X-ray absorption spectrometry

Principles and Characteristics In X-ray absorption spectroscopy (XAS) the absorption coefficient (p.) 

A XAS experiment involves the irradiation of a sample with a tuneable source of monochromatic X-rays, usually from a synchrotron facility (high brilliance). Third-generation synchrotrons have sufficient intensity to observe XAFS spectra up to 100 keV. Nevertheless, laboratory-scale XAFS spectroscopy is of importance, despite the vast availability of synchrotron beam time [305]. 

X-ray absorption spectroscopy is a reliable and routine method to investigate the local atomic environments of selected elements in materials, and provides useful 

XANES spectroscopy is also the basis of chemically sensitive X-ray imaging, as well as qualitative and quantitative microspectroscopy [306], ptXANES is attractive for chemical analysis, with its spatial resolution down to 10 ptm. Variations on the theme are surface EXAFS (SEXAFS), grazing incidence XAS and in situ time-resolved XAS investigations. Grazing angle XAFS can be used for the study of ultrathin multilayer systems. 

EXAFS has recently been reviewed [307] XAS and NEXAFS monographs are also available [308,309]. 

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In order to gain information on the environments of certain atoms in dissolved species, in melts or in solids (crystalline or noncrystalline), which are not accessible to diffraction studies for one reason or another, X-ray absorption spectrometry (XAS) can be applied, with the analysis of the X-ray absorption near-edge structure (XANES) and/or the extended X-ray absorption fine structure (EXAFS). Surveys of these methods are available 39,40 a representative study of the solvation of some mercury species, ElgX2, in water and dimethylsulfoxide (DMSO) by EXAFS and XANES, combined with quantum-chemical calculations, has been published.41... 

The aquated iron(III) ion is an oxidant. Reaction with reducing ligands probably proceeds through complexing. Rapid scan spectrophotometry of the Fe(III)-cysteine system shows a transient blue Fe(lII)-cysteine complex and formation of Fe(II) and cystine. The reduction of Fe(lII) by hydroquinone, in concentrated solution has been probed by stopped-flow linked to x-ray absorption spectrometry. The changing charge on the iron is thereby assessed. In the reaction of Fe(III) with a number of reducing transition metal ions M in acid, the rate law... 

Abstract Mobile Au in soil has been postulated for many years. It has been used by the mineral exploration industry in areas of transported overburden as a vector towards buried deposits. Until now, the nature of this mobile Au has not been known or investigated. Soil samples from a colluvial area above the Bounty Deposit (Yilgarn Craton, Western Australia) investigated by analytical techniques including laser ablation inductively coupled mass spectrometry (LA-ICP-MS) and synchrotron x-ray fluorescence (SXRF) combined with X-ray absorption spectrometry (XAS) have allowed us to map the invisible Au in these soils and suggests that at least some of it occurs in an ionic form. 

Variable recovery is a principal cause of non-equivalence of data and there is no straightforward solution to this problem [26], Artificially made reference samples or pure compounds added to test material cannot be used for estimations of recovery of analytes. Direct speciation analysis from the solid sample [27] is not feasible at present, although analytical methods are appearing that could be useful in the future (X-ray absorption spectrometry, laser mass spectrometry, static secondary ion mass spectrometry). 

Han] Hannoyer, B., Lenglet, M., Chopova, R., Tellier, J.C., Contribution of the Mossbauer Spectrometry and of the X-Ray Absorption Spectrometrie to the Study of Non Stoichiometry in CuFc204 (in French), Mater. Chem. Phys., 13(5), 449-465 (1985) (Crys. Structure, Eleetro-nic Structure, 18)... 

In the applications of X-ray absorption spectrometry (XAS, also called X-ray absorption fine structure spectroscopy, XAFS) the energy dependence of the inner shell photoelectric cross is exploited to increase specificity of measurements or to obtain information on the chemical environment (speciation analysis). 

Abstract This chapter deals with the analytical applications of synchrotron radiation sources for trace-level analysis of materials on microscopic and submicroscopic scales. Elemental analysis with X-ray fluorescence is described in detail. Two-dimensional (2D) and three-dimensional (3D) analyses are discussed in their quantitative aspects. Related methods of analysis based on absorption edge phenomena such as X-ray absorption spectrometry (XAS) and near-edge scanning spectrometry (XANES) yielding molecular information, computerized X-ray fluorescence microtomography (XFCT) based on the penetrative character of X-rays, and microscopic X-ray diffraction (XRD) providing structural data on the sample are also briefly discussed. The methodological treatment is illustrated with a number of applications. 

Abbreviations AES, Auger emission spectrometry CRM, Certified reference material DL, Detection limit ED, Energy dispersive ESRF, European Synchrotron Radiation Facility EXAES, Extended X-ray absorption fine structure NEXAFS, Near edge X-ray absorption fine structure PCI, Phase contrast imaging RM, Reference material SR, Synchrotron radiation SRM, Standard reference material TXRF, Total reflection X-ray fluorescence XANES, X-ray absorption near edge structure XAS, X-ray absorption spectrometry XDM, X-ray diffraction microscopy XFCT, X-ray fluorescence computerized microtomography XPEEM, X-ray photoelectron microscopy XPS, X-ray photoelectron spectrometry XRD, X-ray diffraction XRF, X-ray fluorescence... 

Infrared spectroscopy (IR) Raman spectroscopy X-ray absorption spectrometry (XANES, EXAFS) Nuclear magnetic resonance (NMR) Inelastic neutron scattering (INS)... 

Analytical speciation methods, referred to earher, generally differ from the methods adequate for bulk quantrffcation of lead. As with bulk methods, nonetheless, contaminating levels should not be permitted in interfering amounts. Several lead speciation approaches are X-ray absorption spectrometry, X-ray diffraction, and electron-microprobe microanalyses (U.S. EPA, 2006 Welter et al., 1999). 

For the determination of the metallome structure, different nuclear-base techniques can be applied, like X-ray crystallography and solution structure determination by multi-dimensional nuclear magnetic resonance (NMR). Other techniques capable of offering the data mainly include Mossbauer spectroscopy, X-ray absorption spectrometry (XAS), and electron paramagnetic resonance (EPR), and neutron scattering. However, in the structural analysis of nanometallome, XAS is the most often used techniques through literature. 

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