In Fig. we present the titration curves for suspensions of nanoparticles containing 1:2 electrolytes at concentrations: c s = 10 mM (a); c s = 50 mM (b); and c s = 100 mM (c). A perfect agreement between theory and simulations is found for all salt concentrations, in the whole range of pH values. The success of the theory is clearly due to the high accuracy of the mPB equation for predicting the ionic density profiles and due to very accurate description of the electrostatic potential in the vicinity of each site, calculated using the ϕ disc and µ solv . We observe that for pH 8, the number of protonated sites is very low. On the other hand for pH 2 almost all sites are protonated. Addition of electrolyte leads to screening of electrostatic interactions, resulting in lower protonation for the same value of pH. Titation curves for the case of added 1:3 electrolyte at concentration c s are shown in Fig. . To highlight the effect of larger anionic charge, in the panels we also plot the corresponding titration isotherms of suspensions with 1:1 salt at the same concentration. Again, a very good agreement between simulations and theory is observed for all studied electrolyte concentrations. We see that increase of anion valence results in diminished protonation -larger Z ef ffor the same salt concentration and pH. The reason for this is that the large charge of trivalent anions favors their repulsion from the nanoparticle surface, see Fig. . This is further amplified by the electrostatic correlations that also favor bulk solvation of trivalent coions. The net result is that compared to 1:1 electrolyte there are fewer trivalent anion present near the surface of a nanoparticle, making the electrostatic potential less negative -and, therefore, attracting less hydronium ions into this region -leading to diminished protonation and larger Z ef f . The difference in protonation between suspensions containing either 1:3 or 1:1 electrolyte is most pronounced at intermediate pH values, in the range pH ∼ 5 to pH ∼ 7. For example, at pH = 6.0 and c s = 50 mM, the the number of deprotonated groups rises from Z ef f ≈ 179 to Z ef f ≈ 248, when z -is changed from one to three -representing a ∼ 38% increase in the nanoparticle charge. Although the theory proposed in this paper is able to describe very well suspensions containing multivalent coions, we expect it to fail when applied to suspensions containing multivalent counterions, such as Ca ++ . For such suspensions, both proton and Ca ++ will compete for the same adsorption sites, leading to strong correlations between the two near the surface of a nanoparticle. Fig 8, compares the tritation curves obtained using the canonical rMC simulations (symbols) with the predictions of the present theory (solid curve) for suspensions containing 2 : 1 electrolyte. As expected, we see strong deviations between the present theory and the simulations. At this time it is not clear how to include the strong electrostatic correlation effects into the theoretical framework presented in this paper.