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Keywords:

  • Active pharmaceutical ingredient;
  • Counterions;
  • HILIC;
  • Mixed-mode chromatography;
  • Revised-phase, anion-exchange and cation-exchange trimode column

Abstract

The hydrophilic interaction liquid chromatography behavior of a novel trimodal stationary phase with reversed-phase/cation-exchange/anion-exchange characteristics was studied. This material is based on nanopolymer silica hybrid technology and provides reversed-phase, strong cation-exchange and weak anion-exchange properties at the same time. It is constructed with high-purity porous spherical silica particles coated with charged organic polymer nano-beads (dp ∼100 nm). The inner-pore area of the silica gel is covalently modified with an organic layer that provides both reversed-phase and weak anion-exchange properties. The outer surface is modified with strong cation-exchange functionality. This chemistry ensures distinctive spatial separation of the anion-exchange and cation-exchange regions, which allows both retention mechanisms to function simultaneously and provides more flexibility in selectivity control. The new phase exhibits hydrophilic interaction liquid chromatography characteristics: at high acetonitrile levels, the retention for charged analytes is governed by an ion-exchange process, accompanied by hydrophilic interaction (partitioning mechanism). This feature provides good flexibility in pharmaceutical method development such as simultaneous separation of hydrophilic drug molecule and its counterions (e.g. penicillin G potassium salt).