Comprehensive structure-selective characterization of dissolved organic matter by reducing molecular complexity and...

Area of Science:

• Environmental Chemistry
• Organic Geochemistry
• Analytical Chemistry

Background:

• Understanding dissolved organic matter (DOM) is crucial for global element cycles and ecosystem services.
• Current methods for DOM characterization face challenges due to its molecular complexity.

Purpose of the Study:

• To develop a comprehensive characterization method for DOM using polarity-based stepwise solid phase extraction (SPE).
• To reduce molecular complexity and improve resolution for structural analysis of DOM.
• To investigate the fractionation of Suwannee River DOM (SR DOM) and its molecular properties.

Main Methods:

• Employed a stepwise solid phase extraction (SPE) with single methanol elution for DOM fractionation.
• Utilized optical spectroscopy (UV-Vis, fluorescence), high-field Fourier transform ion cyclotron mass spectrometry (FTICR-MS), and nuclear magnetic resonance (NMR) spectroscopy for characterization.
• Analyzed five distinct SPE fractions of SR DOM, achieving 91% DOC recovery.

Main Results:

• The SPE method successfully fractionated SR DOM into five distinct groups, showing hierarchical clustering across analytical techniques.
• Two abundant, moderately hydrophobic fractions contained most compounds, including aliphatics, alicyclic molecules, carbohydrates, and aromatics.
• Hydrophilic and hydrophobic fractions exhibited distinct molecular characteristics, with fractionation governed by O/C ratio, molecular weight, and aromaticity.

Conclusions:

• The polarity-based SPE approach provides robust and versatile fractionation for comprehensive DOM characterization.
• This method enhances molecular resolution, facilitating a deeper understanding of DOM's role in biogeochemical processes.
• The approach is scalable for field applications and adaptable to various DOM sources and SPE conditions.