Spectrophotometric Determination of Chromium Based on Ion-Pair Formation

A sensitive spectrophotometric method for the determination of trace amounts of chromium(VI) is described. Chromium(VI) forms chlorochromate anion in the presence of acid and chloride ion. The formed anion is extracted in toluene as ion-pair with a cationic dye - rhodamine 6G. At 535 nm absorption maximum molar absorptivity is 2×104 1 mol-1 cm-1. The colour is stable for 4 h and the system obeys the Beer's law in the range 0-8 μg of chromium(VI). Chromium(III) is determined after oxidation to chromium(VI) with potassium permanganate. The method has been applied for the determination of chromium in standard alloy steels, pharmaceutical preparations, geological samples and industrial effluents.