Mixed-mode acrylamide-based continuous beds bearing tert -butyl groups for capillary electrochromatography synthesized via complexation of N - tert -butylacrylamide with a water-soluble cyclodextrin. Part I: Retention properties

Construction of adamantane-based monolithic column with three-dimensionally porous structure for small molecules separation and biosample analysis

BACKGROUND

The fabrication technique of capillary column is the key to the development and application of capillary liquid chromatography (cLC) to improve separation efficiency for analytes. The capillary monolithic column possessed three-dimensionally connected porous or channel structures. Unique porous structure endows excellent permeability and high performance in diverse fields, especially in separation. Thereinto, organic monolithic columns have attracted widespread attention due to their advantages of simple preparation and excellent biocompatibility. However, their separation selectivity needs to be further developed and regulated to apply the separation of more diverse samples.

RESULTS

A novel polymeric monolithic column was prepared via thermally initiated in situ copolymerization of 2-methyladamantan-2-yl acrylate (MADA) with ditrimethylolpropane tetraacrylate (DTTA) in fused silica. The prepared poly(MADA-co-DTTA) monolith showed adjustable permeability, developed porous structure and high thermal stability. Consequently, it exhibited excellent separation capability of small molecules (alkylbenzenes and polycyclic aromatic hydrocarbons). Especially, when acetonitrile/water (60/40, v/v) was used as the mobile phase, the theoretical plate numbers reached 84,000 plates m-1 for butylbenzene at a linear velocity of 0.5 mm s-1. Most importantly, the hydrophobicity of the poly(MADA-co-DTTA) monolithic column was regulated via host-guest interaction between adamantyl group and cucurbit [7]uril (CB[7]). Additionally, the poly(MADA-co-DTTA) monolith was further adopted for the analysis of the tryptic digest of proteins from HeLa by cLC-MS/MS. The 33,783 unique peptides and 5,299 proteins were identified on the monolith, which exhibited great separation ability for complex samples.

SIGNIFICANCE AND NOVELTY

Due to abundant pore structure and good chemical properties, the poly(MADA-co-DTTA) monolithic column exhibited high performance for the separations of small molecules and biological sample. Meanwhile, owing to the existence of adamantyl-group, CB[7] was immobilized on the poly(MADA-co-DTTA) monolithic column to fabricate poly(MADA-co-DTTA)-CB[7] by host-guest interaction. It is possible to adjust the surface chemistry of the monolithic materials to accommodate more complex analytes.

Mesoporous nanomaterial-assisted hydrogel double network composite for mixed-mode liquid chromatography

By introducing functional groups such as quaternary amine groups, sulfonic acid groups, triazine groups, and other mespore nanomaterials into the hydrogel, better separation effect of some organic framework materials has been obtained. Due to a reasonable design and preparation strategy, the hydrogel composite-modified silica can be used in the selective separation of various analytes such as pesticides, alkylbenzenes, polycyclic aromatic hydrocarbons, nucleosides/bases, benzoic acids, antibiotics, and carbohydrates. Through the exploration of chromatographic retention behavior, it is proved that the column can be used in mixed-mode liquid chromatography. The intra-day relative standard deviation for retention time of this new stationary phase is 0.12-0.16% (n = 10), and the inter-day relative standard deviation is less than 0.39% (n = 5). This new stationary phase can also be used for separation in complex samples. The limit of detection (LOD) for chlorotoluron in farm irrigation water is 0.21 µg/L and the linear range is 2-250 µg/L. After optimizing the chromatographic conditions, the highest efficiency of the hydrogel column in RPLC and HILIC modes has reached 32,400 plates/m (chlorobenzuron) and 41,300 plates/m (galactose). This new type of hydrogel composite is a porous network material with flexible functional design and simple preparation method and its application has been expanded in liquid chromatography separation successfully. The hydrogel composed of triallyl cyanate cross-linking agent and 3-(2-(methacryloyloxy) ethyl) dimethylamine) propane-1-sulfonate (SBMA) monomer which were co-modified on the surface of mesoporous silica with MOF-919 for separation in mixed-mode liquid chromatography.

Recent advances in mixed-mode chromatographic stationary phases

Mixed-mode phases have become very popular in the last decade, and the number of new mixed/multi-mode sorbents is growing fast. Unlike single-mode stationary phases, perfectly suited for the separation of the analytes possessing similar physicochemical properties, for instance reversed-phase chromatography for hydrophobic solutes, mixed-mode sorbents providing multimodal interactions can render better separation selectivity for complex mixtures of solutes differing significantly in their physicochemical characteristics. The most frequent modern mixed-mode stationary phases are di/tri-mode sorbents embracing the following interactions, hydrophobic, electrostatic (coulombic), and hydrophilic. According to their structures, it is possible to distinguish silica-based, polymer-based, hybrid, and monolithic mixed-mode stationary phases. Herewith, newly synthesized mixed-mode sorbents developed within the last two and half years are categorized, discussed, and summarized. The main attention is devoted to the description of the synthetic routes and characterization methods applied for the new stationary phases.