John G. Dorsey
Research Group
Fundamentals of Chromatography
Mike Bair
BS in Chemistry (2003) Pennsylvania State University
Office: 440 DLC
Phone: 644-7799
Email:
MBair@chem.fsu.edu
Silica-based
LC Stationary Phase Synthesis
Organically-modified
silica-based materials remain the most
widely used stationary phase for reversed-phase liquid chromatography
applications. However, these materials are limited in several respects.
For
one, they are stable only at low to moderate temperatures and within a
narrow
pH range. Also, current organic modification techniques are inherently
incomplete, leaving high-energy adsorption sites known as silanols on
the
surface, yielding a mixed-mode retention mechanism that results in
reduced
efficiency, particularly for basic analytes. Residual silanols also
lead to
increased rate of dissolution of the silica substrate at high pH and
temperature. Therefore, new methods for modifying the silica surface to
improve
stability and efficiency are always being explored.
In the
John Dorsey research group, work is being done to
characterize a novel silica-based stationary phase material called the
“SiC-1”
phase (see: Sunseri, J. D., Dorsey, J. G., et. al. Langmuir.
19, (2003), 8608-8610). This material
differs from all other available bonded phases in two respects. First,
organic
ligands are bonded directly to silicon atoms on the silica surface,
thus avoiding
hydrolytically unstable siloxane linkages typically found in silanized
bonded
phases, which in turn improves low pH stability and diminishes loss of
the
phase modification or “column bleed.” Secondly, complete conversion of
silanols
to methyl ligands is possible, yielding a phase with no residual
silanols. This
not only improves stability at high temperatures and pH, but at the
same time
yields an energetically homogenous sorptive surface that interacts with
analytes via a single-mode solvophobic adsorption mechanism. By
studying this
material we hope to shed some light on the role that the silica
substrate plays
in the chromatographic process, how silanols affect retention and
stability of
bonded stationary phase materials, and lastly to characterize the
single-mode
adsorption mechanism and how it applies to the chromatographic process
in
general.
There are
many other projects in the works that look to better
understand and improve the performance of silica-based stationary
phases. Many
thanks to Dr. Al Stiegman in the Inorganic Chemistry division for his
close
collaboration on these projects.
