OLIGOMER CHARACTERIZATION OF 4-23 KDA POLYMERS BY ELECTROSPRAY FOURIER-TRANSFORM MASS-SPECTROMETRY

Poly(ethylene glycol)s of 4.3, 13, and 23 kDa give mass spectra contai ning resolved isotopic peaks representing the individual oligomers in each sample. Approximately 5000 isotopic peaks of 47 oligomers in 10 c harge states are identified in the 23 kDa spectrum, as well as <0.02%- CH2CH(CH3O- monomer units in the 13 kDa spectrum. As an unexpected adv antage of electrospray ionization (ESI), the degree of mass discrimina tion is much less than that of mass/charge discrimination due to avera ging of the values from different charge states. For the determination of molecular weight distributions, geometric and entropy deconvolutio n methods yield unacceptable artifact peaks and abundance discriminati on, respectively; combining their deconvolution attributes with isotop ic peak restrictions for the 4.3 kDa polymer yields a distribution sim ilar to that from human data reduction, which is consistent with that from GPC separation. ESI/FTMS spectra of polymers can be measured in m inutes and provide far more detailed mass information than that from s uch conventional techniques.