What is Electrophoresis ?
Electrophoresis is an analytical method frequently used in molecular biology and medicine. It is applied for the separation and characterization of proteins, nucleic acids and subcellular-sized particles like viruses and small organelles. Its principle is that the charged particles of a sample migrate in an applied electrical field. If conducted in solution, samples are separated according to their surface net charge density. The most frequent applications, however, use gels (polyacrylamide, agarose) as a support medium. The presence of such a matrix adds a sieving effect so that particles can be characterized by both charge and size. Protein electrophoresis is often performed in the presence of a charged detergent like sodium dodecyl sulfate (SDS) which usually equalizes the surface charge and, therefore, allows for the determination of protein sizes on a single gel. Additives are not necessary for nucleic acids which have a similar surface charge irrespective of their size.
Characterizing samples by exploiting both differences in charge and size can yield much more information. It requires that the same sample is analyzed not only in one, but several gels. This technique is further explained in the chapter on Ferguson plots. The procedure is more laborious, however the use of an automated electrophoresis apparatus can make this a fast, routine procedure (Gombocz, Cortez: Appl. Theor. Electrophoresis 1995, 4, 197-209).