Determination of thorium, uranium and zirconium with Arsenazo III using third-order derivative spectrophotometry

Derivative spectrophotometry of the 3rd-order was used to determine microgram amounts of Th, U(VI) and Zr with Arsenazo III. Complexes of these metals with the reagent form in a strongly acidic (4 M HClO4) and 2-propanol-water (25 % (v/v)) medium. Optimal apparatus parameters and the way of obtaining derivative spectra were established. A determination of the Th and Zr sum is possible after measuring the derivative value at 673.4 nm (where the derivative spectrum of the U(VI)-Arsenazo III complex crosses the zero line). When oxalic and masks Zr, the value of the derivative at 673.4 nm is a measure of the Th concentration, and at 659.2 nm-U. The proposed method allows the determination up to 30 μg of U, 20 μg of Th and 5 μg of Zr, in various relations, without any separation step, with good precision and accuracy. (author)