Ions Dissolved in Liquids

Many compounds dissolve in polar (esp. aqueous) solutions to form charged species (ions). Inorganic salts dissociate (e.g., NaCl Na and Cl ). Depending on solution pH, organic acids may dissociate (e.g., RCOOH RCOO and H ) or bases may 

A particularly useful resin is that formed by the copolymerization of styrene(vinyl-benzene) and divinylbenzene, and is illustrated in Fig. 13.23. By varying the proportion of divinyl benzene incorporated in the polymerization one can vary the extent of cross-linking of the polystyrene chains, which confers greater stability to the polymer structure and 

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  

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 reverse phase or normal phase 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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