Dispersion in Chromatography Columns - Dispersion Processes that take Place in an LC Column > Longitudinal Diffusion > The Diffusion Process > Page 19

              and              

Therefore, dividing by l to obtain the variance per unit length,

                                

In the same manner as the constant (l) introduced by Van Deemter into the function for multipath dispersion, Van Deemter also introduced a constant (g) into the Longitudinal Dispersion contribution to variance to account for some packing inhomogeneity. As a consequence, the expression for the Diffusion contribution to the variance per unit length of the column became,

                                                                    (8)

To be precise, there should be a second longitudinal diffusion contribution to the overall variance that would arise from the stationary phase. The same method of derivation can be used but the time the solute spends in the stationary phase is now, is now a function of the capacity ratio of the column, (k').