X-ray Absorption Near Edge Structure and Extended X-ray Absorption Fine Structure Analysis of Standards and Biological Samples Containing Mixed Oxidation States of Chromium(III) and Chromium(VI)

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Abstract:

For the first time a method has been developed for the extended X-ray absorption fine structure (EXAFS) data analyses of biological samples containing multiple oxidation states of chromium. In this study, the first shell coordination and interatomic distances based on the data analysis of known standards of potassium chromate (Cr(VI)) and chromium nitrate hexahydrate (Cr(III)) were investigated. The standards examined were mixtures of the following molar ratios of Cr(VI):Cr(III), 0:1, 0.25:0.75, 0.5:0.5, 0.75:0.25, and 1:0. It was determined from the calibration data that the fitting error associated with linear combination X-ray absorption near edge structure (LC-XANES) fittings was approximately ±10% of the total fitting. The peak height of the Cr(VI) pre-edge feature after normalization of the X-ray absorption (XAS) spectra was used to prepare a calibration curve. The EXAFS fittings of the standards were also investigated and fittings to lechuguilla biomass samples laden with different ratios of Cr(III) and Cr(VI) were performed as well. An excellent agreement between the XANES data and the data presented in the EXAFS spectra was observed. The EXFAS data also presented mean coordination numbers directly related to the ratios of the different chromium oxidation states in the sample. The chromium oxygen interactions had two different bond lengths at approximately 1.68 and 1.98 Å for the Cr(VI) and Cr(III) in the sample, respectively.

Keywords: BIOMASS; CHROMIUM; EXAFS; EXTENDED X-RAY ABSORPTION FINE STRUCTURE; MIXED OXIDATION STATE; X-RAY ABSORPTION NEAR EDGE STRUCTURE; XANES

Document Type: Research Article

DOI: http://dx.doi.org/10.1366/000370207780220912

Affiliations: 1: Department of Chemistry, The University of Texas at El Paso, 500 West University Avenue, El Paso, Texas 79968-0513 2: Universidad de Guanajuato, Departamento de Ingeniería Química, Facultad de Química, Noria Alta s/n, Guanajuato Gto. 36060, México 3: Department of Chemistry, The University of Texas at El Paso, 500 West University Avenue, El Paso, Texas 79968-0513; Environmental Science and Engineering PhD Program, The University of Texas at El Paso, 500 West University Avenue, El Paso, Texas 79968-0513

Publication date: March 1, 2007

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