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Fourier transform ion cyclotron resonance mass spectrometric analysis of the green fraction of soil humic acids
Author(s) -
Ikeya Kosuke,
Sleighter Rachel L.,
Hatcher Patrick G.,
Watanabe Akira
Publication year - 2013
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.6718
Subject(s) - chemistry , fourier transform ion cyclotron resonance , ion cyclotron resonance , mass spectrometry , fourier transform , analytical chemistry (journal) , ion , cyclotron , environmental chemistry , chromatography , organic chemistry , physics , quantum mechanics
RATIONALE The green fraction of soil humic acids (HAs), designated Pg, contains 4,9‐dihydroxyperylene‐3,10‐quinone (DHPQ) as a chromophore. Although various naturally occurring DHPQ derivatives are known to occur and Pg‐like absorption is observed in the UV‐visible spectra of HAs from various types of soils worldwide, the chemical structure of Pg is still unknown. METHODS For a better understanding of the chemical composition of Pg, the pre‐isolated (crude Pg) and purified Pg (G2) samples and three soil HAs with different degrees of humification were analyzed using negative‐mode electrospray ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS) at 12 Tesla. The Pg samples were characterized using H/C–O/C ratios and based on the type and magnitude of the molecular formulae having DHPQ or related compounds as a potential structure. RESULTS The H/C–O/C diagram indicated that most of the lipids, proteins, other aliphatics, and lignin‐like components were removed, while condensed aromatic components were concentrated during the purification process of crude Pg to G2 using Sephadex G‐50. More than 27 molecular formulae resembling DHPQ, DHPQ substituted with varying numbers of carboxyl and/or hydroxyl groups, and phenyl‐DHPQ derivatives were identified in both Pg samples. The peak magnitudes of these formulae in G2 (accounting for 40% of the total assigned magnitude) were greater than that in the crude Pg (21%). Most of the 27 molecular formulae were also detected in the three soil HAs, suggesting a common existence of Pg‐related compounds in various soil HAs. CONCLUSIONS The important molecular formulae of Pg components were estimated utilizing FTICRMS. Copyright © 2013 John Wiley & Sons, Ltd.