An ultraviolet absorbance method of estimating the percent aromatic carbon content of humic acids

The aromatic C content of humic acids strongly influences the complexation of nonpolar organic solutes by humic substances. A rapid method of estimating the aromatic C content of humic acids would be useful in studies of the fate of nonpolar organic solutes in soils and natural waters. The relationship between the UV absorptivity of nine different dissolved humic substances, measured at a wavelength of 272 nm, and their aromatic C content, as determined by 13C CPMAS NMR, was evaluated. The percent aromatic C (determined by NMR) was strongly correlated (r = 0.94) with the UV absorptivity measurements. It is suggested that determinations of UV absorptivity at 272 nm can be used to provide a quantitative estimate of the aromatic C content of dissolved humic acids.