Based on 31P-NMR titration data, microscopic ionization equilibria of several myo-inositol tetrakisphosphates have been fully resolved. The problem is solved based on a cluster expansion technique of the free energy of the microstate, which leads to a straightforward parameterization and drastically reduces the number of necessary parameters needed to specify the microscopic equilibria. From the NMR titration data, we obtain all microscopic ionization constants as well as the probabilities of the different microstates. This information permits discussing ionization mechanism of these molecules in full detail.