A GRAVIMETRIC AND AN X-RAY-FLUORESCENCE METHOD FOR THE DETERMINATION OF RUBIDIUM IN RB2U(SO4)3

Chemical characterization of rubidium uranium (IV) trisulfate, Rb2U(SO 4)3, a new chemical assay standard for uranium requires accurate analy sis of rubidium. A gravimetric and an X-ray fluorescence method (XRF) for the determination of rubidium in this compound are described. In t he gravimetric method, rubidium is determined as Rb2Na[Co(NO2)6].H2O w ithout separating uranium with a precision of the order of +/-0.5%. In the XRF method, the concentration ratio of rubidium to uranium, C(Rb) /C(U), is determined in the solid samples by the binary ratio method u sing calibration between intensity ratios (I(Rb)/I(U)) and concentrati on ratios (C(Rb)/C(U)). The concentration of rubidium is derived using the uranium value which is known wi.th a precision better than +/-0.0 5%. The XRF method has a precision better than +/-0.8% for rubidium de termination.