Effect of the column length on the characteristics of the packed bed and the column efficiency in a dynamic axial compression column.

The axial homogeneity of preparative-scale chromatography columns was studied by measuring the overall properties of similar columns differing only by their lengths. The properties investigated were the packing density, the external porosity, the permeability and the column efficiency. Two different materials were used, one made of large, irregular silica particles compressed under either high or a low degree of stress; the other of small, spherical and rigid particles. The columns made with the spherical particles were more homogeneous, had a higher external porosity and specific permeability, and a higher efficiency than those made with the irregular ones. For this latter material, the columns prepared with a low level of stress were better than those compressed under high stress. The latter ones experienced extensive particle breakage. These results indicate that the long columns are heterogeneous in their axial direction.