Transport processes and equilibria during electrophoretic separations

2 Transport processes and equilibria during electrophoretic separations 

For a full characterization of the electrophoretic separation it is necessary to consider all equilibria in which individual components of the electrophoretic system take part during the whole separation. 

Besides equilibria in the liquid phase (proteolytic, complex forming, etc.) that influence directly the values of effective mobilities of compounds to be separated, it is necessary to also establish, in the electrophoretic system, equilibria between the liquid and solid phase. In electrophoretic techniques which use solid stabilizing media adsorption of solutes on the sorbent surface is the main consideration. In capillary methods, and with colloid particles, similar effects have also to be considered (the surface of the solid phase that is in contact with the liquid phase is, with respect to the volume of the liquid, rather large). In both these latter cases the interaction between the solid and liquid phases participates in the formation of the electric double layer that conditions the electro-osmotic flow, and attributes the electric charge to colloid particles. 

The electrophoretic separation occurs in solutions of electrolytes. The solvent selection and the selection of the electrolyte system (called sometimes separation media) is done in such a way as to fulfill the following demands  

The transport of any compound during the electrophoretic separation can be the result of different causes — migration in the electric field, diffusion, convection, heat transport. Each of these causes influences the final velocity and direction of migration of the compound v. This final velocity is represented by a vector sum of individual velocities. 

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