Rational method for designing efficient separations by chromatography on polystyrene–divinylbenzene resins eluted with aqueous ethanol

A rational method for designing separation processes by chromatography with polystyrene–divinylbenzene (PS–DVB) resins of different particle diameters (10–400 μm) was developed. As model samples, catechin and epigallocatehin gallate (EGCG) were chosen and the mobile phase was an ethanol–water mixture. Linear gradient elution experiments were carried out with different gradient slopes, and the peak ethanol concentration was plotted against the normalized gradient slope. The plots were similar regardless of particle diameter. From these plots the two parameters describing the distribution coefficient K as a function of ethanol concentration I were determined. The K–I curves obtained were verified by isocratic elution experiments, and the conditions at which a baseline separation of the two polyphenols is possible was sought, and confirmed experimentally. Stepwise elution experiments were also designed and performed successfully on the basis of the K–I curve.