Membrane Absorbers for the Rapid Purification of Medical Isotopes | AIChE

Membrane Absorbers for the Rapid Purification of Medical Isotopes

Authors 

Kulbacki, D. - Presenter, Case Western Reserve University
Duval, C., Case Western Reserve University
Radiopharmaceuticals, such as Technetium-99m (Tc-99m) and Molybdenum-99 (Mo-99), are becoming revolutionary in the field of medicine, as they concentrate themselves in tissues and organs and then decay, releasing gamma emissions that are useful for imaging, in techniques like PET-CT scans, and for localized cancer treatment. Despite the great promise of this new class of drugs, their widespread implementation has been hindered by their availability and by their extremely short half-lives. Isotopes are generally produced by irradiating a metal, such as Uranium, and then dissolving products in a strong acid during purification. After this, we need an efficient yet selective method that allows for fast processing before an excessive amount of decay occurs. Current methods involve using packed resin columns; however, these usually require low flow rates and require a large volume of loading and elution solution, leading to an inefficient separation.

A promising alternative involves using membrane absorbers that are highly selective towards the desired radioactive species over undesired byproducts. Microporous poly(ether-sulfone) (PES) membranes can be functionalized using ethylene glycol methacrylate phosphate (EGMP). Prior to polymerization, an initiator, 2,2’-Azobis(2-methylpropionitrile), is immobilized on the membrane to facilitate the formation of free radicals on the surface. Ethylene glycol methacrylate phosphate is then grafted onto the surface using UV-induced free-radical polymerization by irradiating the membrane surface for 10-15 minutes. Membrane absorbers with varying pore sizes were functionalized to assess the effect of pore size on breakthrough in dynamic binding experiments. A consistent degree of grafting was determined to be 7% ± 2.03%, by using the weight difference and Fourier Transform Infrared Spectroscopy to ensure the surface was, in fact, functionalized. Dynamic binding experiments using a syringe pump have been completed using Lanthanum (La3+), to examine how much La3+ can be retained by the membrane before complete breakthrough. Dynamic binding experiments have shown that there is an early column breakthrough after the first handful of column volumes. We hypothesize that the breakthrough was caused by large pores (high MWCO of the membrane) or defects in the prepared membranes, which led to channeling. To test this hypothesis, EGMP-grafted membranes with smaller pore sizes (lower MWCO) were tested and membranes were stacked (10) to reduce the effect of possible imperfections. Understanding the cause of the early breakthrough allows us to design more efficient membrane processes that limit product loss and reduce purification time.