The Golay equation describes the variance per unit length (H) of an open tubular column in terms of the various physical properties of the column and distribution system, viz, the capacity ratio of the first eluted peak (k'), the diffusivities of the solute in the mobile and stationary phases (D_m and D_s), the radius of the column (r) and the linear velocity of the mobile phase (u)

(23)

or

where

and

Taking the ratio (r) of the second term to that of the first,

(25)

Now it has already been shown that, where (K) is the distribution coefficient of the solute with respect to the stationary phase, (v_s) is the volume of stationary phase per plate and (v_m) is the volume of mobile phase per plate.

Now,

where, (d_f) is the film thickness of the stationary phase.

Substituting for (K) in equation (25),

(26)

Consider a column 250 m I.D. carrying a film 0.2 m thick, and as in GC, D_m ranges from 1 4 x10^-1cm²/s and D_s from 1 4 x 10^-5cm²/s Then

Substituting for and in equation (26)