Simultaneous determination of chromium(III) complexes and chromium(VI) by fast protein anion-exchange liquid chromatography–atomic absorption spectrometry

Abstract

Chromium(III) complexes [oxalate and ethylenediamine-tetraacetic acid (EDTA)] and Cr^VI were separated simultaneously on a fast protein liquid chromatography (FPLC) anion-exchange column of Mono Q HR 5/5. For separation tris(hydroxymethyl)aminomethane (TRIS)–HCl buffer (5 × 10^–3 mol dm^–3, pH 5.5–8.5), and the same buffer with NaCl (0.5 mol dm^–3), were employed in gradient elution (15 min; flow rate, 1 cm³ min^–1). The column was regenerated (NaCl) and equilibrated (TRIS–HCl buffer) in the following 8 min. With this procedure, Cr^III positive species and kinetically labile, negatively charged Cr^III complexes such as Cr^III–citrate passed through the column, whereas relatively stable anionic Cr^III complexes (with EDTA and oxalate), and Cr^VI were separated and determined by ultraviolet molecular (234 and 273 nm, respectively) and atomic (357.9 nm) absorption. Atomic absorption was measured ‘offline’ in 100 or 200 µl eluate fractions. The method was successfully employed for the determination of Cr^VI, Cr^III–EDTA, and Cr^III–oxalate in cabbage xylem at ng cm^–3 levels [limits of detection (LOD), 5, 3, and 80 ng cm^–3, respectively], using a 500 µl sample loop. In addition, chromate was monitored in Cr^VI containing nutrient solutions during plant experiments to investigate Cr uptake by plants (LOD, 5 ng cm^–3).