A polar stationary phase obtained by surface-initiated polymerization of hyperbranched polyglycerol onto silica

An adhesive hydrogel functionalized silica sphere for polar analytes separation and analysis

In response to the challenges associated with the chromatographic separation of polar compounds, this study aims to devise a solution by introducing a novel stationary phase. Hydrogels, characterized by a three-dimensional network structure, have aroused wide attention owing to its functional designability, multiple interaction sites and good adhesion, etc. In this work, an adhesive hydrogel functionalized silica stationary phase (Sil@PVA/TA) was synthesized using physical coating technique. Due to the co-existence of hydroxyl and benzene ring in the hydrogel structure, the obtained composites materials exhibited excellent separation performance for various of compounds and excellent column efficiency up to 71385.6 plates/m for thymidine. Furthermore, the hydrogel functionalized silica demonstrated superior selectivity to bare silica, diol-column and NH2-column for the separation of various of polar molecules, including, nucleosides/bases, alkaloids, organic acids, antibiotics and amino acids. Notably, for alkaloids, which frequently encounter peak tailing issues, Sil@PVA/TA demonstrated superior peak shape compared with C18 column. In short, this study successfully synthesized a hydrogel functionalized silica stationary phase, offering a novel method for the separation and analysis of polar compounds.

A Polymer-Based Polar Stationary Phase Grafted With Modified Lysine for Hydrophilic Interaction Chromatography

The high hydrophobicity and chemical inertness of poly(styrene-divinylbenzene) (PS-DVB) microspheres make their surface hydrophilic modification difficult. Here we describe a facile way to convert PS-DVB microspheres to hydrophilic, then can be used as polar stationary phase for hydrophilic interaction chromatography. This approach utilizes the grafting of an acrylamide-terminated lysine zwitterionic monomer onto PS-DVB microspheres via free radical polymerization. The obtained stationary phase shows good hydrophilicity and a typical retention mechanism of hydrophilic interaction chromatography toward several model polar analytes. It also exhibits obvious zwitterionic properties and is capable of separating cationic and anionic analytes simultaneously. The column shows negligible bleeding level, much superior to silica-based ones.

A polyethyleneimine-functionalized polymer substrate polar stationary phase

A polyethyleneimine (PEI)-functionalized polymer substrate polar stationary phase was prepared for hydrophilic interaction chromatography (HILIC) by grafting PEI onto poly(styrene-divinylbenzene) (PS-DVB) microspheres. The phase shows a U-shape retention profile and it exhibits typical hydrophilic characteristic when the organic solvent fraction in the mobile phase is > 60%. Hydrogen bonding, anion exchange, and hydrophobic interaction are involved in the retention mechanism. Good separation and unique selectivity for acidic, basic and neutral polar analytes were achieved. It showed extremely low column bleed (comparable to that of blank) under gradient elution mode (even to 50% fraction of water) and wide pH tollerance range (at least 1-13).

A Compendium of the Principal Stationary Phases Used in Hydrophilic Interaction Chromatography: Where Have We Arrived?

Hydrophilic interaction liquid chromatography (HILIC) today is a well-known and largely applied technique to analyse polar compounds such as pharmaceuticals, metabolites, proteins, peptides, amino acids, oligonucleotides, and carbohydrates. Due to the large number of stationary phases employed for HILIC applications, this review aims to help the reader in choosing a proper stationary phase, which often represents the critical point for the success of a separation. A great offer is present for achiral applications in contrast to the chiral phases developed for HILIC enantioseparations. In the last case, up-to-date solutions are presented.

A hyperbranched polyglycerol-functionalized polymer polar stationary phase

A polymer polar stationary phase functionalized with hyperbranched polyglycerol for hydrophilic interaction chromatography (HILIC) is described. It is prepared via surface-initiated ring-opening polymerization of hyperbranched polyglycerol onto hydrolzed poly(glycidyl methacrylate-divinylbenzene) microspheres. The capacity of the functional groups can be maniputed by repeating hyperbranch layers. The phase showed typical HILIC character with good separation performance towards tested polar analytes. It also exhibited wider pH tolerance range (e.g. at least 2 to 12) and as well negligible bleed level under gradient elution mode (even to 50% fraction of water).

A Survey of Polar Stationary Phases for Hydrophilic Interaction Chromatography and Recent Progress in Understanding Retention and Selectivity

Various polar stationary phases have become available for hydrophilic interaction chromatography (HILIC) and help drive continuous applications in biomedical, environmental and pharmaceutical areas in the past decade. Although the stationary phases for HILIC have been reviewed previously, it is an appropriate time to take another look at the progresses during the past five years. The current review provides an overview of the polar stationary phases commercially available for HILIC applications in an effort to assist scientists in selecting suitable columns. New types of stationary phase that were published in literature in the past five years are summarized and discussed. The trend in stationary phase research and development is also highlighted. Of particular interest is the experimental evidence for direct interactions of polar analytes with the ligands of the stationary phases under HILIC conditions. In addition, two different approaches have been developed to delineate the relative significance of the partitioning and adsorption mechanisms in HILIC, representing an important advancement in our understanding of the retention mechanisms in HILIC.

Chromatographic performance of zidovudine imprinted polymers coated silica stationary phases

Nowadays, molecularly imprinted polymers (MIPs) coated silica stationary phases (SPs) have aroused great attention, owing to their good properties of high selectivity, good stability, facile synthesis procedure and low cost. In this study, zidovudine imprinted polymers coated silica stationary phases (MIPs/SiO₂ SPs) were synthesized by surface imprinting technique using zidovudine as the template molecule, methacrylic acid as the functional monomer, ethylene glycol dimethacrylate as the cross-linking agent, azobisisobutyronitrile as the initiator, and bare silica spheres (particle size, 5 μm; pore size, 20 nm) as substrates. In the process, reagents with low concentration were used to prepare thin layer of MIPs coating on the surface of silica microbeads. The properties of the materials were characterized by scanning electron microscope (SEM), fourier transform infrared spectrometer (FT-IR), carbon elemental analysis and N₂ adsorption-desorption experiment. The obtained SPs were packed into stainless steel columns (2.1 mm × 150 mm) via a slurry method. The prepared columns were applied for separation of nucleoside analogues with similar chemical structures and strong polarity. The retention mechanism of MIPs/SiO₂ SPs for nucleoside analogues was investigated carefully. And the chromatographic performances of the resulting MIPs based SPs were superior to those of the commercial SPs. Furthermore, the synthesized MIPs/SiO₂ SPs possessed great potentials in separation of ginsenosides. This investigation demonstrated that MIPs based SPs were successfully synthesized and provided a new approach to polar compounds separation and analysis.

A hydrolytically stable amide polar stationary phase for hydrophilic interaction chromatography

A novel amide functionalized polar stationary phase has been described by grafting acrylamide polymer coating onto hydrolysed poly (glycidyl methacrylate-divinylbenzene) (GMA-DVB) microsphere. The grafting of acrylamide coating is performed via free radical polymerization of acrylamide with pendant double bonds of hydrolysed GMA-DVB microsphere. The obtained stationary phase (G-pAM) possesses favorable hydrophilicity, as proved by strong retention and good separation ability towards several types of model polar analytes (e.g. 71913 plates/m plate count of sucrose), and excellent hydrolytically stability, as indicated by extremely low bleed level (much superior to commercial ones, ~23.7-fold-~77.4-fold lower). Negligible baseline drift under gradient elution (water fraction even up to 50%) was observed. It also exhibits good selectivity in the separation of isomers and homologue sugars.

Methoxy terminated poly dimethylsiloxane bonded stationary phase for reversed-phase liquid chromatography

In this work, a methoxy terminated poly dimethylsiloxane modified silica gel material was proposed as a novel stationary phase for reversed-phase liquid chromatography. With 5 μm silica gel as matrix, methoxy terminated poly dimethylsiloxane polymer was grafted by one step chemical bonding reaction. The obtained stationary phase was characterized by scanning electron microscopy, fourier transform infrared spectroscopy and element analysis. To our knowledge, this is the novel methoxy terminated poly dimethylsiloxane bonded stationary phase with good separation efficiency (42107-46988 plates/m for benzene homologues) and high stability (RSD is 0.08-5.09%). Comparing to other traditional columns of the same type, the proposed stationary phase has a wider polarity separation scale and shorter analysis time. In addition to the rapid separation of hydrophobic compound, such column also exhibited great potential in the separation of hydrophilic analytes.

Benzoic acid-modified monolithic column for separation of hydrophilic compounds by capillary electrochromatography with high content of water in mobile phase

Hydrophilic column combined with mobile phase containing high content of water is a green method for the separation of polar compounds, but there are few related studies, and the separation efficiency and performance of existing columns still needs to be improved. In this work, a novel monolithic column for separation of hydrophilic compounds under both high water content and HILIC condition, was prepared by in-situ polymerization using 4-vinylbenzoic acid (VBA) and 1-(Acryloyloxy)-3-(methacryloyloxy)-2-propanol (AMAP) as functional monomers. The poly(VBA-co-AMAP) monolithic column showed good separation performance towards various polar compounds under different chromatographic conditions based on the π-interaction, hydrophobic and hydrogen bonding interactions provided by 4-vinylbenzoic acid functional monomer. The highest column efficiency for adenine was over 2.15 × 10⁵ plates m^-1 (theoretical plate, N). In addition, the monolith showed good stability and reproducibility, the relative standard deviations (RSDs) of retention times within days (n = 5), between days (n = 5), between columns (n = 3) and between batches (n = 3) were 0.47-1.13%, 1.20-2.68%, 0.59-1.78% and 1.54-3.60%, respectively. This novel type of monolith has great application potential in the separation of hydrophilic compounds.

Recent applications of retention modelling in liquid chromatography

Recent applications of retention modelling in liquid chromatography (2015–2020) are comprehensively reviewed. The fundamentals of the field, which date back much longer, are summarized. Retention modeling is used in retention‐mechanism studies, for determining physical parameters, such as lipophilicity, and for various more‐practical purposes, including method development and optimization, method transfer, and stationary‐phase characterization and comparison. The review focusses on the effects of mobile‐phase composition on retention, but other variables and novel models to describe their effects are also considered. The five most‐common models are addressed in detail, i.e. the log‐linear (linear‐solvent‐strength) model, the quadratic model, the log–log (adsorption) model, the mixed‐mode model, and the Neue–Kuss model. Isocratic and gradient‐elution methods are considered for determining model parameters and the evaluation and validation of fitted models is discussed. Strategies in which retention models are applied for developing and optimizing one‐ and two‐dimensional liquid chromatographic separations are discussed. The review culminates in some overall conclusions and several concrete recommendations.