A Comparison of Mobile-Phase Peak Dispersion in Gas and Liquid Chromatography

Abstract

The field of axial and radial dispersion of unsorbed bands in columns or beds packed with spherical particles is reviewed and it is shown that there is broad agreement between various workers: at low reduced velocities both axial and radial dispersion occur by obstructed molecular diffusion. At higher velocities the processes are more complex but at very high velocities and at Reynolds numbers in excess of about 10 the reduced plate height becomes independent of velocity and has a value for axial dispersion of about 2 and for radial dispersion of about 0.2. In the intervening region the dispersion process is complex and shows dependence upon the column-to-particle-diameter ratio. The most inefficient columns appear to be formed when this ratio is between 10 and 30. It is therefore suggested that efforts be made to design and construct columns with greater trans-column uniformity. When trans-column packing inequalities are unimportant, the reduced plate height in the high-velocity region is only slightly affected by fluid velocity, in strong contrast to the situation in open tubes. With gases the reduced plate height does not rise much above 2 for well-constructed columns, whereas with liquids it rises to about 4 before turbulence becomes important and again limits the dispersion, so that it falls to about 2.