# Capillary Chromatography - Capillary Column Theory 1

# Capillary Column Theory

The fundamentals of peak dispersion are treated in detail in book 9 so in this section only the specific dispersion processes that occur in a capillary column will be considered. The equation for the variance per unit length of a capillary column was developed by Golay (1) and the equation he derived took the following form,

(1)

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

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

(DM) is the diffusivity of the solute in the mobile phase,

(DS) is the diffusivity of the solute in the stationary phase,

(r) is the radius of the column,

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

In the development of equation (1), Golay did not take into account that, due to the compressibility of the mobile phase (a gas), the linear velocity changed significantly along the length of the column. Due to the velocity change not being linear the average velocity can not be used in equation (1) to accurately described (H) (the variance of the dispersion that takes pace in the column).