Separation of divalent transition metal β-diketonates and their adducts by supercritical fluid chromatography

A method for separation and detection of divalent transition metal β-diketonates by adduct formation/supercritical fluid chromatography (SFC) with an open-tubular capillary column and a FID detector is described. The crystal structures of copper (Cu)-hexafluoro-acetylacetone (HFA) and Cu bis(2,2,6,6-tetramethyl-3,5-heptanedionato) (THD) complexes have been determined by X-ray crystallography. The SFC behavior of Cu β-diketonates shows a strong correlation with the structure of the complexes. The hydrated cu β-diketonate complexes usually exhibit strong intermolecular interactions or decomposition in SFC. Formation of adducts with a neutral donor, such as tributyl phosphine oxide (TBPO), can greatly improve the SFC behavior and detection sensitivity of Cu(II) and Mn(II) β-diketonates. The stoichiometry and thermal stability of the adducts Cu(II) and Mn(II) β-diketonates with TBPO in supercritical CO2 have also been investigated. The implications of utilizing adduct formation for supercritical fluid extraction (SFE) of divalent transition metals and for on-line coupled SFE/SFC analysis of divalent transition metals are discussed.