Method of Atmospheric Pressure Charge Stripping for Electrospray Ionization Mass Spectrometry and Its Application for the Analysis of Large Poly(Ethylene Glycol)s

We introduce a new atmospheric pressure charge stripping (AP-CS) method for the electrospray ionization mass spectrometry (ESI-MS) analysis of heterogeneous mixtures, utilizing ion/ion proton transfer reactions within an experimental ion source to remove excess charge from sample ions and thereby reduce spectral congestion. The new method enables the extent of charge stripping to be easily controlled, independent of primary ionization, and there are no complications due to adduct formation. Here, we demonstrate AP-CS with a Xevo G2-S Q-TOF from Waters-Micromass using an ion source originally designed for atmospheric pressure-electron capture dissociation (AP-ECD) experiments; repurposing the AP-ECD ion source for AP-CS requires only adding a supplemental reagent (e.g., a perfluorocompound) to scavenge the electrons and generate anions for the charge-stripping reactions. Results from model peptides are first presented to demonstrate the basic method, including differences between the AP-CS and AP-ECD operating modes, and how the extent of charge stripping may be controlled. This is followed by a demonstration of AP-CS for the ESI-MS analysis of several large poly(ethylene glycol)s (PEGs), up to 40 kDa, typical of those used in biopharmaceutical development.