Migration time and peak area artifacts caused by systemic effects in voltage controlled capillary electrophoresis.

The effect of an artificial conductivity step on the migration time for rac-propranolol was investigated with the purpose to give a strict physical background to the intensively studied migration time and integration variations in voltage stabilized capillary electrophoresis. The experiments verified a theoretical derivation of migration time disturbances caused by the sometimes unavoidable conductivity variations in the system. The verified equation describing migration time variations was used for simulations of a number of relevant cases, such as variation in injected sample conductivity, post-injection diffusional broadening of the sample zone, and the physical effect of a selector zone in the partial filling mode. A similar theoretical and experimental treatment of the integration errors caused by non-uniform velocity was also included with special reference to enantiomer separation in the partial filling mode. The same experiments were also used to show that the standard migration time related method for integration correction fails if the velocity of a component is not constant throughout the experiment, such as the situation when a selector is employed in partial-filling mode.