Assistant Professor of Soil Chemistry and Fertility
Soil Science Dept., Faculty of Agriculture, Cairo University, Giza 12613, Egypt
Several techniques was utilized to define the structure of soil organic matter (SOM) but results were not always satisfactory. However, the use of the Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS) is suggested as a powerful tool to identify the molecular composition of natural organic matter. A sequential extraction was used to extract the light fraction (LF), the 500–53 μm particulate organic matter (POM), and the mobile humic acid (MHA) fraction from fertilized soils. Isolated fractions were characterized for C, N and using the the 13C-CPMAS and the FTICRMS techniques. Results showed a continuous increase in the aromaticity of the isolated fractions as the MHA contained the largest content (67%) of aromatic compounds when compared to the LF (24%) or the POM (32%). The van Krevelen diagrams confirmed the higher aromaticity of the MHA in contrast to most of the LF formulae which fell into the region of lipid and protein range while the peaks assigned to molecular formulae similar to condensed hydrocarbon (more polar and aromatic) regions were visible only in the MHA. Further elaborations are being carried out for the relationships between the double bond equivalents (DBE) and m/z or atomic H/C for the assigned molecular formulae.