Supercritical fluid chromatography and extraction of Fe(III) with hydroxamic acids

Representative aliphatic and aromatic mono-hydroxamic acids are shown to be separable by supercritical fluid chromatography (SFC) using methanol modified CO2 on a diol column. Evidence for ligand contamination by Fe(III) from the SFC system is provided, as the ligands are detected as Fe(III) chelates at 420 nm. The ligands and chelates studied were octanohydroxamic acid (OHA), Fe(OHA)3, benzohydroxamic acid (BHA), Fe(BHA)3, heptanohydroxamic acid (HHA), Fe(HHA)3, and a newly synthesised hydroxamic acid, perfluorooctanohydroxamic acid (PFOHA). When the ligands were examined using unmodified supercritical CO2 (SFCO2) for their ability to extract Fe(III) from solid supports by supercritical fluid extraction (SFE), the fluorinated hydroxamic acid showed enhanced performance and solubility.