Determination of Chromium and Manganese Species in Water Samples using X-Ray Resonant Raman Scattering and Principal Component Analysis at the IAEA-Elettra Synchrotron Beamline End-Station Facility

JOSE ROBLEDO; H.J. SÁNCHEZ; JUAN JOSÉ LEANI; A. MIGLIORI; A. KARYDAS

Gotemburgo

Congreso; European Conference on X-Ray Spectrometry (EXRS); 2016

University of Gothenburg

The combination of state-of-the-art techniques is often required to overcome analytical limitations of individual techniques. This is the case of the methodology that combines the merits of X-ray resonant Raman scattering spectroscopy (RRS) and grazing incidence/emission (GI/GE) geometry for irradiation. GI/GE-RRS is particularly suited for the chemical speciation of trace elements in liquid samples, as for instance, in everyday situations of water contaminated with metals. Arsenic is a typical case, where the different species have different levels of toxicity. Another particular case is that of chromium. This is a very common element disposed by industries and factories (like furriers and tanneries); it has six species but only one of them is hazardous. As chromium compounds were used in dyes and paints and in the tanning of leather, these compounds are often found in soil and groundwater at abandoned industrial sites, which require afterwards environmental cleanup and remediation per the treatment of brownfield land. The detection and chemical speciation of Cr species in contaminated water requires the application of a very specialized and sensitive technique. In this study the synchrotron induced GI/GE-RRS combined methodology is investigated to fulfill these analytical challenges.Preliminary measurements of contaminated water with different species of chromium and manganese were measured at the new IAEA end-station operated jointly with Elettra Sincrotrone Trieste (Italy) at the XRF-beamline. Droplets of Cr-III and Cr-VI, and Mn-II, Mn-IV and Mn-VII were deposited on silicon wafers and irradiated at grazing incidence of the incident beam to take advantage of external total reflection. The incident energy was set 10 eV below the absorption K-edge of the element of interest (Cr or Mn) so as to enhance the yield of the X-ray Resonant Raman Scattering.The acquired raw X-ray Resonant Raman spectra from the different Cr and Mn species look all very similar. In order to decode the hidden information Principal Component Analysis (PCA) was applied. It was found out that the definition of only two principal components were enough to discriminate the different Cr and Mn compounds. The results are quite conclusive demonstrating that RRS spectroscopy in combination with PCA are able to discriminate different species in contaminated water measuring a few spectra and with a simple data treatment.