Comparison of the natural fluorescence distribution among size fractions of terrestrial fulvic and humic acids and aquatic natural organic matter

A soil fulvic acid (SOILFA), a soil humic acid (SOILHA) and an aquatic natural organic matter (SUWNOM) sample were separated into a spectrum of size fractions with high performance size exclusion chromatography (HPSEC). Fractions were collected and the synchronously scanned and total luminescence fluorescence (TL) spectra were determined for each fraction. Synchronously scanned spectra were difficult to interpret due to the emphasis placed on peak shoulders in the spectra rather than peak maxima. Total luminescence spectra indicate that despite differences in the size distributions of UV absorbing carbon in the fractions, the fluorescence producing moieties of all three samples occur in the same, relatively small size fractions. For the SOILFA and the SUWNOM, 95% of the UV absorbing carbon was coincident with 95% of the fluorescence. However, in the SOILHA, only about 50% of the UV absorbing carbon was coincident with 90% of the fluorescence. Due to the high (>95%) coincidence of UV absorbing and fluorescent carbon in the same size fractions, in situ fluorescence may offer promise for following the movement of natural organic matter in aquatic systems.