Duplicate 200-yA aliquots of the water samples, as received, are transferred by means of Eppendorf pipettors onto 0.4-g pellets of 2% LiF-98% NaF flux, contained in platinum dishes. The pellets are dried under heat lamps; then fused over special propane burners. The fused pellets are transferred to a Galvanek-Morrison fluoronwter, where they are excited with ultraviolet radiation and the fluorescence is measured. The uranium is calculated by comparing the measured fluorescence with that of other pellets, carried through the same procedure, which contain aliquots of standard uranium solutions. The sensitivity of the method is about 0.2 ppb of uranium, and the precision is approximately 15 relative percent in the 0.2to 10-ppb uranium concentration range.
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Platinum, indium, and rhodium, at concentrations of 0.01 to 1 wt% in uranium-matrix alloys, are measured by a rapid atomic-absorption spectrophotomatric method. The alloys are dissolved in hydrochloric and nitric acids (in a sealed tube if indium is involved), and die noble metals are measured in this solution without separation. The uranium effectively suppresses interelement atomic-absorption effects and at the same time enhances the sensitivities of the individual noble metals. The measurement relative standard deviation generally is no greater dian 1% in analyzing alloys containing 0.1 to 1 wt% of noble metals, and no greater than 7% at the 0.01-W.% alloy level.
Nitride nitrogen in B.C is determined by dissolving the sample in 14M H-SO, in a sealed fused-silica tube, distilling the nitrogen as ammonia from alkaline solution, and titrating the ammonium hydroxide in the distillation receiver with standardized acid. The Winkler distillation and the titration are proven operations that are directly applicable to the analysis of the B4C solution. Recovery of nitrogen from B4C was difficult and time-consuming by the usual caustic-fusion and leach methods, but it was simplified by substituting the technique of high-temperature dissolution in 14M HjSO*. With the sealed-tube method, analysis of six prepared mixtures of BN and B4C gave a mean recovery of 99.9% nitrogen, with a standard deviation of 0.94%. Fourteen portions of B^C production material gave a mean nitrogen value of 917 ppm, with a standard deviation of ± 30 ppm. Twelve analyses of tne same material by the caustic-fusion method gave a mean nitrogen content of 928 ppm, with a standard deviation of ± 84 ppm. The sealed-tube method for determining nitrogen is highly selective; nore of the impurities found in B4C interfere.
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