Determination of Thorium, Uranium and Zirconium with Arsenazo III Using Third-Order Derivative Spectrophotometry

Abstract

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 HC10a) 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 acid masks Zr, the value of the derivative at 673.4nm 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. KeywordsThorium, uranium, zirconium, Arsenazo III, 3rd-order derivative spectrophotometryOne of the trends in UV-VIS spectrophotometry i~ derivative spectrophotometry.Compared to normal (ordinary, zeroth-order) spectrophotometry, derivative spectrophotometry often leads to an increase in both the selectivity and sensitivity)-13 The value of the derivative of the absorption spectrum depends not only on the absorbance, but also on the shape of the zeroth-order spectrum.1,5,13,14 When the order of the derivative increases, the value of the derivative signal decreases for flat bands, but increases for sharp peaks.l5-17Improvements in the selectivity can often be obtained by using a zero-crossing measurement technique, a~ described by O'Haver and Green.9 In this technique. the derivative amplitude is measured at the wavelength al which the interfering derivative band crosses the zerc line.11,12An increase in the sensitivity by using derivative spectrophotometry depends on the shape of the analyte peak, apparatus parameters and the way of obtaining the derivative spectra. l,10,15Our derivative spectrophotometry studies were devoted to a simultaneous determination of platinum and palladium14 and to a direct determination of manganese traces in nickel.ls This paper concerns the direct determination of microgram amounts of U, Th and Zr with Arsenazo III. A classical spectrophotometric method for the determination of these metals using this bisazo reagent i~ characterized by good selectivity and high sensitivity (E=6.0X1041 mol-1 cm 1 for U(VI) and 1.2X105 for Tr and Zr). In a strongly acidic medium, Arsenazo II] reacts only with U, Th, Zr and Hf. The last two metal; can be masked with oxalic acid. 16 The spectra of Arsenazo III complexes with Th, U(VI; and Zr have sharp absorption bands. In Fig. 1 the spectrum of the Th-Arsenazo III complex in 6 M HCI, and the spectrum of the reagent are shown. The spectra of other metals are similar; they differ insignificantly regarding the shape and position of the peaks (the value differences of /~max are only several nm). All of this allows us to suppose that the use of derivative spectrophotometry can enable a simultaneous determination of these metals without any separation...

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A Review on Derivative Uv-Spectrophotometry Analysis of Drugs in Pharmaceutical Formulations and Biological Samples Review

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