Terms:
(1) positive electrode = anode
(2) negative electrode = cathode
(3) negatively charged molecules migrate towards the anode (anionic)
(4) positively charge molecules migrate towards the cathode (cationic)
(5) A zwitterion is a molecule that can be either positively or negatively charged depending on the nature of the medium, especially pH.
Factors affecting the rate of migration:
(1) net electrical charge of the molecule
(2) shape and size of the molecule
(3) properties of the supporting medium
(4) temperature
(5) electric field strength
driving force on a molecule =
= (voltage applied) * (net charge on the molecule) / (distance across the medium)
resisting force on a molecule =
= (6 * π) * (ionic radius of solute) * (viscosity of buffer solution) * (velocity of migration in cm per second)
The result of these two forces being applied in opposite directions is a constant migration velocity. The rate of migration (velocity in cm per second) per unit field strength (voltage per cm) is the electrophoretic mobility.
electrophoretic mobility in (cm^2) / (V•s) =
= (distance traveled in cm) * (width of electrophoretic medium in cm) / ((voltage applied in volts) * (time in seconds))
mobility unit = (10 ^ (-5)) in (cm^2) / (V•s)
(1) If migration is towards anode, then expressed as negative.
(2) If migration is towards cathode, then expressed as positive.
