Investigation of the adsorption of ferroin-type ligands and metal chelates on activated carbons for applications in reagent purification and trace metal enrichment and determination

Abstract

A representative group of ferroin-type ligands and various activated carbons were screened for possible use in trace metal separations. Selected as most promising, 2,2′-dipyridylketone-2-pyrid ylhydrazone (DPPH) and Norit A were investigated more extensively with special attention to p K a values and ionic charges of DPPH species, isotherms and Langmuir parameters for the adsorption of DPPH and its chelates on Norit A, and to conditions and procedures optimal for analytical separations and recoveries of trace metal ions. The results provide evidence of two types of sites on Norit A for adsorption of DPPH and its chelates. These are interpreted in terms of Langmuir parameters and ionic charge types of the adsorbates. Practical applications are demonstrated for removing iron, cobalt, nickel and copper ions from various reagents and for preconcentrating trace amounts of these metal ions prior to their quantitation. Metal ion concentrations remaining unextracted are less than 10 −7 M, 100-fold or higher enrichments are feasible, and recoveries of the metal ions by desorption from Norit A average 99%, with 2–5% relative standard deviations for their determinations.