Application of the liquid-liquid dispersed microextraction based on phase transition behavior of temperature sensitive polymer to rapidly detect 5 BPs in food packaging

External surface hydrophilic 3D-POSS-COF@GDL for the direct adsorption of bisphenols in milk samples

In case of organic frameworks (COFs) as adsorbents in the pretreatment of complex food matrices, challenges such as poor dispersion and non-specific adsorption of interfering macromolecules like proteins are often encountered. To address this issue, this work prepared a three-dimensional covalent organic framework (3D-COF) with a novel bcu topology based on polyhedral oligomeric silsesquioxane (POSS). Subsequently, gluconolactone (GDL) was modified onto the external surface of the material via the reaction with the exposed reactive residues. The resulting POSS-COF@GDL adsorbent has an enhanced hydrophilicity in the external surface, thereby significantly improves the dispersion of materials in aqueous solution and reduces the adsorption ability toward protein. Whereas, the inner of material retains hydrophobic pores that exhibit high adsorption efficiency to small hydrophobic molecules. Compared with the traditional pretreatment methods, POSS-COF@GDL can directly extract bisphenols (BPs) in milk samples without any additional treatment. The established sample pretreatment method is coupled with high-performance liquid chromatography-ultraviolet detection (HPLC-UV), resulting in recoveries of 71.8 to 93.6%, intra- and inter-day relative standard deviations (RSDs) of <8.3%, and limits of detection (LODs) of 0.042-0.16 ng∙mL-1 for four BPs.

Highly efficient nanocomposites based on molecularly imprinted magnetic covalent organic frameworks for selective extraction of bisphenol A from liquid matrices

Highly efficient nanocomposites, hydrophobic molecularly imprinted magnetic covalent organic frameworks (MI-MCOF), have been farbricated by a facile Schiff-base reaction. The MI-MCOF was based on terephthalaldehyde (TPA) and 1,3,5-tris(4-aminophenyl) benzene (TAPB) as functional monomer and crosslinker, anhydrous acetic acid as catalyst, bisphenol AF as dummy template, and NiFe₂O₄ as magnetic core. This organic framework significantly reduced the time consumption of conventional imprinted polymerization and avoided the use of traditional initiator and cross-linking agents. The synthesized MI-MCOF exhibited superior magnetic responsivity and affinity, as well as high selectivity and kinetics for bisphenol A (BPA) in water and urine samples. The equilibrium adsorption capacity (Q_e) of BPA on the MI-MCOF was 50.65 mg g^-1, which was 3-7-fold higher than of its three structural analogues. The imprinting factor of BPA reached up to 3.17, and the selective coefficients of three analogues were all > 2.0, evidencing the excellent selectivity of fabricated nanocomposites to BPA. Based on the MI-MCOF nanocomposites, the magnetic solid-phase extraction (MSPE), combined with HPLC and fluorescence detection (HPLC-FLD), offered superior analytical performance: wide linear range of 0.1-100 μg L^-1, high correlation coefficient of 0.9996, low limit of detection of 0.020 μg L^-1, good recoveries of 83.5-110%, and relative standard deviations (RSDs) of 0.5-5.7% in environmental water, beverage, and human urine samples. Consequently, the MI-MCOF-MSPE/HPLC-FLD method provides a good prospect in selective extraction of BPA from complex matrices while replacing traditional magnetic separation and adsorption materials.

Determination of trace bisphenols in milk based on Fe3O4@NH2-MIL-88(Fe)@TpPa magnetic solid-phase extraction coupled with HPLC

Herein, a covalent organic framework (COF) was grown on a magnetic metal-organic framework (MOF) by a solvothermal method for the efficient extraction of bisphenols (BPs). The magnetic solid-phase extraction (MSPE) of four bisphenols (bisphenol A, bisphenol B, bisphenol AF and bisphenol C) was carried out without adjusting the pH and salt concentration. When 30 mg Fe₃O₄@NH₂-MIL-88(Fe)@TpPa was used to adsorb for 25 min, 6 mL methanol was used to elute for 20 min, and the extract was detected by high-performance liquid chromatography (HPLC). The proposed method has a low detection limit of 0.011-0.036 ng mL^-1, a wide linear range of 0.05-100 ng mL^-1, and a correlation coefficient (R²) of 0.9980-0.9998. The intra-day and inter-day precisions are 0.74-2.54% and 1.68-3.72%, respectively. Bisphenol A was determined by applying the proposed method to the determination of actual milk samples. The standard addition experiment showed that the relative recovery of the four bisphenols was 85.70-119.7%. Pseudosecond-order, first-order, Langmuir and Freundlich models were applied to explore the adsorption characteristics of Fe₃O₄@NH₂-MIL-88(Fe)@TpPa. In general, the established Fe₃O₄@NH₂-MIL-88(Fe)@TpPa-MSPE-HPLC-UV method exhibits attractive sensitivity, simple manipulation, and excellent reusability, and it has excellent prospects for the detection of trace BPs in complex milk matrices.

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.

Hydroxy-Containing Covalent Organic Framework Combined with Nickel Ferrite as a Platform for the Recognition and Capture of Bisphenols

A hydroxy-containing covalent organic framework (COF) was successfully obtained via a simple nitrogen-purge synthetic procedure for the first time. The COF favored a serrated AA-stacking arrangement, which enhanced the stability compared with common AA or AB arrangements. To validate the potential of the COF in environmental applications, we decorated the COF onto NiFe₂O₄ and used the NiFe₂O₄@COF nanocomposite for magnetic solid-phase extraction of trace bisphenols (BPs). The parameters affecting extraction efficiencies were systematically optimized. Under the optimum extraction conditions, calibration plots showed good linearity (5.0-1.0 × 10³ ng mL^-1) for six BPs, and limits of detection varied from 0.14 to 0.73 ng mL^-1. Molecular polarity indexes and molecular dynamics simulations revealed why the COF could efficiently recognize and capture BPs. An adsorption mechanism related to the interaction between BP clusters and the COF was discovered. Ecotoxicological assessment of BPs further unraveled the significance of the developed method for the timely tracking of the concentration, distribution, and migration of BPs in environmental media.

Temperature-responsive graphene oxide/N-isopropylacrylamide/2-allylphenol nanocomposite for the removal of phenol and 2,4-dichlorophenol from aqueous solution

In this study, a novel thermo-responsive polymer was synthesized with efficient grafting of N-isopropylacrylamide as a thermosensitive polymer onto the graphene oxide surface for the efficient removal of phenol and 2,4-dichlorophenol from aqueous solutions. The synthesized polymer was conjugated with 2-allylphenol. Phenol and 2,4-dichlorophenol were monitored by ultra-performance liquid chromatography system equipped with a photodiode array detector. The nanoadsorbent was characterized by different techniques. The nanoadsorbent revealed high adsorption capacity where the removal percentages of 91 and 99% were found under optimal conditions for phenol and 2,4-dichlorophenol, respectively (for phenol; adsorbent dosage = 0.005 g, pH = 8, temperature= 25 °C, contact time = 60 min; for 2,4-dichlorophenol; adsorbent dosage = 0.005 g, pH = 5, temperature = 25 °C, contact time = 10 min). Adsorption of phenol and 2,4-dichlorophenol onto nanoadsorbent followed pseudo-second-order kinetic and Langmuir isotherm models, respectively. The values of ΔG (average value = - 11.39 kJ mol^-1 for phenol and 13.42 kJ mol^-1 for 2,4-dichlorophenol), ΔH (- 431.72 J mol^-1 for phenol and - 15,721.8 J mol^-1 for 2,4-dichlorophenol), and ΔS (35.39 J mol^-1 K^-1 for phenol and - 7.40 J mol^-1 K^-1 for 2,4-dichlorophenol) confirmed spontaneous and exothermic adsorption. The reusability study indicated that the adsorbent can be reused in the wastewater treatment application. Thermosensitive nanoadsorbent could be used as a low-cost and efficient sorbent for phenol and 2,4-dichlorophenol removal from wastewater samples.

Metal-organic framework mixed-matrix membrane-based extraction combined HPLC for determination of bisphenol A in milk and milk packaging

The residues of bisphenol A (BPA) in milk packaging may transfer to milk, adversely affecting the human endocrine system. Consequently, to analyse or monitor BPA, it is imperative to develop rapid and effective approaches to BPA extraction from milk and milk packing as BPA is usually present in trace levels. Herein, we developed a rapid, simple, and low-cost dispersive-membrane-solid-phase-extraction (DME) for BPA with MIL-101(Cr) mixed-matrix-membrane (MMM). The MMM had large surface area (1322.09 m²/g) and pore volume (0.65 cm³/g), possessed great extraction efficiency of BPA, and kept more than 90% extraction efficiency after 20 times of reuse. Using the developed MIL-101(Cr)-MMM-based DME coupled with HPLC-fluorescence detector, we received an adequate linearity in the range of 0.1 ∼ 50 μg/L BPA and a limit of detection as low as 16 ng/L under optimized conditions. The recoveries of BPA in milk and milk bottles were from 74.2% to 110.6%, with RSDs less than 9.4%.