XANES as a tool for iron oxidation state determination in tissues

The X-ray absorption near edge structure (XANES) technique was applied in f luorescence mode for the determination of the iron oxidation state in diffe rent structures of the kidney. The experiment was performed on 20-mum thick tissue sections at the National Synchrotron Light Source in Brookhaven Nat ional Laboratory, USA with the use of a monochromatized beam around 7.2 keV at the X26A beam line. The beam size was defined by four tantalum slits. T he samples were taken from patients who were operated due to kidney cancer. First, two-dimensional scans on the selected areas of the kidney tissue se ctions were done in order to present distribution of iron concentration. Th e scanned areas were visible on analyzed sections after the measurements al lowing the precise matching of tissue structure with analytical data. Other s successfully used similar matching procedures with the particle beams met hods but synchrotron radiation is less damaging to biological materials. Th en, the XANES spectra were taken on selected points that contained high con centration levels of iron. The XANES measurements were done to determine th e iron oxidation state. as this is regarded as one of the oxygen indicators in tissue. and free radicals generation. In order to do so the spectra had to be calibrated and normalized. Therefore, three standards were used. Fol lowing previous work [Geochim. Cosmochim. Acta 58 (1994) 5209] a synthetic fayalite [Fe2SiO4: standard for Fe(II)], pure magnetite [FeO . Fe2O3: stand ard for a mixture of Fe(II) and Fe(III) with the ratio 1:2], and pure hemat ite [Fe2O3: standard for Fe(III)] as standards for iron pre-edge peak posit ion in the XANES spectra were used. It has been found that the iron concent ration level is much higher in kidney glomeruli than in nephron regions and due to XANES spectra analyses in the glomerular regions of the tissue sect ions iron occurs in different oxidation states. (C) 2001 Elsevier Science B .V. All rights reserved.