Journal of Radioanalytical and Nuclear Chemistry, Vol. 240, No. 3 (1999) 883-885

Ascorbic acid as an eluent for 99mTc in 991VIo 99mTc generator system -

-

N. R. Das Nuclear Chemistry Division, Saha Institute of Nuclear Physics, 1/AF, Bidhannagar, Calcutta-700 064, India (Received August 14, 1998)

A simple chromatographic procedure for clean separation of the important radionuclide, 99mTc, in the equilibrium mixture, 99Mo--99mWc,has been demonstrated. Separation of pure 99mTc has been achieved by preferential extraction of the radioisotope through an anion exchange resin column of Amberlite IRA-410 using Na-ascorbate solution at pH 7 as an el uent. The radiochemical purity of the separated radiotracer has been verified by taking recourse to T-ray spectrometry. The potentiality of the developed procedure lies in the facts that the eluting agent, ascorbic acid, itself has got its own biomedical importance as Vitamin C and the concerned radioisotope can be obtained in both Tc(IV) and Tc(VII) states as per requirement for diagnostic purposes.

Introduction

The radioisotope, 99mTc, because of its characteristic nuclear properties, has now become a radionuclide of choice as radiodiagnostic agent in nuclear medicine. The single photon (140.5 keV) emitting property and the favorable half life (6.0 h) of the radionuclide have enhanced its suitability in biological investigations. ! Moreover, the absence of any beta-radiation makes feasible the administration of high doses of radioactivity yielding better counting rates and improved resolution. 99mTc is produced as a daughter product of 99Mo following the decay scheme: 99Mo f l - " Y 99mTc ~" 99Tc

2.7d

6h

fl-

99Ru(stable)

Experimental

Reagen~ Chemical reagents used were all of analytical grade. Amberlite IRA-410 (Standard Grade) was used as the anion exchanger. The radioactive isotope, 99Mo, in equilibrium with 99mTc as fission product in alkaline medium was supplied by BARC, Trombay, India.

2.1.105y

and the parent, 99Mo is produced either as a fission product of neutron irradiated uranium or by thermal neutron activation of molybdenum.2 The specific radionuclide finds its important applications in various diagnostic purposes either as 99mTc or as 99mTc levelled radiopharmaceuticals2,3 in its different valency states. 99mTc, in its higher valency state, [Tc(VII)], is used effectively in scanning of brain, cardiac, liver, bone marrow, etc. Similarly, it has got potential uses in serum albumin, pulmonary and renal scintillography, blood flow studies etc., in its lower valency state after its incorporation in appropriate organic or inorganic compounds.4-6 99Mo-99mTc generator systems have been extensively studied over the last few years and most of the chemical techniques 7-11 such as solvent extraction, chromatography, sublimation, coprecipitation, etc., generally applied to the separation of the daughter, 99mTc, from the parent, 99Mo, are mainly concerned with the higher valency state of the radioisotope. Studies on the separation of 99mTc in its lower valency state is very lacking although it has got some vital applications as such.

0236-5 731/99/USD 17. O0 9 1999 Akad~miai Kiad6, Budapest All rights reserved

With these fact in view, an attempt has been made to develop a 99Mo-99mTc generator system based on ion exchange chromatography in which ascorbic acid, a compound of biomedical importance, has been utilized as a reducing eluent for the daughter, 99mTc.

Procedure Solutions of sodium ascorbate in different concentrations at pH 7 were prepared by gradual addition of requisite amounts of dilute sodium hydroxide to freshly prepared ascorbic acid solutions. The resin column (100 minx5 ram) of Amberlite IRA-410 was first conditioned to POa4--form by passing 1N Na2HPO 4 solution through the column and by washing with water. About 1 ml solution of highly radioactive equilibrium mixture of 99Mo-99mTc was allowed to absorb completely on the top of the column bed and thoroughly washed with water. Separation of the 99mTc from 99Mo was affected by percolating freshly prepared Naascorbate solution of desired concentrations. Drops of effluents at a constant flow rate were collected successively at definite intervals during the course of elution and the activity present in each fraction was measured and characterised by gamma-ray spectrometric studies. After complete elution of the daughter, 99mTc, the parent 99Mo, was left in the column for growth of further amount of the daughter which can be milked out several times a day, as per requirement.

Elsevier Science B. ~, Amsterdam Akad~miai Kiad6, Budapest

N, R. DAS: ASCORBICACIDAS AN ELUENTFOR 99mTc IN 99M0 - 99rnTc GENERATORSYSTEM

Studies on the presence of radioactivities in different fractions of the efficient were performed with a HPGe detector of 30 cm 3 active volume connected to a ND 65 multichannel analyzer. Results and discussion In nuclear medicine or in diagnostic purposes the purity of the concerned radionuclide as well as the medium in which the radiotracer is to be taken up for biological uses are of vital importance. In this respect, the ion exchange procedure developed is found to be very effective for a parent-daughter separation in the radionuclidic generator system 99Mo-99mTc. In the generator, the daughter, 99mTc, can easily be eleuted or milked out in very pure form at appropriate intervals simply by percolating a desired Na-salt solution of ascorbic acid which itself is employed as a drug in biological system. In the chromatographic process, initialy, both 99Mo and 99mTc become completely absorbed on a column of Amberlite IRA-410 resin in PO 4 form, and elution separation of the latter from the former was affected by using Na-ascodiate solution as an eluent. The elution profiles for 99mTc, as shown in Fig. 1, indicate that the concerned radionuclide can be eluted out with the eluent over a wide range of its concentrations (2-5%) at pH 7 without any contamination from the parent 99Mo. However, in elution of the daughter with lower

concentration of ascorbic acid, greater volume of the eluant will be required. Further, the developed procedure has the added advantage in that the Tc(IV) can be transformed into its higher valency state, i.e., Tc(VII), if required, simply- by decomposing Tc-ascorbate complex with glacial acetic acid and then to convert it in its desired form. In the process of elution Tc(VII) is reduced to its lower vallency state, Tc(IV), by the eluent itself and keeps the amount of pertechnate, Tc(VIII), at a minimum level by stabilising Tc(IV) in the ascorbate medium.12 The purity of the separated 99mTc has been verified by taking recourse to gamma-ray spectrometry. Since, the strongest gamma-energies for 99Mo and 99mTc are almost identical (140.5keV), the absence of any photopeak corresponding to gamma-energy of 739.5 keV and 777.9 due to 99Mo as well as the decay study of the separated radiotracer in the eluent confirmed that the 99mTc was completely free form 99Mo (Fig. 2). The parent isotope, 99Mo, after the removal of 99mTc, can be either eluted out with dilute HC1 or HNO 3 or can be retained as such in the column for milking of further amount of 99mTc utilising the system 99Mo-99mTc, as a radionuclides generator. The semplicity of the chromatographic separation procedure using ascorbic acid as an eluent for obtaining 99mTc of high radiochemical purity makes the method potentially useful for setting-up of the generator system, 99Mo-99rnTc, yielding the daughter in high quality.

1

A

2

< 3

I

0

w

w

20

I

I

~0

60

I

80

I

100

Volume, ml

Fig. 1. Elution curves of99mTc eluted by Na-ascorbate solutions o f ( l ) 5%, (2) 4%, (3) 2% and (4) 1% concentration at pH 7

884

N. R. DAS: ASCORB1CACIDAS AN ELUENTFOR 99mTc IN 99M0 - 99mTc GENERATORSYSTEM

99 Mo, 99m Tc(140.5)

99Mo(181.0)

/ 99 ttt~

Mo(739,51 99Mo(777.9)

99Mo(366.4)

t.-, t--

o 0

~ 12o

gmTc (140,5)

~Zo

i~o ~so

~so'7~o

'

/60

'

~6o

Energy, keV

Fig. 2. Gamma-spectra of (a) an equilibrium mixture of 99Mo--99mTc and (b) after separation of 99mTc by 1% Na-ascorbate solution at pH 7

References l. F. ROSCH, A. F. NOVGOROI3OV, S. M QU1M, Radiochim. Actao 64 (1993) 113. 2. K. H. LIESER, Radiochim. Acta, 63 (1993) 5. 3. H. N. WAGNER Jr.(Ed.), Principles o f Nuclear Medicine, W. B. Sanders Company, London, 1968. 4. S. A. C. MESTN1K, C. P. G. DA SILVER, J. Radioanal. Nucl. Chem, 172 (1993) 87. 5. Y. F. SHAFIQ, M. H. S. AL-HISSONI, M. A. JASSIM, M. A. ABDULAZZEZ, J. Radioanal. Nucl. Chem., 19l (1995) 25.

6. M. A. EL-ABSY, I. M. ELNAGGAR, A. I. AUDAH, J. Radioanal. Nucl. Chem., 173 (1993) 185. 7. R. E~ BOYD, Radiochim. Acta, 30 (1982) 123; 35 (1987) 41. 8. V. J. MOL1NSKI, Intern. J. Appl. Radiation /sotopes, 33 (1982) 811. 9. M. T. EL-KOLALY,J. Radioanal, Nucl. Chem., t70 (1992) 293. 10. LE TUONG MINH, T. LENGYEL, J. Radioanal Nuc]. Chem., 128 (1988) 417. 11. S. N. MUDDUKRISHNA, D. V. S. NARASIMANAN, C. N, DESAI, J, Radioanal, Nucl. Chem., 140 (1990) 153. 12. J, L. VUC1NA,J. Radioanal. Nucl. Chem., 212 (1996) 33.

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