A fluorescent sensor for aluminum(III), magnesium(II), zinc(II) and cadmium(II) based on electrostatically immobilized quinolin-8-ol sulfonate

Abstract An optical sensor responding to Al(III), Mg(II), Zn(II) and Cd(II) is prepared by immobilizing quinolin-8-ol-5-sulfonate (QS) on an ion-exchange resin and attaching the resin to the end of a trifurcated fiber-optic bundle. Immobilization leads to weak fluorescence from QS and causes shifts in the fluorescence spectra of the QS/metal complexes. Detection limits for the metal ions studied are all below 1 × 10 −6 M. Response to metal ion concentration is nonlinear. The shape of the response fits a model that assumes a 1:1 metal/QS chelate is formed. Forrnation constants for immobilized QS complexes calculated from the model are similar to those observed for dissolved QS. Immobilized and dissolved QS behave similarly with respect to pH and interferences.