Time resolved fluorescence spectroscopy of Eu(III) complexation with alpha-hydroxy isobutyric acid

Complexation of Eu(III) with alpha-hydroxy isobutyric acid (HIBA), a model compound of humic acid, has been studied by time resolved fluorescence spectroscopy. The ratio of fluorescence intensity of the two peaks at 616 and 592 nm (I(616/592)) was found to increase with increasing ligand to metal ratio. The I(616/592) data was used to deduce the stability constant of Eu-HIBA complexes of the type ML(i) (i=1-3). The formation of multiple ligand complexes was also corroborated by lifetime data which was found to increase with increasing [HIBA]/[Eu] ratio thus indicating replacement of coordinated water molecules by HIBA.