In qualitative terms, the mobile phase characteristics which influence solute retention are the relative affinities of the sample ions and the mobile phase's competing ions. The affinity of the mobile phase ions to the stationary phase is governed by the same factors that effect the affinity of the solute ions, i.e., charge density, degree of hydration, polarizability etc. Mobile phase ions of higher affinity to the stationary phase are stronger, and will result in lower interactions of the sample ions with the stationary phase, hence lower retention times