FIGURE 5.
Mobile buffer concentration determined the kinetics of pH changes in the observation area that was located on the membrane surface at a distance of 73 μm to the area of proton release. τmax was a linear function of the buffer concentration. From the regression, a rough estimate of Ds (s2/4τmax = 8.3 × 10−5 cm2 s−1) at infinite buffer dilution can be made, if it is assumed that H+ release and observation areas are point like. The shades of gray of the circles correspond to the shades of gray of representative experimental traces recorded for 0.1, 0.5, and 0.9 mM CAPSO (pH 9.0). For clarity, the experimental records corresponding to the empty circles are omitted.