Crosslinked polyethylene glycol beads are highly effective to separate ^99mTc-pertechnetate from low specific activity molybdenum

Objectives Aqueous two-phase partitioning can separate ^99mTc-pertechnetate from molybdenum (Mo), and is typically performed on solid support using polyethylene glycol (PEG) chains attached to a polystyrene resin. We report the use of cross-linked, PEG-only beads for the separation of ^99mTc from Mo.

Methods A cross-linked PEG resin developed for solid-phase synthesis of long peptides was used for this project (ChemMatrix, PCAS Biomatrix). Resins with various terminal substituents were tested, including nitrile, Wang (p-alkoxybenzyl alcohol), BOC and aminomethyl resins. Additional modifications were made on aminomethyl Chemmatrix resins to obtain acetyl- and mesyl-substituted resins. 1.5 - 2.0 g of Mo metal powder was dissolved in 20 mL 30% H₂O₂; NaOH was added to a concentration of 4M NaOH. Na[^99mTcO4] was added to the solution. The resins were loaded at a range of flow rates, and eluted with water to release ^99mTc. The ^99mTc solution was then passed through a cation exchange resin and a small Sep-Pak Alumina A Plus Cartridge (280 mg), followed by elution with saline.

Results Optimal results were obtained by loading and eluting 500 mg of resin at a flow rate of 2 ml/min. All resins were highly efficient at trapping ^99mTc, with quantitative (98-100%) extraction of ^99mTc from the Mo solution. Complete release of ^99mTc was also observed with all resins after rinsing with water (98-100%), with the exception of the aminomethyl resin, where elution was less efficient (69-85%). Pure ^99mTc-pertechnetate in 0.9% saline was obtained at the end of the process, with no residual Mo.

Conclusions Cross-linked PEG beads are highly effective at separating and purifying ^99mTc from Mo in solution, with quantitative trapping and elution of ^99mTc. This approach is suitable to purify ^99mTc pertechnetate after direct production by cyclotrons or purification from low-specific activity ⁹⁹Mo obtained by linear accelerators and neutron-enrichment of ⁹⁸Mo.

Research Support Canadian Institutes for Health Research, National Sciences and Engineering Research Council and Natural Resources Canada