A highly sensitive spectrophotometric method for the determination of trace amts. of thallium(III) using Cadion and Triton X-100 is described. It is the most sensitive method for the determination of thallium in aqueous solution In buffered solution (H4Cl-NH4OH) at pH 11.0 and in the presence of a nonionic surfactant, Triton X-100, thallium(III) and Cadion form a complex with the molar ratio of Tl:Cadion = 1:5. The complex exhibits an absorption max. at 470 nm with a molar absorptivity of 1.37 ?105 L mol-1 cm-1. Beer's law obeyed for 0-1.2 ppm Tl.

Key words: SPECTROPHOTOMETRY, TRACE ELEMENTS, COLOUR REAGENTS, CADMIUM, THALLIUM, TRITON X-100