Theoretical and experimental studies of an optode based on complexation reactions with 1-(2'-pyridylazo)-2-naphthol in Nafion membranes

摘要

The processes affecting to a greatest extent the response of an optode derived from l-(2'-pyridylazo)-2-naphthol (PAN) in Nafion are the diffusion of PAN and the analyte metal cations within the Nafion membrane on one hand and the complex chemical equilibria between them on the other. Extensive research on the mechanism extraction of PAN into Nafion membranes from various ethanol-water solutions and of Ni(II) ions from their aqueous solutions were performed. A mathematical model taking into account the coupled character of the diffusion and the protolytic equilibria within Nafion membranes was developed and numerically solved. The values of the self-diffusion and selectivity coefficients of PAN and Ni(II) were determined by fitting the model to experimental membrane extraction data. A detailed study on the solubility and the acidity constant of PAN which influence considerably its incorporation into Nafion, was carried out as well. The results mentioned above form the basis for the development of a general model of the PAN/Nafion optode. The development and the experimental verification of such a model is now in progress.