Continuous counter-current chromatographic processes have been increasingly applied in the last years. For chromatographic systems characterized by linear or Langmuir adsorption equilibria, there are nowadays reliable design rules available to decide whether a separation is feasible and which operating parameters should be used. For more complex equilibrium functions, theoretical methods are less developed. Mole realistic adsorption isotherms are frequently characterized by inflection points in their courses. A flexible model capable to quantify single solute and competitive adsorption isotherms is provided by statistical thermodynamics. In this work, second-order truncations of a statistical model involving inflection points are investigated The classical scanning technique is used to identify the region of applicable operating parameters. Then an alternative approach is suggested, which verifies the existence and shape of the suitable parameter region by infeasibility certificates. Using the True Moving Bed model, both approaches are compared for different feed concentrations, purity requirements and column efficiencies (C) 2009 Elsevier Ltd All rights reserved