Redefining the separation factor: a potential pathway to a unified separation science

Understanding the separation process in capillary electrophoresis (CE) leads to the unification of the theories for separation science. While the separation of analytes is governed by equilibria in chromatography, and by (centrifugal) field in ultracentrifugation, the separation in CE is governed by both equilibria and (electric) field. Therefore, a comprehensive separation theory that describes the separation process of analytes in CE should be able to describe the separation processes in both chromatography and ultracentrifugation. In this paper, we propose that individual capacity factors for each analyte species be used to describe the migration behavior of an analyte. The effect of field on each analyte species, as well as the effect of equilibria are considered in deriving a generalized equation that is applicable for all separation techniques. The separation factor defined at present does not directly relate to the migration rates of the analytes, and therefore can not be used in a generalized theory. We propose that the ratio of the migration rates of a pair of analytes (gamma) should be used as the separation factor, instead of the ratio of the two capacity factors. When gamma is used to describe the separation of two closely migrating analytes, all separation techniques have the same resolution equation.