Theoretical and experimental aspects of fractionation mechanisms in liquid chromatography on macromolecular stationary phases (gel or bonded chains)

Abstract

Abstract-In a preliminary part, we deal with the partition mechanism of low or high molecular weight solutes, by selective dissolution in swollen gels. After summing up the theoretical expressions, we present some experimental evidences for a fractionation mechanism based on such a phenomenon, which may interfere , in many cases, with the classical steric exclusion effect in GPC. Most of this paper is devoted to chemically bonded stationary phases which gained increasing importance in H.P.L.C., during the past few years. Owing to our previous works on gels, we theoretically studied the partition coefficient of low or high molecular weight solutes between a mobile phase and a stationary phase, constituted by macromolecular chains bonded to an inert surface. Variations of partition coefficient with the molecular sizes of solute, solvent and graft, and with the molecular interaction parameters between these species, are presented. In a complementary aspect, we describe the recent preparation of model chemically bonded phases of silica/polyethyleneoxide and silica/polystyrene types. The retention data obtained for various solutes on these bonded phases are discussed in terms of silica loading, grafting chain length, solute size and solvent nature. These theoretical and experimental studies lead to practical consequences concerning the relative parts of the dissolution effect into the grafted phase, the adsorption on the mineral support and the steric exclusion effect due to the residual porosity.

Thermodynamics of retention for small molecules in the polystyrene/chloroform system

“…Several theoretical studies have been published regarding general distribution phenomena (6)(7)(8). The relative polarity of the mobile phase and the gel has also been used to predict nonexclusion effects (9), but there are limitations to this approach (10).…”