From Retention Time to Functional Group Assignment: A Chemical Database-Driven Approach for High-Resolution Mass Data...

Area of Science:

• Marine organic chemistry
• Analytical chemistry
• Environmental science

Background:

• Marine dissolved organic matter (DOM) exhibits high chemodiversity, complicating the identification of individual components.
• Accurate determination of molecular formulas is crucial for inferring chemical structure features of DOM.

Purpose of the Study:

• To assess if empirically determined elution properties of stoichiometrically identical isomers from a chemical database can predict structural features of unknown DOM isomers.
• To correlate database-derived structural features with the retention time of DOM isomers.

Main Methods:

• Analysis of marine DOM (North Sea, Southern Ocean) using liquid chromatography-Fourier transform mass spectrometry (LC-FT-MS).
• Correlation of DOM isomer chromatographic retention with calculated properties of known isomers in PubChem, querying 7.7 million chemical identifiers for logP values.
• Assignment of structural features to logP bins to link database structures to DOM retention times.

Main Results:

• Predicted octanol-water partition coefficients (logP) for DOM isomers in Southern Ocean water agreed well with PubChem values.
• Differences in retention times between North Sea and Southern Ocean DOM isomers suggest variations in functional groups (fewer alcohols, more rings/esters in North Sea DOM).
• Early-eluting DOM formulas are enriched in rings and alcohols, while late-eluting ones are more linear/branched with more esters.

Conclusions:

• The hypothesis that older Southern Ocean DOM elutes earlier than younger North Sea DOM was supported.
• The developed strategy effectively predicts DOM isomer structures and circumvents fragmentation issues.
• Retention time is established as a novel physicochemical descriptor for DOM molecules.