For the separation of A and B by column 2 in Problem 23-32:

(a) If broadening is mainly due to longitudinal diffusion, how should the flow rate be changed to improve the resolution?

(b) If broadening is mainly due to the finite equilibrium time, how should the flow rate be changed to improve the resolution?

(c) If broadening is mainly due to multiple flow paths, what effect will flow rate have on the resolution?

In this section, we'll solve the problems in Problem 23-32 on the separation of and B by column 2.

Examine the Purnell equation for resolution now:

$\mathrm{Resolution}=\frac{\sqrt{\mathrm{N}}}{4}\frac{(\mathrm{\alpha }-1)}{\mathrm{\alpha }}\left[\frac{{\mathrm{k}}_2}{1+{\mathrm{k}}_2}\right]$

Resolution is proportional to$\sqrt{\mathrm{N}}$

a) If the broadening is primarily due to longitudinal diffusion, determine how the flow rate should be altered to improve the resolution:

- The flow rate should be increased for the following reasons:

1. ${\mathrm{u}}_{\mathrm{x}}$is inversely proportional to (as ${\mathrm{u}}_{\mathrm{x}}$increases, H decreases).

2. H and N are inversely proportional (lower H higher N ).

3. The resolution is proportional to$\sqrt{\mathrm{N}}$ (a higher N equals a higher resolution).

b) If broadening is required, determine how the flow rate should be altered to increase resolution.

primarily as a result of the finite equilibrium time:

- The flow rate should be reduced because:

1. ${\mathrm{u}}_{\mathrm{x}}$is proportional to (a lower ${\mathrm{u}}_{\mathrm{x}}$equals a lower H ).

2. H and N are inversely proportional (lower H higher N ).

3. The resolution is proportional to$\sqrt{\mathrm{N}}$ (as N increases, the resolution increases).

c) If the broadening is primarily due to various flow routes, determine the influence of flow rate on the resolution:

- Because A is the only variable in the van Deemeter equation, there is no effect.