Separation of metal complexes of ethylenediaminetetraacetic acid in environmental water samples by ion chromatography with UV and potentiometric detection

Abstract

An ion chromatographic method is described for the analysis of several metal complexes of ethylenediaminetetraacetic acid (EDTA) in water samples. Separations are achieved on C18 bonded silica, typically using a mobile phase comprising 1% (w/v) cetrimide-1.2 mM phosphate buffer (pH 7)-25% (v/v) acetonitrile-15% (v/v) methanol, as well as on a polymer-based anion exchanger using 2 mM phosphate buffer (pH 7) as eluent. Direct UV detection at 250 nm is employed for EDTA complexes of Fe(III), Cu(II), Pb(II) and Ni(II), whilst UV detection at 250 nm after post-column reaction with copper ions is utilized for EDTA complexes of Zn(II), Cd(II), Co(II), Pb(II), Ni(II) and Cu(II). Detection limits are in the range 1.5–4.0 ng for direct UV detection and 30–50 ng for post-column reaction detection. Indirect potentiometric detection after post-column reaction with copper ions is utilized with metallic copper as the indicator electrode, giving detection limits in the range 1.0–1.5 μg. These separations are applied to the determination of metal-EDTA complexes in river water at the ppbb level and to remobilization studies of metal ions in sediment.