Oligosaccharide analysis using anion attachment in negative mode electrospray mass spectrometry

Area of Science:

• Analytical Chemistry
• Mass Spectrometry
• Carbohydrate Chemistry

Background:

• Neutral oligosaccharides present challenges in mass spectrometry due to low deprotonation tendencies.
• Electrospray ionization (ESI) in negative ion mode is crucial for analyzing such compounds.
• Anion adduct formation can significantly improve analyte detection and structural elucidation.

Purpose of the Study:

• To investigate the formation and utility of various anionic adducts with neutral oligosaccharides.
• To assess the impact of different anions on the abundance and fragmentation patterns of oligosaccharide ions.
• To explore the application of these adducts in structural determination and simultaneous analysis of acidic and neutral carbohydrates.

Main Methods:

• Negative ion mode electrospray mass spectrometry (ESI-MS) was used to form anionic adducts.
• Tandem mass spectrometry (ESI-MS/MS) with collision-induced dissociation (CID) was employed for fragmentation analysis.
• Density functional theory (DFT) calculations were used to model the structures of chloride adducts.

Main Results:

• Fluoride (F-) and acetate (Ac-) anions significantly enhanced the abundance of deprotonated neutral oligosaccharides ([M - H](-)) via adduct decomposition.
• Chloride (Cl-) adducts exhibited high stability and consistently appeared in greater abundance than [M - H](-).
• CID of F(-) and Ac(-) adducts yielded analyte-specific product ions, while Cl(-) adducts produced both Cl(-) and analyte ions, facilitating structural analysis and anomeric configuration differentiation.

Conclusions:

• Anion adduct formation, particularly with F(-), Ac(-), and Cl(-), is a powerful strategy for improving the detection and structural analysis of neutral oligosaccharides.
• The decomposition pathways of F(-) and Ac(-) adducts provide structural information without anion interference.
• Chloride adducts offer a stable platform for oligosaccharide analysis and are particularly useful for distinguishing disaccharide anomeric configurations, supported by DFT structural insights.