Advanced materials for sample preparation in recent decade

Porous Polymer Sorbents in Micro Solid Phase Extraction: Applications, Advantages, and Challenges

In recent years, porous polymers have gained significant attention for their application as powerful and selective sorbents in micro solid phase extraction (µSPE). In this review we explore the preparation and utilization of various porous polymer sorbents, highlighting their impact on enhancing µSPE techniques. Molecularly imprinted polymers (MIPs), graphene oxide-modified frameworks, and zeolitic imidazole frameworks (ZIFs) are among the innovative materials discussed. These innovative materials have significantly improved µSPE methods, offering enhanced extraction efficiencies, superior selectivity, and reduced solvent consumption, all of which align with the principles of green chemistry. Key findings of this review include the demonstration that MIPs exhibit excellent target specificity, making them ideal for complex matrices, while graphene oxide frameworks and ZIFs provide increased surface area and stability for diverse analytical applications. Despite these advancements, challenges remain, particularly the high cost of certain innovative materials, limited reusability, and the absence of automation in µSPE workflows. Furthermore, controlling the precise synthesis and functionalization of these sorbents continues to be a limiting factor. To address these issues, future research should focus on developing cost-effectiveness methods, the use of biopolymer or sustainable feedstocks, and scalable synthesis methods; integrating automation into µSPE; and exploring new polymeric materials with enhanced properties. Additionally, novel hybrid materials that combine the strengths of multiple sorbents offer a promising direction for future exploration. We critically analyze the advantages and limitations of each sorbent type, providing a comprehensive overview of their applications in µSPE. This paper also examines the synthesis, characterization, and unique properties of these porous polymers, emphasizing their role in advancing analytical chemistry towards more efficient and environmentally friendly practices. The need for continued development of high-performance, low-cost, and sustainable sorbents is underscored to further enhance the effectiveness of µSPE techniques.

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.

Recent progress on media for biological sample preparation

The analysis of biological samples is highly valuable for disease diagnosis and treatment, forensic examination, and public safety. However, the serious matrix interference effect generated by biological samples severely affects the analysis of trace analytes. Sample preparation methods are introduced to address the limitation by extracting, separating, enriching, purifying trace target analytes from biological samples. With the raising demand of biological sample analysis, a review focuses on media for biological sample preparation and analysis over the last 5 years is presented. High-performance media in biological sample preparation are first reviewed, including porous organic frameworks, imprinted polymers, hydrogels, ionic liquids, and bioactive media. Then, application of media for different biological sample preparation and analysis is briefly introduced, including liquid samples of body fluids, solid samples (hair, feces, and tissues), and gas samples of exhale breath gas. Finally, conclusions and outlooks on media promoting biological sample preparation are presented.

Multiple-component covalent organic frameworks for simultaneous extraction and determination of multitarget pollutants in sea foods

Persistent organic pollutants (POPs), such as perfluoroalkyl and polyfluoroalkyl substances (PFASs), polychlorinated biphenyls (PCBs), and bisphenols (BPs), have been raising global concerns due to their toxic effects on environment and human health. The monitoring of residues of POPs in seafood is crucial for assessing the accumulation of these contaminants in the study area and mitigating potential risks to human health. However, the diversity and complexity of POPs in seafood present significant challenges for their simultaneous detection. Here, a novel multi-component fluoro-functionalized covalent organic framework (OH-F-COF) was designed as SPE adsorbent for simultaneous extraction POPs. On this basis, the recognition and adsorption mechanisms were investigated by molecular simulation. Due to multiple interactions and large specific surface area, OH-F-COF displayed satisfactory coextraction performance for PFASs, PCBs, and BPs. Under optimized conditions, the OH-F-COF sorbent was employed in a strategy of simultaneous extraction and stepwise elution (SESE), in combination with HPLC-MS/MS and GC-MS method, to effectively determined POPs in seafood collected from coastal areas of China. The method obtained low detection limits for BPs (0.0037 -0.0089 ng/g), PFASs (0.0038 -0.0207 ng/g), and PCBs (0.2308 -0.2499 ng/g), respectively. This approach provided new research ideas for analyzing and controlling multitarget POPs in seafood. ENVIRONMENTAL IMPLICATIONS: Persistent organic pollutants (POPs), such as perfluoroalkyl and polyfluoroalkyl substances (PFASs), polychlorinated biphenyls (PCBs), and bisphenols (BPs), have caused serious hazards to human health and ecosystems. Hence, there is a need to develop a quantitative method that can rapidly detect POPs in environmental and food samples. Herein, a novel multi-component fluorine-functionalized covalent organic skeletons (OH-F-COF) were prepared at room temperature, and served as adsorbent for POPs. The SESE-SPE strategy combined with chromatographic techniques was used to achieve a rapid detection of POPs in sea foods from the coastal provinces of China. This method provides a valuable tool for analyzing POPs in environmental and food samples.

Development and Application of a Selective Analytical Method for Indole Metabolites in Urine: Dietary Exposure Biomarkers for Broccoli Consumption

The identification of dietary exposure biomarkers is crucial for advancing our understanding of the health benefits of specific foods. Broccoli, a vegetable with well-known anticancer properties, contains active ingredients, such as isothiocyanates with indole side chains. Hence, indole metabolites related to broccoli consumption have the potential to serve as biomarkers of dietary exposure. In this work, we developed a new analytical method for indole metabolites in urine using a poly(deep eutectic solvents)-molecularly imprinted polymer/vinyl-functionalized graphene oxide (PDESs-MIP/VGO) in miniaturized centrifugal pipet-tip solid-phase extraction (CPT-SPE) coupled with liquid chromatography. This method integrates the strengths of PDESs-MIP/VGO, including rich adsorption interactions, high adsorption capacity, and excellent selectivity, with the simplicity and cost-effectiveness of CPT-SPE. The proposed method demonstrated low limits of quantification (1.2-2.5 ng mL-1), high accuracy (91.7-104.8%), and good precision (relative standard deviation ≤4.4%). By applying this method to analyze indole metabolites in urine, our results suggested that indole-3-carbinol and indole-3-acetonitrile have the potential to emerge as reliable dietary exposure biomarkers for broccoli intake. Furthermore, highly selective analytical methods based on molecular imprinting technology are advantageous for precise screening and analysis of dietary exposure biomarkers associated with food consumption.

Recent advance on microextraction sampling technologies for bioanalysis

The contents of target substances in biological samples are usually at low concentration levels, and the matrix of biological samples is usually complex. Sample preparation is considered a very critical step in bioanalysis. At present, the utilization of microextraction sampling technology has gained considerable prevalence in the realm of biological analysis. The key developments in this field focus on the efficient microextraction media and the miniaturization and automation of adaptable sample preparation methods currently. In this review, the recent progress on the microextraction sampling technologies for bioanalysis has been introduced from point of view of the preparation of microextraction media and the microextraction sampling strategies. The advance on the microextraction media was reviewed in detail, mainly including the aptamer-functionalized materials, molecularly imprinted polymers, carbon-based materials, metal-organic frameworks, covalent organic frameworks, etc. The advance on the microextraction sampling technologies was summarized mainly based on in-vivo sampling, in-vitro sampling and microdialysis technologies. Moreover, the current challenges and perspective on the future trends of microextraction sampling technologies for bioanalysis were briefly discussed.

3D printed microfluidic devices for integrated solid-phase extraction and microchip electrophoresis of preterm birth biomarkers

BACKGROUND

Preterm birth (PTB) is a leading cause of neonatal mortality, such that the need for a rapid and accurate assessment for PTB risk is critical. Here, we developed a 3D printed microfluidic system that integrated solid-phase extraction (SPE) and microchip electrophoresis (μCE) of PTB biomarkers, enabling the combination of biomarker enrichment and labeling with μCE separation and fluorescence detection.

RESULTS

Reversed-phase SPE monoliths were photopolymerized in 3D printed devices. Microvalves in the device directed sample between the SPE monolith and the injection cross-channel in the serpentine μCE channel. Successful on-chip preconcentration, labeling and μCE separation of four PTB-related polypeptides were demonstrated in these integrated microfluidic devices. We further show the ability of these devices to handle complex sample matrices through the successful analysis of labeled PTB biomarkers spiked into maternal blood serum. The detection limit was 7 nM for the PTB biomarker, corticotropin releasing factor, in 3D printed SPE-μCE integrated devices.

SIGNIFICANCE

This work represents the first successful demonstration of integration of SPE and μCE separation of disease-linked biomarkers in 3D printed microfluidic devices. These studies open up promising possibilities for rapid bioanalysis of medically relevant analytes.

Evaluation of deep eutectic solvents in the synthesis of molecularly imprinted fibers for the solid-phase microextraction of triazines in soil samples

Nowadays, molecularly imprinted polymers (MIPs) are well established and are considered excellent materials for performing selective extractions. However, with the progressive implementation of the principles of green chemistry, it is necessary to find greener alternatives for both the synthesis and further use of MIPs in sample preparation. Accordingly, in the present work, different deep eutectic solvents (DES, both hydrophilic and hydrophobic), as an alternative to conventional organic solvents (i.e., toluene), were evaluated as porogens for the synthesis of imprinted fibers (monoliths), using fused silica capillaries as molds, for solid-phase microextraction (SPME). From this study, the polymer prepared with propazine (dummy template), methacrylic acid (monomer), ethylene glycol dimethacrylate (cross-linker), and a formic acid:L-menthol (1:1) DES (porogen) showed the best performance for selective rebinding of triazines. After optimization of the different variables involved in SPME, the new imprinted fibers were successfully applied to the extraction of target analytes (desisopropylatrazine, desethylatrazine, simazine, and atrazine) from soil sample extracts, providing relative recoveries ranging from 75.7 to 120.1%, reaching limits of detection within the range of 6.2-15.7 ng g-1, depending upon the analyte.

A review of aptamer-conjugated nanomaterials for analytical sample preparation: Classification according to the utilized nanomaterials

BACKGROUND

Sample extraction before detection is a critical step in analysis. Since targets of interest are often found in complex matrices, the sample can not be directly introduced to the analytical instrument. Nanomaterials with unique physical-chemical properties are excellent supports for use in sorbent-based extraction. However, they lack selectivity and thus need to be functionalized with target-capturing molecules. Antibodies and molecularly imprinted polymers (MIPs) can be used for this purpose, but they have some problems that limit their practical applications. Hence, functionalization of nanomaterials for selectivity remains a problem.

RESULTS

Nucleic acid aptamers are affinity reagents that can provide superiority to antibodies since they can be selected in vitro and at a lower cost. Moreover, aptamers can be chemically synthesized and easily modified with different functional groups. Hence, aptamers are good candidates to impart selectivity to the nanomaterials. Recent studies focus on the integration of aptamers with magnetic nanoparticles, carbon-based nanomaterials, metal-organic frameworks, gold nanoparticles, gold nanorods, silica nanomaterials, and nanofibers. The unique properties of nanomaterials and aptamers make the aptamer-conjugated nanomaterials attractive for use in sample preparation. Aptamer-functionalized nanomaterials have been successfully used for selective extraction of proteins, small molecules, and cells from different types of complex samples such as serum, urine, and milk. In particular, magnetic nanoparticles have a wider use due to the rapid extraction of the sample under magnetic field.

SIGNIFICANCE

In this review, we aim to emphasize how beneficial features of nanomaterials and aptamers could be combined for extraction or enrichment of the analytes from complex samples. We aim to highlight that the benefits are twofold in terms of selectivity and efficiency when employing nanomaterials and aptamers together as a single platform.

Application of urea-based magnetic covalent organic framework as sorbent for the determination of coumarin and its derivatives in food samples combined with liquid chromatography-mass spectrometry

A magnetic solid-phase extraction (MSPE) protocol using novel Urea-based magnetic covalent organic framework coupled with liquid chromatography-mass spectrometry was developed for the detection of coumarins in food samples (soft drink, biscuit and sesame paste). This adsorbent was synthesized through atom economic polymerization of tetrakis(4-aminophenyl) methane and 1,4-phenylene diisocyanate, which was successfully verified by a series of techniques. Major parameters influencing MSPE efficiency were optimized. This protocol had some advantages, such as organic-reagent-saving (2.0 mL), easy operating, short extraction time, and high repeatability (8 times). The established method exhibited superior linearity (R2 ≥ 0.999) and the limits of detection ranging from 1.0 to 5.0 µg/kg. The recoveries of coumarin and its derivatives ranged from 73.8% to 113.5% and both intra- and inter-day precision were less than 15%. These data indicate the protocol is a highly promising alternative for coumarin extraction and enrichment.

A heteropore covalent organic framework for highly selective enrichment of aryl-organophosphate esters in environmental water coupled with UHPLC-MS/MS determination

The identification of an increasing number of aryl organophosphate esters (aryl-OPEs) in environmental samples has led to growing attention recently. Due to the potential adverse effects on human health and environment, development of new analytical methods for sensitive and selective determination of aryl-OPEs in complex matrices is urgently needed. Here, a novel analytical method for the identification and determination of trace amounts of aryl-OPEs in water samples is developed by using melamine sponge@heteropore covalent organic framework (MS@HCOF) based on vortex-assisted extraction (VAE) prior to UHPLC-MS/MS analysis. The MS@HCOF was rationally designed and synthesized through an in-situ growth strategy and exhibited superior selectivity toward aryl-OPEs compared with that of MS@single-pore COF (MS@SCOF) due to steric effect. A systematic optimization was conducted on important parameters of VAE, resulting in the successful extraction of nine aryl-OPEs in just 6 min. Under optimized conditions, the limits of detection (S/N = 3) and quantification (S/N = 10) were within the ranges of 0.001-0.027 and 0.005-0.091 ng/L for nine aryl-OPEs, respectively. The validated method was proven applicable to real water samples, i.e., the recoveries were 65.3-119.5 % for seawater, 59.4-112.9 % for effluent, and 76.0-117.4 % for tap water. Furthermore, the adsorption mechanisms were explored through density functional theory (DFT) calculations. DFT results revealed that a notable selective enrichment capacity of MS@HCOF towards aryl-OPEs stems from π-π conjugation and hydrogen bonding. The established method benefits from the advantages of high selectivity and sensitivity for the ultra-trace determination of aryl-OPEs.

A review of bioanalytical applications of microextraction techniques combined with derivatization

Microextraction techniques have attracted the attention of many researchers working in the field of bioanalysis due to their unique advantages, mainly in downsizing the scale of sample preparation steps. In parallel, analytical derivatization offers a powerful combination in terms of additional sensitivity, selectivity and compatibility with modern separation techniques. The aim of this review is to discuss the most recent advances in bioanalytical sample preparation based on the combination of microextraction and analytical derivatization. Both innovative fundamental reports and analyte-targeted applications are included and discussed. Dispersive liquid-liquid extraction and solid-phase microextraction are the most common techniques that typically combined with derivatization, while the development of novel and greener protocols is receiving substantial consideration in the field of analytical chemistry.

Application of hollow fiber-protected liquid-phase microextraction combined with GC-MS in determining Endrin, Chlordane, and Dieldrin in rice samples

This paper introduces a novel and minimized sample preparation technique based on hollow fiber-protected liquid-phase microextraction that can be used in joint with gas chromatography-mass spectrometry (GC-MS) detection to extract three organochlorine pesticides-Endrin, Chlordane, and Dieldrin-from rice samples. To that end, a single-walled carbon nanotube (SWCNT) and a proper ionic liquid (IL) were ultrasonically dispersed and injected into the lumen of hollow fiber as the extraction phase for preconcentrating and extracting the target analytes from the rice samples. The effects of the type of nanoparticles, ILs, and desorption solvent on the efficiency of extracting the analytes were investigated based on the one-factor-at-a-time (OFAT) approach. In addition, other parameters influencing the extraction procedure were optimized using an experimental design that decreased the number of experiments, reagent consumption, and costs. Under optimized conditions, the limits of detection and quantification in determining mentioned pesticides varied between 0.019-0.029 and 0.064-0.098 ng mL-1, respectively. The calibration graphs to measure Endrin, Chlordane, and Dieldrin were linear over the concentration range of 0.064-13.2, 0.098-16.7, and 0.092-11.4 ng mL-1, respectively. The relative standard deviations for inter-day and intra-day analysis were below 7.06 and 4.75% for the triplicate determination of three organochlorine pesticides. Besides, the relative recoveries and standard deviations of Endrin, Chlordane, and Dieldrin for analyzing several Iranian rice samples were between 86.0-92.9% and 4.5-5.8%, respectively. The results were compared with other similar works in literature, proving that the proposed method is efficient and useful for routine monitoring of organochlorine compounds in food samples.

Construction of Stable Magnetic Vinylene-Linked Covalent Organic Frameworks for Efficient Extraction of Benzimidazole Fungicides

Covalent organic frameworks (COFs) have attracted impressive interest in separation on aqueous media. Herein, we integrated the stable vinylene-linked COFs with magnetic nanosphere via the monomer-mediated in situ growth strategy to construct a crystalline Fe₃O₄@v-COF composite for enrichment and determination of benzimidazole fungicides (BZDs) from complex sample matrices. The Fe₃O₄@v-COF has a crystalline assembly, high surface area, porous character together with a well-defined core-shell structure, and serves as progressive pretreatment materials for magnetic solid phase extraction (MSPE) of BZDs. Adsorption mechanism studies revealed that the extended conjugated system and numerous polar cyan groups on v-COF provides abundant π-π and multiple hydrogen bonding sites, which are conducive to interact with BZDs collaboratively. Fe₃O₄@v-COF also displayed enrichment effects to various polar pollutions with conjugated structures and hydrogen-bonding sites. Fe₃O₄@v-COF-based MSPE-high-performance liquid chromatography exhibited the low limit of detection, wide linearity, and good precision. Moreover, Fe₃O₄@v-COF showed better stability, enhanced extraction performance, and more sustainable reusability in comparison with its imine-linked counterpart. This work proposes a feasible strategy on constructing the crystalline stable magnetic vinylene-linked COF composite for the determination of trace contaminants in complex food matrices.

Determination of hormones in urine by hollow fiber microporous membrane liquid-liquid extraction associated with 96-well plate system and HPLC-FLD detection

In this work, hollow-fiber microporous membrane liquid-liquid extraction (HF-MMLLE) was associated with a 96-well plate system for the determination of estrone, 17-β-estradiol, estriol and 17-α-ethinylestradiol in urine samples. This method exhibited some advantages, such as low cost, easy application, high-throughput and environmentally-friendly aspects. The type of organic solvent to fill the membrane, ionic strength effect, sample dilution, extraction and desorption time, and desorption solvent were examined. After the optimizations, the conditions were comprised of 45 min of extraction, 1-octanol as organic solvent and 15% (w/v) of NaCl; methanol was used as desorption solvent, and the desorption time was fixed at 10 min. The dilution of the sample increased the sensitivity due to the reduction of matrix effects; thus, urine samples were diluted 40-fold. The limits of detection ranged from 0.03 μg L^-1 for 17-β-estradiol to 15 μg L^-1 for estrone, and the limits of quantification ranged from 0.1 μg L^-1 for 17-β-estradiol to 10 μg L^-1 for estrone. The intra-day precision varied from 1.0% for estriol to 13.3% for 17-α-ethinylestradiol, and inter-day precision varied from 7.3% for estrone to 18.1% for estriol. The relative recoveries varied from 82 to 118%.

Novel chemically cross-linked self-molding particulate sorbents as solid-phase extraction media

Here, we describe novel, chemically cross-linked, self-molding particulate polymer sorbents that are utilized as a molding-type solid-phase extraction medium (M-SPEM), which exhibits high permeability and rigidness. To fabricate such M-SPEM, first, polyethyleneimine (PEI)-modified reversed-phase (RP)-type particulate sorbents were synthesized, thereafter, they were chemically cross-linked by a polymer having many epoxy groups together with additional PEI. By optimizing the binding conditions of the particulate sorbents, the resultant M-SPEM has almost the same adsorption properties as the corresponding unmolded particulate sorbent for some polar (e.g., uracil and adenine) compounds. The binding technique proposed here is expected to facilitate the fabrication of molding-type sorbents and improve the performance of the SPE procedure.

The progress on porous organic materials for chiral separation

Chiral compounds have similar structures and properties, but their pharmacological action is very different or even opposite. Therefore, the separation of chiral compounds has great significance in pharmaceutical and agriculture. Porous organic materials are novel crystalline porous materials, which possess high surface area, controllable pore size, and favorable functionalization. Therefore, porous organic materials are considered to be an ideal material for chiral separation. In this review, we summarized the progress of chiral porous organic materials for chiral separation in recent years. Furthermore, the applications of chiral porous organic materials as chiral separation medias (chromatography stationary phases and membrane materials) in enantioseparation were highlighted. Finally, the remaining challenges and future directions for porous organic materials in chiral separation were also briefly outlined further to promote the development of porous organic materials in chiral separation.

Molecularly Imprinted Polymers: Selective Extraction Materials for Sample Preparation

Highly developed analytical instrumentation (i [...]

Analysis of anticancer compound, indole-3-carbinol, in broccoli using a new ultrasound-assisted dispersive-filter extraction method based on poly(deep eutectic solvent)-graphene oxide nanocomposite

Indole-3-carbinol (I3C), an important anticancer compound found in broccoli, has attracted considerable attention. The rapid extraction and accurate analysis of I3C in the pharmaceutical industry in broccoli is challenging as I3C is unstable at low pH and high temperature. In this study, a rapid, accurate, and low-cost ultrasound-assisted dispersive-filter extraction (UADFE) technique based on poly(deep eutectic solvent)-graphene oxide (PDES-GO) adsorbent was developed for the isolation and analysis of I3C in broccoli for the first time. PDES-GO with multiple adsorption interactions and a fast mass transfer rate was synthesized to accelerate adsorption and desorption. UADFE was developed by combining dispersive solid-phase extraction (DSPE) and filter solid-phase extraction (FSPE) to realize rapid extraction and separation. Based on the above two strategies, the proposed PDES-GO-UADFE method coupled with high-performance liquid chromatography (HPLC) allowed the rapid (15-16 min), accurate (84.3%-96.4%), and low-cost (adsorbent: 3.00 mg) analysis of I3C in broccoli and was superior to solid-phase extraction, DSPE, and FSPE methods. The proposed method showed remarkable linearity (r=0.9998; range: 0.0840-48.0 μg/g), low limit of quantification (0.0840 μg/g), and high precision (relative standard deviation ≤5.6%). Therefore, the PDES-GO-UADFE-HPLC method shows significant potential in the field of pharmaceutical analysis for the separation and analysis of anti-cancer compounds in complex plant samples.

Self-assembly of core-shell structured multiwalled nanotubes@covalent organic frameworks composite for solid-phase extraction of four phytohormones from fruit juices

Covalent organic frameworks (COFs) have attracted considerable attention in sample pretreatment because of their unique characteristics. However, the submicron or micron size of COFs has restricted their wider applications in solid-phase extraction (SPE). Herein, multiwalled nanotubes (MWNTs) were used as substrate materials to synthesize core-shell structured MWNTs@COFs composites (MWNTs@SNW-1) using a simple self-assembly method. The as-prepared MWNTs@SNW-1 composite exhibited a high BET surface area, good thermal stability, and good adsorption capacity. The MWNTs@SNW-1 composite was used as an adsorbent in cartridge-based SPE to extract four phytohormones before determining their levels by high-performance liquid chromatography. The experimental parameters affecting extraction efficiency, including the amount of adsorbents, solution pH, ionic strength, eluent type, and eluent volume, were investigated. The developed method showed a wide linear range (0.37-100 ng mL^-1), low detection limits (0.11-0.32 ng mL^-1), low limits of quantification (0.37-1.07 ng mL^-1), high enrichment factors (45.9-49.3), and good reproducibility (<4.8%) for phytohormones. The developed analytical method was used to analyze trace phytohormones in fruit juices with good recoveries, highlighting the potential of the MWNTs@SNW-1 composite as an adsorbent in sample preparation.

Aptamer-functionalized metal-organic framework-coated nanofibers with multi-affinity sites for highly sensitive, selective recognition of ultra-trace microcystin-LR

A novel aptamer-functionalized metal-organic framework nanofibrous composite (viz. PAN/UiO@UiO2-N₃-aptamer) with a high aptamer coverage density was proposed based on the electrospinning and seeded growth method, and used for specific affinity recognition of trace Microcystin-LR (MC-LR). Heterobifunctional ligand was used to modify the metal-organic framework nanoparticles (MOF NPs) surface, which could passivate the MOF surface with respect to unmodified DNA, followed by coupling massive aptamers on MOF of the solid-phase microextraction (SPME) fiber using click chemistry. Characterizations including morphology, spectra analysis, mechanical stability, binding capacity and specificity were fulfilled. Applied to the analysis of MC-LR, the good selective and sensitive recognition were obtained with the detection limit as low as 0.003 ng/mL, which was better than most non-specific SPME or solid-phase extraction (SPE) protocols. The stability and reproducibility were acceptable, and the intra-day, inter-day and column-to-column relative standard deviations (RSDs) for the recovery of MC-LR were gained in the range from 2.5% to 14.3%, respectively. Satisfactory recoveries of MC-LR in environmental water samples were measured as 96.3 ± 4.7% - 98.9 ± 2.7% (n = 3) in tap water, 94.4 ± 2.5% - 96.1 ± 3.5% (n = 3) in pond water, and 97.0 ± 2.1% - 97.9 ± 3.1% (n = 3) in river water, respectively. This work demonstrated that the electrospun nanofibrous composite with massive aptamers would be a better alternative for ultra-trace MC-LR detection with good selectivity, matrix-resistance ability and high resolution.

Metal organic framework/chitosan/polyethylene oxide composite columnar foam as a sorbent for the enrichment and determination of estrogens in environmental aqueous solutions

A MIL-53(Al)/CS/PEO columnar foam was fabricated for the determination of estrogens in larger-volume environmental water samples by VA-SPE and HPLC-FLD.

Preparation of molecularly imprinted resin/polydopamine nanofibers mat for the highly efficient extraction and determination of sulfonamides in environmental water

With polyacrylonitrile nanofibers mat (PAN NFsM) as a template, molecularly imprinted resin/polydopamine nanofibers mat (MIR/PDA NFsM) was synthesized for the extraction of sulfonamides (SAs) in water. The specific surface area and pore volume were increased obviously due to the functionalization of MIR. The adsorption efficiencies of MIR/PDA NFsM under optimized conditions for SAs were 92.3-99.3%. Possible adsorption mechanisms of imprinting recognition and hydrogen bond interactions were also put forward. Compared with MIR particles, the MIR/PDA NFsM exhibited much superior adsorption performance. Particularly, the outstanding mass transfer efficiency of MIR/PDA NFsM was much higher than the other reported adsorbents for SAs. Finally, a new method based on the solid-phase extraction (SPE) of MIR/PDA NFsM was successfully developed for the detection of five SAs in environmental water with HPLC-MS/MS and applied to the analysis of actual samples. Under the selected conditions, the enrichment factors of MIR/PDA NFsM of SCP, SMT, SMZ, SMR, and SMX were between 23.0 and 25.0. Low detection limits (0.26-0.76 ng L^-1), broad linear range (1.0 ng L^-1 to 10.0 μg L^-1), and satisfactory recoveries (82.8-115.6%) and precisions (RSDs < 7.2%) were obtained. Moreover, the excellent reusability properties and storage stability endowed MIR/PDA NFsM with great value for practical applications.

Aptamer-functionalized metal-organic framework-based electrospun nanofibrous composite coating fiber for specific recognition of ultratrace microcystin in water

A novel aptamer@AuNPs@UiO-66-NH₂ electrospun nanofibrous coating fiber for specific recognition of microcystin-LR (MC-LR) was proposed by using electrospinning, metal-organic frameworks (MOF) seed growth and AuNPs bridging aptamer strategies. Characterization of morphology, structure and stability of the obtained affinity nanofibrous coating fiber were investigated. High loading of MOFs and aptamers on the nanofibrous fiber were achieved and successfully applied for accurate identification of MC-LR by solid-phase microextraction (SPME) coupled with LC-MS. Highly specific recognition of MC-LR with little interference of analogs was achieved with extremely low LOD (0.004 ng/mL), good precision (CV% < 11.0%) and low relative error (RE% = -1.5% to -10.0%), which was rather better than that of the traditional SPME or SPE protocols. Satisfactory recoveries of MC-LR were obtained in the range of 92.0-96.8% (n = 3) in fortified tap water, raw pond water and river water samples. This work revealed an attractive alternative access to specific recognition and super-sensitive analysis of MC-LR in water.

Current overview and perspectives in environmentally friendly microextractions of carbamates and dithiocarbamates

Carbamates and dithiocarbamates are two classes of pesticides widely employed in the agriculture practice to control and avoid pests and weeds, hence, the monitoring of the residue of those pesticides in different foodstuff samples is important. Thus, this review presents the classification, chemical structure, use, and toxicology of them. Moreover, it was shown the evolution of liquid- and solid-phase microextractions employed in the extraction of carbamates and dithiocarbamates in water and foodstuff samples. The classification, operation mode, and application of the microextractions of liquid-phase and solid-phase used in their extraction were discussed and related to the analytical parameters and guidelines of green analytical chemistry.

Green molecularly imprinted polymers for sustainable sample preparation

The use of molecularly imprinted polymers in sample preparation as selective sorbent materials has received great attention during the last years leading to analytical methods with unprecedented selectivity. However, with the progressive implementation of Green Analytical Chemistry principles, it is necessary to critically review the greenness of synthesis and further use of molecularly imprinted polymers in sample preparation. Accordingly, in the present review, the different steps and strategies for the preparation of molecularly imprinted polymers, the used reagents, as well as their incorporation to microextraction techniques are reviewed from a green perspective and recent alternatives to make the use of molecularly imprinted polymers more sustainable are provided.

Recent advances and applications of cyclodextrins in magnetic solid phase extraction

Cyclodextrins (CDs) as a family of cyclic oligosaccharides are toroidal with a hydrophobic interior and a hydrophilic exterior. They are well-known for their ability to form host-guest inclusion complexes with different compounds. They are used as chiral stationary phases in high performance liquid chromatography (HPLC) and gas chromatography (GC) or as chiral reagents in the background electrolyte of capillary electrophoresis (CE). In recent years, they have been used for modification of sorbents or as sorbents in solid phase extraction (SPE) procedures. Magnetic solid-phase extraction (MSPE), as a new type of SPE procedure, has received considerable attention due to its rapid phase separation process as compared to traditional extraction mode. This review covers the synthesis of CD-based magnetic sorbents (such as immobilization of CDs onto the different supports, production of nanosponges, and making hybrid substances with nanomaterials) and the use of these compounds in MSPE of different analytes from biological, environmental, and food samples. Also, prospects of CD-based sorbents for sample pre-treatment are also proposed.

Innovative extraction materials for fiber-in-tube solid phase microextraction: A review

Fiber-in-tube solid-phase microextraction (fiber-in-tube SPME) with short capillary longitudinally packed with fine fibers as extraction device allows direct coupling to high performance liquid chromatography (HPLC) systems to determine weakly volatile or thermally labile compounds. This technique associates the advantages of miniaturized and analytical on-line systems. Major achievements include the use of different capillaries (fused-silica, copper, stainless steel, polyetheretherketone (PEEK), or poly(tetrafluoroethylene) (PTFE)) that are packed with neat fibers (Zylon®, silk, or Kevlar 29®) or fibers (stainless steel, basalt, or carbon) functionalized with selective coatings (aerogels, ionic liquids (ILs), polymeric ionic liquids (PILs), molecularly imprinted polymers (MIPs), layered double hydroxides (LDHs), or conducting polymer). This review outlines the fundamental theory and the innovative extraction materials for fiber-in-tube SPME-HPLC systems and highlights their main applications in environmental and bioanalyses.

Self-rotating stir mesh screen sorptive extraction for analyzing chlorpyrifos by ion mobility spectrometry

A mesh screen was electrochemically coated with polypyrrole and used as a sorptive extractor device, for the first time. This configuration acts in such a way that it is self-rotating in the presence of a magnetic force and can be used for extraction and concentration of analytes. Actually, applying a mesh screen instead of a bar or plate in sorptive extraction provided a more effective contact area between the sorptive materials and sample solution, resulting in higher sorption efficiency. The device performance was assessed by using chlorpyrifos pesticide as a model analyte. A thermal desorption unit was coupled to an ion mobility spectrometer and applied for evaporating the extracted analyte. Different parameters affecting the extraction efficiency during the electro-polymerization and the extraction process, including the time of electrodeposition, the concentration of pyrrole, oxalic acid and salt, temperature and time of extraction, and the stirring rate of the extractor device were investigated and optimized, simultaneously. The detection and quantification limits of the method were calculated to be 0.035 and 0.1 μg L^-1, respectively. The linear dynamic range obtained was from 0.1 to 20 μg L^-1, with a determination coefficient of 0.9984. The intra-day and inter-day-relative standard deviations (RSD, n = 3) were lower than 3% and 8%, respectively. Under the optimal conditions, the absolute recovery and the enrichment factor were found to be 97% and 5820, respectively. Finally, the relative recoveries of the proposed method were calculated to be in the range of 86-111% for spiked water, wastewater, and apple samples. The results obtained from the method were validated by EPA method 622.

Core-shell magnetic zeolite imidazolate framework-8 as adsorbent for magnetic solid phase extraction of brucine and strychnine from human urine

Core-shell magnetic zeolite imidazolate framework-8 (Fe3O4@PAA@ZIF-8) was successfully synthesized and first employed as adsorbent of magnetic solid-phase extraction (MSPE) for the determination of brucine and strychnine in human urine sample coupled with high performance liquid chromatography. The as-prepared Fe3O4@PAA@ZIF-8 was characterized by transmission electron microscopy, Fourier-transform infrared spectrometry, X-ray diffraction, vibrating sample magnetometer and zeta potential analysis. Main parameters affecting the MSPE efficiency, including amount of adsorbent, sample solution pH, extraction time, ionic strength, desorption solvent, desorption time and desorption volume were further optimized. Under the optimized conditions, the proposed method provided good linearity (5.0-1000.0 μg L-1) with determination coefficients between 1.0000 and 0.9998, low limits of detection in the range of 1.1-1.2 μg L-1, and excellent reproducibility with relative standard deviations of less than 7.7%. The intra-day and inter-day precision were 1.5-3.2% and 2.1-7.2%, respectively. Satisfactory spiked recoveries were between97.2% and 115.4% with the relative standard deviations less than 6.3%. The results demonstrated that Fe3O4@PAA@ZIF-8 composite was a promising magnetic adsorbent for the preconcentration of brucine and strychnine in human urine sample.

Exploring the use of cork pellets in bar adsorptive microextraction for the determination of organochloride pesticides in water samples with gas chromatography/electron capture detection quantification

In this study, a biosorbent material with characteristics for the adsorption of organic compounds was used for a cork pellet-based bar adsorptive microextraction technique, as a new greener alternative for the determination of organochlorine compounds. Aldrin, chlordane, dieldrin, endrin, lindane, 4,4-DDD, 4,4-DDE, 4,4-DDT, α-endosulfan and β-endosulfan were analyzed in water samples (drinking water, stream water and river water) with separation/detection by gas chromatography and electron capture detection (GC/ECD). The parameters that can affect the sample preparation efficiency such as desorption solvent and time as well as extraction time and ionic strength were evaluated by multivariate and univariate designs. Cork pellets (10  ×  Ø 3 mm) were used for the extraction of 15 mL of sample in the optimal conditions: 60 min of agitation with no salt added to the sample, followed by desorption of the cork pellet with 120 µL of ethyl acetate for 30 min. The bar-to-bar RSD out with five different bars showed good results with RSD ≤ 15.6%, allowing the use of simultaneous extractions. LOD and LOQ values ranged from 3 to 15 ng L^-1 and 10 to 50 ng L^-1 respectively, and the determination coefficients were greater than 0.9869. The target analytes were not detected in the three analyzed samples. Therefore, the recovery study was performed fortifying the water samples. Analyte recovery ranged from 48.7 - 138.2% for drinking water, 40.2 - 128.2% for stream water and 67.5 - 128.7% for river water.

[Fabrication of nanomaterials incorporated polymeric monoliths and application in sample pretreatment]

Polymeric monolithic columns are fabricated by in situ polymerization of the corresponding monomer, crosslinkers, porogenic solvents and radical initiators within a mold. Compared with the conventional packed solid phase extraction adsorbents, polymeric monolithic columns with a continuous porous structure process distinctive advantages of rapid mass transfer and excellent permeability, which facilitates the extraction of trace amounts of the target from the matrix even at high flow velocities. Besides, these materials can be easily fabricated in situ within various cartridges, avoiding a further packing step associated with packed particulate adsorbents. Additionally, the abundant monomer availability, flexible porous structure, and wide applicable pH range make monoliths versatile for use in separation science. Thus, polymeric monolithic columns have been increasingly applied as efficient and promising extraction media for sample pretreatment food, pharmaceutical, biological and environmental analyses. However, these materials usually have the difficulty in morphology control and their interconnected porous micro-globular structure, which may result in low porosity, limited specific surface area and poor efficiency. In addition, polymeric monoliths suffer from the swelling in organic solvents, thus decreasing the service life and precision while increasing the cost consumption. Recently, the development of nanomaterial-incorporated polymeric monoliths with an improved ordered structure, enhanced adsorption efficiency and outstanding selectivity has attracted considerable attention. Nanoparticles are considered as particulates within the size range of 1-100 nm in at least one dimension, which endows them with unique optical, electrical and magnetic properties. These materials have a large surface area, excellent thermal and chemical stabilities, remarkable versatility, as well as a wide variety of active functional groups on their surface. With the aim of exploiting these advantages, researchers have shown great interest in applying nanomaterial-incorporated polymeric monoliths to separation science. Accordingly, significant progress has been achieved in this field. Nanomaterials can be entrapped via the direct synthesis of a polymerization solution that contains well dispersed nanomaterials in porogens. In addition, nanoparticles can be incorporated into the monolithic matrix by copolymerization and post-polymerization modification via specific interactions. Therefore, nanomaterial-incorporated polymeric monoliths combined the different shapes, chemical properties, and physical properties of the polymers with those of the nanoparticles. The presence of nanoparticles can improve the structural rigidity as well as the thermal and chemical stabilities of monolithic adsorbents. Besides, nanoparticles are capable of increasing the specific surface area and providing multiple active sites, which leads to enhanced extraction performance and selectivity of polymeric monolithic materials. In recent years, diverse types of nanomaterials, such as carbonaceous nanoparticles, metallic materials and metal oxides, metal-organic frameworks, covalent organic frameworks and inorganic nanoparticles have been extensively explored as hybrid adsorbents in the modes of solid phase extraction, solid phase microextraction, stir bar sorption extraction and on-line solid phase extraction. This review specifically summarizes the fabrication methods for nanomaterial incorporated polymeric monoliths and their application to the field of sample pretreatment. The existing challenges and future possible perspectives in the field are also discussed.

Nanoparticle coatings for stir bar sorptive extraction, synthesis, characterization and application

During the last ten years, number of articles published on synthesis and applications of nano-particles (NPs) have been increased by a factor of 40. One of the most interesting applications of NPs is their using as high capacity, robust and highly selective coatings for stir bar sorption extraction (SBSE). Utilizing NPs greatly promoted applications of SBSE and has gained importance on green sample preparation. In this article, all available literature on nano-coatings as media for microextraction by stir bar is reviewed. This includes non-functionalized NPs (mostly, metallic/metallic oxide and graphene based), functionalized coatings, and decorated coatings (both mono- and multifunctional). Various applications, advantages and disadvantages of each nano-coated prepared stir bar are discussed in detail along with critical evaluation of currently available methods.

Insights into the structure-performance relationships of extraction materials in sample preparation for chromatography

Sample preparation is one of the most crucial steps in analytical processes. Commonly used methods, including solid-phase extraction, dispersive solid-phase extraction, dispersive magnetic solid-phase extraction, and solid-phase microextraction, greatly depend on the extraction materials. In recent decades, a vast number of materials have been studied and used in sample preparation for chromatography. Due to the unique structural properties, extraction materials significantly improve the performance of extraction devices. Endowing extraction materials with suitable structural properties can shorten the pretreatment process and improve the extraction efficiency and selectivity. To understand the structure-performance relationships of extraction materials, this review systematically summarizes the structural properties, including the pore size, pore shape, pore volume, accessibility of active sites, specific surface area, functional groups and physicochemical properties. The mechanisms by which the structural properties influence the extraction performance are also elucidated in detail. Finally, three principles for the design and synthesis of extraction materials are summarized. This review can provide systematic guidelines for synthesizing extraction materials and preparing extraction devices.

Fabrication of edge-curled petals-like covalent organic frameworks and their properties for extracting indole alkaloids from complex biological samples

In this study, a functionalized covalent-organic framework (COF) was first synthesized using porphyrin as the fabrication unit and showed an edge-curled, petal-like and well-ordered structure. The synthesized COF was then introduced to prepare porous organic polymer monolithic materials (POPMs). Two composite POPM/COF monolithic materials with rod shapes, referred to as sorbent A and sorbent B, were prepared in stainless steel tubes using different monomers. Sorbents A and B exhibited relatively uniform porous structures and enhanced specific surface areas of 153.14 m²/g and 80.01 m²/g, respectively. The prepared composite monoliths were used as in-tube solid-phase extraction (SPE) sorbents combined with HPLC for the on-line extraction and quantitative analytical systems. Indole alkaloids (from Catharanthus roseus G. Don and Uncaria rhynchophylla (Miq.) Miq. Ex Havil.) contained in mouse plasma were extracted and quantitatively analyzed using the online system. The two composite multifunctional monoliths showed excellent clean-up ability for complex biological matrices, as well as superior selectivity for target indole alkaloids. Method validation showed that the RSD values of the repeatability (n=6) were ≤ 3.46%, and the accuracy expressed by the spiked recoveries was in the ranges of 99.38%–100.91% and 96.39%–103.50% for vinca alkaloids and Uncaria alkaloids, respectively. Furthermore, sorbents A and B exhibited strong reusability, with RSD values ≤ 5.32%, which were based on the peak area of the corresponding alkaloids with more than 100 injections. These results indicate that the composite POPM/COF rod-shaped monoliths are promising media as SPE sorbents for extracting trace compounds in complex biological samples.

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Edge-curled petals-like COF was synthesized using porphyrin as the fabrication unit.

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In-tube monolithic POMP/COF composite SPE sorbents with rod-shape were fabricated.

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The in-tube sorbents were used to extract hence indole alkaloids from complex samples.

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The two homemade sorbents show strong reusability of more than 100 times.