Spectrophotometric determination of uranium in natural waters

A method for the spectrophotometric determination of uranium in samples of natural water is described. Ion exchange with Amberlite IR-120 (H⁺) to concentrate the metal was used. The absorption properties of the complex formed between uranium and the chromogenic reagent Arsenazo III, its stability over several hours, the effect of the pH on the ability of the resin to retain uranium, the reproducibility of the method and the effects of ionic interferences were considered. The sensitivity was 0.67 and 0.05 μg l^?1 of uranium for the direct and the addition methods, respectively. Uranium concentrations for the samples analysed were between 0.10 and 0.50 μg l^?1.