UV absorbance ratio index with size exclusion chromatography (URI-SEC) as an NOM property indicator

An advanced approach is presented for identifying and characterizing biopolymers of natural organic matter (NOM) in water samples. It involves a simple method based on a ratio of peak heights of high performance size exclusion chromatography (HPSEC) chromatograms based on ultraviolet absorbance (UVA) at 210 nm and 254 nm. The HPSECsystem eliminates inorganic interferences and makes it possible to obtain ratio values associated with organic components as a function of molecular weight (MW). Certain biopolymers show a distinctive ultraviolet absorbance ratio index (URI, UVA(210)/UVA(254)) because they contain different compositional proportions of UV-absorbing functional groups and sp2-hybridized carbon. URI values were found to be the lowest for humic acids (1.59 for a humic acid, highest aromaticity), intermediate for fulvic acids (1.88for a fulvic acid, intermediate aromaticity), and highest for proteins (13.50 for BSA, lowest aromaticity). URI increases with eutrophication of natural waters by the increase of microbially derived components that have a high functional group proportion with a low sp2-hybridized carbon, and increases with ozonation by the cleavage of unsaturated bonds (decrease in unsaturated bonds and increase in functional group proportions).