Spectroscopic and compositional comparative characterization of I.H.S.S. reference and standard fulvic and humic acids of various origin

Abstract

Eleven standard and reference fulvic acids (FA) and humic acids (HA) of aquatic and terrestrial origin from the collection of the International Humic Substances Society have been studied by chemical and spectroscopic methods. Aquatic HA appear richer in O and lower in C than terrestrial HA, while the opposite is generally true for the corresponding FA. The N content of aquatic samples is always much lower, and C/N ratio and E 4/E 6 ratio much higher than those of terrestrial samples. The infrared spectra of all samples but soil HA are qualitatively similar one to another, but they differ mainly in the relative intensity of carboxyl, aromatic and aliphatic group bands. Fluorescence of terrestrial HA occurs at higher wavelengths than terrestrial FA and aquatic HA and FA in both emission and excitation modes, while synchronous-scan spectra appear more resolved and informative. ESR spectra are featured by resonances consistent with conjugated semiquinone free radicals and Fe(III) ions, the latter resonance being generally more intense for terrestrial than for aquatic samples.