Nafion-based optode for the detection of metal ions in flow analysis

An optical chemical sensor (optode) is described in which the colorimetric reagent 1-(2′-pyridylazo)-2-naphthol (PAN) is immobilized in a Nafion® membrane. The membrane, which is homogeneous, transparent and mechanically strong, changes color rapidly in the presence of one of several metal ions (Ni(II), Cd(II), Cu(II), Pb(II), Hg(II), Zn(II)), and the color change can readily be reversed by contact with acid. This optode has been incorporated into a modified sequential injection flow system which has been optimized for the determination of Ni(II) in the concentration range 0.02 to 0.12 mM. The advantages of the use of sequential injection with optode membranes are emphasized and the factors which are important in the discrimination between metal ions are discussed.