase extraction (SPE). It provided good adsorption performance for estrogen and estrogen mimics including bisphenol F, bisphenol A, 7β-estradiol, bisphenol B and estrone. The adsorption isotherm, adsorption kinetic model, thermodynamic calculations and adsorption mechanism were investigated to reveal the adsorption behavior. The IM-iCTF was employed for the extraction of the estrogens and estrogen mimics from water, fish and shrimp (fish and shrimp samples were extracted with acetonitrile before the SPE). The analytes were then determined by high-performance liquid chromatography with diode array detection. The limits of detection were 0.008-0.05 ng mL-1 for water, 0.015-0.11 μg g-1 for fish, and 0.012-0.10 μg g-1 for shrimp samples. This research not only offers a new approach to construct cationic covalent triazine framework, but also provides a reliable strategy for the adsorption/enrichment trace level of organic pollutants.

A sensitive fluorescent assay based on gold-nanoclusters coated on molecularly imprinted covalent organic frameworks and its application in malachite green detection

Malachite green (MG), as a parasiticide, is widely used in aquaculture to increase the production of the fishery industry. It poses a great danger to both the food system and the human body. In this study, a one-pot reverse microemulsion polymerization was employed to combine the gold nanoclusters (AuNCs) with molecularly imprinted polymers (MIPs) and covalent organic frameworks (COFs) to synthesize an efficient fluorescent hybrid probe (AuNCs@COFs@MIPs) for selective detection of MG. The specific recognition of AuNCs@COFs@MIPs towards MG triggers the fluorescence quenching of AuNCs. The fluorescent response was linearly related to the concentration over the range of 10-150 nmol/L with a limit of detection of 2.78 nmol/L. In addition, the proposed probe was further applied to fish and water samples. A favorable recovery ranged from 97.34 to 101.51 % toward trace amounts of MG indicating its promising application for detecting residue of veterinary drugs.

Methacrylate bonded covalent organic framework monolithic column online coupling with high-performance liquid chromatography for analysis of trace estrogens in food

Covalent organic frameworks (COFs) are a burgeoning class of crystalline porous materials with unique properties and have been considered as a promising functional extraction medium in sample pretreatment. In this study, a new methacrylate-bonded COF (TpTh-MA) was well designed and synthesized via the aldehyde-amine condensation reaction, and the TpTh-MA was incorporated into poly (ethylene dimethacrylate) porous monolith by a facile polymerization reaction inside capillary to prepare a novel TpTh-MA monolithic column. The fabricated TpTh-MA monolithic column was characterized with scanning electron microscope, Fourier transform infrared spectrometer, X-ray diffraction, and N₂ adsorption-desorption experiments. Then, the homogeneous porous structure, good permeability and high mechanical stability of TpTh-MA monolithic column was used as separation and enrichment media of capillary microextraction, which was coupled with high-performance liquid chromatography fluorescence detection for online enrichment and analysis of trace estrogens. The main experimental parameters influencing the extraction efficiency were systematically investigated. The adsorption mechanism for three estrogens was also explored and discussed based on hydrophobic effect, π-π affinity and hydrogen bonding interaction, which contributed to its strong recognition affinity to target compounds. The enrichment factors of the TpTh-MA monolithic column micro extraction method for the three estrogens were 107-114, indicating a significant preconcentration ability. Under optimal conditions, a new online analysis method was developed and exhibited good sensitivity and wide linearity range of 0.25-100.0 µg·L^-1 with a coefficient of determination (R²) higher than 0.9990 and a low limit of detection with 0.05-0.07 µg·L^-1. The method was successfully applied for online analysis of three estrogens of milk and shrimp samples and the recoveries obtained from spiking experiments were in range of 81.4-113% and 77.9-111%, with the relative standard deviations of 2.6-7.9% and 2.1-8.3% (n = 5), respectively. The results revealed the great potential for the application of the COFs-bonded monolithic column in the field of sample pretreatment.

β-cyclodextrin-functionalized magnetic graphene oxide for the efficient enrichment of bisphenols in milk and milk packaging

In this work, β-cyclodextrin-functionalized magnetic graphene oxide (NiFe₂O₄@GO@β-CD) was synthesized and employed as magnetic solid-phase extraction adsorbent for the extraction of bisphenols before high performance liquid chromatography analysis. The modification of β-cyclodextrin could enhance the adsorption performance of NiFe₂O₄@GO@β-CD towards bisphenols through the host-guest interaction and hydrogen-bond interaction. Under the optimal conditions, good linearities between peak area and concentration of bisphenols (1 - 300 μg L^-1, r ≥ 0.9989) were obtained with the limits of detection (S/N = 3) in the range of 0.050 - 0.10 μg L^-1. The recoveries of bisphenols in milk and milk packaging ranged from 78.0% to 101.6%. Moreover, NiFe₂O₄@GO@β-CD showed stable chemical properties and good reusability with the recoveries of bisphenols remained above 80.0% after 12 MSPE cycles. The adsorption characteristics of NiFe₂O₄@GO@β-CD towards bisphenols fitted well with the pseudo-second-order kinetic model and Langmuir model. The hydrogen-bond interaction, π-π interaction, host-guest interaction and electrostatic interaction between sorbent and bisphenols played important role during the adsorption process. The developed method showed potential applications for the analysis of trace bisphenols in milk and milk packaging.