Organic Modifier Concentration in Eluent

In reversed phase chromatography, the dependence of solute retention on the organic modifier concentration (cp) in the mobile phase is sanctioned by the following relationship [1]  

The addition of an organic modifier to the aqueous eluent modifies its viscosity and lowers its surface tension. As explained in Chapter 3 (Section 3.1.2), by increasing the organic modifier eluent concentration, a quantitatively predictable [2] decrease of the retention factor of the analyte is obtained, as proven by considerable experimental evidence [3-9]. The retention decrease clearly depends on the analyte natme [4]. 

Section 2.5.3 in Chapter 2 elucidated the role of the organic modifier related to ion-pairing equilibrium. The increase of the volume fraction of the organic modifier 

FIGURE 8.1 Family of model IPR adsorption isotherms at different mobile phase concentrations of organic modifier. 

FIGURE 8.2 Theoretical dependence of retention factor of a model analyte oppositely charged to the IPR, as a fnnction of the mobile phase concentration of the IPR, at increasing elnent percentages of organic modifier. 

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