Production of no-carrier-added theranostic Au-199: A systematic evaluation of liquid-liquid extraction from dissolved neutron-irradiated platinum targets.

Abstract

Introduction¹⁹⁹Au (half-life 3.14 d) is of high interest as medical isotope due to its potential use in theranostic applications. It is produced indirectly via neutron capture of ¹⁹⁸Pt to form ¹⁹⁹Pt which subsequently decays by β--emission to ¹⁹⁹Au. Separation of no-carrier-added ¹⁹⁹Au from irradiated natPt target material remains challenging.MethodsA systematic screening of five solvents (toluene, dichloromethane, ethyl acetate, diethyl ether, methyl tertbutyl ether) across five different HCl concentrations (0.1, 0.5, 1.0, 5.0, 7.5 M) for the liquid-liquid extraction of ¹⁹⁹Au from irradiated natPt was performed. KD values for ¹⁹⁹Au and Pt were calculated based on γ-spectroscopy measurements. Additionally, the influence of container vials (glass vs. polypropylene) and recovery of Pt target material were investigated.ResultsSignificant differences between extraction in glass and polypropylene vials were found. Although higher KD values were observed in polypropylene vials, this was attributed to leaching of extractant-active compounds from the polypropylene vials. Therefore, extraction in glass vials from 5 M HCl with diethyl ether was found to be optimal, whereas ethyl acetate was disqualified due to Pt co-extraction and acid hydrolysis. Using this condition, we obtained 98% of ¹⁹⁹Au in two extraction steps with a high molar activity of 40 MBq/nmol and high radionuclidic purity of 99.8%.ConclusionOur optimised process removes the need for chelating agents and back-extraction yielding n.c.a. ¹⁹⁹Au in high molar activity and radionuclidic purity ready for small-molecule radiolabelling. Over 95% of platinum target could be recycled which reduces waste and is expected to increase molar activity in subsequent production cycles.