Increasing Retention through Ordered Mesoporosity:
Re-enabeling WCOT Capillary Electrochromatography
Ide, Matthias*(1); Desmet, Seppe (2); Lynen, Frédéric(2); Sandra, Pat(2); Van Der Voort, Pascal(1)
(1) Department of Inorganic and Physical Chemistry, COMOC, Ghent University.
(2) Department of Organic Chemistry, Laboratory of Separation Sciences, Ghent University.
Krijgslaan 281 (S3(1) & S4bis(2)) B-9000 Ghent, Belgium.
As has been attested long ago in capillary gas chromatograph the open tubular column format
provides significantly improved analytical performance compared to the packed format
providing diffusional distances are sufficiently small to ensure fast mass transfer between the
mobile and the stationary phase and minimal plate heights. The transfer to a liquid mobile phase
and the concomitant drop in diffusion coefficients of about 3 orders of magnitude therefore
requires the use of narrower columns (~2-20 µm ID) to obtain significant plate numbers. This
generally results in columns with exceedingly low sample capacities with subsequent poor
detection sensitivities, low solute retention or very poor efficiencies. In this work, in order to
address above issues, the high plate numbers achievable in capillary electrochromatography are
combined with the use of ordered mesoporous stationary phases as a wall coating. In accordance
with prior work, where mesoporous silica particles were used in packed column HPLC [1], an
increased retention could be ascertained with this type of materials. The benefits of using
ordered mesopores on the sample capacity and solute retention while ensuring fast mass transfer
in CEC are studied here. Typical surface areas of these type of powders are around 1000 m 2/g,
with pore sizes which can be obtained between 2 and 15 nm (with a very narrow pore size
distribution ~0.2nm). This contribution shows preliminary CEC work on open tubular capillaries
with an internal diameter of 50 µm. The porous layer was 600 nm in thickness, depicted a
uniform pore system with a pore size of 4 nm in diameter and exhibited enough retention,
sample capacity, theoretical plates and
resolution to perform the separation of standard
solutes evocative of what can currently be
achieved in reversed phase HPLC. The results
allow for promising projections towards the
development of comparable columns with
narrower internal diameters. The capillary was
compared with a non-coated column to illustrate
the retentive effect. Mixtures of phenones and
parabens were baseline separated on the open
tubular column in this way.
[1] Ide, M.; Wallaert, E.; Van Driessche, I.; Lynen, F.; Sandra, P.; Van Der Voort, P.;
Microporous and mesoporous materials 2011, 142, 282-291.