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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 HCrO_4^- 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)]^+・[HCrO_4]^-. 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 NH_3 solution. Then, each of the concentrations of Cr^<VI> and Cr^<III> could be determined by means of inductively coupled plasma atomic emission spectromrtry (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^<IV> determination in natural water samples

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