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

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 KNO3/HNO3 (pH 2-3). The detection limits were 3 x 10(-7) M for Cr(III) and 1 x 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.