[Spectrophotometric study of color reaction of chromogenic reagent 2-hydroxy-5-sulfo-benzenediazoaminoazobenzene(HSDAA) with thallium(III)].

The chromogenic reaction of the 2-hydroxy-5-sulfo-benzenediazoaminoazobenzene(HSDAA) with thallium was studied in this paper. In the presence of Triton X-100 and in ammonia medium of 0.72-0.99 mol.L-1, HSDAA reacts sensitively with thallium (III) to form a red complex with molar radio of 1:2. The apparent molar absorptivity is 1.04 x 10(5) L.mol-1.cm-1 at the maximum absorption wavelength of 516 nm. Beer's law is obeyed in the concentration range of 0-0.8 mg.L-1 Tl(III). Adding NaC4H4O6 and NaCN in the system can improve selectivity of the chromogenic agent greatly. The method has been applied to the direct determination of trace amounts of thallium in sample of synthetic water with satisfactory results.