Purification of a Au tracer from a Pt target using UTEVA resin column chromatography

Radioactive ¹⁹⁵Au is useful for the long-term biodistribution tracking of gold nanoparticles in cancer diagnostics and therapeutics. This study develops a highly selective separation method for ¹⁹⁵Au produced via the charged particle irradiation of a Pt target using UTEVA resin column chromatography and elucidates the underlying separation mechanism. To optimize the chromatographic conditions, batch experiments were performed with the UTEVA resin in HCl and HNO₃ media using tracer amounts of ¹⁹⁵Au and macro amounts of Pt. ¹⁹⁵Au exhibited high distribution coefficients in HCl, whereas Pt showed negligible adsorption. In HNO₃ media, the distribution coefficients of ¹⁹⁵Au decreased with increasing acid concentration. Subsequent two-step column chromatography using the UTEVA resin achieved a chemical yield of 91.6% and a decontamination factor of 4.6 × 10³ for Pt. To understand this selectivity, density functional theory (DFT) calculations were performed on the interactions between the anionic chloride complexes of Au, Pt, and Ir (a by-product of the nuclear reaction) and the protonated phosphonate cation. The calculations revealed that the Gibbs free energy change for ion-pair formation follows the order of Au < Ir < Pt, suggesting that anionic chloride complexes of Au readily form ion-pair complexes and are extracted. This extraction of Au is driven by a lower dehydration energy and reduced steric hindrance of [AuCl₄]^- compared to the highly charged and octahedral [PtCl₆]^2- and [IrCl₆]^2- ions. This study demonstrates that the UTEVA resin is highly effective for the separation and purification of ¹⁹⁵Au from irradiated Pt targets. The purified ¹⁹⁵Au obtained by this method can be utilized in future research on Au nanoparticles.