## protonation constant

https://doi.org/10.1351/goldbook.P04909
The equilibrium constant $$K_{\text{H}n}$$ for the addition of the $$n$$th proton to a charged or uncharged ligand. The cumulative protonation constant, $$\beta_{\text{H}n}$$, is the equilibrium constant for the formation of HnL from $$n$$ H+ and L. The same equilibrium constant may be described in several ways, depending on how the ligand, L, or the acid, has been defined.
Source:
Orange Book,2nd ed., p. 13