Gas-phase proton-transfer chemistry coupled with TOF mass spectrometry and ion mobility-MS for the facile analysis of poly(ethylene glycols) and PEGylated polypeptide conjugates

Gas-phase ion/molecule chemistry has been combined with ion mobility separation and time-of-flight mass spectrometry to enable the characterization of large poly(ethylene glycol)s (PEGs) and PEGylated molecules (>40 kDa). A facile method is presented in which gas-phase superbases are reacted in the high-pressure source region of commercial TOF mass spectrometers to manipulate the charge states of large ions generated by electrospray ionization (ESI). Charge stripping decreases the spectral congestion typically observed in ESI mass spectra of high molecular weight polydisperse PEGylated molecules. From these data, accurate average molecular weights and molecular weight distributions for synthetic polymers and PEGylated proteins are determined. The average MW measured for PEGylated Granulocyte colony-stimulating factor (rh-GCSF, 40 726.2 Da) is in good agreement with the theoretical value, and a 16 Da mass shift is easily observed in the spectrum of an oxidized form of the heterogeneous PEGylated protein. Ion mobility separations can fractionate PEGs of different chain length; when coupled with charge stripping ion/molecule reactions, ion mobility mass spectrometry (IMMS) offers several analytical advantages over mass spectrometry alone for the characterization of large PEGylated molecules including enhanced dynamic range, increased sensitivity, and specificity. Low abundance free PEG in a PEGylated peptide preparation, which is not directly detectable by mass spectrometry, can be easily observed and accurately quantified with gas-phase ion/molecule chemistry combined with ion mobility mass spectrometry.