Dispersion in Chromatography Columns - Effect of Mobile Phase Compressibility On the HETP Equation for a Packed GC Column > Page 37
(Po) is the pressure at the column exit,
and (uo) is the linear velocity of the mobile phase at the column
Now from the kinetic theory of gases, it can be shown that the diffusivity of a solute in a gas is inversely proportional to the pressure.
Thus, DxPx = DoPo or
where (Do) is the solute diffusivity at the end of the column at (Po)
and (Dx) is the solute diffusivity at point (x) and pressure (Px)