The Column Design Process for Packed Columns

Column design involves the application of a number of specific equations (most of which have been previously derived and/or discussed) to determine the column parameters and operating conditions that will provide the analytical specifications necessary to achieve a specific separation. The characteristics of the separation will be defined by the reduced chromatogram of the particular sample of interest. First, it is necessary to calculate the efficiency required to separate the critical pair of the reduced chromatogram of the sample. This requires a knowledge of the capacity ratio of the first eluted peak of the critical pair and their separation ratio. Employing the Purnell equation (chapter 6, equation (16)). 

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It should be noted that Purnell s equation utilizes the thermodynamic capacity ratio calculated using the thermodynamic dead volume. 

Knowing the number of theoretical plates that are required, the length of the column (L) is defined as the product of the number of plates and the variance per unit length of the column (H), i.e.. 

For convenience the Van Deemter equation for the LC column will be generally used in the following argument. However, when GC columns are considered the equations will be appropriately modified, where 

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