Fluorimetric determination of mercury with a water-soluble porphyrin and porphyrin-doped sol-gel films

Abstract

The fluorimetric determination of mercury ions with 5,10,15,20-tetra( p-sulfonatophenyl)porphyrin in aqueous solutions and in porphyrin doped sol-gel films was investigated. Optimization of complexation conditions such as buffer components, pH range and temperature resulted in a method which enabled the determination of mercury ions in aqueous solutions within 15 min with a detection limit of 1.4 μg/1 Hg(II). The main interfering ions were found to be Cd, Zn and Pb. To develop an optochemical sensing device the porphyrin derivative was immobilized in sol-gel thin films (thickness of about 600 nm) and the sensor properties (i.e., reactivity, stability and morphology of the sensitive layers) were studied. The kind of catalyst used (acid or base) was found to influence the stability and sensitivity. Sensing films prepared with acid were stable and insensitive to mercury. Preparation of the films with alkaline catalysis resulted in mercury sensitive layers with a limited stability. Stability could be improved by covalent binding of the reagent dye.