Ultrasound-assisted cloud point extraction for speciation and indirect spectrophotometric determination of chromium(III) and (VI) in water samples

Ultrasound-assisted cloud point extraction (UACPE) procedure was developed for speciation and indirect spectrophotometric determination of chromium(III) and (VI) in environmental water samples. The method is based on the reduction of Cr(VI) by iodide in acidic media and subsequently formation of I3− anion. The I3− formed can further react with cetyltrimethylammonium bromide (CTAB) and induce its clouding due to formation of an ion-association complex. The formed complex was separated from solution and dissolved in ethanol for spectrophotometric measurement. Cerium(IV) ammonium sulphate was chosen as an oxidizing reagent for pre-oxidation step of Cr(III) to Cr(VI) species before the addition of iodide to the system, up to chromium in trivalent can be determined by the procedure. Experimental parameters for both spectrophotometric reaction and extraction procedure have been optimized. Under optimized conditions Cr(VI) can be determined in the range 20–400 ng mL−1 (R2 = 0.999). Detection limit, preconcentration factor and relative standard deviation were 12 ng mL−1, 20.0 and 2.2% (n = 5), respectively with 10 mL sample volumes. The proposed method has been successfully applied for determination of chromium(V) in spiked water, synthetic seawater and electroplating wastewater samples with average recoveries of 100.1, 99.4 and 99.1%, respectively.

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► Ultrasound-assisted cloud point extraction (UACPE) procedure was developed for speciation and determination of chromium(III) and (VI).
► The reactions and clouding phenomena were accelerated by ultrasonic waves.
► The applicability and accuracy of the developed method was estimated in electroplating and spiked water samples.
► It was found that common coexisting ions did not have significant effect on the separation and determination of Cr(VI).