Molecular Signatures of Humic Acids from Different Sources as Revealed by Ultrahigh Resolution Mass Spectrometry

Figure 1

Van Krevelen diagrams from the mass spectra of (a) humic acids from Jiufeng forest soil, (b) humic acids from Suwannee River, and (c) humic acids from leonardite. The shades of color represent the peak magnitudes of the molecules. Broken lines divide the pattern into 7 areas which indicate major biomolecular compound classes: (1) polycyclic aromatics (PCAs, AI-mod > 0.66), (2) highly aromatic compounds (0.66 ≥ AI-mod > 0.50), (3) highly unsaturated compounds (AI-mod ≤ 0.50 and H/C < 1.5), (4) unsaturated aliphatic compounds (2.0 > H/C ≥ 1.5 and N = 0), (5) unsaturated aliphatic compounds containing N (2.0 > H/C ≥ 1.5 and N > 0), (6) carbohydrates (H/C ≥ 2.0 and O/C ≥ 0.9), and (7) fatty acids and sulfonic acids (H/C ≥ 2.0 and O/C < 0.9). Nor_int is the normalization of the intensity of each molecule.

(a)

(b)

(c)