Separation of Divalent Metal Ions with a Complexing Eluent

4 Separation of Divalent Metal Ions with a Complexing Eluent 

In Chapter 7, a number of separations are described in which a weakly complexing ligand is added to the eluent to partially complex the sample cations. Separation of metal ions may now be based on differences in partial complexation as well as on differences in the selectivity of the ion exchanger for free metal ions. 

Addition of a weak complexing anion (L), such as tartrate or a-hydroxyisobutyrate (HIBA), will convert part of a metal ion to a complexed form that is uncharged or has a lower positive charge than the free metal ion. This will cause the metal ion to elute more rapidly. Referring to Eq. 5.20, the metal ion in solution (Is,in) will be partially complexed  

The ratio of free metal ion (I) to the total amount that is present in solution has 

For convenience, charges are omitted from the ionic species. The quantity, (Isoin) in Eq. 5.21 may now be represented by Tot. Continuing the derivation given earlier (Section 5.2.4), Eq. 5.17 becomes  

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