PREDICTION OF THE MIGRATION BEHAVIOR OF ANIONS IN CAPILLARY ION ANALYSIS

The separation of anions in capillary ion analysis below the critical micellar concentration of the modifier (cationic surfactant) is influenced by two chemical equilibria, the ionic dissociation which depends on the pH of the buffer electrolyte and the formation of ion association complexes in function of the concentration modifier. An expression of the mobility in function of the pH and concentration of the modifier is proposed and evaluated using experimental data. The experimental domain is examined with the aid of a central composite design. The model describes the mobility of anions in terms of physical and chemical constants of each ion (acid dissociation constant K-a, ion association constant K-ia), the pH of the electrolyte, and the concentration of a modifier ([S]) in the buffer. The model is used to predict the mobility of each solute over a two-dimensional pH/[S] space.