Comparison of the steric selectivity on hydrophilic interaction chromatography columns modified with poly(acrylamide) possessing different morphology

Determination of the phase ratio of a dehydroabietic-acid-bonded silica-gel chromatographic stationary phase and its effect on separation thermodynamics

Rosin-based chromatographic columns are widely used for separation purposes, but, to date, their phase ratios (Φ) have been imprecisely measured. This affects the understanding of their separation mechanism and the calculation of related thermodynamic parameters. In this study, a stationary phase was synthesized by bonding dehydroabietic acid (DA) to silica gel (Si-DO) and applied for reversed-phase liquid chromatography. The distribution coefficient (Kdm) of methyl dehydroabietate (MD), which has the same structure as the bonded phase of Si-DO, was used as a surrogate for the determination of the equilibrium coefficient (K) of Si-DO, and the Kdm values of MD in different mobile phases were measured and compared with the K values of Si-DO. It was found that the phase ratio of Si-DO varied with mobile phase composition and temperature, as shown by the Φ values: 0.039-0.122 for the methanol/water system and 0.051-0.116 for the acetonitrile/water system; in addition, the a indices were 0.552-0.757 and 0.564-0.674, respectively. The Kdm of MD was closer to the K of Si-DO than those of other surrogate models, including the octanol-water and octane-mobile phase partition coefficients. In addition, the thermodynamic parameters (ΔG°, ΔH°, and ΔS°) of n-alkylbenzenes on Si-DO were negative, indicating a spontaneous and enthalpy-driven separation process. Overall, the phase ratio of rosin-based columns is crucial for accurate thermodynamic analysis and interpretation of the separation mechanism. Finally, the MD surrogate model allows the estimation of phase ratio of Si-DO and other similar columns, providing a novel method for measuring the phase ratio of rosin-based columns and providing a validated concept and methodology for determining the phase ratios of HPLC columns.

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.

Development and chromatographic exploration of stable-bonded crosslinked amino silica against classical amino phases

The present work reports on a novel stable-bonded amino silica stationary phase obtained by crosslinking of surface aminopropyl moieties using triglycidyl isocyanurate. The obtained crosslinked amido-amino network silica material exhibited superior hydrolytic stability compared to classical 3-aminopropyl phases and showed, inter alia, excellent separation of nine therapeutically effective sulfonamides in hydrophilic interaction / weak anion exchange chromatography elution mode. Additionally, the separation of carbohydrates was investigated under classical hydrophilic interaction chromatography conditions as well proving the suitability of the novel phase for such applications. For the evaluation of the hydrolytic stability the prepared material, as well as two commercially available benchmark columns and a set of in-house synthesized amino modified materials, were exposed to harsh aqueous mobile phase conditions for in total 50 hours at elevated temperature. In this context, the materials were examined by elemental analysis, (¹³ C and ²⁹ Si cross-polarization/magic angle spinning) solid-state NMR and a chromatographic test before and subsequent to the exposure to these stress conditions. Lastly, the new stationary phase was classified in comparison to a set of commercially available stationary phases by principal component analysis of resultant retention factors gained from chromatographic standard tests. This article is protected by copyright. All rights reserved.

Grafting copolymer brushes on polyhedral oligomeric silsesquioxanes silsesquioxane-decorated silica stationary phase for hydrophilic interaction liquid chromatography

A strategy is proposed to develop a stationary phase for hydrophilic interaction liquid chromatography (HILIC) using the synergistic effect of polyhedral oligomeric silsesquioxane (POSS) and copolymer brushes. Octahedral octa-aminopropylsisesquioxane (8NH₂-POSS) was first bound to silica gel, followed by bromination to form a cubic initiator. Then, using acrylamide (AM) and dihydroxypropyl methacrylate (DPMA) as mixed monomers, surface initiated-atom transfer radical polymerization was conducted to prepare a stationary phase comprising cubic copolymer brushes with amide and diol groups. The characterization of the stationary phase confirmed the successful synthesis of Sil-NH₂-POSS/Poly(AM-co-DPMA). The chromatographic properties were investigated using nucleosides, organic acids and β-agonists to find that our designed column has superior hydrophilic property, better separation performance compared with classical HILIC columns consisting of diol- or amino-modified silica. The systematic investigation of the retention mechanism and separation selectivity using various types of polar compounds revealed that Sil-NH₂-POSS/Poly(AM-co-DPMA) follows a mixed-mode retention composed of HILIC and electrostatic interactions. Besides, it exhibits good column efficiency and stability. The role of 8NH₂-POSS in the separation was evaluated by comparing the performance of Sil-NH₂-POSS/Poly(AM-co-DPMA) and poly(AM-co-DPMA)-modified silica without 8NH₂-POSS. In conclusion, our designed based on POSS and hydrophilic copolymer brushes can contribute to the development of HILIC separation materials with enhanced performance.