Development of an analytical method for the determination of Cr(III) and Cr(VI) species in an aqueous medium

Chromium is present in nature mainly as Cr(III) and Cr(VI) species. Cr(III) is known as an essential trace element, whereas Cr(VI) presents acute toxicity. A chromatographic method (HPLC-ionic) was developed for the determination of both chromium species in contaminated aqueous medium during their treatment by phytoremediation. For this, the previous formation of the anionic complex [Cr(III)-EDTA](-) was required. The ionic strength of the mobile phase was evaluated in isocratic mode, while the flow velocity and gradient time were evaluated in gradient mode. Cr(VI) showed a strong interaction with the stationary phase and the determination with 9.0 mM Na2CO3/3.0 mM NaHCO3 of greater ionic strength was adequate, whilst for Cr(III) determination was performed with 2.8 mM Na2CO3/3.4 mM NaHCO3. The use of a concentration gradient allowed for the separation and quantification of both species simultaneously with the appropriate conditions: mobile phase A: 2.8 mM Na2CO32-/3.4 mM NaHCO3 with the gradual introduction of B: 9.0 mM Na2CO3/3.0 mM NaHCO3, t = 0.5 min, flow rate of 1.5 mL/min, and sample volume of 50 mu L. The use of HPLC-ionic represents an efficient, fast alternative with less environmental impact than conventional techniques with the remarkable advantage of the simultaneous determination of these species.