Formation of Chromium(IV, V)-Ethylenediamine-N, N, N′, N′- tetraacetate and Its Application to Spectrophotometric Determination of Cobalt(II) and Chromium(VI)

Abstract

Spectrophotometric and electron spin resonance (ESR) studies on the formation of chromium(IV, V)-ethylene- diamine-N, N, N′, N′-tetraacetate (EDTA) and the spectrophotometric determination of chromium(VI) and cobalt(II) are described. Chromium(V)-EDTA, formed by the oxidation of cobalt(II)-EDTA with chromium(VI) in the presence of excess EDTA and chromium(VI), gives two narrow ESR absorption lines with a g-value of 1.969 and intense absorption at 550nm. The formation of chromium(IV, V)-EDTA depended to a fair degree on the solution pH and the concentration of free excess EDTA. Chromium(IV, V)-EDTA is stable for at least 30min under optimal conditions. The color system obeyed Beer′s law up to 3.8μg/cm³ Co(II) and 3.4μg/cm³ Cr(VI).