Determination of Cr(III) and Cr(VI) in water by wavelength-dispersive X-ray fluorescence spectrometry after preconcentration with an ion-exchange resin disk

A rapid and simple method using an ion-exchange resin disk combined with wavelength-dispersive X-ray fluorescence (WDXRF) spectrometry was developed for the determination of Cr(III) and Cr(VI) in water. A 100-ml water sample was first adjusted to pH 3 with nitric acid and then passed through an anion-exchange resin disk placed on top of a cation-exchange resin disk at a flow rate of 1 ml min(-1) to separate Cr(III) and Cr(VI). Anionic Cr(VI) was preconcentrated on the upper anion-exchange resin disk, whereas cationic Cr(III) was preconcentrated on the lower cation-exchange resin disk. Each ion-exchange resin disk was dried at 100 degrees C for 30 min in an electric oven and coated with a commercially available laminate film. The specimens were measured using a WDXRF spectrometer. The calibration curves of Cr(III) and Cr(VI) showed good linearity in the range 1-10 mu g. The detection limits corresponding to three times the standard deviation (n = 5) of blank values were 0.17 mu g for Cr(III) and 0.16 mu g for Cr(VI). If a 1-I water sample is used, these limits would be 0.17 and 0.16 mu g l(-1), respectively. A spike test for 50 mu g l(-1) Cr(III) and Cr(VI) in tap water and river water showed quantitative recoveries (94-114%), although this was not observed for mineral drinking water owing to the overlap of V K beta with Cr K alpha. The recovery after overlap correction was satisfactory (115%). Copyright (C) 2011 John Wiley & Sons, Ltd.