Fluorescence spectroscopic studies of Al-fulvic acid complexation in acidic solutions

The complexation interaction between a soil fulvic acid (SFA) and aluminum (III) ion has been studied using several different types of fluorescence measurements. Excitation and emission scans have been employed along with total luminescence, fluorescence lifetime and fixed wavelength experiments. Titrations of SFA with Al3+ at fixed pH values of 4.00 and 5.00 as well as pH titrations were used to examine the unique fluorescence behavior of humic material complexes of aluminum. SFA was found to exhibit both fluorescence quenching and enhancement effects upon complexation of Al3+ depending on the pH and wavelengths employed. A pronounced shift in the fluorescence spectral maximum to longer excitation wavelengths and shorter emission wavelengths was observed for the Al-SPA complex. Striking similarities between the fluorescence behavior of the model compound salicylic acid and SFA in the presence of Al3+ were clearly evident.