Tailored Bifunctional Polymer for Plutonium Monitoring

Abstract

Monitoring of actinides with sophisticated conventional methods is affected by matrix interferences, spectral interferences, isobaric interferences, polyatomic interferences, and abundance sensitivity problems. To circumvent these limitations, a self-supported disk and membrane-supported bifunctional polymer were tailored in the present work for acidity-dependent selectivity toward Pu(IV). The bifunctional polymer was found to be better than the polymer containing either a phosphate group or a sulfonic acid group in terms of (i) higher Pu(IV) sorption efficiency at 3-4 mol L(-1) HNO3, (ii) selective preconcentration of Pu(IV) in the presence of a trivalent actinide such as Am(III), and (iii) preferential sorption of Pu(IV) in the presence of a large excess of U(VI). The bifunctional polymer was formed as a self-supported matrix by bulk polymerization and also as a 1-2 μm thin layer anchored on a microporous poly(ether sulfone) by surface grafting. The proportions of sulfonic acid and phosphate groups in both the self-supported disk and membrane-supported bifunctional polymer were found to be the same as expected from the mole proportions of monomers in polymerizing solutions used for syntheses. α radiography by a solid-state nuclear track detector indicated fairly homogeneous anchoring of the bifunctional polymer on the surface of the membrane. Pu(IV) preconcentrated on a single bifunctional bead was used for determination of the Pu isotopic composition by thermal ionization mass spectrometry. The membrane-supported bifunctional polymer was used for preconcentration and subsequent quantification of Pu(IV) by α spectrometry using the absolute efficiency at a fixed counting geometry. The analytical performance of the membrane-supported-bifunctional-polymer-based α spectrometry method was found to be highly reproducible for assay of Pu(IV) in a variety of complex samples.

Chemically selective polymer substrate based direct isotope dilution alpha spectrometry of Pu

“…It was observed in our previous work that HEMP and AMPS monomers are polymerized with equal efficiency leading to mole proportion of phosphate to sulfonate groups same in the bifunctional polymer as that in the polymerizing solution [26]. The PES membranes, used as substrates for surface grafting, had rough and glossy surfaces.…”

“…In our previous work, a membrane based alpha spectrometry has been employed for the determination of ppb to sub-ppb level of Pu in complex aqueous matrices using absolute efficiency [26]. However, this method cannot be applied for the samples in which Pu(IV) chemical recovery is not constant or Pu concentration is higher than Pu(IV) loading capacity of the membrane.…”

“…The procedure used for grafting the functional monomers HEMP and AMPS in 1:1 mol proportion on a microporous PES membrane was similar to that reported in our earlier publication [26]. Briefly, the PES membranes having 0.1 and 0.2 mm pore-sizes were cut into 2 Â 1 cm 2 pieces, washed thoroughly with methanol and dried.…”

“…For this, a thin Pu(IV)-selective bifunctional polymer layer was anchored on the poly(ethersulfone) (PES) membrane by UV grafting for direct isotope dilution alpha spectrometry. The choice of phosphate-sulfate bifunctional polymer thin layer was based on previous work that indicated its high selectivity towards Pu(IV) ions in solutions containing 3 M HNO 3 [26]. The porous substrate for anchoring bifunctional polymer layer was selected to obtain high accessibility of functional groups as the binding sites for Pu (IV) ions.…”

“…The formation of a thin bifunctional layer on the PES membrane by UV grafted method has to be an easy, one step process, reusable and amenable for the routine applications for alpha spectrometric determination of Pu(IV) ions in the solutions having high HNO 3 concentration. The fixed and reproducible alpha counting geometry is also necessary for obtaining a constant efficiency factor for Pu determinations by alpha spectrometry [26]. However, use of isotope dilution technique in the membrane based isotope dilution alpha spectrometry (Mem-IDAS) would account for the unforeseen errors during preconcentration and provide flexibility in mounting the membrane in the alpha counting chamber.…”