Figure 3.

pH-dependent speciation of Mössbauer doublets in Fe(II)-Av MDO. (A) Speciation of Mössbauer doublets (${\delta }_1$ and ${\delta }_2$) observed in Fe(II)-Av MDO for samples prepared at pH 6.5 and 9.5. (B) The theoretical lines (red and blue) show the expected behavior assuming a pH-dependent equilibrium with a $\text{p}{K}_{\text{a}}$ of 9.1. The apparent pH (${\text{pH}}_{\text{app}}$) at cryogenic temperature is obtained by adding 0.4 pH unit to the pH of the solution at room temperature.