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Published:Journal of Chromatographic Science,
ISSN 0021-9665 Volume
47, Number 6, July 2009, pp. 452-458
Surface Diffusion in C18-Silica Monolithic
Stationary Phase
Kanji Miyabe
Graduate School of Science and Engineering for Research, University
of Toyama, 3190, Gofuku, Toyama 930-8555, Japan
A peak parking–moment analysis method was
used for the measurement of surface diffusion coefficient (Ds)
in a reversed-phase liquid chromatography (RPLC) system consisting
of a C18-silica monolithic column and a mixture of
methanol and water (70/30, v/v). The Ds values
experimentally measured were analyzed by considering the correlation
with corresponding values of molecular diffusivity (Dm)
and the retention equilibrium constant (Ka).
It seems that the correlation between Ds/Dm and Ka is
represented by a single curve irrespective of the RPLC conditions
of temperature and the type of sample compounds. The increase
in Ka is accompanied
with the decrease in Ds/Dm.
Oppositely, the ratio of Ds/Dm increases
and approaches around unity when Ka infinitely
decreases. It seems that surface diffusion is originally similar
to molecular diffusion and that it is restricted due to the sample
retention. These characteristics of surface diffusion are the
same between the C18-silica monolithic stationary
phase and the conventional C18-silica gel particles.
In addition, the values of Ka and Ds
are also comparable between them. It is concluded that basic
properties concerning the retention equilibrium and surface diffusion
of the C18-silica monolithic stationary phase are
almost the same as those of the conventional C18-silica
gel particles in spite of the difference between their structural
characteristics.
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