Immobilised reagents for optical heavy metal ions sensing

Many ligands such as 1-nitroso-2-naphthol (NN), 4-(2-pyridylazo)resorcinol (PAR), 2,4-dinitrosoresorcinol (DNR) and 1-(2-pyridylazo)-2-naphthol (PAN) have been investigated in the development of optical sensors for heavy meta l ions found in aquatic environments which include Co2+, Cu2+, Ni2+, Fe3+, Cd2+, Zn2+, Pb2+ and Hg2+. The reagents were immobilised by physical adsorp tion on to polymeric materials such as XAD-4, XAD-7 and Dowex ion-exchange resins, and were found to exhibit chromic characteristics in the absence an d presence of metal ions in solution. Reflectance measurements are used her e. Parameters such as pH, measurement wavelength and reagent concentration have been optimised for a given metal ion, and the reversibility/regenerabi lity characteristics of the sensing reagent have been studied together with the limit of detection and the concentration range producing linear respon se for the metal ion. (C) 1998 Elsevier Science S.A. All rights reserved.