Dispersion in Chromatography Columns - Dispersion Processes that take Place in an LC Column > Longitudinal Diffusion > The Diffusion Process > Page 22


where,  DS is the Diffusivity of the solute in the stationary phase

The total contribution to (H) from longitudinal diffusion will thus be:-


or,                                           (10)


It is seen from equation (10) that the longitudinal diffusion term is a function of (k') the capacity factor of the solute. While this could be significant in an LC capillary column systems, where the film of stationary phase could be continuous along the length of the column, it will not be so in a packed column. The stationary phase in a packed column is broken into segments between each particles and between each pore in each particle so free continuous diffusion in the stationary phase would be impossible. It follows that the longitudinal diffusion term for packed columns should be independent of the k' of the solute or, very nearly so, and in practice the effect of longitudinal diffusion in the stationary phase is ignored.