Analytical Sciences

Application of an Augmentation Method to MCR-ALS Analysis for XAFS and Raman Data Matrices in the Structural Change of Isopolymolybdates

Morihisa SAEKI,*1 Takumi YOMOGIDA,*2 Daiju MATSUMURA,*3 Takumi SAITO,*4 Ryuzo NAKANISHI,*1 Takuya TSUJI,*3 and Hironori OHBA*1

*1 Quantum Beam Science Research Directorate, National Institutes for Quantum and Radiological Science and Technology, 2-4 Tokai-mura, Naka-gun, Ibaraki 319-1106, Japan
*2 Sector of Nuclear Science Research, Japan Atomic Energy Agency, 2-4 Tokai-mura, Naka-gun, Ibaraki 319-1106, Japan
*3 Sector of Nuclear Science Research, Japan Atomic Energy Agency, 1-1-1 Koto, Sayo, Hyogo 679-5148, Japan
*4 Nuclear Professional School, School of Engineering, The University of Tokyo, 2-22 Shirakata Shirane, Tokai-mura, Ibaraki 319-1188, Japan

We measured X-ray absorption fine structure (XAFS) and Raman spectra of isopolymolybdates(VI) in highly concentrated HNO₃ solution (0.15 – 4.0 M), which change their geometries depending on the acid concentration, and performed the simultaneous resolution of the XAFS and Raman data using a multivariate curve resolution by alternating least-squares (MCR-ALS) analysis. In iterative ALS optimization, initial data matrices were prepared by two different methods. For low sensitivity of the XAFS spectra to the geometrical change of the isopolymolybdates, the MCR-ALS result of single XAFS data matrix shows a large dependence on the preparation method of the initial data matrices. This problem is improved by the simultaneous resolution of the XAFS and Raman data: the MCR-ALS result of an augmented matrix of these data has little dependence on the initial data matrices. This indicates that the augmentation method effectively improves the rotation ambiguities in the MCR-ALS analysis of the XAFS data.

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