Experiments performed using ceramic frits yield evidence for the equivalence between the formation factor and the microstructural diffusion coefficient, which is a characterization of the porous microstructure. Due to the complexity of accounting for the chemical behavior of the pore solution, extracting the microstructural diffusion coefficient from diffusion data requires a numerical calculation. While the apparent diffusion coefficient depended upon the chemical makeup of the pore solution, the procedure outlined here was able to extract the microstructural diffusion coefficient for each system, yielding a similar value for the systems studied. The presence of KOH in the pore solution had a noticeable affect on the apparent diffusion coefficient of iodide. Due to the similarity between the self diffusion coefficient of iodide and chloride, one would expect similar effects on chloride ions in cementitious systems. The ability to extract the microstructural diffusion coefficient from observed data has a direct influence on service life modeling that can independently account for changes in either the pore structure or the pore solution chemistry. This is particularly important in cementitious systems containing pore solutions with large ionic strengths.