Electron spin resonance studies under dynamic mobile phase conditions on chemically modified silica

Area of Science:

• Analytical Chemistry
• Materials Science

Background:

• Bonded silica phases are crucial in chromatography.
• Understanding their behavior under dynamic solvent flow is essential for optimizing separations.

Purpose of the Study:

• To investigate the microscopic structure and solvation of bonded silica phases using electron-spin resonance (ESR) techniques.
• To examine the effects of dynamic solvent flow on the bonded phase configuration and dynamics.

Main Methods:

• Utilized ESR spin labeling with DOXYL hexyl siloxane to study bonded phase motional freedom.
• Employed ESR spin probing with TEMPO derivatives in various water-methanol mobile phases.
• Analyzed ESR spectra to infer solvation composition, phase configuration, and solvent-flow effects.

Main Results:

• ESR spectra indicated changes in bonded surface motional freedom correlated with mobile phase composition and elution time.
• Observed chain stiffening of the bonded phase upon introduction of water.
• Probes provided insights into the solvated surface environment influenced by mobile phase composition and probe polarity.

Conclusions:

• ESR spin labeling and probing are powerful tools for characterizing bonded silica phases under chromatographic conditions.
• Dynamic solvent flow significantly impacts the microscopic structure and solvation of bonded phases.
• These findings aid in understanding and optimizing chromatographic separations based on bonded silica stationary phases.