ON THE MEASUREMENTS OF ELECTROPHORETIC MOBILITIES BY MEANS OF CAPILLARY ISOTACHOPHORESIS AT A CONSTANT VOLTAGE

A method for measuring electrophoretic mobilities by means of isotacho phoresis (ITP) at a constant voltage as described by H. Carchon and E. Eggermont (Electrophoresis, 1982, 3, 263-274) is analyzed. An error m ade in this work, disregarding the pH shift arising at the initial dis continuity on the leader-terminator boundary, has been corrected. This method has been carefully studied and generalized for the presence of constant electroosmotic flow in a capillary. The limits of its applic ability and the diffusionless ITP theory in general are discussed. A d etailed study of the evolution of initial discontinuity (stationary bo undary) showed some anomalies not reported previously, particularly no nmonotonic concentration profiles in the vicinity of stationary bounda ries. Moreover, in some cases, diffusion effects and the contribution of H+ ions can also strongly influence the behavior of moving boundari es. Computer modelling (confirmed by experimental data) showed that th ese effects could lead to the decay of the ITP train, despite the fact that the steady state diffusionless ITP theory predicts its stability .