Capillary electrophoresis is best associated with which separation mechanism?

• A. Endosmosis
• B. Iontophoresis
• C. Isoelectric focusing
• D. Electroosmotic flow separation

Answer: (D)

Capillary electrophoresis separates ions primarily through the movement of the entire liquid in the capillary, known as electroosmotic flow. The charged capillary walls impart a net flow of solvent under the electric field, which drags all species toward the detector. Each analyte also has its own electrophoretic mobility based on charge, size, and shape, and the observed migration is the combination of this mobility with the EOF. Different analytes therefore travel at different net speeds, producing separation. The term electroosmotic flow separation reflects this bulk-flow-driven mechanism central to CE. The other options describe processes not governing the standard CE separation: endosmosis is not the primary CE mechanism; iontophoresis is about ion movement under current in tissues; isoelectric focusing is a separate mode based on pH gradients, not the general EOF-driven CE separation.