POROUS ZIRCONIA AND TITANIA AS PACKING MATERIALS FOR HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

Porous amorphous zirconia (ZrO2) and titania (TiO2) packings were synthesized as rigid microparticulate beads by means of a sol-gel process. Sufficient rigidity and desired mesoporosity of the ZrO2 and TiO2 particles were achieved only by a gel hardening process, followed by heat treatment. The mean pore diameter, PBAR(d), the specific surface area, a(s), and the specific pore volume, v(p), were controlled by the heat treatment. Typical values were PBAR(d), = 8 nm, a(s) = 80 m2/g and v(p) = 0.23 ml/g. ZrO2- and TiO2-based revesed-phase packings were prepared by subjecting the native materials to a specific surface activation process and reaction with octadecyltrimethoxysilane. Native ZrO2 and TiO2 of graduated polarity, tested under normal-phase conditions, yielded a solvent strength series similar to those observed with silica and alumina. Retention of lipophilic analytes in n-heptane and dichloromethane was scarcely affected by the relative water content of the mobile phase. Native ZrO2 and TiO2 were found to be suitable for the separation of structural isomers. From calcined ZrO2 and TiO2 amines were eluted with totally symmetrical peaks when water-modified dichloromethane was used as the mobile phase. The retention and selectivity of n-octadecyl-bonded ZrO2 and TiO2 packings were identical with those of silica-based materials, except for showing a pronounced pH stability up to pH 12 in aqueous-organic mobile phases.