Deep eutectic solvent-based extraction of uranium(vi) from a wide range acidity and subsequent determination by direct loading in thermal ionization mass spectrometry

Abstract

An extractive deep eutectic solvent (DES) was formed by trioctylphosphine oxide (TOPO) (hydrogen bond acceptor) and methylidenesuccinic acid (itaconic acid, IA) (hydrogen bond donor) in an optimized mole proportion of 0.6 : 0.4 at which it exhibited minimum dynamical viscosity (283.4 mPa s, 25 °C). The as-formed TOPO–IA DES was found to take up U(VI) from aqueous samples in the pH range of 1–9 as well as from the solutions having the HNO₃ concentration ranging from 1 to 7 mol L⁻¹ with an extraction efficiency of more than 88%. The U(VI)-sorption in TOPO–IA DES from a wide range of acidity suggested the involvement of both ion exchange and complexation modes. The switching between the two mechanisms of sorption seems to depend on the chemical conditions of the equilibrating solution. TOPO–IA DES could be immobilized in the pores of an microporous poly(propylene) membrane in very high concentration (550 wt%) and could, therefore, be used for the pre-concentration of U(VI) and direct loading on the Re filament for analysis via thermal ionization mass spectrometry (TIMS). U(VI) at the ppb range in representative synthetic samples, seawater and ground water samples was determined via ID-TIMS (Isotope Dilution-TIMS) with good analytical merits using this sample treatment procedure.