Thin metal organic frameworks coatings by cathodic electrodeposition for solid-phase microextraction and analysis of trace exogenous estrogens in milk

Synthesis of Magnetic Attapulgite Nanoparticles Via a Novel Surface Covalent Reaction Method and its Application in the Magnetic Solid Phase Extraction

In this study, the attapulgite nanoparticle was immobilized on the surface of magnetic nanoparticle Fe3O4 via a novel surface covalent reaction method for the magnetic solid phase extraction (MSPE) for the first time. The surface covalent reaction method has the advantages of controllable steps, and can make the magnetic attapulgite nanoparticle (MANP) have good homogeneity and high stability. Field emission scanning electron microscopy, equipped with an energy dispersive spectrometer, Nitrogen adsorption BET, X-ray diffraction and Fourier transform infrared spectroscopy were applied to characterize the prepared MANP, confirming that the attapulgite nanoparticle could be effectively immobilized on the surface of magnetic nanoparticle Fe3O4 via covalent reactions. Under optimal conditions of the MSPE experiment based on the MANP, the limits of detection were found to be 10 ng/mL for melamine and 3 ng/mL for cyromazine with a relative standard deviation < 10% by a high-performance liquid chromatography system. Meanwhile, 0.1 mg/mL melamine in milk and 0.1 mg/mL cyromazine in cucumber can also be detected according to our MSPE procedure. More importantly, the MANP still has good magnetism and enrichment efficiency after several decades of use. These results showed that the MANP prepared by our method is a kind of promising material for the MSPE.

Electrospun of functionalized mesoporous UiO-66 as the selective coating of solid phase microextraction Arrow for the determination of nine alkylphenols

A solid-phase microextraction (SPME) Arrow and high-performance liquid chromatography-UV detector (HPLC-UV, detection at 225 nm) based method was developed for the selective determination of nine alkylphenols (APs) in milk. The functionalized mesoporous UiO-66 (4-meso-UiO-66) was utilized as the new coating material, which was synthesized by post-modification of pore-expanded UiO-66-NH2 by an esterification reaction with 4-pentylbenzoic acid. It was fully characterized by X-ray photoelectron spectroscopy (XPS), fourier transformation infrared spectrometry, nitrogen sorption-desorption test, scanning electron microscopy, transmission electron microscopy, and X-ray diffractometer. The characterization results showed the ester groups and benzene rings were introduced into the 4-meso-UiO-66, and the mesoporous structure was predominant in the 4-meso-UiO-66. The extraction mechanism of 4-meso-UiO-66 to APs is the synergistic effect of Zr-O electrostatic interaction and the size exclusion effect resulting from XPS, selectivity test, and nitrogen sorption-desorption test. The electrospinning technique was utilized to fabricate the 4-meso-UiO-66 coated SPME Arrow and polyacrylonitrile (PAN) was used as the adhesive. The mass rate of 4-meso-UiO-66 to PAN and the electrospinning time were evaluated. The extraction and desorption parameters were also studied. The linear range of this method was 0.2-1000 μg L-1 with a coefficient of determination greater than 0.9989 under the optimal conditions. The detection limits were 0.05-1 μg L-1, the inter-day and intra-day precision (RSD) were 2.8-11.5%, and the recovery was 83.6%-112%. The reusability study showed that the extraction performance of this new SPME Arrow could be maintained after 80 adsorption-desorption cycles. This method showed excellent applicability for the selective determination of APs in milk.

The application progress of magnetic solid-phase extraction for heavy metal analysis in food: a mini review

The emerging sample pretreatment technique of magnetic solid-phase extraction (MSPE) has drawn the attention of researchers owing to its advantages of less reagent consumption, fast separation/enrichment process, high adsorption capacity, and simple operation. This paper presents a review of synthesis techniques, classification, and analysis procedures for MSPE in the detection of heavy metals in food. Magnetic adsorbents derived from silica, metal oxides, carbon, polymers, etc., are applied for the detection of heavy metals in food. Then, the recent development of the technology of MSPE for the analysis of heavy metal extraction in food is summarized in detail. Finally, the future outlook for the improvement of MSPE is also discussed.

Detection mechanism and the outlook of metal-organic frameworks for the detection of hazardous substances in milk

Milk has a high nutritional value. However, milk is easily contaminated in the production, processing, and storage processes, which harms consumers' health. Therefore, the harmful substances' detection in milk is important. Metal-organic frameworks (MOFs) have proven high potential in food safety detection due to their unique porous structure, large effective surface area, large porosity, and structural tunability. This article systematically describes the detection mechanism of fluorescence, electrochemical, colorimetric, and enzyme-linked immunosorbent assay based on MOFs. The progress of the application of MOFs in the detection of antibiotics, harmful microorganisms and their toxins, harmful ions, and other harmful substances in milk in recent years is reviewed. The structural tunability of MOFs enables them to be functionalized, giving the ability to be applied to different detection methods or substances. Therefore, MOFs can be used as an advantageous sensing material for detecting harmful substances in the complex environment of milk.

Ultrafast and Scalable Fabrication of Coordination Polymer Films on Network Substrates via Thermal Current-Induced Dewetting

Coordination polymers are among the most favored active materials by researchers due to their broad application prospects. However, most of them are usually difficult to directly process into applicable devices because of their unsatisfied processability. One process of great concern for researchers is the in situ preparation of the coordination polymer on the applicable substrate, especially for the favored network substrates with good mechanical properties and 3D porous structure, which could provide obvious convenience and facilitation in the application process. Herein, we present an ultrafast and scalable thermal current-induced dewetting strategy to obtain uniform coordination polymer film in situ on network substrates, which could enable unprecedented convenience to obtain directly usable coordination polymer composites such as practical catalytic electrodes with excellent electrocatalytic performance. The proposed thermal current-induced dewetting method provides a highly adaptable and efficient practical production approach to integrate coordination polymer materials with network substrates and also provides new inspiration for understanding and applying the dewetting process on complex 3D network substrates.

An electrochemically fabricated ZIF-67/[HOEMIM]BF4 coating for the solid-phase microextraction and detection of polycyclic aromatic hydrocarbons

Coatings are considered to play a crucial role in solid-phase microextraction (SPME). In this work, a novel coating named ZIF-67/[HOEMIM]BF4 was fabricated through in situ potentiostatic electrodeposition in methanol solutions containing ZIF-67 precursors and 1-(2'-hydroxyethyl)-3-methylimidazolium tetrafluoroborate ([HOEMIM]BF4). Compared with the traditional solvothermal method, this method reduced the synthesis time and enabled ZIF-67 to grow directly on the surface of stainless-steel wire, effectively simplifying the preparation process and improving the coating reproducibility. Owing to the inherent characteristics such as high porosity and high thermal and mechanical stability, and the impressive morphological regulation and extraction function of [HOEMIM]BF4, the developed coating exhibited a prolonged service life and a better extraction capacity for trace polycyclic aromatic hydrocarbons (PAHs) compared to single ZIF-67 and commercial fibers. Under the optimal conditions, the linear range of the ZIF-67/[HOEMIM]BF4-based SPME-GC method was 0.01-500 μg L-1, and the detection limit was 0.27-5.2 ng L-1. When applied in the determination of PAHs in a real water sample, recoveries between 85.6-117.3% were obtained, indicating the potential of ZIF-67/[HOEMIM]BF4 in the high efficiency SPME and GC analysis of PAHs.

Hydrophobic Mesoporous Silica-Coated Solid-Phase Microextraction Arrow System for the Determination of Six Biogenic Amines in Pork and Fish

In this study, a functionalized mesoporous silica-coated solid-phase microextraction (SPME) Arrow system was developed for the enrichment of six biogenic amines (BAs) from pork and fish samples before gas chromatographic separation with a mass spectrometer as a detector. MCM-41 was utilized as the substrate material and thereby functionalized by titanate and sodium dodecyl sulfate to adjust its surface acidity and hydrophobicity, respectively. The functionalized MCM-41 (named as MCM-T-H) was coated on a bare SPME Arrow using the dipping method and polyacrylonitrile was used as the adhesive. The extraction capacity and selectivity of the MCM-T-H-SPME Arrow for six kinds of derivatized BAs were studied and compared with commercial SPME Arrows. Experimental parameters, e.g., sample volume, derivatization reagent amount, extraction time, and desorption time, which have a dramatic effect on SPME Arrow pretreatment, were optimized. Acidity enhanced MCM-T-H coating showed a much higher affinity to derivatized BAs compared to a commercial SPME Arrow in terms of extraction capacity. In addition, hydrophobicity modification significantly reduced the interference of water molecules on the interaction between MCM-T-H and the derivatized BAs. The MCM-T-H-SPME Arrow showed efficient separation and enrichment capacity for derivatized BAs from complex matrices and therefore, the sample pretreatment time was saved. According to the experimental results, the optimal condition was to add 10 μL derivatization reagent to a 10 mL sample and maintain an agitation speed of 1250 r min^-1. The MCM-T-H-SPME showed excellent reproducibility (RSD < 9.8%) and fast adsorption kinetics (30 min) and desorption kinetics (5 min) for derivatized BAs under optimal conditions. In summary, the MCM-T-H-SPME Arrow based method was employed for accurate monitoring of the variations of BAs in pork and fish, and good results were achieved.

Metal-organic frameworks for food contaminant adsorption and detection

Metal-organic framework materials (MOFs) have been widely used in food contamination adsorption and detection due to their large specific surface area, specific pore structure and flexible post-modification. MOFs with specific pore size can be targeted for selective adsorption of some contaminants and can be used as pretreatment and pre-concentration steps to purify samples and enrich target analytes for food contamination detection to improve the detection efficiency. In addition, MOFs, as a new functional material, play an important role in developing new rapid detection methods that are simple, portable, inexpensive and with high sensitivity and accuracy. The aim of this paper is to summarize the latest and insightful research results on MOFs for the adsorption and detection of food contaminants. By summarizing Zn-based, Cu-based and Zr-based MOFs with low cost, easily available raw materials and convenient synthesis conditions, we describe their principles and discuss their applications in chemical and biological contaminant adsorption and sensing detection in terms of stability, adsorption capacity and sensitivity. Finally, we present the limitations and challenges of MOFs in food detection, hoping to provide some ideas for future development.

Recent applications of organic molecule-based framework porous materials in solid-phase microextraction for pharmaceutical analysis

Sample preparation is an indispensable part of detection of complex samples in pharmaceutical analysis. Solid-phase microextraction (SPME) has obtained a lot of attention due to its advantages of time saving, less solvent and easily automation. A variety of functional materials are used as sorbents in SPME to carry out selective and high extraction. This review centers around the recent applications of organic molecule-based framework porous materials, such as metal organic frameworks (MOFs) and covalent organic frameworks (COFs), as SPME coating materials mainly focus on pharmaceutical analysis in food, environment, and biological samples. Four representative extraction devices are introduced, including on-fiber SPME, in-tube SPME, thin film SPME, stir bar SPME. The application prospect of other organic porous materials as sorbents for pharmaceutical analysis are also discussed, such as hyper crosslinked polymers (HCPs) and conjugated microporous polymers (CMPs). The progresses and discusses are provided to offer references for further research focusing on application and development of organic molecule-based framework porous materials in the field of SPME.

Novel deep eutectic solvent-based liquid phase microextraction for the extraction of estrogenic compounds from environmental samples

Steroid hormones, such as estrone (E1), 17β-estradiol (E2), 17β-ethinylestradiol (EE2) and estriol (E3) are a group of lipophilic active substances, synthesized biologically from cholesterol or chemically. A pH-switchable hydrophobic deep eutectic solvent-based liquid phase microextraction (DES-LPME) technique was established and combined with gas chromatography-mass spectroscopy for the determination of estrogenic compounds in environmental water and wastewater samples. A DES was synthesized using l-menthol as HBA and (1S)-(+)-camphor-10-sulfonic acid (CSA) as HBD, and used as a green extraction solvent. By adjusting the pH of the solution, the unique behavior of the DES in the phase transition and extraction of the desired analytes was investigated. The homogenization process of the mixture is done only by manual shaking in less than 30 seconds and the phase separation is done only by changing the pH and without centrifugation. Some effective parameters on the extraction and derivatization, such as molar ratio of DES components, DES volume, KOH concentration, HCl volume, salt addition, extraction and derivatization time and derivatization prior or after extraction were studied and optimized. Under the optimum conditions, relative standard deviation (RSD) values for intra-day and inter-day of the method based on 7 replicate measurements of 20 ng L⁻¹ of estrogenic compounds and 10 ng L⁻¹ for internal standard in different samples were in the range of 2.2–4.6% and 3.9–5.7%, respectively. The calibration graphs were linear in the range of 0.5–100 ng L⁻¹ and the limits of detection (LODs) were in the range of 0.2–1.0 ng L⁻¹. The relative recoveries of environmental water and wastewater samples which have been spiked with different levels of target compounds were 91.0–108.8%.

A pH-switchable hydrophobic deep eutectic solvent-based liquid phase microextraction (DES-LPME) technique was established and combined with gas chromatography–mass spectroscopy for the determination of estrogenic compounds in environmental samples.

Metal-organic frameworks for food applications: A review

Metal-organic frameworks (MOFs) are high surface-to-volume ratio crystalline hybrid porous coordination materials composed of metal ions as nodes and organic linkers. The goal of this paper was to provide an updated and comprehensive state-of-the-art review of MOFs for different food applications such as active food contact materials, antimicrobial nanocarriers, controlled release nanosystems for active compounds, nanofillers for food packaging materials, food nanoreactors, food substance nanosensors, stabilizers and immobilizers for active compounds and enzymes, and extractors of food contaminants. Extraction and sensing of several food contaminants have been the main food applications of MOFs. The other applications listed above require further investigation, as they are at an early stage. However, interesting results are being reported for these other fields. Finally, an important limitation of MOFs has been the use of non-renewable feedstocks for their synthesis, but this has recently been solved through the manufacture and use of γ-cyclodextrin-based MOFs.

Determination of bisphenol A: Old problem, recent creative solutions based on novel materials

Bisphenol A is a synthetic compound widely used in industry, in the production of polycarbonate, epoxy resins, and thermal paper, among others. Its annual production is estimated at millions of tons per year, demonstrating its importance. Despite its wide application in various everyday products, once in the environment (due to its disposal or leaching), it has high toxicity to humans and animal life, and this problem has been well known for years. Given this problem, many researchers seek alternatives for its monitoring in matrices such as natural water, waste, food, and biological matrices. For this, new advanced materials have been developed, characterized, and applied in creative ways for the preparation of samples for the determination of bisphenol A. This article aims to present some of these important and recent applications, describing the use of molecularly imprinted polymers, metal and covalent organic frameworks, ionic liquids and magnetic ionic liquids, and deep eutectic solvents as creative solutions in sample preparation for the long-standing problem of bisphenol A determination.

Green solid-phase microextraction fiber coating based on the metal-organic framework CIM-80(Al): Analytical performance evaluation in direct immersion and headspace using gas chromatography and mass spectrometry for the analysis of water, urine and brewed coffee

A new solid-phase microextraction (SPME) fiber coating was prepared by the immobilization of the metal-organic framework (MOF) CIM-80(Al) on nitinol wires by a green in situ growth approach, using an aqueous synthetic approach, and without the need of any additional material to ensure the attachment of the MOF to the nitinol support. The coating was used for the development of headspace (HS) and direct immersion (DI) SPME methods in combination with gas chromatography and mass spectrometry (GC-MS) for the determination of polycyclic aromatic hydrocarbons (PAHs) as model compounds. Both methods were optimized and validated using the MOF-based fiber together with the commercial polydimethylsiloxane (PDMS) fiber. The MOF extraction phase exhibited superior analytical performance for most of the PAHs in HS-SPME mode (and particularly for less volatiles), while the PDMS fiber presented better results in the DI-SPME method. The analytical performance of the MOF sorbent coating in HS- and DI-SPME methods was also evaluated in urine and brewed coffee samples, without requiring any pretreatment step apart from dilution for DI-SPME experiments, thus showing suitability of the novel coatings for the analysis of complex samples. The proposed CIM-80(Al) fiber was efficient and biocompatible (for using a low cytotoxic sorbent and a biocompatible core support), and it also demonstrated stability and robustness, with inter-fiber (and inter-day) relative standard deviation values lower than 19%, and reusability for more than 80 extraction cycles using 280 °C as desorption temperature.

Advances in metal-organic framework coatings: versatile synthesis and broad applications

Metal-organic frameworks (MOFs) as a new kind of porous crystalline materials have attracted much interest in many applications due to their high porosity, diverse structures, and controllable chemical structures. However, the specific geometrical morphologies, limited functions and unsatisfactory performances of pure MOFs hinder their further applications. In recent years, an efficient approach to synthesize new composites to overcome the above issues has been achieved, by integrating MOF coatings with other functional materials, which have synergistic advantages in many potential applications, including batteries, supercapacitors, catalysis, gas storage and separation, sensors, drug delivery/cytoprotection and so on. Nevertheless, the systemic synthesis strategies and the relationships between their structures and application performances have not been reviewed comprehensively yet. This review emphasizes the recent advances in versatile synthesis strategies and broad applications of MOF coatings. A comprehensive discussion of the fundamental chemistry, classifications and functions of MOF coatings is provided first. Next, by modulating the different states (e.g. solid, liquid, and gas) of metal ion sources and organic ligands, the synthesis methods for MOF coatings on functional materials are systematically summarized. Then, many potential applications of MOF coatings are highlighted and their structure-property correlations are discussed. Finally, the opportunities and challenges for the future research of MOF coatings are proposed. This review on the deep understanding of MOF coatings will bring better directions into the rational design of high-performance MOF-based materials and open up new opportunities for MOF applications.

Novel Approaches Utilizing Metal-Organic Framework Composites for the Extraction of Organic Compounds and Metal Traces from Fish and Seafood

The determination of organic and inorganic pollutants in fish samples is a complex and demanding process, due to their high protein and fat content. Various novel sorbents including graphene, graphene oxide, molecular imprinted polymers, carbon nanotubes and metal-organic frameworks (MOFs) have been reported for the extraction and preconcentration of a wide range of contaminants from fish tissue. MOFs are crystalline porous materials that are composed of metal ions or clusters coordinated with organic linkers. Those materials exhibit extraordinary properties including high surface area, tunable pore size as well as good thermal and chemical stability. Therefore, metal-organic frameworks have been recently used in many fields of analytical chemistry including sample pretreatment, fabrication of stationary phases and chiral separations. Various MOFs, and especially their composites or hybrids, have been successfully utilized for the sample preparation of fish samples for the determination of organic (i.e., antibiotics, antimicrobial compounds, polycyclic aromatic hydrocarbons, etc.) and inorganic pollutants (i.e., mercury, palladium, cadmium, lead, etc.) as such or after functionalization with organic compounds.

Zeolitic imidazolate framework-8 coated Fe3O4@SiO2 composites for magnetic solid-phase extraction of bisphenols

A new magnetic composite material ZIF-8 coated Fe₃O₄@SiO₂ was employed for preconcentration and detection of trace BPs in water and plastic products.

Solid-phase extraction followed by deep eutectic solvent based dispersive liquid–liquid microextraction and GC-MS detection of the estrogenic compounds in wastewater samples

SPE combined with deep eutectic solvent based dispersive liquid–liquid microextraction has been developed as a sensitive technique for the ultra preconcentration of estrogenic compounds in wastewater samples prior to their analysis by GC-MS.

Recent Applications and Newly Developed Strategies of Solid-Phase Microextraction in Contaminant Analysis: Through the Environment to Humans

The present review aims to describe the recent and most impactful applications in pollutant analysis using solid-phase microextraction (SPME) technology in environmental, food, and bio-clinical analysis. The covered papers were published in the last 5 years (2014–2019) thus providing the reader with information about the current state-of-the-art and the future potential directions of the research in pollutant monitoring using SPME. To this end, we revised the studies focused on the investigation of persistent organic pollutants (POPs), pesticides, and emerging pollutants (EPs) including personal care products (PPCPs), in different environmental, food, and bio-clinical matrices. We especially emphasized the role that SPME is having in contaminant surveys following the path that goes from the environment to humans passing through the food web. Besides, this review covers the last technological developments encompassing the use of novel extraction coatings (e.g., metal-organic frameworks, covalent organic frameworks, PDMS-overcoated fiber), geometries (e.g., Arrow-SPME, multiple monolithic fiber-SPME), approaches (e.g., vacuum and cold fiber SPME), and on-site devices. The applications of SPME hyphenated with ambient mass spectrometry have also been described.

Electrochemically Fabricated Solid Phase Microextraction Fibers and Their Applications in Food, Environmental and Clinical Analysis

Background:

Designing an analytical methodology for complicated matrices, such as biological and environmental samples, is difficult since the sample preparation procedure is the most demanding step affecting the whole analytical process. Nowadays, this step has become more challenging by the legislations and environmental concerns since it is a prerequisite to eliminate or minimize the use of hazardous substances in traditional procedures by replacing with green techniques suitable for the sample matrix.

Methods:

In addition to the matrix, the nature of the analyte also influence the ease of creating green analytical techniques. Recent developments in the chemical analysis provide us new methodologies introducing microextraction techniques and among them, solid phase microextraction (SPME) has emerged as a simple, fast, low cost, reliable and portable sample preparation technique that minimizes solvent consumption.

Results:

The use of home-made fibers is popular in the last two decades since the selectivity can be tuned by changing the surface characteristics through chemical and electrochemical modifications. Latter technique is preferred since the electroactive polymers can be coated onto the fiber under controlled electrochemical conditions and the film thicknesses can be adjusted by simply changing the deposition parameters. Thermal resistance and mechanical strength can be readily increased by incorporating different dopant ions into the polymeric structure and selectivity can be tuned by inserting functional groups and nanostructures. A vast number of analytes with wide range of polarities extracted by this means can be determined with a suitable chromatographic detector coupled to the system. Therefore, the main task is to improve the physicochemical properties of the fiber along with the extraction efficiency and selectivity towards the various analytes by adjusting the electrochemical preparation conditions.

Conclusion:

This review covers the fine tuning conditions practiced in electrochemical preparation of SPME fibers and in-tube systems and their applications in environmental, food and clinical analysis.

Metal–Organic Frameworks as Key Materials for Solid-Phase Microextraction Devices—A Review

Metal–organic frameworks (MOFs) have attracted recently considerable attention in analytical sample preparation, particularly when used as novel sorbent materials in solid-phase microextraction (SPME). MOFs are highly ordered porous crystalline structures, full of cavities. They are formed by inorganic centers (metal ion atoms or metal clusters) and organic linkers connected by covalent coordination bonds. Depending on the ratio of such precursors and the synthetic conditions, the characteristics of the resulting MOF vary significantly, thus drifting into a countless number of interesting materials with unique properties. Among astonishing features of MOFs, their high chemical and thermal stability, easy tuneability, simple synthesis, and impressive surface area (which is the highest known), are the most attractive characteristics that makes them outstanding materials in SPME. This review offers an overview on the current state of the use of MOFs in different SPME configurations, in all cases covering extraction devices coated with (or incorporating) MOFs, with particular emphases in their preparation.

Metal-Organic Frameworks for Food Safety

Food safety is a prevalent concern around the world. As such, detection, removal, and control of risks and hazardous substances present from harvest to consumption will always be necessary. Metal-organic frameworks (MOFs), a class of functional materials, possess unique physical and chemical properties, demonstrating promise in food safety applications. In this review, the synthesis and porosity of MOFs are first introduced by some representative examples that pertain to the field of food safety. Following that, the application of MOFs and MOF-based materials in food safety monitoring, food processing, covering preservation, sanitation, and packaging is overviewed. Future perspectives, as well as potential opportunities and challenges faced by MOFs in this field will also be discussed. This review aims to promote the development and progress of MOF chemistry and application research in the field of food safety, potentially leading to novel solutions.

Applications of Metal-Organic Frameworks in Food Sample Preparation

Food samples such as milk, beverages, meat and chicken products, fish, etc. are complex and demanding matrices. Various novel materials such as molecular imprinted polymers (MIPs), carbon-based nanomaterials carbon nanotubes, graphene oxide and metal-organic frameworks (MOFs) have been recently introduced in sample preparation to improve clean up as well as to achieve better recoveries, all complying with green analytical chemistry demands. Metal-organic frameworks are hybrid organic inorganic materials, which have been used for gas storage, separation, catalysis and drug delivery. The last few years MOFs have been used for sample preparation of pharmaceutical, environmental samples and food matrices. Due to their high surface area MOFs can be used as adsorbents for the development of sample preparation techniques of food matrices prior to their analysis with chromatographic and spectrometric techniques with great performance characteristics.

Recent advances in metal-organic frameworks and covalent organic frameworks for sample preparation and chromatographic analysis

In the field of analytical chemistry, sample preparation and chromatographic separation are two core procedures. The means by which to improve the sensitivity, selectivity and detection limit of a method have become a topic of great interest. Recently, porous organic frameworks, such as metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), have been widely used in this research area because of their special features, and different methods have been developed. This review summarizes the applications of MOFs and COFs in sample preparation and chromatographic stationary phases. The MOF- or COF-based solid-phase extraction (SPE), solid-phase microextraction (SPME), gas chromatography (GC), high-performance liquid chromatography (HPLC) and capillary electrochromatography (CEC) methods are described. The excellent properties of MOFs and COFs have resulted in intense interest in exploring their performance and mechanisms for sample preparation and chromatographic separation.

Review of geometries and coating materials in solid phase microextraction: Opportunities, limitations, and future perspectives

The development of new support and geometries of solid phase microextraction (SPME), including metal fiber assemblies, coated-tip, and thin film microextraction (TFME) (i.e. self-supported, fabric and blade supported), as well as their effects on diffusion and extraction rate of analytes were discussed in the current review. Application of main techniques widely used for preparation of a variety of coating materials of SPME, including sol-gel technique, electrochemical and electrospinning methods as well as the available commercial coatings, were presented. Advantages and limitations of each technique from several aspects, such as range of application, biocompatibility, availability in different geometrical configurations, method of preparation, incorporation of various materials to tune the coating properties, and thermal and physical stability, were also investigated. Future perspectives of each technique to improve the efficiency and stability of the coatings were also summarized. Some interesting materials including ionic liquids (ILs), metal organic frameworks (MOFs) and particle loaded coatings were briefly presented.