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electrophoresis(ĭlĕk'trōfərē`sĭs): see colloidcolloid
[Gr.,=gluelike], a mixture in which one substance is divided into minute particles (called colloidal particles) and dispersed throughout a second substance. The mixture is also called a colloidal system, colloidal solution, or colloidal dispersion.
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(also cataphoresis), the migration of colloidal particles or ionized macromolecules under the influence of an external electric field. Electrophoresis was discovered by F. F. Reuss in 1807; it is regarded as the most important electrokinetic phenomenon. An approximate relation between the velocity v of the moving particles and the electric field strength E is given by Smoluchowski’s equation:
where η is the viscosity of the medium, D is the dielectric constant, and £ is the electrokinetic potential.
Electrophoresis is used in electrochemistry to study the electric double layer and ion adsorption on a surface; it also has medical applications. In industry it is used to isolate natural rubber from latex, purify water, and separate kaolin from sand. It is used in biochemistry to analyze, separate, and purify biopolymers (chiefly proteins), bacterial cells, viruses, amino acids, and vitamins.
The practical application of electrophoresis began after the Swedish scientist A. Tiselius designed a special apparatus for the moving-boundary electrophoresis of proteins in solution (1937). Electrophoretic methods involving the use of inert carriers, such as paper and gels, have gained the widest application. They have been given the general designation of zone electrophoresis because fractions of the separate substances form separate immiscible zones in the carrier. Electrophoresis is frequently combined with other methods of separating organic compounds, for example, with chromatography. A technique has been developed for concentrating the electrophoretic zones of biopolymers in gels, which increases the resolving power of the method (disk electrophoresis). The combining of the antigen-antibody reaction with electrophoresis was the basis for the creation of immunoelectrophoresis. Electrophoretic analysis of biological fluids, such as blood serum (used primarily to study proteins), is widely used in the diagnosis of many diseases.
REFERENCESLarskii, E. G. Melody zonal’nogo elektroforeza. Moscow, 1971.
Dukhin, S. S., and B. V. Deriagin. Elektroforez. Moscow, 1976.
N. N. CHERNOV