Mathematical modeling of a Nafion membrane based optode incorporating 1-(2′-pyridylazo)-2-naphthol under flow injection conditions

A general mathematical model of a flow-through optical chemical sensor prepared by the immobilization of 1-(2′-pyridylazo)-2-naphthol (PAN) into a commercial Nafion® membrane was developed. The model takes into account the preparation of the optode membrane and in our opinion the most important chemical and physical processes involved in the generation of the analytical signal. The following model parameters were determined separately from the experimental verification of the model: aqueous diffusion coefficient of CuSO4 – 8.75 × 10−10 m2 s−1; membrane self-diffusion coefficient of the Cu2+–PAN complex and Cu2+ – 1.87 × 10−16 and 6.00 × 10−15 m2 s−1, respectively; Nafion/water ion-exchange equilibrium constants for the Cu2+–PAN complex and Cu2+ – 109.2 and 3.65 × 10−3, respectively. Very good agreement was obtained between the experimental optode response and the model predictions thus showing that the model developed could be used successfully for the mathematical description and optimization of the PAN/Nafion optode as well as of other ion-exchange membrane based optodes having a similar response mechanism.