Ionic Liquids (ILs) have been studied as an interesting class of compounds in chromatographic separation and sample preparation science. ILs are commonly introduced as ionic salts comprised of unsymmetrical organic cations paired with organic or inorganic anions that possess melting points at or below 100 °C. Polymeric ionic liquids (PILs) are synthetic polymers synthesized from IL monomers containing polymerizable functional groups. These materials exhibit numerous beneficial properties, including high thermal stability, wide viscosity range, negligible vapor pressure, and multiple solvation interactions with various analytes, which makes them influential compounds in separation science. This thesis describes the application of PILs and ILs in solid-phase microextraction (SPME) as sorbent coatings as well as stationary phases in gas chromatography and multidimensional gas chromatography (MDGC).
SPME has been adopted as a simple and cost-effective pre-concentration technique within the field of sample preparation. In an attempt to enhance analytical performance of target analytes, including selectivity, sensitivity, and limits of detection (LODs) in the analysis of complex matrixes, ILs and PILs have been widely exploited as SPME sorbent coatings. Over a decade, ILs and PILs have proven to be excellent candidates for SPME sorbent coatings. Overall, structural tailoring of ILs and PILs results in suitable physicochemical properties which gives scientists an opportunity to generate tunable selectivity mechanisms towards various target analytes.
Comprehensive two-dimensional gas chromatography (GC×GC), developed by Liu and Phillips, is a powerful technique used to separate analytes in complex samples. In this technique, a sample is vaporized and subjected to a combination of two chemically different GC stationary phases with different selectivities to obtain higher peak capacity through unique interactions with the sample. Hence, GC×GC offers higher separation power compared to one-dimensional gas chromatography (1D-GC). A typical column sequence involves polysiloxane followed by polyethylene glycol-based stationary phases to allow separation of the analytes based on vapor pressure and polarity, respectively. Currently, most separations of complex matrices are done by these traditional phases. However, their solvation capabilities are redundant. During the last decade, ILs have been acknowledged as promising alternative stationary phases in 1D-GC and GC×GC. ILs can be designed to possess ideal physicochemical properties for GC stationary phases. These properties include broad liquid range, high thermal stability, low background bleed, and multiple solvation interactions. When compared to traditional phases, commercial IL-based GC columns allow unique chromatographic separation of mid-polar to polar analytes in samples. However, they exhibit poor retention of non-polar analytes such as aliphatic hydrocarbons. Hence, designing IL-based stationary phases capable of retaining non-polar analytes is highly demanded, as it would expand IL phase versatility to include complex petrochemical separations.
Chapter 1 explains a brief introduction to the fundamental of SPME and the application of ILs and PILs as SPME sorbent coatings.
Chapter 2 focuses on the development of cross-linked PILs as SPME sorbent coatings for high performance liquid chromatography (HPLC). Since the majority of the investigations related to the application of ILs and PILs as SPME sorbent coatings have been focused upon a method coupled with gas chromatography (GC) analysis. For the first time, these materials were fabricated as highly selective and robust sorbent coatings for liquid chromatographic (LC) applications.
Chapter 3 introduces the fundamentals of the MDGC technique and reviews recent applications of IL stationary phases in the field of 1D-GC and MDGC.
The last chapter of this thesis describes tuning the selectivity of IL-based stationary phases in order to enhance separation of aliphatic hydrocarbons from kerosene samples using GC×GC. The structurally tuned trihexyl(tetradecyl)phosphonium tetrachloroferrate ([P66614][FeCl4]) IL stationary phase, exhibited improved separation of aliphatic hydrocarbons by GC × GC compared to the examined commercial columns.