Free-flow electrophoresis. I. Theoretical and experimental investigations of the influence of mechanical and electrokinetic variables on the efficiency of the method.

In the present paper, various types of band-broadening effects in free-flow electrophoresis were investigated. They resulted from the velocity profiles of the liquid curtain and electroosmosis, temperature gradient, thermal diffusion and sample inlet geometry. An analytical free-flow electrophoresis apparatus permitted easy observation of these parameters. The experiments showed that the influence of the temperature gradient was negligible, whereas the effect of the velocity profiles on band broadening was higher than theoretically expected. In preparative work this is of utmost importance, since overlap of bands is not desirable. In this case, the zeta potential of the walls can be adjusted to that of the material to be separated, resulting in a considerable reduction of band broadening. Various approaches are indicated. Further attention was given to the influence of the relaxation effect on the separation. Conditions are shown where particles are separated either according to their surface charge density or to their size. The practical relevance of the results is discussed.