Eichrom’s DGA Resins are extraction chromatographic materials in which the extractant system is either N,N,N’,N’-tetra-n-octyldiglycolamide (DGA Resin, Normal) or N,N,N’,N’-tetrakis-2-éthylhexyldiglycolamide (DGA Resin, Branched). The structure of the DGA molecule is shown Rigure 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 working capacity of 7.23 mg 90Sr per mL of resin and 11 mg Yb per mL of resin.

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

Both forms of DGA Resin show more promise in analytical applications for americium than our other resins. They both have very high affinity for americium under certain conditions and americium is readily eluted under other conditions (See Figures 2 and 3). Diphonix resin shows high affinity towards Am(III), however, its elution is not as easy as with DGA Resin. The TRU Resin also show a good affinity for Am(III) with a retention factor of 100 for 0.5 to 5 M HNO3. At those acid concentrations, however, the retention factor k’Am(III) on either form of DGA Resin is 30 to 500 higher than on TRU!

The properties of the DGA Resins allow for the selective separation of Am(III) without fear of breakthrough due to weak retention. Am(III) is strongly fixed to either DGA Resin in 5 M HNO3 or HCl and can be eluted with 0.01 M HNO3 or 0.5 M HCl (Figures 2 and 3).

Figure 2. k′ for Th(IV), U(VI), Am(III) and Pu(IV) on TRU, DGA Resin, Normal and DGA Resin, Branched (50-100 µm) versus HNO3, 1 hour equilibration time, 22(1)oC.

Retention profiles for U, Pu and Th are also presented Figures 2 and 3. The diagrams show that higher Pu/Am separation factors are obtained for the normal version of DGA Resin. Pu(IV) shows strong affinity for the resin with a retention factor k’> 3000 over the entire acid range studied. U and Th affinities towards the DGA Resins depend upon the acid, its concentration and the type of DGA Resin.

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.

Given these data, the combination of TEVA and DGA Resin, Normal would allow one to first separate tetravalent elements on TEVA, leaving U and Am which would be retained on DGA resin. U would be first eluted with 0.5 M HNO3 followed by Am(III) with 0.5 M HCl. Methods for americium in soil using the DGA Resins are currently being developed in Eichrom’s technical support laboratory.

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 cerium in nitric acid and hydrochloric acid. In HNO3 media, Ra shows no real affinity for the resin (1 < k’Ra < 7). However, Ce has k’ >1000 for concentrations higher than 1M. It can be assumed that actinium and cerium will show similar uptake behavior. So Ac should be well retained on the resin for HNO3 concentrations of 1 – 3 M while Ra is eluted. Ac could then be stripped at low acid concentrations. In HCl media, the separation is efficient at 8 M (selectivity α(Ce/Ra) > 105). Cerium (or actinium) is then stripped at low acid concentrations (<0.5 M HCl). [caption id="attachment_993" align="aligncenter" width="300"] Figure 4: k’ for Ra and Ce in HNO3 and HCl.
Y/Sr Separation[/caption]

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

Finally, Figure 7 shows the uptake of various transition and post transition elements. Bismuth is retained across all concentrations of both nitric acid and hydrochloric acid. Care should be taken if decontamination from Bi is critical to the analysis.

Iron is strongly retained from higher concentrations of HCl, but shows no uptake at all 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.

Source for all published data: 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)