Survey of Existing Retention Models

According to the model of ion pair formation [6,11], the solute ion E interacts with the lipophilic ion H forming a complex EH. This complex can be reversibly bound at 

The respective equilibrium constants can be expressed by Eqs. (126) and (127). The concentration of individual species in the mobile and the stationary phases is indicated by the indices m and s, respectively. 

According to the ion-exchange model [8-10], the lipophilic ion is adsorbed at the surface of the stationary phase forming LH. This renders the non-polar resin a dynamic ion exchanger. The solute ion E may subsequently interact with LH  

Under the condition that solute ions and lipophilic ions can interact completely independently with the stationary phase, one obtains, according to Horvath [12], a very complicated equilibrium system (see Fig. 5-1). 

Hence the equilibrium system must be extended as follows  

According to the model of ion-pair formation [6,11], the solute ion E interacts with the lipophilic ion H to form a complex, EH. This complex can be reversibly bound at the nonpolar surface of the stationary phase L (chemically bonded reversed phase or divinylbenzene resin), giving LEH. The equilibria thus established may be described as follows  

When the stationary and mobile phases are in equilibrium, the concentration of lipophilic ions is constant With 

---