The characterization of polymers and surfaces with a large number of d
ifferent sites is difficult, mainly due to problems in the numerical s
olution of the integral equation involved. New numerical tools develop
ed which can be used on PCs allow to solve these problems today at the
bench. This opens new possibilities to characterize equilibria in het
erogeneous systems and polymer solutions. We encourage analytical chem
ists to use these new tools and to develop a feeling for the limits of
the method in different applications. In this contribution, we report
the interpretation of the titration curves of different types of poly
ethylenimines in aqueous solution as an example of this new approach.