Figure 1.

Scheme of the effect of pH shift upon one-sided addition of Na-Asc to the trans side of the membrane where an acidic pH ensures a high ascorbic acid (AscH) concentration. Once arriving on the alkaline cis-side, almost all acid molecules deprotonate and release a proton (encircled). Hence, the pH drops on the cis in the vicinity of the membrane. Since each compartment is stirred, this effect is occurring only within the unstirred layer of thickness δ. Scanning electrochemical microscopy serves to measure this pH shift.