Monday, June 18, 2007 - 8:05 AM
Snake River (Boise Centre on the Grove)

Fluorescence sensitization and anisotropy of terbium associated with humic acid size fractions

Ray Von Wandruszka and Jeremy Riggle. University of Idaho, Moscow, ID

The fluorescence sensitization and anisotropy characteristics of a series of Tb(III) complexes with a leonardite humic acid (LHA) were investigated, in order to evaluate the interactions between the metal and different components of the humate. Ultrafiltration was used to separate LHA into six size fractions, which were used to form the Tb(III) complexes. Each fraction was first characterized by 13C-NMR and UV-Vis spectroscopy, which showed that the smaller ones (<3 kDa) had a significantly lower aliphatic content than the larger ones. These smaller components were good energy donors, which could effectively sensitize Tb(III) fluorescence. At the same time, the fluorescence anisotropy of Tb(III) increased significantly when these LHA fractions were added, indicating the formation of tightly bound complexes. In this sense, the smaller LHA fractions were comparable to EDTA, although their effect was not as strong. In contrast, the larger LHA sizes had little or no influence on Tb(III) sensitization or anisotropy. The results obtained suggest that the sizes and aliphatic content of humic polymers play a major role in their aqueous interactions with trivalent metal ions. Divalent metals are expected to behave in a similar way.