Abstract
A simple method for the separation and determination of chromium (III) and chromium (VI) in water samples using a powder of calcium compounds was examined. It was found that CaO, CaCO3, CaSO4 and CaHPO4 are applicable to the collection of chromium (III) over the range of pH 8 to 13. To a 100 ml sample solution (pH 10) containing less than 0.25 mg of chromium (III) and chromium (VI), 100 mg of CaHPO4 powder was added, and the mixture was stirred for 10 min by a stirrer. Then, chromium (III) in the sample solution was collected on CaHPO4 powder. The mixture was separated into CaHPO4 containing chromium (III) and a liquid phase containing chromium (VI) through a membrane filter by vacuum filtration. The liquid phase containing chromium (VI) was added to 1 g of N2H6SO4 for the reduction to chromium (III). We found that chromium (VI) was reduced 100% to chromium (III) within 3 min by N2H6SO4. Similarly, the chromium (III) that was reduced from chromium (VI) was collected on CaHPO4 powder. The obtained CaHPO4 powder samples were dissolved with hydrochloric acid (final concentration, 2 mol l−1 HCl) and prepared to a constant volume (25 ml). The concentrations of chromium in the obtained solutions were determined by ICP-AES. When this method was used, the detection limits (3σ) from a 500 ml sample solution was 0.3 μg l−1. The proposed method has been applied to several water samples.
