Eichrom’s DGA Resins are extraction chromatographic materials containing either N,N,N’,N’-tetra-n-octyldiglycolamide (DGA Resin, Normal) or N,N,N’,N’-tetra-2-ethylhexyldiglycolamide (DGA Resin, Branched). The structure of the DGA molecule is shown in Figure 1, where the R-groups are straight chain or branched C8 groups. The bed density of both DGA Resins is approximately 0.38 g/mL, with a functional capacity of 7-8 mg Eu per mL of resin.

Assumed extraction equilibrium: Where M = Ln, Ac = DGA (Extractant) in the stationary phase.

Data for the extraction of selected metal ions by TRU, DGA, Normal and DGA, Branched resins are shown in Figures 2 and 3. The unique properties of the DGA Resins allow them to compliment or provide an alternative to TRU Resin in many applications. The primary advantage of the DGA Resins is their high affinity for trivalent rare earths and actinides, such as Am(III). Trivalent actinides and rare earths are strongly retained from HNO3, while Fe(III), Na(I), K(I), Mg(II) and many other common matrix ions are rejected. The trivalent actinides and rare earths can be recovered from the DGA Resins with dilute HCl. Light rare earths may also be stripped from DGA, Branched using dilute (0.01-0.05M) HNO3.

Figure 3. k′ for Th(IV), U(VI), Am(III) and Pu(IV) on TRU Resin, DGA Resin, Normal and DGA Resin, Branched (50-100 µm) versus HCl, 1 hour equilibration time, 22(1)oC.

DGA resin can also be used for the separations of radium – actinium and yttrium – strontium.

Ra/Ac separation

Figure 4 shows the acid dependency of k’ for radium and actinium in nitric acid and hydrochloric acid on DGA, Normal. In HNO3 media, Ra shows no real affinity for the resin, while Ac has k’ >1000 for 1-3M HNO3.  Ac can then be stripped from DGA with 0.1-2M HCl. Using 2M HCl to recover Ac can provide additional decontamination from Th isotopes, which will remain on DGA, Normal in 2M HCl.

Figure 4. k’ Ac and Ra on DGA, Normal from HNO3 and HCl.

The k’ for Ac decreases above 2-3M HNO3, while the k’ for rare earth cations continues to remain >1000. This provides a mechanism for the separation of Ac and rare earths. Ac can be eluted with 8-10M HNO3, while the rare earths remain on the DGA Resin (Mastren, et al.).

Figure 5 shows the uptake of four alkaline earth cations on DGA Resin, Normal. None show any significant uptake from HCl and only Sr and Ca show moderate uptake from nitric acid concentrations of ~0.5M to ~5 M. Samples containing high Ca content should be loaded from 8M HNO3 to keep the k’ value for Ca low. Figure 6 compares the uptake of Sr and Y in both nitric acid and hydrochloric acid. Y(III) is much more strongly retained on the resin than Sr(II) from both acids across all concentrations. Coupling Eichrom’s Sr Resin with DGA-Normal would allow for excellent separation of Y from Sr for radiopharmaceutical purification or a single step Sr-89/90 measurement procedure.

Figure 5. k′ for alkaline earth cations on DGA Resin, Normal (50-100 µm) versus HNO3 and HCl, 1 hour equilibration time, 22(1)oC.

Figure 6. k′ for Y(III) and Sr(II) on DGA Resin, Normal (50-100 µm) versus HNO3 and HCl, 1 hour equilibration time, 22(1)oC.

Figure 7 shows the uptake of various transition and post transition elements on DGA, Normal. Bismuth is retained from 0.05-8M HNO3 and 0.05-1M HCl. Care should be taken if decontamination from Bi is critical to the analysis. Bi may be removed from DGA, Normal resin with 9-10M HCl, before recovering Ac, Am or rare earths in dilute HCl.

Iron is strongly retained from higher concentrations of HCl, but shows little uptake from nitric acid.

Figure 7. k′ for selected transition and post transition elements on DGA Resin, Normal (50-100 µm) vs. HNO3 and HCl, 1 hour equilibration time, 22(1)oC.

1) Horwitz E.P., McAlister D.R., Bond A.H., Barrans R.E., Novel Extraction Chromatographic Resins Based on Tetraalkyldiglycolamides: Characterization and Potential Applications, Solvent Extraction Ion Exch., 23, 219 (2005). (HP104)

2) Mastren, T., Radchenko, V., Owens, A., Copping, R., Boll, R., Griswold, J.R., Mirzadeh, S., Wyant, L.E., Brugh, M., Engle, J.W., Nortier, F.M., Birnbaum, E.R, John, K.D., Fassbender, M.E. 2017. Simultaneous Separation of Actinium and Radium Isotopes from a Proton Irradiated Thorium Matrix. Nature Scientific Reports, 7, 8216. doi:10.1038/s41598-017-08506-9.