# Dispersion in Chromatography Columns - The Random Walk Model > Page 9

_{}

In practice the value of (j) will lie between 0.5 and 1.0, but, for simplicity the value of (j) will be taken as unity. This implies that one lateral step will be taken by a given molecule for every step traveled axially equivalent to one particle diameter .

Thus,
_{ }

or,
_{ } (3)

Consider a sample injected precisely at the center of a 4 mm diameter LC column. Employing equation (3) allows the distance traveled axially by the solute band before the radial standard deviation of the sample of solute is numerically equal to the column radius to be calculated. That is, the band has now spread evenly across the column and the solute is in radial equilibrium.