If I460/I403 is plotted against pH, the Slogistic1 model available at OriginPro® (Equation ( )) is frequently employed; in this case, 𝑥 = pH and 𝑦 = I460/I403, and a, c, and k are model-derived calibration constants. Calibration is a critical step in this process and must be conducted carefully. It is highly advisable to perform it in conditions that mimic, as much as possible, those of the transport experiments to obtain reliable results.