Browsing by Author "Saowapon, Matthew Tatchai"

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    Novel Chromatographic Separations Through Dynamically Controlled Stationary Phase Removal
    (2019-05-02) Saowapon, Matthew Tatchai; Thurbide, Kevin B.; Kimura-Hara, Susana; Shi, Yujun; Thangadurai, Venkataraman
    This thesis explores the removal of a water stationary phase as a novel means of tuning separations in supercritical fluid chromatography. The first area investigated is the systematic dehydration of the stationary phase to achieve gradient style elutions. Here, the gradual removal of the water stationary phase is used to maintain the separation of early eluting analytes while speeding up the elution of well retained analytes. The dehydration gradient allows analyses to be performed more rapidly and is shown to reproducibly and predictably adjust analyte retention times. Additionally, the removal of the stationary phase is observed to focus the peaks of well retained compounds, making them sharper and easier to quantify. Together, these effects are used to facilitate the analysis of several polar and ionizable compounds, which are typically well retained in supercritical fluid chromatography and elute with poor peak shape. Thus, the dehydration gradient represents an attractive new method with several advantages over conventional approaches that use toxic organic modifiers or pressure gradients for similar analyses. Next, the use of axial thermal gradients to control the hydration and dehydration of the water stationary phase is explored. Here, the temperature is varied along the length of the column so that the stationary phase can be maintained on a section of the column, while other areas are left uncoated. Therefore, the effective column length can be changed by adjusting the thermal gradient. The length of the column is shown to respond rapidly to changes in the axial thermal gradient and, once a length has been established, retention times are highly reproducible. This approach to tuning column length allows the resolution between analytes and the total analysis time to easily be optimized to meet the needs of different separations. Notably, it is much faster, simpler and more affordable than the conventional method of switching between columns of different lengths. Thus, the control of column length through the partial removal of the water stationary phase presents a more flexible and convenient means of tuning chromatographic separations.