Determination of chromium(VI) and total chromium by inductively coupled plasma atomic emission spectrometry after preconcentration using solvent extraction and back-extraction

Abstract

A method for determining of Cr^VI and Cr^III in water samples by inductively coupled plasma atomic emission spectrometry after solvent extraction with tributylphosphate (TBP) and back-extraction is described. The method utilizes 10 ml of TBP and 500 ml of sample solution at pH 1. Chromium(VI) is back-extracted from the organic phase by 20 ml of solution containing ammonium acetate (3 mol l^–1) and ammonium carbonate (3 mol l^–1), and determined by ICP-AES. The optimum conditions for quantitative extraction and back-extraction of Cr^VI were examined, including, pH of sample solution, ratio of aqueous-to-organic phase and concentration and volume of ammonium acetate–ammonium carbonate for back-extraction. Total Cr can be determined after oxidation of Cr^III to Cr^VI by KMnO₄ in acid media. Chromium(III) can be calculated by difference. The relative standard deviations for ten replicate analyses were 1.8%(for 20 µg l^–1 of Cr^VI) and 1.6%(for 40 µg l^–1 of total Cr). The detection limits for Cr^VI and total Cr were calculated to be 1.0 and 0.9 µg l^–1, respectively.