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Table 2 Acidic groups’ concentration and distribution of C intensity of 13 C NMR spectra of humic fractions

From: Chemical and spectroscopic characterization of insoluble and soluble humic acid fractions at different pH values

Fraction Acidic groupsa(meq g−1) 13C NMR distribution (%) HB/HI
  Carboxyl Phenol Total acidity 0 to 45 ppm 45 to 95 ppm 95 to 160 ppm 160 to 195 ppm  
pH 1 Insoluble 3.8 7.3 11.1 23.0 16.0 33.1 28.0 1.3
Soluble 4.0 6.7 10.7 14.2 58.8 2.9 24.2 0.2
pH 3 Insoluble 3.1 5.9 8.9 21.0 18.3 33.9 26.9 1.2
Soluble 2.8 6.7 9.4 14.5 42.1 7.5 35.9 0.3
pH 5 Insoluble ndb ndb   ndc ndc ndc ndc -
Soluble ndb ndb   20.8 6.0 38.7 34.5 1.5
pH 7 Insoluble ndb ndb   ndc ndc ndc ndc -
Soluble ndb ndb   19.1 1.3 35.2 44.3 1.2
  1. aValues are the means of three replicates. The standard error values are < 10%; banalytical method not applicable at these pH; cnot determinable because of the poor signal-to-noise ratio of the spectra.