Study of the extraction of 1-(2′-pyridylazo)-2-naphthol from ethanol-water solutions into Nafion® membranes

The extraction of PAN (1-(2'-pyridylazo)-2-naphthol) from neutral ethanol-water solutions into Nafion(R) membranes was studied using a system consisting of two thermostated (25 degrees C) extraction cells clamped on opposite sides of a circular Nafion(R) membrane. Solutions of identical concentration of PAN in ethanol-water solutions containing 35-100% (v/v) ethanol in both cells were mechanically stirred and the concentration of PAN was monitored spectrophotometrically with time. A general mathematical model was developed and numerically solved in cylindrical coordinates and by fitting the model to experimental extraction data, the diffusion coefficient of PAN within the membrane and the ion-exchange equilibrium constant for protonated PAN were determined. By extrapolating the results for the extraction of PAN from various ethanol-water solutions to 0% ethanol concentration, the corresponding values of the two model parameters mentioned above in water were calculated. The results obtained are essential for the development of a mathematical model describing an optode consisting of PAN immobilised into a Nafion(R) membrane which we are working on. (C) 1999 Elsevier Science B.V. All rights reserved.