General model for the separation of large molecules by gradient elution : Sorption versus precipitation

Solute retention in the gradient elution separation of polymers and other macromolecules can occur by either sorption of individual molecules to the stationary phase or by a precipitation-redissolution process. Which process applies in a given situation depends on the sample solubility, the strength of the interaction of sample molecules with the stationary phase and the amount of sample injected on to the column. A general model is presented for these separations, and experimental data for the reversed-phase gradient elution separation of a 50 000-dalton polystyrene sample are reported and compared with the model. In this case, “normal” retention by a sorption process for samples smaller than 200 μg.