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Dissolved organic matter (DOM) is a master variable in aquatic systems. Modern fluorescence techniques couple measurements of excitation emission matrix (EEM) spectra and parallel factor analysis (PARAFAC) to determine fluorescent DOM (FDOM) components and DOM quality. However, the molecular signatures associated with PARAFAC components are poorly defined. In the current study we characterized river water samples from boreal Québec, Canada, using EEM/PARAFAC analysis and ultrahigh resolution mass spectrometry (FTICR-MS). Spearman’s correlation of FTICR-MS peak and PARAFAC component relative intensities determined the molecular families associated with 6 PARAFAC components. Molecular families associated with PARAFAC components numbered from 39 to 572 FTICR-MS derived elemental formulas. Detailed molecular properties for each of the classical humic- and protein …