One step sample treatment and loading using a deep eutectic solvent immobilized in a porous substrate for thermal ionization mass spectrometry of Pu(iv) ions

Abstract

A deep eutectic solvent (DES) consisting of a 2 : 1 molar mixture of undecanoic acid and tetraheptylammonium bromide was prepared and characterized for its physical properties such as density, dynamic viscosity, decomposition temperature, and melting point and weight gain of the microporous poly(propylene) membrane (PPM) after immobilization of the DES. The AFM images showed that the morphology of the pristine microporous poly(propylene) membrane completely changed upon immobilization of the DES. The contact angle of the DES-PPM (69.2 ± 0.4°) indicates its wettability with water, therefore, resulting in good contact with the equilibrating solution for the preconcentration of the analyte. This sorbent DES-PPM showed a very high selectivity and distribution coefficient towards Pu(IV) in the 1 to 7 mol L⁻¹ HNO₃ concentration range studied, with no significant sorption of the representative actinides U(VI) and Am(III). A segment of the DES-PPM with sorbed Pu was directly decomposed on a rhenium loading filament. Thermal ionization mass spectrometric (TIMS) analyses were carried out for measuring the isotopic composition and concentrations of plutonium in the SRM standard and actual research and power reactor samples using the DES-PPM loading method and compared with those of the conventional anion-exchange purified solution and loading method. The DES-PPM based isotope dilution TIMS showed good analytical merits such as high selectivity towards Pu(IV) with minimum sample manipulation and improved ionization characteristics during TIMS analysis. Solidification of the floating organic drop bearing the microextracted Pu(IV) using the DES as the microextractant from the HNO₃ medium was demonstrated. The alpha spectrum with minimum tailing was recorded after direct deposition of the separated floating drop on a SS planchet.