Theoretical background for the distribution of ion-pairs

The basic expressions for ion-pair extraction are given by eqns. (1) and (2). The distribution ratio expression (3) derived therefrom is valid if further processes can be disregarded. 

However, in many instances the ions or the ion-pair in the organic phase can participate in other equilibria, which have to be taken into consideration in the calculations necessary to arrive at suitable extraction conditions. Side reactions may give increased extraction recovery and selectivity or cause unexpected disturbances in ion-pair extraction processes. 

Secondary equilibria such as dissociation and association of the ion-pair in the organic phase are dependent on the concentration of the extracted compound. 

The expression (11) shows an increases of the distribution ratio with decreasing concentration of the extracted compound HA.  

Association of the ion-pair, such as dimerization and tetramerization, in the organic phase also increases the degree of extraction  

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