Helmueller, Shawn2017-11-272017-11-272015-12https://hdl.handle.net/11299/191278University of Minnesota M.S. thesis. December 2015. Major: Chemistry. Advisor: Donald Poe. 1 computer file (PDF); viii, 56 pages.A well-known problem in supercritical fluid chromatography is the drastic decrease in chromatographic performance at temperatures above 40 C and outlet pressures below 120 bar. This phenomenon has been attributed to isenthalpic expansion and cooling of the mobile phase and poor heat transport under these temperatures and pressures. If the temperature of the fluid does not match the temperature of the column surroundings, a radial temperature gradient forms due to heat transfer between the column and the thermal environment surrounding the column. This radial temperature gradient causes a radial fluid density profile inside the column and radial distributions in important solute parameters such as diffusion coefficients and retention factors. This ultimately results in solute band broadening and a decrease in band resolution. For this reason, method development and method transfer can be complex and the pressure-temperature region near the critical point of the mobile phase is routinely avoided. A novel dual-zone still-air column heater has been developed that can be set to match the adiabatic temperature profile of the fluid inside the column as predicted by the equation of state for the fluid. As a result, the efficiency loss associated with the formation of radial temperature gradients can be largely avoided in packed analytical scale columns. For example at 60 C with 5% methanol modifier and a flow rate of 3mL/min, a 250mm x 4.6mm x 5μm Kinetex (Coreshell) C18 column began to lose efficiency (>25% decrease in the number of theoretical plates) at outlet pressures below 140 bar in a forced air (non-adiabatic) thermal environment. The minimum outlet pressure was decreased to 120 bar in a traditional isothermal still air (near-adiabatic) column heater and to 100 bar in the new near-ideal adiabatic still-air heater before observing excess efficiency loss. Decreasing the minimum outlet pressure from 140 bar to 120 bar and 100 bar resulted in a corresponding increase in the retention factor for n-octadecylbenzene from k=3.6 to k=5.5 and k=16.9 respectively. Simulations for the relative effect of axial gradients in the retention factor on the apparent plate height suggest that in a perfectly adiabatic environment, negligible efficiency loss should be observed. As a result, efficient separations can be carried out at higher temperatures and lower outlet pressures compared to traditional column thermostatting techniques by operating the SFC column adiabatically.enAdiabatic SFCEfficiencyLow Outlet PressurePacked Column SFCSupercritical Fluid ChromatographyTemperature ControlThesis or Dissertation