An isotope dilution method has so far been used for accurate determination of uranium contained in sea water, but this method necessitates a special room for using uranium isotope. In this paper, a study was made to improve the separation method and fluorophotometric method for the determination of uranium in sea water without using the isotope dilution method.
The separation of uranium in sea water was carried out under the foliwing procedure. Ten micro-grams of uranium was added to 4 liters of sea water sample, and the sample solution was warmed at about 80°C. Uranium in the sample was adsorbed into titanic acid which was prepared by homogeneous precipitation method using urea. The uranium adsorbed into titanic acid was extracted with mixture of sodium carbonate and sodium hydrogen carbonate at 100°C. The extracted solution was passed through in anion exchange resin of carbonate type, and the uranium adsorbed into the resin was eluted with hydrochloric acid solution. The recovery of uranium by this method represented 90%, which was higher than the conventional methods but was still incomplete. Therefore, the condition of adsorption must be kept stable to obtain the recovery with small variation, and the determinated value was corrected with the recovery.
A given amount of this pretreated solution was pipetted into a plutinum dish, dried, and melted at 665°C with carbonate-sodium fluoride flux, and the fluorescence strength of the dish was measured. The error caused by the variation of melting condition could be decreased by using a furnace with a fan and correction by simultanious operation with the uranium standard solution.
The unevenness of the fluorescence strength in the dish could be decreased by using the temporary standard and rotating the fused dish during the measurement, and the measuring error was below 2%. Uranium content in sea water collected along the coast of Odawara showed 3.34μg/l by this method.