Journal of Nuclear and Radiochemical Sciences, Vol. 6, No. 1, pp. 65-67, 2005

Accepted
A Continuous Flow System for In-Situ XANES Measurements of Change in Oxidation
State of Ce(III) to Ce(IV)Toshihiko Ohnuki,*, a Takahiro Yoshida,a Takuya Nankawa,a Takuo Ozaki,a Naofumi Kozai,bFuminori Sakamoto,a Yoshinori Suzuki,c and Arokiasamy J. Francisd
aAdvanced Science Research Center, Japan Atomic Energy Research Institute, Shirakata-2, Tokai, Ibaraki
319-1195, JapanbDepartment of Environmental Sciences, Japan Atomic Energy Research Institute, Shirakata-2, Tokai, Ibaraki
319-1195, Japanc
Department of Materials, Physics, and Energy Engineering, Graduate School of Engineering, Nagoya University,Furocho, Chikusa-ku, Nagoya 464-8603, Japan
dEnvironmental Sciences Department, Brookhaven National Laboratory, Upton, New York 11973, USA
Received: November 15, 2004; In Final Form: April 21, 2005
To develop a microsystem for determining the oxidation state of actinides, we tested the performance of a mm-scalecontinuous-flow system in measuring the change in oxidation state of Ce(III) to Ce(IV) with time using X-ray
absorption near-edge structure (XANES) analysis. A 1 mM Ce(III) solution mixed with a 1 mM desferrioximine
B solution (DFO) was pumped into the system, and then the solution was carried through it at a constant flow rate
to the point at which the XANES spectra were captured. The system revealed the distinct peaks of Ce(III) andCe(IV) in LIII edge Ce XANES spectra. The peak intensity of Ce(IV) increased when the reaction time after
mixing the two solutions was extended, reflecting the continued oxidation state change of Ce(III) by DFO. FiveXANES spectra repeated taken during the test showed no changes in the spectra, indicating the constancy of theoxidation states of Ce throughout the duration of the measurements. Measurements of XANES spectrum overlonger periods in the system revealed only low fluctuations in the spectrum around the Ce(III) and Ce(IV) peaks.
These results indicate that the mm-scale continuous flow system with XANES analysis is suitable for measuringchanges in the oxidation state of actinides with time.

1. Introduction
Actinides migration are of great concern in the environment
because of their radioactivity and long half-lives. 1 Theirmigratory behavior depends on their oxidation states 2 thatdiffer among the III, IV, V, and VI.
The amounts of actinides that can be used in experiments
are limited by regulations. These state that the chemical statesof actinides should be determined with limited amounts ofactinides, thus requiring precise measurements on low concentrations. One resolution for this problem is to develop a micromeasurement system. Various microfluodic devices fabricatedby micromachining technologies have been successfullyapplied in miniaturizing analytical and chemical systems. 3−5
Micro-reaction systems offer many advantages over the traditional large-scale systems: efficient mass transfer, highly effective heat management, a highly specific surface area, lesswaste and toxic materials generated in chemical reactions, andso on.6
X-ray absorption near-edge structure (XANES) is one of themethods that might be useful for analyzing oxidation states inchemicals at low concentrations,7 and have applied to determine oxidation state of actinides. 8−10 Thus, combining themicro devices with XANES analysis opens the possibility ofin-situ measurements of oxidation states of the actinides.
However, before developing a microfluodic device foractinides, the performance of a larger continuous flow system,
using non-actinides, should first be assessed.
For the present study, we developed a mm-scale continuous
flow system for in-situ XANES measurements of the oxidation*Corresponding author. E-mail: ohnuki@sparclt.tokai.jaeri.go.jp.
FAX: +81-29-282-5927.

state of Cerium (Ce). Ce was selected because it is an analogueof trivalent actinides. Further, the oxidation state of Ce(III)changes to Ce(IV) after exposure a desferrioximine B (DFO)
solution.11
2. ExperimentalIn-situ flow system for XANES measurement. Figure 1 isa diagram of the continuous-flow system to measure the in-situ
XANES spectra. The system is installed at beam line 27B inthe Photon Factory of the High Energy Research Organization(Tsukuba, Japan). It employs two micro-tube pumps controlling flow rate of the contained solutions. Each solution
PF BL27B

X-ray
Pump

7-elements
detector

Mixing point

LDFO Ce(III)solution solution
Figure 1. Conceptual diagram of the mm-scale continuous flowsystem 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.

© 2005 The Japan Society of Nuclear and Radiochemical Sciences
Published on Web 07/31/2005

OhnukiJ. Nucl. Radiochem. Sci., Vol. 6, No. 1, 2005

pumped up from a polyethylene bottle is mixed at the system’smixing point. The hand-made mixer consisted of a silicon tubeof 5 mm internal diameter. Through this tube, the mixed solution is introduced to the measurement cell made of a siliconplate with 5 × 5 mm trench. The reaction time, t, in seconds
was determined by t = L·A·r −1, where r is flow rate (cm3/s), L
length between the mixing point and the measurement point(cm), and A is a cross section of the silicon tube (cm2). Notethat the mixer is simply a tube, and nothing inside the tube toensure that the two solutions were mixed.
Solution. Desferrioxamine B (DFO), purchased from Sigma
Co. Ltd., was used as received. The chemicals employed wereanalytical grade. 1 mM solutions of Ce(III)(NO3)3 and DFO
were prepared by dissolving them in deionized water. The pHsof the resulting solutions were adjusted to 7.0 by adding 1 M
HCl and NaOH solution.
Measurement of XANES spectra. XANES spectra weremeasured in the fluorescence mode for the mixed solutions
using a 7-element Ge array detector interfaced to singlechannel analyzers. XANES spectra for the Ce LIII edge wereobtained at the measurement point by changing the energy ofthe induced X-ray that was scanned at intervals of 0.2 eV. Thefluorescent X-ray of the mixed solution was measured for 5 sat each energy interval of the induced X-ray. To obtain theXANES spectra at different reaction times, the flow rate waschanged to 3, 8, 18, or 180 s. The flow rate of the Ce and DFOsolutions was the same.
XANES spectra were measured at different reaction timesfor the Ce LIII edge in the Ce(III) solution alone, and after theCe solution was mixed with DFO solution. Cerium(III)(NO3)3and Ce(IV)O2 were used as the standard materials for trivalentand tetravalent Ce, respectively. Energy calibration wasperformed based on the energy of the first peak of Ce(IV)O2 at5731 eV.
Constancy and stability of XANES spectrum. Since thechange in the oxidation state change of Ce(III) to Ce(IV) took
place in the silicon tube after mixing the solutions, the performance of the in-situ XANES measurement system was rated
by the constancy and stability of XANES spectrum. Five
repetitive XANES spectra were captured to verify constancy.
Each XANES spectrum was obtained by measuring the CeDFO solution at the measurement point for 5 s at each energy
interval of the induced X-ray. The reaction time was 18 s after
mixing. Measuring at 1- and 5- s at each energy interval of theinduced X-ray assessed the stability of the XANES spectrum.

spectrum of the Ce(III) standard, denoting that Ce was presentas Ce(III) in the solution. Three seconds after mixing with a 1mM DFO solution, the spectrum was the same as that in theunmodified Ce solution.
By 8 s, a small peak at approximately 5738 eV was distinguishable in the spectrum. The first peak energy was nearly
the same as that of the Ce(III) standard solution, but its halfvalue width was broader than that of the standard. The energyof the first peak shifted to higher energy in the spectracollected at 18 and 180 s after mixing. Yoshida et al. indicatedthat the energy of the first peak shifts with a change in the fraction of Ce(III) to Ce(IV).11 This finding showed that Ce(IV)oxidized by the reaction with DFO. Our results indicated thatthe in-situ continuous flow system detected the change of theoxidation states of Ce in the Ce-DFO complex.
Performance of the system. Figure 3 depicts the XANES
spectra of Ce measured repetitively five times at 18 s after
mixing a 1 mM Ce(III) solution with 1 mM DFO solution.
Two peaks around 5727 and 5737 eV were distinguished in all
the spectra with energies different from that of Ce(III) orCe(IV). This result indicated that some fractions of Ce werepresent as Ce(III) and Ce(IV). The peaks energies wereconstant in all the spectra, demonstrating that the XANES
spectrum was invariant with time, showing constant oxidation
states of Ce at the measurement point.
Figure 4 gives the XANES spectra of Ce measured for 1 and5 s at each energy interval of the induced X-ray. The reaction
time of a Ce(III) solution with a DFO solution was 18 s. Bothspectra showed two peaks around 5727 and 5737 eV that did
not changed with time. Thus, measuring the spectra for longer
periods lowered fluctuations in the peaks’ intensity, rendering
them more distinct.
These results clearly affirmed the sufficiency of the system’s
performance in measuring the changes in oxidation states withCe(IV)543Counts

66

21Ce(III)

3. Results and Discussion

5700

XANES spectra measurements of Ce-DFO mixtures.
The L III edge Ce XANES spectra of a 1 mM Ce solution
without DFO (Figure 2: Without DFO) showed one strong
peak at 5726 eV. The peak energy was the same as that in the5710

5720

5730
Energy (eV)

5740

5750

5760

Figure 3. The XANES spectra of Ce collected 18 s after mixing a 1mM Ce(III) solution with a 1 mM DFO solution and repeating themeasurements 5 times. The reference spectra of Ce(III) and Ce(IV)are shown. The small numbers denote the sequential order of themeasurements.

Ce(IV)
120 s

Counts

18 s

5s

8s

Counts3sWithout DFO
Ce(III)

5700

5710

5720

5730
Energy (eV)

5740

1s
5750

5760

Figure 2. The LIII edge Ce XANES spectra of a 1 mM Ce solutionalone (Without DFO), at 3, 8, 18, and 120 s after mixing a 1 mMCe(III) solution with a 1mM DFO solution. The spectra shown byCe(III) and Ce(IV) are obtained from the standard solutions forCe(III)(NO3)3 and Ce(IV)O2.

5700

5710

5720

5730

5740

5750

5760

Energy (eV)Figure 4. The XANES spectra of Ce measured at 18 s after mixing a1 mM Ce(III) solution with a 1 mM DFO solution for 1s and for 5 s ateach energy interval of the induced X-ray.

A Continuous Flow System for In-Situ XANES Measurements

time. Therefore, we conclude that the mm-scale continuous
flow system with XANES analysis is applicable for measuring
such changes in the actinides.
Acknowledgments. Part of this study was supported by aGrant-in-Aid from the Ministry of Education, Culture, Sports,
Science and Technology of Japan to T. Ohnuki. The XANES
experiments were conducted at KEK-PF, which is operated by
the High Energy Accelerator Research Organization, Japan.
References(1) G. R. Choppin, Distribution and movement of a plutonium.
In A. Kudo, (ed.), Radioactivity in the environment, Vol 1Plutonium in the environment. Elsevier, Amsterdam, TheNetherlands, 91 (2001).
(2) R. J. Silva and H. Nitsche, Radiochim. Acta 70/71, 377(1995).
(3) A. Manz and H. Becker, Microsystem technology in chemistry and life science, Springer-Verlag, Berlin (1999).

J. Nucl. Radiochem. Sci., Vol. 6, No. 1, 2005

67

(4) D. J. Harrison and A. Van Den Berg, Micro total analysis
systems '98, Kluwer Academic Publishers, Dordrecht(1998).
(5) Y. Baba, S. Shoji, and A. Van Den Berg, Micro total analysis
systems '2002, Kluwer Academic Publishers, Dordrecht(2002).
(6) W. Ehrfeld, V. Hessel, and H. Lowe, Microreactors: New
technology for modern chemistry, Wiley-VCH Verlag,Weinheim (2000).
(7) S. Sueno, Eur. J. Mineral. 7, 1273 (1995).
(8) Y. Suzuki, S. Kelly, K. M. Kemner, and J. F. Banfield,
Nature 419, 134 (2002).
(9) A. J. Francis, J. B. Gillow, C. J. Dodge, R. Harris, T. J.
Beveridge, and H. W. Papenguth, Radiochim. Acta 92, 481(2004).
(10) T. Ohnuki, T. Yoshida, T. Ozaki, M. Samadfam, N. Kozai,K. Yubuta, T. Mitsugashira, T. Kasama, and A. J. Francis,
Chem. Geol. 220, 237 (2005).
(11) T. Yoshida, T. Ozaki, T. Ohnuki, and A. J. Francis,
Radiochim. Acta 92, 749 (2004).