from my book it says: The chemical interactions of the mobile phase and sample, with the column, determine the degree of migration and separation of components contained in the sample. For example, those samples which have stronger interactions with the mobile phase than with the stationary phase will elute from the column faster and thus have a shorter retention time, while the reverse is also true. what do they mean when they say "while the reverse is also true." ? :yuck: hope very much for ideas! thanks!