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

Porous poly(styrene-divinylbenzene) (PS-DVB) HPLC packings give broad, tail ed peaks for some types of solutes. This phenomenon is due to sorption of t hese solutes into the polymer matrix where they experience very slow, hinde red diffusion. It is known that the presence of small amounts of tetrahydro furan (THF) in the methanol (MeOH)-H2O mobile phase yields narrower and les s tailed peaks for such solutes. In this study, Hamilton PRP-infinity, a no nporous 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-infinity as a function of activity of MeOH and THF in aqueous solution; and both sorption isotherms and sorpti on rate curves for the solute naphthalene from various solvent mixtures. Th e addition of 2% THF to 70:30 MeOH-H2O produced an additional 0.4% swelling , an 11% decrease in the sorption capacity and a 90% increase in the diffus ion coefficient of naphthalene in PRP-infinity. The increase in the diffusi on coefficient, which is responsible for the improved elution peak shape of naphthalene, is shown to be caused by the decrease in sorption capacity, r ather than by the additional swelling. The sorbed THF serves to fill and "b lock" the smallest, most highly hindered micropores in the polymer matrix. (C) 1999 Elsevier Science B.V. All rights reserved.