Mechanistic Investigation of Co(II) Extraction by TODGA to Aid Nuclear Forensic Separations

Nuclear forensic (NF) analysis supports law enforcement inquiries by analyzing evidence tainted with radioactive substances. Separation techniques can be used to identify and quantify actinides and fission products in post-detonation (PD) debris. Environmental transition metals, also present in PD residues, have been observed to impact critical isotope extractions. For example, radio stable cobalt (Co), ubiquitous in urban environments, particularly in corrosion-resistant alloys, paint-drying agents, dyes, and pigments, can impact the separation of important actinides and fission products. The presented work aims to elucidate the chemistry governing Co extraction in samples pertinent to post-detonation nuclear forensics (PDNF). Chemistry between Co and N,N,N',N'-tetraoctyl diglycolamide (TODGA), the ligand present in the commercial chromatographic resin diglycolamide (DGA), were studied via solvent and chromatographic extraction and spectroscopic analyses. The results indicate that a tetrahedral Co(II) species is extracted by TODGA from highly acidic (>5 M HCl) solutions via a spontaneous entropy-driven reaction. Extraction trends in varied acid concentrations are consistent between solvent extraction and chromatographic extraction methods.