Gradient elution solvent strength prediction isocratic

The conceptual basis for understanding the connection between isocratic and gradient elution is well established and is called "linear solvent strength theory".22 27 Linear solvent strength theory proposes that, for a given solute, mobile phase, and column, if one measures the retention time of an analyte at two organic component concentrations, it will be possible to predict the retention time with any other mobile phase composition. The k value that would be observed in pure water, kw, is related to the actual k by the relationship... 

Abbott et al. [4] devised a method designed to predict the retention times in gradient elution under the assumption that the retention factor as determined under isocratic conditions is a log-linear function of solvent composition according to Eq. (5), where k is the retention factor obtained in water, ipo refers to the volume fraction of the organic component, and S refers to the solvent strength for which the values can be obtained as the negative slope of plots of log k versus volume fraction ... 

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