Abstract: The invention concerns electrophoresis and methods and electrolyte compositions for decoupling or isolating the dual functions of the electrolyte composition in order to increase separation selectivity or reduce electromigration dispersion, or both. An electrolyte composition is used in electrophoresis to separate a charged analyte having a mobility .mu..sub.a in an electric field. The composition includes a buffer system having an ionic component that controls the pH of the composition and mobility matching ions having a mobility .mu..sub.2 in the electric field, such that .mu..sub.a /.mu..sub.2 equals about one. Alternatively, the buffer system may maintain the composition's pH and a complexing agent may complex with the buffer system to alter the mobility .mu..sub.2 of an ionic component of the buffer system, such that .mu..sub.a /.mu..sub.2 equals about one. The pH of the composition is within a pH range selected based on the analyte to be separated, and .mu..sub.