Previous
publications have demonstrated the tuning of ion-transfer
(IT) processes across ion-selective membranes (ISMs) with thicknesses
in the nanometer order by modulating the oxidation state of a film
of a conducting polymer, such as poly(3-octylthiophene) [POT], that
is in back-side contact. Attempts on the theoretical description of
this charge transfer (CT)–IT system have considered the Nernst
equation for the CT, while there is no empirical evidence confirming
this behavior. We present herein the first experimental characterization
of the CT in POT films involved in different CT–IT systems.
We take advantage of the absorbance change in the POT film while being
oxidized, to monitor the CT linked to nonassisted and assisted ITs
at the sample–ISM interface, from one to three ionophores,
therefore promoting a change in the nature and number of the ITs.
The CT is visualized as an independent sigmoid in different potential
ranges according to the assigned IT. Herein, we have proposed a simple
calculation of the empirical CT utilizing the mathematical Sigmoidal–Boltzmann
model. The identification of the physical meaning of the mathematical
definition of CT opens up new possibilities for the design of sensors
with superior analytical features (mainly in terms of selectivity)
and the calculation of apparent binding constants in the ISM.