# Dispersion in Chromatography Columns - The Random Walk Model > Page 10

For the conditions
given above s_{R }= 0.2.

Thus, substituting this value in equation (3),

_{}

or,
_{ } (4)

The distance that a solute band must pass along a column before a sample, injected at the center of the packing, is evenly spread across its diameter, can be calculated for columns packed with different sized particles using equation (4). The results are shown as a graph relating length against particle diameter in figure (3). The particle diameter range normally employed in liquid chromatography is about 2-25 micron and so from figure 3, it is clear that radial equilibrium would never be achieved for those column lengths commonly in use in LC.