High-resolution mass spectrometry (HRMS) combined with electrospray ionization (ESI) has been the most useful technique for molecular characterization of dissolved organic matter (DOM) derived from diverse sources. However, the comprehensive detection of DOM composition was hindered by ionization suppression observed in ESI sources. The HRMS couple with liquid chromatography (LC) is a potential tool for comprehensive molecular characterization of DOM. The Suwannee River fulvic acids (SRFA) and two DOM form a seawater and a refinery wastewater extracted by solid phase extraction (SPE) were analyzed by LC-Orbitrap MS coupled with ESI. The mobile phases, solvents composition and gradient in the LC-Orbitrap MS analysis were optimized. The number of detected molecular formulae of SRFA by online LC-Orbitrap MS was significantly increased by approximately 40% compared to direct injection. These additional detected compounds are mainly composed of protein and lignin-like compounds, with a low O/C ratio and high H/C ratio. For SRFA, the relative standard deviation (%) of reproducibility are 5.51, 2.33, 7.97, and 1.80 for average O/C, H/C, DBE, and AI_mod, respectively. This study proposed a simple and rapid method based on LC-Orbitrap MS for an in-depth analysis of molecular composition of DOM, achieving a remarkable analysis time of only five minutes per sample. The rapid method provides a dependable and efficient approach for the molecular characterization of DOM, thereby advancing our comprehension and investigation of DOM across diverse ecosystems.
 

LC-Orbitrap MS,Dissolved Organic Matter,Rapid analysis,Molecular composition