J Radioanal Nucl Chem (2010) 286:661–663 DOI 10.1007/s10967-010-0737-8
Preparation of
95m
Tc radiotracer
Marek Fikrle • Jan Kucˇera • Ferdinand Sˇebesta
Received: 19 July 2010 / Published online: 19 August 2010 Ó Akade´miai Kiado´, Budapest, Hungary 2010
Abstract Several procedures for preparation of the 95mTc radiotracer following irradiation of a thin Mo target with deuterons were tested. The procedures consisting of alkaline-oxidative fusion of the irradiated target in a mixture of Na2O2 ? NaOH and subsequent liquid–liquid extraction with 2-butanone, and acid decomposition of the target in a mixture of H2SO4 ? HNO3 followed by extraction chromatography with PAN-Aliquat 336 composite material appeared suitable for the given purpose. Keywords 95mTc preparation Alkaline-oxidative fusion Acid decomposition Extraction with 2-butanone Extraction chromatography, PAN-Aliquat 336
Introduction The radionuclide 95mTc is frequently used radiotracer for studies concerning determination and behaviour of 99Tc in the environment. The nuclide has a favourable half-life of 61 days compared with other short-lived Tc radioisotopes, such as 99mTc (T1/2 = 6.01 h). Three different nuclear reactions are used for the 95mTc production: (1) irradiation of 93Nb with alpha particles using the reaction
M. Fikrle (&) J. Kucˇera Nuclear Physics Institute ASCR, 25068 Rˇezˇ, Czech Republic e-mail:
[email protected] J. Kucˇera Research Centre Rˇezˇ Ltd., 25068 Rˇezˇ, Czech Republic F. Sˇebesta Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague, Brˇehova´ 7, 11519 Prague, Czech Republic
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Nb(a,2n)95m,gTc [1]; (2) irradiation of Mo with protons using the reactions 95Mo(p,n)95mTc, 96Mo(p,2n)95mTc, and 97 Mo(p,3n)95mTc [2–4]; (3) irradiation of Mo with deute94 rons employing the reactions Mo(d,n)95mTc, 95 95m 96 95m Mo(d,2n) Tc, and Mo(d,3n) Tc [5]. When the radionuclide 95mTc is produced with the above mentioned proton reaction on natural molybdenum the radionuclide 99 Tc is also produced. This may present a problem if 95mTc is used as a yield monitor, e.g., in ICP–MS determination of 99Tc [6]. In such cases 95mTc obtained with the 93 Nb(a,2n)95m,gTc is to be used. The excitation function of the 93Nb(a,2n)95m,gTc reaction is well known [1 and references therein]. On the contrary, excitation functions for the (p,xn) and (d,xn) reactions are not satisfactorily known, especially for reactions with deuterons. Therefore, we studied these excitation functions in more detail. The results obtained will be published separately [7, 8]. However, it can be briefly stated here that the reactions of natural molybdenum with protons and deuterons provide about the same yield of 95mTc when bombardment is carried out with particles with energy in the range of 10–20 MeV. In the present paper we report the procedures tested for separation of 95mTc from the irradiated Mo target. Concerning Tc separation from the irradiated Mo target several methods has been described in the literature based on both wet and dry chemistry (e.g. [9, 10]). Recently Bonardi et al. [2] developed a no carrier added separation of Tc from thick Mo target irradiated with protons. They dissolved Mo target in 7 M HNO3 and the precipitate of molybdic acid was filtered off. The residue of Mo (VI) in the filtrate containing Tc has been extracted with diethylhexylphosphoric acid (DEHPA) in mesitylene. After extraction the aqueous phase was washed with isopropylether to remove traces of DEHPA, evaporated to almost dry
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and residue dissolved in physiological saline. For the purification of Tc from Y the cationic exchange chromatography (Bio-Rad AG50Wx8) was used. Several different procedures approaches to separation of Tc from Mo target irradiated with deuterons are described in this paper.
procedure took about 30 min. Retention of 95mTc in the BaSO4 precipitate was measured with gamma spectrometry. Separation of 1.
Experimental Irradiation For the production of 95mTc, a stack of four 110 lm thick foils with a diameter of 20 mm made of natural Mo was bombarded in the external deuteron beam of the U-120 cyclotron of the Nuclear Physics Institute at Rˇezˇ [11]. Typical irradiation conditions were tirr = 120 min, I = 5.5 lA, and Emax = 17.6 MeV. Approximately one month after irradiation, when the formed short- and medium-lived Tc radioisotopes (93m,gTc, 94m,gTc, 96m,gTc, 99mTc, and 101 Tc) decayed, the separation of 95mTc was carried out. Mo target dissolution Three different target decomposition methods and two Tc separation procedures were tested. 1.
2.
3.
Alkaline-oxidative fusion: The irradiated Mo foils were fused with 3 g of Na2O2 and 1 g of NaOH at 850 °C in a glassy carbon crucible. The fusion cake was dissolved in approximately 20–25 mL of water. The whole procedure takes about 5 min, however it has to be repeated twice or three times to achieve complete dissolution of one Mo foil with the mass of *400 mg. Dissolution in a mixture of HNO3 and H2O2: The target was dissolved in a mixture of 10 mL of hot concentrated HNO3 and 1 mL of 30% H2O2. During the dissolution an orange-yellowish precipitate appeared (probably molybdic or peroxo-molybdic acid). The precipitate was separated by centrifugation. Retention of 95mTc in the precipitate was measured with gamma spectrometry. The dissolution procedure takes about 20 min. Dissolution in a mixture of H2SO4 and HNO3: The molybdenum foil was dissolved in a mixture of concentrated H2SO4 (2.4 mL) and HNO3 (100 lL) using microwave assisted pressurized digestion. To remove sulphate ions, which would interfere in the subsequent separation, an excess of concentrated solution of barium chloride (35.8 g/100 mL) was added to the solution. The precipitate of barium sulphate was separated by centrifugation (4,000 rpm for 10 min) and filtration using membrane filters (Pragopore, Czech Republic, pore size 0.85 lm). This
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95m
Tc
Liquid–liquid extraction: After alkaline-oxidative fusion of the Mo target, extraction of 95mTc with 2-butanone (methyl ethyl ketone, MEK) is the most simple separation of Tc. The solution resulting from dissolution of the fusion cake is diluted to make 5 M NaOH and extraction is carried out twice with 5 mL of MEK for 1 min. The extraction yield is almost quantitative ([99%), similarly as for extraction of Re [12]. To transfer the extracted Tc to the water phase, the organic phase with Tc was evaporated with a few drops of NH4OH and H2O2 (to keep Tc in the heptavalent state) to dryness and the residue was dissolved in 2 M HNO3. Extraction chromatography: Separation of Tc with extraction chromatography is convenient after acid dissolution of the irradiated Mo target. After dissolution in the HNO3 ? H2O2 mixture, the solution was evaporated to dryness, the residue was dissolved in 0.1 M HCl and Tc was separated by extraction chromatography using a selective chromatographic resin PAN-Aliquat 336 prepared by impregnation of polyacrylonitrile (PAN) beads with AliquatÒ 336 extraction agent. This material has similar properties for separation of Tc [13], and also for Re, as TevaÒ Resin [14]. A 1.2 mL Supelco (Empty ResorianTM tube—1 mL) column was filled with 0.65 g of dry PAN-Aliquat 336 chromatographic material, which was preconditioned by rinsing with 20 mL of 0.1 M HCl. The 0.1 M HCl solution obtained after decomposition of the Mo target was passed through the column with the aid of a peristaltic pump at a flow rate of 0.3 mL per min. The retained Tc was eluted with 5 mL of 8 M HNO3 at the flow rate of 0.05 mL/min.
Results and discussion The procedure of 95mTc separation consisting of alkalineoxidative fusion of the irradiated Mo target and Tc separation with MEK extraction gave satisfactory results. The total separation yield of this procedure was in the range of 68–85%. Although the extraction yield is almost quantitative, volatilization losses of Tc occur on evaporation of the organic fraction with NH4OH and H2O2 to dryness, which is a necessary step to get rid of MEK and to convert the separated Tc from the organic to the water phase.
Preparation of
95m
Tc radiotracer
663
this work are by a few percent lower than those achieved by Bonardi et al. [2], who developed a complex procedure to prepare 95mTc free of radionuclidic impurities for biological applications.
20
Eluate/feed activity ratio [%]
18 16 14 12
Acknowledgments This work was supported by grant 203/08/1276 provided by the Czech Science Foundation and project MSM 2672244501.
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References
4 2 0 0
0.5
1
1.5
2
2.5
3
Elution volume [BV]
Fig. 1 Elution of Tc from PAN-Aliquat 336 with 8 M HNO3 (1.2 mL chromatographic column, flow rate 0.05 mL/min)
The combination of acid decomposition of the irradiated Mo target in the HNO3 and H2O2 mixture with subsequent Tc separation using extraction chromatography with the PAN-Aliquat 336 material appeared unsuitable. The reason was that traces of H2O2 remaining after acid decomposition partially destroy the column bed and deteriorate chromatographic properties of the PAN-Aliquat 336. Pressurized microwave assisted decomposition of the Mo target in the mixture of H2SO4 and HNO3 is quick and provides quantitative recovery of Tc. However, the need to remove SO42- anions by precipitation of BaSO4 prior to extraction chromatography with PAN-Aliquat 336 prolongs this procedure of Tc separation up to 70 min. Moreover, the BaSO4 retains some 95mTc, thus decreasing the overall yield of this separation procedure to 75–85%. The advantage is that the elution peak is sharp (Cf. Fig. 1), so that 95mTc can be eluted into a small volume of 8 M HNO3. Typical specific activity of 95mTc obtained in the described experimental conditions was 200 kBq mL-1.
Conclusions Of the Mo target dissolution and Tc separation procedures, the combination of alkaline-oxidative fusion of the target followed with MEK extraction of Tc and acid decomposition of the target in the mixture of H2SO4 and HNO3 with subsequent Tc separation with PAN-Aliquat 336 extraction chromatography material appeared well applicable for the preparation of 95mTc radiotracer in quality suitable for development of analytical procedures for determination of 99 Tc in environmental samples. The latter method provided somewhat higher overall separation yields compared with the former method. The best separation yields obtained in
1. Ta´rka´nyi F, Ditro´i F, Szelecse´nyi F, Sonck M, Hermanne A (2002) Measurement and evaluation of the excitation functions for alpha particle induced nuclear reactions on niobium. Nucl Instr Meth Phys Res B 198:11–31 2. Bonardi M, Birattari C, Groppi F, Sabbioni E (2002) Thin-target excitation functions, cross-sections and optimized thick-target yield for natMo(p,xn)94g,95m,95g,96(m?g)Tc nuclear reactions induced by protons from treshold up to 44 MeV. No carrier added radiochemical separation and quality control. Appl Radiat Isot 57:617–635 3. Uddin MS, Hagiwara M, Tarkanyi F, Ditroi F, Baba M (2004) Experimental studies on the proton-induced activation reactions of molybdenum in the energy range 22–67 MeV. Appl Radiat Isot 60:911–920 4. Khandaker MU, Uddin MS, Kim KS, Lee YS, Kim GN (2007) Measurement of cross-section for the (p, xn) reactions in natutal molybdenum. Nucl Instr Meth Phys Res B 262:171–181 5. Rˇanda Z, Svoboda K (1977) Excitation functions and yields of the (d, p) reactions on natural molybdenum for deuteron energies less than 13 MeV. J Inorg Nucl Chem 39:2121–2123 6. Tagami K (2003) Technetium-99 behaviour in the terrestrial environment–field observations and radiotracer experiments. J Nucl Radiochem Sci 4:A1–A87 7. Lebeda O, Pruszynski M (2010) New measurement of excitation functions for (p,x) reactions on natMo with special regard to the formation of 95mTc, 96m?gTc, 99mTc and 99Mo. Appl Radiat Isot. doi:10.1016/j.apradiso.2010.05.011 8. Lebeda O, Fikrle M (2010) New measurement of excitation functions for (d,x) reactions on natMo with special regard to the formation of 95mTc, 96m?gTc, 99mTc and 99Mo. Appl Radiat Isot. doi:10.1016/j.apradiso.2010.07.007 9. Anders E (1960) The radiochemistry of technetium. National Academy of Sciences—National Research Council 3021, Washington, DC 10. Schwochau K (2000) Technetium—chemistry and radiopharmaceutical applications. Willey-VCH, Weinheim 11. Parameters of NPI cyclotron U120M listed under code c6 at http://accelconf.web.cern.ch/AccelConf/c07/OTHERS/Cyclotron %20List%202007%20-Full.pdf 12. Mizera J, Kucˇera J, Rˇanda Z, Lucˇanı´kova´ M (2006) Advanced liquid and solid extraction procedures for ultratrace determination of rhenium by radiochemical neutron activation analysis. Czech J Phys 56:D1–D7 13. Andris B (2006) Determination of 99Tc in radioactive wastes. Diploma thesis, Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering, 57 pp (in Slovak) 14. Lucˇanı´kova´ M, Kucˇera J, Sˇebesta F (2008) New extraction chromatographic material for rhenium separation. J Radioanal Nucl Chem 277:479–485
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