Determination of trace molybdenum in water samples by electrothermal atomic absorption spectrometry after preconcentration with miniaturized coprecipitation

Miniaturized coprecipitation with hydrous manganese(IV) oxide was studied for the preconcentration of sub mu g dm(-3) levels of molybdenum in water samples. Manganese(IV) oxide was produced by a reaction of permanganate ion with ethanol in the presence of 0.1 mol dm(-3) hydrochloric acid. A nanogram amount of molybdenum in a 10 cm(3) sample was quantitatively coprecipitated. The amount of manganese required was 0.1-0.40 mg for a 10 cm(3) sample. The precipitate was collected on a 10 mu m membrane filter, and then dissolved in 50 mm(3) of 5.6 mol dm(-3) nitric acid and 75 mm(3) of 1% hydrogen peroxide. An 80-fold preconcentration factor was obtained by this procedure. The molybdenum concentration was determined by electrothermal atomic absorption spectrometry using a pyrolytic graphite coated cuvette. The detection limit (3 sigma) was found to be 8.9 ng dm(-3). The proposed method was successfully applied to river water and snow samples.