PARTITIONING AND ADSORPTION OF CHAIN MOLECULES AT CHEMICALLY MODIFIED SURFACES IN REVERSED PHASE LIQUID-CHROMATOGRAPHY

To describe retention in reversed phase liquid chromatography an extension of a self-consistent-field theory for adsorption is used to model surfaces with flexible grafted chains and the retention of chain molecules at these modified surfaces. The effects of grafted chain length, solvent quality, and surface coverage on the conformation of the grafted chains are shown. In RPLC both aliphatic and amphiphilic solutes enrich in the boundary region between the aliphatic grafted layer and the solvent. The retention of a homologous series of apolar and amphipolar molecules on surfaces with grafted chains increases approximately linearly with hydrocarbon chain length, also when the solute chain is longer than the grafted chain. Retention passes through a maximum as a function of surface coverage. It is shown that, although liquid/liquid partition coefficients can be closely approximated by RPLC, solutes are not distributed uniformly in a grafted layer.