Journal
APPLIED SPECTROSCOPY
Volume 63, Issue 8, Pages 961-970Publisher
SAGE PUBLICATIONS INC
DOI: 10.1366/000370209788964359
Keywords
Mixed oxidation states; Arsenic; X-ray absorption near edge structure; XANES; Extended X-ray absorption fine structure; EXAFS; Calibration curves
Categories
Funding
- University of Texas at El Paso's Center for Environmental Resource Management through funding front the Office of Exploratory Research of the U.S. Environmental Protection Agency [CR-819849-01]
- National Science Foundation NSF [0723115, 0521650]
- Department of Energy
- Office of Biological and Environmental Research
- National Institutes of Health
- National Center for Research Resources
- Biomedical Technology Program
- National Science Foundation and the Environmental Protection Agency [EF 0830117]
- University of Texas System
- Direct For Biological Sciences
- Div Of Biological Infrastructure [0830117] Funding Source: National Science Foundation
- Direct For Mathematical & Physical Scien
- Division Of Materials Research [0521650] Funding Source: National Science Foundation
- Division Of Materials Research
- Direct For Mathematical & Physical Scien [0723115] Funding Source: National Science Foundation
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The speciation of elements without pre-edge features preformed with X-ray absorption near edge structure (XANES) can lead to problems when the energy difference between two species is small. The speciation of arsenic (As) in plant samples was investigated using the mixtures As2S3/ As2O5, As2S3/As2O3, or As2O3/As2O5. The data showed that the energy separation (eV) between As2O5 and As2S3 was 5.8, between As2O3 and As2O5 was 3.6, and between As2S3 and As2O3 was 2.1. From the intensity of the white-line feature and the concentration of As species, calibration curves showing a limit of detection of approximately 10% were generated. In addition, an error of +/- 10% was determined for the linear combination-XANES (LC-XANES) fitting technique. The difference between the LC-XANES fittings and calculations from the calibration curves was <10%. The data also showed that the speciation of As in a sample can be determined using EXAFS (extended X-ray absorption fine structure). Finally, it was also shown that both EXAFS and XANES of the sample should be examined to determine the true speciation of an element. Even though there is a difference of 2 eV between As(III) bound to O and As(III) bound to S, in the EXAFS region the As(III)-S and As(III)-O ligands are clearly visible. However, distinction between the As(III)-O and As(V)-O ligands in the EXAFS spectra was not clearly visible in this study.
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