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Home ›› About Speciation ›› Speciation News

X-ray absortption spectroscopy for speciation analysis

(23.12.2024)

X-ray absorption spectroscopy (XAS) is a powerful technique used for speciation analysis, which involves identifying and quantifying the different chemical forms of an element in a sample.

Basics of X-Ray Absorption Spectroscopy

XAS involves measuring the absorption of X-rays as a function of energy near and above the core-level binding energies of an element. The technique is divided into three main regions (see figure ):

The absorption threshold determined by the transition to the lowest unoccupied states.
X-ray Absorption Near Edge Structure (XANES, also called NEXAFS): This region, close to the absorption edge, provides information about the oxidation state and coordination environment of the absorbing atom.
Extended X-ray Absorption Fine Structure (EXAFS): This region, extending beyond the absorption edge, provides detailed information about the distances, coordination numbers, and types of neighboring atoms around the absorbing atom.

Figure: Three regions of XAS data for the K-edge

Steps in Speciation Analysis Using XAS

Sample Preparation: Samples can be in various forms, such as solids, liquids, or thin films. Proper preparation is crucial to ensure representative measurements.

Data Collection:
XAS spectra are collected using synchrotron radiation sources, which provide intense and tunable X-ray beams. The photon beam is tuned by using a crystalline monochromator, to a photoon energy to a range where core electrons can be excited (0.1-100 keV). The sample is exposed to these beams, and the absorption is measured as the X-ray energy is varied. The edges are, in part, named by which core electron is excited: the principal quantum numbers n = 1, 2, and 3, correspond to the K-, L-, and M-edges, respectively.
XANES Analysis:
Oxidation State Determination: The edge position in the XANES region shifts with changes in the oxidation state of the element. By comparing the edge position with reference compounds of known oxidation states, the oxidation state of the element in the sample can be determined.
Coordination Environment: The shape and features of the XANES spectrum can indicate the coordination geometry and type of ligands around the absorbing atom.
EXAFS Analysis:
Local Structure: The EXAFS region provides information about the distances between the absorbing atom and its neighbors, the number of neighboring atoms (coordination number), and the type of neighboring atoms. This is achieved through Fourier transform analysis of the EXAFS oscillations.
Quantitative Fitting:
The experimental EXAFS data is fitted with theoretical models to extract quantitative structural parameters. Software tools like ATHENA and ARTEMIS (part of the Demeter software package) are commonly used for this purpose.

The experimental analysis focusing on both the XANES and EXAFS regions is called X-ray absorption fine structure (XAFS).

Applications of XAS in Speciation Analysis

Environmental Science: Determining the speciation of heavy metals (e.g., arsenic, lead, mercury) in soils, sediments, and water to understand their mobility, bioavailability, and toxicity.
Biological Systems: Studying the speciation of metal ions in biological systems, such as metalloproteins and enzymes, to understand their functional roles and interactions.
Catalysis: Investigating the active sites and oxidation states of catalysts during reactions to improve catalytic processes.
Material Science: Analyzing the speciation of elements in complex materials like glasses, ceramics, and alloys to understand their properties and behavior.

Advantages of XAS for Speciation Analysis

Element-Specific: XAS is highly element-specific, allowing for the selective study of individual elements in complex matrices.
Non-Destructive: The technique is generally non-destructive, preserving the sample for further analysis.
Applicable to Diverse Samples: XAS can be applied to a wide range of sample types, including solids, liquids, and gases.
In Situ Capabilities: XAS can be performed under in situ conditions, enabling the study of dynamic processes in real-time.

Limitations

Requires Synchrotron Source: High-quality XAS measurements typically require access to synchrotron radiation facilities, which may not be readily available to all researchers.
Complex Data Analysis: The analysis and interpretation of XAS data can be complex and often require specialized software and expertise.

In summary, X-ray absorption spectroscopy is a versatile and powerful tool for speciation analysis, providing detailed information about the chemical state, local structure, and environment of specific elements in a wide range of samples.

Related Information: Synchrotron facilities

As of the most recent data, there are approximately 50 operational synchrotron light sources worldwide. These facilities are distributed across various regions and serve as crucial resources for a wide range of scientific research fields, including materials science, biology, chemistry, environmental science, and physics.

Here are some prominent synchrotron facilities by region:

North America

Advanced Light Source (ALS) - Lawrence Berkeley National Laboratory

Advanced Photon Source (APS) - Argonne National Laboratory, USA

Center for Advanced Microstructures and Devices (CAMD) - Louisiana State University in Baton Rouge

Cornell High Energy Synchrotron Source (CHESS)

National Synchrotron Light Source II (NSLS-II) - Brookhaven National Laboratory, USA

Stanford Synchrotron Radiation Lightsource (SSRL) - Stanford University, USA

Canadian Light Source (CLS) - Saskatoon, Canada

South America

Sirius - Brazilian Synchrotron Light Laboratory (LNLS)

Europe

ALBA - Barcelona, Spain

BESSY II - HZB Berlin, Germany

Diamond Light Source - Oxfordshire, UK

Elettra Synchrotron - Trieste, Italy

European Synchrotron Radiation Facility (ESRF) - Grenoble, France

KIT Light Source - Karlsruhe Research Accelerator (KARA) - Karlsruhe, Germany

MAX IV Laboratory - Lund, Sweden

PETRA III at DESY - Hamburg, Germany

SOLARIS National Synchrotron Radiation Centre, Jagiellonian University - Krakow, Poland

SOLEIL - Saint-Aubin, France

Swiss Light Source (SLS) - Villigen, Switzerland

Asia

Beijing Synchrotron Radiation Facility (BSRF) - Beijing, China

Hiroshima Synchrotron Radiation Center

Korean Synchrotron Radiation Facility (Pohang Light Source) - Pohang, South Korea

National Synchrotron Radiation Research Center (NSRRC) - Hsinchu, Taiwan

National Synchrotron Radiation Laboratory (NSRL) - University of Science and Technology of China(USTC)

Photon Factory (PF) - Tsukuba, Japan

Ritsumeikan Synchrotron Radiation Center - Ritsumeiksn University, Japan

SAGA Light Source (SAGA-LS) - Tosu City, Japan

Shanghai Synchrotron Radiation Facility (SSRF) - Shanghai, China

Singapore Synchrotron Light Source (SSLS) -

SPring-8 - Hyogo, Japan

Synchrotron-light for Experimental Science and Applications in the Middle East (SESAME) - Allan, Jordan

Synchrotron Light Research Institute (SLRI) - Nakhon Ratchasima, Thailand

Australia

Australian Synchrotron - Clayton (Vic.), Australia

Tutorial web material related to X-ray absorption fine structure

Grant Bunkers's Tutorials on XAFS

XAS Overview from Iztok Arcon, University of Nova Gorica, Jozef Stefan Institute, Slovenia

X-ray Spectroscopy mini courses from Jim Penner-Hahn, University of Michigan.

XAS Education from Bruce Ravel, National Institute of Standards and Technology

XAFS Overview from Matt Newville, University of Chicago

Reviews of X-ray absorption spectroscopy (newest first)

Mark A., Newton, Patric Zimmermann, Jeroen A. van Bokhoven, X-Ray Absorption Spectroscopy (XAS): XANES and EXAFS, in: I.E. Wachs, M.A. Bañares (eds.), Springer Handbook of Advanced Catalyst Characterization, Springer, 2023, 565-600. DOI: 10.1007/978-3-031-07125-6_27

Valentina Bonanni, Alessandra Gianoncelli, Soft X-ray Fluorescence and Near-Edge Absorption Microscopy for Investigating Metabolic Features in Biological Systems: A Review, Int. J. Mol. Sci., 24 (2023) 3220. DOI: 10.3390/ijms24043220

Anne Marie Aucour, Geraldine Sarret, Hester Blommaert, Matthias Wiggenhauser, Coupling metal stable isotope compositions and X-ray absorption spectroscopy to study metal pathways in soil-plant systems: a mini review, Metallomics, 15/4 (2023) mfad016. DOI: 10.1093/mtomcs/mfad016

Mina Magdy, X-Ray Techniques Dedicated to Materials Characterization in Cultural Heritage, ChemistrySelect, 8/33 (2023) 202301306. DOI: 10.1002/slct.202301306

B.V. Kerr, H.J. King, C.F. Garibello, P.R. Dissannayake, A.N. Simonov, B. Johannessen, D.S. Eldridge, R.K. Hocking, Characterization of Energy Materials with X-ray Absorption Spectroscopy - Advantages, Challenges, and Opportunities, Energy & Fules, 36/5 (2022) 2369-2389. DOI: 10.1021/acs.energyfuels.1c04072

Dominique Bazin, Solenn Reguer, Delphine Vantelon, Jean-Philippe Haqymann, Emmanuel Letavernier, Vincent Frochotd, Michel Daudon, Emanuel Esteve, Hester Colboc, XANES spectroscopy for the clinician, C.R. Chimie, 25/SI (2022) 189-208. DOI: 10.5802/crchim.129

Mihai R. Gherase, David E.B. Fleming, Probing Trace Elements in Human Tissues with Synchrotron Radiation, Crystals, 10/1 (2020) 12. DOI: 10.3390/cryst10010012

Roberto Terzano, Melissa A. Denecke, Gerald Falkenberg, Bradley Miller, David Paterson, Koen Janssens, Recent advances in analysis of trace elemnets in environmental samples by X-ray based techniques (IUPAC Technical Report), Pure Appl. Chem., 92/6 (2019) 1029-1063. DOI: 10.1515/pac-2018-0605

M. Newville, Fundamentals of XAFS, Rev. Mineral. Geochem., 78/1 (2014) 33-74. DOI: 10.2138/rmg.2014.78.2

Grant S. Henderson, Frank M.F. de Groot, Banjamin J.A. Moulton, X-ray Absorption Near-Edge Structure (XANES) Spectroscopy, Rev. Mineral. Geochem., 78/1 (2014) 75-138. DOI: 10.2138/rmg.2014.78.3

Mark A. Newton, Wouter van Beek, Combining synchrotron-based X-ray techniques with vibrational spectroscopies for the in situ study of heterogeneous catalysts: a view from a bridge, Chem. Soc. Rev., 39/12 (2010) 4845-4863. DOI: 10.1039/b919689g

J.J. Rehr, A.L. Ankudinov, Progress in the theory and interpretation of XANES, Coord. Chem. Rev., 249/1-2 (2005) 121.140. DOI: 10.1016/j.ccr.2004.02.014

C. Hardacre, Application of EXAFS to molten salts and ionic liquid technology, Annu. Rev. Mater. Res., 35 (2005) 29-49. DOI: 10.1146/annurev.matsci.35.100303.121832

J. J. Rehr and R. C. Albers, Theoretical approaches to x-ray absorption fine structure, Rev. Modern Phys., 72 (2000) 621-892. DOI:10.1103/RevModPhys.72.621.

S.E. Fendorf, D.L. Sparks, G.M. Lamble, M.J. Kelley, Applications of X-Ray-Absorption Fine-Structure Spectroscopy to Soils, Soil Sci. Soc. Am. J., 58/6 (1994) 1583-1595. DOI: 10.2136/sssaj1994.03615995005800060001x

EVISA Database system

Scientists working with X-ray absorption spectroscopy

Link database: Synchrotron based techniques for speciation analysis