Estuarine/marine UDOM as characterized by size-exclusion chromatography and organic mass spectrometry

High performance size-exclusion chromatography (HPSEC) and direct temperature-resolved mass spectrometry (DT-MS) were used to explore molecular weight distributions and molecular level characteristics within marine/estuarine ultrafiltered dissolved organic matter (UDOM, >1 kDa) collected from the lower Chesapeake Bay, USA and the Oosterschelde estuary, The Netherlands. Initial HPSEC characterization indicates that the overall size distribution is similar in all the UDOM samples; however, there are distinct variations among the samples, especially in the low molecular weight region. As a preliminary study of molecular level variations with apparent molecular size, the Oosterschelde UDOM sample was separated into molecular weight fractions using HPSEC. These fractions were then analyzed by DT-MS. The size fractions within the UDOM sample yielded distinctly different mass spectra; the larger size classes were enriched in aminosugars, deoxysugars, and methylated sugars while the smaller size classes were enriched in hexose sugars. There is also evidence that hexose sugars appear in at least two structures with highly different molecular weights and potentially highly different source and sink functions within the marine water column.