Which term describes the migration of small ions during electrophoresis?

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

Answer: (A)

Migration of small ions under an electric field in a gel or buffer is described by zone electrophoresis, where charged species move and separate as distinct bands or zones. Iontophoresis, although also driven by electricity, refers to delivering ions into tissues across the skin, not the general analytical separation in electrophoresis. Endosmosis describes solvent movement across a membrane by osmotic pressure, not ion migration in a gel. Isoelectric focusing uses a pH gradient to trap molecules at their isoelectric point, concentrating them rather than just migrating to separate by charge. So the term that best fits the described migration during electrophoresis is zone electrophoresis.