Determining Cr(III) and Cr(VI) in urine using a flow injection on-line sorption separation system coupled with electrothermal atomic absorption spectrometry and a UV/nano-Au/TiO2 photocatalysis reduction device

In this study, an on-line nano-Au/TiO2 photocatalysis reduction device coupled with flow injection electrothermal atomic absorption spectrometry was developed for chromium speciation in urine samples. The nano-Au/TiO2 photocatalysis reduction device comprised a UV lamp and a Tygon tube coated with nanocrystalline Au/TiO2 films. The process of chromium speciation in urine was based on the adsorption of Cr(III) and Cr(VI) on this photocatalysis reduction device. The absorbed Cr(VI) was photoreduced to Cr(III), and Cr(III) was eluted using 1 M formic acid. Suitable conditions for adsorption, photoreduction, elution, and subsequent ETAAS determination of the levels of Cr(III) and Cr(VI) were established. The detection limits for Cr(III) and Cr(VI) using this analytical method were 0.08 and 0.13 ng mL−1, respectively. This intra- and inter-assay precisions (relative standard deviation) for the analyses of 1 μg L−1 Cr(III) and 3.0 μg L−1 Cr(VI) were less than 10%. When urine samples were spiked at levels of 1 μg L−1 Cr(III) and 2 μg L−1 Cr(VI), the analyzed recoveries were 98.3–96.0%, respectively (n = 3). We applied this method to the determination of Cr(III) and Cr(VI) in urine samples of human volunteers before and after supplementing their diet with chromium picolinate.