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Published on: February 23, 2017
Concentration polarization and nonequilibrium electroosmotic slip in hierarchical monolithic structures
Ivo Nischang1, Alexandra Höltzel, Andreas Seidel-Morgenstern
1Institut für Verfahrenstechnik, Otto-von-Guericke-Universität, Magdeburg, Germany.
Electrophoresis
|January 26, 2008
Summary
Concentration polarization (CP) in monolithic fixed beds influences electrohydrodynamics in capillary electrophoresis. Changes in ionic strength and electrical field strength control CP zones and electroosmotic flow (EOF) velocities.
Area of Science:
- Analytical Chemistry
- Electrochemistry
- Separation Science
Background:
- Concentration polarization (CP) significantly impacts electrical-field-assisted separation techniques.
- Hierarchically structured monolithic fixed beds are utilized as stationary phases in capillary electrochromatography (CEC).
- Understanding CP in these complex structures is crucial for optimizing separation efficiency.
Purpose of the Study:
- To illustrate the appearance and electrohydrodynamic consequences of CP in monolithic fixed beds.
- To investigate the influence of ionic strength and electrical field strength on CP.
- To correlate CP dynamics with nonlinear electroosmotic flow (EOF) and buffer properties.
Main Methods:
- Utilized silica-based monoliths with bimodal pore size distribution in a capillary format.
- Employed quantitative confocal laser scanning microscopy to resolve CP at the local skeleton scale.
- Analyzed macroscopic EOF velocities and correlated them with CP phenomena and buffer properties (pH).
Main Results:
- Observed depleted and enriched CP zones at anodic and cathodic interfaces of cation-selective mesoporous skeletons.
- Demonstrated that CP extent is governed by fluid phase ionic strength and applied electrical field strength.
- Correlated the transition from intraskeleton to interskeleton transport with the onset of nonlinear EOF velocities, explained by nonequilibrium electroosmotic slip.
Conclusions:
- CP significantly influences transport phenomena and EOF in monolithic fixed beds.
- Nonlinear electrokinetics can be tuned by buffer properties, particularly pH, affecting surface charge density and selectivity.
- Differences in CP dynamics between monolithic and particulate fixed beds are attributed to their distinct hierarchical morphologies.
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