Fig. 9 Bar graph plot of the composition of five peat humic acids (HAs), as obtained from direct-polarization magic-angle spinning (DPMAS) corrected by cross-polarization spin- lattice relaxation time-total sideband suppression (CP/T₁– TOSS). Bar graphs of the compositions calculated from six models of HA structures are also shown. The bars (from left to right) represent nine chemical-shift ranges (identified by numbers as defined in Table 2): 1 (ketone–quinone), 2 (quinone–carboxyl), 3 (phenol), 4–5 (aromatic), 6 (complex aromatic–anomeric), 7 (carbohydrate), 8 (ether–methyne), 9 (complex aliphatic), 10–11 (simple aliphatic)