Journal of Nuclear and Radiochemical Sciences, Vol. 6, No. 3, pp. 223-225, 2005

Recent Developments in the Analysis of Techetium-99
Michael Fern,* Anil Thakkar, and Lawrence Jassin
Eichrom Technologies, Inc., 8205 S. Cass Ave., Suite 106 Darien, IL 60561 USA
Received: July 31, 2005; In Final Form: September 30, 2005
Analysis of 99Tc using an extraction chromatographic resin to isolate technetium from other elements, followed byliquid scintillation counting has become common worldwide. The method is robust and has been applied to awide variety of matrix types. Recently, high biases have been reported when samples with high levels of naturally
occurring uranium were analyzed. The problem was traced to incomplete decontamination of the technetium
fraction from 234Th (daughter of 238U) present in the samples. A variety of protocol modifications to the load andrinse solutions were attempted in order to improve the decontamination of the technetium fraction. It was determined that complexing agents were required to remove thorium from the column. Oxalate solutions provided
better decontamination than nitric acid and hydrochloric acid solutions alone for samples with low levels of natural uranium. However, fluoride was found to be necessary to ensure adequate decontamination from samples
containing up to 44 Bq of natural uranium.

1. Introduction
In recent years the use of extraction chromatography has
grown significantly in methodologies for technetium-99 measurement. An aliphatic quaternary amine, impregnated on apolymeric support, trade named TEVA® Resin1 has become astandard in separating and pre-concentrating pertechnetate
prior to technetium-99 measurement by liquid scintillation orICP-MS.
TEVA Resin has a very high affinity for pertechnetate anion
from low acid and even basic solutions. Figure 1 shows theuptake of TcO4− as a function of nitric acid and HCl concentration. It can be seen that the TcO 4 − uptake increases withdecreasing acid concentration, while all the actinide elements
show declining retention. This behavior indicates that theTEVA Resin can be used to separate pertechnetate anion from awide variety of potentially interfering radionuclides. The k’ values in the range of 10 4 –105 show that the resin can be used topre-concentrate pertechnetate from very large volume samples(e.g. up to 4 liters of water.)
The technique has been applied to a variety of matrices including water, soil, urine and waste samples. It has also been applied
to process control samples in nuclear fuel reprocessing andwaste treatment applications.1−5 TEVA Resin has been used inseveral formats: slurry-packed columns for gravity flow use, dry
packed cartridges for us in vacuum manifold systems, and glass
fiber filter discs to process very large liquid samples with fastflow rate (~100 mL/min.)As this methodology has been applied to broader andbroader sample types, several challenging matrix interferences
have been encountered that have made accurate measurements
difficult. One example of a matrix challenge is the effect ofhigh levels of Th-234 present in natural uranium samples on
the quantitation of Tc-99 in the sample. In this case, the beta
emissions from the interfering isotope are measured in the Tc99 window of the LSC. This can lead to a bias in the measurement of Tc-99.
2. Experimental

Figure 1. The acid dependency of k’ for various ions at 23 ˚C, TEVAResin (published by Horwitz, et al.1)*Corresponding author. E-mail: mfern@eichrom.com. FAX:
+1-630-963-1928.

All experiments were conducted using reagent grade materials. TEVA Resin packaged in columns is commercially available
from Eichrom Technologies (Darien, IL, USA.) UltimaGold®
LLT liquid scintillation counting cocktail was obtained fromPerkinElmer Life Sciences (Boston, MA, formerly Packard
Instrument Company.)
Technetium-99 was loaded onto a 2 mL pre-packed columnof TEVA Resin from 0.01 M HNO3. The column was thenrinsed with 0.01 M HNO3 (typically 20–25 mL.) The resin wasthen removed from the plastic column and transferred to a plastic 20 mL scintillation vial. UltimaGold LLT cocktail wasadded. Samples vials were placed in a Packard 2750 Liquid
Scintillation Counter and allowed to equilibrate to the dark.
Count time was 30 minutes. Typical counting uncertainly was© 2005 The Japan Society of Nuclear and Radiochemical Sciences
Published on Web 12/28/2005

224 J. Nucl. Radiochem. Sci., Vol. 6, No. 3, 2005

Fern

5–10%. Reagent blanks were determined by rinsing a TEVAResin column with 0.01 M HNO3, removing the resin andtransferring to a scintillation vial. UltimaGold LLT was added
and the vial counted for 30 minutes. Since blank levels werevery consistent between experiments and lots of resin, blanks
were not run with all experiments.
3. Results and Discussion
A number of customer comments about high spikes recoveries in samples from nuclear facilities lead to an internal investigation at Eichrom. A hypothesis emerged that thorium-234
present in natural uranium samples was causing a high bias in
the counts observed in the technetium-99 window of the LSCspectrum. Initially, this seemed improbable since the retentionof both uranium and thorium is quite low on the TEVA Resinunder the load and rinse conditions of the method. Extrapolationof the Th uptake curve in the nitric acid graph in Figure 1, indicates that thorium should have a k’ of less than10−1. (The dimensionless value, “k’”, represents the retention of an element on achromatographic column as a multiple of free column volumes
to peak maximum.) It would be expected that at this uptake
level, there should be no thorium present on the column if
loaded and rinsed with sufficient 0.01 M HNO3 (40–50 mL.)
However, the problem was replicated in our internal technicalsupport laboratory and confirmed to be reproducible on multiple replicates of several different lots of TEVA Resin. Table 1
shows results of natural uranium spiked(3.6 Bq) into 0.01 M
HNO3, loaded onto TEVA Resin columns, rinsed and counted
as indicated above. No technetium-99 was spiked into thesesamples. Net counts in the technetium-99 region were in therange of 0.2 to 0.4 cps. Counting efficiency was not measuredfor this experiment, but typically is in the range of 90%.
TABLE 1: Effect of Natural Uranium Spikes on Counts inthe Tc-99 Window in LSC
TEVAResin
Lot #Naturaluranium
spike/BqBlank
counts/cps

Mean counts
Tc-99
region/cps

σ/cps.
n=3

10170
11270
08280

3.6
3.6
3.6

0.23
0.23
0.26

0.62
0.53
0.47

0.10
0.06
0.05

To resolve this problem various options were considered. The
uptake of thorium is lower from HCl than from nitric acid anduse of HCl in load or rinse solution would be expected to elutethe thorium more completely from the column. Additionally,various complexants including oxalate and fluoride should keep
the thorium in a complexed state and prevent loading on theresin. Various concentrations and volumes of these solutions
were tried and the results are shown in Tables 2–4.
TABLE 2: The Effect of Various Load/Rinse Combinations
Containing Hydrochloric Acid on Counts in the Tc-99
Region Due to Natural Uranium Spike
Blank
Mean
σ/cps
counts/cps counts
Tc-99
region/cps

Naturaluranium
spike/Bq

Load(20 mL)

Rinse(25 mL)

3.6

0.01 M HCl

0.01 M HCl

0.24

1.18

0.08
(n = 9)3.60.5 M HNO3

0.05 M HCl

ND

0.92

0.21(n = 5)8.9

0.5 M HNO3

0.05 M HCl

ND

0.93

0.13(n = 5)

3.6

0.01 M HNO3

0.1 M HCl

ND

1.130.05(n = 4)

Attempts to reduce the thorium-234 bias in the technetium99 fraction using HCl were not successful. Despite the indication that Th would be less strongly retained from HCl, the bias
in the technetium-99 window actually increased. Results werereproducible between various numbers of replicates.
The use of oxalate as a complexant actually helped to reduce
the problem but did not eliminate it completely. The data forthis experiment are shown in Table 3. Higher spikes of naturaluranium (234U/ 238U) were added, in this case 37.4 Bq. Various
concentrations and volumes of oxalic acid in the rinse solution
were evaluated. With no oxalate and 25 mL of rinse, the same
conditions as the initial experiments which replicated the problem, 5.4 cps were observed in the technetium-99 window.
Addition of oxalate in the range of 0.05 M to 0.5 M with rinse
volumes of 25 and 50 mL reduced the counts in the Tc-99 window to 1.1 cps or less. However, in the best case, 50 mL of 0.5
M oxalic acid, there were still approximately 0.3 net cps. Thisis a marked improvement and may be acceptable as a solution
in cases were the amount of interfering thorium-234 is low.
However, a universal solution that can address even very highlevels of thorium-234 is desirable.
TABLE 3: The Effect of Increasing Concentration and Volume of Oxalic Acid Rinses on the Counts in the Technetium99 Window
Naturaluranium
spike/BqOxalicacid conc.

RinsevolumeBlank
counts/cps

37.437.4
37.4
37.4
37.4
37.4

None
0.05 M
0.1 M
0.1 M
0.5 M
0.5 M

25 mL
25 mL
25 mL
50 mL
25 mL
50 mL

0.27
0.25
0.25
0.25
0.25
0.24

Mean σ/cps
counts n = 2
Tc-99
region/cps
5.4
1.1
0.78
0.64
0.80
0.53

1.1
0.01
0.2
0.11
0.13
0.09

Fluoride added as HF was evaluated next. The results of thisexperiment are shown in Table 4. In this case, the load solution
was 0.01 M HNO3 and the rinse was 25 mL of 0.5 M HF/0.02
M HNO3. Varying spike levels of natural uranium were added.
At all of these levels the net counts in the technetium-99 region
were effectively zero. Subsequent evaluations of actual samples
and technetium-99 spikes indicated that the HF in the rinse
solution did not adversely affect technetium-99 recoveries.
TABLE 4: Counts in the Technetium-99 Region for Various
Spikes of Natural Uranium where the Load Solution was0.01 M HNO3 and the Rinse Solution was 25 mL 0.5 M HF/
0.02 M HNO3
Naturaluranium
spike/BqBlank
counts/cps

Mean counts
Tc-99
region/cps

σ/cps

3.6

0.26

0.250.004
n=3220.27

0.260.003
n=2440.26

0.220.005
n=44. Conclusion
The use of complexants is necessary to eliminate the thorium interference caused by samples containing natural uranium. Oxalic acid may be sufficient to solve the problem forcases where the amount of thorium-234 is not large relative tothe technetium-99 content. Further experimentation would be

J. Nucl. Radiochem. Sci., Vol. 6, No. 3, 2005 225

Recent Developments In The Analysis of Techetium-99

required to determine the limits of thorium-234 concentration
for which this solution would be acceptable. Addition of fluoride as hydrofluoric acid to complex the thorium seems to solve
this problem even at concentrations of natural uranium as highas 44 Bq. Though not shown here, use of sodium fluoride wasalso found acceptable and may be suitable in cases where thehazards of HF are to be avoided.

References(1) E. P. Horwitz, M. Dietz, R. Chiarizia, H. Diamond, S.
Maxwell, and M. Nelson, Analytica Chimica Acta 310, 63(1995).
(2) A. Banavali, Radioactivity & Radiochemistry 6, No. 3. 26(1995).
(3) J. Butterworth, F. Livens, and P. Makinson, Elsevier, The
Science of the Total Environment 173/174, 293 (1995).
(4) O. Egorov, et al. Analytical Chemistry 70 (5), 977 (1998).
(5) K. Tagami and S. Uchida, Journal of Radioanalytical andNuclear Chemistry 239, No. 3 643 (1999).