Spectroscopic studies on soil organic fractions - II. IR and 1H-NMR spectra of methylated and unmethylated fulvic acids
The IR and 1H-NMR spectra of fulvic acids (FA) are discussed. The FA, extracted by traditional methods, were fractionated on the basis of molecular weight (m.w.). Three fractions were obtained labelled FA I (m.w. > ∼ 2000), FA II (m.w. > ∼ 12000) and FA III (∼2000 < m.w. < ∼ 12000). Fraction FA II was methylated with CH 3I-Ag 2O. The 1H-NMR spectra of unmethylated FA fractions show some signals common to all three fractions and some differences in the 3-5 ppm range due to the resonances of OCH 3 and O-CH 2 groups. The proton spectrum of the methylated fraction shows absorption areas for OCH 3 groups of phenols and carboxyls. The results confirm that NMR spectroscopy is a convenient technique which can contribute to defining the chemical structure of humic substances.