USE OF CHELEX RESIN FOR DETERMINATION OF LABILE TRACE-METAL FRACTIONS IN AQUEOUS LIGAND MEDIA AND COMPARISON OF THE METHOD WITH ANODIC-STRIPPING VOLTAMMETRY

The use of Ca-Chelex to determine labile fractions of Cd (II), Cu (II), Pb (II), and Zn (II) in the presence of the model ligands nitrilotriacetic acid (NTA), ethylenediaminetetracetic acid (EDTA), glycine, and humic acid was investigated. Under conditions where resin kinetics are fast and batch uptake is quantitative, the slow dissociation of soluble metal-ligand complexes can limit trace metal uptake by Chelex columns, as with EDTA and with an NTA impurity whose Cd complex dissociates two orders of magnitude slower than the corresponding Cd-NTA complex. Labile fractions determined by the Chelex method are generally larger than the fractions obtained by anodic stripping voltammetry, reflecting different time scales of measurement of the two techniques. The concept of a metal binding spectrum for trace metals in aqueous media is proposed. © 1979, American Chemical Society. All rights reserved.