Mechanisms of Zone Broadening

Several kinds of random events other than molecular diffusion contribute to zone spreading in separation systems. With each increment in zone spreading there is a corresponding loss of resolution it is thus important to understand these processes in order to minimize them. The random processes described below are responsible for effective diffusion in many engineering and chemical systems as well as in separations. 

It is important to note that the displacement of sample components in all the above processes is described by the basic mass transport equations developed earlier. However, some special considerations are needed to properly account for the random component of transport. Thus the basic equation of flow and transport, Eq. 3.35, is now expressed as 

The random nature of the second term on the right assures us, through the central limit theorem, that it contributes an effective diffusion term to zone spreading [11]. Thus, this term must have the equivalent form 

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