Ph.D. in Analytical
Chemistry,
Speed and Efficiency in
Supercritical Fluid Chromatography.
Improvements
in the speed and efficiency of chromatographic separations are important goals
for many chromatographers. Supercritical
fluid chromatography (SFC) holds inherent advantages over liquid chromatography
in this regard due to the favorable transport properties of supercritical fluids, but their high compressibility
can lead to nonuniform mobile phase conditions in packed-column SFC, resulting
in complex behavior in terms of retention and efficiency. Under certain operating conditions, large
pressure drops can result in significant loss of efficiency and shifts in
retention. Recent research in my
laboratory has shown that axial and radial temperature gradients associated
with large pressure drops are primary causes of these phenomena. Our investigations into the fundamental
processes controlling retention and efficiency in SFC have lead to the
development of new approaches to designing SFC instrumentation and
methodology. For example, we have
demonstrated that effective elimination of radial temperature gradients with
thermal insulation results in significant improvements in efficiency and
analysis times for some experimental conditions. We have also demonstrated that the diameter
of a column operated without thermal insulation can have a significant effect
on efficiency. Instrumentation for these
studies includes two SFC systems, including one specifically designed for
studies of retention and efficiency, as well as modern computerized data
acquisition and analysis tools.
A
long-term goal of this research is to provide a firm experimental basis for the
development of a theoretical model for retention and efficiency in
chromatography with highly compressible mobile phases, with particular emphasis
on SFC. Such a model would be extremely
useful for the design of SFC separations where optimum speed and efficiency are
required. To this end, much of the
research involves experiments with simple solute systems, such as elution of n-alkanes with pure CO2 from
packed columns. Recent efforts also
include application of approaches suggested by our research on these model
systems to established SFC methods, such as the analysis of petroleum and
pharmaceuticals, to yield real improvements in speed and efficiency of those
methods.
Xu, Wensheng; Peterson, Dawn
L.; Schroden, Jonathan J.; Poe, Donald P., J.
Chromatography, 2005, 1078, 162-170.
Efficiency for unretained
solutes in packed column supercritical fluid chromatography: II. Experimental results for elution of
methane using large pressure drops.
D. P. Poe, J. Chromatography, 2005, 1078, 152-161.
Efficiency for unretained
solutes in packed column supercritical fluid chromatography: I. Theory for isothermal conditions and
correction factors for carbon dioxide
D. P. Poe, J. Chromatography, 1997, 785, 129-134.
Use of a thermally insulated
column for improved speed, efficiency and resolution in packed column
supercritical fluid chromatography.
D. P. Poe, P. J. Marquis, T.
Tomlinson, J. Dohm and J. He, J.
Chromatography, 1997, 785, 135-148.
A supercritical fluid
chromatograph for studies of retention and efficiency.
D. P. Poe, J. Chromatography, 1992, 625, 299-309.
Model for Retention and
Efficiency in Open Tubular Supercritical Fluid Chromatography.