[Resonance light scattering of aurintricarboxylic acid]

Resonance light scattering (RLS), absorption and fluorescence spectra of aurintricarboxylic acid (ATA) were studied. In solutions with pH 3.7 to pH 11.0, the RLS signal was very weak, but increased sharply with a decrease in pH when pH < 3.7 and reached a maximum at pH 2.7. This enhancement effect of RLS occurred because the negative charged species of ATA were transformed into neutral molecules when pH decreased, and the neutral molecules assembled into supermolecular aggregates. Two peaks at 260 nm and 340 nm, respectively, and a valley at 300 nm, appeared in the RLS spectrum, whereas an absorption peak appeared at 300 nm in the absorption spectrum. This spectral feature reveals that the RLS spectrum was related to the absorption spectrum of ATA. The change in RLS intensity with the wavelength was not accordant with Rayleigh scattering law. The fluorescence excitation and emission spectra of ATA do not overlap, so resonance fluorescence was not involved in the RLS spectrum. Under a given set of experimental conditions, the RLS intensity increased with the increase in ATA concentration, which, however, was not a strictly linear relationship.