Abstract
Nanogram quantities of cadmium in 100ml of water are quantitatively coprecipitated with indium hydroxide (100μg as indium) at pH 9.5. The precipitate is separated from the mother liquor by filtration with a 1-μm Nuclepore membrane filter and ultrasonically dissolved in 1M nitric acid. The cadmium in the final solution (1ml) is directly determined by graphite-furnace atomic absorption spectrometry without any serious background absorption due to indium. For the analysis of river water, coprecipitation is combined with sorption on a Sephadex A-25 anion exchanger for the separation of humic substances. The proposed method allows discrimination between negatively and positively charged cadmium species, with a detection limit as small as 2ngCd l-1of water.
