•Silica-based column packings
•Porous silica can be prepared in a wide range of particle and pore sizes (with a narrow particle size distribution).
•Both particle size and pore diameter are important with regard to HPLC separations.
•Small particles reduce the distance a solute must travel between stationary and mobile phases. This facilitates equilibration and results in good column efficiencies.
•However, small particles also mean greater to flow velocity.
•Spherical particles of 3,5, or 10 μmdiameter are used in analytical columns. Larger (sometimes irregular shaped) particles may be used for industrial-scale preparative chromatography since they are less expensive.