Yttrium-90 Separation

86Y and 90Y are a potential theranostic pair for the PET imaging and treatment of disease. 86Y is produced by the irradiation of Sr targets. Following dissolution of the targets with concentrated HNO3 or HCl, the feed is adjusted to 8 M acid and 86Y is selectively extracted using DGA resin. After rinsing to remove additional Sr and to reduce the acid concentration, the 86Y is stripped from DGA with 0.25 M HCl and can be loaded onto a LN resin column for additional purification. The LN resin retains the Y, while remaining Sr impurities pass through. Y is then stripped from LN with 8M HCl through a second DGA cartridge. 86Y is then recovered in very high purity in a small volume of 0.10- 0.25 M HCl.

90Y is separated from its 90Sr parent. After adjusting the 90Sr solution to 3-8 M HNO3, the combined 90Y/90Sr is loaded through stacked cartridges of Sr resin and DGA resin. Sr resin removes the bulk of the 90Sr, while DGA retains 90Y.  There are several options for the elution scheme which can help to preserve and purify the 90Sr source material and obtain 90Y in high purity.

Early EXC separations of 90Sr and 90Y used stacked cartridges of Sr Resin with TRU or RE resin in place of DGA. The TRU and RE Resins were prone to leach of TBP into the 90Y fraction, so TRU-2 and RE-2 resin, containing CMPO in DAAP, were developed to reduce the amount of extractant leach (DAAP is more lipophilic than TBP). DGA, normal resin was a further improvement over the TRU and RE Resins, offering lower extractant leach, increased Y retention, improved separation from Fe (which is strongly retained on TRU and RE Resins from 8M HNO3), and recovery of 90Y in dilute HCl. In these early separations, 90Sr/90Y in 8M HNO3 was loaded onto stacked cartridges of Sr Resin (top) with TRU or RE Resin on the bottom. Sr Resin retained >99% of the 90Sr, while 90Y was retained on TRU or RE Resin. RE Resin, containing a higher concentration of CMPO in TBP offered higher retention of 90Y than TRU Resin. Following a rinse with additional 8M HNO3 to complete the transfer of the 90Y to the TRU or RE resin, the cartridges were separated, 90Sr recovered from Sr Resin with 0.05M HNO3, and 90Y recovered from TRU or RE Resin with 0.1M HNO3.

A variation on the classic approach for Sr/Y separations is to use stacked cartridges with Sr Resin on top and DGA, normal resin below. The combined 90Y/90Sr is loaded onto the stacked cartridges from 8 M HNO3 to maximize retention of 90Sr on the Sr Resin. Under these conditions, >99% of 90Sr should be retained on the Sr Resin, while any 90Sr breakthrough from the Sr Resin will pass through the DGA, normal resin. A small volume of 8M HNO3 rinse completes the 90Y transfer to the DGA, normal resin, the cartridges are separated and 90Sr is recovered from Sr resin with 0.05M HNO3. The DGA, normal cartridge is then rinsed with additional 8 M HNO3 to remove additional impurities (Sr, Ca, Fe, Al), 0.25 M HNO3 to reduce the acidity, and 2 M HCl to convert the system to HCl. The 90Y is then recovered from the DGA, normal resin with 0.10-0.25 M HCl.

An alternative approach loads the 90Sr/90Y onto the Sr Resin/DGA, normal Resin cartridges from 3 M HNO3. The uptake of Sr on Sr Resin from 3 M HNO3 is somewhat lower than from 8M HNO3, however, from 3 M HNO3, the Sr breakthrough from Sr Resin is retained on the DGA Resin. Following the loading step and a small rinse with 3 M HNO3, the cartridges are separated, and the DGA, normal Resin cartridge is placed on top of the Sr Resin cartridge. The Sr content of the DGA, normal Resin and the Sr Resin is then recovered using with 2M HCl. This removes the Sr from DGA and Sr Resin, converts the system to HCl, and removes several impurities from the DGA resin (Ca, Al, Sr). The 90Y can then be recovered from the DGA, normal Resin with 0.10-0.25M HCl.

References

McAlister, D.R. and Horwitz, E.P. 2011. Chromatographic radionuclide generator systems for the Actinides and Natural Decay Series Elements, Radiochimica Acta, 99, 151-159.

McAlister, D.R. Horwitz, E.P. 2007. The Characterization and Novel Applications of Extraction Chromatographic Materials Containing Bis(2-ethyl-1-hexyl)phosphoric Acid, 2-ethyl-1-hexylphosphonic acid, mono 2-ethyl-1-hexyl ester and 2,4,4-trimethyl-1-pentylphosphinic acid, Solv. Extr. Ion Exch., 25(6), 757-769.