Ion Chromatography of Tri-Substituted Imidazolium Ionic Liquid Cations: Method and Application for Octanol–Water Partition Coefficient (K_OW) Determination

Abstract

A method was developed for simultaneous determination of four trisubstituted imidazolium ionic liquid cations (1-ethyl-2,3-dimethylimidazolium, 1-propyl-2,3-dimethylimidazolium, 1-butyl-2,3-dimethylimidazolium, 1-pentyl-2,3-dimethylimidazolium) by ion chromatography using a carboxylic acid cation exchanger bonded to a silica-based column and direct (nonsuppressed) conductivity detection. The effects of the type of eluents, organic acid concentration, acetonitrile volume fraction, and column temperature on the cations retention were investigated. The optimal conditions for the method were 5 mmol L⁻¹ methanesulfonic acid +10% acetonitrile as an eluent, 1.0 mL min⁻¹ flow rate, and a column temperature of 30°C. The detection limit (S/N = 3) were 0.82–2.39 mg L⁻¹ for the cations. The method was validated, accurate, and reproducible. This method was successfully applied to determine trisubstituted imidazolium ionic liquid cations in spiked tap water. The octanol–water partition coefficients (K_ow) of these four trisubstituted imidazole substances were also reported in this study.

Keywords:

• cation exchange
• conductivity detection
• ion chromatography
• ionic liquids
• octanol–water partition coefficient
• trisubstituted imidazolium cations