BOOK OF ABSTRACTS 25 IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 Monday, 24 August 2026 / Hall B+C Analysis and Characterization SL6 Fourier Transform Ion Cyclotron Resonance Mass Spectra of the Entire IHSS Standard and Reference Sample Collection E. Michael Perdue1, Mourad Harir2,3, Philippe Schmitt-Kopplin2,3 1 Georgia Institute of Technology, School of Earth and Atmospheric Sciences (Retired), 311 Ferst Drive, Atlanta, GA 30332-0340, USA, emperdue@comcast.net 2 Helmholtz Munich, Research Unit Analytical Biogeochemistry, Ingolstädter Landstraße 1, P.O. Box 1129, D-85758 Neuherberg, Germany 3 Technical University of Munich, Chair of Analytical Food Chemistry, Maximus-von-ImhofForum 2, 85354 Freising, Germany All available standard (19) and reference (15) samples of the International Humic Substances Society (IHSS) have been characterized by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS). The sample collection includes 15 fulvic acids (FA), 15 humic acids (HA), and four samples of natural organic matter (NOM). Ten samples were isolated from the Suwannee River (Georgia, USA). Ten samples were isolated from Elliott Soil (Illinois, USA). Five samples were isolated from Pahokee Peat (Florida, USA). One sample was isolated from Gascoyne Leonardite (North Dakota, USA). Eight samples were isolated from five sites in Antarctica (1), New Zealand (1), Norway (3), and the USA (3). Altogether, 15 samples were isolated from aquatic sources, and 19 samples were isolated from terrestrial sources. An FTICR-MS analysis of 33 of these IHSS samples was published recently [1]. Assuming that detected ions have charges of -1 or -2, mass lists of massto-charge (m/z) ratio and peak intensity were analyzed using CHOFIT3 software [2,3] to obtain all valid molecular formulae containing 0-3 N and 0-2 S, with a maximum allowed fitting error of 0.2 ppm. Possible formulae were ranked using several heuristic tools in CHOFIT3. The results that are presented here include only pairs of isotopologues (all C atoms are 12C in one formula and one of the C atoms is a 13C in the other formula). Furthermore, both formulae must have a heuristic rank of 1. Formulae meeting these criteria are referred to here as gold-standard formulae. Gold-standard formulae account for 9.6% of assigned formulae, and they account for 39.9% of assigned peak intensity. The majority of gold-standard formulae (85.5%) contain only C, H, and O (CHO formulae), with the remaining 14.5% also containing N and/or S (CHONS formulae). The average percentage of CHONS formulae is greater in samples from terrestrial sources (17.7%) than in samples from aquatic sources (10.5%).
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