INVESTIGATION OF CHROMIUM(III) AND CHROMIUM(VI) SPECIATION IN WATER BY ION CHROMATOGRAPHY WITH CHEMILUMINESCENCE DETECTION

This paper describes the development of an ion chromatography system for the separation and determination of Cr(III) and Cr(VI) species in aqueous samples. The separation was carried out on a Dionex AS4A anion exchange column containing a small proportion of cation exchange groups. Very high sensitivity was achieved using a chemiluminescence post-column reaction detector based on the catalytic oxidation of luminol. Linear calibrations were obtained over the range 0.1 to 500 mu g l(-1). Reproducibility was better than +/- 5% at the 10 mu g l(-1) level with detection limits of 0.05 and 0.1 mu g l(-1) for Cr(III) and Cr(VI) respectively. A preliminary study of chromium speciation in a fresh water standard reference material showed that the conditions necessary for simultaneous determination of the two chromium-species was critical, as Cr(VI) was vulnerable to reduction in acidic solutions and Cr(III) was strongly hydrolysed above pH 3.