Photochemical Analysis. I. Photonometric Titration of Thallic Ion by Uranyl Photoreduction Reaction

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Abstract
Photonometric titration of thallic ion is described, in which uranous ion, the titrant, is generated by photoreduction of uranyl ion in a sulfuric acid solution containing sodium lactate. Uranyl ion could be reduced with the light at wavelengths longer than 300 mμ, whereas thallic ion could not be reduced with the light in this wavelength range. Selective photoreduction of uranyl ion was accomplished by eliminating wavelengths below 300 mμ with a filter. In this photonometric titration, reaction solutions were irradiated without stirring at 29.5±0.5°C. The absorbance of uranous ion produced was measured at 655 mμ, every fixed irradiation time, and the absorbance was plotted against the irradiation time. Induction period, which means the period during which the absorbance remains actually zero, was in a linear relation with thallic concentration. Thus the titration of thallic ion was satisfactorily carried out in the concentration range from 0.01 to 0.1 mm. The results proved the feasibility of titration in a completely sealed container and suggest a possibility of titration on a microvolume of reaction solution.