A hyperbranched polyethylenimine functionalized stationary phase for hydrophilic interaction liquid chromatography

Preparation of polyacrylamide hydrophilic stationary phases with adjustable performance

Polymer modified silica materials are widely used as stationary phases in hydrophilic interaction liquid chromatography (HILIC), whereas a stationary phase with excellent performance is highly desired. In this study, vinyl modified silica was first synthesized through a silane coupling reaction, and then a polyacrylamide modified silica (PAM-SIL) stationary phase was successfully prepared using acrylamide as a copolymer monomer via free radical polymerization. The retention behaviors of polar analytes on the stationary phase under various chromatographic conditions, including acetonitrile content, buffer concentration and pH values were investigated, and a typical hydrophilic interaction retention mechanism was inferred. Exceptionally, the separation performance of the stationary phases could be regulated by controlling the polymer structure. Model analytes separated rapidly on the stationary phase which has an optimal grafting amount of vinyl, with the highest number of theoretical plates of orotic acid reaching 119,966/m. While the stationary phases with high acrylamide concentrations exhibited enhanced retention behavior and higher resolution for analytes. The adjustable separation performance will have huge potential in future separation and analysis applications.

Hydrophilic interaction chromatography-type sorbent prepared by the modification of methacrylate-base resin with polyethyleneimine for solid-phase extraction of polar compounds

Hydrophilic interaction chromatography (HILIC)-type sorbents were newly developed for the solid-phase extraction (SPE) of polar compounds. Two methacrylate-base resins with different cross-linking monomers and pore properties were synthesized, and three polyethyleneimines (PEIs) with different molecular weights were modified onto each base resin. In both cases, PEIs with a molecular weight of 10,000 (PEI-10,000) exhibited the highest adsorption properties for polar compounds (uracil, uridine, adenosine, cytidine, and guanosine). To control the water-enriched layer at the surface of the PEI-10,000-modified sorbents, the additive amount of PEI-10,000 in the modified reaction was also optimized. When 10 times the amount of PEI-10,000 to each base resin was added, an improvement in adsorption property was observed. Moreover, the use of a nonaqueous sample solution (100% acetonitrile) during the sample loading process drastically improved adsorption, especially for uracil (about 80%) and adenosine (100%). These results indicate that the formation of a strong water-enriched layer at the surface of sorbents with an effective expression of hydrophilic interaction was an important factor in the adsorption properties of polar compounds in HILIC mode-SPE.

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 review of the design of packing materials for ion chromatography

The development of ion chromatography has made remarkable progress in the past few decades, and it is now widely used for the analysis of common ions and organic compounds. Ion chromatography has many advantages, such as fast, high sensitivity, good selectivity and support for simultaneous analysis of multiple ionic compounds. In order to meet the high requirements of material analysis, new packing materials for ion chromatography with higher sensitivity and selectivity have been developed. In this paper, a lot of knowledge of ion chromatography is reviewed, and the development of ion chromatographic packings in recent years, especially in the last five years, is summarized.

Preparation and evaluation of a polymer-based sulfobetaine zwitterionic stationary phase

We describe a polymer-based sulfobetaine zwitterionic stationary phase for hydrophilic interaction liquid chromatography (HILIC). It was prepared by grafting acrylamide-type sulfobetaine monomer instead of common methacrylate-type sulfobetaine onto hydrolysed poly (glycidyl methacrylate-divinylbenzene) (GMA-DVB) microspheres via pendant double bonds of DVB. The phase has been characterized by elemental analysis, scanning electron micrograph and N₂ adsorption-desorption experiment. It shows wider pH tolerance range (from 2 to 12) and excellent separation ability towards common strong polar analytes such as nucleosides and nucleic bases, water-soluble vitamins, amino acids, inorganic anions and cations. Notably, it exhibits negligible baseline noise level (~0.15 pA) under typical HILIC mobile phase. Excellent selectivity in separation of α- and β-anomers of reducing sugars and lactose/lactulose has also been observed.

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.

Hyperbranched Polyglycerol Functionalized Silica Stationary Phase for Hydrophilic Interaction Liquid Chromatography

Surface-initiated anionic-ring-opening multibranching polymerization was employed to prepare a hyperbranched polyglycerol (HPG) functionalized silica stationary phase for hydrophilic interaction liquid chromatography (HILIC). The obtained stationary phase was characterized by Fourier-transform infrared spectrometry (FT-IR) and thermogravimetric analysis (TGA). The chromatographic properties of the prepared stationary phase were systematically investigated. The abundance and multitude distribution of hydroxyl groups in HPG endowed the stationary phase with improved hydrophilicity and enhanced separation performance compared with the stationary phase functionalized with monolayer of hydroxyl groups. The stationary phase showed excellent retention of various polar compounds, such as nucleosides, necleobases, phenols and sulfanilamides, indicating great potential in the separation of complex biosamples.