New Dicationic Quinolinium Ionic Liquids for Capillary Gas Chromatography

Highly polar capillary columns with liquid stationary phases (LSPs) based on dicationic quinolinium ionic liquids (ILs) are studied. These ILs are characterized by high polarity and strong dipole–dipole and π–π interactions in a linear free energy relationship model, and can separate complex mixtures (containing aromatic hydrocarbons, phenols, catechols, and hydroquinones) that are problematic for columns with conventional LSPs. It is shown that the high thermal stability of dicationic quinolinium ILs allows to perform chromatographic separation up to a temperature of at least 300°C, which is impossible for any conventional polar and highly polar LSPs. The thermal stability of the studied LSPs is virtually independent of the structure of a dicationic quinolinium IL and the length of an alkyl bridge.