Simultaneous measurement of Cr(III) and Cr(VI) in freshwaters with a single Diffusive Gradients in Thin Films device

Abstract : Few attempts have been made to sample labile chromium with the DGT passive sampler (Diffusive Gradients in Thin Films) and, currently, no single device allows the simultaneous determination of both Cr(III) and Cr(VI). In this work, a procedure based on only one device combined with innovative selective elution is evaluated to assess chromium speciation. A zirconium binding gel is used to accumulate both Cr(III) and Cr(VI). Cr(VI) is quantitatively and selectively eluted by NaOH, allowing the subsequent determination of Cr(III). Accurate quantification of both species is demonstrated in synthetic solutions for pH ranging from 4 to 6 and ionic strength ranging from 10−3 to 5×10−2 M. Cr(VI) quantification is altered only for [SO42−]≥5×10−3 M. The method allows successful quantification of labile Cr(III) and Cr(VI) in spiked natural water. The limit of quantification of the procedure is suitable for trace level monitoring (0.03 µg L−1 for Cr(VI) and 1 µg L−1 for Cr(III), for a one-week deployment at 20 °C) and the effective capacity of the sampler (∼25 µg for each Cr oxidation state) should allow long term deployments. These results highlight the potential of this new procedure for a simple and effective chromium speciation analysis in natural waters