Simultaneous determination of Cr(III) and Cr(VI) using differential pulse polarography and application to Gerede River


Abstract: Determination of Cr(III) in the presence of Cr(VI) from one polarogram is not easy. No such procedure was found in the literature. In polarographic studies Cr(III) had a peak only in acidic medium, while Cr(VI) had either 1 or 2 peaks in both acidic and basic solutions. In solutions that contain these 2 ions, the peak obtained in acidic medium for Cr(III) will be the sum of both ions. Thus, Cr(III) cannot be determined directly from one polarogram. In this work, a new and simple polarographic method is established for the determination of Cr(III) and Cr(VI) by using only one polarogram. The most suitable electrolyte for this purpose was 0.1 M KNO_3/HNO_3 (pH 2-3). The detection limits were 3 \times 10^{-7} M for Cr(III) and 1 \times 10^{-6} M for Cr(VI) in this medium. No interference was observed from most common ions. For validation, a sample containing both Cr(VI) and Cr(III) was analyzed also using 2 polarograms and good agreement was obtained. The proposed newly established direct method is applied to a real sample. For this purpose Gerede River in Turkey, which is surrounded by many leather factories, was analyzed for its chromium content, and agreement with ICP -- OES was very good.

Keywords: Chromium speciation, Cr(VI) and Cr(III) determination, differential pulse polarography, application to wastewater

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