title: Oxidative degradation of bis(2,4,4-trimethylpentyl)dithiophosphinic acid in nitric acid studied by electrospray ionization mass spectrometry.
abstract: BACKGROUND
  The selective separation of the minor actinides (Am, Cm) from the lanthanides is a topic of ongoing nuclear fuel cycle research, and dithiophosphinic acids are candidate ligands in these processes. Ligand instability has been noted under radiolytic and harsh acid conditions but explicit degradation pathways for ligands such as bis(2,4,4-trimethylpentyl)-dithiophosphinic acid (CyxH), the major compound in the commercial product Cyanex 301, have been elusive.
  
  
  METHODS
  Organic solutions of CyxH were contacted with aqueous solutions of HNO(3), and their degradation was studied by analyzing samples from these experiments by direct infusion electrospray ionization mass spectrometry. Ions were identified using accurate mass measurement and collision-induced dissociation.
  
  
  RESULTS
  The positive ion spectra contained cationized CyxH cluster ions, and oxidatively coupled species (designated Cyx(2)) cationized by either H or Na. The Cyx(2)-derived ions increased with acid contact time. The negative ion spectra consisted almost entirely of the CyxH conjugate base. The negative ion spectra of the HNO(3)-contacted samples also contained conjugate bases corresponding to the dioxo and perthio derivatives of CyxH.
  
  
  CONCLUSIONS
  CyxH is oxidized by acid contact to form the coupled species Cyx(2), and the dioxo species arise from subsequent oxidation of Cyx(2). Oxidative coupling increases with contact time, and with higher HNO(3) concentrations. The direct infusion measurements provided a simple approach for assessing degradation pathways and kinetics.
authors.affiliation: Idaho National Laboratory, 2351 North Boulevard, Idaho Falls, ID 83415-2208, USA. gary.groenewold@inl.gov
authors.forename: Gary S
authors.initials: GS
authors.lastname: Groenewold
authors.forename: Dean R
authors.initials: DR
authors.lastname: Peterman
authors.forename: John R
authors.initials: JR
authors.lastname: Klaehn
authors.forename: Laetitia H
authors.initials: LH
authors.lastname: Delmau
authors.forename: Philippe
authors.initials: P
authors.lastname: Marc
authors.forename: Radu
authors.initials: R
authors.lastname: Custelcean