# Capillary Chromatography - The Optimum Velocity and Minimum Variance per Unit Length 1

It is clear that the column radius is the critical property of the system, significantly effecting both the column efficiency and the analysis time. It is also seen that the contribution to dispersion from longitudinal diffusion is the same for both columns and so the striking difference between the performance of the two columns depends solely on the effect of the column radius on the resistance to mass transfer terms. This is clearly illustrated by the large difference in slopes of the two linear curves for the resistance to mass transfer shown in figure 17.

## The Optimum Velocity and Minimum Variance per Unit Length

Equation (4) can be put in the simple form,

(5)

where B = 2Dm

and C=

In order to determine the optimum velocity where (H) is a minimum and thus the maximum efficiency is obtained, equation (5) must be differentiated and equated to zero.

That is,

solving for (uopt) (6)