Journal of Nuclear and Radiochemical Sciences, Vol. 14, No.1, pp. 1-5, 2014

ArticlesPreparation and characterization of cerium(IV) tellurium molybdate gel and its application
as a bed for chromatographic 99Mo/ 99mTc generator
M. A. El-Amir, M. Mostafa*, H. E. Ramadan
Radioactive Isotopes and Generators Dept., Hot Labs. Center, Atomic Energy Authority, P.O.B. 13759, Cairo,
Egypt
Received: October 15, 2013; In Final Form: February 5, 2014
Cerium(IV) tellurium molybdate was prepared as a new gel bed for chromatographic 99Mo/ 99mTc generator. The
gel material prepared with the optimum conditions was characterized with IR spectroscopy, thermal analysis,
XRD, EDX and FESEM. The highest precipitation yield of 99Mo within the formed gel was found to be 97.6 % at
a Ce:Te:Mo molar ratio of 1:0.2:1. The prepared 99Mo/ 99mTc chromatographic column based on Ce(IV) tellurium
molybdate gel bed showed a good performance. The 99mTc elution yield was 77.8±3.0 % with a radionuclidic
purity of ≥ 99.99 %, radiochemical purity of 96.5±1.3 % (as 99mTcO 4 - ) and pH-value in the range of 5-7.
Molybdenum and cerium levels in 99mTc eluates did not exceed 1 and 0.3 ppm, respectively, while no tellurium was
detected.

1. Introduction

2. Experimental

Chromatographic column generators of (n,γ) 99Mo/ 99mTc gel
have low-specific activity 99Mo, but they represent an alternative option to those of alumina loaded with higher specificactivity fission-99Mo. Gel generators can participate in thesolution of the problem of the increasing demand of 99mTc,
which is used in more than 80 % of nuclear medicine applications, all over the world. Among the advantages of gel generators are the easy and quick preparation of (n,γ) 99Mo solution,
low cost and minimal radioactive waste.1 Criteria for good gel
generators include high-content of 99Mo in the gel bed, highelution yield and high radionuclidic, radiochemical and chemical purities of the 99mTc eluates. Many gel materials, including
acidic salts of polyvalent metals and salts of heteropolyacids,
have been used as beds for 99Mo/ 99mTc generators, e.g., zirconium molybdate,2-6 stannic molybdate,7 titanium molybdate,8
cer iu m ( I V ) molybd ate, 9 12-molybdocerate ( I V ), 1 0 6 tungstocerate(IV)11 magnesium molybdate12 and zirconium
molybdophosphate.13 Zirconium molybdate is the most famousmaterial used as a bed for 99Mo/ 99mTc generators, but the synthesis and study of other gel materials constitute a renewable
research filed in literature to obtain more alternatives.
For zirconium molybdate gel, replacement of 5 % (molar) of
zirconium with Ce(IV) enhances the 99mTc elution yield due toovercoming the reduction of 99mTc species, because of radiolysis, and oxidation of its species to 99mTcO4-.14 Thus, in the present work, using such high molar ratio of cerium (IV) will beadvantageous especially in case of high-99Mo activity generators in which the radiolysis effect will be higher. In addition,
adding a small ratio of tellurium (IV) was found to increase the99
Mo uptake by the formed gel comparing with the case of
CeMo gel.9
This work aims at the preparation of cerium(IV) tellurium
molybdate gel material containing a high content of molybdenum which can be used as a new bed material for a chromatographic 9 9 Mo / 9 9 m Tc radioisotope generator of a good
performance.

All the chemicals used were of AR grade. Distilled water
was used for preparing solutions.
A γ-ray spectrometer composed of a multichannel analyzer(MCA) of Inspector 2000 model (Canberra Series, USA), coupled with a high-purity germanium (HPGe) coaxial detector of
GX2518 model, was used for γ-radioactivity identification andmeasurement.
A pH-meter with a microprocessor (Hanna Instruments
pH211 model, Portugal) was used for measuring pH-values ofsolutions. An analytical balance (A&D Engineering Inc., AND
HR-202 model, USA) having dual range (42 g/0.01 mg, 210
g/ 0.1 mg) was used for weighing. A centrifuge (REMI
Laboratory, R32A model, India) was used for centrifugation of
the mixtures to efficiently separate the precipitated gel materials from the supernatants.
A UV-VIS spectrophotometer (Shimadzu, UV-160 A model,
Japan) was used for detection of Ce and Mo in 99mTc eluted
from the Ce(IV) tellurium molybdate–99Mo column.
The IR spectrum was recorded with an FT-IR spectrometer(Bomem, model MB157S, Canada) in the range from 4000 to
400 cm–1 at room temperature.
Thermal analysis, including simultaneous TGA and DTA,
was carried out with a thermal analyzer (Shimadzu, model
DTG-60H, Japan). X-ray diffraction was performed with an
18 kV diffractometer (Bruker, model D8 Advance, USA) withmonochromated CuKα radiation (λ = 1.54178 Å).
Elemental analysis was performed using energy dispersive
X-ray spectrometer (ISIS-300, Oxford EDX). FESEM images
were taken using field emission scanning electron microscope(FESEM) (JEOL JSM-6500F, USA).
2.1. Molybdenum-99 radiotracer. 99Mo was obtained byeluting commercial 99Mo/ 99mTc generators with alumina-packed
columns (Mon-Tek Generator, Monrol Nuclear Products
Industry and Trade Inc., Turkey; loaded with 20 GBq on calibration date). Each column was eluted with 20 ml of 2 M NH3
solution 20 days after the calibration date. Then the NH3 solution was evaporated to dryness, and the residual 99 Mo was
redissolved in 5 ml of 0.1 M NaOH.
2.2. Preparation of cerium(IV) tellurium molybdate(CeTeMo) gel. A 0.1 M Mo(VI) solution was prepared by dissolving 2.42 g of Na 2 MoO 4 ·2H 2 O in 20 ml of distilled H 2 O*Corresponding author. E-mail: mmostafa95@yahoo.com© 2014 The Japan Society of Nuclear and Radiochemical Sciences
Published on Web 02/21/2014

Mostafa

J. Nucl. Radiochem. Sci., Vol. 14, No. 1, 2014

rate of 140-keV peak in the γ-ray spectrum of the eluate to thetotal count rate.
The radiochemical purity of the eluted 99mTc (contribution of
99m
TcO4- count rate to the total count rate the eluted 99mTc) was
determined by ascending paper chromatography using
Whatman no. 1 chromatographic paper and a mixture of 85%
methanol + 15% H 2O as a developing solvent.16 The activity
distribution along the chromatogram was traced using the γ-ray
spectrometer to determine Rf, where:

Rf =traveled distance of the radioactivity from the start point to the peak position
traveled distance of the solvent from the start point to the solvent front

The possible impurities of molybdenum, cerium and tellurium originated from the CeTeMo gel matrix, were determinedin 99mTc eluates spectrophotometrically by using thiocyanate
method (maximum absorption at 470 nm), persulfate method(maximum absorption at 320 nm), Bismuthiol II method (maximum absorption at 330 nm), respectively.17
3. Results and discussion
CeTeMo gels were prepared with different Ce:Te:Mo molar
ratios. As indicated by Figure 1, precipitation yield of 99Mo
increased gradually from 32.2 % at Ce:Te:Mo molar ratio of
1:1:0.5 till reaching a first lower maximum value of 61 % at themolar ratio of 0.2:1:1and then, it slightly decreased to 48.5 % at
the molar ratio of 0:1:1:1. Thereafter, the precipitation yield
sharply increased to a second higher maximum value of 97.6 %at the molar ratio of 1:0.2:1 and then sharply decreased to 58.1
% at the molar ratio of 1:0.5:1. Further change of the molar
ratio to 1:1:1 yielded a precipitation yield of 52.4 %. Hence,
Ce:Te:Mo molar ratio of 1:0.2:1 was chosen for characterization of the prepared CeTeMo gel (via IR, thermal analysis,
XRD, EDX and FESEM) and further preparation and quality
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with the addition of 2.5 ml of Mo solution along with few
drops of 30% H2O2. The volume of the Mo(VI) solution wascompleted to 100 ml with distilled H2O. A 0.1 M Ce(IV) solution was prepared by dissolving 6.32 g of (NH4 ) 4 Ce(SO 4 ) 4 ·2H2O in 100 ml of dilute H2SO4 to obtain a solution of pH1. A
0.1 M Te(IV) solution was prepared by dissolving 1.60 g of
TeO2 in 100 ml of 5 M NaOH. Mixtures with different Ce(IV):
Te(IV):Mo(VI) molar ratios were prepared by adding Mo(VI)solution dropwise to Ce(IV) solution and, then, Te(IV) solution
was added dropwise to the Mo(VI)-Ce(IV) mixture. Varied
volumes of the three solutions were used to obtain different
molar ratios. Thereafter, pH of the final mixture was adjusted
to 5.5 by using H2SO4 / NaOH solutions. The final volume ofeach mixture was 50 ml. The mixtures were left for 10 h toallow the formed precipitates to settle and then were centrifuged. The supernatant of each mixture was checked radiometrically to determine the precipitation yield of 99Mo within
the formed gel material.
The precipitated gel obtained from the mixture with the
optimum Ce:Te:Mo molar ratio (i.e., the mixture with which
the highest precipitation yield of 99Mo was achieved) was foundto be that with 1 Ce: 0.2 Te: 1 Mo. The mixture with the optimum molar ratio was prepared again by adding 50 ml of 0.1 M
Mo(VI) solution, containing 99Mo radiotracer, dropwise to 50
ml of 0.1 M Ce(IV) and then 10 ml of 0.1 M Te(IV) was added
dropwise to the Mo(VI)-Ce(IV) mixture. The pH-value wasthereafter adjusted to 5.5 by using H 2 SO 4 / NaOH solutions.
The mixture was left for 10 h to allow the precipitate to settle.
The mixture was then centrifuged, the supernatant wasremoved by decantation while the precipitate was spread as athin layer on a watch glass and dried for 12 h at 50°C. The
dried gel was pulverized to ~ 0.1–0.2 mm particle size and,then, used as a column bed for a 99Mo/ 99mTc chromatographic
generator. The latter mixture was prepared again by the same
method, but without adding 99Mo radiotracer and with washingthe dried gel with excess distilled water followed by re-drying
overnight at 50°C, to characterize the prepared gel.
2.3. Characterization of CeTeMo gel. The inactive prepared CeTeMo gel (with the optimum molar ratio) was characterized by IR spectroscopy, thermal analysis (TGA and DTA),
XRD, EDX and FESEM.
2.4. Preparation of 99Mo/ 99mTc chromatographic column
generator. A 0.7 cm i.d. glass column was used as a bed forthe 99Mo/ 99mTc generator. The column was provided with asmall piece of glass wool, as a support for the gel bed, and abottom stopcock. 1 g of the pulverized CeTeMo gel bed was
packed into the column by settling from distilled water. The
column was excessively washed with distilled water and subsequently conditioned with 50 ml of 0.9 % NaCl for further elution of 99mTc.
2.5. Elution of 99Mo/ 99mTc generator and quality controlof the eluted 99mTc. Technetium-99m was firstly eluted 23 hafter the conditioning time by passing 10 ml of 0.9 % NaClsolution through the CeTeMo gel column. The column was
eluted 14 times with different flow rates (0.25, 0.5, 0.75 and 1
ml/min) over the course of 25 days. The time between each
two successive elutions was ≥ 23 h. The 99mTc elution yield wasdetermined by comparing the counting rates of the 140-keV
peak in the γ-ray spectrum of the column directly before andafter elution, taking the contribution of 99Mo to this peak into
account.15 The elution profiles were drawn for various elution
flow rates. pH-values of the eluate solutions were determinedusing the pH-meter.
The percent 99Mo content in the eluate was determined, inthe case of its presence, as the contribution of the count rate of181- or 739-keV peak in the γ-ray spectrum to the total countrate. The γ-ray spectrum of the eluate was measured directly
after elution and after 5 days. The radionuclidic purity of theeluted 99mTc was determined as the contribution of the countMo precipitation yield, %

99

99

2

Ce:Te:Mo molar ratio
Figure 1. Precipitation yield of 99Mo as a function of Ce:Te:Mo
molar ratio used for preparing CeTeMo gel.

Preparation and characterization of cerium(IV) tellurium molybdate9999m

control of Mo/ Tc generator. Thus, the addition of tellurium during gel preparation, with a Ce:Te:Mo molar ratio of
1:0.2:1, increased the precipitation yield of 99Mo to 97.6 %,which is markedly higher than the yields of 35.8 and 63 %99
Mo in the case of CeMo gel with Mo:Ce molar ratios of 1:1
and 2:1, respectively.9
Figure 2 shows IR spectrum of CeTeMo gel. The IR spectrum includes peaks at 501 cm -1 (due to Te-O-Te bendingmode), 874 cm-1 (due to Mo-O stretching mode), 1401 cm-1
(due to Ce–O–H bending mode), 1614 and 3411 cm-1 (due toO–H bending and stretching modes of lattice water, respectively).9,18-21
Figure 3 shows the TGA and DTA curves of the CeTeMogel. There was a 8.3 % weight loss on TGA curve in the temperature range from 16 to 200°C due to the loss of lattice waterwith an endothermic peak on DTA curve at 71°C. The presence of lattice water in a suitable amount is important toenhance the diffusion of 99mTcO4- through the gel material during elution.22 In the range of 200–800°C, there was anotherweight loss of 4.1% due to decomposition of the gel material to

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J. Nucl. Radiochem. Sci., Vol. 14, No. 1, 2014

cerium, molybdenum and tellurium oxides, in addition to subsequent sublimation of molybdenum oxide.21,23 The thermal
gravimetric behavior of CeTeMo gel resembles to a great extent
that of cerium(IV) molybdate (CeMo) gel.9
Energy dispersive X-ray (EDX) spectrometric elemental
analysis indicated that the prepared gel material incorporated~27 % (wt./wt.) of molybdenum. This Mo content is considered high (where gel matrices used in 99Mo/ 99mTc generators
should contain high Mo content; > 25 %) and comparable with
Mo content in zirconium molybdate gels (30 %).24
Figure 4 shows the XRD pattern of the CeTeMo gel, whichindicates a nearly amorphous structure (low-crystallinity structure) of the prepared CeTeMo gel. The amorphous structure isusually preferred to the rigid crystalline structure, where thelatter one hinders the mobility of 99mTc leading to a decrease in
the elution yield. In addition, the amorphous structure has amore mechanical strength than the crystalline one, i.e., it ismore resistant to abrasion and dissolution.25
Figure 5 shows FESEM images of the CeTeMo gel. Image(a) indicates the gel particles with a size range of ~100-200μm(~0.1-0.2 mm), while the more magnified images (b) and (c)indicates many meanders and cavities, the presence of whichfacilitates the diffusion of saline solution through the gel bed
during 99mTc elution.
Figure 6 compiles the elution profiles of the 99Mo/ 99mTc generator at flow rates of 0.25, 0.5, 0.75, and 1 ml min–1. The elution yield of 99mTc was 77.8 ±3.0 %. Thus, the average 99mTc
elution yield for CeTeMo gel is slightly higher than that for
CeMo gel (75.4 %).9 Sharp elution peaks were obtained withthe flow rates of 0.25, 0.5 and 0.75 (the most sharp one wasobtained with the flow rate of 0.75 ml min-1), while a relatively
broad one was obtained with the flow rate of 1 ml min-1. A
maximum percent fraction of 99mTc activity was obtained at the
2nd ml of eluate for the flow rates of 0.25, 0.5 and 1 ml min-1(49.7, 54.1 and 33.1 %, respectively), while it was obtained at
the 1st ml of eluate for the flow rate of 0.75 ml min-1 (82.5 %).
Radionuclidic purity of the obtained 99mTc eluates was ≥99.99 %, i.e., in all cases 99Mo content in the eluate did not

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value in the range of 5-7.
(b)References(c)Figure 5. FESEM images of CeTeMo gel.

exceed 1×10 -3 %. pH-values of 99mTc eluates ranged from 5-7.
Radiochemical purity was 96.5±1.3 % as 99mTcO4 -. Chemical
impurities of molybdenum and cerium in 99mTc eluates did notexceed 1 and 0.3 ppm, respectively, while no tellurium was
detected.
4. Conclusion
Cerium(IV) tellurium molybdate (CeTeMo) gel was successfully prepared as a high-Mo content material with a high 99Mo
precipitation yield. CeTeMo gel was used as a new bed material for a chromatographic 99Mo/ 99mTc radioisotope generator
showing a good performance; suitable 99mTc elution yield, highradionuclidic, radiochemical and chemical purities and pH-(1) IAEA, Alternative Technologies for 99mTc Generators,
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