Study of XAFS spectroscopic methods of speciation using mixtures of Cu(I) and Cu(II) chlorides

Abstract

Speciation concerns determination of the chemical forms along with the relative quantities of the different species in a given sample. The aim of the present work is to make a comparative study of the different methods of speciation using X-ray absorption fine structure (XAFS) spectroscopy. For this purpose, mixtures have been prepared by mixing CuCl2 and CuCl in different proportions. The X-ray absorption spectra have been recorded at the copper K-edge in the mixtures and the two chlorides separately. The different characteristic features of the XANES spectra of the two chlorides, useful for speciation, have been identified. Firstly, Principal component analysis (PCA) and target transformation (TT) methods have been used to check the number and identity of components in the mixtures. After the identification of the components, the percentages of the species in the mixtures have been quantitatively determined by linear combination fitting (LCF) of XANES, derivative XANES, and EXAFS (k3chi and k2chi) spectra. The other methods of speciation which have been employed are normalized difference absorption edge spectra analysis (NDAES), methods based on derivative XANES spectra of species and the method based on the relative position of the absorption edge. Results obtained from these methods have been compared and their relative merits discussed. It is probably for the first time that such a study has been done. The first section in your paper