Abstract

Polyethylene (PEG) glycols oligomers, H(OC2H4)xOH, were analyzed bygas chromatography mass spectrometry for oligomers, n = 2-11, without indications of pyrolysis of higher oligomers at oven temperature of 330o C. The Electron Ionization (EI) mass spectra (70 an 12-14 eV) of these PEG oligomers contain only low molecular weight frag 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 the EI spectra are (CH2OH)nH+ ions at mass m/z 45, 89, 133,and 177. The base peak in the low voltage spectra varies with molecular weight and suggest preferential cleave at the second and third ether linkages. The relative molar sensitivities (70 eV EI) of PEG oligomers (n=1-6) are linear function of molecular weight or polarizability ratios. The CH4 chemical ionization mass spectrometry of PEG oligomers predominantly contain (CH2OH)nH+ 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 by sample ion-sample molecule reactions. Proton transfer from CH5+ to C2H5+ to the PEGal oligomers are most entirely dissociative. The i-C4H10 CI mass spectra of PEG oligomers containly MH+ as base peak. The relative abundances of the MH+ ions do not vary significantly across the chromatographic peak but do increase with increasing pressure of i-C4H10. the extent of decomposition of MH+ ions in i-C4H10 mass spectra increases with increasing molecular weight of the PEG oligomers. Relative molar sensitivities (CH4 and i-C4H10 CI) of PEG oligomers (n=1-6) are essentially the same linear function of molecular weight ratio.