Electrophoresis is a separation method that is based on the migration of charged species in a supporting medium (a liquid or a hydrophilic gel) under the influence of an electric field.
The main applications of electrophoresis have been in the separation of biological molecules, which includes molecules with relatively lower relative molecular masses such as amino acids, and also molecules of higher relative molecular masses such as proteins and polynucleotides (including RNA and DNA molecules).
Colloidal particles of a solution either carry positive or negative charge. Sols in which the colloidal particles carry positive charge are called positive sols. When colloidal particles carry negative charge, the sols are called negative sols.
The existence of charge on the colloidal particles can be demonstrated by a phenomenon called electrophoresis. Sols of basic dye stuffs, ferric hydroxide, aluminum hydroxide etc., are some common examples of positive sols. Colloidal solutions of gums, starch, soap solution, metals (Ag, Cu, Au, Pt etc.), metal sulphides, and some acid dyestuffs are the examples of negative sols.