In an ideal world, isotherms are important to all forms of chromatography, including displacement. Everybody wants to calculate the isotherms to predict displacement. However, it is no more important to do this for a displacement experiment than it is for an elution experiment. It would be nice to know about all the binding isotherms in order to understand the displacement characteristics, but they are rarely available and take a lot of work to get You can do displacement without knowing the isotherms just as you can do elution without first doing a van Deempter analysis. In fact, it may be more practical to do so in a commercial development setting.
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How do the two methods - elution and displacement - compare when