Rapid spectrophotometric determination of trace amounts of uranium in sea water

A batch process was developed for the rapid determination of trace amounts of uranium in sea water by using Dowex A-1 as an adsorbent. The analytical procedure is as follows : Filter one liter of sea water, through a filter paper (pore size, 7μ), and acidify with 10 ml of concentrated hydrochloric acid. Boil for 20 minutes, and allow to cool to room temperature. Adjust the pH of the solution to 3 with 3 M ammonium hydroxide, add 5 ml of 1% CyDTA solution and 4 g (wet base) of Dowex A-1 chelating resin {(50100) mesh; sodium type}, and stir with magnetic stirrer for 70 minutes. Filter off the resin to separate it from the solution, transfer the resin into a 50 ml beaker, add 20 ml of 3% ammonium carbonate solution as an eluent of uranium. Shake the beaker and allow to stand for 20 minutes. Filter off the resin and evaporate the filtrate to dryness and dissolve the residue in 12 ml of (68) M hydrochloric acid. Add (12) g of metal zinc to reduce uranium(VI) to uranium(IV), and allow to stand for 30 minutes. Transfer the solution into a 25 ml volumetric flask by decantation to eliminate residual zinc, add 5 ml of 6 M hydrochloric acid saturated with oxalic acid and 1 ml of 0.1% arsenazo III solution, and make up to the mark with 8 M hydrochloric acid. Measure the absorbance of the colored solution at 665 nm by using 50 mm cell against the reagent blank. The uranium content is obtained with the calibration curve in the concentration range of 05μg uranium/25 ml. The relative standard deviation of this method with 3μg of uranium was found to be 2.2% in eight runs. In general thorium (IV) and zirconium(IV) interfere significantly with the determination of uranium. The interference from thorium(IV) up to 2 μg is eliminated by the presence of CyDTA, and that from zirconium(IV) up to 50μg is eliminated by the presence of oxalic acid. Time required for this method is about 3 hours. Uranium in sea water from Tokuyama Bay was determined by this method and the column method. The analytical results was 3.15 μg/l and 3.20 μg/l, respectively.