Using Column Efficiency to Optimize Resolution

If the capacity factor and a are known, then equation 12.21 can be used to calculate the number of theoretical plates needed to achieve a desired resolution (Table 12.1). For example, given a = 1.05 and kg = 2.0, a resolution of 1.25 requires approximately 24,800 theoretical plates. If the column only provides 12,400 plates, half of what is needed, then the separation is not possible. How can the number of theoretical plates be doubled The easiest way is to double the length of the column however, this also requires a doubling of the analysis time. A more desirable approach is to cut the height of a theoretical plate in half, providing the desired resolution without changing the analysis time. Even better, if H can be decreased by more than 

Number of Theoretical Plates Needed to Achieve Desired Resolution for Selected Values of ks and a 

Schematics illustrating the contributions to band broadening due to (a) multiple paths, (b) longitudinal diffusion, and (c) mass transfer. 

One contribution to band broadening in which solutes diffuse from areas of high concentration to areas of low concentration. 

it also may be possible to achieve the desired resolution with an even shorter analysis time by decreasing ki or a. 

---