X-ray Absorption Near-Edge Spectra in Analysis of Mixtures
Stanford Synchrotron Radiation Laboratory
Wednesday, October 9, 2002
Orange Room, SLAC
Organizers: Ingrid Pickering & Graham George

A workshop on "X-ray Absorption Near-edge Spectra in Analysis of Mixtures" chaired by Ingrid Pickering (SSRL) and Graham George (SSRL) was held on October 9, 2002. X-ray absorption near-edge spectroscopy is a sensitive probe of local atomic environment, oxidation state and electronic structure, and can thus be used as a fingerprint of particular chemical environments. No special sample preparation is required and the incident x-rays probe a given element regardless of its physical form (solid, liquid or gaseous). Because of this, x-ray absorption near-edge spectroscopy can be a powerful method for analysis of chemical form in complex samples such as mixtures and has already found a wide range of applications. Least-squares fitting can be used to quantitatively determine the abundances of various chemical species in a mixture. In the case of a set of related mixtures, principal component analysis can be used to determine the number of individual components in the set, and target transformation can be used to test whether a given standard spectrum is one of the components.

After an introductory talk by Roger Prince (ExxonMobil Research and Engineering), presentations were made concerning the methodology of edge analysis by Graham George (SSRL) and Stephen Wasserman (Advanced X-ray Analytical Services). Applications were drawn from a broad range of disciplines and included identification of Mn particulates emitted from auto engines (Joe Wong, LLNL), arsenic speciation in Bangladeshi aquifers (Andrea Foster, USGS), elucidating the chemistry of Ascidian blood cells (Pat Frank, SSRL) and proposing preservation methods for the Swedish warship Vasa (Farideh Jalilehvand, U. Calgary). During final sessions, participants were given the opportunity to try out principal component analysis and other edge analysis routines using the suite of programs EXAFSPAK (written by Graham George, SSRL) running on either in-house PCs or on personal laptops.


9:00 Welcome

9:05 Overview and Introduction
   (Roger Prince, ExxonMobil Research and Engineering Company)

9:40 Analysis of Near-edge Spectra
   (Graham George, SSRL)

10:15 Principal Component Analysis
   (Stephen Wasserman, Advanced X-ray Analytical Services, Inc.)

10:50 Break

11:10 Quantitative Analysis using XANES Spectroscopy in Combination iwth PCA and LSF: A Case Study for Mn Particulates Emitted from Auto Engines
   (Joe Wong, Lawrence Livermore National Laboratory)

11:45 Coupled Principal Component/Least-Squares Analysis of As K-edge XANES Spectra: Model and Natural Systems
   (Andrea Foster, U.S. Geological Survey)

12:20 Lunch

1:20 Metallobiochemistry at pH 0: Fits to the Vanadium K-edge XAS Spectra of Ascidian Blood Cells
   (Pat Frank, Stanford University)

1:55 Sulfur Spectroscopy and the 17th Century Swedish Warship Vasa
   (Farideh Jalilehvand, University of Calgary)

2:30 Preview of EXAFSPAK PCA/Target Analysis Programs
   (Graham George, SSRL)

2:45 Discussion

3:00 Break

3:15 Hands-On Analysis Sessions (Building 50, SCS)
Room 111 (SCS Computer Lab) for SLAC PCs
Room 115 (Video Conferencing Center SLAC 1) for laptops
(Tutors: Pat Frank, Serena George, Hugh Harris, Graham George & Ingrid Pickering)

5:00 Close