Which of the following techniques is based on electro-osmotic flow?

• A. Capillary electrophoresis
• B. Zone electrophoresis
• C. Iontophoresis
• D. Isoelectric focusing

Answer: (A)

Electro-osmotic flow is the bulk movement of liquid in a charged capillary when an electric field is applied. In capillary electrophoresis, this flow is the driving force that moves the whole buffer (and anything dissolved in it) through the capillary toward the detector. The separation then occurs mainly because analytes have different electrophoretic mobilities, so they move relative to the bulk flow at different speeds depending on their charge and size. This combination—the solvent moving as a stream due to the electric field and the solutes migrating at their own rates—produces the high-efficiency separations capillary electrophoresis is known for.

Zone electrophoresis and isoelectric focusing rely more on the properties of the sample or the pH gradient rather than pushing the bulk solvent along the capillary, and iontophoresis uses an electric field to move ions into tissues rather than separating them in a capillary.