Simultaneous determination of chromium(III) complexes and chromium(VI) by fast protein anion-exchange liquid chromatography–atomic absorption spectrometry
Chromium(III) complexes [oxalate and ethylenediamine-tetraacetic acid (EDTA)] and CrVI 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, CrIII positive species and kinetically labile, negatively charged CrIII complexes such as CrIII–citrate passed through the column, whereas relatively stable anionic CrIII complexes (with EDTA and oxalate), and CrVI 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 CrVI, CrIII–EDTA, and CrIII–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 CrVI containing nutrient solutions during plant experiments to investigate Cr uptake by plants (LOD, 5 ng cm–3).