The place where, F= F or QE= 6Πηr v

The electrophoretic mobility v is given by:

As Q=ze, where z is the valency and e is the electronic charge, the electrophoretic mobility can be expressed as:

Hence, electrophoretic mobility v is directly proportional to the charge and inversely proportional to the viscosity of the medium, size and shape of the molecule. In the case of relative mobility, it is directly related to the charge/radius of the molecule. For a globular protein, the radius (r) of the molecule is related to the molecular mass of the macromolecule. The relative mobility, v' is as follows

(13.4)

Electrophoretic techniques: Different types of electrophoresis techniques are designed depending upon whether it carried out in the presence or absence of a supporting media.

Moving boundary electrophoresis- In this method, the electrophoresis is carried in solution, without a supporting media. The sample is dissolved the buffer and molecules move to their respective counter charge electrodes. Moving boundary electrophoresis is carried out in a U shape tube with platinum electrodes attached to the end of both arms (Figure 13.2). At the respective ends, tube has refractometer to measure the change in refractive index of the buffer during electrophoresis due to presence of molecule. Sample is loaded in the middle of the U tube and then the apparatus is connected to the external power supply. Charged molecule moves to the opposite electrode as they passes through the refractometer, a change can be measured. As the desirable molecule passes, sample can be taken out from the apparatus along with the buffer.

Figure 13.2 : Movement of the charged particle in a moving boundary electrophoresis.