Zone Formation in Two Dimensions

The amount of excess solute E (in moles per unit area of filter) that can accumulate in the polarization layer is the excess concentration above that of the background solution, c - (70/u), integrated over coordinate y 

Usually the separation is effective in proportion to E because E represents either the amount of contaminant removed if the rejected solute is undesirable or the amount of product concentrated if the solute is desirable. However, the degree to which the concentration at the interface c0 can be increased to this end is limited because high values augment leakage, resistance to flow, and the risk of precipitation. Consequently, to increase E, efforts are generally made to increase effective diffusivity Dr, which is best done through stirring or convective processes. Thus these processes become important considerations to effective operation. 

In summary, the mathematical similarity of different steady-state solute zones, critical to the success of seemingly unrelated separation methods, demonstrates the impressive unifying power of the basic transport approach to chemical separations. This unity is emphasized again in the next chapter, where we delve into the classification and comparison of separation methods. 

Chapter 5 dealt with the evolution of thin starting zones into concentration pulses distributed along a single axis. This treatment is appropriate for some important analytical separation methods, such as column chromatography carried out in thin one-dimensional tubes. However, as an alternate method 

The area A of the elliptical spot, given by ir(a/2)(b/2), therefore equals 

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