Preparation of ionic liquid modified magnetic metal-organic frameworks composites for the solid-phase extraction of α–chymotrypsin

Molecular-Level Interactions in Binary Mixtures of 1-Ethyl-3-methylimidazolium Ethylsulfate and Propane-1,2-diol: The Interplay between Intermolecular and Intramolecular Hydrogen Bonding

In this study, volumetric properties of an ionic liquid, 1-ethyl-3-methylimidazolium ethylsulfate ([C2mim]C2H5SO4), propane-1,2-diol, and their binary mixtures were studied by measurements of density and viscosity. The excess molar volume (VmE), dynamic viscosity deviation (Δη), and excess molar Gibbs free energy of activation for viscous flow (ΔGm*) were calculated and fitted with the Redlich-Kister (RK) type polynomial equation. The results suggested that intermolecular interactions are weaker in the mixture compared to the pure components and the interactions decrease with increasing mole fraction of [C2mim]C2H5SO4. The thermodynamic activation parameters were also calculated from the Eyring equation, and their variations with mole fraction of [C2mim]C2H5SO4 were correlated to the molecular-level interactions. The near-infrared (NIR) spectroscopic measurements were carried out in the temperature range from 293.15 to 333.15 K. The raw NIR data were analyzed further by two-dimensional correlation spectroscopy and principal component analysis. When [C2mim]C2H5SO4 was introduced to the propane-1,2-diol system, the stronger intermolecular hydrogen bonds were destroyed. Propane-1,2-diol and [C2mim]C2H5SO4 produce some weaker hydrogen bonds, but the effect of breaking hydrogen bonds predominates. On the basis of volumetric and NIR spectroscopic investigations, molecular-level interactions are predicted. The interplay between intermolecular and intramolecular hydrogen bonding decides unique molecular-level interactions and dictates enhanced thermodynamic properties of the binary mixtures to make them tunable for a multitude of applications.

Ionic Liquids Functionalized MOFs for Adsorption

Metal-organic frameworks (MOFs) and ionic liquids (ILs) represent promising materials for adsorption separation. ILs incorporated into MOF materials (denoted as IL/MOF composites) have been developed, and IL/MOF composites combine the advantages of MOFs and ILs to achieve enhanced performance in the adsorption-based separation of fluid mixtures. The designed different ILs are introduced into the various MOFs to tailor their functional properties, which affect the optimal adsorptive separation performance. In this Perspective, the rational fabrication of IL/MOF composites is presented, and their functional properties are demonstrated. This paper provides a critical overview of an emergent class of materials termed IL/MOF composites as well as the recent advances in the applications of IL/MOF composites as adsorbents or membranes in fluid separation. Furthermore, the applications of IL/MOF in adsorptive gas separations (CO2 capture from flue gas, natural gas purification, separation of acetylene and ethylene, indoor pollutants removal) and liquid separations (separation of bioactive components, organic-contaminant removal, adsorptive desulfurization, radionuclide removal) are discussed. Finally, the existing challenges of IL/MOF are highlighted, and an appropriate design strategy direction for the effective exploration of new IL/MOF adsorptive materials is proposed.

Triblock copolymer–grafted restricted access materials with zwitterionic polymer outer layers for highly efficient extraction of fluoroquinolones and exclusion of proteins

High-selectivity and high-exclusion restricted access materials (RAMs) benefit the analysis of biological samples. Herein, triblock copolymer-functionalized poly(4-vinylbenzyl chloride-co-divinylbenzene) (P_VBC/DVB) microspheres were prepared via the sequential surface-initiated atom radical polymerization of hydrophobic styrene (St), ionic vinylimidazole (VIm), and zwitterionic sulfobetaine methacrylate (SBMA), affording RAMs with multiple interaction-adsorption sites and zwitterionic polymer exclusion sites on the internal and external surfaces of P_VBC/DVB. The preferential extraction of fluoroquinolones (FQs) is realized based on the hydrophobic/π-π/ion exchange interactions due to the grafted poly-St-VIm, and the zwitterionic poly-SBMA block in the triblock copolymers can efficiently exclude various proteins. A sensitive detection method for FQs in chicken was established by solid phase extraction with RAMs as adsorbent combined with UPLC-MS/MS, achieving wide linearity (2.0-200.0 ng mL^-1), low limit of detection (0.5 μg kg^-1) and limit of quantification (1.5 μg kg^-1), and good inter- and intraday precision with satisfactory recoveries (104.1%-117.7% and 115.3%-121.2% with RSDs < 12%).

Separation and Enrichment of Selected Polar and Non-Polar Organic Micro-Pollutants—The Dual Nature of Quaternary Ammonium Ionic Liquid

In this study, the dual nature of quaternary ammonium ionic liquid–didecyldimethylammonium perchlorate, [DDA][ClO4], was evaluated. A novel and sensitive in situ ionic liquid dispersive liquid–liquid microextraction method (in situ IL-DLLME) combined with magnetic retrieval (MR) was applied to enrich and separate selected organic micro-pollutants, both polar and non-polar. The magnetic support relied on using unmodified magnetic nanoparticles (MNPs) prepared by the co-precipitation of Fe2+/Fe3+ (Fe3O4). The separation technique was on-lined with high-performance liquid chromatography (HPLC–DAD) verified by inverse gas chromatography. An anion exchanger, NaClO4, was added to form an in situ hydrophobic IL. The fine droplets of [DDA][ClO4], molded in aqueous samples, functioned as an extractant for isolating the studied compounds. Then the carrier MNPs were added to separate the IL from the water matrix. The supernatant-free sample was desorbed in acetonitrile (MeCN) and injected into the HPLC system. The applicability of [DDA][ClO4] as an extraction solvent in the MR in situ IL-DLLME method was checked by the selectivity parameters (Sij∞) at infinite dilution. The detection limit (LOD) ranged from 0.011 to 0.079 µg L−1 for PAHs and from 0.012 to 0.020 µg L−1 for benzophenones. The method showed good linearity with correlation coefficients (r2) ranging from 0.9995 to 0.9999.

Ionic liquid-based magnetic nanoparticles for magnetic dispersive solid-phase extraction: A review

Due to their highly tunable nature and outstanding physicochemical properties, ionic liquids (ILs) have been widely reported for use in the synthesis of multitudinous magnetic nanoparticles (MNPs). IL-based magnetic nanoparticles (IL-MNPs) have great potential in magnetic dispersive solid-phase extraction (MDSPE). At present, IL-MNPs have been successfully applied in the pretreatment of MDSPE samples from medicines, pesticides, veterinary drugs, heavy metals, dyes, additives, and proteins in agricultural products, foods and beverages, environmental water, and biological samples. In this review, the preparation of IL-MNPs and their application in MDSPE are comprehensively summarized. The structural characteristics of the introduced ILs used to prepare the IL-MNPs and the synthetic routes employed to obtain the IL-MNPs are described, including physical coating and chemical bonding methods. The IL-MNPs are then classified and described according to different modified materials, including silica-based materials, carbon-based materials, metal-organic frameworks, molecularly imprinted polymers and other interesting large/small molecules. Finally, the research prospects and development directions of IL-MNPs in the context of MDSPE are further identified.

Pyridine ionic liquid functionalized bimetallic MOF solid-phase extraction coupled with high performance liquid chromatography for separation/analysis sunset yellow

An effective method based on the pyridine ionic liquid functionalized bimetallic MOF solid-phase extractant (Cu/Co-MOF@[PrPy][Br]) coupled with high performance liquid chromatography (HPLC) for the separation/analysis sunset yellow was established. Cu/Co-MOF@[PrPy][Br] was characterized by FTIR, XRD, SEM and TEM. Several important factors, such as pH, amount of extractant, extract time, and types of eluents were investigated in detail. Under the optimal conditions, linear range of the method was 0.05–40.00 μg mL⁻¹, the detection limit was 0.02 μg mL⁻¹, and the linear correlation was good (R² = 0.9992). The analysis of sunset yellow in soda, effervescent tablet and jelly proved that the method was simple and effective.

An effective method based on the pyridine ionic liquid functionalized bimetallic MOF solid-phase extractant (Cu/Co-MOF@[PrPy][Br]) coupled with high performance liquid chromatography (HPLC) for the separation/analysis sunset yellow was established.

A green deep eutectic solvent modified magnetic titanium dioxide nanoparticles for the solid-phase extraction of chymotrypsin

Magnetic titanium dioxide nanoparticles modified with green deep eutectic solvent (DES) composed of choline chloride (ChCl) and xylitol (Xyl) (Fe₃O₄@TiO₂@[ChCl][Xyl]) were synthesized and applied to the solid-phase extraction(MSPE) of chymotrypsin (Chy). The physicochemical properties and morphology of Fe₃O₄@TiO₂@[ChCl][Xyl] was characterized by Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), Zeta potential, X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and transmission electron microscope (TEM). The experiment parameters such as initial concentration of Chy, extraction time, pH value, ionic strength, extraction temperature and sample matrix were effectively optimized. Under the optimal experimental conditions, the extraction capacity of Fe₃O₄@TiO₂@[ChCl][Xyl] obtained a significantly improvement after the modification of Fe₃O₄@TiO₂ nanoparticles by [ChCl][Xyl], and reached up to 347.8 mg g^-1. In the elution experiment, 10% sodium dodecyl sulfate-acetic acid (SDS-HAc) was used as eluent, achieving an elution rate of 85.9% for the Chy on Fe₃O₄@TiO₂@[ChCl][Xyl]. And the Fe₃O₄@TiO₂@[ChCl][Xyl] still maintained a good extraction capacity for Chy after six times of reuse. The application result in the extraction of Chy from porcine pancreas crude extract showed a good practical application ability for Chy extraction. All the results indicated that the synthesized Fe₃O₄@TiO₂@[ChCl][Xyl] has good application potential in the extraction of biomolecular molecules such as protein.

Application of magnetic nanomaterials in bioanalysis

The importance of magnetic nanomaterials and magnetic hybrid materials, which are classified as new generation materials, in analytical applications is increasingly understood, and research on the adaptation of these materials to analytical methods has gained momentum. Development of sample preparation techniques and sensor systems using magnetic nanomaterials for the analysis of inorganic, organic and biomolecules in biological samples, which are among the samples that analytical chemists work on most, are among the priority issues. Therefore in this review, we focused on the use of magnetic nanomaterials for the bioanalytical applications including inorganic and organic species and biomolecules in different biological samples such as primarily blood, serum, plasma, tissue extracts, urine and milk. We summarized recent progresses, prevailing techniques, applied formats, and future trends in sample preparation-analysis methods and sensors based on magnetic nanomaterials (Mag-NMs). First, we provided a brief introduction of magnetic nanomaterials, especially their magnetic properties that can be utilized for bioanalytical applications. Second, we discussed the synthesis of these Mag-NMs. Third, we reviewed recent advances in bioanalytical applications of the Mag-NMs in different formats. Finally, recently literature studies on the relevance of Mag-NMs for bioanalysis applications were presented.

Solid-Phase Extraction of Aristolochic Acid I from Natural Plant Using Dual Ionic Liquid-Immobilized ZIF-67 as Sorbent

(1) Background: ZIF-67 is one of the most intriguing metal–organic frameworks already applied in liquid adsorption. To increase its adsorption performance, dual ionic liquids were immobilized on ZIF-67 in this research; (2) Methods: The obtained sorbent was used to adsorb aristolochic acid I (AAI) in standard solutions. Then, the sorbent was applied in solid-phase extraction to remove AAI from Fibraurea Recisa Pierre extracted solution. (3) Results: By analyzing the adsorption models, the highest adsorption capacity of immobilized sorbent (50.9 mg/g) was obtained at 25 °C within 120 min. In the SPE process, 0.02 mg of AAI was removed per gram of herbal plant, the adequate recoveries were in the range of 96.2–100.0%, and RSDs were 3.5–4.0%; (4) Conclusions: The provided experimental data revealed that ZIF-67@EIM-MIM was an excellent potential sorbent to adsorb and remove AAI from herbal plant extract, and the successful separation indicated that this sorbent could be an ideal material for the pretreatment of herbal plants containing AAI.

Greenness of magnetic nanomaterials in miniaturized extraction techniques: A review

Green analytical chemistry principles should be followed, as much as possible, and particularly during the development of analytical sample preparation methods. In the past few years, outstanding materials such as ionic liquids, metal-organic frameworks, carbonaceous materials, molecularly imprinted materials, and many others, have been introduced in a wide variety of miniaturized techniques in order to reduce the amount of solvents and sorbents required during the analytical sample preparation step while pursuing more efficient extraction methods. Among them, magnetic nanomaterials (MNMs) have gained special attention due to their versatile properties. Mainly, their ability to be separated from the sample matrix using an external magnetic field (thus enormously simplifying the entire process) and their easy combination with other materials, which implies the inclusion of a countless number of different functionalities, highly specific in some cases. Therefore, MNMs can be used as sorbents or as magnetic support for other materials which do not have magnetic properties, the latter permiting their combination with novel materials. The greenness of these magnetic sorbents in miniaturized extractions techniques is generally demonstrated in terms of their ease of separation and amount of sorbent required, while the nature of the material itself is left unnoticed. However, the synthesis of MNMs is not always as green as their applications, and the resulting MNMs are not always as safe as desired. Is the analytical sample preparation field ready for using green magnetic nanomaterials? This review offers an overview, from a green analytical chemistry perspective, of the current state of the use of MNMs as sorbents in microextraction strategies, their preparation, and the analytical performance offered, together with a critical discussion on where efforts should go.

Determination of fluoroquinolones in foods using ionic liquid modified Fe3O4/MWCNTs as the adsorbent for magnetic solid phase extraction coupled with HPLC

In this work, a simple and sensitive method based on Fe₃O₄/multi-walled carbon nanotubes/ionic liquid (Fe₃O₄/MWCNTs/IL) as the adsorbent for magnetic solid phase extraction coupled with high performance liquid chromatography was developed for the determination of trace fluoroquinolones in foods. After a simple one-pot solvothermal synthesis, Fe₃O₄/MWCNTs were further modified with an amine-terminated ionic liquid to enhance their dispersibility and extraction capacity. The morphology, structure and magnetic properties of the composite adsorbent were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction spectrometry and vibrating-sample magnetometry. Under the optimized extraction and detection conditions, the studied fluoroquinolones were enriched effectively and separated well and their UV signals were linear to their concentrations in the range of 4-1000 ng mL^-1, with correlation coefficients ranging from 0.9958 to 0.9990. The enrichment factors were 29.1-43.9 fold and the limits of detection were 0.33-0.78 ng mL^-1. The spiked recoveries were 85.4-105.9% for milk and 85.2-103.7% for pork samples, with relative standard deviations of 0.8-5.7%. The developed method provided a fast, sensitive and reliable determination platform for fluoroquinolones in complex real samples.

Role of Ionic Liquids in Composites in Analytical Sample Preparation

Ionic liquids (ILs) are a group of non-conventional salts with melting points below 100 °C. Apart from their negligible vapor pressure at room temperature, high thermal stability, and impressive solvation properties, ILs are characterized by their tunability. Given such nearly infinite combinations of cations and anions, and the easy modification of their structures, ILs with specific properties can be synthesized. These characteristics have attracted attention regarding their use as extraction phases in analytical sample preparation methods, particularly in liquid-phase extraction methods. Given the liquid nature of most common ILs, their incorporation in analytical sample preparation methods using solid sorbents requires the preparation of solid derivatives, such as polymeric ILs, or the combination of ILs with other materials to prepare solid IL-based composites. In this sense, many solid composites based on ILs have been prepared with improved features, including magnetic particles, carbonaceous materials, polymers, silica materials, and metal-organic frameworks, as additional materials forming the composites. This review aims to give an overview on the preparation and applications of IL-based composites in analytical sample preparation in the period 2017–2020, paying attention to the role of the IL material in those composites to understand the effect of the individual components in the sorbent.

Designed Fabrication of Polymer-Mediated MOF-Derived Magnetic Hollow Carbon Nanocages for Specific Isolation of Bovine Hemoglobin

It is highly required to develop well-designed separation materials for the specific isolation of certain proteins in proteomic research. Herein, the new type of metal-organic framework (MOF)-derived polymer-mediated magnetic hollow nanocages was fabricated via stress-induced orientation contraction, which was further applied for specific enrichment of proteins. The core-shell nanocomposites comprised of polymer-mediated ZIF-67 cores and polydopamine (PDA) shells, after annealing, generated magnetic hollow carbon nanocages with hierarchical pores and structures. Particularly, the magnetic carbonized PDA@F127/ZIF-67 hollow nanocages exhibited a remarkable adsorption capacity toward bovine hemoglobin (BHB) up to 834.3 mg g^-1, which was significantly greater than that of the directed carbonized ZIF-67 nanoparticles. The results also exhibited the notable specificity of the obtained nanocages on complex biosamples, including intact mixed proteins and fetal calf serum. The hierarchically hollow porous structure greatly improves the specific surface area and reduces the mass transfer resistance, leading to enhanced high adsorption for target protein BHB. This novel method will be promising for the applications in purification and enrichment of biomacromolecules for complex biosamples, which successfully solve the problem of low adsorption efficiency and tedious separating process of the previous MOF-derived materials.

Self-assembly of poly(ionic liquid) functionalized mesoporous magnetic microspheres for the solid-phase extraction of preservatives from milk samples

In this work, a novel, rapid, and simple analytical method was proposed for the detection of parabens in milk sample by gas chromatography coupled with mass spectrometry. At the same time, milk sample was pretreated by magnetic solid phase extraction, which detected up to five parabens. A series of important parameters of magnetic solid phase extraction were investigated and optimized, such as pH value of loading buffer, amount of material, adsorption time, ionic strength, eluting solvents, and eluting time. Under the optimized conditions, the corresponding values were more than 0.9991, limits of detection and the limit of quantification were 0.1 and 0.5 ng/mL, respectively. In addition, the recoveries were achieved in range of 95-105%, the liner range were within 0.1-600 ng/mL, and the relative standard deviations were even lower than 5%.

Magnetic solid-phase extraction of pyrethroid insecticides from tea infusions using ionic liquid-modified magnetic zeolitic imidazolate framework-8 as an adsorbent

A simple, sensitive, and reliable magnetic solid-phase extraction (SPE) method coupled with GC-MS/MS for the effective analysis of four pyrethroids from tea infusions was developed. A magnetic adsorbent, named ionic liquid-modified magnetic zeolitic imidazolate framework-8 (Fe3O4/ZIF-8/IL), was prepared by immobilizing an ionic liquid (IL) on the surface of Fe3O4/ZIF-8. The textures of Fe3O4/ZIF-8/IL were confirmed by material characterization, and the results suggested that the adsorbent possessed high magnetism (59.0 emu g-1), an adequate Brunauer-Emmett-Teller (BET) surface area (104 m2 g-1), and a large pore volume (0.68 cm3 g-1). To confirm the extraction performance of the prepared Fe3O4/ZIF-8/IL, several experimental conditions affecting the extraction efficiency were investigated. Under the optimum conditions, the limits of determination (LODs) for the four pyrethroids were in the range of 0.0065-0.1017 μg L-1 (S/N = 3 : 1) with an intra-day relative standard deviation (RSD) of ≤9.70% and inter-day RSD of ≤11.95%. The linear ranges were 0.5-50 μg L-1 for bifenthrin and 0.5-500 μg L-1 for permethrin, cypermethrin, and flucythrinate, with determination coefficients higher than 0.999. Finally, the proposed technique was successfully applied for the determination of pyrethroids in real tea infusions. This work could be extended to other IL-modified metal-organic frameworks (MOFs) and to the development of different sample pretreatment techniques.

Magnetic Solid-Phase Extraction of Dichlorodiphenyltrichloroethane and Its Metabolites from Environmental Water Samples Using Ionic Liquid Modified Magnetic Multiwalled Carbon Nanotube/Zeolitic Imidazolate Framework-8 as Sorbent

As persistent organic pollutants, dichlorodiphenyltrichloroethanes (DDTs) and their metabolites pose considerable risks to human health and the environment. Therefore, monitoring DDTs in the environment is essential. Here, we developed a green, simple, and effective magnetic solid-phase extraction (MSPE) method coupled with gas chromatography tandem triple-quadrupole mass spectrometry to determine the DDT content of environmental water samples. A magnetic ionic liquid (IL) adsorbent was developed based on a modified magnetic multiwalled carbon nanotube/zeolitic imidazolate framework-8 (MM/ZIF-8/IL), synthesized by immobilizing the IL on the surface of MM/ZIF-8. We confirmed successful synthesis of MM/ZIF-8/IL by material characterization, and our results suggested that the MM/ZIF-8/IL had a high Brunauer-Emmett-Teller surface area (159.9 m2 g-1), good thermostability (<800 °C), and a high degree of superparamagnetism (52.9 emu g-1). Several experimental conditions affecting the MSPE efficiency were optimized. Under the best conditions, good detection linearity was achieved (0.5-500 µg L-1) with determination coefficients ranging from 0.9927 to 0.9971. The lower limits of detection (0.0016-0.0072 µg L-1) also had good precision, having an intraday relative standard deviation (RSD) ≤ 6.5% and an interday RSD ≤ 8.9%. Finally, we used the as-developed method to determine DDT levels in environmental water samples.

Synthesis of magnetic metal–organic framework composites, Fe3O4-NH2@MOF-235, for the magnetic solid-phase extraction of benzoylurea insecticides from honey, fruit juice and tap water samples

Herein, a novel, fusiform-like magnetic metal–organic framework material (Fe₃O₄-NH₂@MOF-235) was fabricated by a facile two-step solvothermal approach.

Creating magnetic ionic liquid-molecularly imprinted polymers for selective extraction of lysozyme

A novel magnetic (Fe3O4) surface molecularly imprinted polymer (MIP) based on ionic liquid (IL) (Fe3O4@VTEO@IL-MIPs) was prepared for the selective extraction of lysozyme (Lys). As the functional monomer of the MIPs, an imidazolium-based IL with vinyl groups was prepared. It can provide multiple interactions with template molecules. The amount of IL was optimized (200 mg). Fourier transform infrared spectrometry (FT-IR), transmission electron microscopy (TEM), dynamic light scattering (DLS), thermogravimetric analysis (TGA) and a vibrating sample magnetometer (VSM) were used to characterize the MIP. The results indicate the successful formation of an imprinting polymer layer. The concentration of Lys in the supernatant was determined by UV-vis spectrophotometry at a wavelength of 280 nm. The maximum adsorption capability of the MIP is 213.7 mg g-1 and the imprinting factor (IF) is 2.02. It took 2.5 h for the MIP to attain adsorption equilibrium. The structure of the protein was evaluated using circular dichroism (CD) spectra and UV-visible spectra. The adsorption performance was further investigated in detail by selective adsorption experiments, competitive rebinding tests, and reusability and stability experiments. Furthermore, it was utilized to separate the template protein from a mixture of proteins and real samples successfully because of the high adsorption capacity for Lys.

Magnetic solid-phase extraction for the removal of mercury from water with ternary hydrosulphonyl-based deep eutectic solvent modified magnetic graphene oxide

A novel ternary hydrosulphonyl-based deep eutectic solvent (THS-DES) comprised of choline chloride/itaconic acid/3-mercaptopropionic acid (molar ratio 2:1:1) was firstly synthesized. The composition, property and microscopic structure of the new magnetic adsorbent (THS-DES@M-GO) based on the THS-DES modified the magnetic graphene oxide (M-GO) was characterized by the system. Magnetic solid-phase extraction (MSPE) based THS-DES@M-GO was firstly researched for the removal of mercury (Hg²⁺) from water. Various influencing factors such as the mass of adsorbent, solution pH, initial Hg²⁺ concentration, the removal time and temperature had been systematically tested. Under optimized conditions the removal efficiency (R%) could achieved 99.91%. The precision, repeatability and stability experiments were investigated in detail to evaluate the presented method. The relative standard deviations (RSD) of the removal efficiency were 0.053%, 1.49% and 1.55%, respectively. The maximum adsorption capacity (Q_max) was 215.1 mg g^-1 and the data of the experiment fitted well with Langmuir model. Elution experimental studies shown that 94.94% of Hg²⁺ could be eluted by ethylenediaminetetraacetic acid (EDTA). After seven cycles of adsorption-desorption processes, the THS-DES@M-GO still retained a high removal efficiency of 90.23%. Compared with other adsorbents prepared in this work, THS-DES@M-GO displayed higher removal efficiency for Hg²⁺. Interference study proved the composites was tolerated and stabled under the complex matrix. What's more, the analysis of mercury contaminated water (from Guizhou, P.R., China) proved that the proposed method could be used to remove Hg²⁺ in practical application.