01221naa a2200169 a 450000100080000000500110000800800410001910000160006024501370007626000090021352006880022265300200091065300310093065300200096170000200098177300500100110288852005-03-28       2003    bl ---       0--  u    #d1 aSAAB, S. C.  aUse of the EPR technique to determine thermal stability of some humified organic substances found in soil organic-mineral fractions.  c2003  aIn 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 &lt 2 µm fraction and a residual EPR signal of semiquinone free radical for the 2-20 µm and 20-53 µm 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.  aEstabilização  aMatéria orgânica do solo  aRadicais livres1 aMARTIN-NETO, L.  tQuímica Novagv. 26, n. 4. p. 497-498, 2003.