An adequate characterization of adsorption isotherms is mandatory for chromatographic process development. Here, the elution by characteristic point (ECP) is a suitable method with low consumption of material and time. However, the ECP method requires a highly ideal behavior of the measured system. An innovative extended ECP approach is presented to characterize a non-ideal system by the example of protein ion-exchange adsorption. A marker, here bovine hemoglobin, is used to quantify all non-idealities, e.g., convection, dispersion, or low number of theoretical plates. The system signal of the marker is used to compensate the system signal of the interesting solute, here bovine serum albumin. The resulting isotherm agrees well with the control results of a validated static approach.