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 °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 µg. The detection limits corresponding to three times the standard deviation (n = 5) of blank values were 0.17 µg for Cr(III) and 0.16 µg for Cr(VI). If a 1‐l water sample is used, these limits would be 0.17 and 0.16 µg l−1, respectively. A spike test for 50 µg 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 Kβ with Cr Kα. The recovery after overlap correction was satisfactory (115%). Copyright © 2011 John Wiley & Sons, Ltd.