STATIONARY-PHASE EFFECTS IN REVERSED-PHASE LIQUID-CHROMATOGRAPHY

Selectivity of reversed-phase packing materials was discussed based on the solute-stationary phase interaction. Solute retention on a silica C-18 phase is primarily determined by the hydrophobicity of a solute, whereas the long alkyl groups result in preferential retention of rigid, planar solutes over non-planar, bulky ones. An organic solvent imbibed in the stationary phase also contributes to the retention. Thus an electron donor, such as tetrahydrofuran, tends to give longer retention for acidic compounds or electron acceptors. The presence of micropores in polymer gel packing materials results in the preferential retention of solutes with rigid, compact structures, and the presence of dipolar groups (ester and ether linkages) contributes to the preferential retention of dipolar and/or aromatic compounds based on dipole-dipole or dipole-pi interactions. Attractive interaction between the graphite carbon surface and solutes, presumably based on the dispersion force, results in selective retention of planar compounds compared with non-planar ones. Attractive interactions provided by electron-donor-acceptor bonded phases are also shown to be very effective for structural recognition.