Controlled Dispersion in the Stationary Phase

The major difference between diffusion controlled dispersion and that resulting from adsorption and desorption is that the transfer process is concentration controlled. Reiterating equation (7), 

during solute transfer between the phases, (t) is now the average diffusion time (to) and (o) is the mean distance through which the solute diffuses, Le., the depth or thickness of the film of stationary phase (df). Thus, 

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The value of (q) takes into account the precise shape of the pool of stationary phase for a uniform liquid film as in a GC capillary column, q = 2/3. Diffusion in rod shaped and sphere shaped bodies (e.g., paper chromatography and LC) gives q=l/2 and 2/15, respectively [2]. 

The validity of equation (18) for LC packed columns has also been experimentally demonstrated and will be discussed in a later chapter. 

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