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39016-B7
Porous Polymer Monoliths for Capillary Electrochromatography
Michelle Marie Bushey, Trinity University
We have investigated a variety of porous polymer
monoliths for use in capillary electrochromatography
in the butyl and lauryl acrylate
family. Our test analytes typically include a homologous
series of toluene through 1-phenyl nonane and
selected polycyclic aromatic hydrocarbons. We have also investigated using our
polymer monoliths for separations of charged species such as anilines, a series
of benzoic acids, and biological samples such as plant extracts. Our investigations
have ranged broadly over the course of this grant. In our system, the polymer
monolith is cast in situ in fused
silica capillaries. Heat initiates the polymerization and the resulting
monoliths are conductive as cast. In previous grant years, our investigations have
involved the following: establishing the reproducibility of separation results
on one column and from column-to-column, exploring the longevity of individual
columns, obtaining selectivity information from plots of retention factor
versus carbon number for several polymer types, examining van Deemter curves for analytes with
a range of retention factors for several polymer types, examining van Deemter curves as a function of temperature. We have also examined
retention as a function of the amount of organic solvent in the mobile phase,
and determined the enthalpy partitioning. Mixed polymers have been
investigated. These systems have relatively small amounts of tert-butyl, hexyl, or lauryl acrylates substituted for some
of the butyl acrylate monomer. In the case of lauryl acrylate, polymers ranging
from 100% butyl to 100% lauryl, as well as
intermediate compositions have been investigated. We have determined the
obstruction factor of 100% lauryl acrylate
columns to be in the range of 0.70-0.73. We have modeled the van Deemter curves to obtain estimates of the A, B, and C term
for lauryl acrylate based
columns. Some of this material is described in our two publications,
other material is in preparation for publication.Most recently we have broadened our investigations
to some areas that have proved to be a bit riskier. In one study we attempted
to use the porous polymer monoliths as plug or frit material for capillaries
which we then proceeded to pack with commercially available C18 particles.
These short plugs did not prove to be very durable and their lifetime was far
too short to pursue this study. We have also attempted to use these columns
with pressure driven flow to compare the performance to that obtained with electroosmotic driven flow. Although this would be a very
informative study, our current instrumentation compromises the results that are
obtained with pressure driven flow and so a reasonable comparison cannot be
obtained. We may return to this system at a later date when an instrument
upgrade is available. We have recently returned to mixed monomer systems
and investigated porous polymers containing both lauryl
acrylate and benzyl methacrylate
monomers. Several compositions have been studied but replacement of 10% (mole) the
lauryl acrylate monomer
with benzyl methacrylate has proved to be an
interesting mixture that performs well. Retention factors for three selected analytes compare as follows for three column types:Monomer Retention factor for: fluorene chrysene benzo[a]pyrene100%
butyl acrylate 1.63 4.16 6.39100%
lauryl acrylate 2.78 7.05 10.710%
benzyl methacrylate/90%
lauryl acrylate 2.84 9.52 18.0
The
retention of the larger PAH analytes increases
dramatically with the mixed polymer. The enthalpies of partitioning for the mixed
polymer are also more negative for each of these test analytes
as compared to the 100% butyl acrylate polymer. We
are completing studies on the 100% lauryl acrylate column. The mixed polymer has minimum H values
that are comparable to our other columns and are in the range of 8 micrometers.
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