Plate Height A Zone Spreading Index

It has been emphasized that zones universally diffuse outward during their transport through a separation system. Corresponding to the total effective diffusion coefficient Dr, each zone acquires a variance which the form of Eq. 5. 25 shows to equal 

This equation shows that r2 is proportional to time t providing DT is constant. 

For a zone in uniform translation at a constant velocity W the distance X traversed by the zone in time t is simply 

When this is substituted into Eq. 5.37, it yields the simple proportionality 

The concept of theoretical plates evolved from studies of distillation and countercurrent distribution, where distinct stages frequently exist. The widespread adoption of plate concepts in chromatography can be traced 

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