Ionic liquids and deep eutectic solvents as gas chromatographic stationary phases for separation and characterization

Recent developments have been made to improve the separation of complex molecules. The following chapters describe the optimization and characterization of two unique stationary phases: ionic liquids (ILs) and deep eutectic solvents (DESs). The versatility of ILs have expanded over the years and one of their most interesting applications are their use as gas chromatographic stationary phases. As shown in literature, they can either act as a nonpolar or polar phase depending on the analytes of interest. By manipulating the structure of the ILs, the molecular interactions exhibited between the stationary phase and probes can be tailored for favorable interactions. Imidazolium and phosphonium ILs are commonly used as cations with a variety of different counter anions. One of the major drawbacks of ILs is their low thermal stabilities compared to many other commercial phases. The first study addresses this by incorporating phenyl substituents within the cation to reduce the probability of decomposition pathways. High boiling point analytes such as polycyclic aromatic hydrocarbons (PAHs) and polycyclic biphenyls (PCBs) were separated due to their capability of undergoing π-π interactions with the stationary phase. The second study is also relating to molecular interactions but instead of an IL-based stationary phase, DESs were the materials of interest. Using multiple combinations of hydrogen bond acceptors and donors to form the DESs, in depth molecular insight was gained using inverse gas chromatography (GC). The Abraham solvation parameter model was used to characterize the deep eutectic based stationary phases. As stationary phases, both materials displayed unique interactions where the ILs showed enhanced π-π interactions while the DESs displayed increased hydrogen bond basicity compared to traditional ILs.