Spectrophotometric Determination of Microgram Quantities of Thorium in Various Aqueous Samples using Arsenazo-III

Author: Ming-Sing Hsu

Abstract：

The spectrophotometric determination of microgram quantities of thorium in various aqueous samples using Arsenazo-III as reagent was studied.
I. When the ratio of thorium to elements is not in excess of: 1 to 100(1+,2+ charged cations); 1 to 30(rare earth and 3+ charged cations); 1 to 2 (UO₂⁺²,Zr⁺⁴), they can be determined directly by spectrophotometry as follows: Add 1.5ml of 10% solu'n of ascorbic acid and 1.5ml of 10% solu'n of hydroxylamine hydrochloride to the sample, boil, cool to 23-25℃, mix with 0.5ml of 0.1% solu'n of Arsenazo-III reagent, dil, to 10ml with water, adjust to pII 0.5, and measure at 665mμ with a red filter. The system conforms Beer's law over the range of 0.4-28 r Th per sample.
II. In the presence of the quantites of any cations exceed the above statement or 1 ml 0.1M of any anions of F-, SO₄^-2, NO₃- , SiO₃^-2, the samples can be separated and determined effectively by procedure (a) which consists of adding 1 ml of 62% HCIO₄ to be fumed and precipitating twice with Fe(OH)₃ as carrier. As for great quantities of UO₃⁺²，U⁺⁴，Zr⁺⁴，Ti⁺⁴，procedure (b) using CaC₂O₄ as carrier is preferred to procedure (a)
The estn. Error in Th is less than 2.5% in all the above procedures.

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