CHARACTERIZATION OF SILICA SOLS USING CAPILLARY ZONE ELECTROPHORESIS

Separations of silica sols ranging in size from 5 to 500 nanometers have been accomplished with capillary zone electrophoresis (CZE). Separations were achieved by free-zone electrophoresis in 50-mu-m internal diameter (id) fused silica capillaries filled with pH 9.0 ammonia buffers; detection of separated bands was accomplished via on-capillary turbidity measurements at 190 nm. Separations are relatively fast and moderately high-efficiency, with essentially baseline resolution of sub-100 nanometer sols differing by a factor of 2 accomplished in under 20 minutes. The ionic strength of the separation buffer was found to have a significant effect on the resolution and electrophoretic mobilities of the silica sols, with higher ionic strengths substantially improving resolution of smaller silica colloids while greatly increasing the elution time of the larger silica sols. Several areas of application of the CZE technique for separation and characterization of charged particulate species are discussed.