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• A hydrophobic NH 2 -UiO-66@H COF hybrid was successfully fabricated and explored as a promising SPE sorbent. • The NH 2 -UiO-66@H COF hybrid exhibited better extraction performance than NH 2 -UiO-66 and H COF via synergistic effects. • A sensitive detection method was established for analysis of flavonoids in food samples. Metal-organic framework (MOF) and covalent organic framework (COF) exhibit excellent extraction performance in sample pretreatment, but their wider application is hindered by some inherent drawbacks. Herein, we successfully synthesized a novel MOF@COF hybrid material with large specific surface area, good chemical stability and reusability, which is suitable as a solid phase extraction (SPE) sorbent for the efficient extraction of flavonoids. Importantly, due to the synergistic effect, the obtained MOF@COF hybrid material showing a higher extraction efficiency than individual MOF and COF. This is mainly due to the obtained MOF@COF hybrid material combines the high specific surface area of MOF and multiple interactions (hydrophobic interaction, hydrogen bonding and π-π stacking interaction) with flavonoids conferred by the COF structure. Then, a sensitive analytical method for flavonoids with ideal linear range (1–500 ng mL−1), low detection limit (0.15–0.41 ng mL−1) and good repeatability (2.64–6.20%) was developed under optimized conditions. In addition, the MOF@COF hybrid sorbent has better selectivity for hydrophobic targets containing multiple hydrogen bond acceptors/donors. Finally, the established method was applied to the determination of flavonoids in different food samples, and satisfactory recoveries (81.4–102.1%) were obtained, which initially confirmed its applicability. [ABSTRACT FROM AUTHOR]

• A functionalized MOFs-based composite with dispersed hierarchical pores was fabricated. • It was applied as mixed-mode stationary phase for fast and efficient separation. • It exhibited superior selectivity for separation of various analytes. • It highlighted the role of the defect of MOFs and function of L-Cysteine. The micropores of the metal-organic frameworks (MOFs) endow with the advantages of size selectivity and large specific surface area, etc., but they limit their applications toward the control of diffusion and transport processes. Here, we report a strategy to prepare the hierarchical porous material, functional defect, which allows incorporation of L-Cysteine in the MOF by defect-loading. Silica microspheres were modified with these materials to form core-shell composites and used as mixed-mode stationary phases for chromatographic separations. Compared with the traditional MOFs-based stationary phase, it exhibited superior efficiency and selectivity for separation of various analytes and highlighted the role of defect of MOFs and function of L-Cysteine. In addition to the rapid separation of hydrophobic compounds, the stationary phase showed great potential in the separation of hydrophilic analytes, especially for separation of ten carbohydrates and eight sulfonamides. It showed excellent chromatographic reproducibility and stability, and the repeatability of preparation was investigated by relative standard deviations of retention time and/or column efficiency of objective compounds, which was among different batches less than 1.81%. This demonstration provided deep understanding of separation mechanism between MOF-based composites with functional defect and analytes, and stimulated the wide applications of such defective MOFs complexes in separations and analysis. [ABSTRACT FROM AUTHOR]

• A stable core-shell MOF@COF composite was synthesized and utilized as SPE adsorbent. • The covalent integration of hydrophobic COF shell successfully enhanced the hydrophobicity of MOF core. • The excellent extraction efficiency was attributed to the presence of multiple interactions. • A sensitive method for the quantification of flavonoids in grape juice and honey samples was developed. Hydrophobization and stability is crucial for the practical application of most metal-organic frameworks (MOFs) in extraction technique. In this study, a stable core-shell MOF@COF composite (NH 2 -MIL-101(Fe)@TAPB-FPBA-COF) was successfully prepared by Schiff base reaction and applied to solid-phase extraction (SPE) of hydrophobic flavonoids. Notably, the TAPB-FPBA-COF shell acts as a hydrophobic "shield", which not only improves the hydrophobicity and stability of hydrophilic NH 2 -MIL-101(Fe), but also makes the extraction efficiency of flavonoids from MOF@COF composite significantly higher than that of pure NH 2 -MIL-101(Fe) and TAPB-FPBA-COF. In addition, a sensitive analytical method with excellent linearities (0.1–500 ng mL−1, R2 ≥ 0.9967), low limits of detection (0.02–0.04 ng mL−1 for water; 0.04–0.07 ng mL−1 for grape juice; 0.06–0.08 ng mL−1 for honey), good repeatability (intra-day/inter-day precision are 1.86–5.37%/1.82–7.79%, respectively) and only 5 mg of adsorbent per cartridge was established by optimizing the SPE process combined with high performance liquid chromatography with ultraviolet-visible detector (HPLC-UV). Meanwhile, selectivity study and comparative experiments with the commercial C18 adsorbent showed that the MOF@COF adsorbent exhibited satisfactory extraction efficiency for flavonoids due to multiple interactions such as hydrogen bonding, hydrophobic, and π-π interactions. Finally, the good recoveries in grape juice (84.5–102.5%) and honey (87.5–104.6%) samples further validated the applicability of the proposed method in complex samples. [ABSTRACT FROM AUTHOR]

Highlights: [•] Nanoporous array anodic titanium wire was functionalized and used as fiber support. [•] Two imidazolium ILs were synthesized and copolymerized in situ on metal support. [•] Good extraction performance was obtained by combination of NAAT and ILs copolymer. [•] Aliphatic alcohols in liquors were quantified by the GS–SPME–GC method. [Copyright &y& Elsevier]

Abstract: A new specific stationary phase based on poly(1-allylimidazole)-grafted silica has been synthesized and characterized, by infrared spectra, elemental analysis, thermogravimetric analysis and X-ray photoelectron spectroscopy. The results of test showed that poly(1-allylimidazole) can effectively mask the residual silanol groups and reduce the adverse effect of residual silanol. Using this stationary phase, phenol compounds, aniline compounds, and polycyclic aromatic hydrocarbons were successfully separated with symmetric peak shapes in the reversed-phase chromatography. Inorganic anions (IO3 −, BrO3 −, Br−, NO3 −, I−, SCN−) were also separated completely in the anion-exchange chromatography using sodium chloride solution as the mobile phase. The effects of pH and the concentration of eluent on the separation of inorganic anions were studied. The separation mechanism appears to involve the mixed interactions of hydrogen bonding, hydrophobic, π–π, electrostatic, and anion-exchange interactions. [Copyright &y& Elsevier]

Highlights • A guanidyl functionalized graphene oxide-grafted silica was designed for the extraction of acidic compounds. • Experiment parameters were optimized using the response surface methodology. • The adsorption mechanism was investigated and evaluated. • The proposed method is suitable for the determination of acidic herbicides. Abstract A highly selective and efficient extraction material was synthesized through the functionalization of guanidyl onto the graphene oxide-grafted silica via a simple chemical modification, which was designed and proposed to improve the enrichment capacity for acidic herbicides. The extraction material was confirmed by scanning electron microscopy, Fourier transform infrared spectrometry, X-ray photoelectron spectrometry, thermal gravimetric analyzer and zeta potential analysis. Theoretical adsorption energies, static- and dynamic-state binding experiments, and comparative experiments with various adsorbents were investigated to elucidate the adsorption mechanism. The introduction of guanidyl endowed the sorbent with stronger Lewis base property and electron-donating ability, hence, excellent extraction recoveries for acidic herbicides could be obtained. Besides, electrostatic and π-π interactions were considered as two major driving impetuses in the adsorption process. Single-factor experiment and response surface methodology were utilized for the optimization of extraction and desorption conditions. Under the optimized conditions, the wide linearities were obtained with correlation coefficients ranging from 0.9904 to 0.9980, and the method detection limits were in the range of 0.5–2 μg L−1. The relative standard deviation values of the recoveries of five different extractions were 3.0–7.1%. Coupled with high performance liquid chromatography, the as-proposed method was successfully applied to detect five acidic herbicides in Lycium barbarum (Goji). It turned out that the proposed method provided a promising perspective for the selective extraction and determination of polar acidic compounds in complex samples. [ABSTRACT FROM AUTHOR]

• A novel mosaic structure was formed by embedding Ni nanoparticles on the surface of silica microspheres (Sil@C/Ni) via coordination and carbonization reduction. • Sil@C/Ni can be used as an efficient magnetic solid phase extraction sorbent. • Sil@C/Ni was applied to extract benzoylurea insecticides and the recovery remained 74.87–91.95% after 15 cycles. A novel mosaic structured core-shell composite, Silica@C/Ni (Sil@C/Ni), has been prepared by embedding Ni nanoparticles on the surface of silica microspheres via coordination and carbonization reduction, and was used as magnetic solid-phase extraction sorbents in combination with high performance liquid chromatography (HPLC) for the extraction and determination of four benzoylurea insecticides (BUs) in tea leaves. Based on the fact that hydrogen bonding and hydrophobic interactions exist between the material and BUs, allowing BUs on the surface of the material can achieve rapid mass transfer and improved sorption performance, satisfactory extraction recoveries have been achieved in practical sample applications. Under the optimized experimental conditions, the linear ranges were 0.5–200 µg L−1 for diflubenzuron and triflumuron, 1.0–200 µg L−1 for teflubenzuron and 0.8–200 µg L−1 for flufenoxuron with the correlation coefficients R2 ≥ 0.9991. The method has limits of detection and limits of quantification of 0.2–0.4 µg L−1 and 0.5–1.0 µg L−1, respectively. The intra-day and inter-day relative standard deviations were less than 5%. The actual sample recoveries were 76.63–95.26%. In addition, Sil@C/Ni was used repeatedly for 15 times and still showed a relatively satisfactory recovery of the four BUs. Therefore, Sil@C/Ni has a high stability and can be used as an ideal magnetic solid phase extraction sorbent for the trace enrichment of BUs in tea-leaf samples. [ABSTRACT FROM AUTHOR]

A solid-phase extraction method for the efficient analysis of the excretion-dynamics of flavonoids in urine was established and described. In this work, in situ surface radical chain-transfer polymerization and in situ anion exchange were utilized to tune the extraction performance of poly(1-vinyl-3-hexylimidazolium bromide)-graphene oxide-grafted silica (poly(VHIm + Br − )@GO@Sil). Graphene oxide (GO) was first coated onto the silica using a layer-by-layer fabrication method, and then the anion of poly(VHIm + Br − )@GO@Sil was changed into hexafluorophosphate (PF 6 − ) by in situ anion exchange. The interaction energies between two PILs and four flavonoids were calculated with the Gaussian09 suite of programs. A Box-Behnken design was used for the optimization of four greatly influential parameters after single-factor experiments to obtain more accurate and precise results. Coupled to high performance liquid chromatography, the poly(VHIm + PF 6 − )@GO@Sil method showed acceptable extraction recoveries for the four flavonoids, with limits of detection in the range of 0.1–0.5 μ g L −1 , and wide linear ranges with correlation coefficients (R) ranging from 0.9935 to 0.9987. Under the optimum conditions, the proposed method was applied to analyze the urines collected from a healthy volunteer. The excretion amount-time profiles revealed that 4–15 h was the main excretion time for the detected flavonoids. The results indicated that the newly developed method offered the advantages of being feasible, green and cost-effective, and could be successfully applied to the extraction and enrichment of flavonoids in human body systems allowing the study of the metabolic kinetics. [ABSTRACT FROM AUTHOR]

• The hydrogel@SiO 2 column has an acceptable degree of swelling in LC. • The hydrogel@SiO 2 column has flexible selectivity for many polar analytes. • The double network structure is composed of hydrogel and metal organic framework. • A kind of hydrogel-MOF composite functionalized silica column was used in LC. Hydrogel is a kind of three-dimensional network structure polymer that can absorb water and swell in water. It has been widely used in many fields due to its flexible functionality. We proposed the design strategy of dual-network hydrogel assisted by a metal-organic-framework (MOF) and modified them on the surface of silica (with average particle diameter of 5 μm and average pore diameter of 76 Å). On the basis of effectively avoiding shortcomings such as osmotic pressure caused by swelling, abundant mesh types of composite material also improves the separation selectivity of the stationary phase. A variety of analytes such as nucleosides/bases, antibiotics, organic acids, carbohydrates, alkylbenzenes, polycyclic aromatic hydrocarbons, pesticides and anions can be selectively separated. The research on the retention behavior and the interaction mechanism proves that the column can be used in mixed mode liquid chromatography. By comparing with the optimized chromatographic conditions of commercial HILIC column and C18 column, this new type of stationary phase also has some significant advantages in the selective separation of mixed analytes. This new stationary phase also has excellent acid/base stability. The intraday relative standard deviation of their retention time under acidic conditions is 0.05%-0.26% (n = 10), and the intraday relative standard deviation under basic conditions is 0.11–0.14% (n = 10). After optimizing the chromatographic conditions, the efficiency of this new type of chromatographic column can reach 90,300 plates/m (sucrose). In short, a new strategy for applying hydrogel to liquid chromatography with high selectivity and chromatographic separation performance is proposed. [ABSTRACT FROM AUTHOR]

• 2D bimetallic magnetic mesoporous carbon (Ni/ZnO@C) were fabricated. • The Ni/ZnO@C nanosheet was gained by calcining 2D bimetallic Ni-ZIF-8. • The materials were used as magnetic solid phase extraction adsorbents. • The method was used to analyze nitroimidazoles from real water samples. We prepared two-dimensional (2D) bimetallic metal-organic frameworks (Ni-ZIF-8) nanosheets by a simple solvent-free method at room temperature. The morphology and composition of Ni-ZIF-8 can be controlled through adding different amounts of Ni. And then, the 2D magnetic mesoporous nanosheets (Ni/ZnO@C) were synthesized by directly pyrolyzing Ni-ZIF-8 under argon atmosphere and explored as magnetic solid phase extraction (MSPE) adsorbents for the determination of nitroimidazole antibiotics (NIABs). Magnetic Ni nanoparticles embedded in carbon nanosheets uniformly resulted in high magnetization saturation of Ni/ZnO@C for easy separation. The Ni/ZnO@C can form hydrogen bond and π-π interaction with three NIABs resulting from their rich N-H containing imidazole, π-electron. Due to the high specific surface area and high mass transfer rate of 2D Ni/ZnO@C, the materials showed satisfactory adsorption capacity and rapid adsorption kinetics for NIABs. A rapid and effective method of Ni/ZnO@C-MSPE combined with high-performance liquid chromatography was proposed for the determination of NIABs. Several main parameters affecting MSPE were investigated. Under the optimal conditions, wide linear was achieved ranging from 0.1 to 500 µg⋅L−1 with a low detection limit of 0.025-0.05 µg⋅L−1. The established method has been successfully applied to analyze NIABs from environmental water samples with satisfactory recovery from 74.33 to 105.71%. [ABSTRACT FROM AUTHOR]

• The adhesion of organic gel simplify the synthesis of stationary phase materials. • It doesn't need any silane coupling agent so it reduces the waste of raw materials. • The prepared stationary phase materials can separate in multiple separation modes. • A new idea of using organic gel as liquid chromatography packing for separation. Organic gel (OG) has excellent characteristics, including a large surface area, adjustable pore/channel size, and good chemical stability, and has attracted great attention in the field of materials. However, the OG packed column is difficult to pack due to the weak mechanical strength and poor monodispersity. Herein, 1-allyl-3-methyl imidazolium hexafluorophosphate-co-1-dodecanethiol ([AMIm]PF 6 -co-TDDM) was prepared on the silica microsphere for chromatographic packing available in multimode liquid chromatography (LC) mode with the good mechanical properties of silica microspheres through a simple OG synthesis method. [AMIm]PF 6 -co-TDDM@SiO 2 hybrid microspheres with uniform particles and narrow particle size distribution are used as stationary phases of LC. These microspheres are used in anion-exchange (IEC), reversed-phase (RP), and hydrophilic interaction (HILIC) mode for the separation of different analytes. Such microspheres can also be used for the preliminary qualitative analysis of active ingredients in actual samples in addition to organic acids, alkylbenzenes, and nucleoside bases. The [AMIm]PF 6 -co-TDDM@SiO 2 chromatography packing also has good reproducibility and stability. The adhesive properties of organogels and the adsorption properties of silica gel simplify the synthesis of stationary phase materials. This simple and effective strategy for preparing [AMIm]PF 6 -co-TDDM@SiO 2 composite microspheres by one-pot method can expand the application of OG as a functional additive on silica microspheres in LC. [ABSTRACT FROM AUTHOR]

• A novel Fe 2 O 3 @C was synthesized by carbonizing MOF-235 under Ar atmosphere. • The magnetic Fe 2 O 3 particles were evenly embedded in porous carbon matrix. • The Fe 2 O 3 @C was used to extract benzoylurea insecticides from tea drink samples. • This work studied the removal effect of three washing on residues from tea leaf. • This method showed satisfactory recovery, wide linear range and low LODs. Ferric oxide/carbon (Fe 2 O 3 @C) was fabricated via direct carbonization of metal-organic framework of iron (MOF-235) under argon atmosphere. The magnetic Fe 2 O 3 nanoparticles are evenly embedded in porous carbon matrix, while original morphology of MOF-235 was well-maintained. The synthesized Fe 2 O 3 @C was used as magnetic sorbent for extracting five benzoylurea insecticides (BUs). The materials exhibited excellent extraction performance, which benefited not only from the strong π-π interaction and hydrophobic interaction (π-conjugated system), but also to the abundant adsorption sites and flexible transport channel (the interconnected 3D porous structure). A three-factor-three-level Box-Behnken design (BBD) was selected to optimize three greatly influential parameters: amount of adsorbent (A), desorption time (B) and volume of desorption solvent (C) by response surface methodology. The established method coupled to HPLC-UV detection showed wide linearity with the range of 0.2–450 μg•L−1, relatively low limits of detection (0.05–0.10 μg•L−1) with the relative standard deviation (RSD) (n = 7) lower t than 5.47%. Moreover, the proposed method was successfully applied to analyze BUs in tea samples and investigate the removal effect of different washing on BUs residues from tea leaf. These results indicated that the synthesized Fe 2 O 3 @C is a promising adsorbent material for magnetic solid phase extraction of BUs at trace concentrations from tea samples. [ABSTRACT FROM AUTHOR]

• Magnetic carbonized polyaniline nanotube was prepared for colorants extraction. • Fe 3 O 4 nanparticals contributed to the separation and adsorption. • Adsorption kinetics and isotherms studies proved the adsorption mechanisms. • The proposed method was used to detect xanthene colorants in beverage and fish samples. Magnetic carbonized polyaniline nanotube composite (Fe 3 O 4 @c-PANI) was synthesized via a self-assemble approach for the extraction and determination of three xanthene colorants including erythrosine B (EB), phloxine B (PB) and rhodamine B (RB). The scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectrometry, X-ray photoelectron spectroscopy and X-ray diffraction were adopted to confirm the successful synthesis of Fe 3 O 4 @c-PANI. When Fe 3 O 4 @c-PANI was applied for extracting three xanthene colorants, satisfactory extraction recoveries ranging from 89.48% to 94.15% were obtained with the relative standard deviation value of 1.09%–4.01%. Compared with Fe 3 O 4 , c-PANI and commercial adsorbents, Fe 3 O 4 @c-PANI achieved better retraction recovery for three colorants. Furthermore, adsorption kinetics and isotherms studies were analyzed to prove the adsorption mechanism of anionic and cationic colorants on Fe 3 O 4 @c-PANI. The graphite layers and pyrrole groups of the as-prepared composite can provide hydrophobic, π–π and hydrogen bonding interaction with xanthene colorants. Fe 3 O 4 nanoparticles played dual-functional roles contributing to the separation and adsorption. Coupled with high performance liquid chromatography, the established magnetic solid phase extraction method was used for the analysis of beverage and fish samples. [ABSTRACT FROM AUTHOR]

• A super-large weight Polyacrylamide coated silica spheres were first prepared. • The stationary phase preparation method was facile and simple. • The stationary phase showed good separation performance for high polar molecules. A polyacrylamide (PAM)-coated silica packing as a novel stationary phase for hydrophilic interaction liquid chromatography (HILIC) was produced firstly by thermal immobilization. The coated layer was formed by a simple and facile physical method that dipping silica spheres into a PAM solution and then stirring the mixture until the solution was evaporated absolutely, leaving a certain amount of PAM on the silica particles. Although there are no chemical bonds involved, the bleeding measurement and the background noise are acceptable. Polyacrylamide coated silica (PAM-Sil, mean diameter: 5 μm) demonstrated a good hydrophilic property and excellent separation efficiency, which was observed especially for several high polar analytes such as saccharides. It is much higher than bare silica or amino columns under the same conditions. Moreover the obtained stationary phase demonstrated good stability under our operation conditions. The specific preparing method offers an easy and economical way to manipulate the thickness of PAM coating and can be extended as a universal way to produce various polymer coated stationary phases with dipping-heating/stirring-evaporating procedure. [ABSTRACT FROM AUTHOR]