Porous organic polymers with different pore structures for sensitive solid-phase microextraction of environmental organic pollutants

Synthesis of imidazolium ionic liquid immobilized on magnetic mesoporous silica: A sorbent material in a green micro-solid phase extraction of multiclass pesticides in water

In this study, we synthesized an imidazolium ionic liquid immobilized on magnetic mesoporous silica (IL-MMS) and evaluated its performance as a sorbent material for a green micro-solid phase extraction (μ-SPE) of multiclass pesticides in water. The synthesized IL-MMS was characterized by various analytical techniques, including Fourier-transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) analyses (N2 adsorption/desorption), Vibrating Sample Magnetometer (VSM), energy-dispersive spectroscopy (EDS) and Field emission scanning electron microscopy (FESEM). Our synthesized IL-MMS demonstrated excellent magnetic properties (31.5 emu/g), high surface area (1177.4 m2/g), proper pore size (⁓4.2 nm) and volume (1.80 cm3/g). Under optimized extraction conditions, the IL-MMS exhibited a high adsorption capacity for a variety of pesticides, including organophosphates, carbamates, and pyrethroids. The proposed μ-SPE method using IL-MMS showed good linearity (R2 > 0.99), low limits of detection (LODs) ranging from 0.04 to 1.63 ng/L, and suitable recovery rate was between 82.4% and 109.8% for different pesticides. In addition, the method also exhibited excellent reproducibility, with relative standard deviations (RSDs) of less than 8% for both intra and inter-day precision. In overall, the synthesized IL-MMS has proven to be a highly promising material for sorbent-based micro-solid phase extraction (μ-SPE) of multiclass pesticides in water. With its simple, efficient, and eco-friendly approach to pesticide analysis, this method shows great potential for future pesticide detection and monitoring efforts due to its sensitivity, accuracy, and adaptability to various environmental conditions.

Silver nanoparticle-functionalized melamine-formaldehyde aerogel for online in-tube solid-phase microextraction of polycyclic aromatic hydrocarbons followed by HPLC-DAD analysis

Based on the π-metal interaction between silver nanoparticles (AgNPs) and aromatic compounds, AgNPs were in-situ grown to melamine-formaldehyde (MF) aerogel for improving the extraction performance to polycyclic aromatic hydrocarbons (PAHs). The AgNPs/MF aerogel was regulated through varing the concentration of reactants, and characterized by scanning electron microscopy, X-ray photoelectron spectroscopy and X-ray powder diffraction. As a new extraction coating, the AgNPs/MF aerogel was coated to stainless-steel wires for in-tube solid-phase microextraction (IT-SPME). The extraction effects of MF aerogels before and after the modification of AgNPs were compared, and the AgNPs greatly improved the extraction ability for PAHs reaching to 166.4 %. Combining IT-SPME with high performance liquid chromatographic detection, an online analytical system was constructed. Furthermore, the sampling volume and rate, concentration of organic solvent, and desorption time were optimized factor by factor. The online analytical method with low detection limits (0.003-0.010 μg L-1) and efficient enrichment factors (1998-3237) for PAHs was established, which fastly detected trace level of PAHs in drinking and environmental water samples. Compared with other methods, the method was comparable or better in the detection limit and linear range, indicating prospective application of the AgNPs/MF aerogel for sample preparation.

Enhancing the water-resistance of MOF-199 film through incorporation of microporous organic networks for solid-phase microextraction of BTEX in aqueous environments with improved efficiency

BACKGROUND

The practical application of moisture sensitive metal organic frameworks (MOFs) in extraction technology faces challenges related to competitive adsorption and water stability. The target analytes cannot be effectively extracted under humid conditions due to the competitive moisture adsorption and/or framework structure collapse of MOFs. In this study, the microporous organic networks (MONs) were synthesized through Sonogashira coupling reaction to use for hydrophobic modification on the surface of MOF-199.

RESULTS

The MOF-199@MON as coating was deposited on stainless steel wires for solid-phase microextraction (SPME) of benzene series (BTEX) in aqueous environments. Under the optimal extraction conditions, the MOF-199@MON coated fiber for SPME coupled with GC-MS for the determination of BTEX gave the linear range of 0.5-500 μg L-1, the limit of detections (LODs, S/N = 3) of 0.01-0.04 μg L-1, the limit of quantifications (LOQs, S/N = 10) of 0.04-0.12 μg L-1, the enhancement factors of 3567-4878, and the intra-day, inter-day and fiber-to-fiber precisions (relative standard deviations, RSDs) of 1.0-9.8, 1.9-7.9 and 4.5-9.5 %, respectively. The developed method was successfully applied to the analysis of BTEX in water samples with the recoveries of 71.0 %-113 %.

SIGNIFICANCE

This work reveals the home-made SPME fibers have a long service life (the extraction efficiency of fiber decreased by only 7.26 %-13.14 % after 100 cycles). The potential of MON functionalized MOFs as effective adsorbents for the SPME of pollutants in the water environment.

Quinoline Bridging Hyperconjugated Covalent Organic Framework as Solid-Phase Microextraction Coating for Ultrasensitive Determination of Phthalate Esters in Water Samples

Phthalate esters (PAEs) are widely distributed in the environment, and this has caused serious health and safety concerns. Development of rapid and ultrasensitive identification and analysis methods for phthalate esters is urgent and highly desirable. In this work, a novel nitrogen-rich covalent organic framework (N-TTI) derived quinoline bridging covalent organic framework (N-QTTI) was fabricated and used as a solid-phase microextraction (SPME) coating for the ultrasensitive determination of phthalate esters in water samples. The physical and chemical properties of N-QTTI were investigated sufficiently. The N-QTTI-coated fiber demonstrates a superior enrichment performance than either the N-TTI-coated fiber or commercial fibers under the optimized SPME conditions. For the first time, we propose a semi-immersion strategy for the extraction of PAEs from water samples based on N-QTTI-coated SPME fibers. Combined with gas chromatography-mass spectrometry (GC-MS), the developed method N-QTTI-SPME-GC-MS exhibits a wide linear range with a satisfactory linearity (R2 ≥ 0.995). The limits of detection (LOD, S/N = 3) and the limits of quantification (LOQs, S/N = 10) were 0.17-1.70 and 0.57-5.60 ng L-1, respectively. The repeatability of the new method was examined using relative standard deviations (RSDs) between intraday and interday data, which were 0.38-7.98% and 1.22-6.60%, respectively. The spiked recoveries at three levels of 10, 100, and 1000 ng L-1 were in the range of 90.0-106.2% with RSDs of less than 7.48%. The enrichment factors ranged from 291 to 17180. When compared to previously published works, the LODs of the newly established method were improved 5-5400 times, and the enrichment factors were increased by at least 8 times. The absorption mechanism was investigated by X-ray photoelectron spectroscopy and noncovalent interaction force analysis. The technique was successfully employed for detecting PAEs in water 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%).

Aramid-wrapped CNT hybrid sol–gel sorbent for polycyclic aromatic hydrocarbons

This work describes the preparation of an analytical microextraction sorbent using a simple and versatile sol–gel hybrid composite, i.e., aramid oligomers wrapping multi-walled carbon nanotubes (CNTs) covalently bonded to a porous silica network.

Membrane-protected covalent organic framework fiber for direct immersion solid-phase microextraction of 17beta-estradiol in milk

17beta-estradiol (E2) could accumulate in human body through milk and cause various diseases by interfering with the endocrine system. Herein, we coated stainless steel wire with covalent organic framework LZU1 (COF-LZU1) and Nafion protected by dialysis membrane for direct immersion solid phase microextraction (DI-SPME) and coupled with gas chromatography-flame ionization detection (GC-FID) for the detection of trace E2 in milk samples. With dialysis membrane protection, the stability of SPME fiber was improved and the extraction efficiency was only reduced by 7% after repeated use of 160 times. The extraction efficiency of E2 with the home-made fiber COF-LZU1 was 22.1, 8.4, 3.6 times higher than that of bare stainless steel wire, PDMS/DVB and PDMS, respectively. The method had been successfully applied to milk samples, and the relative recoveries were between 77.27% and 108.26%. It can provide an effective and general method for the pretreatment of complex matrix samples.

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.

Magnetic Solid Phase Extraction Based on Nanostructured Magnetic Porous Porphyrin Organic Polymer for Simultaneous Extraction and Preconcentration of Neonicotinoid Insecticides From Surface Water

In this study, a magnetic porphyrin-based porous organic polymer (MP-POP) nanocomposite was successfully synthesized according previous studies and applied as an adsorbent for simultaneous extraction and preconcentration of four neonicotinoid insecticides from surface river water. The MP-POP was characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy/energy dispersive x-ray spectroscopy (SEM/EDS), N₂-adsorption/desorption analysis, Fourier Transform infrared spectroscopy (FTIR). The neonicotinoid insecticides were quantified using high performance chromatography coupled with diode array detector (HPLC-DAD). The MP-POP shown to have a high surface area, highly porous structure and strong affinity toward the investigated analytes. The adsorption capacities were 99.0, 85.5, 90.0, and 79.4 mg g⁻¹ for acetamiprid, clothiandin, thiacloprid and imidacloprid, respectively. The influential parameters affecting the magmatic μ-solid phase extraction (M-μ-SPE) procedure were investigated using fractional factorial design and surface response methodology (RSM). Under optimum conditions, the method exhibited relatively low limit of detection in the range of 1.3–3.2 ng L⁻¹, limit of quantification in the range of 4.3–11 ng L⁻¹ and wide linearity (up to 600 μg L⁻¹). The intraday and interday precision, expressed as the relative standard deviation (RSD) were <5%. The percentage recoveries for the four target analytes ranged from 91 to 99.3% for the spiked river water samples. The method was applied for determination of neonicotinoids in river water samples and concentrations ranged from 0 to 190 ng L⁻¹.

Realizing Catalytic Acetophenone Hydrodeoxygenation with Palladium-Equipped Porous Organic Polymers

Porous organic polymers (POPs) constructed through covalent bonds have raised tremendous research interest because of their suitability to develop robust catalysts and their successful production with improved efficiency. In this work, we have designed and explored the properties and catalytic activity of a template-free-constructed, hydroxy (-OH) group-enriched porous organic polymer (Ph-POP) bearing functional Pd nanoparticles (Pd-NPs) by one-pot condensation of phloroglucinol (1,3,5-trihydroxybenzene) and terephthalaldehyde followed by solid-phase reduction with H₂. The encapsulated Pd-NPs rested within well-defined POP nanocages and remained undisturbed from aggregation and leaching. This polymer hybrid nanocage Pd@Ph-POP is found to enable efficient liquid-phase hydrodeoxygenation (HDO) of acetophenone (AP) with high selectivity (99%) of ethylbenzene (EB) and better activity than its Pd@Al₂O₃ counterpart. Our investigation demonstrates a facile, scalable, catalyst-template-free methodology for developing novel porous organic polymer catalysts and next-generation efficient greener chemical processes from platform molecules to produce value-added chemicals. With the aid of comprehensive in situ ATR-IR spectroscopy experiments, it is suggested that EB can be more easily desorbed in a solution, reflecting from the much weaker but better-resolved signal at 1494 cm^-1 in Pd@Ph-POP compared to that in Pd@Al₂O₃, which is the key determining factor in favoring an efficient catalytic mechanism. Density functional theory (DFT) calculations were performed to illustrate the detailed reaction network and explain the high catalytic activity observed for the fabricated Pd@Ph-POP catalyst in the HDO conversion of AP to EB. All of the hydrogenation routes, including direct hydrogenation by surface hydrogen, hydrogen transfer, and the keto-enol pathway, are evaluated, providing insights into the experimental observations. The presence of phenolic hydroxyl groups in the Ph-POP frame structure facilitates the hydrogen-shuttling mechanism for dehydration from the intermediate phenylethanol, which was identified as a crucial step for the formation of the final product ethylbenzene. Besides, weaker binding of the desired product ethylbenzene and lower coverage of surface hydrogen atoms on Pd@Ph-POP both contributed to inhibiting the overhydrogenation reaction and explained well the high yield of EB produced during the HDO conversion of AP on Pd@Ph-POP in this study.

Rapid microwave synthesis of dioxin-linked covalent organic framework for efficient micro-extraction of perfluorinated alkyl substances from water

To synthesize covalent organic framework (COF) via irreversible reactions is more challenging than by reversible ones. In this work, microwave-assisted synthesis is used to facilitate the nucleophilic substitution of 2,3,5,6-tetrafluoro-4-pyridinecarbonitrile with 2,3,6,7,10,11-hexahydroxy triphenylene. The dioxin-linked COF, named TH-COF, was efficiently synthesized with extraordinarily large surface area of 1254 m² g^-1. With its high crystallinity, excellent thermal and chemical stabilities, TH-COF is used as the coating for the solid-phase micro-extraction (SPME) of perfluorinated alkyl substances (PFASs). The adsorptive mechanism was evaluated with adsorption isotherm and kinetic adsorption. Adsorption energies are calculated based on the density functional theory. Following SPME with TH-COF-coated fibers, PFASs were eluted using 1 mL of 0.6% trifluoroacetic acid/methanol and analyzed through the ultra-performance liquid chromatography equipped with triple quadrupole mass spectrometer (UPLC-MS/MS). When applied to spiked real water samples, this method demonstrates good linearity (0.01-1000 ng L^-1) with R² ≥ 0.9945. The TH-COF-SPME-UPLC-MS/MS technique provides low limits of detection (0.0020-0.0045 ng L^-1), excellent precision (≤ 7.9%), and good fiber-to-fiber reproducibility (≤ 7.1%). The TH-COF-coated fibers can be reused at least 20 times without the loss of extraction performance. In addition, the relative recoveries from spiked real water samples are 89.5%-105%.

Flower-like architecture magnesia-carbon composite material for highly sensitive solid-phase microextraction

The development of carbon sorbents with high specific surface areas remains a hot research field in analytical community. In the current study, a novel three-dimensional hierarchical flower-like magnesium glycollate sphere was synthesized. Then, the obtained magnesium glycollate sphere was carbonized to obtain magnesia-carbon composite material with enhanced performance. The flower-like carbon material exhibited good adsorption capacity towards polycyclic aromatic hydrocarbons due to the large surface area, the strong π-π interaction force and hydrophobic forces. The flower-like MgO&C material was used as a solid-phase microextraction fiber coating for the analysis of polycyclic aromatic hydrocarbons in real river water samples. Good linearity (5-1000 ng L^-1), satisfactory relatively recoveries (86.2-113.5%) and low limits of detections (0.01-0.20 ng L^-1) were obtained under the optimized conditions.

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

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

Meso-/microporous carbon as an adsorbent for enhanced performance in solid-phase microextraction of chlorobenzenes

There is urgent demand for the design of advanced coating materials for solid-phase microextraction (SPME) for water quality monitoring and assessment because of the global occurrence of chlorobenzenes (CBs). In this study, we proposed a dual-order activation method in which potassium hydroxide is used to modify pre-activated calcium citrate to synthesize a highly developed meso-/microporous carbon (MMC). The as-obtained MMC presented well-developed porosity with a super-high specific surface area (2638.09 m² g^-1), abundant meso-/micropores (0.5-10 nm), high hydrophobicity, excellent thermal stability (>720 °C), and a partly graphitized structure. As a coating material for headspace-SPME, the MMC-coated fiber exhibited outstanding extraction capability for CBs (up to 48.5 times higher than that of commercial fibers), which may be attributed to multiple interactions between the MMC and the pollutants, including size selectivity, micropore filling, π-π stacking and hydrophobicity. Finally, a satisfactory method using an MMC-coated fiber coupled with gas chromatography and electron capture detection was developed with good linearity (1-1000 ng L^-1, R² > 0.9982), high enrichment efficiencies (enrichment factors, 861-7819), low limits of detection (0.003-0.072 ng L^-1), excellent repeatability (0.7-5.3%) and reproducibility (1.7-5.1%), and outstanding recoveries (90.18-103.02%) when applied to determine trace CBs in real water samples. These results suggest that MMC is a promising coating material for the SPME of CBs.

Electroless deposition of silver nanofractals on copper wire by galvanic displacement as a simple technique for preparation of porous solid-phase microextraction fibers

A novel and porous solid-phase microextraction fiber was prepared by quick and simple galvanic displacement reaction and applied to the determination of some polycyclic aromatic hydrocarbons in sunflower oil. The parameters affecting the porosity and thickness of the fiber, and parameters affecting the extraction efficiency, including the extraction time, temperature, and ionic strength, were investigated and optimized. The morphology of prepared fiber was characterized by optical and scanning electron microscopy and thermal and chemical stabilities of the fiber were studied. Under the optimum conditions, the limits of detection ranged between 0.1 ng/mL for pyrene to 1.2 ng/mL for anthracene, and LOQ ranged between 0.3 ng/mL for pyrene to 3.6 ng/mL for anthracene. The relative standard deviations, including repeatability (within fibers) and reproducibility (between fibers), varied between 3.2-8.9 and 5.6-9.8%, respectively.

Promoting charge separation of biochar-based Zn-TiO2/pBC in the presence of ZnO for efficient sulfamethoxazole photodegradation under visible light irradiation

A novel and effective photocatalyst namely titanium dioxide doped with zinc elements stacked on reed straw biochar which was pretreated by acid (Zn-TiO₂/pBC) with visible light response was successfully prepared by a simple modified sol-gel method firstly. The prepared samples were characterized by scanning microscopy (SEM), energy dispersive X-ray spectrum (EDS), X-ray diffraction (XRD), nitrogen adsorption-desorption (BET) and UV-Vis diffuse reflectance spectra (DRS). The photocatalytic activity of Zn-TiO₂/pBC was further investigated through the photodegradation of sulfamethoxazole (SMX). Compared with TiO₂ and TiO₂/pBC, Zn-TiO₂/pBC had better photocatalytic activity under visible light due to zinc elements effectively inhibiting the agglomeration of TiO₂ and hindering the combination of photogenerated electrons and holes. The removal rate of SMX could reach 81.21%, which was 1.37 times higher than that of TiO₂/pBC(300). Three common anions (SO₄^2-, Cl^-, NO₃^-) existing in the Yellow River exhibited detrimental effects on the SMX photodegradation to a certain degree. It might mainly occurred hydroxylation, cleavage of SN bond and opening of isoxazole ring reactions during the photodegradation process of SMX. Meanwhile, there might be four main degradation pathways proposed throw the LC/MS/MS analysis. Finally, good reusability and stability illustrated Zn-TiO₂/pBC owned good practicality and feasibility for removal of organic pollutants in environment remediation area.

A spherical metal-organic coordination polymer for the microextraction of neonicotinoid insecticides prior to their determination by HPLC

The authors describe a new spherical metal-organic coordination polymer (MOCP) for use as an adsorbent in solid-phase microextraction (SPME). By applying the ions Co(II), Fe(II), Cu(II), and Zn(II) in these polymers, MOCP with different morphology were obtained. The respective coatings for SPME display different extraction efficiency towards neonicotinoid insecticides (neo-nics). The Co(II)@MOCP coating displays an improved extraction capability for neo-nics when compared to the four commercially available coatings studied. Following extraction with the Co(II)@MOCP-coated fiber, the neo-nics were eluted using 1 mL of trifluoroacetic acid/acetonitrile solution and quantified by high performance liquid chromatography. The method, when applied to spiked honey samples, has good linearity (0.5-600 μg kg^-1) and a low limit of detection (0.05-0.15 μg kg^-1). The precision (n = 6) for a single fiber was in the range of 3.6-8.3%. The reproducibility (for n = 5) from fiber-to-fiber ranges between 5.4 and 8.8%. The Co(II)@MOCP-coated fiber can be reused more than 80 times without any apparent reduction in its performance. In addition, the relative recoveries from spiked honey samples are very good (91.5%-103.5%). Graphical abstract A spherical metal-organic coordination polymer (MOCP) was synthesized under the regulation of Co(II) and used for the solid-phase microextraction (SPME) of neonicotinoid insecticides found in honey.

Porous Organic Frameworks: Advanced Materials in Analytical Chemistry

Porous organic frameworks (POFs), a general term for covalent-organic frameworks (COFs), covalent triazine frameworks (CTFs), porous aromatic frameworks (PAFs), etc., are constructed from organic building monomers with strong covalent bonds and have generated great interest among researchers. The remarkable features, such as large surface areas, permanent porosity, high thermal and chemical stability, and convenient functionalization, promote the great potential of POFs in diverse applications. A critical overview of the important development in the design and synthesis of COFs, CTFs, and PAFs is provided and their state-of-the-art applications in analytical chemistry are discussed. POFs and their functional composites have been explored as advanced materials in "turn-off" or "turn-on" fluorescence detection and novel stationary phases for chromatographic separation, as well as a promising adsorbent for sample preparation methods. In addition, the prospects for the synthesis and utilization of POFs in analytical chemistry are also presented. These prospects can offer an outlook and reference for further study of the applications of POFs.

Covalent Organic Framework as Fiber Coating for Solid-Phase Microextraction of Chlorophenols Followed by Quantification with Gas Chromatography-Mass Spectrometry

Headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry was adopted for the simultaneous determination of seven chlorophenols (CPs) from honey and canned-yellow-peach samples. A covalent organic framework made of 1,3,5-triformylphloroglucinol (Tp) and benzidine (BD) was used as the SPME fiber coating to preconcentrate the acetylation derivatives of the CPs. The main experimental parameters including derivatization conditions, extraction temperature and time, headspace volume, salt concentration, and desorption temperature were investigated. The fiber showed a high extraction capability for the CPs. The limits of detection (LODs) for the analytes were 0.3-0.7 μg kg^-1 for honey and 0.8-1.8 μg kg^-1 for canned-yellow-peach samples, suggesting good sensitivity for the method. The response linearity was 2.4-250 μg kg^-1 for 2-CP and 3,4-CP and 1.0-150 μg kg^-1 for the other remaining analytes in the honey samples. For the canned-yellow-peach samples, the response linearity was 6.0-300 μg kg^-1 for 2-CP and 3,4-CP and 3.0-200 μg kg^-1 for the others. The correlation coefficients were higher than 0.9919. Good repeatability (RSD < 11.9%) for the method and high recoveries (70.2-113%) of the analytes were observed under the optimal conditions. The established method was satisfactorily applied for the analysis of honey and canned-yellow-peach samples.

Molecularly imprinted covalent organic polymers for the selective extraction of benzoxazole fluorescent whitening agents from food samples

Molecularly imprinted covalent organic polymers were constructed by an imine-linking reaction between 1,3,5-triformylphloroglucinol and 2,6-diaminopyridine and used for the selective solid-phase extraction of benzoxazole fluorescent whitening agents from food samples. Binding experiments showed that imprinting sites on molecularly imprinted polymers had higher selectivity for targets compared with those of the corresponding non-imprinted polymers. Parameters affecting the solid-phase extraction procedure were examined. Under optimal conditions, actual samples were treated and the eluent was analyzed with high-performance liquid chromatography with diode-array detection. The results showed that the established method has a wide linearity, satisfactory detection limits and quantification limits, and acceptable recoveries. Thus, this developed method possesses the practical potential for the selective determination of benzoxazole fluorescent whitening agents in complex food samples.