Separation of chromium (VI) and chromium (III) with crown ether by means of ion-pair extraction

A new method for the separation of chromium(VI) and chromium(III) with dicyclohexyl 18-crown-6 (DC18C6) in 1,2-dichloroethane was developed by means of solvent extraction. In this process, Cr-VI as HCrO4- was extracted as an ion-pair complex with the potassium-crown ether complex cation in the organic phase within 1 min. The extracted species was ascertained to be [K(DC18C6)]+. [HCrO4](-). When mixtures of Cr-VI and Cr-III were extracted under the optimum condition, Cr-VI alone was extracted quantatively, whereas Cr-III remained in the aqueous phase. After extraction, Cr-VI in the organic phase was quantatively back-extracted by a 0.1 M NH3 solution. Then, each of the concentrations of Cr-VI and Cr-III could.be determined by means of inductively coupled plasma atomic emission spectrometry (ICP-AES). Cations, such as iron(III), zinc(II) and cadmium(II), interfered with this extraction. The present method was applied to recover Cr-VI trace in the presence of Cr-III in real samples, and clarified to be applicable to Cr-VI determination in natural water samples.