By Sunil Bhardwaj

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Migration of colloidal particles under the influence of an electric field is called electrophoresis or cataphoresis.

It is possible to detect the type of charge present on the colloidal particles by noting the direction of movement of particles.

The electrophoresis apparatus consists of U tube provided with a stop cock. A funnel shaped reservoir is connected to Utube through this stop cock. A small amount of water or a solution of some suitable electrolyte of lower density than sol is first placed in the Utube. Now the sol is introduced slowly. The electrolyte or water is displaced upwards and sharp boundaries are produced in both the arms of Utube.

The suitable electrodes are then inserted as shown in the figure and connected to suitable source of potential. The movement of colloidal particles can be easily observed by looking at the position of boundary. From the direction of movement of boundary, it is possible to detect the rate at which colloidal particles migrate in an electric field.

It is generally expressed in terms of electrophoretic mobility (\(\mu\)). It is defined as the distance traveled by the particle in one second under a potential gradient of one volt per cm. Electrophoresis is used for the separation of proteins, nucleic acids, Polysaccharides etc. Zeta potential (\(\zeta\)) and electrophoretic mobility (\(\mu\)) are related by the equation. $$ \zeta = \frac { 4\pi \eta \mu }{ D } $$Where \(\eta\) = viscosity of the medium and D = dielectric constant of the medium