DEVELOPMENT AND APPLICATION OF ANALYTICALMETHOD· FOR THE DETERMINATION OF

LOW-LEVEL 99Tc BY HIGH RESOLUTION ICP-MS

Syarbaini*

Abstract

DEVELOPMENT AND APPLICATION OF ANALYTICAL METHOD FOR THE, DETERMINATION OF LOW-LEVEL 99Tc BY HIGH RESOLUTION ICP-MS.

An analytical method has been investigated for determining low level 99Tc in environmentalsamples by High Resolution Inductively Coupled Plasma Mass Spectrometry (HR-ICP-MS).This analytical method consists of leaching of 99Tc from soil and/or sediment samples byHN03, separation and purification by three stages of solvent extractions with 30 % TOA(trioctylamine)-xylene, MEK (methyl ethyl ketone) and followed by cycIohexanone. Finally,purified 99Tc was passed through an annion exchange column to reduce the content ofdissolved solids. The solution was adjusted to 1M HN03 for introducing into theHR-ICP-MS. This method has been applied to sediment samples from the Esk Estuary, IrishSea. Information on sedimentary behaviour ofTc was obtained by comparing inventories with

total discharges. The potential affinity to sediment decreased in the order ofPu ~ Am>Np>Cs> Tc, suggesting that Tc is more soluble and mobile than other nuclides inthe sediment.

INTRODUCTION

The determination of 99Tc (T1/2 = 2.14 X 105 y) in environmentalsamples posseses sever:al problems, because 99Tc is a weak 13emitter with Ea

99max = 292 keY. For the measurement of low-level Tc, 13-rayspectrometryusing low-background gas flow proportional counter has been widely used[1], but requires a careful chemical separation from any other 13-emitter and a

rather long counting til!le. Beside this method, a liquid scintillation countingmethod has been studied by several authors. The method, however, alsopossesses demerits to those in the low-background gas flow proportionalcounter.

Recently, inductively coupled plasma mass spectrometry (ICP-MS) hasbeen developed very rapidly in the field of analytical chemistry. It provides avery low detection limit, relatively simple spectra and has the capability ofisotopic analysis. The conventional version ICP-MS using a quadrupole

mass analyser was capable of measuring several long-lived radionuclides2~7 239240 238 232 .such as Np, , Pu, U and Th at the plcogramme level [2,3].This technique although succesful, needs a higher sensitivity and lowerdetection limit. For this purpose, High Resolution Inductively Coupled

• Center of Radwaste Management Technology - BAT AN

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Plasma Mass Spectrometry (HR-ICP-MS) equipped with a double-focusingmass spectrometer is suitable for higher mass resolution and sensitivity [4].

In the present work, the analytical method for the determination oflow-level 99Tc by HR-ICP-MS has been developed with emphasis on theelimination of isobaric interferences at mass number 99 (99Ru). This methodhas been applied to sediment core from the Esk Estuary, South East ofSellafield Reprocessing Plant UK. The sedimentary behaviour of 99Tccompared with transuranium elements and 137Cs in the water to sediment

transfer system was als~ investigated.

EXPERIMENTAL

Chemical reagents and materials

All reagents used were of analytical grade except for TOA(tri-n-octylamine), Xylene, MEK (methyl ethyl ketone) and cyclohexanonewhich were purchased from Wako Pure Chemical Industries Ltd., Japan.The nitric and hydrochloric acids used for preparing anion exchange resin,standard solutions, and final solutions to be introduced into HR-ICP-MSwere of super analytical reagent grade (Tama Pure AA-l 00, Tama ChemicalLtd., Japan).

In order to develop the analytical method and to determine the chemicalyield of the radiochemical procedures, the following Tc standard solutionswere used in the experiment. Technetium-99 as pertechnetate was obtainedfrom Amersham International pIc., and used as a standard solution for

makin~ calibration curve for HR-ICP-MS. Technetium-99m milked from99Mo_ mTc generator (Daiichi Radioisotope Laboratories Ltd., Japan) wasalso used in some stages for the optimisation of chemical yield. Furthermore,95mTcas pertechnetate supplied by Du Pont NEN Products (USA) was usedfor determining overall chemical yield of 99Tc. Atomic absorption gradesolution of J03Rh (Wako Pure Chemical Industries Ltd., Japan) was used asan internal standard to check any drift in the response of the instrument.Atomic absorption grade Ru solution was used for its decontamination.Atomic absorption grade Mo, Rb and Sr solutions were used to check anisobaric overlap and is.obaric polyatomic ion interferences. All the standardsolutions were prepared by successive dilution of the stock solution with1M HN03. De-ionized water (Milli-Q, Japan Millipore, Kita-Shinagawa,Tokyo Japan) was used to prepare these solutions.

Analytical procedure

The analytical method presently developed is schematically shown inFigure 1. The procedure consists of 3 steps : (1) leaching of Tc from the

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sample, (2) separation of99Tc by solvent extractions with 30 % TOA-xylene,MEK and cyclohexanone and (3) purification of 99Tc through anionexchange resin column.

A small amount of 95mTc was added to the sample as a yield tracer.Technetium-99 in the sample was leached twice with concentrated HN03,

with the addition of small amounts of 30% H202. The leachate obtained byfiltration was gently evaporated to dryness and then dissolved with 30 ml of2M HN03• The Tc in the solution was firstly extracted 3 times with 20 ml of30% TOA-xylene. After washing the organic phase with 20 ml 2M HN03,Tc was back of-extracted 3 times with 20 ml of 5M NaOH. The Tc in this

aqueous phase was then extracted 3 times with 20 ml MEK. After washingwith 20 ml of 5M NaOH, 30 ml benzene was added to the MEK phase andthen Tc was back-extracted 3 times with 20 ml deionized water.

An aliquot of 5M K2C03 solution was added to the resultant solution foradjusting to 1M K2C03 solution. This solution was then shaken for 30 minafter adding 2 ml of H202 to change Ru to inextractable valence state. andthen io ml cyclohexanone was added. The resultant mixture was shaken toextract Tc into the organic phase. This extraction was repeated further twotimes. After washing the organic phase with two times 20· ml of 1M K2C03

solution, 30 ml benze!1e was added. Tc was back-extracted 3 times with15 ml of deionized water. Each step of the above solvent extraction wascarried out by shaking mechanically for 10 min. The Tc fraction was thenconcentrated to 10 ml. After adjusting the pH to about 2 with 1 M HN03, thesolution was passed through a column (3 cm in length and 0.6 cm indiameter) of the nitrate form of Dowex I-X 8 anion exchange resin(100 - 200 mesh).

The column was washed successively with 20 ml of 0.5M HCI, 10 mlcold and then hot deionized water and 10 ml of 1M HN03 to remove mainlyMo and salts from the resin. Finally, Tc was eluted from the column with8 ml of 10M HN03• The purified Tc solution was gently evaporated todryness and dissolved with 20 ml of 1M HN03 for introducing into theHR- ICP-MS. Rhodium standard solution was added in this final solution

(usually 75 pg.mr1) as an internal standard to check the drift of theHR-ICP-MS. The chemical yield was determined by gamma-countingOf95mTc in the solution using Ge(Li) detector.

Measurement by HR-ICP-MS

The measurement of 99Tc were carried out by using a high massresolution double-focusing type of ICP-MS supplied by VG Elemental,Windsford Chesire, England. Final solution has to be in a suitable form :<1M HN03 and salt concentration of less than 100 pg.mrl• Details of the

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systems are described elsewhere [5]. The operating conditions of theHR-ICP-MS instrument are given in Table I.

Sampling of Sediment Core

Sediment core samples were collected at sampling site shown inFigure 3. The sediment of21 cm in depth, 3.7 cm in diameter was carefullycollected, and cut at 1 cm intervals. Aliqouts of sample, 0.5 - 2 g of dryweight were subjected to analysis of Technetium.

RESULTS AND DISCUSSION

Separation of Technetium from interferring elements

For measurement of 99Tc based on the mass, isobaric interferences atb 99 99 99mass num er 99 ( Ru and Mo) are a key problem. Although Mo

(TI/2 = 66.02 h) decays out completely after a few weeks, Mo must still beconsidered in the case of a probable down and up-mass tailing effect by

bl' 98 100sta e Isotopes Mo (natural abundance. 24.4 %) and Mo(natural abundance 9.6 %). Many papers [6-9] have reviewed the methodsavailable for the decontamination from interfering elements, in particularRu : evaporation, precipitation, solvent extraction, NaOH elution from anionexchange resin colum!l etc. In the method presently developed, solventextraction and anion exchange techniqnes were chosen. It was found that thecombination of these .techniques have a high recovery of Tc and gooddecontamination ofRu and Mo.

Technetium leached from the sample was firstly extracted with 30%TOA-xylene from 2M HN03 solution as described previously by Hirano etal.[10]. Preliminary experiments performed by addition of 95mTc and/or99mTc tracers to 2 g of soil showed a sufficient recovery of Tc more than95%. The next separation step is the extraction of Tc from 5 M NaOH withMEK as reported by Riley et al.[6], in which Tc extracted in MEK phase isstripped into water by evaporating MEK phase. In the method presentlydeveloped, back-extraction of Tc from MEK was succesfully performed byusing benzene as a diluent. Until this second solvent extraction stage,decontamination factor (DF) for Ru was calculated to be about 103.

Further decontamination of Ru is still required to determine low level 99Tc insoil sample by HR-ICP-MS because Ru has stable isotope with massnumber 99 (atomic abundance, 12.7 %) and its natural abundance is about0.01 ppm in natural soil material. As far as 106_107ofDF for Ru is expectedto measure pg level of99Tc in soil sample with HR-ICP-MS.

For this purpose, the third solvent extraction stage by usingcyclohexanone was applied in this method. Solvent extraction using

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cyclohexanone is known to allow excellent separation of Tc from Ru [7].Technetium as pertechnetate was efficiently extracted from basic carbonate

solution with cyclohexa!10ne. Ru was oxidized by H202 to an inextractablevalence state and remain in the aqueous phase during the extraction. Tc wasstripped from cyclohexanone into water by adding benzene as diluent.Then Tc was adsorped on anion exchange resin column. Mo was removed bywashing resin column with 0.5 M HCI. Washing with cold and then hotdistilled water was also provided sufficient reduction of total dissolvedsolids content for the' subsequent HR-ICP-MS. Finally, decontaminationfactor of Ru for overall procedure higher than 106 was achieved.

Example of a mass spectrum of Tc separated from about 50 g of soilsample spiked with known amounts of 99Tc is shown in Figure 4. Rutheniumcan be eliminated completely by this method. When Ru is still detected in

the purified solution, ~eak overlap from 99Ru can be corrected on the basis of99Ru/IOJRu or 99Ru/1 2Ru count ratio. Peaks of 98Mo and looMo are still

detected. Mo can not be eliminated completely by this method, but there isno contribution to mass number 99 at this level concentration due to lower

and higher mass tailing from 98Mo and looMo.

Accuracy and Precision

The accuracy and precision of the method developed here wereexamined by applying it to the determination of 99Tc in' IAEA standardreference material AG-B-I prepared from marine algae, because of the non­

availability of intercomparison sample for soil. The results of the ana~sisusing about 5 g dry material are ~resented in Table 2. The recovery of , Tcranged from 84% to 92%. The 9 Tc contents in this material was found toagree well with the reported values within the errors. Relative standard

deviation of replicate determinati~n was about 3%.

Measurement of 99Tc concentration in the sediment core from the Esk

Estuary of Irish Sea, UK

The analytical method developed has been applied to determine 99Tc in0.5-2.0 g of sediment sample from the Esk Estuary ofIrish Sea. The range ofchemical yield ranged from 72 to 95 % with an average of 84 %.The chemical yields obtained are shown in Table 3. This procedure has

sufficiently high chemical ~ield to be applied to environmental samples.The concentration of Tc in this sediment core was found to be ranging

widely from 19 to 160 Bqlkg as shown in Table 3. Comparison of depthprofiles of Tc with transuranium elements and Cs determined previously inthis sediment core are shown in Figure 5. The technetium pattern is rathersimilar to Pu, Cs and Am except in deep layer. The inventories of Tc andothers elements in sediment core are given in Table 4. Technetium inventory

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of 25 kBq/m2 is two orders of magnitude lower than Cs, Pu and Am but isone order higher than Np. Measured inventories of 99Tc, transuraniumelements and 137Cs are interpreted by comparison with the dischargehistories from the Sellafield reprocessing plant. As shown in Table 4,information on sedimentary behaviour of these radionuclides can be obtainedby comparing total inventories with total discharges from the Sellafieldnuclear fuel reprocessing plant. The potential affinity of these radionuclidesto the sediment decreases in the order of Pu ~ Am>Np>Cs>Tc, suggestingthat Tc is more soluble and mobile than others nuclides in the sediment.

CONCLUSION

A new analytical method has been developed for the determination of99Tc with emphasis on the elimination of Ru from sample matr~x by 3 stagesof solvent extractions and followed by anion exchange technique.

The accuracy and precision were studied by applying this method to thedetermination of 99Tc in IAEA marine algae sample (AG-B-l). The 99Tc

content was found t<;>agree well with' the reported value within theexperimental error. This method has been found to has sufficiently highchemical yield to be applied to environmental samples.

The analytical method developed in the present work has succesfullybeen applied to determine 99Tc in the sediment core collected from EskEstuary, Irish Sea U.K. Depth profile of 99Tc in the sediment core was rathersimilar to Pu, Cs anQ Am. The affinity to the sediment decreases in the orderofPu ~ Am>Np>Cs>Tc, suggesting that Tc is more soluble and mobile thanother radionuclides in the sediment.

ACKNOWLEDGEMENTS

The author was grateful to Dr. M. Yamamoto, Dr. K. Komura andProf. K. Ueno from Kanazawa University, Japan for their guidance and help,which made this work possible. He is also grateful to the Asahi GlassCompany, Japan and National Atomic Energy Agency, Indonesia for ascholarship and study leave respectively.

REFERENCES

l. J. L. RIOSECO, "Technetium-99-Radioanalytical and RadiologicalStudies", Thesis, Lund University, Sweden, (1987)

2. C. K. KIM, Y. TAKAKU, M. YAMAMOTO, H. KAWAMURA,K. SmRAISm, Y. IGARASm, S. IGARASm , H. TAKAMAYA,N. IKEDA, " Determination of 237Np in Environmental Samples Using

26

Inductively Coupled Plasma Mass Spectrometry", J. Radioanal. Nucl.Chern., 132 (1989) 131

3. Y. IGARASHI, C. K. KIM, Y. TAKAKU, K. SHIRAISm,M. YAMAMOTO, N. IKEDA, "Application of ICP-MS to theMeasurement of Long-lived Radionuclides in Environmental Samples",Anal. Sci., 6 (1990) 157

4. C. K. KIM, R. SEKI, S. MORITA, Y. YAMASAKI, A TSUMURA,Y. TAKAKU, Y. IGARASHI, M. YAMAMOTO, "Application ofHR­ICP-MS to the Measurement of Long-lived Radionuclides", J. Anal.Atomic Spectrometry, 6 (1991) 205

5. A Tsumura, S. Yamasaki, in : Application of Plasma Source MassSpectrometry, eds. G. Holland, AN. Eaton The Royal Society ofChemistry, UK (1991) 119

6. J. P. RILEY, S. A SIDDIQUI, "The Determination of 99Tc in Seawaterand Marine Algae", Anal. Chim. Acta, 139 (1982) 167

7. L. C. BATE, in: Radioelement Analysis - Progress and Problems,eds.W.S. LYON, Ann Arbor Science Publishers Inc, Ann Arbor,

Michigan (1980) 175

8. IHSANULLAH, "Losses of Technetium During Various Steps in theDevelopment of a Procedure for Environmental Samples", J. Radioanal.Nucl. Chern. Letters, 176 (1993) 303

9. E. HOLM, J.' RIOSECO, S. BALLESTRA, A. WALTON,."Radiochemical Measurements of 99Tc : Sources and Environmental

levels", J. Radioanal. Nucl. ,Chern. Article, 123 (1988) 167

10. S. HIRANO, M. MATSUBA, H. KAMADA, "The Determination of99Tc in Marine Algae", Radioisotopes, 38 (1989) 186

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Table 1. HR-ICP-MS operating condition

ICP-condition

Rf powerPlasma gas flowAuxilary gas flowNebulizer gas flowSolution uptake rate

Mass spectrometer settingSampler orifice diameterskimmer orifice diameter

Interface running pressureMass spectrometer running pressureData acquisition mass rangeNumber of channelsDwell time

Channels for one peak searchNumbers of scans

1.2 kw14 Vmin0.7 Vmin1.1 Vmin0.5 mVmin

Imm0.5mm1.0 x 10-4mbar3.0 x 10-7 mbar98 - 104480

80 ms802

Table 2. Results of intercomparison for 99Tc measurement in IAEA marinealgae sample (AG-B-l t

Run Weight (g)99

Yield ( % )Tc found (mBq/g dry)

1

4.914 12.2 ± 0.6b91.5 ± 1.02

5.025 11.7±0.787.3 ± 1.03

5.064 11.5 ± 0.683.8 ± 0.9

Average

11.8 ± OAc

a : Reported value: confidence interval (a = 0.05 ) 11.1 - 14.7 mBq/gdry, median 1(5 mBq/g dry.

b : One sigma standard deviation of 4 times measurements.c : One sigma stan'dard deviation

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Table 3. Concentrations of99Tc in sediment Core

Sample No Depth( cm)Concentration (Bq/kg-dry)Recovery (%)1.

0- 1 24.2 ± 1.386.1 ± 2.1

2.

1 - 2 29.7 ± 1.486.9 ± 0.9

3.

2-3 33.9 ± 2.087.4 ± 2.4

4.

3-4 33.6 ± 2.0.83.6 ± 0.9

5.

4-5 33.7 ± 1.790.1 ± 2.4

6.

5-6 50.0 ± 3.085.3 ± 0.9

7.

6-7 59.3 ± 3.577.0 ± 0.9

8.

7-8 78.6 ± 4.694.6 ± 1.2

9.

8-9 86.2 ± 4.586.4 ± 0.9

10.9 - 1.0 109.0 ± 6.087.6 ± 0.9

11.

10-11 87.0 ± 5.080.8 ± 0.9

12.

11-12 95.8 ± 5.191.3 ± 1.0

13.

12 - 13 110.0 ± 6.185.5 ± 0.9

14.

13 - 14 160.0 ± 8.373.6± 1.1

15.

14 - 15 112.4 ± 6.380.7 ± 0.9

16.

15 - 16 36.7 :f: 2.292.3 ± 1.0

17.

16-17 19.2 ± 1.075.1 ±2.2

18.

17 - 18 22.7±1.375.4 ± 0.9

19.

18-19 19.3 ± 1.488.6 ± 2.2

20.

19 - 20 24.3 ± 1.471.7 ± 0.8

21.

20 - 21 31.7±2.083.1 ±2.1

Table 4. Correlation of the inventories of 99Tc, 137Cs and transuranium

elements with total 'discharges from Sellafield nuclear fuelreprocessing plant.

99Tc137Cs237NpPu-a.241Am

Total discharge(TBq).

7.7x1023.0xl046.47.3x1028.6xl02

2

2.5xl02.9x1032.22.4x1032.6x103

Inventory (kBq/m ) Inventories/0.030.100.353.253.05

Total discharge

Pu-a. = Pu-238, 239, 240

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Sample

L Tc-95m spike

Leaching (cone. HNO) and H202)

LEvaporate to dryness and

dissolve in 2M HNO)!30 % TOA-xylene extraction!

5M NaOH back extraction!MEK extraction

( to remove Ru and Mo )!Back extraction into H20

( benzene as diluent)!Adjust soln. to 1M K2CO)

and shake for 30 min. with HP2!Cyclohexanone extraction

(to remove Ru)

Back extraction into H20( benzene as diluent)!

Evaporate to 10 mland adjust pH to 2!

Anion exchange coloumn( IMHNO), Dowex I-X8)

-+ Feed solution

-+ 0,5M HCI (Mo off)-+ Cold & Hot water ( salts off)-+ 1M HNO)-+ 10M HNO) ( Tc elution)

!Evaporate to dryness and dissolve

in 1M HNO) ( 20 ml )!Rh (internal stand.) spikeTc-95m measurement

( gamma spectrometry )!Tc-99 measurement

(HR-ICP-MS)

Figure 1. Analytical flowsheet for the detennination of low level 99Tc Inenvironmental samples

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Electricsector

Sourceslit

ICPtorch box

Spectrometerelectronics

Sourceelectronics

Expansionchamber

R.I. generator

Gas control

Collector slit

Collector

Collectorelectronics

Computer

Figure 2. A schematic diagram of High Resolution ICP-MS

••••••••••••••....... ,...~....~ ..'Esk Estu~ " •':====~::I ••

•,.... ....~ ....••••••••••••••••••

............ ~...•••••••••••••• ••••••••••••• •••• • • • • 'l=:skEstuary • • • •••••• If-" ••••.................••••••••••••••••••••••••••••••••••

Figure 3. Location of sampling site

) Ian

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800

600-~..c::

CJ-.. 400

§ 0CJC0..... 200

o97 98 99 100 101 102

mass number (Mle)

103 104

Figure 4. Example of mass spectrum of Tc separated from about 50 g soilsample spiked with 99Tc.

10'

---<:>- Pu-241

-- Cs-137

-0- Am-24 I--6- Pu·239.240

__ Pu-238

--+-- Tc·99

-0- Np-237

5 10 15 20 25

Depth (cm)

Figure 5. Concentration - depth profiles of 99Tc, 137Cs and transuraniumelements in sediment core.

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