NAFION-BASED OPTODE FOR THE DETECTION OF METAL-IONS IN FLOW-ANALYSIS

An optical chemical sensor (optode) is described in which the colorime tric reagent 1-(2'-pyridylazo)-2-naphthol (PAN) is immobilized in a Na fion(R) membrane. The membrane, which is homogeneous, transparent and mechanically strong, changes color rapidly in the presence of one of s everal metal ions (Ni(II), Cd(II), Cu(II), Pb(II), Hg(II), Zn(II)), an d 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 th e concentration range 0.02 to 0.12 mM. The advantages of the use of se quential injection with optode membranes are emphasized and the factor s which are important in the discrimination between metal ions are dis cussed.