Influence of solvent uptake and swelling by poly(styrene–divinylbenzene) column packings on sample sorption rate and band broadening in reversed-phase liquid chromatography

Abstract

Porous poly(styrene–divinylbenzene) (PS–DVB) HPLC packings give broad, tailed peaks for some types of solutes. This phenomenon is due to sorption of these solutes into the polymer matrix where they experience very slow, hindered diffusion. It is known that the presence of small amounts of tetrahydrofuran (THF) in the methanol (MeOH)–H 2O mobile phase yields narrower and less tailed peaks for such solutes. In this study, Hamilton PRP-∞, a nonporous PS–DVB polymer, serves as a model for the matrix of porous polymers. The following measurements were made: sorption isotherms for MeOH and THF from aqueous solution; swelling of PRP-∞ as a function of activity of MeOH and THF in aqueous solution; and both sorption isotherms and sorption rate curves for the solute naphthalene from various solvent mixtures. The addition of 2% THF to 70:30 MeOH–H 2O produced an additional 0.4% swelling, an 11% decrease in the sorption capacity and a 90% increase in the diffusion coefficient of naphthalene in PRP-∞. The increase in the diffusion coefficient, which is responsible for the improved elution peak shape of naphthalene, is shown to be caused by the decrease in sorption capacity, rather than by the additional swelling. The sorbed THF serves to fill and “block” the smallest, most highly hindered micropores in the polymer matrix.