2 research outputs found
Effect of residual vanadyl ions on the spectroscopic analysis of humic acids: a multivariate approach
6 pages, 3 figures, 2 tables, 29 references.In 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 (T1q
H) indicate that this suppression is due to an inefficient H-C cross
polarization, which is a consequence of a shortening of T1q
H. 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.The authors are grateful to the Fundacxa˜o de Amparo a` Pesquisa
do Estado de Sa˜o Paulo (FAPESP) and to the Irish Research
Council for Science, Engineering and Technology (IRCSET)
for post-doctoral support.Peer reviewe