13C NMR spectra of soil organic fractions extracted with organic solvents

Abstract

Soil organic fractions extracted in sequence with ethyl ether, acetone, benzene and dioxane have been investigated with 13C NMR spectroscopy. The spectra of ethyl ether and acetone fractions are identical and show the presence of signals assigned to normal long chain ( C 23±2) fatty acids. A very similar spectral pattern is displayed by the benzene fraction which appears to consist of a mixture (50 ± 10)% of normal fatty acids and normal alkanes ( C 21±3). A comparison with data in the literature indicates that the well developed signals at 14, 23, 30 (very intense) and 32 ppm are a common feature of the lipid fraction extracted from different soils. A completely different spectrum has been obtained from the dioxane fraction. Most signals appearing in the range 55–75 ppm can be attributed to oxygen bonded sp 3 carbon atoms. The lack of aromatic signals seems to exclude the possibility that this fraction was derived from lignin residues. The comparison with 1H NMR spectra and the occurrence of distinct and sharp signals indicate that 13C NMR is a valuable tool in the study of soil organic fractions extracted with organic solvents.