Development of ionic liquid-based stationary phases for gas chromatographic separations

Ionic liquids (ILs) are a class of molten salts that fulfill many of the requirements of GC stationary phases including negligible vapor pressure, high thermal stability, wide liquid range, and tunable viscosity. The chemical structure of ILs can be tailored to exhibit a wide range of solvation properties for the selective separation of various types of analytes. The work presented in this dissertation is focused on the development of various types of IL-based stationary phases with unique selectivities and high thermal stabilities to further expand the capability of one-dimensional gas chromatography (1D-GC) and comprehensive two-dimensional (2D) gas chromatography (GC × GC). A series of ILs and zwitterionic liquids (ZILs) containing sulfonate functional groups were employed as GC stationary phases to separate volatile carboxylic acids (VCAs). The highly polar and acidic nature of VCAs significantly limits the number of currently available GC stationary phases, which are all largely based on acid-modified polyethylene glycol. In this study, it is shown that this class of ZILs exhibit strong retention of VCAs with excellent peak symmetry. Unique chromatographic selectivity toward VCAs is also demonstrated by tuning the structural features of the ZILs. The solvation properties of the three ZILs and their structural homologues were characterized using the Abraham solvation parameter model. The solvation properties of eight room temperature ILs containing various transition and rare earth metal centers (e.g., Mn(II), Co(II), Ni(II), Nd(III), Gd(III), and Dy(III)) are characterized using the Abraham solvation parameter model. These metal-containing ILs (MCILs) consist of the trihexyl(tetradecyl)phosphonium cation and functionalized acetylacetonate ligands chelated to various metals. Depending on the metal center and chelating ligand, significant differences in solvation properties were observed. MCILs containing Ni(II) and Mn(II) metal centers exhibited higher retention factors and higher peak asymmetry factors for amines (e.g., aniline and pyridine). Alcohols (e.g., phenol, 1-octanol, and 1-decanol) were strongly retained on the MCIL stationary phase containing Mn(II) and Dy(III) metal centers. Silver ion or argentation chromatography utilizes stationary phases containing silver ions for the separation of unsaturated compounds. In this study, a mixed-ligand silver-based ionic liquid (IL) was evaluated for the first time as a gas chromatographic (GC) stationary phase for the separation of light olefin/paraffin mixtures. The selectivity of the stationary phase toward olefins can be tuned by adjusting the ratio of silver ion and the mixed ligands. In addition, a stationary phase containing silver(I) ions was successfully designed and employed as a second dimension column using comprehensive two dimensional gas chromatography (GC × GC) for the separation of mixtures containing alkynes, dienes, terpenes, esters, aldehydes, and ketones. Compared to a widely used non-polar and polar column set, the silver-based column exhibited superior performance by providing better chromatographic resolution of co-eluted compounds. Lipidic ILs possessing long alkyl chains as well as low melting points have the potential to provide unique selectivity as well as wide operating ranges. A total of eleven lipidic ILs containing various structural features (i.e., double bonds, linear thioether chains, and cyclopropanyl groups) were examined as stationary phases in comprehensive two-dimensional gas chromatography (GC × GC) for the separation of nonpolar analytes in kerosene. Compared to a homologous series of ILs containing saturated side chains, lipidic ILs exhibit improved selectivity toward the aliphatic hydrocarbons in kerosene. The palmitoleyl IL provided the highest selectivity compared to all other lipidic ILs as well as the commercial SUPELCOWAX10 column. This study provides the first comprehensive examination into the relation between lipidic IL structure and the resulting solvation characteristics