Speciation of chromium through aqueous two-phase extraction of complexes of Cr(III) with 4-(2-pyridylazo)resorcinol and Cr(VI) with 1,5-diphenylcarbazide

A green, sensitive and selective methods are described for the pre-concentration and speciation of chromium species in natural waters. The developed methods are based on the environmentally friendly aqueous two-phase extraction with a system consisted of ammonium sulfate and polyethylene glycol, or, alternatively, alcohol (ethanol, isopropanol). The extraction of chromium species from aqueous solution into the upper organic phase was performed with 4-(2-pyridylazo)resorcinol and 1,5-diphenylcarbazide as chelating agents for Cr(III) and Cr(VI), respectively. Some predominant factors affecting the preconcentration and speciation of both Cr(III) and Cr(VI) species were evaluated and optimized. The concentration of chromium species in upper organic phase was determined by both spectrophotometric and electrothermal atomic absorption spectrometry (ET AAS) methods. Under the optimum conditions, the calibration graphs obtained with spectrophotometric method were linear over the concentration ranges from 5 to 500 mu g L-1 for Cr(III) and from 2.5 to 50 mu g L-1 for Cr(VI). Corresponding concentration ranges determined by using ET AAS method were from 1 to 10 mu g L-1 for both chromium species. The proposed methods were applied to the determination of chromium species in mine and waste waters with satisfactory results.