Anion selective optical sensing with metalloporphyrin-doped polymeric films

Abstract

Metalloporphyrins (Mn(III) and In(III)] are investigated as active polymer film components in the design of reversible anion-selective optical sensors. The optical measurements are made by casting thin plasticized polymer films (PVC, polyurethane, etc.) containing the given metalloporphyrins on glass plates. When bathed in aqueous test solutions, the optical response of such films is based upon the selective extraction of anions by metalloporphyrins into the organic membrane phase. Changes in optical absorbance occur via either of two mechanisms. For films based on Mn(III) tetraphenylporphyrins, the porphyrin itself can serve simultaneously as the ionophore and chromophore for the detection of iodide ions. In this instance, direct ligation of iodide as an axial ligand of the central (Mn(III) results in a change in the molar absorptivitiy of the soret band of the porphyrin. In the case of In(III) octaethylporphyrin, the incorporation of an appropriate pH-indicator dye along with the metalloporphyrin is required to achieve films with optical selectivity toward nitrite and chloride. The analytical characteristics of these porphyrin-based films with respect to anion response time, dynamic measurement range, and reproducibility, are discussed.