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... sulfobetaine-based coating, which consists of positively charged quaternary ammonium and negatively charged sulfonic acid groups in a 1:1 ratio, is a typical zwitterionic phase and has a wide range of applications in HILIC [25]. As shown in Fig. 1a, the oppositely charged groups are distributed perpendicular to the silica with the sulfonic group at the distal end of the zwitterionic moiety. Another zwitterionic phosphorylcholine phase has also been reported previously [26]. It was prepared by graft poly- merization of 2-methacryloyloxyethyl phosphorylcholine onto the surface of ...
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... charged groups are distributed perpendicular to the silica with the sulfonic group at the distal end of the zwitterionic moiety. Another zwitterionic phosphorylcholine phase has also been reported previously [26]. It was prepared by graft poly- merization of 2-methacryloyloxyethyl phosphorylcholine onto the surface of silica gel. As shown in Fig. 1b, the oppositely charged groups are also perpendicular to the silica but with different spatial arrangement of positive and negative charged groups. In addition to these zwitterionic phases, Shen et al. [14] developed a new type of cysteine-bonded stationary phase with uniform dis- tribution of both positively and negatively charges ...
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... perpendicular to the silica but with different spatial arrangement of positive and negative charged groups. In addition to these zwitterionic phases, Shen et al. [14] developed a new type of cysteine-bonded stationary phase with uniform dis- tribution of both positively and negatively charges which were parallel to the surface of the silica gel (Fig. 1c). This stationary phase exhibited high hydrophilicity and achieved successful separation of oligosaccharides, peptides and basic compounds. The major difference between those zwitterionic phases is the various functional groups and spatial arrangement of positive and nega- tive charged groups, resulting in different surface charge and ...
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... with existing zwitterionic stationary phases, we propose tertiary amine-carboxyl-based silica (ACS) zwitterionic stationary phases. The tertiary amine groups cannot form Schiff bases with carbonyl compounds, which may result in improved lifetime with respect to typical aminopropyl silica. As shown in Fig. 1d, the oppositely charged tertiary amine and carboxyl groups are parallel to the surface of the silica. More importantly, the ratio of those two oppositely charged groups could be easily adjusted by changing the proportion of initial reactants. Such adjustable dis- tribution of positively and negatively charged groups could pro- vide an ...
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... initial reactants (mercaptoacetic acid, vinyltriethoxysilane and dimethoxybenzoin) and the final product were analyzed by GC-MS. Diluted analytes (50 ppb) were prepared using acetone as a solvent and 5.0 μL solutions were injected for analysis. The GC- MS chromatograms were shown in Fig. S1 (Supporting informa- tion). The peaks of the initial reactants were completely unde- tectable in the chromatogram of the final product, indicating that nearly 100% conversion of the reaction was achieved. Additionally, we characterized the final product with 13 C NMR analysis. As shown in Fig. S2, the result showed that the expected ...
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... The resultant material exhibited a high efficiency in the separation of both polar (e.g., organic acids and bases) and highly hydrophilic (e.g., cephalosporins and carbapenems) solutes. 414 Cheng et al. 200 prepared and characterized zwitterionic stationary phases in which the ratio of positively and negatively charged groups can be controlled. The molar ratios of the tertiary amine (trimethylamine) and carboxyl groups (2-((2-(trimethoxysilyl)ethyl)thio)acetic acid) can be chosen according to the assumed ratio of the oppositely charged moieties. ...
... The authors noted quite different selectivities and retention behaviors for various polar compounds (e.g., nucleosides and water-soluble vitamins) depending on the ratio of positively and negatively charged groups within a given stationary phase. 200 Most recently, Hou et al. 415 prepared and developed a fully pH-stable, positively charged HILIC porous graphitic carbon stationary phase. This material was prepared by creating a thin coating of poly(vinyl alcohol) (PVA) and poly(diallyldimethylammonium chloride) (DDAC) copolymer on porous graphitic carbon. ...
Reversed-phase high-performance liquid chromatography (RP-HPLC) is the most popular chromatographic mode, accounting for more than 90% of all separations. HPLC itself owes its immense popularity to it being relatively simple and inexpensive, with the equipment being reliable and easy to operate. Due to extensive automation, it can be run virtually unattended with multiple samples at various separation conditions, even by relatively low-skilled personnel. Currently, there are >600 RP-HPLC columns available to end users for purchase, some of which exhibit very large differences in selectivity and production quality. Often, two similar RP-HPLC columns are not equally suitable for the requisite separation, and to date, there is no universal RP-HPLC column covering a variety of analytes. This forces analytical laboratories to keep a multitude of diverse columns. Therefore, column selection is a crucial segment of RP-HPLC method development, especially since sample complexity is constantly increasing. Rationally choosing an appropriate column is complicated. In addition to the differences in the primary intermolecular interactions with analytes of the dispersive (London) type, individual columns can also exhibit a unique character owing to specific polar, hydrogen bond, and electron pair donor–acceptor interactions. They can also vary depending on the type of packing, amount and type of residual silanols, “end-capping”, bonding density of ligands, and pore size, among others. Consequently, the chromatographic performance of RP-HPLC systems is often considerably altered depending on the selected column. Although a wide spectrum of knowledge is available on this important subject, there is still a lack of a comprehensive review for an objective comparison and/or selection of chromatographic columns. We aim for this review to be a comprehensive, authoritative, critical, and easily readable monograph of the most relevant publications regarding column selection and characterization in RP-HPLC covering the past four decades. Future perspectives, which involve the integration of state-of-the-art molecular simulations (molecular dynamics or Monte Carlo) with minimal experiments, aimed at nearly “experiment-free” column selection methodology, are proposed.
... C8-H 2 PO 3 and Silica-COOH SPE sorbents were synthesized according to our previous work (Cheng et al., 2015). For synthesis of C8-H 2 PO 3 , vinylphosphonic acid (1.07 g, 10 mmol), c-mercapto propyltrimethoxysilane (1.96 g, 10 mmol), dimethoxybenzoin (0.10 g, 0.4 mmol), and trimethylamine (4.0 g, 40 mmol) were mixed in a 20-mL borosilicate glass bottle containing 5 mL dimethyl formamide (DMF) and then irradiated for 24 h with a 20 W blacklight (k max = 365 nm). ...
... It might be because nucleosides and nucleobases in this study were almost uncharged compounds that the influence of their retention on HILIC stationary phases was light by mobile phase pH. Besides, solutes and residual silanol groups on the stationary phase surface might be partially protonated at the acid conditions [35]. In other words, they would get more positively charged, so the electrostatic repulsion between solutes and silanol groups got stronger. ...
... The net surface charge of the mixed-mode phase has been balanced by the introduction of ionic co-ligands with opposite charge to the one of the mixed-mode RP/WAX ligand as endcapping groups (Fig. 1). The resultant zwitterionic surfaces [44][45][46][47][48][49][50] revealed carefully shifted pI values in dependence on the type and density of the introduced ionic endcapping groups, respectively. The new mixed-mode phases have been characterized by elemental analysis, pH-dependent -potential determinations and by liquid chromatographic studies at distinct organic modifier, pH and counterion concentrations. ...
Green chromatography techniques using low-toxic mobile phase are getting increasingly attention in recent years. The core is developing stationary phases that possess adequate retention and separation under the mobile phase of high content water. Using thiol-ene click chemistry, an undecylenic acid-bonded silica stationary phase (UAS) was prepared in a facile manner. Elemental analysis (EA), solid-state 13C NMR spectroscopy and Fourier transform infrared spectrometry (FT-IR) confirmed the successful preparation of UAS. The synthesized UAS was employed for per aqueous liquid chromatography (PALC), which uses little organic solvent during separation. Due to the hydrophilic carboxy, thioether group and hydrophobic alkyl chains of the UAS, various categories of compounds (including nucleobases, nucleosides, organic acids and basic compounds) with different properties can achieve enhanced separation under the mobile phase of high content water compared with commercial C18 and silica stationary phases. Overall, our present UAS stationary phase shows excellent separation ability toward highly polar compounds and meets the requirements of green chromatography.
A novel polyhedral oligomeric siloxane (POSS)-based zwitterionic monolithic capillary column was prepared via one-pot polymerization in ionic liquid porogen, using N,N-dimethyl-N-methacryloxyethyl-N-(3-sulfopropyl)ammonium betaine (DMMSA) and methacrylic ethyl trimethylammonium chloride (META) as binary functional monomers, and methacryl substituted POSS as cross-linker. The pore structure, permeability and homogeneity were well tuned by optimizing the polymerization conditions. The resultant monolith was characterized by scanning electron microscopy, nitrogen adsorption/desorption isotherm and Fourier transform infrared spectroscopy. The incorporation of zwitterionic ligand (DMMSA), quaternary amine group (META) and rigid POSS skeleton endows the hybrid organic-silica monolith with high hydrophilicity, electrostatic interaction and good mechanical stability, as well as a tunable electroosmotic flow over wide pH range. A close investigation of capillary electrochromatographic separations of different types of polar compounds such as bases, nucleosides and benzoic acids on such stationary phase exhibited a retention independent column efficiency up to 118,000 plates/m (thiourea), as well as a mixed-mode hydrophilic interaction chromatography (HILIC) retention mechanism including weak electrostatic interaction, hydrophobic interaction and anion exchange.
Stationary phases with multiple-mode mechanism are beneficial to meet the needs of complex samples, but there are few multiple-mode stationary phases which can adjust the relative strength among multiple-forces imposed on the solutes. This work presents a facile preparation method of reverse-phase/hydrophilic interaction/ion-exchange tri-mode stationary phase, in which three functional monomers, lauryl methacrylate (LMA), hydroxyethyl methylacrylate (HEMA) and dimethylaminoethyl methacrylate (DMAEMA) as co-monomers underwent surface initiated-atom transfer radical polymerization (SI-ATRP) on the surface of silica. The structure of stationary phases was characterized and their chromatographic properties were investigated using various solutes. By comparison with classical single-mode columns, it is found that the newly designed columns can offer multiple interactions including hydrophobic, hydrophilic and electrostatic interactions and show good separation abilities to the tested solutes. Besides, changing the ratios of LMA, HEMA and DMAEMA in SI-ATRP system can easily adjust the relative strength of three interactions imposed on the solutes, inducing adjustable separation selectivity of the columns. The improved separation of multivitamin sample and the successful use of the columns in Per aqueous liquid chromatography indicate the potential of the tri-mode stationary phases.
Surface‐bonded zwitterionic stationary phases have showed highlighted performances in separation of polar and hydrophilic compounds under hydrophilic interaction chromatography mode. So, it would be helpful to evaluate the characteristics of zwitterionic stationary phases with different arranged charged groups. The present work involved the preparation and comparison of three zwitterionic stationary phases. An imidazolium ionic liquid was designed and synthesized, and the cationic and anionic moieties respectively possessed positively charged imidazolium ring and negatively charged sulfonic groups. Then, the prepared ionic liquid, phosphorylcholine and an imidazolium‐based zwitterionic selector were bonded on the surface of silica to obtain three zwitterionic stationary phases. The selectivity properties were characterized and compared through the relative retention of selected solute pairs, and different kinds of hydrophilic solutes mixtures were used to evaluate the chromatographic performances. Moreover, the zwitterionic stationary phases were further characterized by the modified linear solvation energy relationship model to probe the multiple interactions. All the results indicated that the types and arrangement of charged groups in zwitterionic stationary phases mainly affect the retention and separation of ionic or ionizable compounds, and for interaction characteristics the contribution from n and π electrons and electrostatic interactions displayed certain differences. This article is protected by copyright. All rights reserved
