Comparative evaluation of positive and negative LC-MS modes for DOM profiling

Area of Science:

• Marine biogeochemistry
• Analytical chemistry
• Organic geochemistry

Background:

• Dissolved organic matter (DOM) is vital for marine nutrient cycling and carbon storage.
• Traditional DOM analysis uses negative electrospray ionization (ESI-), but positive electrospray ionization (ESI+) is emerging.
• Limited comparative studies exist on ESI+ versus ESI- for DOM profiling.

Purpose of the Study:

• To compare DOM profiling using ESI+ and ESI- mass spectrometry.
• To investigate DOM characteristics in the Sansha Yongle Blue Hole (SYBH).
• To assess the impact of ionization mode on DOM characterization.

Main Methods:

• High-performance liquid chromatography-Orbitrap-mass spectrometry/mass spectrometry (HPLC-Orbitrap-MS/MS).
• Analysis of DOM from the Sansha Yongle Blue Hole (SYBH).
• Dual-mode ionization: ESI+ and ESI-.

Main Results:

• ESI+ detected a broader spectrum of DOM ions, including nitrogen-rich compounds (CHN, CHON, CHONS).
• ESI- excelled in identifying sulfur-rich compounds (CHOS), particularly in anoxic zones.
• Both modes identified similar carbohydrates, CRAM, and UA; ESI+ detected more HU, peptides, and polyphenols.

Conclusions:

• Using a single ionization mode (ESI+ or ESI-) can bias DOM interpretation.
• Multi-mode ionization is recommended for comprehensive DOM profiling in marine environments.
• Ionization mode significantly influences the detection of specific DOM classes and molecular parameters.