Effect of the Eluent Composition

Effect of the eluent composition could be discussed on the basis of equation (2-55). In the simple case of binary eluent (organic/water mixture), we can consider in the first approximation that Gibbs free energy of the eluent interaction with the packing material surface is a linear function of the eluent composition 

Equation (2-60) represents linear dependence of the logarithm of the retention factor on the eluent composition  

This simple dependence of the retention factors on the eluent composition could be used for practical rough estimation of the retention variation with the variation of the concentration of organic modifier in the mobile phase. If the retention of particular analyte was measured at two different eluent compositions, then the retention of that same analyte at any other composition could be roughly evaluated from the following expression  

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