Extraction mechanism of Cr(VI) on the aqueous two-phase system of tetrabutylammonium bromide and (NH4)2SO4 mixture

An aqueous two-phase system of tetrabutylammonium bromide (TBAB) and (NH4)2SO4 mixture has been developed for the extractive preconcentration and separation of certain compounds. TBAB concentration in upper phase is much higher than that of bottom solution. This new aqueous two-phase system is proposed for the highly selective extraction of Cr(VI) from large amounts of Cr3+. The Cr(VI) is found to be extracted into the TBAB-rich upper phase due to ion pair formation such as HCrO4− · TBAB+. The Cr(VI) was sufficiently extracted into the upper phase in the pH range from 1 to 5. The proposed method has been applied to the determination of trace of Cr(VI) in wastewater samples with a coefficient of variation less than 3.2%. The recovery obtained was not lower than 90%. The determination limit for the Cr(VI) was found to be 60 μg l−1 in 10 ml of sample solution.