Lewis acid sites are present on the surface of metal oxide chromatographic supports and are responsible for the very strong adsorption of Lewis bases. Such sites must be masked or modified to elute solutes which contain Lewis base groups. Fluoride ion coordinates strongly with these sites on zirconium oxide and forms a surface whose composition is pH and ionic strength dependent. Coverages range from 13.7 μmol/m2 fluoride at pH 4.8 to 0 μmol/m2 fluoride at pH 13. Washing the particles with 0.1 M sodium hydroxide quantitatively desorbs all bound fluoride without harming the underlying zirconium oxide particle. Readsorption of the fluoride can be accomplished by equilibrating the particles in a buffer of suitable fluoride concentration. Such fluoride modification has been found to occur on a time scale suitable for displacement chromatography on the Lewis acid sites.