A direct injection method using reversed-phase liquid chromatography (RPLC) coupled with Fourier transform ion cyclotron resonance mass spectrometry (LC-FT-ICR MS) was developed for the analysis of marine dissolved organic matter (DOM) without the need for solid-phase extraction (SPE). This method enables the direct analysis of seawater samples at native salt and DOM concentrations, overcoming the challenges posed by the high salt content in seawater. The method involves an extended isocratic aqueous step and a post-column counter gradient to reduce salt buildup in the ion source, resulting in excellent repeatability and sensitivity. Over 5,500 unique molecular formulas were detected from just 5.5 nmol of carbon in 100 µL of filtered Arctic Ocean seawater. The method demonstrated a highly linear detector response and robustness against the salt matrix, with superior sensitivity for heteroatom-containing DOM compared to SPE methods. The direct analysis of seawater offers fast and simple sample preparation and avoids fractionation introduced by extraction. The method facilitates studies in environments where only minimal sample volume is available, such as marine sediment pore water, ice cores, or permafrost soil solution. The small volume requirement also supports higher spatial or temporal sample resolution. Chromatographic separation adds further chemical information to molecular formulas, enhancing our understanding of marine biogeochemistry, chemodiversity, and ecological processes. The method was tested with DOM samples from the Central Arctic Ocean and peat pore water, showing comparable results to SPE extracts. The method provides a less biased view of marine DOM composition and allows better comparability with other approaches using original water samples. The results indicate that the method can better study the biogeochemical dynamics of marine DOM, including the long-term stability of marine organic matter and the fate of terrestrial organic matter in the ocean. The method also supports the development of novel biomarkers for environmental studies.A direct injection method using reversed-phase liquid chromatography (RPLC) coupled with Fourier transform ion cyclotron resonance mass spectrometry (LC-FT-ICR MS) was developed for the analysis of marine dissolved organic matter (DOM) without the need for solid-phase extraction (SPE). This method enables the direct analysis of seawater samples at native salt and DOM concentrations, overcoming the challenges posed by the high salt content in seawater. The method involves an extended isocratic aqueous step and a post-column counter gradient to reduce salt buildup in the ion source, resulting in excellent repeatability and sensitivity. Over 5,500 unique molecular formulas were detected from just 5.5 nmol of carbon in 100 µL of filtered Arctic Ocean seawater. The method demonstrated a highly linear detector response and robustness against the salt matrix, with superior sensitivity for heteroatom-containing DOM compared to SPE methods. The direct analysis of seawater offers fast and simple sample preparation and avoids fractionation introduced by extraction. The method facilitates studies in environments where only minimal sample volume is available, such as marine sediment pore water, ice cores, or permafrost soil solution. The small volume requirement also supports higher spatial or temporal sample resolution. Chromatographic separation adds further chemical information to molecular formulas, enhancing our understanding of marine biogeochemistry, chemodiversity, and ecological processes. The method was tested with DOM samples from the Central Arctic Ocean and peat pore water, showing comparable results to SPE extracts. The method provides a less biased view of marine DOM composition and allows better comparability with other approaches using original water samples. The results indicate that the method can better study the biogeochemical dynamics of marine DOM, including the long-term stability of marine organic matter and the fate of terrestrial organic matter in the ocean. The method also supports the development of novel biomarkers for environmental studies.