01701naa a2200205 a 450000100080000000500110000800800410001902400580006010000190011824501300013726000090026752010080027665300210128465300300130570000160133570000200135170000220137170000200139377300820141313397402021-10-27       2008    bl uuuu     u00u1 u    #d7 ahttps://doi.org/10.1111/j.1365-2389.2007.00983.x2DOI1 aNOVOTNY, E. H.  aEffect of residual vanadyl ions on the spectroscopic analysis of humic acidsba multivariate approach.h[electronic resource]  c2008  aIn a study of the vanadyl (VO2þ)-humic acids system, the residual vanadyl ion suppressed fluorescence and specific electron paramagnetic resonance (EPR) and NMR signals. In the case of NMR, the proton rotating frame relaxation times (T1qH) indicate that this suppression is due to an inefficient H-C cross polarization, which is a consequence of a shortening of T1qH. Principal components analysis (PCA) facilitated the isolation of the effect of the VO2þ ion and indicated that the organic free radical signal was due to at least two paramagnetic centres and that the VO2þ ion preferentially suppressed the species whose electronic density is delocalized over O atoms (greater g-factor). additionally, the newly obtained variables (principal components ? PC) indicated that, as the result of the more intense tillage a relative increase occurred in the accumulation of: (i) recalcitrant structures; (ii) lignin and long-chain alkyl structures; and (iii) organic free radicals with smaller g-factors.  aÁcidos húmicos  aAnálise espectroscópica1 aKNICKER, H.1 aMARTIN NETO, L.1 aAZEREDO, R. B. V.1 aHAYES, M. H. B.  tEuropean Journal of Soil Science, Oxfordgv. 59, n. 3, p. 439-444, Jun. 2008.