Optimization of the simultaneous determination of Cr(VI) and Cr(VI) by ion chromatography with chemiluminescence detection

An optimized method for the simultaneous determination of Cr(III) and Cr(VI) in aqueous solutions using ion chromatography with chemiluminescence detection is described. Excellent resolution of the two chromium species was obtained using a single mixed-bed ion-exchange column with continuous elution. After postcolumn reduction of Cr(VI) to Cr(III), the light emitted during the Cr(III)-catalyzed oxidation of luminol with hydrogen peroxide was measured. Parameters affecting the postcolumn reactions such as reductant concentration, reductant mixing, point of luminol introduction, and luminol flow rate were optimized. The calibration curves in the range tested (0.01-50 mu g L-1) were linear, and detection limits of 0.002 pg L-1 for both Cr(III) and Cr(VI) were obtained. The results of the analyses of the water reference materials LGC CRM6010 and NIST SRM1643d with certified chromium values of 49 +/- 4 and 18.53 +/- 0.20 Pg L-1 and found to contain only Cr(III) were 49.2 +/- 1.8 and 19.0 +/- 1.5 mu g L-1, respectively. Values of 10.6 +/- 0.5 and 10.1 +/- 0.5 mu g L-1 were obtained when a simulated water sample containing 10 mu g L-1 Cr(III) and Cr(VI) was analyzed.