New Stationary Ionic Liquid Phases with Quinolinium Cations for Capillary Gas Chromatography

Abstract

The work provides the study of quinolinium ionic liquids (ILs)—a new class of stationary phases for capillary gas chromatography (GC). Quinolinium ILs were shown to have new attractive properties. They are not only highly polar, but also very selective for aromatic compounds and oxygenates. Depending on the substituents in the quinolinium ring, the studied ILs possess polarity numbers from 64 to 99, so they are polar and strongly polar. By the variation of the substituent and its position, changes in the prevailing types of interactions with analytes are observed. It is worth noting that Abraham’s constants for the quinolinium phases are significantly different from the previously known imidazolium and pyridinium ionic liquids (ILs) that cause significant variations in their selectivity. The most significant differences are observed in the π–π interactions and hydrogen bond acidity parameters. The investigation of background mass spectra for quinolinium ILs showed the most intense signals related to peaks at m/z 69 and 143 belonging to [CF3]+ and quinolinium ring fragments. The most thermostable ILs are N-propyl-6-methylqionoinium and bis(6-methylquinolinium)hexane that are stable up to 300 °C. With regard to the possible use of quinolinium ILs, apart from the separation of polar substances, it is expected that they will find applications in two-dimensional chromatography for the separation of complex mixtures compose of compounds that differ substantially in their properties. The applications of the columns for the determination of aromatic hydrocarbons in gasoline and phenolic compounds in pyrolysis biodiesel are demonstrated.