DETERMINATION OF CHROMIUM(VI) AND TOTAL CHROMIUM BY INDUCTIVELY-COUPLED PLASMA-ATOMIC EMISSION-SPECTROMETRY AFTER PRECONCENTRATION USING SOLVENT-EXTRACTION AND BACK-EXTRACTION

A method for determining of Cr-VI and Cr-III in mater 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 1(-1)) and ammonium carbonate (3 mol 1(-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 acid 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 mere 1.8% (for 20 mu g 1(-1) of Cr-VI) and 1.6% (for 40 mu g 1(-1) of total Cr). The detection limits for Cr-VI and total Cr mere calculated to be 1.0 and 0.9 mu g 1(-1), respectively.