# Dispersion in Chromatography Columns - Resistance to Mass Transfer Dispersion > Page 25

# Resistance to Mass Transfer Dispersion

Both the
resistance to mass transfer in the mobile phase and that in the stationary
phase, can be treated quantitatively using the random walk model. Recalling
that if each molecule of a group takes a series of steplike movements,
(positive or negative) the direction being completely random, then after (p)
steps have been taken, each step having an average length (s), the average of
the molecules will have moved some distance from the starting position and will
form a Gaussian type distribution curve with a variance of s^{2},

where

_{}^{ or
}_{}^{ }

^{
}

In the first instance, consider that the distribution is energy controlled and not diffusion controlled, thus, a solute molecule will desorb from the stationary phase when it randomly has sufficient kinetic energy to break its association with a molecule of stationary phase (see Principles and Practice of Chromatography). Similarly, a molecule will be absorbed under the same conditions.