DOM is one of the most complex natural mixtures and thus poses the greatest challenges to chemical characterization using instrumental analytics. The characterization of marine DOM is further complicated by the fact that the salt concentration in the ocean exceeds the DOM concentration by a factor of 35,000. At the same time, the low DOM concentrations challenge the analytical sensitivity. To improve sensitivity and robustness, solid-phase extraction (SPE) is often used for DOM desalting and enrichment. However, SPE is not quantitative leaving more than half of the DOM analytically undetectable. The chemical composition of the extracts obtained is strongly influenced by the type and loading of the adsorbent. Here we present a new method for characterizing DOM that allows direct injection of seawater samples with native salt and DOC concentrations. The method uses reversed-phase chromatography in combination with Fourier transform ion cyclotron resonance mass spectrometry (LC-FT-ICR MS). It allows effective salt separation and highly sensitive detection of organic compounds in as little as 100 µL of seawater. We determined analytical metrics such as reproducibility, robustness, sensitivity, and linear detection range. The method was tested with DOM samples of different carbon and salt concentrations and applied to samples from the central Arctic Ocean with DOC concentrations as low as 20 µmol / L. In addition to a quantitative DOC response, liquid chromatographic separation opens an analytical window that supports separation of structural isomers based on polarity.

Primary Presenter: Boris Koch, Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung (boris.koch@awi.de)

Authors:

Boris Koch, Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung  (boris.koch@awi.de)

Jan Kaesler, Helmholtz Centre for Environmental Research  (jan.kaesler@ufz.de)

Elaine Jennings, Helmholtz Centre for Environmental Research  (elaine.jennings@ufz.de)

Oliver Lechtenfeld, Helmholtz Centre for Environmental Research  (oliver.lechtenfeld@ufz.de)