Solute-solvent interactions on the surface of reversed phases : I. Stationary phase interactions and their dependence on bonding characteristics

Abstract

The retention characteristics of a number of “brush”- and “bulk”-type reversed-phase column packing materials that are commercially available for high-performance liquid chromatography are examined in the situation where an abrupt change in mobile phase from pure methanol to pure water occurs. It is shown that the brush-type reversed phases are slow to come into equilibrium with pure water, and in contact with water it would appear that the hydrocarbon chains dispersively interact with themselves. This dispersive intramolecular interaction of the hydrocarbon chains results in a reduction in effective chromatographic surface area and consequently anomalously low retentive characteristics. In contact with solvent containing 10% (w/v) or more of organic solvent such as methanol, the brush-type materials exhibit normal retention characteristics. The bulk or polymeric bonded phases, however, equilibrate rapidly with water, and due to their more rigid structure do not appear to exhibit dispersive intramolecular interactions and thus exhibit normal retention characteristics. The bulk or polymeric type reversed phases, therefore, are to be preferred for examining solute-solvent/stationary phase interactions due to their more consistent chromatographic properties.