Spectrophotometric Determination of Uranium and Thorium Using Norwogonin

Uranium(VI) and thorium(IV) form orange-coloured complexes with norwogonin (5,7,8-trihydroxy­flavoue). The complexes are voluble in aqueous ethanol. The use of this reagent for spectrophotometric deter­mination of uranium and thorium has been investigated. Beer's law is obeyed over the range cf 4 to 20 p.p. m. of metal ion. The thorium complex is stable between pH 2.7 and 3.9 and that of uranium, between pH 2.7 and 5.0. Solutions of the thorium complex become opalescent at or above pH 3.6 on keeping for a few hours. The molar compositions of the complexes formed by uranium and thorium have been found to be 1:2 and 1:1 respectivel