Introduction : “Electrophoresis” literally means running in the electric field. The charged molecule moves to their counter charge electrodes but electric field is removed before it reaches the electrode. Movement of charged species in an electric field gives differential mobility to the sample based on the charge and consequently resolve them. Movement of the charged particle is retarded with the addition a polymeric gel so that a sufficient time is available for resolving the sample. The polymeric gel is inert, uncharged and does not cause retardation by binding the molecule. Instead it, forms pores of different size (depending on the concentration of polymer) and sample pass through these pore and as a result their electrophoretic mobility is reduced (Figure 13.1).

Figure 13.1 : Movement of the charged particle in an external field.

Suppose a charged particle has net charge Q and the external electric field is E, then the force F responsible for giving electrophoretic mobility,

F= Q.E

(13.1)

The friction forces F which is opposing the movement of the charged particle is as follows

F = ƒ. v

(13.2)

here ƒ is the friction coefficient and the v is the velocity of the electrophoretic mobility. The movement of a spherical through a liquid medium (gel) of the viscosity η, the friction coefficient ƒ is given by :

ƒ = 6Πηr v

(13.3)