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Eur. J. Mass Spectrom. 7, 279 - 291 (2001) |
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Gas chromatography/mass spectrometry of polyethylene glycol oligomers | ||
Adebayo Onigbinde, Gordon Nicol and Burnaby Munson* |
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ABSTRACT: | ||
Polyethylene glycol (PEG) oligomers, H(OC2H4O)nH, were analyzed by gas chromatography/mass spectrometry (GC/MS) for oligomers, n = 211, without indications of pyrolysis of the higher oligomers at oven temperatures of 330ụC. The electron ionization (EI) mass spectra (70 eV and 1214 eV) of these PEG oligomers contain only low molecular weight fragment ions and, essentially, no M+ ions. The low-voltage EI spectra contain more abundant high mass ions and allow easier identification of the PEG oligomers. The major fragment ions in all EI spectra are (C2H4O)xH+ at m/z 45, 89, 133 and 177. The base peak in the low-voltage spectra varies with molecular weight and suggests preferential cleavage at the second and third ether linkages. The relative molar sensitivities (70 eV EI) of PEG oligomers (n = 16) are linear functions of molecular weight or polarizability ratios. The CH4 chemical ionization mass spectra of the PEG oligomers contain, predominantly, (C2H4O)xH+ ions at m/z 45, 89, 133 and 177. The relative abundances of MH+ ions vary markedly across the chromatographic peaks because these ions are formed predominantly by sample ion / sample molecule reactions. Proton transfer reactions from CH5+ and C2H5+ to the PEG oligomers are almost entirely dissociative. The i-C4H10 CI mass spectra of PEG oligomers contain MH+ as the base peaks. The relative abundances of MH+ ions do not vary significantly across the chromatographic peaks but do increase with increasing pressure of i-C4H10. The extent of decomposition of MH+ ions in i-C4H10 CI mass spectra increases with increasing molecular weight of the PEG oligomers. Relative molar sensitivities (CH4 CI and i-C4H10 CI) of PEG oligomers (n = 16) are essentially the same linear functions of molecular weight ratio. | ||
Keywords: GC/EIMS, GC/CIMS, PEG oligomers, ion molecule reactions, relative molar sensitivities, low voltage EIMS |
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