Estimation of UWL Thickness from pH Measurements Near the Membrane Surface

5 Estimation of UWL Thickness from pH Measurements Near the Membrane Surface 

Antonenko and Bulychev [84] measured local pH changes near BLM surfaces using a variably positioned 10 pm antimony-tip pH microelectrode. Shifts in pH near the membrane surface were induced by the addition of (NH4)2S04. As the neutral NH3 permeated, the surface on the donor side of the BLM accumulated excess H+ and the surface on the acceptor side of the membrane was depleted of H+ as the permeated NH3 reacted with water. These effects took place in the UWL. From measurement of the pH profile as a function of distance from the membrane surface, it was possible to estimate /raq as 290 pm in the stirred solution. 

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