Effect of adsorption of organic solvents on the band profiles in reversed-phase non-linear chromatography

The influence of the mobile phase composition on the adsorption equilibria in non-linear reversed-phase chromatography has been investigated. RP-18 and RP-18 endcapped columns have been selected with methanol-water and acetonitrile-water as a mobile phase and cyclopentanone as a solute. Due to its structure, cyclopentanone exhibited affinity to the active adsorption sites on alkyl chains as well as to the polar, uncovered surface of the adsorbent. The adsorption equilibria of solvents-methanol-water, acetonitrile-water on RP-18 and RP-18e columns-have been measured and the excess adsorption isotherms accounting for non-ideality of the mobile and adsorbed phase have been determined. The competitive heterogeneous adsorption model for the solute and organic solvent has been proposed and coupled with a model of column dynamics. The model predictions have been verified by comparison to experimental chromatograms.