The study introduces a novel approach to analyze marine dissolved organic matter (DOM) using direct injection, reversed-phase liquid chromatography coupled with ultrahigh resolution mass spectrometry (LC-FT-ICR MS). This method eliminates the need for solid-phase extraction (SPE), simplifying sample preparation and avoiding fractionation. The technique effectively separates salt and DOM using a large chromatographic column and an extended isocratic aqueous step, followed by post-column dilution with buffer-free solvents and a counter gradient to reduce salt buildup in the ion source. This setup allows for excellent repeatability and robustness against the salt matrix. Over 5,500 unique molecular formulas were detected from 5.5 nmol carbon in 100 μL of filtered Arctic Ocean seawater, demonstrating a highly linear detector response for variable sample carbon concentrations. Compared to SPE-extracted DOM, the direct injection method showed superior sensitivity for heteroatom-containing DOM. The method's small volume requirement supports studies with minimal sample volumes, such as in marine sediment pore water, ice cores, or permafrost soil solutions, and enhances spatial or temporal resolution. Chromatographic separation adds chemical information to molecular formulas, enhancing our understanding of marine biogeochemistry, chemodiversity, and ecological processes.The study introduces a novel approach to analyze marine dissolved organic matter (DOM) using direct injection, reversed-phase liquid chromatography coupled with ultrahigh resolution mass spectrometry (LC-FT-ICR MS). This method eliminates the need for solid-phase extraction (SPE), simplifying sample preparation and avoiding fractionation. The technique effectively separates salt and DOM using a large chromatographic column and an extended isocratic aqueous step, followed by post-column dilution with buffer-free solvents and a counter gradient to reduce salt buildup in the ion source. This setup allows for excellent repeatability and robustness against the salt matrix. Over 5,500 unique molecular formulas were detected from 5.5 nmol carbon in 100 μL of filtered Arctic Ocean seawater, demonstrating a highly linear detector response for variable sample carbon concentrations. Compared to SPE-extracted DOM, the direct injection method showed superior sensitivity for heteroatom-containing DOM. The method's small volume requirement supports studies with minimal sample volumes, such as in marine sediment pore water, ice cores, or permafrost soil solutions, and enhances spatial or temporal resolution. Chromatographic separation adds chemical information to molecular formulas, enhancing our understanding of marine biogeochemistry, chemodiversity, and ecological processes.