Separation of chromium (III) and chromium (VI) by capillary electrophoresis using 2,6-pyridinedicarboxylic acid as a pre-column complexation agent

A simple method was developed for the simultaneous determination of Cr (III ) and Cr(VI) by capillary zone electrophoresis (CZE), where Cr(III) was che lated with ligands to form anionic complexes. Nitrilotriacetic acid, N-2-hy droxyethylenediaminetriacetic acid, ethylenediaminetetraacetic acid, diethy lenetriaminepentaacetic acid, and 2,6-pyridinedicarboxylic acid (PDCA) were investigated as Cr(IH) complexing ligands. Of all the ligands studied, 2,6 -PDCA with Cr(III) gave the largest UV response and high selectivity for Cr (III). In addition, the condition for pre-column derivatization, including pH, concentration ratio [Cr(III)/2,6-PDCA] and the stability of Cr(III) com plexes were also examined. The separation of anionic forms of Cr(III) and C r(Vl) was achieved using co-CZE with UV detection at 185 nm. The electrolyt e contained 30 mM phosphate, 0.5 mM tetradecyltrimethylammonium bromide, 0. 1 mM 2,6-PDCA and 15% (v/v) acetonitrile at pH 6.4. The detection limits we re 2 muM for Cr(III) and 3 muM for Cr(VI) and linear plots were obtained in a concentration range of 5-200 muM. The utility of the method was demonstr ated for the determination of Cr(III) and Cr(VI) in contaminated soils. (C) 2001 Elsevier Science B.V. All rights reserved.