Isoelectric focusing in laboratory Isoelectric focusing (IEF), also known as electrofocusing, is a technique for separating different molecules by their electric charge differences. It is a type of zone electrophoresis, usually performed in a gel, that takes advantage of the fact that a molecule's charge changes with the pH of its surroundings. A protein that's in a pH region below its isoelectric point (pI) will be positively charged and so will migrate towards the cathode. As it migrates thro… (More on Electrofocusing)