Spectrophotometric determination of thorium with quercetinsulfonic acid:Spectrophotometric studies on organometallic complexes used in analytical chemistry. IX

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Thorium forms two sorts of yellow colored chelates with quercetinsulfornic acid which were easily soluble in water, and one of them formed at about pH 5.0 has been used in the spectrophotometric determination of minute amounts of thorium in this paper. The chelate had an absorption maximum at around 438mμ. When the concentration of quersetinsulfonic acid was above 4.8×10-4M, the absorbancies of the chelate were definite at 435mμ in the range of pH 5.0 to 6.5. However, at pH above 5.5, the absorption of quercetinsulfonic acid increased rapidly with increasing of pH. Therefore, the optimum pH for the determination of thorium must be defined in the range of pH 5.0 to 5.5. In these conditions, the Beer's law obeyed in the concentration range from 1.0γTh/ ml to 6.76γ Th/ml, in the wavelengths between 435mμ and 460mμ, and the molar absorption coefficient was calculated as 33, 100 at 435mμ. It was found with the Job's method of continuous variations that one chelate which had an absorption maximum at about 412mμ was formed with one molecule of thorium and quercetinsulfonic acid respectively, and another which had an absorption maximum at about 438mμ was formed with one molecule of thorium and two molecules of quercetinsulfonic acid.
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