IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 BOOK OF ABSTRACTS 180 Poster Session / Analysis and Characterization Hall A P1.2 Multiple Formula Assignments in Ultra-High Resolution Mass Spectra Detected in Samples from Nitrogen and Sulfur Rich Environments Peter Herzsprung1, Wolf von Tümpling2, Norbert Kamjunke2, Oliver Lechtenfeld3, Shuxian Gao3 1 UFZ – Helmholtz Centre for Environmental Research, Dep. Lake Research, Brückstraße 3a, Magdeburg 39114, Germany, peter.herzsprung@ufz.de 2 UFZ – Helmholtz Centre for Environ. Research, Dep. River Ecology, Brückstraße 3a, Magdeburg 39114, Germany 3 UFZ – Helmholtz Centre for Environ. Research, Dep. Environ. Anal. Chem., Permoserstr. 15, Leipzig 04318, Germany Ultrahigh resolution mass spectrometry analysis of organic matter (OM) in samples which contain components with high numbers of non-oxygen hetero-atoms, e.g. nitrogen and sulfur, is challenging with respect to multiple formula assignment (MultiAs). Several replacement pairs specific to the number of nitrogen and / or sulfur had been reported which led to MultiAs with extreme low mass differences (∆m). The replacement of 5 N, 2 S and 3 H by one 13C, 5 12C, and 4 O atoms (∆m = 0.027 mDa) was already addressed in 2015 [1]. The 13C1 isotopologues were shown to be the more reliable MFs, rendering MF with multiple non-oxygen heteroatoms implausible [1,2]. Similarly, the replacement of 2 N, 3 S and 8 H by 7 C and 3 O, the CHO components were evidenced to be more reliable compared to the corresponding N2S3 components [2]. While the replacement pairs with low ∆m among MultiAs with few nitrogen / sulfur atoms were well investigated for real DOM samples [2,3], those MultiAs with replacements of sulfur atoms by nitrogen atoms were reported earlier [1] but their reliability was not fully addressed. To overcome this research gap, the water extractable organic matter in sediment samples from a fish pond has been analyzed by Fourier-transform ion cyclotron resonance mass spectroscopy coupled with liquid chromatography [4]. For molecular formula assignments, detected mass peaks were assigned for the mass range 150 – 1000 Da with an error threshold of 1 ppm using inhouse software. Up to 8 14N and 3 32S were allowed during molecular formula assignment, along with up to 122 H, 40 O, 60 12C, 1 13C and 1 34S. The resulting data set involved most MultiAs from replacement of one S, 8 C and 4 H by 6 N and 3 O (denoted as N6/S1) with ∆m of 0.182 mDa, and showed major relevance on evaluation of reliability of components. The second prevalent MultiAs (∆m = 0.469 mDa) was found by replacement of 2 S and 8 H by 4 N and 1 O (denoted as N4/S2). A
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