Molecular size distribution and spectroscopic characterization of humic substances

Spectroscopic examination of four humic substances and their molecular size (MS) fractions indicates that differences in the UV-VIS spectra, as measured by the ratio of absorbances at 465 and 665 nm (E4/E6), can be correlated to MS, as determined by ultrafiltration. However, the usefulness of the E4/E6 ratio is limited as a process-monitoring parameter, because of its strong concentration dependence in the dilute concentration range (below 10 g/m3). UV absorbance at 254 nm was found to be a good surrogate parameter for dissolved organic carbon. The chemical composition, as determined by the IR spectra, does not measurably differ after ultrafiltration of the humic substances into MS fractions.