A novel technique for the effective concentration of 99mTc from a large alumina column loaded with low specific-activity (n,γ)-produced 99Mo

Molybdenum-99 of low-to-medium specific activity, 7.4–14.8 GBq/g, obtained by the 98Mo(n,γ)99Mo reaction in research reactors requires a large alumina column to adsorb the molybdenum since the capacity of alumina to adsorb Mo is limited (20 mg Mo/g of alumina). The large size of alumina column, in turn, requires large eluant volumes to elute the 99mTc, and the radioactive concentration (RAC) of the pertechnetate becomes unacceptably low for radiopharmaceutical applications. This study describes a method for obtaining high RAC pertechnetate solutions from a column generator loaded with 99Mo of low specific activity. Molybdenum-99 of specific activity, 7.4 GBq/g, was absorbed on an alumina column [60 g, 70 mm, (H)×35 mm (diam.)]. The 99mTcO4−, eluted with 60 ml normal saline (0.15 N NaCl), was applied to a 12 mm (H)×1 mm (diam.) column containing 15 mg of the strong anion exchanger Dowex 1×8. The retained pertechnetate was eluted with 5 ml of 0.5 mM tetrabutylammonium bromide (TBAB) solution in methylene chloride. The organic solvent was subsequently removed under vacuum and the dry residue was reconstituted with the desired volume of normal saline. All the operations were carried out in a closed cycle with sterile connecting tubes and multi-way stop-cocks. The concentrated pertechnetate obtained contained about 90% of the total saline eluate and had a pH of 6–7, a radiochemical purity (RCP) consistently >99%, the 99Mo breakthrough was around 10−4%. Colorimetric spot tests (limit tests) for Al and Mo showed <10 ppm in the final 99mTcO4− solution. The RCP of the labelled compounds prepared using the pertechnetate obtained and five different radiopharmaceutical kits were >95%. The procedure may be equally applicable for the effective concentration of 188ReO4− from 188W–188Re generators.