The dipole approach in ion-interaction chromatography of zwitterions

The chromatographic behavior of zwitterions in Ion-interaction chromatograp hy (IIC) is, investigated theoretically for the first time. The modificatio n of the stationary phase in the presence of Ion-interaction reagent (IIR), and adsorption competition between test analytes and IIR for inner layer s ites ore shown theoretically to change the partition coefficient for Zwitte rions. Experimental results from the literature concerning retention behavior of z witterions in IIC, were used to test the new thermodynamic theory. Very rea sonable estimates of (i) DeltaG degrees values for the IIR adsorption onto the stationary phase (ii) total ligand concentration, and (iii) dipolar mom ents validate the present thermodynamic model for the IIC of zwitterionic a nalytes. Retention equations are compared to those which can be obtained, if the net charge of the analyte is zero, from the most important retention models in IIC. None of them is able to explain, even in a qualitative way, the reten tion behavior of zwitterions in IIC whereas, the present model is quantitat ively able to do this.