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Abstract Marine dissolved organic carbon and nitrogen (DOC and DON) are major global carbon and nutrient reservoirs, and their characterization relies on extraction methods for preconcentration and salt removal. Existing methods optimize for capturing and describing DOC. Here, we report an optimized analytical strategy to recover marine DON for subsequent molecular characterization. Retention efficiencies between 5% and 95% are reported for seven solid phase extraction (SPE) sorbents, with PPL recovering 23% of marine DON compared to 95% recovered with C18. Additional comparisons of the effect of varying sample volumes and elution speed, and the resulting molecular composition of DON extracts, were investigated using C18and PPL sorbents. Sample volumes > 200 mL decreased DON retention efficiency independent of SPE sorbent, and gravity elution recovered 1.7‐ to 4.2‐fold more DON compared to vacuum elution. Characterization of extracted DON by negative‐ion electrospray ionization Fourier transform‐ion cyclotron resonance mass spectrometry (FT‐ICR MS) highlights compositional differences between DON species recovered by each method. DON isolated with optimized methods includes low molecular weight (< 600 Da) peptide‐like compounds with low O:C ratios (0.2 to 0.5) that are not detected by other SPE sorbents (e.g., PPL). The majority of additional DON isolated with this approach was undetectable by direct infusion negative mode FT‐ICR MS analysis.
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This content will become publicly available on September 1, 2026
Unsaturated aliphatic and sulfur-containing organic matter as surfactants in the surface microlayer
The surface microlayer (SML) is a 10s–100s μm thick layer which mediates fluxes across the air-sea interface. Organic matter (OM) enrichments at the SML are known to influence SML physical properties and air-sea exchanges, but the role of detailed molecular level OM composition in influencing those processes hasn’t been fully explored. SML and subsurface (SUB, 8–15 cm) water at four stations encompassing different influences (marine/ fluvial/salt marsh) on the Delaware Bay system were sampled and examined for relationships between SML/SUB OM composition and surface tension. Samples collected December 2018–October 2019 show SML dissolved organic carbon (DOC) enrichments of 0.87 to 4.42 times the SUB concentration. Excitation-emission matrix spectroscopy (EEMs) and negative electrospray ionization (-ESI) Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) show marine samples have higher contributions from photobleached material and higher relative abundances of CHON compounds relative to inner bay sites, respectively. Principal component analyses further reveal consistent differences in SML OM composition relative to SUB. The SML contains higher abundances of compounds with H/C > 1.7 and O/C < 0.2, including sulfur-containing compounds - compositions suggestive of surfactant-like molecules, able to depress surface tension at the air-sea interface. Surface tension depressions were significantly correlated with unsaturated aliphatic and sulfur-containing compounds identified from FT-ICR MS data, yet showed no relationship with DOC abundances or enrichments, highlighting the need for compositional assessments for understanding OM influences on SML properties and air-sea exchanges. The sources and structures of SML surfactant molecules should be a focus of future work.
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- Award ID(s):
- 2123402
- PAR ID:
- 10638320
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Marine Chemistry
- Volume:
- 272
- Issue:
- C
- ISSN:
- 0304-4203
- Page Range / eLocation ID:
- 104547
- Subject(s) / Keyword(s):
- surfactants organic matter surface microlayer FTICR MS
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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