# Capillary Chromatography - Capillary Column Theory 2

Ogan *et al*.(10), used an alternative approach to take into account the compressibility of the gas and developed the following modified form of the Golay equation.

(2)

where (u(o)) is the mobile phase velocity at the column exit and at

atmospheric pressure,

D(m(o)) is the diffusivity of the solute in the mobile phase,

measured at atmospheric pressure

and (g) is the inlet/outlet pressure ratio of the column.

A description of the various dispersion processes that take place in a column are given in book 9 of this series. In the case of the capillary column the first expression in equation (2) describes the effect of longitudinal diffusion, the second expression described the effect of the resistance to mass transfer in the mobile phase and the last expression the resistance to mass transfer in the stationary phase.

It is interesting to estimate the relative magnitude of the two components of the resistance to mass transfer by examining the ratio of the resistance to mass transfer in the mobile phase to that in the stationary phase, *i.e.*,

(3)

In order to evaluate equation (3) for any given column and phase system the relationship between (h) and (uo) needs to be identified.