With a pH of 8.0–9.0 for protein electrophoresis, proteins take on a negative charge, and a negative ion cloud forms. The proteins are pulled to the anode as the negative ion cloud migrates to the anode. Several gels used routinely for protein electrophoresis attract positive ions from the buffer and form a positive ion cloud. This ion cloud moves in the opposite direction to the cathode. This phenomenon is called electroendosmosis or endosmosis.
The tension created by these oppositely moving ion clouds can affect the movement of sample macromolecules. The migration of some proteins can be slowed; some proteins can become immobile, and others are pushed toward the cathode.
Many protein electrophoresis methods use this tension to better separate protein bands. The gamma globulin band in serum, urine, and other body fluids will separate more sharply when pushed to the cathode and appear behind the sample application point.
