In Figure we compare the populations of different charge states of the weak acid in both, supernatant and interpolyelectrolyte complex. As a reference, we use the Henderson-Hasselbalch equation, which neglects all interactions and predicts the ionization state in the ideal limit. In Figure ) we observe that the population of the uncharged state, H 2 SuA, in the supernatant phase is slightly suppressed, as compared to the ideal result at pH ≈ 4 ≈ pK A,1 . At this pH, the monovalent state, HSuA -, is favoured more than the uncharged one. The population of the monovalent state reaches a maximum at a pH slightly lower than the maximum of the ideal curve, which is at pH = (pK A,1 + pK A,2 )/2. At pH ≈ 5.5 ≈ pK A,2 , we observe that the population of the monovalent state is significantly suppressed in favour of the divalent state, SuA 2 -. These differences can be alternatively viewed as a shift of the ideal curves to lower pH values (dashed lines in Figure ). According to the Debye-Hückel theory (see Sec. S2.4), this shift should be proportional to valency of the respective ion. However, our simulations show that the population of the divalent species is shifted by about 0.3 units of the pH, more than twice as much as the population of the monovalent one, demonstrating the non-linear effect of electrostatic correlations.