Origin of Separation in Displacement

In this book the mechanisms of both separative and dispersive transport are discussed, with an emphasis on their role in analytical separation processes. 

Inasmuch as all chemical separations require the movement of components from a region commonly shared to (or toward) individual regions, processes of differential displacement must underlie the entire methodology. Thus, by its most fundamental nature, a separation process must entail a selective movement through space of one component with respect to another (1,2). As a result, the science of separations is rooted foremost in transport phenomena. 

While the displacement of components must be selective—different for each species—we need to focus first on the underlying phenomenon the mechanism for getting a single component transported from one location to another. All such displacements fall into one of two broad classes (1, 2). These are described below. 

We can displace the medium that contains the component in bulk, in which case the component follows the gross movement of mass. This displacement can be achieved in two ways by direct mechanical means or by flow. 

Direct mechanical transfer simply means that the component, alone or in solvent, is physically moved by relocating it or the container holding it. This occurs, for example, in many fraction collectors where fractions accumulate in small tubes that are periodically shifted in position to allow for new collections. 

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