A simple assessment of hydrophilicity and shielding degree of HPLC mixed-mode resins with anion-exchange...

The goal of this study was the identification of the most promising ways to obtain hydrolytically stable mixed-mode stationary phases with anion-exchange functionalities. For that purpose, a set of parameters was utilized to assess hydrophilicity and shielding degree of 34 in-house designed mixed-mode resins in suppressed ion chromatography (IC), hydrophilic interaction liquid chromatography (HILIC), and, in some cases, in reversed-phase (RP) mode. The prerequisites for using the parameters to evaluate properties of the polymer-based stationary phases in IC mode are examined in detail using literature‑reported anion exchangers based on hydrolytically stable substrates. The correlation between resin's hydrophilicity parameter α(NO₃^-/Cl^-) and substrate shielding degree parameter α(BrO₃^-/Cl^-) was observed in suppressed IC mode. It was demonstrated that α(p-toluenesulfonate/uridine), which is usually used as a marker of anion-exchange selectivity for silica-based HILIC phases, reflects the substrate shielding degree for polymer-based mixed-mode stationary phases. The combination of PEI grafting and its quaternization with glycidol, along with glycidol polymerization, was found to be the most beneficial for increasing hydrophilicity in IC mode among the approaches considered in the work. Polyelectrolyte grafting or its combination with preliminary PEI grafting turned out to be more promising in HILIC mode, whereas glycidol polymerization was, conversely, disadvantageous.