Investigation on the binary ionization choices for large conjugated amines during electrospray ionization

Area of Science:

• Analytical Chemistry
• Mass Spectrometry
• Electrochemistry

Background:

• Amines typically form protonated cations ([M+H]+) in positive electrospray ionization (ESI).
• Large conjugated amines (LCAs) demonstrate a unique binary ionization behavior, producing either radical cations (M•+) or protonated cations ([M+H]+).
• Understanding the mechanism of this dual ionization is crucial for advancing ESI techniques.

Purpose of the Study:

• To investigate the binary ionization mechanism of large conjugated amines (LCAs) during electrospray ionization (ESI).
• To identify internal and external factors influencing the formation of radical cations (M•+) and protonated cations ([M+H]+).
• To elucidate the independent pathways for M•+ and [M+H]+ generation in LCAs.

Main Methods:

• Systematic investigation of LCAs' binary ionization behavior.
• Analysis of internal factors: functional groups and conjugated system size.
• Evaluation of external factors: solvent type, flow rate, and electrode position.

Main Results:

• Electron-donating groups and larger conjugated systems in LCAs favor M•+ formation.
• Aprotic solvents, higher flow rates, and shorter electrode-spray distances promote M•+ generation.
• These conditions concurrently hinder the formation of [M+H]+.

Conclusions:

• The formation of M•+ and [M+H]+ in LCAs are independent processes.
• M•+ cations originate from electrochemical oxidation on the electrode surface.
• [M+H]+ cations are generated through the conventional ESI pathway.
• External factors offer effective modulation of LCA ionization outcomes.