Overview
This post explains how reverse electroosmotic flow (EOF) differs from normal EOF in capillary electrophoresis (CE). Under normal polarity, EOF pushes the bulk solution toward the cathode, sweeping most analytes—regardless of charge—toward the detector. With reversed polarity, EOF moves toward the anode, dramatically altering migration patterns. Anions migrate to the anode and are swept past the detector efficiently, while cations migrate toward the cathode and may reach the detector only very slowly, if at all. Neutral species migrate solely at the EOF velocity and therefore remain co‑migrating and inseparable in both normal and reversed modes.
Understanding these differences is essential when choosing operating polarity for CE separations.
Reverse EOF Differs from Normal EOF in Capillary Electrophoresis
In reverse electroosmotic flow (EOF), the instrument is operated under reverse polarity. As a result, the EOF moves toward the anode, the opposite direction from normal CE operation.
Under these conditions:
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Negatively charged species (anions) will migrate toward the anode and will be carried past the detector by the reversed EOF.
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Positively charged species (cations) will migrate toward the cathode. Because the EOF is moving in the opposite direction, cations may reach the detector very slowly or may not reach it at all, depending on their electrophoretic mobility.
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Neutral species will migrate at the speed of the EOF in either polarity mode. Because they have no charge, they will not separate from each other and will co‑migrate.
Understanding these migration behaviors is essential for selecting the appropriate polarity mode for a particular CE separation.
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