Preconcentration of Trace Metal Ions from Natural Waters: Complexation with Meso-Tetra (p-sulfonatophenyl) porphine and Adsorption onto XAD Resins

Abstract

<P> A new preconcentration method had been developed for the determination of some trace-metal ions in lakewater. This method is based on the formation of their TPPS4 complexes at elevated temperatures in solution and adsorption of the complexes onto a column of the macroporous acrylic ester resin, XAD-7. The complexes are eluted with a methanolic solution and the metal concentration determined by graphitefurnace atomic absorption spectroscopy. Optimal conditions were established for the group preconcentration of Cd, Cu, Ni and Pb. The concentration of these trace metals in several lakewater samples were determined successfully, with a precision comparable to that of the accepted Chelex-100 method. Application of the method to natural seawater samples failed, largely because of aggregation in the highly saline medium. </p> <P> Adsorption isotherms of TPPS4 and its complexes on XAD resins were obtained. Adsorption onto XAD-2 and XAD-4 resins likely involves n-n interactions while adsorption onto XAD-7 is probably due to weak Van der Waals forces. The adsorption at high TPPS4 concentrations is complicated by aggregation. </p> <P> An attempt to create a simple chelating ion-exchange resin by adsorption of TPPS4 onto XAD resin failed. Similarly, the development of a rapid room-temperature preconcentration method specifically for Pb and Cd in natural waters was not successful. </p>