CONCENTRATION-EFFECT ON THE FLUORESCENCE-SPECTRA OF HUMIC SUBSTANCES

Concentration effect on the fluorescence excitation, emission, and synchronous excitation spectra of humic substances from various sources had thoroughly,been studied. Based on the results, it is emphasized that the spectra should be determined at sufficiently law concentrations because red-shift, distortion, and even quenching often occur especially in the excitation and synchronous excitation spectra at relatively higher concentrations. With the use pf two polarizers perpendicular to each other, the effect of scattered light is dramatically suppressed and thus the excitation and synchronous excitation spectra of humic substances at low concentrations can be conviently obtained. Since many fluorescence data and the correspondingly conclusive remarks in the literatures were obtained at relatively high concentrations (e.g., 50-100 mg/L), they should be re-evaluated. Same new fluorescence characteristics of humic substances have been outlined in this paper.