Effect of the ionic strength on the adsorption process of an ionic surfactant onto a C18-bonded charged surface hybrid stationary phase at low pH

► Nortriptylinium adsorption behavior on CSH-C18 is studied at various pH and ionic strengths. ► Overloaded band profiles recorded and derived from several isotherm models are compared. ► At low loading factors, electrostatic repulsion of ions by the surface affects this behavior. ► At high loading factors the ions are mostly adsorbed as neutral species. ► At high loading factors, a Langmuir-Moreau isotherm best accounts for adsorption behavior.