Published:Journal of Chromatographic Science,
ISSN 0021-9665 Volume
45, Number 9, October 2007, pp. 578-586
Evaluation of Polymeric Methacrylate-based Monoliths
in Capillary Electrochromatography for their Potential to
Separate Pharmaceutical Compounds
Debby Mangelings[1], Indiana Tanret[1], Vanessa
Meert[1], Sebastiaan Eeltink[2], Peter J. Schoenmakers[2],Wim
Th. Kok[2], and Yvan Vander Heyden[1],
[1]Department of Analytical Chemistry
and Pharmaceutical Technology, Vrije Universiteit Brussel-VUB,
Laarbeeklaan 103, B-1090 Brussels, Belgium and
[2]Polymer-Analysis
Group, Department of Chemical Engineering, University of Amsterdam,
Nieuwe Achtergracht 166, 1018WV Amsterdam, The Netherlands
Polymeric methacrylate-based monoliths are evaluated
in capillary electrochromatography (CEC) and pressurized capillary
electrochromatography (p-CEC) for their potential in pharmaceutical
analysis. Using a given polymerization mixture as a basis for
the monolith synthesis, different mobile phase pH at constant
organic modifier concentrations are tested in both CEC and p-CEC.
The test set consists of basic, acidic, amphoteric, and neutral
compounds, which are mainly pharmaceuticals. Because of the mainly
hydrophobic character of the stationary phase, the interactions
are largest when the compounds appear in an uncharged state,
but some ion-exchange phenomena with negatively charged compounds
can also be observed. In CEC, acidic substances are most retained
at low pH. For amphoteric and neutral compounds, no preference
regarding analyzing pH can be derived from these experiments.
For basics, a high pH is chosen, but a reduced solvent strength
is needed to enhance the retention of these compounds. The retention
mechanism in p-CEC can also be assigned to both hydrophobic and
ionic interactions. For acidic, amphoteric, and neutral compounds,
acceptable retention is seen. For the basic compounds, the retention
with a mobile phase containing 50% organic modifier is low, as
in CEC. However, when the organic modifier content in the mobile
phase is decreased, retention increases and the selectivity of
the stationary phase is more pronounced. This mode of operation
presents a possibility for separating some test mixtures, thus
some potential for pharmaceutical analysis is seen. More efforts
are needed to obtain higher efficiencies and better peak shapes,
which might be solved by a further optimization of both the stationary
phase synthesis and the mobile phase composition.
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