実験室系X線吸収分光分析装置を用いる土壌及びプラスチック中クロムの価数評価

Abstract

Hexavalent {Cr(VI)} and trivalent chromium {Cr(III)} in environmental materials such as soil and plastics were investigated using a laboratory X-ray absorption fine structure (XAFS) spectrometer equipped a W anode X-ray tube. The Cr-K X-ray absorption edges were observed on the XANES spectra of soil (total chromium 606 ppm) and plastic (213 ppm) samples with a fluorescence mode, while the signal-to-noise (SN) ratios of these spectra were too low to determine the height of pre-edge peak of Cr(VI) and the value of the energy on the Cr-K X-ray absorption edge. The XANES spectra of reference samples prepared by Cr2O3 {Cr(III)} and CrO3 {Cr(VI)} particle reagents were also recorded with the transmission mode. In order to improve the SN ratios of XANES spectra, a smoothing treatment by Savitzky-Golay method was applied to the XANES spectra of the soil and plastic samples. By the smoothing treatment, SN ratios of these spectra were improved, though the height of pre-edge peak on the XANES spectra of Cr(VI) reference sample had decreased less than 5%. The height of pre-edge peak and the value of the energy on the Cr-K X-ray absorption edge of soil and plastic samples were given by smoothed XANES spectra. Using the height of pre-edge peak and the value of the energy on the Cr-K X-ray absorption edge of reference samples, the ratios of Cr(VI)/Cr(III) on the soil and plastic samples were calculated.