The chromatographic properties of porous microparticulate zirconium oxide surfaces in aqueous media are highly dependent upon the chemical composition of the eluent. In particular, retention is controlled by the type and concentration of “hard” Lewis bases when these species are present in the eluent. Ligand exchange is the dominant mechanism for the retention of solutes which are Lewis bases. Consequently, the capacity factor and plate height depend on both the thermodynamic and kinetic properties of whatever competing Lewis bases may be present in the eluent. These Lewis base eluent components act to control retention in two ways. They modify the net ligand exchange contribution to retention, and they serve as sites for secondary interactions, such as hydrogen bonding and hydrophobic interactions between solutes and the dynamic stationary phase.