Introduction

 

The separation technique of electrophoresis has been known for over 150 years, the motion of dispersed particles (originally clay granules) in an electric field being first noticed as long ago as 1807 by Reuss. However, it was not until 1937 that Tiselius employed the electrophoretic process as an analytical and preparative separation tool. Employing the technique, Tiselius separated the serum proteins into their four main constituents, serum albumin and the ,  and  globulins and also isolated the virus that produced mouse paralysis. Today, electrophoresis is now recognized as the most effective separation technique for the analysis of proteins and other complex substances of biological origin.

 

Electrophoresis, as its name implies, is basically an electrically driven separation system and, thus, in discussing the theory of the process it is necessary to start with some basic concepts of electricity, the characteristics of charged particles and the effect of an electric field upon them.

 

Fundamental Theoretical Aspects of Electrophoresis

 

The first relationship that must be considered is that derived by Faraday for the mass of an element deposited or dissolved by an electrolytic process carried out in a bath containing an electrolyte and two electrodes, viz,

 

 

 where (w) is the mass of element dissolved or released electrolytically.

            (Q) is the amount of electricity passed between the electrodes,

            (F) is Faraday’s Constant (96.48 coulombs).

            (z) is the valency of the element,

(A)   is the Atomic Weight of the element,

     and (E) is the Equivalent Weight of the element.

 

The second concept of importance is the Transport Number of an ion. The transport number of a specific ion is defined as that fraction of the total current passing through the electrolytic system that is carried by that specific ion. This can be expressed in a simple equation,

 

where (T_r) is the transport number of ion (r).

      and (n) is the number of different ions.

 

The concept of transport numbers, however, must be limited to ion constituents that are defined as non-dissociable ions in free form and/or complex-bound to other ions. For example in a phosphate solution the transport number for the phosphate ion would include phophite and hypophosphite ions. Although the transport number is of interest in electrolytic processes, its use in electrophoresis, as given above, is limited and is not of general use for protein separations.