Ion Evaporation From Gas-Phase Polyethylene Glycol Ions

Area of Science:

• Analytical Chemistry
• Physical Chemistry
• Polymer Science

Background:

• Multiply charged gas-phase ions, such as polyethylene glycol (PEG), can undergo spontaneous charge loss, a process known as ion evaporation.
• Understanding ion evaporation is crucial for mass spectrometry and ion mobility spectrometry applications.

Purpose of the Study:

• To investigate the spontaneous loss of charge (ion evaporation) from multiply charged gas-phase polyethylene glycol (PEG) ions.
• To determine the influence of ion structure (globular vs. linear chain segments) and temperature on ion evaporation.

Main Methods:

• Utilized two ion mobility instruments in series with a heated reactor.
• Electrosprayed purified PEG samples from ammonium acetate solutions in methanol into the gas phase.
• Analyzed ion evaporation from PEG ions across a mass range of 1.25 to ~5.25 kDa.

Main Results:

• Globular PEG cations did not evaporate ions even at 100°C.
• PEG cations evaporated ions at 20°C when the charge distribution led to both linear and globular chain segments.
• Naturally charged PEG anions, typically globular, spontaneously evaporated single charges even at room temperature.
• The binding energy of ammonium to globular PEG was significantly higher than to linear PEG segments.

Conclusions:

• Ion evaporation from PEG ions is strongly dependent on the ion's conformation and charge distribution.
• Temperature plays a role, but ion structure is a primary factor in spontaneous charge loss.
• Future research will focus on determining binding energies of various ions to different PEG conformations using tandem ion mobility.