Implementation of spectroscopic parameters for practical monitoring of natural organic matter

Abstract

Humic acids have been widely studied in the literature as a representative to natural organic matter (NOM) in drinking water supplies due to their composite heterogeneous nature comprising a variety of different molecular weight compounds. However, humic acids are difficult to isolate from water primarily due to their low concentration, resulting in time-consuming and laborious processes for their isolation and purification. In this study the applicability of surrogate parameters such as E 250/E 365, E 254/E 436, E 365/E 465 and E 465/E 665, which are widely used in the literature for NOM characterization, were investigated in relation to aquatic and terrestrial model humic acids and a natural water sample. Molecular size fractionation of the samples was employed in an approach to understand the UV-vis properties of each size fraction. The specified ratios for both aquatic and terrestrial humic acids do not exhibit any significant differences up to 30 kDa. Lower molecular size fractions are differentiated in comparison to the natural water sample. E 254/E 436 and E 250/E 365 ratios exhibit a molecular size specific distribution with respect to the type of humic acids. The ratio of E 254/E 436 was proposed to assess the composition of altered NOM provided that the total removal of color-forming moieties is not required. Under conditions of total decolorization, the use of E 250/E 365 is also recommended relevant to the spectroscopic changes acquired during treatment.