Photon Factory Activity Report 2004 #22 Part B (2005)
Biological Science

27A,27B/ 2003G302

In-situ XANES measurement of change of oxidation states of Ce(III) to Ce(IV)Toshihiko OHNUKI*1, Naofumi KOZAI1, Takahiro Yoshida1, Takuo OZAKI1,
Takuya Nankawa1, Hiroshi ISOBE2
1
JAERI, Toaki, Ibaraki 319-1195, Japan
2
Kumamoto Univ., Kumamoto, Kumamoto 860-8555, Japan
Introduction
Actinides migration are of great concern in theenvironment because of their radioactivity and long halflives. Their migratory behavior depends on theiroxidation states [1] that differ among the III, IV, V, andVI. For the present study, we developed a continuous
flow system for in-situ XANES measurements of theoxidation state of Cerium (Ce). Ce was selected because
it is an analogue of trivalent actinides. Further, theoxidation state of Ce(III) changes to Ce(IV) afterexposure a desferrioximine B (DFO) solution [2].
Experimental
In-situ flow system for XANES measurement
Figure 1 is a diagram of the continuous-flow system tomeasure the in-situ XANES spectra. The system isinstalled at beam line 27B in the Photon Factory of theHigh Energy Research Organization (Tsukuba, Japan). Itemploys two micro-tube pumps controlling flow rate of
the contained solutions. Each solution pumped up from apolyethylene bottle is mixed at the system’s mixing point.
The hand-made mixer consisted of a silicon tube of 5 mminternal diameter. Through this tube, the mixed solution is
introduced to the measurement cell made of a siliconplate with 5 x 5 mm trench. The reaction time, t, inseconds was determined by t=L·A·r-1, where r is flow rate(cm3/s), L length between the mixing point and themeasurement point (cm), and A is a cross section of thesilicon tube (cm2). Note that the mixer is simply a tube,and nothing inside the tube to ensure that the twosolutions were mixed.
Solution
Desferrioxamine B (DFO), purchased from Sigma Co.
Ltd., was used as received. The chemicals employed wereanalytical grade. 1mM solutions of Ce(III)(NO3)3 andDFO were prepared by dissolving them in deionizedwater. The pHs of the resulting solutions were adjusted to7.0 by adding 1 M HCl and NaOH solution.
Measurement of XANES spectra
XANES spectra were measured in the fluorescencemode for the mixed solutions using a 7-element Ge array
detector interfaced to single-channel analyzers. XANESspectra for the Ce LIII edge were obtained at themeasurement point by changing the energy of the induced
X-ray that was scanned at intervals of 0.2 eV. The
fluorescent X-ray of the mixed solution was measured for
5 s at each energy interval of the induced X-ray.

XANES spectra were measured at different reaction
times for the Ce LIII edge in the Ce(III) solution alone,
and after the Ce solution was mixed with DFO solution.
Cerium(III)(NO3)3 and Ce(IV)O2 were used as thestandard materials for trivalent and tetravalent Ce,
respectively. Energy calibration was performed based on
the energy of the first peak of Ce(IV)O2 at 5731 eV.
Results
PF BL27B

X-ray
Pump
Mixing point

7-elements
detector

L

DFO
solutionCe(III)
solutionFig. 1 Conceptual diagram of the mm-scalecontinuous flow system for measuring the oxidation
states of elements by in-situ XANES analysis. PF
BL27B means KEK, PF beam line, and L in cm. See
the details of the system shown in Experimental.
XANES spectra measurements of Ce-DFO mixtures
The LIII edge Ce XANES spectra of a 1 mM Cesolution without DFO showed one strong peak at 5726 eV.
The peak energy was the same as that in the spectrum ofthe Ce(III) standard, denoting that Ce was present as
Ce(III) in the solution. For the mixture of Ce and DFO
solutions, a peak at approximately 5738 eV wasdistinguishable in the spectrum. The energy of the firstpeak shifted to higher energy in the spectra. Yoshida et al.
indicated that the energy of the first peak shifts with achange in the fraction of Ce(III) to Ce(IV) [2]. Thisfinding showed that Ce(IV) oxidized by the reaction withDFO.
References[1] R. J. Silva and H. Nitsche, Radiochim. Acta 70/71,
377 (1995).
[2] T. Yoshida, T. Ozaki, T. Ohnuki, and A. J. Francis,
Radiochimica Acta 92, 749 (2004)* ohnuki@sparclt.tokai.jaeri.go.jp

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