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

Complexation of Eu(III) with α-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 (I616/592) was found to increase with increasing ligand to metal ratio. The I616/592 data was used to deduce the stability constant of Eu–HIBA complexes of the type MLi (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.