Investigation Of Novel Stationary Phase For Capillary Gas Chromatography And Solid-phase Microextraction Fiber

Gas chromatography (GC) stationary phase and solid phase microextraction (SPME),two core techniques embraced in capillary GC are the focuses of analytical chemistry. Thecore part of SPME technique is the SPME fiber. In recent years, varieties of SPME fibershave been developed. However the SPME fbers which have been reported inherentlypossess the following disadvantages such as tedious and time-consuming coating process,easy stripping of the coated layers, short lifetime, poor stability at high temperature and inorganic solvents and having difficulty in the large scale production. In the past decade, GCstationary phase have attracted considerable attention. Applicable GC stationary phaseswhich have been reported still have some shortcomings in thermal stability andchromatographic selectivity. To overcome the limits of the above-mentioned shortcomings,this dissertation focuses on two aspects: the preparation of SPME fiber and thedevelopment of highly selective GC stationary phases, which include the followingsections:1. Graphene is an ideal SPME material due to its excellent thermal stability, specialstructure and good adsorption properties. In this work, monolithic graphene fbers with theexpected features were prepared via a facile one-step dimension-confned hydrothermalstrategy using a sealed glass pipeline as a reactor instead of a conventionally-usedTefon-lined autoclave. The proposed strategy can fabricate a uniform graphene fber aslong as several meters or more at a time. Compared with the conventional methods forSPME fbers fabrication, the strategy in this work is simple to enforce, easily adjustable infber dimensions, producible at a large scale and can be a solution to overcome thedrawbacks of the currently-used SPME fbers. Moreover, the fiber has a3D cross-linkingporous structure of graphene sheets densely stacking, which provids high specifc surfacearea favorable for extraction effciency.2. Coupled to capillary GC, the extraction selectivity of the monolithic graphene fberis investigated. Three types of organic compounds, namely PAHs, PAEs and n-alkanes, were used for the purpose and the results show that the monolithic graphene fbers achievedhigher extraction effciencies for aromatics, especially for PAHs, thanks to π-π stackinginteraction and hydrophobic effect. Under the optimized extraction conditions, the graphenefbers coupled to GC analysis was used for the quantitation of seven PAHs in aqueoussamples. Compared with previous reports for the analysis of the same analytes, theproposed method is of lower limits of detection and wider linear ranges. The proposedmethod also can be used for analysis of PAHs in environmental water samples, achievingsatisfactory results.3. Graphene possesses unique structure and properties as well as excellent thermalstability that appear to be an ideal candidate as stationary phase for capillary GCseparations. However, its poor solubility in organic solvents imposes great difficulties inusing it for the intended purpose. In this work, graphene was statically coated onto fusedsilica capillary columns using suspension. The as-prepared graphene column was evaluatedin terms of polarity, column efficiency and thermal stability. The results of separationperformance show that the graphene stationary phases exhibit excellent selectivity for awide range of analytes including alcohols, alkanes, esters, aldehydes, BTEX, PAHs, PAEset al. This may partially stem from their specific interactions such as hydrophobicinteractions,-interactions, electron-donor–acceptor (EDA) effect and H-bonding owingto the unique structural shape. Especially the-interactions play a critical role on theselectivity of stationary phase, and it can be attributed to better separation ability andselectivity than HP-5MS in PAEs.The thermal stability of the columns was investigated byGC separations of different analytes, showing excellent resolution ability at least up to260℃. This work proves that graphene has a promising future as a new generation GCstationary phases.4. Calix[4]pyrroles offer a great potential as stationary phases for gas chromatography(GC) due to their unique structures and physicochemical properties, but no reports areavailable for this purpose up to now. In this work, two calix[4]pyrroles, namelymeso-tetracyclohexylcalix[4]pyrrole (THCP) and meso-octamethylcalix[4]pyrrole (OMCP), were statically coated onto fused silica capillary columns. Calix[4]pyrroles stationaryphases show unique separation performance for a wide range of analytes. The THCPstationary phase exhibits high selectivity toward analytes from nonpolar to polar as well asnice peak shapes for analytes that prone to severe peak tailing in GC analysis such asalcohols, aldehydes while the OMCP shows preferential selectivity for nonpolar analytessuch as hexane isomers. Moreover, the THCP stationary phase exhibits outstandingselectivity toward the positional isomers of dimethylanilines, methylanilines, nitroanilinesand benzenediols and much better resolution for most of the analytes than the HP-5MScolumn that failed to separate some of them. The thermal stability of the columns wasinvestigated by GC separations of different analytes, showing excellent resolution ability atleast up to260℃. All the ideal performances above demonstrates that calix[4]pyrroles arehighly selective GC stationary phases, which may partially stem from specific shapeselectivity in combination with other interactions such as dispersion, dipole-dipole,H-bonding and-interactions owing to the unique structural shape and flexibility ofcalix[4]pyrroles.