Speciation of Ru through A4F-MALS, Spectrophotometry UV-Visible and LDI-TOF for a 103-Ru/103m-Rh generator
Résumé
Objectives: Ruthenium is considered to be an interesting element for establishing a 103Ru/103mRh generator for Auger therapy. In radiochemical processes, Ru may be present as Ru(II), (III), (IV), (VI), (VII), or (VIII), with Ru (III) and Ru (IV) the most numerous and stable compounds [1, 2]. But a chloride solution initially contains both Ru(III) and Ru(IV) species [1]. Ru species chemical behaviors are strongly pH dependent, leading to polynuclear complexes. This tendency to form polynuclear complexes linked by oxide and hydroxide bounds is most prominent for the oxidation states +III and +IV [3]. Additionally, colloidal ruthenium hydroxides are formed by the hydrolysis of Ru(III) and Ru(IV) compounds. These polynuclear, polymeric and colloidal species are not desirable for establishing a well-controlled chromatographic 103Ru/103mRh generator. Methods: It is of utmost importance to avoid the formation of colloidal species for the use of a 103Ru/103mRh generator for Auger therapy. Asymmetrical Flow-Field- Flow Fractionation (AF4) has been be used to analyze different Ru(IV) solutions in different HCl concentrations to check the presence / absence of Ru colloids in order to establish suitable HCl conditions for elution, i.e. keeping monomeric Ru(IV) on the resin when avoiding Ru colloids formation. The speciation of Ru was carried out by Asymmetrical Flow Field-Flow Fractionation (AF4) coupled to a Multi-Angle Light Scattering (MALS) detector. Results: The presence of ruthenium colloid in aqueous solution was evidenced with a polymodal and polydisperse profile. Ruthenium colloids formation appears before a precipitation within RuO2, visible at pH 2 and pH 4. Ruthenium colloids observed in the supernatant seems to be more stable at pH 4 than at pH 2 since no colloid has been observed at pH 2 either by MALS or by UV. These data lead to assume that it is possible to make generator in acidic pH conditions because in this case, all the species are in solution, and no colloids are formed 1. Lawrence MAW, Bullock JL, Holder AA (2017) Basic Coordination Chemistry of Ruthenium. In: Browne WR, Holder AA, Lawrence MA, et al (eds) Ruthenium Complexes. Wiley, Germany 2. Epperson CE (1975) Generator Separation of Ru-103/Rh-103m. University of Perdue, PhD Thesis 3. Niedrach LW, Tevebaugh AD (1951) The Polarography of Ruthenium (IV) in Perchloric Acid Solutions. J Am Chem Soc 73:2835–2837. https://doi.org/10.1021/ja01150a119
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