Use of the EPR technique to determine thermal stability of some humified organic substances found in soil organic-mineral fractions

Abstract

In this work, using the EPR spectroscopy, we analysed the thermal stability of some organic-mineral compounds found in a Gleysoil from Rio Janeiro. It was observed a complete disappearance of the EPR signal around 600°C for the ≤ 2 μm fraction and a residual EPR signal of semiquinone free radical for the 2-20 μm and 20-53 pm fractions at the same temperature. Also, the experiments showed that the 2-20 μm fraction had a larger concentration of semiquinone free radical per g of carbon and a smaller line width indicated a larger humification of this fraction. This is an evidence that the soil organic matter of this fraction (2-20 μm) is more stable than the other ones.