Characterisation of a newly available marine dissolved organic matter reference material (TRM-0522)

Recent methodological advances have greatly increased our ability to characterise aquatic dissolved organic matter (DOM) using high resolution instrumentation, including nuclear magnetic resonance (NMR) and mass spectrometry (HRMS). Reliable DOM reference materials are required for further method development and dataset alignment, but do not currently exist for the marine environment. This presents a major limitation for marine biogeochemistry and related fields, including natural product discovery. To fill this resource gap, we have prepared a marine DOM reference material (TRM-0522) from 45 m deep coastal seawater obtained ~ 1 km offshore of Sweden’s west coast. Over 3000 molecular formulas were assigned by direct infusion HRMS, confirming sample diversity, and the distribution of formulas in van Krevelen space was typical for a marine sample, with the majority of formulas in the region H/C 1-1.5 and O/C 0.3-0.7. The extracted DOM pool was more nitrogen (N) and sulfur (S) rich than a typical terrestrial reference material (SRFA). MZmine3 processing of UPLC-HRMS/MS data revealed 494 resolvable features (233 in negative mode; 261 in positive mode) over a wide range of retention times and masses. NMR data indicated low contributions of the aromatic protons, and generally speaking lignin, humic, and fulvic substances associated with terrestrial samples. Instead, carboxylic-rich aliphatic molecules (CRAM) were the most abundant components, followed by carbohydrates and aliphatic functionalities. This is consistent with a very low specific UV absorbance SUVA254 value of 1.36 L mg C-1 m-1. When combined with comparisons with existing terrestrial reference materials (SRFA and PLFA), these results suggest that TRM-0522 is a useful and otherwise unavailable reference material for use in marine DOM biogeochemistry.