Modeling Selectivity and Cross-sensitivity in membrane-based potentiometric sensors

We propose a steady state model for ion selective membranes (ISM) as selectivity element in potentiometric sensors. The model solves the Poisson-Boltzmann equation, coupled to distributed chemical reactions between ionophores and two types of competing ions. We show that a Donnan potential arises when ionic sites are present, while selectivity is achieved only if using ionophore-doped ISMs. The model allows to evaluate cross-sensitivities and can explain steady state non-Nernstian responses. We also provide an application example of sensor parameter design supported by the proposed model.