Dispersion in Chromatography Columns - The Van Deemter Equation > Page 54

Now, if it is assumed that df << dp (which in practice will always be true) and (x) is close to zero (i.e. the diffusivities of the solute in the two phases is about the same) which for liquid chromatography will also be true, then,

                  

Furthermore, when k'>> 1, that is, for well retained peaks, and taking (g) as 0.6

   (36).

Under these circumstances, it is seen that the optimum velocity is directly proportional to the solute diffusivity in the mobile phase and inversely proportional to the particle diameter of the packing. The quality of packing,  also plays some part, but to a very less significant extent. It is now possible to determine the factors that control the magnitude of Hmin. Substituting the function for uopt from equation (34) in equation (33) an expression for Hmin is obtained.