Chromatography of Ions Dissolved in Liquids

Note that the cupric ion is shown to be associated with two resin functional groups, releasing two sodium ions. Half the number of moles of doubly charged copper is equivalent on the basis of charge to sodium or hydrogen. If the copper were present as singly charged cuprous ion, the equivalents would contain equal numbers of moles. 

The relative affinities (i.e., selectivities) of ions for the functional groups on the resin are governed by two rules  

Ions with higher charge have higher affinity (e.g., Na Ca AT and Cl 

The fundamental parameters controlling relative residence times of analyte or other eluent ions in the resin stationary phase or the ionic solution mobile phase are both the relative selectivity of the resin for the ions and their relative concentrations in each phase. In contrast, in RP or NP-HPLC, selectivity is controlled by the relative polarity interactions of different analytes with both phases. Until an overload occurs, this is independent of analyte concentration. 

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