[Preparation and physicochemical properties for zirconia as high performance liquid chromatographic packing...

There has been an increasing importance in the application of zirconia as column packing material for high performance liquid chromatography (HPLC) because of its excellent chemical, thermal, and mechanical stabilities as well as bioanalysis suitability. Zirconia spheres could be synthesized by polymerization-induced colloid aggregation (PICA), oil emulsion methods (OEM), or spray-dry method. It has been found that preparative procedure of zirconia support can affect its chromatographic behavior significantly. The review analyzes the relationship between zirconia packings' physicochemical properties and their preparative procedures. Specific surface area, pore structure, pore volume, pore size distribution, and particle size distribution are discussed in detail. At present, zirconia has not become highly competitive because of its limitations such as small specific surface area and pore volume, broad pore size distribution and particle distribution, and unfavorable pore structure. The review also describes silica-zirconia composite HPLC materials prepared by sol-gel method, coating and co-precipitation procedure. However, their chemical stability as HPLC column packings was suspicious because of the residual silica on the material surface. Furthermore, the study showed that zircon (ZrSiO4) is present in all silica-coated zirconia or silica-zirconia composites. It could be deduced that co-existence of more than one crystallines on the material surface could produce chemical heterogeneity, resulting in complex chromatographic separation mechanism. It leads a conclusion that a new synthetic way is needed for preparing zirconia-based HPLC packings with ideal chromatographic parameters. A novel material with higher specific surface area and pore volume, good pore structure, narrower pore size distribution and more uniform particle size distribution was prepared by layer-by-layer self-assembly technique (LbL SA), consisting of micrometer-sized silica spheres as core and nanometer-size zirconia particles as surface coating. The chemical stability of the material is as good as that of zirconia, and its specific surface area is as high as that of silica.