The kinetic model was used to fit the traces of v(COester) and v(COamide) intensities simultaneously (Figure ) and demonstrates a very good description of the sigmoidal evolution of EB intensity in presence of Na + . At the same time, the truncated version of this model, i.e. neglecting the autocatalytic process, can be used to provide a very good fit for the experiments in K + buffer showing that spontaneous incorporation is sufficient in this case (the same is the case in Cs + , Figure ). Using this model, we can directly compare the evolution of only the membrane-incorporated component (blue dashed lines) in presence of each ion. Accordingly, we note that interaction of EB with Na + leads to a considerably delayed incorporation than with K + , but exceeds in level of incorporation by a factor of ca. 4 judging solely based on SEIRA intensity. Furthermore, this model and the fitting results are in line with the loss of intensity after wash with new buffer, which removes surface-bound EB at the membrane interface and leads to a decrease of intensities towards the level of incorporated EB according to the kinetic model (blue dashed lines).