Movement and band spreading of unsorbed solutes in liquid chromatography

Abstract

The different mobile phase velocities which can be measured in liquid chromatography have been described in order to facilitate an unambiguous specification of the velocity frame and the mobile phase hold-up volumes required to relate experimental data to the theory. The interplay of convective and diffusional mixing, which is responsible for band spreading in the mobile phase, has been treated by using the interstitial stagnant fluid model. Plate height equations have been derived for unsorbed tracers, which are totally excluded from the column material, as well as for unsorbed solutes, which permeate the stagnant mobile phase inside the particles. Band spreading was measured over a wide range of the reduced velocity with a single column packed with glass beads. The results show that the equation derived from the interstitial stagnant fluid model describes the velocity dependence of plate height more accurately than those found in the literature. It is suggested that the packing structure of a column be characterized by three dimensionless parameters.