The functional groups on the stationary phase's surface are fixed positively charged species (M+). At equilibrium these positively charged functional groups are neutralized by the counter ions from the running mobile phase (C-). In the second and the third steps, the anionic sample components (A-) enter the column and distribute between the stationary and the mobile phases by displacing the counter ions, and being displaced by the mobile phase ions back and forth. The distribution equilibrium is determined by the competition between the sample components and the anions of the mobile phase on the charged sites of the stationary phase