Preconcentrative separation of chromium(III) species from chromium(VI) by cloud point extraction and determination by flame atomic absorption spectrometry

We describe a high-throughput technique for the determination of chromium species in water samples by flame atomic absorption spectrometry (FAAS) after preconcentrative separation of Cr(III) species from Cr(VI) by cloud point extraction (CPE) using diethyldithiocarbamate (DDTC) as the chelating agent and the nonionic surfactant Triton X-100 as the extractant. The Cr(III)-DDTC complex is extracted if the temperature is higher than the CPE temperature of Triton X-100, while Cr(VI) remains in the aqueous phase. The Cr(III) in the surfactant phase was analyzed by FAAS, and the concentration of Cr(VI) was calculated by subtraction of Cr(III) from total chromium which was directly determined by FAAS. The effect of pH, concentration of chelating agent, surfactant, and equilibration temperature were investigated. The detection limit for Cr(III) was 0.08 μg L−1with an enrichment factor of 98, and the relative standard deviation was 1.2% (n = 3, c = 100 μg L−1). A certified reference material and several water samples were analyzed with satisfactory results. Figure(A) original solution with metals (circles) in low concentration; (B) metal chelates (squares) formed by addition of complexing reagent in the matrix solution; (C) addition of surfactant in the solution and trapping of metallic chelates into micellar cores; (D) micellar phase segregate after heating and separation after centrifugation. The determination of chromium species in water samples by FAAS after separation of Cr(III) from Cr(VI) by cloud point extraction using diethyldithiocarbamate and Triton X-100 was described. The LOD for Cr(III) was 0.08 μg L−1with enrichment factor of 98, and the relative standard deviation was 1.2% (n = 3, c = 100 μg L−1).[graphic not available: see fulltext]