Ion Evaporation From Gas-Phase Polyethylene Glycol Ions.

The spontaneous loss of charge (ion evaporation) from multiply charged gas-phase polyethylene glycol (PEG) ions (1.25 to ~5.25 kDa) is investigated with two ion mobility instruments placed in series with a heated reactor in between. Several purified PEG samples are electrosprayed into the gas phase from 10 mM ammonium acetate solutions in methanol. Globular PEG cations do not evaporate small ions even when heated to 100°C. Yet, they evaporate them at 20°C when charged beyond the point where part of the chain is linear and the rest forms a globule. The binding energy of ammonium to the globule is accordingly considerably larger than to the linear chain. Although naturally charged PEG anions are generally slightly charged and globular, they do evaporate single charges spontaneously, even at room temperature. Future work using this tandem ion mobility methodology will hopefully determine the binding energy of small anions and cations to the globular and the linear portion of PEG ions.