Transport and Theoretical Plates

When the flow velocity v is zero, the total solute displacement velocity W= U + v reduces to W= U. Transport therefore follows the equation 

We note that Dr may or may not equal the molecular diffusion coefficient D, depending on the absence or presence of extraneous random dispersion mechanisms as discussed in Chapter 5. For simplicity, we relate DT to D by 

We would like to know the plate height and the number of theoretical plates generated in Sc separations. Equation 5.38 gives plate height as H = 2Dt/W. By writing DT = 0D and W= U, this becomes 

We observe that friction coefficient / (appearing both in D and U) is absent from H because it cancels out in forming the ratio D/U. Thus H is independent of /. 

It was shown in Chapter S that the number of theoretical plates provides a direct measure of separation efficiency. Using N = XIH, Eq. 5.41, we have 

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SEPARATION BY EXTERNAL FIELDS (Sc METHODS) 8.2 TRANSPORT AND THEORETICAL PLATES... 

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