Thermal Analysis of Lanthanide Hexafluoroacetylacetone Chelates

摘要

In the field of nuclear forensics, a rapid technique to separate and quantify fission product isotopes is desired. 1,1,1,5,5,5-hexafluoroacetylacetone (hfac) is a ligand that can be used in the chromatographic separation of metals from other fission products via chelation. Volatile organometallic complexes can be separated from each other via gas phase chromatographic separations due to variations in adsorption enthalpy. Because adsorption and sublimation thermodynamics are linearly correlated, there is considerable motivation to determine sublimation enthalpies of the compounds. A recent method of TGA is employed in this study on thirteen lanthanide hexafluoroacetylacetone complexes (Ln[hfac]4). A method based on the Langmuir and Clausius-Clapeyron equations is used to determine sublimation enthalpies using stages of isothermal heating. An empirical correlation is used to estimate adsorption enthalpies of lanthanide complexes on a quartz column from the sublimation data. Kinetic or thermodynamic models can be used to estimate retention time of the compounds on a column, which allow for the characterization of unknown mixtures of lanthanide fission products. Additionally, thermal analysis of the chelates, including melting point and thermogravimetric analysis (TGA) coupled with mass spectrometry, is reported. Hydration and/or coordination with water is observed in each compound, and large mass loss events occur prior to the melting point, indicating sublimation of the chelate.