Covalent Organic Frameworks in Sample Preparation

Practicality evaluation of novel microextraction techniques for the determination of PFAS in food and water samples using the Blue Applicability Grade Index

BACKGROUND

Due to their high stability, persistence, and non-degradability, per- and polyfluoroalkyl substances (PFAS) are considered to be "forever chemicals" that can be present in a wide range of samples. Towards the development of novel analytical strategies for the reduction of the environmental impact of the analytical scheme, a plethora of novel solid-phase microextraction and miniaturized extraction techniques have been proposed for the determination of PFAS. However, the evaluation of the applicability of these protocols in terms of their practicality is still scarce.

RESULTS

In this article, the Blue Analytical Grade Index (BAGI) was used to evaluate the practicality of the sorbent-based microextraction techniques that were developed during the last decade for PFAS. In total thirty-four protocols were evaluated, resulting in a minimum score of 50.0 and a maximum score of 77.5.

SIGNIFICANCE

These findings clearly indicate that there is significant room for improvement and there is still a need for the development of microextraction approaches with higher practicality. Moreover, with regards to the best-performing protocols, their greenness was also assessed using the AGREEprep metric to enable a more comprehensive comparison.

Advances in covalent organic frameworks for sample preparation

Sample preparation is crucial in analytical chemistry, impacting result accuracy, sensitivity, and reliability. Solid-phase separation media, especially adsorbents, are vital for preparing of liquid and gas samples, commonly analyzed by most analytical instruments. With the advancements in materials science, covalent organic frameworks (COFs) constructed through strong covalent bonds, have been increasingly employed in sample preparation in recent years. COFs have outstanding selectivity and/or excellent adsorption capacity for a single target or can selectively adsorb multiple targets from complex matrix, due to their large specific surface area, adjustable pore size, easy modification, and stable chemical properties. In this review, we summarize the classification of COFs, such as pristine COFs, COF composite particles, and COFs-based substrates. We aim to provide a comprehensive understanding of the different classifications of COFs in sample preparation within the last three years. The challenges and development trends of COFs in sample preparation are also presented.

Optimization of glycopeptide enrichment techniques for the identification of clinical biomarkers

INTRODUCTION

The identification and characterization of glycopeptides through LC-MS/MS and advanced enrichment techniques are crucial for advancing clinical glycoproteomics, significantly impacting the discovery of disease biomarkers and therapeutic targets. Despite progress in enrichment methods like Lectin Affinity Chromatography (LAC), Hydrophilic Interaction Liquid Chromatography (HILIC), and Electrostatic Repulsion Hydrophilic Interaction Chromatography (ERLIC), issues with specificity, efficiency, and scalability remain, impeding thorough analysis of complex glycosylation patterns crucial for disease understanding.

AREAS COVERED

This review explores the current challenges and innovative solutions in glycopeptide enrichment and mass spectrometry analysis, highlighting the importance of novel materials and computational advances for improving sensitivity and specificity. It outlines the potential future directions of these technologies in clinical glycoproteomics, emphasizing their transformative impact on medical diagnostics and therapeutic strategies.

EXPERT OPINION

The application of innovative materials such as Metal-Organic Frameworks (MOFs), Covalent Organic Frameworks (COFs), functional nanomaterials, and online enrichment shows promise in addressing challenges associated with glycoproteomics analysis by providing more selective and robust enrichment platforms. Moreover, the integration of artificial intelligence and machine learning is revolutionizing glycoproteomics by enhancing the processing and interpretation of extensive data from LC-MS/MS, boosting biomarker discovery, and improving predictive accuracy, thus supporting personalized medicine.

Developments and Applications of Molecularly Imprinted Polymer-Based In-Tube Solid Phase Microextraction Technique for Efficient Sample Preparation

Despite advancements in the sensitivity and performance of analytical instruments, sample preparation remains a bottleneck in the analytical process. Currently, solid-phase extraction is more widely used than traditional organic solvent extraction due to its ease of use and lower solvent requirements. Moreover, various microextraction techniques such as micro solid-phase extraction, dispersive micro solid-phase extraction, solid-phase microextraction, stir bar sorptive extraction, liquid-phase microextraction, and magnetic bead extraction have been developed to minimize sample size, reduce solvent usage, and enable automation. Among these, in-tube solid-phase microextraction (IT-SPME) using capillaries as extraction devices has gained attention as an advanced "green extraction technique" that combines miniaturization, on-line automation, and reduced solvent consumption. Capillary tubes in IT-SPME are categorized into configurations: inner-wall-coated, particle-packed, fiber-packed, and rod monolith, operating either in a draw/eject system or a flow-through system. Additionally, the developments of novel adsorbents such as monoliths, ionic liquids, restricted-access materials, molecularly imprinted polymers (MIPs), graphene, carbon nanotubes, inorganic nanoparticles, and organometallic frameworks have improved extraction efficiency and selectivity. MIPs, in particular, are stable, custom-made polymers with molecular recognition capabilities formed during synthesis, making them exceptional "smart adsorbents" for selective sample preparation. The MIP fabrication process involves three main stages: pre-arrangement for recognition capability, polymerization, and template removal. After forming the template-monomer complex, polymerization creates a polymer network where the template molecules are anchored, and the final step involves removing the template to produce an MIP with cavities complementary to the template molecules. This review is the first paper to focus on advanced MIP-based IT-SPME, which integrates the selectivity of MIPs into efficient IT-SPME, and summarizes its recent developments and applications.

Microextraction techniques for occupational biological monitoring: Basic principles, current applications and future perspectives

The application of green microextraction techniques (METs) is constantly being developed in different areas including pharmaceutical, forensic, food and environmental analysis. However, they are less used in biological monitoring of workers in occupational settings. Developing valid extraction methods and analytical techniques for the determination of occupational indicators plays a critical role in the management of workers' exposure to chemicals in workplaces. Microextraction techniques have become increasingly important because they are inexpensive, robust and environmentally friendly. This study aimed to provide a comprehensive review and interpret the applications of METs and novel sorbents and liquids in biological monitoring. Future perspectives and occupational indicators that METs have not yet been developed for are also discussed.

Covalent organic frameworks: spotlight on applications in the pharmaceutical arena

Covalent organic frameworks (COFs) have much potential in the field of analytical separation research due to their distinctive characteristics, including easy modification, low densities, large specific surface areas and permanent porosity. This article provides a historical overview of the synthesis and broad perspectives on the applications of COFs. The use of COF-based membranes in gas separation, water treatment (desalination, heavy metals and dye removal), membrane filtration, photoconduction, sensing and fuel cells is also covered. However, these COFs also demonstrate great promise as solid-phase extraction sorbents and solid-phase microextraction coatings. In addition to various separation applications, this work aims to highlight important advancements in the synthesis of COFs for chiral and isomeric compounds.

A miniaturized stir bar sorptive dispersive microextraction method for the determination of bisphenols in follicular fluid using a magnetic covalent organic framework

BACKGROUND

Bisphenols, particularly bisphenol A (BPA), are the primary monomers used as additives in the manufacturing of many consumer products. The exposure to these compounds is related to endocrine-disrupting and reproductive effects, among others. For this reason, the development of analytical methods for their determination in biological matrixes is needed to monitor the population exposure to these compounds. Their quantification at ovarian level (i.e., follicular fluid) is interesting for the assessment of the bisphenol content to draw conclusions about infertility problems. However, the background does not meet all requirements by focusing mainly on BPA.

RESULTS

In this work, a miniaturized stir bar sorptive dispersive microextraction (mSBSDME) approach has been developed for the determination of BPA and eight analogues in follicular fluid. In the proposed method, the sample is previously cleaned-up using a zirconia-based solid-phase extraction cartridge, removing proteins and phospholipids, and then subjected to the mSBSDME for the preconcentration of the analytes. For this purpose, a magnetic covalent organic framework was used as sorbent. A Plackett-Burman design was applied to select the significant variables affecting the mSBSDME. Afterwards, the only significant variable (i.e., sorbent amount) was optimized. Under the optimized conditions, the proposed method was properly validated, and satisfactory analytical parameters in terms of linearity (up to 50 ng mL-1), enrichment factors (8.5-14.3), limits of detection in the low ng mL-1 range, and precision (relative standard deviations below 11.5 %) were obtained. Finally, the method was successfully applied to five samples, detecting BPA and other two analogues.

SIGNIFICANCE

This method expands the potential applicability of the mSBSDME to other low-availability complex matrixes, which would otherwise be difficult to analyze. Moreover, it offers a valuable tool for monitoring the female population's exposure to bisphenols with the final aim of evaluating if infertility problems of women might be associated to the exposure to these highly endocrine disrupting compounds.

Synthesis of composite materials combining magnetic metal-organic frameworks and conjugated organic frameworks for selective extraction of carbendazim and thiabendazole residues from Chinese herbal medicine samples

A magnetic metal-organic framework MIL-68(Al) and a covalent organic framework were used as magnetic solid-phase extraction (MSPE) adsorbents in combination with high-performance liquid chromatography ultraviolet detection (HPLC-UV) to detect carbendazim (CBZ) and thiabendazole (TBZ). The main parameters affecting the extraction in the MSPE process were studied and optimized. Fe3O4@MIL-68(Al) coated with 1,3,5-tris(4-aminophenyl)benzene and terephthaldehyde (Fe3O4@MIL-68(Al)@TAPB-PDA-COF) was analyzed and verified. The material was proven to be suitable for adsorbing CBZ and TBZ. Various adsorption models were used to study its adsorption mechanism. The adsorption results were in good agreement with the pseudo-second-order kinetic model and Langmuir isotherm model. The maximum adsorption capacities of Fe3O4@MIL-68(Al)@TAPB-PDA-COF over CBZ and TBZ were 54.24 and 67.87 mg g-1, respectively, and the equilibrium adsorption time was 200 min. Fe3O4@MIL-68(Al)@TAPB-PDA-COF with excellent recyclability showed higher adsorption capacity and selectivity. A method based on Fe3O4@MIL-68(Al)@TAPB-PDA-COF combined with HPLC-UV was established under the optimal extraction conditions and used to separate and detect trace imidazole drugs in Chinese herbal samples, achieving a low limit of detection (0.65-1.30 μg L-1) with excellent linear correlation (r > 0.999). The recovery rate and relative standard deviation were 86.05-99.78 % and 0.15-4.90 %, respectively. Therefore, the Fe3O4@MIL-68@TAPB-PDA-COF can be regarded as an effective adsorbent for the pretreatment of CBZ and TBZ drugs in Chinese herbal samples.

Preparation of COF-coated nickel foam adsorbents for dispersive solid-phase extraction of 16 polycyclic aromatic hydrocarbons from Chinese herbal medicines

Covalent organic framework coated nickel foam (NF@COF) was prepared as a sorbent for the dispersive solid phase extraction (DSPE) of polycyclic aromatic hydrocarbons (PAHs) from Chinese herbal medicines (CHMs) prior to their determination by gas chromatography-mass spectrometry (GC-MS). The structure and morphology of the as-synthesized NF@COF were characterized by different techniques. Various key parameters affecting the performance of the DSPE method, including the amount of sorbent, desorption solvent, desorption volume and time, extraction time, and sample volume, were investigated. Under the optimized conditions, NF@COF combined with GC-MS was successfully applied to the determination of 16 PAHs in CHMs. The method showed wide linearity (20-2000 ng mL-1), low limits of determination (0.3-2.7 ng mL-1), and high recoveries (78.0-124%). These results revealed that NF@COF has the potential for efficient extraction of PAHs from complex samples.

Covalent organic framework in situ grown on the metal-organic framework as fiber coating for solid-phase microextraction of polycyclic aromatic hydrocarbons in tea

A novel MIL-88-NH2@COF composite was produced by in situ growth of covalent organic framework (COF) on the metal-organic framework (MOF) surface. To obtain a coating fiber for solid-phase microextraction (SPME), the MIL-88-NH2@COF composite physically adhered to the stainless steel wire. Combined with gas chromatography-flame ionization detection (GC-FID), various analytes such as chlorophenols (CPs), phthalates (PAEs), and polycyclic aromatic hydrocarbons (PAHs) were extracted and determined to evaluate the extraction performance of MIL-88-NH2@COF coated fibers and explore their extraction mechanism. This composite exhibit excellent extraction performance and adsorption capacity for various analytes, especially for PAHs with enrichment factor up to 9858. The SPME-GC-FID method based on MIL-88-NH2@COF fiber was established for the determination of five PAHs after the main extraction conditions were optimized. Under optimal conditions, the proposed technique showed a wide linear range (1-150 ng mL-1) with a low limit of detection (0.019 ng mL-1) and a high coefficient of determination (R2 > 0.99). The developed SPME-GC-FID method was used to determine PAHs in green tea and black tea samples, with good recoveries of 51.70-103.64% and 68.56-103.64%, respectively. It is worth mentioning that this is the first time MIL-88-NH2@COF composites have been prepared and applied to SPME. The preparation method of the composite provides a new idea in adsorbent preparation, which will contribute to the field of SPME.

In situ growth of porous organic framework on iron wire for microextraction of polycyclic aromatic hydrocarbons

In this work, a novel spherical metal organic framework (MOF) was first in situ grown on the surface of iron wire (IW), in which IW served as the substrate and metal source for MOF (type NH₂-MIL88) growth without adding additional metal salts in the process, while spherical NH₂-MIL88 provided more active sites for further construction of multifunctional composites. Subsequently, a covalent organic framework (COF) was covalently bonded to the surface of the NH₂-MIL88 to obtain the IW@NH₂-MIL88@COF fibers, which were used for headspace solid-phase microextraction (HS-SPME) of polycyclic aromatic hydrocarbons (PAHs) in milk samples prior to determination by gas chromatography-flame ionization detection (GC-FID). Compared with the fiber prepared by physical coating, the IW@NH₂-MIL88@COF fiber prepared by in situ growth and covalent bonding exhibits better stability and possesses more uniform layer. The extraction mechanism of the IW@NH₂-MIL88@COF fiber for PAHs was discussed, which mainly owed to π-π interactions and hydrophobic interactions. After optimization of the primary extraction conditions, the SPME-GC-FID method was established for five PAHs with a wide linear range (1-200 ng mL^-1), good linearity coefficient (0.9935-0.9987) and low detection limits (0.017-0.028 ng mL^-1). The relative recoveries for PAHs detection in milk samples ranged from 64.69 to 113.97%. This work not only provides new ideas for the in situ growth of other types of MOF, but also provides new methods for the construction of multifunctional composites.

Fabrication of covalent organic frameworks modified nanofibrous membrane for efficiently enriching and detecting the trace polychlorinated biphenyls in water

Enriching and detecting the trace pollutants in actual matrices are critical to evaluating the water quality. Herein, a novel nanofibrous membrane, named PAN-SiO₂@TpPa, was prepared by in situ growing β-ketoenamine-linked covalent organic frameworks (COF-TpPa) on the aminated polyacrylonitrile (PAN) nanofibers, and adopted for enriching the trace polychlorinated biphenyls (PCBs) in various natural water body (river, lake and sea water) through the solid-phase micro-extraction (SPME) process. The resulted nanofibrous membrane owned abundant functional groups (-NH-, -OH and aromatic groups), outstandingly thermal and chemical stability, and excellent ability in extracting PCBs congeners. Based on the SPME process, the PCBs congeners could be quantitatively analyzed by the traditional gas chromatography (GC) method, with the satisfactory linear relationship (R²>0.99), low detection limit (LODs, 0.1∼5 ng L^-1), high enrichment factors (EFs, 2714∼3949) and multiple recycling (>150 runs). Meanwhile, when PAN-SiO₂@TpPa was adopted in the real water samples, the low matrix effects on the enrichment of PCBs at both 5 and 50 ng L^-1 over PAN-SiO₂@TpPa membrane firmly revealed the feasibility of enriching the trace PCBs in real water. Besides, the related mechanism of extracting PCBs on PAN-SiO₂@TpPa mainly involved the synergistic effect of hydrophobic effect, π-π stacking and hydrogen bonding.

A “peptide-target-aptamer” electrochemical biosensor for norovirus detection using a black phosphorous nanosheet@Ti3C2-Mxene nanohybrid and magnetic covalent organic framework

Norovirus (NoV) is a major foodborne pathogen responsible for acute gastroenteritis epidemics, and establishing a robust detection method for the timely identification and monitoring of NoV contamination is of great significance. In this study, a peptide-target-aptamer sandwich electrochemical biosensor for NoV was fabricated using Au@BP@Ti₃C₂-MXene and magnetic Au@ZnFe₂O₄@COF nanocomposites. The response currents of the electrochemical biosensor were proportional to the NoV concentrations ranging from 0.01-10⁵ copies/mL with a detection limit (LOD) of 0.003 copies/mL (S/N = 3). To our best knowledge, this LOD was the lowest among published assays to date, due to the specific recognition of the affinity peptide and aptamer for NoV and the outstanding catalytic activity of nanomaterials. Furthermore, the biosensor showed excellent selectivity, anti-interference performance, and satisfactory stability. The NoV concentrations in simulative food matrixes were successfully detected using the constructed biosensor. Meanwhile, NoV in stool samples was also successfully quantified without complex pretreatment. The designed biosensor had the potential to detect NoV (even at a low level) in foods, clinical samples, and environmental samples, providing a new method for NoV detection in food safety and diagnosing foodborne pathogens.

Recent Advances in the Application of Covalent Organic Frameworks in Extraction: A Review

Covalent organic frameworks (COFs) are a class of emerging materials that are synthesized based on the covalent bonds between different building blocks. COFs possess unique attributes in terms of high porosity, tunable structure, ordered channels, easy modification, large surface area, and great physical and chemical stability. Due to these features, COFs have been extensively applied as adsorbents in various extraction modes. Enhanced extraction performance could be reached with modified COFs, where COFs are presented as composites with other materials including nanomaterials, carbon and its derivatives, silica, metal-organic frameworks, molecularly imprinted polymers, etc. This review article describes the recent advances, developments, and applications of COF-based materials being utilized as adsorbents in the extraction methods. The COFs, their properties, their synthesis approaches as well as their composite structures are reviewed. Most importantly, suggested mechanisms for the extraction of analyte(s) by COF-based materials are also discussed. Finally, the current challenges and future prospects of COF-based materials in extraction methods are summarized and considered in order to provide more insights into this field.

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.

Recent trends on the implementation of reticular materials in column‐centered separations

Advances in the development of column‐based analytical separations are strongly linked to the development of novel materials. Stationary phases for chromatographic separation are usually based on silica and polymer materials. Nevertheless, recent advances have been made using porous crystalline reticular materials, such as metal‐organic frameworks and covalent organic frameworks. However, the direct packing of these materials is often limited due to their small crystal size and nonspherical shape. In this review, recent strategies to incorporate porous crystalline materials as stationary phases for liquid‐phase separations are covered. Moreover, we discuss the potential future directions in their development and integration into suitable supports for analytical applications. Finally, we discuss the main challenges to be solved to take full advantage of these materials as stationary phases for analytical separations.

Miniaturized green sample preparation approaches for pharmaceutical analysis

The development of green sample preparation procedures is an extremely important research field in which more and more applications are constantly being proposed in different areas, including pharmaceutical analysis. This review article is aimed at providing a general overview of the development of miniaturized green analytical sample preparation procedures in the pharmaceutical analysis field, with special focus on the works published between January 2017 and July 2021. Particular attention has been paid to the application of environmentally friendly solvents and sorbents as well as nanomaterials or high extraction capacity sorbents in which the solvent volumes and reagents amounts are drastically reduced, with their subsequent advantages from the sustainability point of view.

Recent advances in porous organic frameworks for sample pretreatment of pesticide and veterinary drug residues: a review

Rapid and accurate detection of pesticide and veterinary drug residues is a continuing challenge because of the complex matrix effects. Thus, appropriate sample pretreatment is a crucial step for the effective extraction of the analytes and removal of the interferences. Recently, the development of nanomaterial adsorbents has greatly promoted the innovation of food sample pretreatment approaches. Porous organic frameworks (POFs), including polymers of intrinsic microporosity, covalent organic frameworks, hyper crosslinked polymers, conjugated microporous polymers, and porous aromatic frameworks, have been widely utilized due to their tailorable skeletons and pores as well as fascinating features. This review summarizes the recent advances for POFs to be utilized in adsorption and sample preparation of pesticide and veterinary drug residues. In addition, future prospects and challenges are discussed, hoping to offer a reference for further study on POFs in sample pretreatment.

Heteroporous 3D covalent organic framework-based magnetic nanospheres for sensitive detection of bisphenol A

Covalent organic frameworks (COFs) showed great promise in effective adsorption of target molecule via size selectivity. Although various magnetic 2D COFs composites have been studied and exhibited the intensive applications, the incorporation of 3D COFs and magnetic nanoparticles to form a new class of magnetic adsorbents with enhanced function still has no reports. Herein, a novel Fe₃O₄@3D COF with heteroporous structure matching to the sizes of bisphenol A (BPA) was firstly synthesized for better adsorption of BPA than common magnetic 2D-COFs. Three Fe₃O₄@3D COFs nanospheres were synthesized under the solvothermal conditions in autoclave, and the optimum Fe₃O₄@3D-COF denoted as Fe₃O₄@COF-TpTAM (Tp, 1,3,5-triformylphloroglucinol; TAM, tetra(p-aminophenyl)-methane) was selected and employed. Detailed characteristics of Fe₃O₄@COF-TpTAM were evaluated via various techniques including TEM, FTIR, TGA, XRD and BET. Excellent chemical and thermal stability, high surface area (294.6 m² g^-1) and pore volume (0.2 m³ g^-1) with multiple pore sizes comparable with the simulated three-dimensional sizes of BPA were exhibited. A high adsorption capacity of BPA up to 209.9 mg/g that was better than common 2D-COFs was achieved, and the sensitive MSPE-LC-MS method with wide linear range (10-5000 pg/mL), low detection limit (4 pg/mL, S/N = 3) was built. Satisfactory recoveries of BPA as 93.8 ± 1.4%-101.4 ± 5.1% (n = 3) and 100.4 ± 1.9% ~ 107.3 ± 1.2% (n = 3) were obtained in milk and river water samples, respectively. This work demonstrates the promising application of Fe₃O₄@3D COF as efficient adsorbents of trace BPA, and opens up a new access for the efficient MSPE in sample pretreatment for food or environmental safety analysis.

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.

Application of stimuli-responsive materials for extraction purposes

Stimuli-responsive materials, frequently designated as "smart/intelligent materials", can modify their structure or properties by either a biological, physical, or chemical stimulus which, if properly controlled, could be used for specific applications. Such materials have been studied and exploited in several fields, like electronics, photonics, controlled drugs administration, imaging and medical diagnosis, among others, as well as in Analytical Chemistry where they have been used as chromatographic stationary phases, as part of sensors and for extraction purposes. This review article pretends to provide an overview of the most recent applications of these materials (mostly polymeric materials) in sample preparation for extraction purposes, as well as to provide a general vision of the current state-of-the-art of this field, their potential use and future applications.

Covalent Organic Framework Composites: Synthesis and Analytical Applications

In the recent years, composite materials containing covalent organic frameworks (COFs) have raised increasing interest for analytical applications. To date, various synthesis techniques have emerged that allow for the preparation of crystalline and porous COF composites with various materials. Herein, we summarize the most common methods used to gain access to crystalline COF composites with magnetic nanoparticles, other oxide materials, graphene and graphene oxide, and metal nanoparticles. Additionally, some examples of stainless steel, polymer, and metal-organic framework composites are presented. Thereafter, we discuss the use of these composites for chromatographic separation, environmental remediation, and sensing.