Core-shell microparticles formed by the metal-organic framework CIM-80(Al) (Silica@CIM-80(Al)) as sorbent material in miniaturized dispersive solid-phase extraction

Applications of metal organic frameworks in dispersive micro solid phase extraction (D-μ-SPE)

Metal-organic frameworks (MOFs) are a fascinating family of crystalline porous materials made up of metal clusters and organic linkers. In comparison with other porous materials, MOFs have unique characteristics including high surface area, homogeneous open cavities, and permanent high porosity with variable shapes and sizes. For these reasons, MOFs have recently been explored as sorbents in sample preparation by solid-phase extraction (SPE). However, SPE requires large amounts of sorbents and suffers from limited contact surfaces with analytes, which compromises extraction recovery and efficiency. Dispersive SPE (D-SPE) overcomes these limitations by dispersing the sorbents into the sample, which in turn increases contact with the analytes. Miniaturization of the microextraction procedure, particularly the amount of sorbent reduces the amount consumed of the organic solvent and shorten the time required to attain the equilibrium state. This may explain the reported high efficiency and applicability of MOFs in dispersive micro SPE (D-µ-SPE). This method retains all the advantages of solid phase extraction while also being simpler, faster, cheaper, and, in some cases, more effective in comparison with D-SPE. Besides, D-µ-SPE requires smaller amounts of the sorbents which reduces the overall cost, and the amount of waste generated from the analytical process. In this review, we discuss the applications of MOFs in D-µ-SPE of various analytes including pharmaceuticals, pesticides, organic dyes from miscellaneous matrices including water samples, biological samples and food samples.

Synthesis and Characterization of the Metal–Organic Framework CIM-80 for Organic Compounds Adsorption

Metal–organic frameworks (MOF) are a new type of porous materials that have great potential for adsorption of voltaic organic compounds (VOCs). These types of materials composed of metal ions and organic ligands are easy to synthesize, have high surface areas, their surface chemistry can be adjusted to the desired application, and they can also have good chemical and thermal stability. Therefore, this work focuses on the synthesis of a highly hydrophobic MOF material called CIM-80, a porous material that is made up of the Al³⁺ cation and the mesaconate linker. This MOF has a B.E.T. of approximately 800 m²/g and has potential applications for the adsorption of hydrophobic organic compounds. However, its synthesis is expensive and very dirty. Therefore, we have studied the synthesis conditions necessary to achieve high synthesis yields (85%) and materials with high crystallinity and accessible porosity. To achieve these results, we have used urea as a mild deprotonation reagent and modulator as an alternative to NaOH, which is traditionally used for the synthesis of this MOF. Once the synthesis of this material was controlled, its adsorption/desorption behavior of water and organic compounds such as toluene, cyclohexane and m-xylene was studied by means of vapor adsorption isotherms. The results show the hydrophobic character of the material and the greater affinity the material has toward aliphatic compounds than toward aromatic ones, with toluene being the most adsorbed compound, followed by cyclohexane and m-xylene.

Fabrication of Magnetic Al-Based Fe3O4@MIL-53 Metal Organic Framework for Capture of Multi-Pollutants Residue in Milk Followed by HPLC-UV

The efficient capture of multi-pollutant residues in food is vital for food safety monitoring. In this study, in-situ-fabricated magnetic MIL-53(Al) metal organic frameworks (MOFs), with good magnetic responsiveness, were synthesized and applied for the magnetic solid-phase extraction (MSPE) of chloramphenicol, bisphenol A, estradiol, and diethylstilbestrol. Terephthalic acid (H₂BDC) organic ligands were pre-coupled on the surface of amino-Fe₃O₄ composites (H₂BDC@Fe₃O₄). Fe₃O₄@MIL-53(Al) MOF was fabricated by in-situ hydrothermal polymerization of H₂BDC, Al (NO₃)₃, and H₂BDC@Fe₃O₄. This approach highly increased the stability of the material. The magnetic Fe₃O₄@MIL-53(Al) MOF-based MSPE was combined with high-performance liquid chromatography-photo diode array detection, to establish a novel sensitive method for analyzing multi-pollutant residues in milk. This method showed good linear correlations, in the range of 0.05–5.00 μg/mL, with good reproducibility. The limit of detection was 0.004–0.108 μg/mL. The presented method was verified using a milk sample, spiked with four pollutants, which enabled high-throughput detection and the accuracies of 88.17–107.58% confirmed its applicability, in real sample analysis.

Uniform Core-Shell Microspheres of SiO2@MOF for CO2 Cycloaddition Reactions

A SiO₂@MOF core-shell microsphere for environmentally friendly applications was introduced in this study. Several types of metal-organic framework core-shell microspheres were successfully synthesized. To achieve high stability and favorable catalytic performance, modification and coating methods were necessary for optimization. The improved SiO₂@MOF core-shell microspheres were used in the cycloaddition reaction of carbon dioxide and propylene oxide. Dispersion ability was enhanced by the addition of core-shell microspheres, which also produced high catalytic activity. Accompanied with tetrabutylammonium bromide as a co-catalyst, SiO₂@ZIF-67 had a maximum conversion of 97%, and the results revealed that SiO₂@ZIF-67 could be used for 5 reaction cycles while maintaining high catalytic performance. This recycling catalyst was also reacted with a series of terminal epoxides to form corresponding cyclic carbonates with high conversion rates, indicating that SiO₂@MOF core-shell microspheres exhibit promise in the field of catalysis.

Hybrid Materials Formed with Green Metal-Organic Frameworks and Polystyrene as Sorbents in Dispersive Micro-Solid-Phase Extraction for Determining Personal Care Products in Micellar Cosmetics

Hybrid materials based on polystyrene (PS) and green metal-organic frameworks (MOFs) were synthesized, characterized, and evaluated as potential sorbents in dispersive micro-solid-phase extraction (µ-dSPE). Among the resulting materials, the hybrid PS/DUT-67(Zr) was selected as the adequate extraction material for the monitoring of six personal care products in micellar cosmetic samples, combining the µ-dSPE method with ultra-high performance liquid chromatography (UHPLC) coupled to ultraviolet/visible detection (UV/Vis). Univariate studies and a factorial design were performed in the optimization of the microextraction procedure. The compromise optimum extraction conditions included 20 mg of PS/DUT-67(Zr) for 10 mL of sample, 2 min of extraction time, and two desorption steps using 100 µL of acetonitrile and 5 min assisted by vortex in each one. The validated μ-dSPE-UHPLC-UV/Vis method presented limits of detection and quantification down to 3.00 and 10.0 μg·L-1, respectively. The inter-day precision values were lower than 23.5 and 21.2% for concentration levels of 75 μg·L-1 and 650 μg·L-1, respectively. The hydrophobicity of the resulting PS/DUT-67(Zr) material was crucial for the improvement of its extraction capacity in comparison with its unitary components, showing the advantages of combining MOFs with other materials, getting new sorbents with interesting properties.

Highly selective magnetic dual template molecularly imprinted polymer for simultaneous enrichment of sulfadiazine and sulfathiazole from milk samples based on syringe-to-syringe magnetic solid-phase microextraction

Antibiotics, such as sulfadiazine and sulfathiazole, are widely used in veterinary applications which can result in remains in edible animal products. Therefore, there is an immense need for a reliable, selective, sensitive, and simple analytical technique for monitoring the concentration of sulfadiazine (SDZ) and sulfathiazole (STZ) in edible animal products. In this regard, we developed a magnetic dual template molecularly imprinted polymer (MMIP) to determine the SDZ and STZ in milk samples. For the sensitive and selective extraction and determination of target analytes, MMIPs have been combined with the syringe-to-syringe magnetic solid-phase microextraction (SS-MSPME) method. In addition, we used central composite design (CCD) for the extraction of SDZ and STZ. With optimum conditions, an efficient, rapid, and convenient technique for the preconcentration and determination of SDZ and STZ in milk samples by SS-MSPME coupling with HPLC-UV was developed. Using our combined approach, the limits of detection are 0.9 and 1.3 ng mL^-1 for SDZ and STZ, respectively, along with good linearity and determination coefficients higher than 0.98. Our method demonstrates a practical approach for the deduction of antibiotics in milk samples with high recoveries and selectivity.

Application of magnetic nanomaterials in magnetic in-tube solid-phase microextraction

Development of magnetic nanomaterials has greatly promoted the innovation of in-tube solid-phase microextraction. This review article gives an insight into recent advances in the modifications and applications of magnetic nanomaterials for in-tube solid-phase microextraction. Also, different magnetic nanomaterials which have recently been utilized as in-tube solid-phase microextraction sorbents are classified. This study shows that magnetic nanomaterials have gained significant attention owing to large specific surface area, selective absorption, and surface modification. Magnetic in-tube solid-phase microextraction has been applied for the analysis of food samples, biological, and environmental. However, for full development of magnetic in-tube SPME, effort is still needed to overcome limitations, such as mechanical stability, selectivity and low extraction efficiency. To achieve these objectives, research on magnetic in-tube SPME is mainly focused in the preparation of new extractive phases.

Magnetic Cu: CuO-GO nanocomposite for efficient dispersive micro-solid phase extraction of polycyclic aromatic hydrocarbons from vegetable, fruit, and environmental water samples by liquid chromatographic determination

In this research, we presented a magnetic dispersive micro-solid phase extraction (MD-μ-SPE) method coupled with high performance liquid chromatography (HPLC) based on the use of magnetic Cu: CuO-Graphene Oxide (GO) nanocomposite (Fe₃O₄/Cu: CuO/GO-NC) for the separation and preconcentration of polycyclic aromatic hydrocarbons (PAHs), i.e. naphthalene (Nap), phenanthrene (Phe), anthracene (Ant), and pyrene (Pyr), in vegetable (onion, tomato, carrot, herb, watermelon, lettuce, eggplant, and chili pepper), fruit (apple, watermelon, and grape), wastewater, and water samples. The MD-μ-SPE of PAHs in matrix samples was carried out, and the impacts of pH, ionic strength, extraction time, temperature, eluent volume, and sorbent mass on the recovery of PAHs were investigated by using Placket-Burman design (PBD). In addition, by using the central composite design (CCD), the best combination of each important variable was measured. Sorbent mass of 14 mg, eluent volume of 200 μL, and 12 min extraction time at the central level of other factors were optimal conditions of pretreatment for the highest extraction recovery (ER%) of trace PAHs. Under the optimal conditions, the method proposed herein provided high enrichment factors ranged from 116.51 to 133.05, good linearity in the range of 10-3800 ng mL^-1 for Pyr, 3.0-3500 ng mL^-1 for Phe, 5.0-3200 ng mL^-1 for Nap, and 5.0-3000 ng mL^-1 for Ant with coefficient of determination (R²) values between 0.9889 and 0.9963, low limits of detection (LOD) and quantification (LOQ) in the range of 0.015-0.061 and 0.485-2.034 ng mL^-1, respectively, and also satisfactory spiked recoveries (between 95.1% and 106.8%) with the relative standard deviations (RSDs) values in the range of 1.73%-5.62%. The Fe₃O₄/Cu: CuO/GO-NC-based MD-μ-SPE followed by HPLC-UV corroborated promising results for the convenient and effective determination of PAHs in the samples of vegetables, fruits, and environmental water. The results of this study revealed that our developed method is easy, feasible, precise, highly effective, and convenient to operate for the trace analysis of PAHs in different real samples. The extraction recovery was about 90% of the initial recovery after the sorbent usage for three times; therefore, the Fe₃O₄/Cu: CuO/GO-NC can readily be regenerated.

Reduced graphene oxide-based magnetic composite for trace determination of polycyclic aromatic hydrocarbons in cosmetics by stir bar sorptive dispersive microextraction

This work describes a sensitive and rapid analytical method for trace determination of polycyclic aromatic hydrocarbons (PAHs) in cosmetic samples. The proposed method is based on stir bar sorptive-dispersive microextraction (SBSDME). A magnetic composite made of CoFe₂O₄ magnetic nanoparticles embedded into reduced graphene oxide sheets is used as sorbent phase. After the extraction, the target analytes are desorbed in toluene and then analyzed by gas chromatography-mass spectrometry (GC-MS). The main parameters involved in the extraction procedure (i.e., composite amount, extraction time and desorption time) were evaluated and optimized to provide the best extraction efficiency. The method was successfully validated under the selected conditions, showing a linear range of at least up to 125 ng mL^-1, instrumental and method limits of detection from 0.02 to 2.50 ng mL^-1 and from 0.15 to 24.22 ng g^-1, respectively, and relative standard deviations (RSD) below 10 % for all the target analytes. Standard addition combined with internal standard calibration was employed for quantification. The proposed method was successfully applied to the analysis of ten PAHs in four cosmetic products of different matrix. Several analytes between 14 and 464 ng g^-1 were found, some of them prohibited in cosmetic products. This work expands the analytical potential of SBSDME technique to other analytes and to the use of new sorbent phases, showing the great versatility of this approach depending on the characteristics of the analytes.

Recent Progress on Luminescent Metal-Organic Framework-Involved Hybrid Materials for Rapid Determination of Contaminants in Environment and Food

The high speed of contaminants growth needs the burgeoning of new analytical techniques to keep up with the continuous demand for monitoring and legislation on food safety and environmental pollution control. Metal-organic frameworks (MOFs) are a kind of advanced crystal porous materials with controllable apertures, which are self-assembled by organic ligands and inorganic metal nodes. They have the merits of large specific surface areas, high porosity and the diversity of structures and functions. Latterly, the utilization of metal-organic frameworks has attracted much attention in environmental protection and the food industry. MOFs have exhibited great value as sensing materials for many targets. Among many sensing methods, fluorometric sensing is one of the widely studied methods in the detection of harmful substances in food and environmental samples. Fluorometric detection based on MOFs and its functional materials is currently one of the most key research subjects in the food and environmental fields. It has gradually become a hot research direction to construct the highly sensitive rapid sensors to detect harmful substances in the food matrix based on metal-organic frameworks. In this paper, we introduced the synthesis and detection application characteristics (absorption, fluorescence, etc.) of metal-organic frameworks. We summarized their applications in the MOFs-based fluorometric detection of harmful substances in food and water over the past few years. The harmful substances mainly include heavy metals, organic pollutants and other small molecules, etc. On this basis, the future development and possible application of the MOFs have prospected in this review paper.