[Spectrophotometric determination of microamounts of thorium with 3,5-dibromosalicylfluorone by ion-exchange separation].

A method for the determination of Thorium reacting with 3,5-dibromosalicylfluorone, cetyltrimethylammonium bromide and EDTA is proposed. This method is based on the formation of a red-violet colored multicomponent complex in pH 8.8-10.2. The complex has an absorption maximum at 557 nm and its molar absorptivity is 2.19 x 10(5) L.mol-1.cm-1. The Beer Law is obeyed in the concentration range of 0-7 micrograms.25 mL-1 for Th(i.v.). The composition of Th to 3,5-DBSF in the complex is 1:4. All interfering ions may be removed by eluting with 6 mol.L-1 HCl through cation-exchange resin. This method has been used for the determination of Th in Rare-Earth sample ores by ion-exchange separation.