Dispersion in Chromatography Columns - Dispersion Processes that take Place in an LC Column > Longitudinal Diffusion > The Diffusion Process > Page 15
where (Dm) is the Diffusivity of the solute in the fluid.
and is the concentration gradient at (x).
Now, mass of solute leaving the slice (dx) thick, at (x+dx), i.e., (mx+dx), is,
Thus, the net change in mass per unit time in the slice (dx) thick will be