Speciation Studies of Metals in Trace Concentrations: The Mononuclear Uranyl(VI) Hydroxo Complexes

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• 作者：Björn Drobot ; Anne Bauer ; Robin Steudtner ; Satoru Tsushima ; Frank Bok ; Michael Patzschke ; Johannes Raff ; Vinzenz Brendler
• 刊名：Analytical Chemistry
• 出版年：2016
• 出版时间：April 5, 2016
• 年：2016
• 卷：88
• 期：7
• 页码：3548-3555
• 全文大小：549K
• ISSN：1520-6882

文摘

A direct luminescence spectroscopic experimental setup for the determination of complex stability constants of mononuclear uranyl(VI) hydrolysis species is presented. The occurrence of polynuclear species is prevented by using a low uranyl(VI) concentration of 10^–8 M (2.4 ppb). Time-resolved laser-induced fluorescence spectra were recorded in the pH range from 3 to 10.5. Deconvolution with parallel factor analysis (PARAFAC) resulted in three hydrolysis complexes. A tentative assignment was based on thermodynamic calculations: UO₂²⁺, UO₂(OH)⁺, UO₂(OH)₂, UO₂(OH)₃^–. An implementation of a Newton–Raphson algorithm into PARAFAC allowed a direct extraction of complex stability constants during deconvolution yielding log(β_1M,1°C)_1:1 = −4.6, log(β_1M,1°C)_1:2 = −12.2, log(β_1M,1°C)_1:3 = −22.3. Extrapolation to standard conditions gave log(β⁰)_1:1 = −3.9, log(β⁰)_1:2 = −10.9, and log(β⁰)_1:3 = −20.7. Luminescence characteristics (band position, lifetime) of the individual mononuclear hydroxo species were derived to serve as a reference data set for further investigations. A correlation of luminescence spectroscopic features with Raman frequencies was demonstrated for the mononuclear uranyl(VI) hydroxo complexes for the first time. Thereby a signal-to-structure correlation was achieved and the complex assignment validated.