Core-shell silica@pyridyl conjugated microporous polymer as a stationary phase for high performance liquid chromatography.

BACKGROUND: Because of the advantages of good selectivity, high sensitivity, and fast analysis, high performance liquid chromatography (HPLC) has become one of the modern analytical techniques in wide application range, such as biological analysis, environmental detection, pharmaceutical and food inspection, agriculture and other fields. The stationary phase greatly decides the chromatographic separation performance, so the development of novel stationary phase is most important for HPLC. RESULTS: Pyridyl conjugated microporous polymers (P-CMP) with one to four layers were modified on the surface of amino silica to obtain a novel core-shell material (SiO2@P-CMP) by the layer-by-layer assembly strategy and Chichibabin reaction. The relationship between the structure of SiO2@P-CMP and chromatographic performance was carefully investigated, and the retention mechanism was revealed. The interactions including π-π stacking, hydrophobic effect and hydrogen bond gradually enhanced with the increase of P-CMP layers on the silica surface. Compared with C18 column, SiO2@P-CMP columns displayed better separation selectivity for polycyclic aromatic hydrocarbons (PAHs). According to the relative retention values (α), the separation performance of SiO2@P-CMP columns (α = 1.144-1.884) for PAH isomers and other analytes was obviously better than that of C18 column (α = 0.998-1.487). Furthermore, the SiO2@P-CMP column with four layers was selected to separate different types of analytes (eight PAHs, four bisphenols, four estrogens and nine phthalates), and the peak order of analytes was different from that on the C18 column due to the influence of hydrogen-bonding and π-π interactions. The relative standard deviations (n = 10) of retention time and peak area on SiO2@P-CMP column were between 0.28 % and 1.98 %. SIGNIFICANCE AND NOVELTY: Pyridyl conjugated microporous polymer was introduced as the stationary phase for the first time in HPLC. The proposed column displayed better separation characteristics compared to Zorbax SB-C18 column. It provided a new idea for the separation of small molecules and the development of chromatographic packing or extraction material.

Extraction improvement of ionic liquid-functionalized silica by in situ anion-exchange for online solid-phase extraction of estrogens in honey.

The accurate detection of analytes in honey is affected by the complex substrates, making it crucial to employ an effective sample preparation technique. In this work, an imidazolium ionic liquid was functionalized to the silica surface by a click reaction for solid-phase extraction (SPE) column, and in situ anion-exchange process was performed with different organic anions (dodecyl sulfonate, dodecyl benzene sulfonate, and naphthalene sulfonate). These SPE columns were evaluated through extracting the estrogens. The naphthalene sulfonate-based SPE column displayed the best extraction ability among these, and it was combined with high-performance liquid chromatography-diode array detection to establish an online enrichment and analysis system. Under the optimal test conditions, an online analytical method was developed, with high enrichment factors (1872-4744), wide linear ranges (0.0033-1.50, 0.0165-1.50, and 0.0330-1.50 µg g-1), and low detection limits (0.001-0.010 µg g-1). The method successfully determined several estrogens in some honey samples, and achieved satisfactory recovery results.

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.

[Recent application advances of covalent organic frameworks for solid-phase extraction].

Covalent organic frameworks (COFs) are a type of crystalline porous polymers. It firstly prepared by thermodynamically controlled reversible polymerization to obtain chain units and connecting small organic molecular building units with a certain symmetry. These polymers are widely used in gas adsorption, catalysis, sensing, drug delivery, and many other fields. Solid-phase extraction (SPE) is a fast and simple sample pretreatment technology that can enrich analytes and improve the accuracy and sensitivity of analysis and detection; it is extensively employed in food safety detection, environmental pollutant analysis, and several other fields. How to improve the sensitivity, selectivity, and detection limit of the method during sample pretreatment have become a topic of great interest. COFs have recently been applied to sample pretreatment owing to their low skeleton density, large specific surface area, high porosity, good stability, facile design and modification, simple synthesis, and high selectivity. At present, COFs have also attracted extensive attention as new extraction materials in the field of SPE. These materials have been applied to the extraction and enrichment of diverse types of pollutants in food, environmental, and biological samples, such as heavy metal ions, polycyclic aromatic hydrocarbons, phenol, chlorophenol, chlorobenzene, polybrominated diphenyl ethers, estrogen, drug residues, pesticide residues, etc. COFs can be synthesized from different materials and exert different effects on different extracts. New types of COFs can also be synthesized via modification to achieve better extraction effects. In this work, the main types and synthesis methods of COFs are introduced, and the most important applications of COFs in the fields of food, environment and biology in recent years are highlighted. The development prospects of COFs in the field of SPE are also discussed.

[Recent advances in the use of graphene for sample preparation].

Sample preparation is playing an increasingly important role in sample analysis. The enrichment efficiency of the target and the removal effect of the sample matrix are strongly dependent on the extraction material. Therefore, the development of efficient extraction materials is an important research focus in the field of sample preparation. Various advanced materials such as nanomaterials, mesoporous materials, ionic liquids, aerogels, carbon materials, metal-organic frameworks, and covalent organic frameworks have been introduced to produce a diverse range of extraction materials for sample preparation. Owing to its unique physical and chemical properties, graphene, an excellent carbon nanomaterial, has attracted significant attention in different areas. Due to their unique advantages of large surface area, large π-electrons, excellent adsorption properties, abundant functional groups, and facile chemical modification, graphene-based materials have displayed excellent extraction performance for diverse analytes. Furthermore, graphene-based extraction materials have been applied to pretreat real samples from different fields. This paper provides an overview of the recent advances in graphene sample preparation from 2020 to date. The manuscript covers the use of graphene, graphene oxide, and the related functionalized materials as sorbents, as well as their specific applications in cartridge solid-phase extraction, dispersive solid-phase extraction, magnetic solid-phase extraction, stir bar sorptive extraction, fiber solid-phase microextraction, and in-tube solid-phase microextraction. To prevent the aggregation of graphene, three-dimensional graphene, porous graphene aerogels, graphene-modified silica, and stainless-steel mesh were developed for cartridge solid-phase extraction. Furthermore, some graphene-based extraction materials were used to develop online solid-phase extraction, which allowed for automatic and high-throughput tests. Graphene nanosheets and their hybrid materials with molybdenum disulfide or zinc oxide nanoparticles have been applied to dispersive solid-phase extraction, and several types of contaminants, including metal ions, bisphenol endocrine disruptors, paraben preservatives, and phthalates, could be captured. By combination with magnetic materials using the coprecipitation method or via chemical post-modification, many magnetic graphene extraction materials have been produced for magnetic solid-phase extraction. The introduction of magnetic graphene not only enhanced the extraction efficiency but also simplified the test process, making it highly suitable for complex samples such as food and biological samples. Similar to magnetic solid-phase extraction, stir bar sorptive extraction is a very simple and efficient extraction method that shows good extraction performance for metal ions and organic pollutants from environmental water, medicines in urine, and organic pollutants in cosmetics. In addition to its excellent applicability to solid-phase extraction, graphene delivered satisfactory performance for solid-phase microextraction. Graphene has been used as an extraction coating for the extraction of fibers or tubes by coupling solid-phase microextraction with chromatographic detection, and many kinds of organic pollutants, including polychlorinated biphenyls, phthalates, polycyclic aromatic hydrocarbons, toluene, xylenes, organophosphorus pesticides, phenoxy acid herbicides, and antibiotics, in environmental or biological samples have been successfully determined. The extraction mechanism, including π-π, electrostatic, hydrophobic, hydrophilic, and hydrogen-bonding interactions, is also discussed. Because of the mixed-mode interactions and rich functionalization, graphene-based extraction materials could effectively capture and selectively enrich different types of species. These extraction or microextraction techniques have been coupled with detection methods such as chromatography, mass spectrometry, and atomic absorption spectroscopy and widely used in environmental monitoring, food safety, and biochemical analysis. The future development of graphene in the field of sample pretreatment focuses on the following aspects: 1) functionalization of graphene with specific groups such as affinity groups, chelating groups, and molecularly imprinted sites to achieve unique extraction selectivity; 2) combination of graphene with the advanced materials, including covalent organic frameworks, metal organic frameworks, aerogels, and nanomaterials, thus realizing the complementary advantages between materials, so that the hybrid graphene materials find broad application prospects in sample preparation; 3) combination of electromagnetic materials with graphene to form electromagnetic composites, as well as the use of electromagnetic fields to improve extraction selectivity and efficiency; 4) exploiting the good performance of graphene-based materials to overcome the difficulty encountered in the pretreatment of complex samples; 5) development of more green methods to prepare graphene-based extraction materials or functionalize graphene, in line with the trends in green chemistry; 6) application of more graphene-based materials to online sample preparation for meeting the development trends in the field of analytical chemistry.