Structure, Anion, and Solvent Effects on Cation Response in ESI-MS

Area of Science:

• Analytical Chemistry
• Mass Spectrometry

Background:

• Ion abundance in electrospray ionization mass spectrometry (ESI-MS) is influenced by numerous factors beyond simple solution concentration.
• Permanently charged ions, such as ammonium and phosphonium, are still affected by cation structure, molecular weight, solvent, and anion identity.

Purpose of the Study:

• To investigate the impact of various factors on ion abundance in ESI-MS for permanently charged analytes.
• To identify key parameters that influence ion response and provide predictive insights.

Main Methods:

• Systematic screening of diverse cation-anion and solvent combinations.
• Analysis of ion abundance variations under different experimental conditions.

Main Results:

• Rigid cations and anions conferring high conductivity generally resulted in the highest ion responses.
• Acetonitrile best reflected actual solution composition, whereas methanol, acetonitrile/water, and dichloromethane showed greater ion discrimination.
• Functional groups with high solvent affinity tended to decrease ion response.

Conclusions:

• Cation structure, anion identity, and solvent choice are critical determinants of ion abundance in ESI-MS.
• Understanding these factors allows for better prediction of ion response, especially for reactive analytes.
• Optimizing solvent and ion pairing can improve analytical accuracy in mass spectrometry.