Polydimethylsiloxane/covalent triazine frameworks coated stir bar sorptive extraction coupled with high performance liquid chromatography-ultraviolet detection for the determination of phenols in environmental water samples

Removal and detection of phenols through an SPE-HPLC method using microporous organic networks as adsorbent

The design and development of a facile synthesis approach to construct novel materials for the rapid adsorption and removal of environmental pollutants are of significant interest. In this work, we report the rational design and facile synthesis of magnetic core-shell-based microporous organic networks, Fe3O4@MON-TBPT-TEB (TTMON, achieved by reacting 2,4,6-tris(p-bromophenyl) triazine and 1,3,5-triethynylbenzene) and Fe3O4@MON-TBPM-DEBP (TDMON, achieved by reacting tetrakis (4-bromophenyl) methane and 4-4'-diethynylbiphenyl). These MONs possessed excellent dispersity, electrostatic attraction as well as plenty of π-π and hydrophobic interaction sites enabled them to efficiently absorb targeted environmental pollutants. TTMON and TDMON exhibited excellent adsorption capacities of 440 and 510 mg g-1, respectively, at 25 °C for 2,4,6-trichlorophenol (TCP). TCP, 2,4-dichlorophenol (DCP), 2-naphthol (2-NT) and 4-nitrophenol (4-NP) from aqueous solution were treated by both MONs, followed by their analysis with high-performance liquid chromatography (HPLC). For TDMON, the proposed SPE-HPLC-UV method showed an LOD of 0.03 μg L-1, LOQ of 0.11 μg L-1, and a wide linear range of 1-1000 μg L-1 for TCP. The adsorption kinetics, thermodynamics, isotherms, effect of pH and humic acid (HA), ionic strength, regeneration, and reusability of the MONs were also studied. The results revealed that the novel-designed MONs have potential applications as efficient adsorbents in sample pretreatment.

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.

Dual optical detection approach for capillary electrophoresis following two-step liquid-liquid extraction to determine ten phenols in water samples

In this research, the analytical method was developed and evaluated for determining phenol and its nine derivatives belong to the US EPA priority pollutant list in water samples by using dual-channeled capillary electrophoresis (CE) coupled with two types of optical detectors, namely LED-induced fluorescence (LEDIF) and ultraviolet (UV) detectors. The optimal background electrolytes for the first and second CE channels were 20 mM borate (pH 9.80) with 400 µM fluorescein and 55 mM borate (pH 11.75), respectively. The two-step liquid-liquid extraction (LLE) was used for sample preparation and enrichment, in which phenol and its derivatives were extracted from the aqueous phase using 10 mL of n-hexane/1-octanol (60/40, v/v) and then were back extracted into a 0.1 M NaOH as a final acceptor phase. Under the optimal CE and two-step LLE conditions, the enrichment factors of 10 phenols were 184 - 1120-fold, and the method detection limits were lowered to 0.02-0.60 µg/L. The obtained intra-day and inter-day precisions in terms of relative standard deviations (RSD) were between 4.0 and 7.3 % and 6.7 and 14 %, respectively. This approach was used to determine phenols in water samples, with recoveries ranging from 82.0 to 108.9 %. In combination with sample enrichment by two-step LLE extraction, this is the first CE study conducted to determine phenols in the EPA list using two detector approaches, specifically CE-LEDIF/CE-UV.

Advanced porous organic materials for sample preparation in pharmaceutical analysis

The development of novel sample preparation media plays a crucial role in pharmaceutical analysis. To facilitate the extraction and enrichment of pharmaceutical molecules in complex samples, various functionalized materials have been developed and prepared as adsorbents. Recently, some functionalized porous organic materials have become adsorbents for pharmaceutical analysis due to their unique properties of adsorption and recognition. These advanced porous organic materials, combined with consequent analytical techniques, have been successfully used for pharmaceutical analysis in complex samples such as environmental and biological samples. This review encapsulates the progress of advanced porous materials for pharmaceutical analysis including pesticides, antibiotics, chiral drugs, and other compounds in the past decade. In addition, we also address the limitations and future trends of these porous organic materials in pharmaceutical analysis.

An overview on human exposure, toxicity, solid-phase microextraction and adsorptive removal of perfluoroalkyl carboxylic acids (PFCAs) from water matrices

Perfluoroalkyl carboxylic acids (PFCAs) are sub-class of perfluoroalkyl substances commonly detected in water matrices. They are persistent in the environment, hence highly toxic to living organisms. Their occurrence at trace amount, complex nature and prone to matrix interference make their extraction and detection a challenge. This study consolidates current advancements in solid-phase extraction (SPE) techniques for the trace-level analysis of PFCAs from water matrices. The advantages of the methods in terms of ease of applications, low-cost, robustness, low solvents consumption, high pre-concentration factors, better extraction efficiency, good selectivity and recovery of the analytes have been emphasized. The article also demonstrated effectiveness of some porous materials for the adsorptive removal of the PFCAs from the water matrices. Mechanisms of the SPE/adsorption techniques have been discussed. The success and limitations of the processes have been elucidated.

Pyridine-linked covalent triazine frameworks with bidirectional electron donor-acceptor for efficient organic pollution removal

Simultaneous regulation of adsorption and photocatalytic performance of covalent triazine frameworks (CTFs) to achieve efficient control of organic pollution in water is a promising strategy, but remains a formidable challenge. Herein, pyridine linkers were innovatively introduced into pristine CTF (p-CTF) and the bidirectional electron donor-acceptor (EDA) system of contaminant-to-pyridine and pyridine-to-triazine was constructed inside. Experimental results combined with theoretical calculations revealed that pyridine units with π-deficient properties performed as electron acceptors and electron donors in the adsorption and photocatalytic processes, respectively. This special structure provided a directional pathway for electron transfer, which endowed CTFs with excellent adsorption and photocatalytic properties. Compared to p-CTF, pyridine-linked CTF (M-CTF) showed a 16-fold increase in adsorption capacity for naphthalene (973.4 μmol·g^-1). Benefiting from the optimized light absorption and electron transfer form (n → π*transition), M-CTF exhibited high regeneration efficiency after adsorption of both bisphenol A (94 % after 4 cycles) and naphthalene (95 % after 4 cycles). Besides, the removal performance of organic micropollutants from natural water showed a great advantage thanks to the bidirectional EDA system. Overall, the present study provides new insights into the optimization of electronic structures for carbon-based environmental functional materials applied to organic pollution control in water.

GO/ZnO nanocomposite - as transducer platform for electrochemical sensing towards environmental applications

Graphene Oxide-Zinc Oxide (GO-ZnO) - a new nanomaterial that has queued the interest of researchers. Their intriguing promising physical and electrochemical features of electrode material have led to its widespread use in electrochemical sensor applications. GO-ZnO based nanomaterial were extensively exploited in the construction of electrochemical sensors due to their adaptability and distinct qualities. On understanding the structural role of these materials, their modification processes are critical for realizing their full potential. The advancement of technology on new concepts and strategies has revolutionized the field of sensor devices with high sensitivities and selectivity. These tools can test a range of contaminants quickly, accurately, and affordably while performing automated chemical analysis in complicated matrices. This paper highlights the electrochemical transducer surface for sensing various analytes and current research activity on GO-ZnO nanocomposite. Additionally, we talked about current developments in GO-ZnO nanostructured composites to identify relevant analytes (i.e., Nitrophenols, Antibiotic Drugs, Biomolecules). While being used in the laboratory, the majority of produced systems have proven to bring about excellent gains. Their monitoring application still has a long way to go before it is fixed due to problems like technological advancements and multifunctional strategies to get around the challenges for improving the sensing systems.

A Schiff base networks coated stir bar for sorptive extraction of pyrethroid pesticide residues in tobacco

Schiff base networks (SNWs) were introduced as a new stir bar coating, and a method of SNWs- coated stir bar sorptive extraction (SBSE) coupled to high performance liquid chromatography-ultraviolet detector (HPLC-UV) was developed for determination of pyrethroid pesticide residues in tobacco. The prepared amorphous SNWs polymer from melamine and 3,5-dihydroxybenzaldehyde riches in triazine rings, hydroxyl groups and amino groups, and the SNWs/polydimethylsiloxane (PDMS) stir bar prepared by sol-gel method can extract weakly polar pyrethroid pesticides through hydrophobic, π-π and hydrogen bonding. The SNWs/PDMS stir bar exhibited high extraction efficiency toward pyrethroid pesticides (70-76%) and good mechanical stability with reused time more than 50 times. Under the optimal experimental conditions, the limits of detection were 0.20 - 0.66 µg/L with relative standard deviation varying in the range of 2.3-8.2%, which meets the requirements of trace analysis of pesticide residues in the tobacco industry. The method was applied to the determination of six pyrethroid pesticides in cigarette samples, and the recovery for the spiked samples ranged from 82 to 117%, showing a great applicability for the analysis of pesticide residues in real samples with a complex sample matrix.

Temperature-responsive graphene oxide/N-isopropylacrylamide/2-allylphenol nanocomposite for the removal of phenol and 2,4-dichlorophenol from aqueous solution

In this study, a novel thermo-responsive polymer was synthesized with efficient grafting of N-isopropylacrylamide as a thermosensitive polymer onto the graphene oxide surface for the efficient removal of phenol and 2,4-dichlorophenol from aqueous solutions. The synthesized polymer was conjugated with 2-allylphenol. Phenol and 2,4-dichlorophenol were monitored by ultra-performance liquid chromatography system equipped with a photodiode array detector. The nanoadsorbent was characterized by different techniques. The nanoadsorbent revealed high adsorption capacity where the removal percentages of 91 and 99% were found under optimal conditions for phenol and 2,4-dichlorophenol, respectively (for phenol; adsorbent dosage = 0.005 g, pH = 8, temperature= 25 °C, contact time = 60 min; for 2,4-dichlorophenol; adsorbent dosage = 0.005 g, pH = 5, temperature = 25 °C, contact time = 10 min). Adsorption of phenol and 2,4-dichlorophenol onto nanoadsorbent followed pseudo-second-order kinetic and Langmuir isotherm models, respectively. The values of ΔG (average value = - 11.39 kJ mol^-1 for phenol and 13.42 kJ mol^-1 for 2,4-dichlorophenol), ΔH (- 431.72 J mol^-1 for phenol and - 15,721.8 J mol^-1 for 2,4-dichlorophenol), and ΔS (35.39 J mol^-1 K^-1 for phenol and - 7.40 J mol^-1 K^-1 for 2,4-dichlorophenol) confirmed spontaneous and exothermic adsorption. The reusability study indicated that the adsorbent can be reused in the wastewater treatment application. Thermosensitive nanoadsorbent could be used as a low-cost and efficient sorbent for phenol and 2,4-dichlorophenol removal from wastewater samples.

Covalent triazine-based frameworks for efficient solid-phase microextraction of phthalic acid esters from food-contacted plastics

Owing to various health threats associated with phthalic acid esters (PAEs), this category of endocrine-disrupting compounds has attracted more and more public scrutiny. However, the efficient preconcentration of PAEs from complex food-contacted plastics still remains challenging. Herein, three covalent triazine-based frameworks (CTFs) were constructed by facile Friedel-Crafts reactions of cyanuric chloride (CC), with triptycene (TPC), fluorene (FL) and 1,3,5-triphenylbenzene (TPB), respectively. Three CTFs were then employed as solid-phase microextraction (SPME) coatings for the extraction of PAEs. Benefiting from the large surface area and high pore volume, the newly-synthesized CC-TPC based SPME method exhibited large enrichment factors (978-2210), low limits of detection (0.027-0.10 ng g ^- 1), satisfactory linear ranges (0.09-20 ng g ^- 1), acceptable repeatabilities (4.3-9.6%) and high relative recoveries (92.0-104.6%).

Fluorine-Functionalized Covalent-Organic-Framework-Coated Stir Bar for the Extraction of Benzoylurea Insecticides in Pear Juice and Beverage Followed by High-Performance Liquid Chromatography-Ultraviolet Detection

A fluorinated covalent organic framework (COF), named F-COF, was fabricated via simple room-temperature synthesis. With the characteristics of rich fluorine atoms, hydrophobicity, and large conjugated structure, F-COF was evaluated for the extraction of five benzoylurea insecticides (BUs) containing fluorine atoms, benzene ring, and urea bridge. Specifically, F-COF-coated stir bars were prepared by physical adhesion and exhibited higher extraction recovery (73-93 versus 40-85%) toward BUs than commercial stir bars in a shorter extraction time (50 min versus 24 h). The adsorption behavior of BUs on F-COF was explored, and it was assumed that the halogen bond (O-F), hydrophobic interaction, electrostatic interaction, and π-π stacking contributed to the adsorption. On the basis of it, a method combining stir bar sorptive extraction with liquid chromatography-ultraviolet detector was developed for trace analysis of five BUs. Under the optimal conditions, the limits of detection for BUs were found to be 0.301-0.672 μg/L, with the linear range of 1.0/2.0-500 μg/L and relative standard deviations of <8.0% (c = 5 μg/L and n = 7). The accuracy of the proposed method was validated by the recovery test, and the recoveries of target BUs in spiked pear juice and pear beverage were 82.0-113 and 84.0-112%, respectively.

Porous organic framework as coating for stir bar sorptive extraction of carbamate pesticides from corn and potato samples

Three porous organic frameworks (POFs) were synthesized by the reaction between phloroglucinol and 1,4-phthalaldehyde, 4,4'-biphenyldialdehyde or tris-(4-formylphenyl) amine; the products are named as POF-a, POF-b and POF-c, respectively. They were used to prepare POFs coated stir bars respectively for the extraction of four carbamate pesticides (CMPs). POF-c coated stir bar exhibited better adsorption performance than POF-a/b coated stir bar and commercial stir bars, probably due to the stronger conjugated structure and hydrophobicity of POF-c, and resultant hydrophobic, π-π and hydrogen bonding interactions between them. The adsorption mechanism for target CMPs was verified by characterization techniques and molecular dynamics simulation. A method of POF-c coated stir bar sorptive extraction-high performance liquid chromatography-variable wavelength ultraviolet detector was developed for the analysis of four CMPs in corn and potato samples. Under the optimal conditions, LODs of the method were between 0.017 and 0.048 μg/L, and the linear range for four CMPs was 0.1/0.2-200 μg/L.

[Application progress of covalent organic framework materials in extraction of toxic and harmful substances]

Toxic and hazardous substances constitute a category of compounds that are potentially hazardous to humans, other organisms, and the environment. These substances include pesticides (benzoylureas, pyrethroids, neonicotinoids), persistent organic pollutants (polycyclic aromatic hydrocarbons, polychlorinated biphenyls, perfluorinated compounds), plasticizers (phthalate esters, phenolic endocrine disruptors), medicines (sulfonamides, non-steroid anti-inflammatory drugs, tetracyclines, fluoroquinone antibiotics), heterocyclic aromatic amines, algal toxins, and radioactive substances. Discharge of these toxic and harmful substances, as well as their possible persistence and bioaccumulation, pose a major risk to human health, often to the extent of being life-threatening. Therefore, it is important to analyze and detect toxic and hazardous substances in the environment, drinking water, food, and daily commodities. Sample pretreatment is an imperative step in most of the currently used analytical methods, especially in the analysis of trace toxic and harmful substances in complex samples. An efficient and fast sample pretreatment technology not only helps improve the sensitivity, selectivity, reproducibility, and accuracy of analytical methods, but also avoids contamination of the analytical instruments and even damages the performance and working life of instruments. Sample pretreatment techniques widely used in the extraction of toxic and hazardous substances include solid-phase extraction (SPE), solid-phase microextraction (SPME), and dispersed solid-phase extraction (DSPE). The adsorbent material plays a key role in these pretreatment techniques, thereby determining their selectivity and efficiency. In recent years, covalent organic frameworks (COFs) have attracted increasing attention in sample pretreatment. COFs represent an exciting new class of porous crystalline materials constructed via the strong covalent bonding of organic building units through a reversible condensation reaction. COFs present four advantages: (1) precise control over structure type and pore size by consideration of the target molecular structure based on the connectivity and shape of the building units; (2) post-synthetic modification for chemical optimization of the pore interior toward optimized interaction with the target; (3) straightforward scalable synthesis; (4) feasible formation of composites with magnetic nanoparticles, carbon nanotubes, graphene, silica, etc., which is beneficial to enhance the performance of COFs and meet the requirement of diverse pretreatment technologies. Because of the well-defined crystalline porous structures and tailored functionalities, COFs have excellent potential for use in target extraction. However, some issues need to be addressed for the application of COFs in the extraction of toxic and hazardous substances. (1) For the sample matrix, most of the reported COFs are highly hydrophobic, which limits their dispersibility in water-based samples, leading to poor extraction performance. COFs with good dispersibility in water-based samples are urgently required. (2) Besides, COFs rely on hydrophobic interaction, size repulsion, π-π stacking, and Van der Waals forces to extract target substances, but they are not effective for some polar targets. Thus, it is necessary to develop COFs with high affinity for polar toxic and hazardous substances. (3) Methods for the synthesis of COFs have evolved from solvothermal methods to room-temperature methods, mechanical grinding, microwave-assisted synthesis, ion thermal methods, etc. Most of the existing methods are time-consuming, laborious, and environmentally unfriendly. The starting materials are too expensive to prepare COFs in large quantities. More effort is required to improve the synthesis efficiency and overcome the obstacles in the application of COFs for extraction. This article summarizes and reviews the research progress in COFs toward the extraction of toxic and hazardous substances in recent years. Finally, the application prospects of COFs in this field are summarized, which serves as a reference for further research into pretreatment technologies based on COFs.

An efficient differential sensing strategy for phenolic pollutants based on the nanozyme with polyphenol oxidase activity

To realize the efficient differential sensing of phenolic pollutants in sewage, a novel sensing strategy was successfully developed based on one nanozyme (GMP-Cu) with polyphenol oxidase activity. Phenolic pollutants can be oxidized by GMP-Cu, and the oxidation products reacts subsequently with 4-aminoantipyrine to produce a quinone-imine compound. The absorption spectra of final quinone-imine products resulted from different phenolic pollutants showed obvious differences, which were due to the interaction difference between GMP-Cu and phenolic pollutants, as well as the different molecular structures of the quinone-imine products from different phenolic pollutants. Based on the difference of absorption spectra, a novel differential sensing strategy was developed. The genetic algorithm was used to select the characteristic wavelengths at different enzymatic reaction times, HCA and PLS-DA algorithms were utilized for the discriminant sensing of seven representative phenolic pollutants, including hydroquinone, resorcinol, catechol, resorcinol, phenol, p-chlorophenol, and 2,4-dichlorophenol. Scientific wavelength selection algorithm and recognition algorithm resulted in the successful identification of phenolic pollutants in sewage with a discriminant accuracy of 100%, and differentiation of the phenolic pollutants regardless of their concentration. These results indicate that sensing strategy can be used as an effective tool for the efficient identification and differentiation of phenolic pollutants in sewage.

Triazine 2D Nanosheets as a New Class of Nanomaterials: Crystallinity, Properties and Applications

Based on the recent (2015–2021) literature data, the authors analyze the mutual dependence of crystallinity/amorphism and specific surface area and porosity in covalent triazine frameworks (CTFs), taking into account thermodynamic and kinetic control in the synthesis of these 2D nanosheets. CTFs have now become a promising new class of high-performance porous organic materials. They can be recycled and reused easily, and thus have great potential as sustainable materials. For 2D CTFs, numerous examples are given to support the known rule that the structure and properties of any material with a given composition depend on the conditions of its synthesis. The review may be useful for elder students, postgraduate students, engineers and research fellows dealing with chemical synthesis and modern nanotechnologies based on 2D covalent triazine frameworks.

Covalent organic frameworks-derived hierarchically porous N-doped carbon for 2,4-dichlorophenol degradation by activated persulfate: The dual role of graphitic N

A series of hierarchically porous carbon catalysts with high N content and large surface area were prepared via self-templated carbonization of covalent organic frameworks (COFs). The catalyst was used to activate persulfate (PS) for degrading 2,4-dichlorophenol (2,4-DCP). Experimental results demonstrated that the prepared catalyst treated at 700 °C (PNC-700) showed both strong adsorption ability and enhanced PS activity for 2,4-DCP degradation. A variety of characterization techniques were used to investigate the properties of prepared catalysts. We found that the graphitic N functional groups acted as both activity sites and electron transfer access. The activity of the catalyst was also closely related to the hierarchical pore structure and good electrical conductivity. The influencing factors of PNC-700/PS system in 2,4-DCP degradation were discussed. In addition, PNC-700 displayed excellent recyclability. The activation process especially non-radical pathway was promoted by increasing graphitic N contents. The possible reaction mechanism and degradation pathways were also proposed.

Imine-linked covalent organic frameworks coated stir bar sorptive extraction of non-steroidal anti-inflammatory drugs from environmental water followed by high performance liquid chromatography-ultraviolet detection

In this study, spherical imine-linked covalent organic frameworks (COFs) were fabricated from 2,5-dimethoxybenzene-1,4-dialdehyde (DMTP) and 1,3,5-tris (4-aminophenyl) benzene (TAPB) and named as TAPB-DMTP-COFs. The resulting powders were coated onto bare glass bars via physical-adhesion to obtain TAPB-DMTP-COFs coated stir bars. The self-made stir bars exhibited higher extraction efficiency (74-85%) and faster dynamics (50 min) towards non-steroidal anti-inflammatory drugs (NSAIDs) over ethylene glycol-Silicone (42-68%, 180 min) and polydimethylsiloxane (3-61%, 180 min) coated stir bars. Fourier transform infrared (FT-IR) spectra, X-ray photoelectron spectroscopy (XPS), zeta potential and water contact angle were employed to provide a comprehensive understanding of the adsorption mechanism between the coating and analytes. The results displayed that methoxy group worked as an adsorption site helping the adsorption of interest NSAIDs onto the TAPB-DMTP-COFs coating and hydrogen bonds formed between the O atoms and the analytes. Additionally, the adsorption mechanisms possibly also involved π-π interaction and hydrophobic interaction. Moreover, TAPB-DMTP-COFs coated stir bars exhibited good stability and could be reused more than 60 times. Subsequently, a method by combining TAPB-DMTP-COFs coated stir bar sorptive extraction (SBSE) with liquid chromatography (HPLC)-ultraviolet detector (UV) was established for the determination of four NSAIDs in environmental waters. Under the optimized conditions, the established method showed a wide linear range of 0.2/1-500 μg/L for interest NSAIDs, the limits of detection varied from 0.039 to 0.312 μg/L. Yangtze River water, East Lake water and Spring water were subjected to the proposed method, the recoveries in spiked samples were 84.7-104%, 81.2-101% and 82.6-97.6%, respectively.

Recent developments in sample preparation techniques combined with high-performance liquid chromatography: A critical review

This review article compares and contrasts sample preparation techniques coupled with high-performance liquid chromatography (HPLC) and describes applications developed in biomedical, forensics, and environmental/industrial hygiene in the last two decades. The proper sample preparation technique can offer valued data for a targeted application when coupled to HPLC and a suitable detector. Improvements in sample preparation techniques in the last two decades have resulted in efficient extraction, cleanup, and preconcentration in a single step, thus providing a pathway to tackle complex matrix applications. Applications such as biological therapeutics, proteomics, lipidomics, metabolomics, environmental/industrial hygiene, forensics, glycan cleanup, etc., have been significantly enhanced due to improved sample preparation techniques. This review looks at the early sample preparation techniques. Further, it describes eight sample preparation technique coupled to HPLC that has gained prominence in the last two decades. They are (1) solid-phase extraction (SPE), (2) liquid-liquid extraction (LLE), (3) gel permeation chromatography (GPC), (4) Quick Easy Cheap Effective Rugged, Safe (QuEChERS), (5) solid-phase microextraction (SPME), (6) ultrasonic-assisted solvent extraction (UASE), and (7) microwave-assisted solvent extraction (MWASE). SPE, LLE, GPC, QuEChERS, and SPME can be used offline and online with HPLC. UASE and MWASE can be used offline with HPLC but have also been combined with the online automated techniques of SPE, LLE, GPC, or QuEChERS for targeted analysis. Three application areas of biomedical, forensics, and environmental/industrial hygiene are reviewed for the eight sample preparation techniques. Three hundred and twenty references on the eight sample preparation techniques published over the last two decades (2001-2021) are provided. Other older references were included to illustrate the historical development of sample preparation techniques.

Triazine-triphenylphosphine based porous organic polymer as sorbent for solid phase extraction of nitroimidazoles from honey and water

A triazine-based porous organic polymer was prepared by facile solvothermal polymerization with cyanuric chloride and triphenyl phosphine as functional monomers. The polymer was characterized and then used for the first time as the sorbent for the effective solid-phase extraction of some nitroimidazoles (NDZs) (metronidazole, ronidazole, secnidazole, dimetridazole and ornidazole). The main experimental influencing parameters for the extraction including the eluent solvent, eluent volume, sample loading rate, sample solution pH, salt concentration and sample volume were investigated. The adsorption kinetics and adsorption isotherms were investigated to elucidate the possible adsorption mechanism. With the triazine-based porous organic polymer as the SPE adsorbent, trace NDZs were effectively extracted. The good enrichment capability for the NDZs was mainly attributed to the hydrogen binding interactions by the aromatic 1,3,5-trizine rings. After the SPE, the extracted analytes were analyzed by high-performance liquid chromatograph with ultraviolet detection. Under the selected conditions, the method had a good linear response for the analytes in the range of 0.06-120 ng mL^-1 for water and 1.5-1200 ng g^-1 for honey samples. The limits of detections (S/N=3) fell in the range of 0.02-0.06 ng mL^-1 for water and 0.5-1.5 ng g^-1 for honey samples. The method recoveries for the analytes for spiked samples were in the range of 80.3-118%. The method can be applied for the determination of the NDZs from real samples.

Recent Advances of Triazine-Based Materials for Adsorbent Based Extraction Techniques

This review mainly focused on the synthesis and properties of triazine-based materials as well as the state-of-the-art development of these materials in adsorption-based extraction techniques in the past 5 years, such as solid-phase extraction, magnetic solid-phase extraction, solid-phase microextraction and stir bar sorptive extraction, and the detection of various pollutants, including metal ions, drugs, estrogens, nitroaromatics, pesticides, phenols, polycyclic aromatic hydrocarbons and parabens. In the triazine-functionalized composites, triazine-based polymers and covalent triazine frameworks have been developed as the adsorbents with potential for environmental pollutants, mainly relying on the large surface area and the affinity of triazinyl groups with the targets. Triazine-based adsorbents have satisfactory sensitivity and selectivity towards different types of analytes, attributed from various mechanisms including π-π, electrostatics, hydrogen bonds, and hydrophobic and hydrophilic effects. The prospects of the materials for adsorption-based extraction were also presented, which can offer an outlook for the further development and applications.

Porous thin-film molecularly imprinted polymer device for simultaneous determination of phenol, alkylphenol and chlorophenol compounds in water

A porous water-compatible molecularly imprinted polymer (MIP) coating using catechol as a pseudo-template and a water-soluble functional monomer (4-vinyl benzoic acid) with ethylene glycol dimethacrylate as the crosslinker was developed for extraction of phenols from environmental water samples. The MIP devices were combined with ultra high performance liquid chromatography with a photodiode array detector (UHPLC-PDA) suitable for the simultaneous determination of trace levels of phenolic compounds with a wide range of polarities -phenol, alkylphenols and chlorophenols- in seawater and produced water. Parameters that influence extraction efficiency (salinity, pH, polymer mass, desorption solvent, and desorption time) were optimized to give method detection limits (LOD) ranging from 0.1 to 2 μg L^-1 and linearity (R²>0.99) over at least three orders of magnitude for the hydrophobic phenols (e.g., 0.5-1000 μg L^-1 for 2,4,6-trichlorophenol) and ~2 orders of magnitude for the light phenols (e.g., 10-120 μg L^-1 for phenol, 5-120 μg L^-1 for methylphenols and 2-chlorophenol, 0.5-120 μg L^-1 3-methyl-4-chlorophenol and 2,4-dichlorophenol). The recoveries from authentic spiked samples ranged from 85 to 100% with %RSDs of 0.2-14% for seawater and 81-107% with %RSD of 0.1-11% for produced water. The resulting MIP-based extraction requires no pre-conditioning of the sorbent, and because the required sample size is small and sample manipulation is limited, the method is easy to multiplex for high throughput sample processing.

Stir bar sorptive extraction and its application

Recent progress of stir bar sorptive extraction (SBSE) in the past six years is reviewed. The preparation methods including electrodeposition, self-assembly, solvent exchange, physical magnetic adsorption and electrostatic spinning, for the coated stir bar are summarized and compared, specifically for a specific material for coatings fabrication, e.g., carbon-based materials and metal organic frameworks. The emerging materials (e.g., graphene, graphene oxide, carbon nanotubes, monolith, metal-organic frameworks and porous organic polymers) applied for coated stir bar fabrication are one of the focus of this review, along with their respective advantages in extraction process and application in trace analysis. The development and application of extraction apparatus of SBSE are also involved. Based on these information, the development status and prospects of SBSE as an efficient sample pretreatment technique in real sample analysis are discussed.

Hydroxyl-containing porous organic framework coated stir bar sorption extraction combined with high performance liquid chromatography-diode array detector for analysis of triazole fungicides in grape and cabbage samples

In this work, a hydroxyl-containing porous organic framework (HC-POF) was prepared by a simple solvothermal reaction with 1,4-phthalaldehyde and phloroglucinol as monomers. Sol-gel method was used to coat HC-POF on the glass stir bar. The prepared HC-POF coated stir bar shows better extraction performance for six triazole fungicides (TFs) compared to commercial polydimethylsiloxane and ethylene glycol-silicone coated stir bars. Fourier transform infrared Spectrometry and X-ray photoelectron Spectrometry were used to explore interactions between HC-POF coating and TFs. It is assumed that the coating mainly adsorbs TFs through π-π interactions, hydrogen bonding and hydrophobic interactions. Based on this fact, a new method of HC-POF coated stir bar sorptive extraction combined with high performance liquid chromatography-diode array detector was developed for the determination of six TFs in grape and cabbage samples. A series of extraction and desorption conditions were carefully optimized, including salt concentration, sample solution pH, stirring rate and desorption solvent. Under the optimized experimental conditions, the proposed method displayed limits of detection in the range of 0.022 -0.071 μg L^-1, which is the lowest among the reported SBSE methods for target TFs analysis. The linear range for six TFs was 0.1/0.2-500 μg L^-1 and the recoveries for the spiked grape and cabbage were 81.0-109% and 80.7-111%, respectively.

Preparation of sheet-like covalent organic frameworks and their application for efficient preconcentration of 4-(tert-octyl)-phenol and 4-nonylphenol in textiles

In the design of highly ordered (covalent organic frameworks) COFs with "ordered domains size and orientation" construction in a well-defined arrangement, the molecular monomers are the key factors. Here, the effect of molecular monomers on the construction of COFs has been studied, and two kinds of molecular monomers, i.e., ethanediamine (flexible amine ligand) and 4,4'-diaminobiphenyl (rigid amine ligand) have been used for developing sheet-like COFs-I and sheet-like COFs-II, respectively. Furthermore, they have been evaluated in the dispersive solid phase extraction (dSPE) procedure for textiles prior to the analysis of alkylphenol by liquid chromatography-tandem quadrupole mass spectrometry (LC-MS/MS). The results showed that, the optimal usage amount of sheet-like COFs-II used in the dSPE procedure was less than that of sheet-like COFs-I, which may be explained by much higher adsorption capacity of sheet-like COFs via hydrogen-bonding and π-π stacking interactions. Rectilinear calibration graphs were obtained for 4-(tert-octyl)-phenol (4-tOP) and 4-nonylphenol (4-NP) in the range 0.2-20 µg/kg with determination coefficient (r²) higher than 0.9990, and the limits of detection (LODs) of 4-tOP and 4-NP were 0.039 µg/kg and 0.048 µg/kg, respectively. The developed method has been successfully applied to analysis of 50 textile samples, in which 4-tOP and 4-NP were found in six samples with concentrations in the range of 1.6 μg/kg-20.9 μg/kg.

Highly sensitive determination of 4-nitrophenol with coumarin-based fluorescent molecularly imprinted poly (ionic liquid)

A coumarin-based fluorescent molecularly imprinted poly (ionic liquid) (FL-MIPIL) was prepared using a new coumarin-based alkenyl fluorescent ionic liquid (coumarin-FL-IL) as the functional monomer, IL [V₂C₄(mim)₂][(PF₆)₂] and ethyleneglycol dimethacrylate as the cross-linkers, and 4-NP as the template molecule. The absolute quantum yields of coumarin-FL-IL and FL-MIPIL were 7.26 % and 30.66 %, respectively. As a result of the electron transfer between coumarin-FL-IL which contains amino groups and 4-NP bearing hydroxyl groups, FL-MIPIL fluorescence was effectively quenched by 4-NP. The prepared FL-MIPIL sensor can rapidly respond to 4-NP within 60 s. The FL-MIPIL sensor had good linear response to 4-NP from 0.001-7.5 μM and low detection limit of 0.5 nM (S/N = 3). The FL-MIPIL sensor exhibited high sensitivity and good selectivity for 4-NP. The outstanding performance of FL-MIPIL could be ascribed to high fluorescence intensity of FL-MIPIL without matrixes and more interactions between FL-MIPIL and 4-NP. The FL-MIPIL sensor has successfully applied to the determination of 4-NP in lake, rain and waste water samples, river sediment, soil and urine samples.

Covalent Organic Frameworks in Sample Preparation

Covalent organic frameworks (COFs) can be classified as emerging porous crystalline polymers with extremely high porosity and surface area size, and good thermal stability. These properties have awakened the interests of many areas, opening new horizons of research and applications. In the Analytical Chemistry field, COFs have found an important application in sample preparation approaches since their inherent properties clearly match, in a good number of cases, with the ideal characteristics of any extraction or clean-up sorbent. The review article is meant to provide a detailed overview of the different COFs that have been used up to now for sample preparation (i.e., solid-phase extraction in its most relevant operational modes-conventional, dispersive, magnetic/solid-phase microextraction and stir-bar sorptive extraction); the extraction devices/formats in which they have been applied; and their performances and suitability for this task.

Controlled Fabrication of Silica@Covalent Triazine Polymer Core-Shell Spheres as a Reversed-Phase/Hydrophilic Interaction Mixed-Mode Chromatographic Stationary Phase

The unique properties of covalent triazine-based organic framework/polymers, including large surface area, hydrophilic-lipophilic-balanced adsorption, and economical preparation, make it a promising candidate as a stationary phase for high-performance liquid chromatography. However, irregular shapes and wide size distributions of such particles hinder column packing, resulting in a low column efficiency or a high back pressure. Herein, we describe the fabrication of SiO₂@ covalent triazine-based organic polymer (CTP) core-shell microspheres with a distinct sphere-coating-sphere appearance using aminosilica as the supporting substrate to grow the CTP shell. By adjusting the amount of reactants, the thickness of the CTP shell, which consists of triazine and 1,3,5-triphenylbenzene monomers, was easily controlled. The developed core-shell microspheres were characterized via scanning electron microscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy, solid-state ¹³C nuclear magnetic resonance analysis, and N₂ adsorption experiments. The synergism of the triazine and aromatic moieties on CTP provides the new stationary phase with multiple retention mechanisms, including hydrophobic, π-π, electron donor-acceptor, hydrogen-bonding interactions, and so forth. On the basis of these interactions, successful separation and higher shape selectivity were achieved among several analytes that vary in polarity under both reversed-phase and hydrophilic interaction liquid chromatography conditions. Therefore, SiO₂@CTP microspheres combine the advantages of good column packing properties of the uniform monodisperse silica microspheres and the recognition performance of CTP, generating flexible selectivity and application prospect for both hydrophilic and hydrophobic analytes.

An amino-functionalized ordered mesoporous polymer as a fiber coating for solid phase microextraction of phenols prior to GC-MS analysis

An amino-functionalized ordered mesoporous polymer (OMP-NH₂) was synthesized and applied as a fiber coating for solid phase microextraction of polar phenols from environmental samples. The fiber coating was prepared by loading the OMP-NH₂ powder onto a stainless steel wire through silicone gel. Combined with GC-MS, the fibers were employed to quantify trace of phenols in water through headspace-SPME. The characterization showed the OMP-NH₂ to have a large specific surface area (420 m² g^-1) and good thermal stability (>400 °C). Due to its mesoporous structure and favorable interactions via hydrogen bonding and π stacking interactions with phenols, the sorbent represents a promising candidate for the separation and enrichment of polar phenols. Extraction conditions, such as temperature, extraction time, salt concentration, pH value and desorption time, were fully optimized. Under the optimized conditions, the coating exhibits an enrichment effect that is ~2-10 times better than that of a commercial polyacrylate coating. Figures of merit include (a) low limits of detection (0.05-0.16 ng L^-1), (b) wide linear ranges (0.2-10,000 ng L^-1), and (c) high enrichment factors (510-2272). The relative standard deviations for one fiber and fiber-to-fiber were in the range of 4.0-6.1% and 4.6-7.4%, respectively. The method was applied to the determination of phenols in water samples and gave satisfactory recoveries between 85.4 and 112.2%. Graphical abstract An amino-functionalized ordered mesoporous polymer (OMP-NH₂) was synthesized by a solventless method and applied as headspace solid phase microextraction (HS-SPME) fiber coating for the extraction of polar phenols from the environmental samples.