Three-dimensional hydroxylated covalent organic frameworks for solid phase extraction of glucocorticoids in environmental water samples

Hydroxylated hierarchical flower-like COF for solid-phase extraction of adrenergic receptor agonists in milk

A new detection platform based on a hydroxylated covalent organic framework (COF) integrated with liquid chromatography-tandem mass spectrometry (LC-MS/MS) was constructed and used for detecting adrenergic receptor agonists (ARAs) residues in milk. The hydroxylated COF was prepared by polymerization of tris(4-aminophenyl)amine and 1,3,5-tris(4-formyl-3-hydroxyphenyl)benzene and applied to solid-phase extraction (SPE) of ARAs. This hydroxylated COF was featured with hierarchical flower-like morphology, easy preparation, and copious active adsorption sites. The adsorption model fittings and molecular simulation were applied to explore the potential adsorption mechanism. This detection platform was suitable for detecting four α2- and five β2-ARAs residues in milk. The linear ranges of the ARAs were from 0.25 to 50 µg·kg-1; the intra-day and the inter-day repeatability were in the range 2.9-7.9% and 2.0-10.1%, respectively. This work demonstrates this hydroxylated COF has great potential as SPE cartridge packing, and provides a new way to determine ARAs residues in milk.

High-sensitive determination of tetracycline antibiotics adsorbed on microplastics in mariculture water using pre-COF/monolith composite-based in-tube solid phase microextraction on-line coupled to HPLC-MS/MS

Microplastics (MPs) act as carriers for organic pollutants (e.g. antibiotics) and microorganisms (e.g. bacteria) in waters, leading to the proliferation of antibiotic resistance genes. Moreover, the antibiotics adsorbed on MPs may exacerbate this process. For further research, it is necessary to understand the types and amounts of antibiotics adsorbed on MPs. However, due to the heavy work of MPs collection and sample pretreatment, there is a lack of analytical methods and relevant data. In this study, an in-tube solid phase microextraction (IT-SPME) on-line coupled to HPLC-MS/MS method based on amorphous precursor polymer of three-dimensional covalent organic frameworks/monolith-based composite adsorbent was developed, which could efficiently capture, enrich and analyze tetracycline (TCs) antibiotics. Under the optimal extraction parameters, the developed method was capable of detecting TCs at levels as low as 0.48-1.76 pg. This method was applied to analyze the TCs adsorbed on MPs of different particle sizes in mariculture water for the first time, requiring a minimum amount of MPs of only 1 mg. Furthermore, it was observed that there could be an antagonistic relationship between algal biofilm and TCs loaded on MPs. This approach could open up new possibilities for analyzing pollutants on MPs and support deeper research on MPs.

Large-size porous spherical 3D covalent organic framework for preconcentration of bisphenol F in water samples and orange juice

Large-size spherical sorbents with particle size of 10-50 μm are widely applied in separation fields, however it is still a great challenge to synthesize such large-size spherical covalent organic framework (COF). In this work, a type of large-size porous 3D COF was size-controablly synthesized via a two-step strategy, in which a large-size porous 3D spherical polymer was prepared first through a Pickering emulsion polymerization using nano silica as the stabilizer, and subsequently it was converted into porous spherical 3D COF by a solvothermal method. The as-prepared porous spherical COF (COF-320 as a model) showed size-controllable uniform spherical morphology within 15-45 μm, large specific surface area, fine crystalline structure, and good chemical stability. When used as the sorbent for dispersive solid-phase extraction (d-SPE) of bisphenol F (BPF), the porous spherical COF-320 (15 μm) displayed high adsorption capacity (Qmax = 335.6 mg/g), high enrichment factor (80 folds), and good reusability (at least five cycles). By coupling the d-SPE method to HPLC, a new analytical approach was developed and successfully applied to the determination of trace BPF in two water samples, an orange juice and a standard sample with recoveries of 96.0-102.2 % (RSD = 1.1-1.5 %), 95.7-97.4 % (RSD = 1.4-4.4 %) and 98.7 % (RSD = 2.3 %), respectively. The limit of detection (S/N = 3) and limit of quantification (S/N = 10) were 0.1 and 0.3 ng/mL, respectively. The new synthesis strategy opens a viable way to prepare large-size porous spherical COFs, and the developed analytical method can be potentially applied to sensitively detect the trace BPF in water samples and beverages.

Size-controllable synthesis of large-size spherical 3D covalent organic frameworks as efficient on-line solid-phase extraction sorbents coupled to HPLC

BACKGROUND

Covalent organic frameworks (COFs) have found promising applications in separation fields due to their large surface area and high adsorption capacity, but the exiting COFs can not be directly used as the packing materials of on-line solid-phase extraction (SPE) coupled to HPLC and HPLC because their nano/submicron size or irregular shapes might cause ultrahigh column back pressure and low column efficiency. To synthesize the large-size spherical COFs larger than 3 μm as sorbents might be able to address these problems, however it is still a great challenge till now.

RESULTS

In this work, two large-size spherical 3D COFs (COF-320 and COF-300) were size-controllably synthesized within 10-90 μm via a two-step strategy. These two spherical COFs showed large surface area, fine crystallinity, good chemical/mechanical stability, and good reproducibility. As an application case, when used as the on-line SPE sorbents coupled to HPLC, the large-size spherical COF-320 displayed high binding capacity for bisphenol F (Qmax of 452.49 mg/g), low column back pressure (6-8 psi at flow rate of 1 mL/min), and good reusability (at least 30 cycles). The developed on-line-SPE-HPLC-UV method presented good analytical performance with enrichment factor of 667 folds, linear range of 1.0-400 ng/mL, limit of detection (LOD, S/N = 3) of 0.3 ng/mL, limit of quantification (LOQ, S/N = 10) of 1.0 ng/mL, and recoveries of 100.3-103.2 % (RSDs of 2.0-3.5 %) and 95.2-97.0 % (RSDs of 4.3-5.6 %) for tap water and lake water samples, respectively.

SIGNIFICANCE

This is the first case to synthesize the large-size spherical COFs within 10-90 μm, and this work made it possible to directly use COFs as the filling materials of on-line SPE coupled to HPLC and HPLC. The developed analytical method can be potentially applied to the rapid and sensitive detection of trace bisphenol F in environmental water samples.

Exploration of porous imine-based covalent organic framework for solid-phase extraction of five trace sulfonamides in food samples

In this article, a highly crystalline porous imine-based covalent organic framework was synthesized at room temperature and used as solid-phase extraction (SPE) adsorbent for the purification and enrichment of trace sulfonamides (SAs) from food samples. The structure of the obtained material was characterized and studied in detail. The extraction process was optimized and the final elution was determined by the ultra-high-performance liquid chromatography-quadrupole time of flight mass spectrometry method. Low limits of detection (0.02-0.19 μg/kg) were obtained under optimal conditions, with the recoveries ranging from 70.5% to 105.3% when spiked at different levels. The adsorption process of the material for SAs was fitted by the Langmuir and Freundlich adsorption isotherm model, and the extraction capacity for Nitrofuran metabolites from food samples was also investigated for comparison. The results demonstrated that the framework was a good candidate SPE adsorbent that can be used for the enrichment of drug residues in complex matrix, and the work may provide a systematic study method for the development of porous adsorbents.

Derivatization-Enhanced Analysis of Glucocorticoids for Structural Characterization by Gas Chromatography-Orbitrap High-Resolution Mass Spectrometry

Glucocorticoids are classified in section S9 of the Prohibited List of the World Anti-Doping Agency, due to a potential risk to improving physical performance and causing harm to the health of athletes. Based on the similar physiological actions of glucocorticoids, both differentiating known glucocorticoids and identifying unknown glucocorticoids are important for doping control. Gas chromatography coupled with mass spectrometry plays an important role in structural characterization because of abundant structural diagnostic ions produced by electron ionization. It also provides a chance to study the fragmentation patterns. Thus, an enhanced derivatization procedure was optimized to produce trimethylsilylated glucocorticoids and structural diagnostic ions of nineteen trimethylsilylated glucocorticoids were obtained by gas chromatography-orbitrap high-resolution mass spectrometry. In our study, glucocorticoids were classified as: 3-keto-4-ene, 1,4-diene-3-keto, 3α-hydroxy with saturated A-ring, 21-hydroxy-20-keto and halo substituent glucocorticoids based on their structural difference. Structural diagnostic ions that contributed to structural characterization were specifically presented and the fragment patterns were demonstrated according to the above categories. This study not only gave new insights into the structural characterization of these glucocorticoids but also provided evidence for tracing unknown glucocorticoids or chemically modified molecules.