# Dispersion in Chromatography Columns - The Golay Equation > Page 71

This is the fundamental difference between the two types of column. The variance from a packed column is largely determined by the magnitude of the particle diameter, in contrast, the variance obtained from a capillary or open tubular column is determined by the magnitude of the radius

The Golay equation takes the following form:-

(52)

Where (H) is the variance per unit length of the column for the given

solute,

(k)' is the capacity factor of the solute,

(K) is the distribution coefficient of the solute between the two

phases,

(D_{M)} is the diffusivity of the
solute in the mobile phase,

(D_{S)} is the diffusivity of the
solute in the stationary phase,

(r) is the radius of the column,

and (u) is the linear velocity of the mobile phase.

If the solute
is unretained (*i.e*. k'=0 ) then the Golay equation

reduces
to,
_{} (53)

**Figure 17. Graph of H against
U for an Uncoated Capillary Column**