Speciation of inorganic chromium in water samples by energy dispersive X-ray fluorescence spectrometry

A simple and effective speciation procedure for the determination of inorganic chromium species in water samples was developed. The method is based on the combination of dispersive micro solid-phase extraction (DMSPE) and energy dispersive X-ray fluorescence spectrometry (EDXRF). In this system graphene oxide nanoparticles were used as solid sorbents for preconcentration of Cr(III) species. After the reduction of Cr(VI) ions with concentrated H2SO4 and ethanol, the procedure was applied for the determination of the total chromium concentration. The Cr(VI) content was calculated from the difference between the total chromium and Cr(III) concentration. In order to obtain the best recovery of Cr(III) ions some parameters affecting the sorption process, including pH, amount of graphene oxide, sample volume and sorption time, were investigated. Under optimal preconcentration conditions a detection limit of 0.06 ng mL(-1) with a relative standard deviation lower than 1.7% for Cr(III) determination was obtained. A linear response between the chromium concentration and fluorescent radiation intensity was achieved in the 1-150 ng mL(-1) range with a recovery of 98 +/- 3%. The proposed method was successfully applied to the speciation of trace chromium in water samples. The accuracy of the developed system was tested with the use of samples spiked with a known concentration of the studied element and by the determination of the total chromium concentration in the certified material NIST 1640a (trace elements in natural water).