ICP-AES Determination of Micro-Amounts of Thorium in Flammable Poison(Gd,U)O2 Chips After Anion-Exchange Separation

0.500 0 g of the sample was dissolved in HNO3 with addition of several drops of HCl,and then fumed with 4 mL of H2SO4(1+1).After cooling,acidity of the solution was adjusted to pH 2.0-2.5 with 3.0 mol·L-1 NaOH solution.Thorium,together with the matrix uranium were adsorbed on the anion exchange resin column in the form of anionic complex with SO2-4 anion,and separated from Gd(Ⅲ) and other co-existing cation by elution with 0.01 mol·L-1 H2SO4 (20 mL) at a flow-rate of 0.5-1.0 mL·min-1.The eluate was rejected.6.0 mol·L-1 HCl was then used as eluant and passed through the resin column at same flow-rate.The first 7 mL of the eluate were discarded,and the next 18 mL of the eluate,which contained the thorium,were collected in a small beaker and evaporated to near dryness.The residue in the beaker was taken up with 1.0 mol·L-1 HNO3 and diluted to 5 mL with the same HNO3 solution in a volumetric flask,and ready to be used for ICP-AES determination.Optimum working conditions of the instrument and for the determination were described in detail.Detection limit of the method was found to be 0.2 μg·g-1.Values of RSD (n=6) and av.recovery were found to be 9.6% and 105% respectively.