Speciation using X-ray absorption fine structure (XAFS)

Abstract

X-ray absorption fine structure (XAFS) spectroscopy is in use as a unique fingerprinting technique. By employing spectra of well-defined chemical species (standards), XAFS can be analyzed for speciation, i.e., identification and quantification of the different chemical species present in a sample. Several approaches to analyze the XAFS data for speciation have been developed. The principal component analysis and target transformation method are the two methods generally applied to check the number and identity of components in a sample. A widely used method for quantitatively determining the percentage of the species in the sample is linear combination fitting method, which can be applied to XANES spectra, derivative XANES spectra and EXAFS spectra. Other methods include residual phase analysis, normalized difference absorption edge analysis, pre-edge analysis method, derivative spectra methods and a method based on the relative position of the edge. The aim of the present article is to review the different (nearly all) methods of speciation using XAFS. The theory and principle of the different methods have been described and the analysis procedures for the methods have been illustrated with the help of examples. Some selected studies involving different elements have been reviewed and discussed.