Rapid quantification of imidazolium-based ionic liquids by hydrophilic interaction liquid chromatography: Methodology and an investigation of the retention mechanisms

J Chromatogr A. 2015 Jun 26;1400:54-64. doi: 10.1016/j.chroma.2015.04.047. Epub 2015 May 2.

Abstract

The separation of nine N,N'-dialkylimidazolium-based ionic liquids (ILs) by an isocratic hydrophilic interaction high-performance liquid chromatographic method using an unmodified silica column was investigated. The chosen analytical conditions using a 90:10 acetonitrile-ammonium formate buffer mobile phase on a high-purity, unmodified silica column were found to be efficient, robust, and sensitive for the determination of ILs in a variety of solutions. The retention window (k' = 2-11) was narrower than that of previous methods, resulting in a 7-min runtime for the nine IL homologues. The lower limit of quantification of the method, 2-3 μmol L(-1), was significantly lower than those reported previously for HPLC-UV methods. The effects of systematically modifying the IL cation alkyl chain length, column temperature, and mobile-phase water and buffer content on solute retention were examined. Cation exchange was identified as the dominant retention mechanism for most of the solutes, with a distinct (single methylene group) transition to a dominant partitioning mode at the highest solute polarity.

Keywords: Aqueous normal phase; HPLC; Ionic liquid determination; Mixed-mode retention; Rapid separation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acetonitriles / chemistry
  • Buffers
  • Cations / chemistry
  • Chemistry Techniques, Analytical / methods*
  • Chromatography, Liquid*
  • Hydrophobic and Hydrophilic Interactions
  • Ionic Liquids / analysis*
  • Silicon Dioxide / chemistry
  • Temperature
  • Water / chemistry

Substances

  • Acetonitriles
  • Buffers
  • Cations
  • Ionic Liquids
  • Water
  • Silicon Dioxide
  • acetonitrile