The potentiometric method was established for the determination of uranium and plutonium in mixed oxide samples. A weighed sample was dissolved in a nitric-hydrofluoric acid mixture. The plutonium is oxidized to the sexivalent state with Ag(II) oxide in nitric acid solution, and the excess of oxidant is destroyed with sulfamic acid. A known small excess of Fe(II) sulfate solution is then added to reduce the sexivalent plutonium to the quadrivalent, and the excess is titrated potentiometrically with standard Ce(IV) sulfate solution. The total amounts of uranium and plutonium are obtained by reduction with Cr(II) sulfate and titration with standard Ce(IV) sulfate. The amount of uranium is calculated by subtracting the amount of plutonium. This method is suitable for the determination of 5-90% plutonium in mixed oxide samples. The coefficient of variation was 0.07-0.32% for 5-90% plutonium when more than 10mg of mixed oxides were analyzed.
