Breakthrough curves and elution profiles of single solutes in case of adsorption isotherms with inflection points

There is a well developed theory available which is capable to predict the evolution of band profiles in chromatographic columns provided the systems closely follow equilibrium conditions [1-3]. Equilibrium theory and the method of characteristics allows to derive analytical expressions describing the shapes of elution profiles for different injection times and concentrations under diluted and overloaded conditions. They explain the strong relation between these shapes and the adsorption equilibrium functions characterising the system under consideration. The method is used extensively in order to predict the chromatographic process for systems obeying the competitive Langmuir model. It explains the firmation of shock waves and simple waves in such systems. It is also the basis of the ECP-method which is capable to determine adsorption isotherms form measured elution profiles. Based on earlier work summarised in [1-3] it is the subject of the presentation to apply the methods of characteristic in order to explain the development of single solute elution profiles for systems possessing adsorption isotherms with inflection points. Under these conditions the adsorption and desorption branches will be characterised by composite waves and unusual band profiles result. Besides predicting and explaining the shapes of these profiles a possibility to solve the inverse problem (i. e. the determination of the isotherms) will be explained. Experimental results will be presented for illustratoin. References: [1] G. Helfferich, G. Klein, Multicomponent chromatography, Marcel Dekker, New York, 1970. [2] H. K. Rhee, R. Aris, N. R. Amundson, First-order partial differential equations, Prentice-Hall, Englewood Cliffs, New Jersey, Vol. I, 1986, and Vol. II, 1989. [3] G. Guiochon, S. Golshan-Shirazi, A. Katti, Fundamentals of preparative and nonlinear chromatography, Academic Press, New York, 1994