Application of mixed-micelle cloud point extraction for speciation analysis of chromium in water samples by electrothermal atomic absorption spectrometry

A simple mixed-micelle cloud point extraction procedure has been developed for speciation analysis of chromium in water samples by electrothermal atomic absorption spectrometry (ET-AAS). A mixed micelle consisting of sodium dodecyl sulfate (SDS) and Triton X-114 is used as an extracting agent. Cr(VI) was complexed with 1,5 diphenyle carbazid (DPC) in an HCl medium and it was concentrated in the surfactant rich phase after phase separation. Total chromium is subjected to a similar extraction procedure after oxidation. Then Cr(III) has been calculated by subtracting Cr(VI) from the total chromium. The main factors affecting the mixed-micelle cloud point extraction, such as concentration of HCl, DPC, SDS and Triton X-114, equilibrium temperature and incubation time, were investigated in detail. Under the optimum conditions, a detection limit of 1 ng L− 1 with preconcentration factor of 92 was achieved. Also the relative standard deviation for five replicate determinations of 0.1 μg L− 1 Cr(VI) was 3.5%. The proposed method was successfully applied to speciation of Cr(III) and Cr(VI) in environmental water samples.