Separation and Determination of Trace Quantities of Uranium in Presence of Plutonium SIR: Existing spectrophotometric methods for the determination of uranium in the presence of large amounts of plutonium are unsatisfactory. An excellent review by 1300man and Rein ( 1 ) describes many of the available methods for the separation and analysis of uranium. Plutonium interferes in the color development of the existing methods and must be separated. Qualitative separation of a small amount of uranium is difficult and none of the procedures described by Booman and others ( 3 , 4 )gave qualitative separations in a short length of time. This paper reports a rapid and qualitative separation of the two elements even when there are several thousand times as much plutonium a5 urauium. I n this procedure uranium is separated from plutonium with tri-noctylphosphine oxide (TOPO) ( 4 ) from 2M H N 0 3 . Small quantities of sulfamic acid, ferrous ammonium sulfate, and sodium fluoride are added to the nitrate media to prevent the extraction of plutonium, which is reduced to plutonium(II1). The separated uranium is then determined spectrophotometrically in the organic phase using 1-(2-pyridylazo)-2-naphthol (PAN) to develop a n intense red complex ion at pH 10 in ethanol-cyclohexane. EXPERIMENTAL
Apparatus and Reagents. Standard uranium solution (0.85 mg. of U per ml.) in 2ilf " 0 3 , 0.05M ToPo dissolved in cyclohexane, 0.1 wt. yo P A S dissolved in ethanol, and 10 vol. yo triethanolamine dissolved in ethanol. The absorbancy curves of the solutions contained in 1-cni. matched silica cells were measured with a Beckman D1
