In high-performance liquid chromatography porous uni-sized particles, between 3-7µm in diameter are used as the stationery phases. Improvement in the detection limit and speed of analysis has been achieved by particle miniaturisation. As pumps and detection equipment improve then particles below 2µm will allow on-line analysis. However, regular and size monodsiperse particles of this size are difficult to prepare. Here we report methods by which small porous microspheres may be prepared by combining advances colloidal particle and mesoporous material synthesis. The synthesis of mesoporous silica spheres with uni-directional and tuneable mesoporous diameters have not previously been reported. Organic micelles (e.g. formed block copolymer surfactants) and silica hydrolysis are used to generate ordered mesoporosity. Careful reaction control allows size-monodisperse spherical particles, ± 5 RMS with tuneable diameters between 1-5 µm to be formed. We show that the mesopores are aligned through the spherical structure to provide an open porous surface with high surface areas, typically between 1000-1500 m²g^-1. Doping of silica microspheres with ceria is also carried out in attempt modify chromatographic performance (more selective to bio-entities). It is shown that using different reaction routes that the ceria can either be distributed homogeneously through the structure or in the form of discrete and thermally stable nanoparticles at the surface. These nanoparticles can increase the rate of sintering by necking. We also demonstrate that relatively large diameter mesopores can be obtained by a unique method, between 6-11 nm, using supercritical carbon dioxide (sc-CO₂) as a swelling agent during synthesis. Finally, materials were packed into columns for chromatographic testing. Results are presented that illustrate the application of these microspheres in UHPLC.

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