Immobilization of a phosphonium ionic liquid on a silica monolith for hydrophilic interaction chromatography

Fabrication of monolithic capillary columns with inner diameter 50-530 μm employing a mixture of pentaerythritol tetraacrylate and polyhedral oligomeric silsesquioxane-methacrylate as crosslinkers

Highly crosslinked monolithic capillary columns with inner diameters in the range of 50-530 μm were prepared by radical polymerization of pentaerythritol tetraacrylate, polyhedral oligomeric silsesquioxane-methacrylate, and n-octadecyl methacrylate in the presence of methanol, dodecyl alcohol, and polyethyleneglycol lauryl ether. Columns were evaluated by inverse size-exclusion chromatography employing a set of polystyrene standards of narrow molecular-size distribution and by scanning electron microscopy. Chromatographic performance under reversed-phase conditions was also evaluated. The combination of two effective crosslinkers as pentaerythritol tetraacrylate and polyhedral oligomeric silsesquioxane-methacrylate in the polymerization mixture allows for the preparation of robust and efficient monolithic capillary columns within a fairly wide range of internal diameters. This article is protected by copyright. All rights reserved.

Polymerized phosphonium ionic liquid functionalized silica microspheres as mixed-mode stationary phase for liquid chromatographic separation of phospholipids

There is a large and growing demand for the vigorous development of new high performance liquid chromatography stationary phases in order to solve complex phospholipids separation. Herein, phosphonium-based ionic liquid trioctyl(allyl)phosphonium bromide ([P_888Allyl]Br) was first synthesized with trioctylphosphine and allyl bromide. With [P_888Allyl]Br as the polymerizable monomer, polymerized phosphonium ionic liquid functionalized silica microsphere (PIL@SiO₂) was further synthetized via click chemistry reaction. Significantly, based on the inherent amphiphilic nature of the introduced [P_888Allyl]Br, the packed PIL@SiO₂ column displayed hydrophilic/hydrophobic mixed-mode retention mechanisms. The PIL@SiO₂ column can achieve separation of nucleic acid bases and nucleosides, sulfonamides, amides and anilines with excellent selectivity in a shorter separation time. The column efficiency reached 109,700 N/m for 2-iodoacetamide. One of the important characteristics of the PIL@SiO₂ column is that both phospholipid classes and species can be efficiently separated via the same column, outperforming that of the commercial amino column. Furthermore, the application potential of the PIL@SiO₂ column was further verified via separation of phospholipids extracted from soy lecithin. The proposed PIL@SiO₂ column provides a promising candidate for separation of complex phospholipid samples.

Total Triterpenoid Extraction from Inonotus Obliquus Using Ionic Liquids and Separation of Potential Lactate Dehydrogenase Inhibitors via Ultrafiltration High-Speed Countercurrent Chromatography

Extracts of the fungus Inonotus obliquus exhibit cytotoxic properties against different cancers; hence, this fungal species has been extensively studied. This study aimed to extract total triterpenoids from Inonotus obliquus using ionic liquids (ILs) and separate potential lactate dehydrogenase (LDH) inhibitors via ultrafiltration (UF)-high-speed countercurrent chromatography (HSCCC). Total triterpenoids from Inonotus obliquus were extracted by performing a single-factor experiment and employing a central composite design via ultrasonic-assisted extraction (UAE) and heat-assisted extraction (HAE). The extract was composed of 1-butyl-3-methylimidazolium bromide as the IL and methanol as the dispersant. Ultrafiltration-liquid chromatography (UF-LC) was used to rapidly scan the LDH inhibitors and betulin and lanosterol were identified as potential inhibitors. To obtain these target compounds, betulin and lanosterol with the purities of 95.9% and 97.8% were isolated from HSCCC within 120 min. Their structures were identified using several techniques, among which IL-HAE was fast and effective. This study reports the extraction of triterpenoids from Inonotus obliquus by IL for the first time. Collectively, the findings demonstrate that UF-LC is an effective tool for screening potential LDH inhibitors from crude extracts of I. obliquus and may help to identify bioactive substances against myocardial infarction, whereas high-purity compounds can be separated via UF-HSCCC.

Advancements in the preparation and application of monolithic silica columns for efficient separation in liquid chromatography

Fast and efficient separation remains a big challenge in high performance liquid chromatography (HPLC). The need for higher efficiency and resolution in separation is constantly in demand. To achieve that, columns developed are rapidly moving towards having smaller particle sizes and internal diameters (i.d.). However, these parameters will lead to high back-pressure in the system and will burden the pumps of the HPLC instrument. To address this limitation, monolithic columns, especially silica-based monolithic columns have been introduced. These columns are being widely investigated for fast and efficient separation of a wide range of molecules. The present article describes the current methods developed to enhance the column efficiency of particle packed columns and how silica monolithic columns can act as an alternative in overcoming the low permeability of particle packed columns. The fundamental processes behind the fabrication of the monolith including the starting materials and the silica sol-gel process will be discussed. Different monolith derivatization and end-capping processes will be further elaborated and followed by highlights of the performance such monolithic columns in key applications in different fields with various types of matrices.

Challenges and Advances in the Fabrication of Monolithic Bioseparation Materials and their Applications in Proteomics Research

High-performance liquid chromatography integrated with tandem mass spectrometry (HPLC-MS/MS) has become a powerful technique for proteomics research. Its performance heavily depends on the separation efficiency of HPLC, which in turn depends on the chromatographic material. As the "heart" of the HPLC system, the chromatographic material is required to achieve excellent column efficiency and fast analysis. Monolithic materials, fabricated as continuous supports with interconnected skeletal structure and flow-through pores, are regarded as an alternative to particle-packed columns. Such materials are featured with easy preparation, fast mass transfer, high porosity, low back pressure, and miniaturization, and are next-generation separation materials for high-throughput proteins and peptides analysis. Herein, the recent progress regarding the fabrication of various monolithic materials is reviewed. Special emphasis is placed on studies of the fabrication of monolithic capillary columns and their applications in separation of biomolecules by capillary liquid chromatography (cLC). The applications of monolithic materials in the digestion, enrichment, and separation of phosphopeptides and glycopeptides from biological samples are also considered. Finally, advances in comprehensive 2D HPLC separations using monolithic columns are also shown.

Click chemistry at the microscale

This manuscript reviews recent developments in click chemistry in microscale systems.

Monolithic Silica Capillary Columns with Improved Retention and Selectivity for Amino Acids

A strategy for the preparation of silica-based monolithic capillary columns (150 × 0.1 mm) with high selectivity to amino acids is presented. The zwitterionic columns were prepared by coating the silica monolith with [2-(methacryloyloxy)ethyl]-dimethyl-(3-sulfopropyl)-ammonium hydroxide via 3-(trimethoxysilyl)propyl methacrylate. The columns were evaluated under isocratic conditions in hydrophilic interaction liquid chromatography. The best separation of amino acids was obtained on the monolithic column prepared by a stepwise modification procedure where the modification step was repeated four times. The mixture of fifteen amino acids was separated within 13 min using the mobile phase consisting of 75% acetonitrile and 25% 5 mmol/L ammonium acetate at pH 4.5.